@article{king_nemanich_davis_2015, title={Band alignment at AlN/Si (111) and (001) interfaces}, volume={118}, ISSN={["1089-7550"]}, DOI={10.1063/1.4927515}, abstractNote={To advance the development of III-V nitride on silicon heterostructure semiconductor devices, we have utilized in-situ x-ray photoelectron spectroscopy (XPS) to investigate the chemistry and valence band offset (VBO) at interfaces formed by gas source molecular beam epitaxy of AlN on Si (001) and (111) substrates. For the range of growth temperatures (600–1050 °C) and Al pre-exposures (1–15 min) explored, XPS showed the formation of Si-N bonding at the AlN/Si interface in all cases. The AlN/Si VBO was determined to be −3.5 ± 0.3 eV and independent of the Si orientation and degree of interfacial Si-N bond formation. The corresponding AlN/Si conduction band offset (CBO) was calculated to be 1.6 ± 0.3 eV based on the measured VBO and band gap for wurtzite AlN. Utilizing these results, prior reports for the GaN/AlN band alignment, and transitive and commutative rules for VBOs, the VBO and CBO at the GaN/Si interface were determined to be −2.7 ± 0.3 and −0.4 ± 0.3 eV, respectively.}, number={4}, journal={JOURNAL OF APPLIED PHYSICS}, author={King, Sean W. and Nemanich, Robert J. and Davis, Robert F.}, year={2015}, month={Jul} }
 @article{king_nemanich_davis_2015, title={Cleaning of pyrolytic hexagonal boron nitride surfaces}, volume={47}, ISSN={["1096-9918"]}, DOI={10.1002/sia.5781}, abstractNote={Hexagonal boron nitride (h‐BN) has recently garnered significant interest as a substrate and dielectric for two‐dimensional materials and devices based on graphene or transition metal dichalcogenides such as molybdenum disulfide (MoS2). As substrate surface impurities and defects can negatively impact the structure and properties of two‐dimensional materials, h‐BN surface preparation and cleaning are a critical consideration. In this regard, we have utilized X‐ray photoelectron spectroscopy to investigate the influence of several ex situ wet chemical and in situ thermal desorption cleaning procedures on pyrolytic h‐BN surfaces. Of the various wet chemistries investigated, a 10 : 1 buffered HF solution was found to produce surfaces with the lowest amount of oxygen and carbon contamination. Ultraviolet/ozone oxidation was found to be the most effective ex situ treatment for reducing carbon contamination. Annealing at 1050 °C in vacuum or 10−5 Torr NH3 was found to further reduce oxygen and carbon contamination to the XPS detection limits. Copyright © 2015 John Wiley & Sons, Ltd.}, number={7}, journal={SURFACE AND INTERFACE ANALYSIS}, author={King, Sean W. and Nemanich, Robert J. and Davis, Robert F.}, year={2015}, month={Jul}, pages={798–803} }
 @article{king_tanaka_davis_nemanich_2015, title={Hydrogen desorption from hydrogen fluoride and remote hydrogen plasma cleaned silicon carbide (0001) surfaces}, volume={33}, ISSN={["1520-8559"]}, DOI={10.1116/1.4921526}, abstractNote={Due to the extreme chemical inertness of silicon carbide (SiC), in-situ thermal desorption is commonly utilized as a means to remove surface contamination prior to initiating critical semiconductor processing steps such as epitaxy, gate dielectric formation, and contact metallization. In-situ thermal desorption and silicon sublimation has also recently become a popular method for epitaxial growth of mono and few layer graphene. Accordingly, numerous thermal desorption experiments of various processed silicon carbide surfaces have been performed, but have ignored the presence of hydrogen, which is ubiquitous throughout semiconductor processing. In this regard, the authors have performed a combined temperature programmed desorption (TPD) and x-ray photoelectron spectroscopy (XPS) investigation of the desorption of molecular hydrogen (H2) and various other oxygen, carbon, and fluorine related species from ex-situ aqueous hydrogen fluoride (HF) and in-situ remote hydrogen plasma cleaned 6H-SiC (0001) surfaces. Using XPS, the authors observed that temperatures on the order of 700–1000 °C are needed to fully desorb C-H, C-O and Si-O species from these surfaces. However, using TPD, the authors observed H2 desorption at both lower temperatures (200–550 °C) as well as higher temperatures (>700 °C). The low temperature H2 desorption was deconvoluted into multiple desorption states that, based on similarities to H2 desorption from Si (111), were attributed to silicon mono, di, and trihydride surface species as well as hydrogen trapped by subsurface defects, steps, or dopants. The higher temperature H2 desorption was similarly attributed to H2 evolved from surface O-H groups at ∼750 °C as well as the liberation of H2 during Si-O desorption at temperatures >800 °C. These results indicate that while ex-situ aqueous HF processed 6H-SiC (0001) surfaces annealed at <700 °C remain terminated by some surface C–O and Si–O bonding, they may still exhibit significant chemical reactivity due to the creation of surface dangling bonds resulting from H2 desorption from previously undetected silicon hydride and surface hydroxide species.}, number={5}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A}, author={King, Sean W. and Tanaka, Satoru and Davis, Robert F. and Nemanich, Robert J.}, year={2015}, month={Sep} }
 @article{king_davis_carter_schneider_nemanich_2015, title={Hydrogen desorption kinetics for aqueous hydrogen fluoride and remote hydrogen plasma processed silicon (001) surfaces}, volume={33}, ISSN={["1520-8559"]}, DOI={10.1116/1.4926733}, abstractNote={The desorption kinetics of molecular hydrogen (H2) from silicon (001) surfaces exposed to aqueous hydrogen fluoride and remote hydrogen plasmas were examined using temperature programmed desorption. Multiple H2 desorption states were observed and attributed to surface monohydride (SiH), di/trihydride (SiH2/3), and hydroxide (SiOH) species, subsurface hydrogen trapped at defects, and hydrogen evolved during the desorption of surface oxides. The observed surface hydride species were dependent on the surface temperature during hydrogen plasma exposure with mono, di, and trihydride species being observed after low temperature exposure (150 °C), while predominantly monohydride species were observed after higher temperature exposure (450 °C). The ratio of surface versus subsurface H2 desorption was also found to be dependent on the substrate temperature with 150 °C remote hydrogen plasma exposure generally leading to more H2 evolved from subsurface states and 450 °C exposure leading to more H2 desorption from surface SiHx species. Additional surface desorption states were observed, which were attributed to H2 desorption from Si (111) facets formed as a result of surface etching by the remote hydrogen plasma or aqueous hydrogen fluoride treatment. The kinetics of surface H2 desorption were found to be in excellent agreement with prior investigations of silicon surfaces exposed to thermally generated atomic hydrogen.}, number={5}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A}, author={King, Sean W. and Davis, Robert F. and Carter, Richard J. and Schneider, Thomas P. and Nemanich, Robert J.}, year={2015}, month={Sep} }
 @article{king_nemanich_davis_2015, title={Photoemission investigation of the Schottky barrier at the Sc/3C-SiC (111) interface}, volume={252}, ISSN={["1521-3951"]}, DOI={10.1002/pssb.201451340}, abstractNote={The Schottky barrier and interfacial chemistry for interfaces formed by evaporation of Sc onto 3C‐SiC (111)‐(1x1) surfaces at 600 °C has been investigated using in situ X‐ray and ultra‐violet photoelectron spectroscopy (XPS and UPS) and low energy electron diffraction (LEED). Sc was observed to grow in a two‐dimensional manner and exhibit a (1x1) LEED pattern up to thicknesses of ∼2 nm beyond which diffraction patterns were no longer observable. XPS measurements of these same films showed a clear reaction of Sc with the 3C‐SiC (111)‐(1x1) surface to form a ScSix and ScCx interfacial layer in addition to the formation of a metallic Sc film. XPS measurements also showed the deposition of Sc induced ∼0.5 eV of upward band bending resulting in a Schottky barrier of 0.65 ± 0.15 eV.}, number={2}, journal={PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS}, author={King, Sean W. and Nemanich, Robert J. and Davis, Robert F.}, year={2015}, month={Feb}, pages={391–396} }
 @article{king_davis_nemanich_2014, title={Desorption and sublimation kinetics for fluorinated aluminum nitride surfaces}, volume={32}, ISSN={["1520-8559"]}, DOI={10.1116/1.4891650}, abstractNote={The adsorption and desorption of halogen and other gaseous species from surfaces is a key fundamental process for both wet chemical and dry plasma etch and clean processes utilized in nanoelectronic fabrication processes. Therefore, to increase the fundamental understanding of these processes with regard to aluminum nitride (AlN) surfaces, temperature programmed desorption (TPD) and x-ray photoelectron spectroscopy (XPS) have been utilized to investigate the desorption kinetics of water (H2O), fluorine (F2), hydrogen (H2), hydrogen fluoride (HF), and other related species from aluminum nitride thin film surfaces treated with an aqueous solution of buffered hydrogen fluoride (BHF) diluted in methanol (CH3OH). Pre-TPD XPS measurements of the CH3OH:BHF treated AlN surfaces showed the presence of a variety of Al-F, N-F, Al-O, Al-OH, C-H, and C-O surfaces species in addition to Al-N bonding from the AlN thin film. The primary species observed desorbing from these same surfaces during TPD measurements included H2, H2O, HF, F2, and CH3OH with some evidence for nitrogen (N2) and ammonia (NH3) desorption as well. For H2O, two desorption peaks with second order kinetics were observed at 195 and 460 °C with activation energies (Ed) of 51 ± 3 and 87 ± 5 kJ/mol, respectively. Desorption of HF similarly exhibited second order kinetics with a peak temperature of 475 °C and Ed of 110 ± 5 kJ/mol. The TPD spectra for F2 exhibited two peaks at 485 and 585 °C with second order kinetics and Ed of 62 ± 3 and 270 ± 10 kJ/mol, respectively. These values are in excellent agreement with previous Ed measurements for desorption of H2O from SiO2 and AlFx from AlN surfaces, respectively. The F2 desorption is therefore attributed to fragmentation of AlFx species in the mass spectrometer ionizer. H2 desorption exhibited an additional high temperature peak at 910 °C with Ed = 370 ± 10 kJ/mol that is consistent with both the dehydrogenation of surface AlOH species and H2 assisted sublimation of AlN. Similarly, N2 exhibited a similar higher temperature desorption peak with Ed = 535 ± 40 kJ/mol that is consistent with the activation energy for direct sublimation of AlN.}, number={5}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A}, author={King, Sean W. and Davis, Robert F. and Nemanich, Robert J.}, year={2014}, month={Sep} }
 @article{king_davis_nemanich_2014, title={Gas source molecular beam epitaxy of scandium nitride on silicon carbide and gallium nitride surfaces}, volume={32}, ISSN={["1520-8559"]}, DOI={10.1116/1.4894816}, abstractNote={Scandium nitride (ScN) is a group IIIB transition metal nitride semiconductor with numerous potential applications in electronic and optoelectronic devices due to close lattice matching with gallium nitride (GaN). However, prior investigations of ScN have focused primarily on heteroepitaxial growth on substrates with a high lattice mismatch of 7%–20%. In this study, the authors have investigated ammonia (NH3) gas source molecular beam epitaxy (NH3-GSMBE) of ScN on more closely lattice matched silicon carbide (SiC) and GaN surfaces (<3% mismatch). Based on a thermodynamic analysis of the ScN phase stability window, NH3-GSMBE conditions of 10−5–10−4 Torr NH3 and 800–1050 °C where selected for initial investigation. In-situ x-ray photoelectron spectroscopy (XPS) and ex-situ Rutherford backscattering measurements showed all ScN films grown using these conditions were stoichiometric. For ScN growth on 3C-SiC (111)-(√3 × √3)R30° carbon rich surfaces, the observed attenuation of the XPS Si 2p and C 1s substrate core levels with increasing ScN thickness indicated growth initiated in a layer-by-layer fashion. This was consistent with scanning electron microscopy (SEM) images of 100–200 nm thick films that revealed featureless surfaces. In contrast, ScN films grown on 3C-SiC (111)-(3 × 3) and 3C-SiC (100)-(3 × 2) silicon rich surfaces were found to exhibit extremely rough surfaces in SEM. ScN films grown on both 3C-SiC (111)-(√3 × √3)R30° and 2H-GaN (0001)-(1 × 1) epilayer surfaces exhibited hexagonal (1 × 1) low energy electron diffraction patterns indicative of (111) oriented ScN. X-ray diffraction ω-2θ rocking curve scans for these same films showed a large full width half maximum of 0.29° (1047 arc sec) consistent with transmission electron microscopy images that revealed the films to be poly-crystalline with columnar grains oriented at ≈15° to the [0001] direction of the 6H-SiC (0001) substrate. In-situ reflection electron energy loss spectroscopy measurements determined the band-gap for the NH3-GSMBE ScN films to be 1.5 ± 0.3 eV, and thermal probe measurements indicated all ScN films to be n-type. The four point probe sheet resistance of the ScN films was observed to increase with decreasing growth temperature and decreased with unintentional oxygen incorporation. Hg probe capacitance–voltage measurements indicated ND-NA decreased with decreasing growth temperature from 1019 to 1020/cm3 for the lowest resistivity films to ≅5 × 1016/cm3 for the highest resistivity films. In-situ ultraviolet photoelectron spectroscopy measurements additionally showed the valence band maximum moving from 1.4 to 0.8 eV below the Fermi level with decreasing growth temperature consistent with the increased resistivity and reduction in carrier concentration. These results suggest that additional reductions in ScN carrier concentrations can be achieved via continued optimization of ScN growth conditions and selection of substrate orientation and surface termination.}, number={6}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A}, author={King, Sean W. and Davis, Robert F. and Nemanich, Robert J.}, year={2014}, month={Nov} }
 @article{king_nemanich_davis_2014, title={Valence and conduction band alignment at ScN interfaces with 3C-SiC (111) and 2H-GaN (0001)}, volume={105}, ISSN={["1077-3118"]}, DOI={10.1063/1.4894010}, abstractNote={In order to understand and predict the behavior of future scandium nitride (ScN) semiconductor heterostructure devices, we have utilized in situ x-ray and ultra-violet photoelectron spectroscopy to determine the valence band offset (VBO) present at ScN/3C-SiC (111) and 2H-GaN (0001)/ScN (111) interfaces formed by ammonia gas source molecular beam epitaxy. The ScN/3C-SiC (111) VBO was dependent on the ScN growth temperature and resistivity. VBOs of 0.4 ± 0.1 and 0.1 ± 0.1 eV were, respectively, determined for ScN grown at 925 °C (low resistivity) and 800 °C (high resistivity). Using the band-gaps of 1.6 ± 0.2 and 1.4 ± 0.2 eV previously determined by reflection electron energy loss spectroscopy for the 925 and 800 °C ScN films, the respective conduction band offsets (CBO) for these interfaces were 0.4 ± 0.2 and 0.9 ± 0.2 eV. For a GaN (0001) interface with 925 °C ScN (111), the VBO and CBO were similarly determined to be 0.9 ± 0.1 and 0.9 ± 0.2 eV, respectively.}, number={8}, journal={APPLIED PHYSICS LETTERS}, author={King, Sean W. and Nemanich, Robert J. and Davis, Robert F.}, year={2014}, month={Aug} }
 @article{tedesco_rowe_nemanich_2010, title={Titanium silicide islands on atomically clean Si(100): Identifying single electron tunneling effects}, volume={107}, ISSN={["0021-8979"]}, DOI={10.1063/1.3437049}, abstractNote={Titanium silicide islands have been formed by the ultrahigh vacuum deposition of thin films of titanium (<2 nm) on atomically clean Si(100) substrates followed by annealing to ∼800 °C. Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy have been performed on these islands to record current-voltage (I-V) curves. Because each island forms a double barrier tunnel junction (DBTJ) structure with the STM tip and the substrate, they would be expected to exhibit single electron tunneling (SET) according to the orthodox model of SET. Some of the islands formed are small enough (diameter <10 nm) to exhibit SET at room temperature and evidence of SET has been identified in some of the I-V curves recorded from these small islands. Those curves are analyzed within the framework of the orthodox model and are found to be consistent with that model, except for slight discrepancies of the shape of the I-V curves at current steps. However, most islands that were expected to exhibit SET did not do so, and the reasons for the absence of observable SET are evaluated. The most likely reasons for the absence of SET are determined to be a wide depletion region in the substrate and Schottky barrier lowering due to Fermi level pinning by surface states of the clean silicon near the islands. The results establish that although the Schottky barrier can act as an effective tunnel junction in a DBTJ structure, the islands may be unreliable in future nanoelectronic devices. Therefore, methods are discussed to improve the reliability of future devices.}, number={12}, journal={JOURNAL OF APPLIED PHYSICS}, author={Tedesco, J. L. and Rowe, J. E. and Nemanich, R. J.}, year={2010}, month={Jun} }
 @article{tedesco_rowe_nemanich_2009, title={Conducting atomic force microscopy studies of nanoscale cobalt silicide Schottky barriers on Si(111) and Si(100)}, volume={105}, ISSN={["0021-8979"]}, DOI={10.1063/1.3100212}, abstractNote={Cobalt silicide (CoSi2) islands have been formed by the deposition of thin films (∼0.1–0.3 nm) of cobalt on clean Si(111) and Si(100) substrates in ultrahigh vacuum (UHV) followed by annealing to ∼880 °C. Conducting atomic force microscopy has been performed on these islands to characterize and measure their current-voltage (I-V) characteristics. Current-voltage curves were analyzed using standard thermionic emission theory to obtain the Schottky barrier heights and ideality factors between the silicide islands and the silicon substrates. Current-voltage measurements were performed ex situ for one set of samples (termed “passivated surfaces”) where the silicon surface surrounding the islands was passivated with a native oxide. Other samples (termed “clean surfaces”) remained in UHV, while I-V curves were recorded. By comparing the barrier heights and ideality factors for islands on passivated surfaces and clean surfaces, the effects of the nonpassivated surfaces on conduction have been studied. The barrier heights measured from CoSi2 islands on clean surfaces are found to be ∼0.2–0.3 eV below barrier heights measured from similar islands on passivated surfaces. The main cause of the reduced Schottky barrier in the clean surface samples is attributed to Fermi level pinning by nonpassivated surface states of the clean silicon surface. However, the measured barrier heights of the islands are equivalent on both clean Si(111) and Si(100) surfaces, suggesting that the nonpassivated surface is influenced by cobalt impurities. Furthermore, the barrier heights of islands on the clean surfaces are lower than what can be explained by Fermi level pinning alone, suggesting the presence of additional reductions in the Schottky barrier heights. These variations are greater than what can be attributed to experimental error, and the additional barrier height lowering is primarily attributed to spreading resistance effects. Schottky barrier inhomogeneity is also identified as a possible cause of the additional barrier height lowering and nonideality in the Schottky contacts. Current-voltage measurements of the clean surface samples were also obtained at several temperatures. The barrier heights were found to decrease, and the ideality factors were found to increase with decreasing temperature. The dependence of the barrier height is attributed to the temperature variation of the Fermi level.}, number={8}, journal={JOURNAL OF APPLIED PHYSICS}, author={Tedesco, J. L. and Rowe, J. E. and Nemanich, R. J.}, year={2009}, month={Apr} }
 @article{sakon_ribeill_garguilo_perkins_weninger_nemanich_2009, title={Fluorescence quenching effects of nanocrystalline diamond surfaces}, volume={18}, ISSN={["1879-0062"]}, DOI={10.1016/j.diamond.2008.10.028}, abstractNote={Undoped diamond has conductive properties when terminated by hydrogen and exposed to air or aqueous solution. Here, it is shown that nanocrystalline diamond, fabricated with hydrogen termination and deposited on quartz substrates using chemical vapor deposition, significantly quenched the fluorescence of adsorbed, dye-labeled fibrinogen protein in aqueous solutions at near neutral pH. Smaller levels of quenching were observed from oxygen terminated NCD surfaces. We suggest that these near-surface fluorescence quenching effects may arise from surface conductance effects in hydrogen terminated NCD. It is also shown that despite bulk quenching effects, single molecules of fibrinogen could be imaged on nanocrystalline diamond surfaces using epi-fluorescence techniques.}, number={1}, journal={DIAMOND AND RELATED MATERIALS}, author={Sakon, John J. and Ribeill, Guilhern J. and Garguilo, Jacob M. and Perkins, Jarnes and Weninger, Keith R. and Nemanich, Robert J.}, year={2009}, month={Jan}, pages={82–87} }
 @misc{king_davis_nemanich_2009, title={Hydrogen desorption kinetics and band bending for 6H-SiC(0001) surfaces}, volume={603}, ISSN={["1879-2758"]}, DOI={10.1016/j.susc.2009.08.023}, abstractNote={The desorption kinetics of hydrogen from polished 6H–SiC(0 0 0 1) surfaces exposed to various sources of hydrogen have been determined using temperature programmed desorption (TPD). For (3 × 3) 6H–SiC(0 0 0 1) surfaces prepared via annealing and cooling in SiH4, desorption of 0.2 ± 0.05 monolayer of molecular hydrogen was observed to occur at ≈590 °C. This β1 H2 desorption peak exhibited second order kinetics with an activation energy of 2.4 ± 0.2 eV. For (3 × 3) 6H–SiC surfaces exposed to atomic hydrogen generated via either a hot rhenium filament or remote hydrogen plasma, low energy electron diffraction patterns showed an eventual conversion back to (1 × 1) symmetry. Spectra acquired using Auger electron and X-ray photoelectron spectroscopies revealed that the atomic hydrogen exposure removed the excess Si. Photoelectron spectroscopy results also showed a 0.5 eV increase in binding energy for the Si2p and C1s core levels after removal of the Si–Si bilayer that is indicative of a decrease in band bending at the SiC surface. TPD from the (3 × 3) 6H–SiC(0 0 0 1) surfaces exposed to atomic hydrogen showed substantially more molecular hydrogen desorption (1–2 ML) through the appearance of a new desorption peak (β2,3) that started at ≈200 °C. The β2,3 peak exhibited second order desorption kinetics and a much lower activation energy of 0.6 ± 0.2 eV. A third smaller hydrogen desorption state was also detected in the 650–850 °C range. This last feature could be resolved into two separate desorption peaks (α1 and α2) both of which exhibited second order kinetics with activation energies of 4.15 ± 0.15 and 4.3 ± 0.15 eV, respectively. Based on comparisons to hydrogen desorption from Si and diamond surfaces, the β and α desorption peaks were assigned to hydrogen desorption from Si and C sites, respectively.}, number={20}, journal={SURFACE SCIENCE}, author={King, S. W. and Davis, R. F. and Nemanich, R. J.}, year={2009}, month={Oct}, pages={3104–3118} }
 @article{smith_bilbro_nemanich_2009, title={Theory of space charge limited regime of thermionic energy converter with negative electron affinity emitter}, volume={27}, ISSN={["1071-1023"]}, DOI={10.1116/1.3125282}, abstractNote={A theory of the space charge limited output current regime of a vacuum thermionic energy conversion device (TEC) employing a negative electron affinity (NEA) diamond emitter electrode is derived. The theory is developed by assuming that the electrons behave as a collisionless gas and self-consistently solving Vlaslov’s equation and Poisson’s equation. Special cases of the theory are addressed. Calculations are performed to model a TEC with a nitrogen doped diamond emitter material under various conditions. It is shown that the NEA material outperforms a similar positive electron affinity material in terms of output power and efficiency because the NEA lowers the electrostatic boundary condition at the emitter and therefore mitigates the negative space charge effect.}, number={3}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B}, author={Smith, Joshua Ryan and Bilbro, Griff L. and Nemanich, Robert J.}, year={2009}, month={May}, pages={1132–1141} }
 @article{kulkarni_porter_koeck_tang_nemanich_2008, title={Electrical and photoelectrical characterization of undoped and S-doped nanocrystalline diamond films}, volume={103}, ISSN={["1089-7550"]}, DOI={10.1063/1.2908884}, abstractNote={Nanocrystalline diamond (NCD) films are being intensively researched for a variety of potential applications, such as optical windows, electrochemical electrodes, and electron emitting surfaces for field emission displays. In this study Zr, Ti, Cu, and Pt on intrinsic and lightly sulfur-doped (n-type) NCD films were electrically and photoelectrically characterized. Intrinsic and sulfur-doped NCD films were synthesized on 1in. diameter quartz and silicon substrates by microwave plasma assisted chemical vapor deposition. All metals showed linear (Ohmic) current-voltage characteristics in the as-deposited state. The Schottky barrier heights (ΦB) at the metal-film interface were investigated using x-ray and ultraviolet photoelectron spectroscopies. The undoped NCD films exhibited a negative electron affinity and a band gap of 5.0±0.4eV. The ΦB were calculated based on this band gap measurement and the consistent indication from Hall measurements that the films are n-type. The ΦB values were calculated from shifts in the core-level (C1s) peaks immediately obtained before and after in situ, successive metal depositions. The ΦB values for Zr, Ti, and Pt on undoped films were calculated to be 3.3, 3.2, and 3.7eV, respectively. The S-doped films also showed increasing ΦB with metal work functions: 3.0, 3.1, and 3.4eV for Zr, Ti, and Pt, respectively. In general accordance with the barrier height trends, the specific contact resistivity (ρc) values increased with the metal work functions for both undoped and S-doped films. For the undoped films ρc increased from 3×10−5Ωcm2 for Zr to 6.4×10−3Ωcm2 for Pt. The ρc values for the S-doped films were approximately two orders of magnitude lower than those for the undoped films: 3.5×10−7–4.5×10−5Ωcm2 for Zr and Pt, respectively. The Hall-effect measurements indicated that the average sheet resistivity and carrier concentration values were 0.16 and 3.5×1018cm−3 for the undoped films and 0.15Ωcm and 4.9×1019cm−3 for the S-doped films.}, number={8}, journal={JOURNAL OF APPLIED PHYSICS}, author={Kulkarni, P. and Porter, L. M. and Koeck, F. A. M. and Tang, Y. -J. and Nemanich, R. J.}, year={2008}, month={Apr} }
 @article{king_davis_nemanich_2008, title={Kinetics of Ga and In desorption from (7x7)Si(111) and (3x3)6H-SiC(0001) surfaces}, volume={602}, ISSN={["1879-2758"]}, DOI={10.1016/j.susc.2007.10.034}, abstractNote={The desorption characteristics of Ga and In on (7 × 7) Si(1 1 1) and (3 × 3) 6H-SiC(0 0 0 1) surfaces have been determined using temperature programmed desorption. Two peaks were observed for desorption of a 1.5 ± 0.25 monolayer of Ga from the latter surface. The peak at Tmax = 670 °C exhibited zeroth order kinetics; the activation energy and pre-exponential were determined to be 2.6 ± 0.1 eV and 6 × 1027 ± 0.5 atom/cm2 s, respectively. The peak at Tmax = 535 °C exhibited first order desorption kinetics with an activation energy and pre-exponential of 6.2 ± 0.3 eV and 7 × 1021 ± 2 s−1, respectively. In contrast, only zeroth order kinetics and a lower activation energy of 2.0 ± 0.1 eV were determined for desorption of a 1.5 ± 0.25 monolayer of Ga from (7 × 7) Si(1 1 1). The values of these results in tandem with those of related studies of desorption from Si and SiC surfaces indicate that the low and high temperature Ga peaks from SiC are due to desorption from either a wetting layer or adatom sites and from Ga islands, respectively. The difference in desorption activation energies for Ga on Si(1 1 1) and on 6H-SiC(0 0 0 1) surfaces is attributed to differences in lattice matching of Ga to these surfaces. By contrast, only multilayer desorption was observed for 4 ± 1 monolayer of In on SiC(0 0 0 1). The zeroth order desorption activation energy and pre-exponential were 2.4 ± 0.1 eV and 6 × 1027±0.5 atom/cm2 s; they are consistent with the heat of sublimation (2.45–2.5 eV) for liquid In.}, number={2}, journal={SURFACE SCIENCE}, author={King, S. W. and Davis, R. F. and Nemanich, R. J.}, year={2008}, month={Jan}, pages={405–415} }
 @article{chromik_winfrey_luening_nemanich_wahl_2008, title={Run-in behavior of nanocrystalline diamond coatings studied by in situ tribometry}, volume={265}, ISSN={["1873-2577"]}, DOI={10.1016/j.wear.2007.11.023}, abstractNote={The friction performance of nanocrystalline diamond coatings was evaluated using in situ tribometry with sapphire counterfaces. Coatings were grown by microwave plasma assisted chemical vapor deposition in an Ar–H–CH4 plasma, with H ranging from 0 to 36%. In situ examination of the sliding contact, combined with ex situ analysis of the sapphire counterface revealed that the velocity accommodation mode was interfacial sliding of a carbonaceous transfer film versus the coating wear track. For most tests, the contact diameter increased during the first 50 sliding cycles and then remained constant. The in situ measure of the contact diameter was found to correlate confidently to ex situ measurements of counterface wear. The performance of the diamond coatings, characterized by quick run-in to low friction was best when a small but detectable graphite peak was present in the X-ray diffraction (XRD) profile. The relative intensity of the XRD graphite peak was also found to directly correlate with the peak position of the C1s → π* transition as measured by near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. Increasing the relative amount of graphite-bonded sp2 carbon in the NCD films decreased run-in cycles to low friction.}, number={3-4}, journal={WEAR}, author={Chromik, Richard. R. and Winfrey, A. Leigh and Luening, Jan and Nemanich, Robert J. and Wahl, Kathryn J.}, year={2008}, month={Jul}, pages={477–489} }
 @article{kong_rowe_nemanich_2008, title={Single molecule measurements with photoelectron emission microscopy}, volume={26}, ISSN={["2166-2746"]}, DOI={10.1116/1.2932094}, abstractNote={In this research, variable wavelength photoelectron emission microscopy (PEEM) with tunable UV light from the Duke University free electron laser is applied to image single fibrinogen molecules adsorbed onto n-type silicon surfaces. High resolution PEEM images (∼10nm) are obtained with photon energies from 4to6eV. Wavelength-dependent image sequences are analyzed to determine the photoionization spectrum and the photoelectron emission threshold of individual molecules. The experimental data are fitted using temperature dependent Fowler law, square-root law, and cube-root law. The details of the theoretical models are discussed. The square-root and cube-root fittings reveal the ionization threshold of 5.0eV for fibrinogen adsorbed onto n-type silicon, while temperature dependent Fowler law shows a threshold of 4.9eV. The accuracy of the measurements is calculated to be ±0.2eV. The authors conclude that no significant difference is observed from the three theoretical fitting approaches.}, number={4}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B}, author={Kong, Xianhua and Rowe, J. E. and Nemanich, R. J.}, year={2008}, month={Jul}, pages={1461–1465} }
 @article{brukman_gao_nemanich_harrison_2008, title={Temperature dependence of single-asperity diamond-diamond friction elucidated using AFM and MD Simulations}, volume={112}, ISSN={["1932-7455"]}, DOI={10.1021/jp711959e}, abstractNote={Complementary experimental (atomic force microscopy) and theoretical (molecular dynamics) techniques were used to investigate friction between diamond−diamond junctions as a function of temperature. The simulation and experimental conditions were designed to correspond as closely as possible. In the atomic force microscopy (AFM) experiments, two microcrystalline-diamond (μCD) AFM tips of differing contact radii were used to examine the friction of diamond (111) and (001) single crystals from 24 to 225 K in an ultrahigh vacuum. At all temperatures, the experimentally determined dependence of friction on load was consistent with the occurrence of single-asperity interfacial friction, where friction is proportional to contact area. In addition, the behavior of the contact was fit well by the Derjaguin−Muller−Toporov continuum model. Friction measurements within a given series were highly repeatable; however, as is typical with AFM measurements, there was some variation in measurements taken from different re...}, number={25}, journal={JOURNAL OF PHYSICAL CHEMISTRY C}, author={Brukman, Matthew J. and Gao, Guangtu and Nemanich, Robert J. and Harrison, Judith A.}, year={2008}, month={Jun}, pages={9358–9369} }
 @article{burnette_kiesel_sayers_nemanich_2008, title={Titanium Interlayer Mediated Epitaxy of CoSi2 on Si1-xGex}, volume={516}, ISSN={["0040-6090"]}, DOI={10.1016/j.tsf.2007.08.045}, abstractNote={Abstract Titanium Interlayer Mediated Epitaxy (TIME) has been shown to promote the formation of epitaxial CoSi2 on Si (100). Similarities between Si and Si1−xGex alloys have motivated a study of whether the TIME process could be successful in forming epitaxial CoSi2 on Si1−xGex. Titanium layers of varying thickness were deposited as interlayers between a Co layer and c-Si/Si0.8Ge0.2 grown epitaxially onto Si (100) to investigate their role in the formation of epitaxial CoSi2 on Si1−xGex alloys. The effect of Ti interlayer thickness on the orientation of CoSi2 to the Si1−xGex substrate, and the conditions under which a polycrystalline CoSi2 film has been formed have been studied. It was found that Ti was beneficial in promoting epitaxy to the substrate in all cases. The experimental results indicate that with a Ti interlayer thickness of ∼ 50 A, the formation of epitaxial CoSi2 adjacent to the substrate was achieved, and pinhole formation was minimized. It was also observed that for increased interlayer thickness, Ti reacted with Si to form a titanium silicide.}, number={8}, journal={THIN SOLID FILMS}, author={Burnette, James E. and Kiesel, Sharon and Sayers, Dale E. and Nemanich, Robert J.}, year={2008}, month={Feb}, pages={1809–1817} }
 @article{yang_zeman_nemanich_2007, title={Coarsening dynamics of nanoscale Ti-silicide islands on Si surfaces}, volume={50}, DOI={10.3938/jkps.50.575}, abstractNote={The late-stage coarsening dynamics of nanoscale Ti-silicide (TiSi2) islands on Si surfaces is explored in ultra high vacuum (UHV) by using ultraviolet photoelectron emission microscopy (UVPEEM). The UV-PEEM is employed for real-time, in-situ monitoring of the nanostructure dynamics and evolution at high temperatures. Continuous annealing at ∼1150 ◦C leads to an increase in the size of the initially nucleated silicide islands and to a reduction in the number density. By monitoring the relative position and the size of individual islands, we find that islands grow through Ostwald ripening and attractive migration and coalescence (AMC). The AMC is a new coarsening process where nearby islands are observed to migrate directly towards each other and subsequently coalesce. This process has been attributed to a growth-decay flow of the island edges driven by a non-uniform chemical potential around the islands. The non-uniform chemical potential results from a varying adatom surface concentration induced by local variations in size, number, and location of the neighboring islands. Significant shape distortions of the coarsening islands, migration of each island towards the center of mass of a group of islands, and screening of attractive migration of islands with a continuous Ti flux support our suggested model for the AMC mechanism. The mass exchange between the coarsening TiSi2 islands in the AMC process is explained in terms of a Ti adatom surface-diffusion-limited process.}, number={3}, journal={Journal of the Korean Physical Society}, author={Yang, W. C. and Zeman, M. and Nemanich, R. J.}, year={2007}, pages={575–580} }
 @article{smith_bilbro_nemanich_2007, title={Considerations for a high-performance thermionic energy conversion device based on a negative electron affinity emitter}, volume={76}, ISSN={["1098-0121"]}, DOI={10.1103/physrevb.76.245327}, abstractNote={A theory is developed to model the effect a negative electron affinity (NEA) emitter electrode has on the negative space charge effect of a vacuum thermionic energy conversion device (TEC). The theory is derived by treating the electrons in the interelectrode space as a collisionless gas and self-consistently solving the Boltzmann transport equation and Poisson equation. The theory determines the point on the voltage-current characteristic such that the maximum motive due to space charge is at the same level as the conduction band minimum. It is shown that emitter electrodes with an NEA significantly mitigate the negative space charge effect; therefore a TEC employing such an electrode will outperfrom a similar TEC with conventional electrodes in terms of output power. Additionally, it is shown that a TEC with an NEA emitter electrode can have a greater interelectrode spacing than a TEC with conventional electrodes operating under similar conditions where the outputs of both TEC's are comparable.}, number={24}, journal={PHYSICAL REVIEW B}, author={Smith, Joshua Ryan and Bilbro, Griff L. and Nemanich, Robert J.}, year={2007}, month={Dec} }
 @article{neeyakorn_varma_jaye_burnette_lee_nemanich_grant_krim_2007, title={Dynamics of vapor-phase organophosphates on silicon and OTS}, volume={27}, ISSN={["1573-2711"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-34547211720&partnerID=MN8TOARS}, DOI={10.1007/s11249-007-9224-y}, number={3}, journal={TRIBOLOGY LETTERS}, author={Neeyakorn, Worakarn and Varma, Manju and Jaye, Cherno and Burnette, James E. and Lee, Sang M. and Nemanich, Robert J. and Grant, Christine S. and Krim, Jacqueline}, year={2007}, month={Sep}, pages={269–276} }
 @article{garguilo_hong_edwards_nemanich_simon_2007, title={The surface oxidation potential of melanosomes measured by free electron laser-photoelectron emission microscopy}, volume={83}, ISSN={["1751-1097"]}, DOI={10.1562/2006-09-11-RA-1037}, abstractNote={A technique for measuring the photoionization spectrum and the photoelectron emission threshold of a microscopic structured material is presented. The theoretical underpinning of the experiment and the accuracy of the measurements are discussed. The technique is applied to titanium silicide nanostructures and melanosomes isolated from human hair, human and bovine retinal pigment epithelium cells, and the ink sac of Sepia officinalis. A common photothreshold of 4.5 ± 0.2 eV is found for this set of melanosomes and is attributed to the photoionization of the eumelanin pigment. The relationship between the photoionization threshold and the electrochemical potential referenced to the normal hydrogen electrode is used to quantify the surface oxidation potential of the melanosome. The developed technique is used to examine the effect of iron chelation on the surface oxidation potential of Sepia melanosomes. The surface oxidation potential is insensitive to bound Fe(III) up to saturation, suggesting that the metal is bound to the interior of the granule. This result is discussed in relation to the age‐dependent accumulation of iron in human melanosomes in both the eye and brain.}, number={3}, journal={PHOTOCHEMISTRY AND PHOTOBIOLOGY}, author={Garguilo, Jacob and Hong, Lian and Edwards, Glenn S. and Nemanich, Robert J. and Simon, John D.}, year={2007}, pages={692–697} }
 @article{zeman_fulton_lucovsky_nemanich_yang_2006, title={"Thermal stability of TiO2, ZrO2, or HfO2 on Si(100) by photoelectron emission microscopy" (vol 99, pg 023519, 2006)}, volume={99}, ISSN={["0021-8979"]}, DOI={10.1063/1.2201707}, abstractNote={First Page}, number={10}, journal={JOURNAL OF APPLIED PHYSICS}, author={Zeman, MC and Fulton, CC and Lucovsky, G and Nemanich, RJ and Yang, WC}, year={2006}, month={May} }
 @article{hong_garguilo_anzaldi_edwards_nemanich_simon_2006, title={Age-dependent photoionization thresholds of melanosomes and lipofuscin isolated from human retinal pigment epithelium cells}, volume={82}, ISSN={["1751-1097"]}, DOI={10.1562/2006-03-14-RA-846}, abstractNote={Abstract Melanosomes and lipofuscin were isolated from 14-, 59-, and 76-year-old, human retinal pigment epithelium specimens and examined. The morphological features of these samples were studied by scanning electron microscopy and atomic force microscopy, and the photoionization properties were examined by photoelectron emission microscopy. Ovoid- and rod-shaped melanosomes were observed. The size of the granules and the distribution between the two shapes show no significant age-dependent change. However, there is a higher occurrence of irregularly shaped aggregates of small round granules in older samples which suggests degradation or damage to melanosomes occurs with age. The melanosomes from the 14-year-old donor eye are well characterized by a single photoionization threshold, 4.1 eV, while the two older melanosomes exhibit two thresholds around 4.4 and 3.6 eV. Lipofuscin from both young and old cells show two thresholds, 4.4 and 3.4 eV. The similarity of the potentials observed for aged melanosomes and lipofuscin suggest that the lower threshold in the melanosome sample reflects lipofuscin deposited the surface of the melanosome. The amount, however, is not sufficient to alter the density of the melanosome, and therefore these granules do not separate in a sucrose gradient at densities characteristic of the typical melanolipofuscin granule. These data suggest that thin deposits of lipofuscin on the surface of retinal pigment epithelium melanosomes are common in the aged eye and that this renders the melanosomes more pro-oxidant.}, number={6}, journal={PHOTOCHEMISTRY AND PHOTOBIOLOGY}, author={Hong, Lian and Garguilo, Jacob and Anzaldi, Laura and Edwards, Glenn S. and Nemanich, Robert J. and Simon, John D.}, year={2006}, pages={1475–1481} }
 @article{koeck_obraztsov_nemanich_2006, title={Electron emission microscopy of nano-crystal graphitic films as high current density electron sources}, volume={15}, ISSN={["1879-0062"]}, DOI={10.1016/j.diamond.2005.12.051}, abstractNote={Abstract Electron emission can be described by thermionic and field effects or a combination of both and can be characterized by the laws of Richardson–Dushman and Fowler–Nordheim, respectively. Nano-crystal graphitic films exhibit a film morphology comprised mainly of crystalline graphite sheets which are vertically aligned with respect to the substrate surface. Field emission from these films exhibits a low threshold field of}, number={4-8}, journal={DIAMOND AND RELATED MATERIALS}, author={Koeck, F. A. M. and Obraztsov, A. N. and Nemanich, R. J.}, year={2006}, pages={875–879} }
 @article{fulton_lucovsky_nemanich_2006, title={Electronic properties of the Zr-ZrO2-SiO2-Si(100) gate stack structure}, volume={99}, ISSN={["1089-7550"]}, DOI={10.1063/1.2181282}, abstractNote={The interface electronic structure of a layered Zr–ZrO2–SiO2–Si(100) system was studied with x-ray (hν=1254eV) and ultraviolet (hν=21.2eV) photoemission spectroscopies. In situ growth and characterization allow the structures to be deposited and studied in a stepwise manner without the risk of contamination. This study discusses the electronic properties including electron affinities and work functions, valence band maxima, band bending in the Si, and internal fields in a layered high-κ gate stack. With this information the band alignments can be reconstructed and compared to predictions of the vacuum alignment models (i.e., the Schottky-Mott model for metal-semiconductor interfaces or the electron affinity model for heterojunctions) and the interface induced gap states model. The vacuum alignment models are first order approaches to determine the electronic barrier height for a heterojunction, and interface bonding can contribute to charge transfer across the interface, affecting the dipole contribution and altering the barrier heights. In this study, the band offsets and vacuum levels are independently measured, thereby determining the deviation from the vacuum level alignment models. The valence band offsets at the Si–SiO2, SiO2–ZrO2, and ZrO2–Zr are found to be 4.4±0.1, 0.67±0.24, and 4.9±0.44eV, respectively. For these same interfaces the deviations from the electron affinity or Schottky-Mott model are determined to be 0.2±0.14, −1.43±0.29, and 1.3±0.39eV, respectively.}, number={6}, journal={JOURNAL OF APPLIED PHYSICS}, author={Fulton, CC and Lucovsky, G and Nemanich, RJ}, year={2006}, month={Mar} }
 @article{koeck_nemanich_2006, title={Emission characterization from nitrogen-doped diamond with respect to energy conversion}, volume={15}, ISSN={["1879-0062"]}, DOI={10.1016/j.diamond.2005.08.045}, abstractNote={Vacuum thermionic energy converters utilize electron emissive materials as a key component in the transformation of thermal into electrical energy. Electron emission from nitrogen-doped diamond films was characterized with respect to the thermionic emission relation derived by Richardson–Dushman. Key parameters, which describe the emitter material, are the work function φ and the Richardson constant A. A fitting procedure has been employed to determine φ and A for nitrogen-doped diamond. However, a simultaneous solution to the Richardson–Dushman relation was limited due to the strongly coupled parameters φ and A. Additionally, the emission was characterized at various applied fields indicating a change in the electronic structure of the material contrary to classical thermionic emitters.}, number={2-3}, journal={DIAMOND AND RELATED MATERIALS}, author={Koeck, FAM and Nemanich, RJ}, year={2006}, pages={217–220} }
 @article{hanson_rodriguez_nemanich_gruverman_2006, title={Fabrication of metallic nanowires on a ferroelectric template via photochemical reaction}, volume={17}, ISSN={["0957-4484"]}, DOI={10.1088/0957-4484/17/19/028}, abstractNote={Fabrication of silver nanowires on a domain-patterned lithium niobate template by inducing a photochemical reaction in an aqueous solution is reported. Silver deposition occurs preferentially along the domain boundaries which separate antiparallel domains. The nanowires can reach lengths of hundreds of micrometres, and their location can be controlled by generating domain patterns of a desired configuration while their width depends on deposition conditions, such as temperature, solution concentration and ultraviolet (UV) light exposure time. The selective deposition process is explained by a combination of the inhomogeneous distribution of the electric field in the vicinity of the domain wall and the polarization screening mechanism of the template material. Controllable and selective deposition of metal species onto nanoscale domain-patterned ferroelectric templates may provide an alternative bottom-up route to lithographic fabrication methods.}, number={19}, journal={NANOTECHNOLOGY}, author={Hanson, J. N. and Rodriguez, B. J. and Nemanich, R. J. and Gruverman, A.}, year={2006}, month={Oct}, pages={4946–4949} }
 @article{koeck_nemanich_2006, title={Field penetration and its contribution to field enhanced thermionic electron emission from nanocrystalline diamond films}, volume={15}, ISSN={["0925-9635"]}, DOI={10.1016/j.diamond.2006.08.002}, abstractNote={Field emission from sulfur doped nanocrystalline diamond films is characterized by intense emission sites with nm scale diameters. Field emission measurements were obtained at room temperature and analyzed in terms of the Fowler–Nordheim expression where electron emission is due to tunneling through a diminished barrier. The electron emission versus temperature was also recorded at a series of applied fields from 0.5 to 0.8 V/μm. These results were analyzed in terms of a modified Richardson–Dushman relation which describes field dependent thermionic emission. It was found that both sets of data could be fit with a work function of 2.0 eV and a field enhancement factor of ∼ 1750. The large field enhancement could not be correlated with specific structures on the relatively flat surfaces. The field and thermionic-field emission from the sulfur doped nanocrystalline diamond films is evaluated by a model which includes barrier lowering as a result of field penetration effects.}, number={11-12}, journal={DIAMOND AND RELATED MATERIALS}, author={Koeck, F. A. M. and Nemanich, R. J.}, year={2006}, pages={2006–2009} }
 @article{li_perkins_collazo_nemanich_sitar_2006, title={Investigation of the effect of the total pressure and methane concentration on the growth rate and quality of diamond thin films grown by MPCVD}, volume={15}, ISSN={["1879-0062"]}, DOI={10.1016/j.diamond.2006.09.008}, abstractNote={The influence of total gas pressure (50–125 Torr) and methane concentration (0.75%–10%) on diamond growth by microwave plasma chemical vapor deposition (MPCVD) was investigated. Within the regimes studied, the growth rate was proportional to the methane concentration in the source gas while it exhibited a super-linear dependence on total pressure. For a fixed methane concentration, characterization by Raman spectroscopy, scanning electron microscopy and X-ray diffraction indicated there was a minimum pressure required for the growth of large grain diamond, and conversely, for a fixed pressure, there was a maximum methane concentration that yielded diamond deposition. Higher pressures and higher carbon concentrations yielded diamond growth rates more than 10 times higher than achieved by the conventional low pressure MPCVD process.}, number={11-12}, journal={DIAMOND AND RELATED MATERIALS}, author={Li, Xianglin and Perkins, James and Collazo, Ramon and Nemanich, Robert J. and Sitar, Zlatko}, year={2006}, pages={1784–1788} }
 @article{bilbro_nemanich_2006, title={Localized emission from flat diamond cathodes}, volume={15}, ISSN={["1879-0062"]}, DOI={10.1016/j.diamond.2005.10.045}, abstractNote={We analyze steady-state field emission from an n-type semiconductor under the assumption that its surface presents no barrier for electron emission from the conduction band into the vacuum. We construct a classical Lagrangian field theory for the coupled electric and quasi-fermi potentials and use it to show that uniform emission is unstable against laterally nonuniform perturbations. We use a two-parameter model of normal emission current to show that the Lagrangian of the linearized system is minimal when all electrons are emitted from a single site. In addition to this intensely localized emission, we show the normal electric field at the surface is moderately enhanced at the solitary emission site even though the surface itself is planar. We use the result to explain the isolated emission sites observed in nanocrystalline n-type diamond films.}, number={9}, journal={DIAMOND AND RELATED MATERIALS}, author={Bilbro, Griff L. and Nemanich, Robert J.}, year={2006}, month={Sep}, pages={1418–1423} }
 @article{koeck_zumer_nemanic_nemanich_2006, title={Photo and field electron emission microscopy, from sulfur doped nanocrystalline diamond films}, volume={15}, ISSN={["1879-0062"]}, DOI={10.1016/j.diamond.2006.01.008}, abstractNote={Room temperature electron emission from carbon and diamond films is usually based on tunnelling effects and can be implemented by application of an electric field to the emitter surface. Field emission from nanocrystalline thin films exhibits intense emission sites but a direct correlation with morphology has not been established. Thus the emission has to be formulated in terms of the electronic structure of the film as well as the geometric structure. Sulfur doped nanocrystalline diamond films were prepared by plasma assisted chemical vapor deposition utilizing 50 ppm hydrogen sulfide in hydrogen (H2S:H2) and pure methane (CH4) as the carbon source. Emission from these films is characterized by individual emitting sites with diameters < 100 nm and an emission site density of ∼5 × 103 cm− 2. This emission character is attributed to field enhancement where a contribution from geometric as well as electronic effects is discussed.}, number={4-8}, journal={DIAMOND AND RELATED MATERIALS}, author={Koeck, F. A. M. and Zumer, M. and Nemanic, V. and Nemanich, R. J.}, year={2006}, pages={880–883} }
 @article{ye_hong_garguilo_pawlak_edwards_nemanich_sarna_simon_2006, title={Photoionization thresholds of melanins obtained from free electron laser-photoelectron emission microscopy, femtosecond transient absorption spectroscopy and electron paramagnetic resonance measurements of oxygen photoconsumption}, volume={82}, ISSN={["1751-1097"]}, DOI={10.1562/2006-01-02-RA-762}, abstractNote={ABSTRACT}, number={3}, journal={PHOTOCHEMISTRY AND PHOTOBIOLOGY}, author={Ye, Tong and Hong, Lian and Garguilo, Jacob and Pawlak, Anna and Edwards, Glenn S. and Nemanich, Robert J. and Sarna, Tadeusz and Simon, John D.}, year={2006}, pages={733–737} }
 @article{smith_nemanich_bilbro_2006, title={The effect of Schottky barrier lowering and nonplanar emitter geometry on the performance of a thermionic energy converter}, volume={15}, ISSN={["1879-0062"]}, DOI={10.1016/j.diamond.2005.12.057}, abstractNote={An extension of the classical model of thermionic emission was developed to include the effects of nonplanar emitter surfaces and Schottky barrier lowering (SBL) on the output of a thermionic energy converter (TEC). Nonplanar emitter geometries along with Schottky barrier lowering may be useful in increasing both the maximum output power and output current of a thermionic energy converter. The finite element method was used to calculate the enhanced normal electric field at the surface of an emitter coated with an ultra-nanocrystalline diamond (UNCD) film and patterned with field enhancing tips. The result was used to determine the local enhanced output current and power. For the geometries considered the increased surface area of the emitter plays a significant role in increasing the output power and output current. Moreover, a calculation of the single electron time of flight shows that electrons traveling through a field enhanced region of the interelectrode space might spend half as long in transit, thus helping to mitigate the negative space charge effect that degrades the performance of vacuum TECs.}, number={4-8}, journal={DIAMOND AND RELATED MATERIALS}, author={Smith, J. R. and Nemanich, R. J. and Bilbro, G. L.}, year={2006}, pages={870–874} }
 @article{bush_garguilo_zucca_albertini_zecca_edwards_nemanich_simon_2006, title={The surface oxidation potential of human neuromelanin reveals a spherical architecture with a pheomelanin core and a eumelanin surface}, volume={103}, ISSN={["0027-8424"]}, DOI={10.1073/pnas.0604010103}, abstractNote={Neuromelanin (NM) isolated from the substantia nigra region of the human brain was studied by scanning probe and photoelectron emission microscopies. Atomic force microscopy reveals that NM granules are comprised of spherical structures with a diameter of ≈30 nm, similar to that observed forSepiacuttlefish, bovine eye, and human eye and hair melanosomes. Photoelectron microscopy images were collected at specific wavelengths of UV light between 248 and 413 nm, using the spontaneous-emission output from the Duke OK-4 free electron laser. Analysis of the data establishes a threshold photoionization potential for NM of 4.5 ± 0.2 eV, which corresponds to an oxidation potential of −0.1 ± 0.2 V vs. the normal hydrogen electrode (NHE). The oxidation potential of NM is within experimental error of the oxidation potential measured for human eumelanosomes (−0.2 ± 0.2 V vs. NHE), despite the presence of a significant fraction of the red pigment, pheomelanin, which is characterized by a higher oxidation potential (+0.5 ± 0.2 V vs. NHE). Published kinetic studies on the early chemical steps of melanogenesis show that in the case of pigments containing a mixture of pheomelanin and eumelanin, of which NM is an example, pheomelanin formation occurs first with eumelanin formation predominantly occurring only after cysteine levels are depleted. Such a kinetic model would predict a structural motif with pheomelanin at the core and eumelanin at the surface, which is consistent with the measured surface oxidation potential of the ≈30-nm constituents of NM granules.}, number={40}, journal={PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA}, author={Bush, William D. and Garguilo, Jacob and Zucca, Fabio A. and Albertini, Alberto and Zecca, Luigi and Edwards, Glenn S. and Nemanich, Robert J. and Simon, John D.}, year={2006}, month={Oct}, pages={14785–14789} }
 @article{zeman_fulton_lucovsky_nemanich_yang_2006, title={Thermal stability of TiO2, ZrO2, or HfO2 on Si(100) by photoelectron emission microscopy}, volume={99}, ISSN={["1089-7550"]}, DOI={10.1063/1.2163984}, abstractNote={The thermal stability of thin films (3nm) of transition-metal (TM) oxides (TiO2, ZrO2, and HfO2) grown on ultrathin (∼0.5nm) SiO2 buffer layers on Si(100) surfaces was investigated with ultraviolet photoelectron emission microscopy (UV-PEEM). The decomposition of the TM oxides was observed in the PEEM during ultrahigh-vacuum annealing at temperatures of ∼870, ∼900, and ∼1000°C for the TiO2, ZrO2, and HfO2, respectively. Following the decomposition reaction, atomic force microscopy measurements of the annealed surfaces revealed a high density of islands in the decomposed regions. The degradation of the TM oxide films is attributed to a reaction occurring at defects at the TM oxide/SiO2∕Si interfaces, which forms SiO species. Once a portion of the interfacial SiO2 layer is desorbed as a result of this reaction, Si from the substrate can diffuse into contact with the TM oxide layer, resulting in the formation of a TM silicide and the evolution of SiO. This process continues until the entire TM oxide layer is consumed and only silicide islands remain.}, number={2}, journal={JOURNAL OF APPLIED PHYSICS}, author={Zeman, MC and Fulton, CC and Lucovsky, G and Nemanich, RJ and Yang, WC}, year={2006}, month={Jan} }
 @article{smith_bilbro_nemanich_2006, title={Using negative electron affinity diamond emitters to mitigate space charge in vacuum thermionic energy conversion device}, volume={15}, ISSN={["0925-9635"]}, DOI={10.1016/j.diamond.2006.09.011}, abstractNote={A negative electron affinity (NEA) diamond surface is employed as an emitter electrode in a vacuum thermionic energy conversion device in order to mitigate the negative space charge effect. The motive diagram of an NEA device operating at the virtual saturation point is compared to a similar device with a conventional emitter material operating in the space charge limited regime in order to understand how NEA mitigates space charge. Output current characteristics are calculated for various NEA values, and the results are compared to an ideal (no space charge) model. Increasing the value of the NEA causes the output current characteristic to approach that of the ideal model. Motive diagrams for various values of NEA are calculated and used to explain this phenomenon. It is shown that an NEA device can achieve a maximum output power density equal to the maximum output power density of a similar ideal device.}, number={11-12}, journal={DIAMOND AND RELATED MATERIALS}, author={Smith, J. R. and Bilbro, G. L. and Nemanich, R. J.}, year={2006}, pages={2082–2085} }
 @article{dalmau_schlesser_rodriguez_nemanich_sitar_2005, title={AlN bulk crystals grown on SiC seeds}, volume={281}, ISSN={["1873-5002"]}, DOI={10.1016/j.jcrysgro.2005.03.012}, abstractNote={AlN layers with thickness between 0.1 and 3 mm were grown on on-axis and off-axis (0 0 0 1), Si-face SiC seeds by physical vapor transport (PVT) from an AlN powder source. A two-step deposition process was developed for the growth of thick layers. Cracks formed in the AlN layers due to the thermal expansion mismatch between AlN and SiC were observed to decrease with increase in AlN thickness. AlN grown on on-axis SiC was primarily Al-polar, but contained N-polar inversion domains (IDs) revealed by wet etching in hot, aqueous phosphoric acid or potassium hydroxide solutions. Regions of opposite polarity on basal plane surfaces were imaged by piezoresponse force microscopy (PFM). IDs were not observed in crystals grown on off-axis seeds. The influence of SiC seed orientation and stability on the polarity of the AlN layers is discussed.}, number={1}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Dalmau, R and Schlesser, R and Rodriguez, BJ and Nemanich, RJ and Sitar, Z}, year={2005}, month={Jul}, pages={68–74} }
 @misc{edwards_allen_haglund_nemanich_redlich_simon_yang_2005, title={Applications of free-electron lasers in the biological and material sciences}, volume={81}, ISSN={["1751-1097"]}, DOI={10.1562/2004-11-08-IR-363R.1}, abstractNote={Abstract Free-Electron Lasers (FELs) collectively operate from the terahertz through the ultraviolet range and via intracavity Compton backscattering into the X-ray and gamma-ray regimes. FELs are continuously tunable and can provide optical powers, pulse structures and polarizations that are not matched by conventional lasers. Representative research in the biological and biomedical sciences and condensed matter and material research are described to illustrate the breadth and impact of FEL applications. These include terahertz dynamics in materials far from equilibrium, infrared nonlinear vibrational spectroscopy to investigate dynamical processes in condensed-phase systems, infrared resonant-enhanced multiphoton ionization for gas-phase spectroscopy and spectrometry, infrared matrix-assisted laser-desorption–ionization and infrared matrix-assisted pulsed laser evaporation for analysis and processing of organic materials, human neurosurgery and ophthalmic surgery using a medical infrared FEL and ultraviolet photoemission electron microscopy for nanoscale characterization of materials and nanoscale phenomena. The ongoing development of ultraviolet and X-ray FELs are discussed in terms of future opportunities for applications research.}, number={4}, journal={PHOTOCHEMISTRY AND PHOTOBIOLOGY}, author={Edwards, GS and Allen, SJ and Haglund, RF and Nemanich, RJ and Redlich, B and Simon, JD and Yang, WC}, year={2005}, pages={711–735} }
 @article{dehoff_rodriguez_kingon_nemanich_gruverman_cross_2005, title={Atomic force microscopy-based experimental setup for studying domain switching dynamics in ferroelectric capacitors}, volume={76}, ISSN={["1089-7623"]}, DOI={10.1063/1.1850652}, abstractNote={This article describes an experimental setup for combined measurements of domain switching dynamics and switching currents in micrometer scale ferroelectric capacitors. The setup is based on a commercial atomic force microscope (AFM) that is equipped with a piezoresponse mode for domain imaging and with a wide bandwidth current amplifier for switching current recording. The setup allows combined domain/current measurements in capacitors as small as 1μm2 with switching times resolved down to 10ns. The incorporation of switching current measurement capability into piezoresponse AFM makes detailed analysis of switching behavior in ferroelectric memory devices possible.}, number={2}, journal={REVIEW OF SCIENTIFIC INSTRUMENTS}, author={Dehoff, C and Rodriguez, BJ and Kingon, AI and Nemanich, RJ and Gruverman, A and Cross, JS}, year={2005}, month={Feb} }
 @article{lucovsky_hong_fulton_stoute_zou_nemanich_aspnes_ade_schlom_2005, title={Conduction band states of transition metal (TM) high-k gate dielectrics as determined from X-ray absorption spectra}, volume={45}, ISSN={["0026-2714"]}, DOI={10.1016/j.microrel.2004.11.038}, abstractNote={This paper uses X-ray absorption spectroscopy to study the electronic structure of the high-k gate dielectrics including TM and RE oxides. The results are applicable to TM and rare earth (RE) silicate and aluminate alloys, as well as complex oxides comprised of mixed TM/TM and TM/RE oxides. These studies identify the nature of the lowest conduction band d∗ states, which define the optical band gap, Eg, and the conduction band offset energy with respect to crystalline Si, EB. Eg and EB scale with the atomic properties of the TM and RE atoms providing important insights for identification high-k dielectrics that meet performance targets for advanced CMOS devices.}, number={5-6}, journal={MICROELECTRONICS RELIABILITY}, author={Lucovsky, G and Hong, JG and Fulton, CC and Stoute, NA and Zou, Y and Nemanich, RJ and Aspnes, DE and Ade, H and Schlom, DG}, year={2005}, pages={827–830} }
 @article{lucovsky_fulton_zhang_luning_edge_whitten_nemanich_schlom_afanase'v_2005, title={Conduction band-edge d-states in high-k dielectrics due to Jahn-Teller term splittings}, volume={486}, ISSN={["0040-6090"]}, DOI={10.1016/j.tsf.2004.11.233}, abstractNote={X-ray absorption spectroscopy (XAS) is used to study conduction band edge electronic structure of high-k transition metal (TM) and trivalent lanthanide series rare earth (RE) oxide dielectrics. Empty TM/RE d-states are studied by intra-atomic transitions originating in core level spin-orbit split p-states, and conduction band states are studied in inter-atomic transitions which originate in the oxygen atom 1s core level state. In non-crystalline Zr and Hf silicate alloys, the local bonding symmetry, or crystal field splits these d-states into doubly and triply degenerate features. In nano-crystalline oxides, there are additional d-state splittings due to contributions of more distant neighbors that completely remove d-state degeneracies via the Jahn–Teller effect mechanism. This gives rise to highly localized band edge states that are electronically active in photoconductivity, internal photoemission, and act as bulk traps in metal oxide semiconductor (MOS) devices.}, number={1-2}, journal={THIN SOLID FILMS}, author={Lucovsky, G and Fulton, CC and Zhang, Y and Luning, J and Edge, L and Whitten, JL and Nemanich, RJ and Schlom, DG and Afanase'v, VV}, year={2005}, month={Aug}, pages={129–135} }
 @article{lucovsky_fulton_zhang_zou_luning_edge_whitten_nemanich_ade_schlom_et al._2005, title={Conduction band-edge states associated with the removal of d-state degeneracies by the Jahn-Teller effect}, volume={5}, ISSN={["1558-2574"]}, DOI={10.1109/TDMR.2005.845804}, abstractNote={X-ray absorption spectroscopy (XAS) is used to study band edge electronic structure of high-/spl kappa/ transition metal (TM) and trivalent lanthanide rare earth (RE) oxide gate dielectrics. The lowest conduction band d/sup */-states in TiO/sub 2/, ZrO/sub 2/ and HfO/sub 2/ are correlated with: 1) features in the O K/sub 1/ edge, and 2) transitions from occupied Ti 2p, Zr 3p and Hf 4p states to empty Ti 3d-, Zr 4d-, and Hf 5d-states, respectively. The relative energies of d-state features indicate that the respective optical bandgaps, E/sub opt/ (or equivalently, E/sub g/), and conduction band offset energy with respect to Si, E/sub B/, scale monotonically with the d-state energies of the TM/RE atoms. The multiplicity of d-state features in the Ti L/sub 2,3/ spectrum of TiO/sub 2/, and in the derivative of the O K/sub 1/ spectra for ZrO/sub 2/ and HfO/sub 2/ indicate a removal of d-state degeneracies that results from a static Jahn-Teller effect in these nanocrystalline thin film oxides. Similar removals of d-state degeneracies are demonstrated for complex TM/RE oxides including Zr and Hf titanates, and La, Gd and Dy scandates. Analysis of XAS and band edge spectra indicate an additional band edge state that is assigned Jahn-Teller distortions at internal grain boundaries. These band edges defect states are electronically active in photoconductivity (PC), internal photoemission (IPE), and act as bulk traps in metal oxide semiconductor (MOS) devices, contributing to asymmetries in tunneling and Frenkel-Poole transport that have important consequences for performance and reliability in advanced Si devices.}, number={1}, journal={IEEE TRANSACTIONS ON DEVICE AND MATERIALS RELIABILITY}, author={Lucovsky, G and Fulton, CC and Zhang, Y and Zou, Y and Luning, J and Edge, LF and Whitten, JL and Nemanich, RJ and Ade, H and Schlom, DG and et al.}, year={2005}, month={Mar}, pages={65–83} }
 @article{gruverman_rodriguez_dehoff_waldrep_kingon_nemanich_cross_2005, title={Direct studies of domain switching dynamics in thin film ferroelectric capacitors}, volume={87}, ISSN={["1077-3118"]}, DOI={10.1063/1.2010605}, abstractNote={An experimental approach for direct studies of the polarization reversal mechanism in thin film ferroelectric capacitors based on piezoresponse force microscopy (PFM) in conjunction with pulse switching capabilities is presented. Instant domain configurations developing in a 3×3μm2 capacitor at different stages of the polarization reversal process have been registered using step-by-step switching and subsequent PFM imaging. The developed approach allows direct comparison of experimentally measured microscopic switching behavior with parameters used by phenomenological switching models. It has been found that in the low field regime (just above the threshold value) used in the present study, the mechanism of polarization reversal changes during the switching cycle from the initial nucleation-dominated process to the lateral domain expansion at the later stages. The classical nucleation model of Kolmogorov–Avrami–Ishibashi (KAI) provides reasonable approximation for the nucleation-dominated stage of switching but is inapplicable to the slow switching stage. It has been suggested that the switching dynamics can be approximated by averaging the KAI model over a broad distribution of switching times.}, number={8}, journal={APPLIED PHYSICS LETTERS}, author={Gruverman, A and Rodriguez, BJ and Dehoff, C and Waldrep, JD and Kingon, AI and Nemanich, RJ and Cross, JS}, year={2005}, month={Aug} }
 @article{rodriguez_nemanich_kingon_gruverman_kalinin_terabe_liu_kitamura_2005, title={Domain growth kinetics in lithium niobate single crystals studied by piezoresponse force microscopy}, volume={86}, ISSN={["1077-3118"]}, DOI={10.1063/1.1845594}, abstractNote={The kinetics of sidewise domain growth in an inhomogeneous electric field has been investigated in stoichiometric LiNbO3 single crystals by measuring the lateral domain size as a function of the voltage pulse magnitude and duration using piezoresponse force microscopy. The domain size increases linearly with the voltage magnitude suggesting that the domain size is kinetically limited in a wide range of pulse magnitudes and durations. In spite of that, the written domains exhibit strong retention behavior. It is suggested that the switching behavior can be described by the universal scaling curve. Domain kinetics can be described as an activation process by calculating the field distribution using the charged sphere model under the assumption of an exponential field dependence of the wall velocity. The activation energy is found to be a function of the external field.}, number={1}, journal={APPLIED PHYSICS LETTERS}, author={Rodriguez, BJ and Nemanich, RJ and Kingon, A and Gruverman, A and Kalinin, SV and Terabe, K and Liu, XY and Kitamura, K}, year={2005}, month={Jan} }
 @article{kock_garguilo_nemanich_2005, title={Field enhanced thermionic electron emission from sulfur doped nanocrystalline diamond films}, volume={14}, ISSN={["1879-0062"]}, DOI={10.1016/j.diamond.2004.12.056}, abstractNote={Thermal activation of field enhancement based emitters can provide efficient means of lowering the emission barrier, thus enabling high current density electron sources. Microwave plasma assisted chemical vapour deposition was employed to synthesize sulfur doped nanocrystalline diamond films with various sulfur/carbon concentrations. Electron emission at elevated temperatures was characterized by direct imaging of the emission utilizing electron emission microscopy. Sulfur doped nanocrystalline diamond films exhibit electron emission from singular sites indicating a non-uniform distribution of the local field enhancement. The threshold field for electron emission changes significantly by varying the sulfur/carbon concentration in the gas phase. At elevated temperatures the emission is strongly enhanced but remains confined to the intense emission sites.}, number={3-7}, journal={DIAMOND AND RELATED MATERIALS}, author={Kock, FAM and Garguilo, JM and Nemanich, RJ}, year={2005}, pages={704–708} }
 @article{lucovsky_zhang_fulton_zou_nemanich_ade_whitten_2005, title={Final state effects in VUV and soft X-ray absorption spectra of transition metal oxides and silicate alloys: comparisons between experiment and ab initio calculations}, volume={144}, ISSN={["1873-2526"]}, DOI={10.1016/j.elspec.2005.01.251}, abstractNote={This paper uses X-ray absorption spectroscopy and vacuum ultra-violet spectroscopic ellipsometry to study the electronic structure of high-k transition metal (TM) oxide gate dielectrics. The results are applicable to TM and rare earth (RE) silicate and aluminate alloys, as well as complex oxides comprised of mixed TM/TM and TM/RE oxides. These studies identify the nature of the lowest conduction band d* states, which define the optical band gap, including their relationship to the band gap, Eg, of the oxide.}, journal={JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA}, author={Lucovsky, G and Zhang, Y and Fulton, CC and Zou, Y and Nemanich, RJ and Ade, H and Whitten, JL}, year={2005}, month={Jun}, pages={917–919} }
 @article{burnette_nemanich_sayers_2005, title={Formation of stable titanium germanosilicide thin films on Si1-xGex}, volume={97}, ISSN={["1089-7550"]}, DOI={10.1063/1.1923164}, abstractNote={The sequential deposition of strained Si1−xGex with concentrations x=0.20 and 0.30, amorphous silicon, and titanium on Si (100) after annealing at 700°C leads to the formation of a C54 Ti(Si1−yGey)2∕Si1−xGex bilayer, the phase formation and interface stability of which are studied. The use of an amorphous layer of Si is employed to eliminate or decrease the formation of germanium-rich Si1−zGez alloy precipitates found in the solid-phase reaction of Ti and Si1−xGex. It has been proposed that the precipitation phenomenon was driven by differences in the enthalpy of formation as a function of concentration in the Ti(Si1−yGey)2 layer, resulting from the enthalpy difference between TiSi2 and TiGe2 compounds, both of which are assumed to be completely miscible with one another. Layers of amorphous silicon of varying thicknesses were incorporated between a 300-Å Ti layer and the strained Si1−xGex substrate layer to achieve Ti(Si1−yGey)2 films that are in equilibrium with the Si1−xGex substrate. The use of amorphous silicon layers of varying thicknesses indicated that Ti(Si1−yGey)2∕Si1−xGex films could be formed with the absence of germanium-rich precipitates at the grain boundaries, depending on the amorphous silicon layer thickness.}, number={11}, journal={JOURNAL OF APPLIED PHYSICS}, author={Burnette, JE and Nemanich, RJ and Sayers, DE}, year={2005}, month={Jun} }
 @article{wang_gupta_garguilo_liu_qin_nemanich_2005, title={Growth and field emission properties of small diameter carbon nanotube films}, volume={14}, ISSN={["1879-0062"]}, DOI={10.1016/j.diamond.2004.10.003}, abstractNote={Vertically aligned carbon nanotube films with diameters smaller than 5 nm, high densities up to 1012/cm2, and lengths of ∼ 5–8 μm were deposited by microwave plasma-assisted chemical vapor deposition. Experiments show that, by continuous reduction in the thickness of the iron film (i.e., ∼0.3–0.5 nm), small diameter carbon nanotubes can be achieved with diameters that ranged from 1–5 nm, and the films are comprised of both single- and double-wall nanotubes. The electron field emission properties of the films were investigated by variable distance field emission and temperature-dependent field electron emission microscopy (T-FEEM). The films showed an emission site density of ∼104/cm2 and a threshold field of 2.8 V/μm similar to multiwalled nanotubes (1.9 V/μm). In addition, they also exhibited a temperature dependence of the emission site intensity.}, number={3-7}, journal={DIAMOND AND RELATED MATERIALS}, author={Wang, YY and Gupta, S and Garguilo, JM and Liu, ZJ and Qin, LC and Nemanich, RJ}, year={2005}, pages={714–718} }
 @article{scheer_wieser_wurz_bochsler_hertzberg_fuselier_koeck_nemanich_schleberger_2005, title={High negative ion yield from light molecule scattering}, volume={230}, ISSN={["0168-583X"]}, DOI={10.1016/j.nimb.2004.12.063}, abstractNote={Molecular oxygen and hydrogen ions were scattered at grazing incidence from several diamond-like carbon (DLC) surfaces in the energy range from 190 eV to 2400 eV. Most surfaces were hydrogen terminated. For incident positive oxygen ions, scattered negative ion fractions of up to 33% were recorded, and for incident positive hydrogen ions, negative ion fractions of more than 5% were measured. These values are among the highest ever reported, especially for oxygen. They have been matched only by results of scattering experiments using a hydrogen terminated surface of natural diamond.}, journal={NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS}, author={Scheer, JA and Wieser, M and Wurz, P and Bochsler, P and Hertzberg, E and Fuselier, SA and Koeck, FA and Nemanich, RJ and Schleberger, M}, year={2005}, month={Apr}, pages={330–339} }
 @article{wang_gupta_nemanich_liu_qin_2005, title={Hollow to bamboolike internal structure transition observed in carbon nanotube films}, volume={98}, ISSN={["1089-7550"]}, DOI={10.1063/1.1946198}, abstractNote={The transition of the internal structure in microwave chemical-vapor-deposited carbon nanotubes is investigated using scanning electron microscopy and high-resolution transmission electron microscopy. By controlling the thickness of the iron catalyst layer, a sequence of carbon nanotube films was obtained with diameters ranging from a few nanometers to over 100nm. Experiments have established that by continuous reduction of the Fe layer thickness to <1nm, single- and double-wall carbon nanotube films can be produced, whereas for an Fe film thickness >1nm, multiwall carbon nanotube films can be synthesized. It was also found that for an Fe thickness ⩾5nm, interlayers (i.e., bamboolike or periodically compartmentalized nanotubes) were formed, while for an iron thickness <2nm the tubes were primarily hollow. For an intermediate Fe thickness the internal structure of the carbon nanotubes was a mixture of hollow and bamboolike. A growth model which considers bulk and surface diffusions of carbon into and∕or onto the Fe catalyst surface is proposed to describe this transition and the internal periodic structure.}, number={1}, journal={JOURNAL OF APPLIED PHYSICS}, author={Wang, YY and Gupta, S and Nemanich, RJ and Liu, ZJ and Qin, LC}, year={2005}, month={Jul} }
 @article{gupta_wang_garguilo_nemanich_2005, title={Imaging temperature-dependent field emission from carbon nanotube films: Single versus multiwalled}, volume={86}, ISSN={["1077-3118"]}, DOI={10.1063/1.1850616}, abstractNote={Field emission properties of vertically aligned single- and multiwalled carbon nanotube films at temperatures up to 1000°C are investigated by electron emission microscopy, enabling real-time imaging of electron emission to provide information on emission site density, the temporal variation of the emission intensity, and insight into the role of adsorbates. The nanotube films showed an emission site density of 104∼105∕cm2, which is compared to the areal density (from 1012–1013∕cm2to108–109∕cm2). At ambient temperature, the emission indicated temporal fluctuation (∼6%–8%) in emission current with minimal changes in the emission pattern. At elevated temperatures, the emission site exhibited an increase in emission site intensity. From the experimental observations, it is proposed that the chemisorbed molecules tend to desorb presumably at high applied electric fields (field-induced) in combination with thermal effects (thermal-induced) and provide a contrasting comparison between semiconducting (single-walled) and metallic (multiwalled) nanotubes.}, number={6}, journal={APPLIED PHYSICS LETTERS}, author={Gupta, S and Wang, YY and Garguilo, JM and Nemanich, RJ}, year={2005}, month={Feb} }
 @article{wang_gupta_liang_nemanich_2005, title={Increased field-emission site density from regrown carbon nanotube films}, volume={97}, ISSN={["1089-7550"]}, DOI={10.1063/1.1897836}, abstractNote={Electron field-emission properties of as-grown, etched, and regrown carbon nanotube thin films were investigated. The aligned carbon nanotube films were deposited by the microwave plasma-assisted chemical vapor deposition technique. The surface of the as-grown film contained a carbon nanotube mat of amorphous carbon and entangled nanotubes with some tubes protruding from the surface. Hydrogen plasma etching resulted in the removal of the surface layer, and regrowth on the etched surface displayed the formation of a new carbon nanotube mat. The emission site density and the current–voltage dependence of the field emission from all of the samples were analyzed. The results showed that the as-grown sample had a few strong emission spots and a relatively high emission current density (∼20μA∕cm2 at 1V∕μm), while the regrown sample exhibited a significantly increased emission site density.}, number={10}, journal={JOURNAL OF APPLIED PHYSICS}, author={Wang, YY and Gupta, S and Liang, M and Nemanich, RJ}, year={2005}, month={May} }
 @article{rodriguez_gruverman_kingon_nemanich_cross_2005, title={Investigation of the mechanism of polarization switching in ferroelectric capacitors by three- dimensional piezoresponse force microscopy}, volume={80}, ISSN={["1432-0630"]}, DOI={10.1007/s00339-004-2925-2}, abstractNote={A mechanism for the switching behavior of (111)-oriented Pb(Zr,Ti)O3-based 1×1.5 μm2 capacitors has been investigated using three-dimensional piezoresponse force microscopy (3D-PFM). A combination of vertical and lateral piezoresponse force microscopy (VPFM and LPFM) has been used to map the out-of-plane and the in-plane components of the polarization. The three-dimensional polarization distribution was reconstructed by quantitative analysis of the PFM amplitude images of poled PZT capacitors while taking into account contrast variations in the PFM phase images. The switching behavior of the capacitors was determined by comparison of the static domain patterns in the same capacitors after both positive and negative poling. While 180° degree switching was observed, surprisingly, the switching process was dominated by 90° polarization vector rotation. Furthermore, central regions of the capacitors were characterized by the presence of charged domain boundaries, which could lead to imprint (preference of one polarization state over another).}, number={1}, journal={APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING}, author={Rodriguez, BJ and Gruverman, A and Kingon, AI and Nemanich, RJ and Cross, JS}, year={2005}, month={Jan}, pages={99–103} }
 @article{monteiro-riviere_nemanich_inman_wang_riviere_2005, title={Multi-walled carbon nanotube interactions with human epidermal keratinocytes}, volume={155}, ISSN={["1879-3169"]}, url={http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000226645800005&KeyUID=WOS:000226645800005}, DOI={10.1016/j.toxlet.2004.11.004}, abstractNote={Carbon nanotubes have widespread applications in multiple engineering disciplines. However, little is known about the toxicity or interaction of these particles with cells. Carbon nanotube films were grown using a microwave plasma enhanced chemical vapor deposition system. Human epidermal keratinocytes (HEK) were exposed to 0.1, 0.2, and 0.4 mg/ml of multi-walled carbon nanotubes (MWCNT) for 1, 2, 4, 8, 12, 24 and 48 h. HEK were examined by transmission electron microscopy for the presence of MWCNT. Here we report that chemically unmodified MWCNT were present within cytoplasmic vacuoles of the HEK at all time points. The MWCNT also induced the release of the proinflammatory cytokine interleukin 8 from HEKs in a time dependent manner. These data clearly show that MWCNT, not derivatized nor optimized for biological applications, are capable of both localizing within and initiating an irritation response in a target epithelial cell that composes a primary route of occupational exposure for manufactured nanotubes.}, number={3}, journal={TOXICOLOGY LETTERS}, author={Monteiro-Riviere, NA and Nemanich, RJ and Inman, AO and Wang, YYY and Riviere, JE}, year={2005}, month={Mar}, pages={377–384} }
 @article{wieser_wurz_bochsler_moebius_quinn_fuselier_ghielmetti_defazio_stephen_nemanich_2005, title={NICE: an instrument for direct mass spectrometric measurement of interstellar neutral gas}, volume={16}, ISSN={["1361-6501"]}, DOI={10.1088/0957-0233/16/8/019}, abstractNote={The direct measurement of the neutral interstellar gas requires a very sensitive neutral particle imaging instrument in the energy range of 10 eV–1000 eV. For successful detection and identification, the neutral particles have to be ionized first, which will be accomplished via surface ionization. This method is successfully employed in the Low Energy Neutral Atom imager (LENA) instrument on the IMAGE spacecraft launched on 25 March 2000, which still operates well. We present the laboratory prototype of the Neutral Interstellar Composition Experiment (NICE), a neutral particle mass spectrometer dedicated to the measurement of interstellar gas, and will discuss its instrumental characteristics. Performance is evaluated with emphasis on the neutral to negative ion conversion for hydrogen and oxygen and the collection of these ions by the mass spectrometer. Measurements of the detection efficiency of the prototype for primary neutral hydrogen and oxygen atoms are presented. Several conversion surfaces, conductive and insulating, were investigated and all are potential candidates for a next generation neutral particle imaging instrument.}, number={8}, journal={MEASUREMENT SCIENCE AND TECHNOLOGY}, author={Wieser, M and Wurz, P and Bochsler, P and Moebius, E and Quinn, J and Fuselier, SA and Ghielmetti, A and DeFazio, JN and Stephen, TM and Nemanich, RJ}, year={2005}, month={Aug}, pages={1667–1676} }
 @article{samokhvalov_hong_liu_garguilo_nemanich_edwards_simon_2005, title={Oxidation potentials of human eumelanosomes and plheomelanosomes}, volume={81}, ISSN={["1751-1097"]}, DOI={10.1562/2004-07-23-RC-245.1}, abstractNote={Abstract Eumelanosomes and pheomelanosomes isolated from black and red human hair, respectively, were studied by photoelectron emission microscopy (PEEM). PEEM images were collected at various wavelengths between 207 and 344 nm, using the spontaneous emission output of the Duke OK-4 free electron laser (FEL). Analysis of the FEL-PEEM data revealed ionization thresholds of 4.6 and 3.9 eV corresponding to oxidation potentials of −0.2 and +0.5 V vs normal hydrogen electrode for eumelanosomes and pheomelanosomes, respectively. The difference in oxidation potential is attributed to the pigment content of the melanosome, namely whether it contains primarily eumelanin and pheomelanin. The effect of added melanosomes on the reduction of Fe(III)-cytochrome showed pheomelanosomes are stronger reducing agents than eumelanosomes, consistent with the measured oxidation potentials. The FEL-PEEM experiment offers to be an important new approach for quantifying the effects of age, oxidation and metal accumulation on the oxidation potentials of intact melanosomes.}, number={1}, journal={PHOTOCHEMISTRY AND PHOTOBIOLOGY}, author={Samokhvalov, A and Hong, L and Liu, Y and Garguilo, J and Nemanich, RJ and Edwards, GS and Simon, JD}, year={2005}, pages={145–148} }
 @article{yang_rodriguez_gruverman_nemanich_2005, title={Photo electron emission microscopy of polarity-patterned materials}, volume={17}, ISSN={["1361-648X"]}, DOI={10.1088/0953-8984/17/16/012}, abstractNote={This study presents variable photon energy photo electron emission microscopy (PEEM) of polarity-patterned epitaxial GaN films, and ferroelectric LiNbO3 (LNO) single crystals and PbZrTiO3 (PZT) thin films. The photo electrons were excited with spontaneous emission from the tunable UV free electron laser (FEL) at Duke University. We report PEEM observation of polarity contrast and measurement of the photothreshold of each polar region of the materials. For a cleaned GaN film with laterally patterned Ga- and N-face polarities, we found a higher photoelectric yield from the N-face regions compared with the Ga-face regions. Through the photon energy dependent contrast in the PEEM images of the surfaces, we can deduce that the threshold of the N-face region is less than ∼4.9 eV while that of the Ga-face regions is greater than 6.3 eV. In both LNO and PZT, bright emission was detected from the negatively poled domains, indicating that the emission threshold of the negative domain is lower than that of the positive domain. For LNO, the measured photothreshold was ∼4.6 eV at the negative domain and ∼6.2 eV at the positive domain, while for PZT, the threshold of the negative domain was less than 4.3 eV. Moreover, PEEM observation of the PZT surface at elevated temperatures displayed that the domain contrast disappeared near the Curie temperature of ∼300 °C. The PEEM polarity contrast of the polar materials is discussed in terms of internal screening from free carriers and defects and the external screening due to adsorbed ions.}, number={16}, journal={JOURNAL OF PHYSICS-CONDENSED MATTER}, author={Yang, WC and Rodriguez, BJ and Gruverman, A and Nemanich, RJ}, year={2005}, month={Apr}, pages={S1415–S1426} }
 @article{hartman_naniwae_petrich_nemanich_davis_2005, title={Photo-electron emission and atomic force microscopies of the hydrogen etched 6H-SiC(0001) surface and the initial growth of GaN and AlN}, volume={242}, ISSN={["0169-4332"]}, DOI={10.1016/j.apsusc.2004.09.021}, abstractNote={Photo-emission electron microscopy (PEEM) and atomic force microscopy (AFM) have been used to characterize the surfaces of hydrogen etched 6H-SiC(0 0 0 1) wafers and the microstructure of the initial stages of growth of GaN and AlN on these surfaces via molecular beam epitaxy. The PEEM images were obtained using a free electron laser as the photon source. A stepped structure was evident in these images of the surfaces etched at 1600–1700 °C for 15 min. Comparison with the AFM images revealed that emission was occurring from the intersection of the steps and the terraces. Images of the initial stages of deposition of the GaN thin films at 700 and 800 °C revealed three-dimensional island growth. The degree of coalescence of these films was dependent upon the step structure: regions containing steps having unit cell height exhibited complete or nearly complete coalescence; regions containing steps with half unit cell height showed voids in the films parallel to the steps. PEEM of the initial stages of growth of AlN revealed immediate nucleation and rapid coalescence during deposition at 900 °C, except in areas on the substrate surface containing steps having half unit cell height. Incomplete coalescence and pits were also observed in the latter areas.}, number={3-4}, journal={APPLIED SURFACE SCIENCE}, author={Hartman, JD and Naniwae, K and Petrich, C and Nemanich, R and Davis, RF}, year={2005}, month={Apr}, pages={428–436} }
 @article{mecouch_wagner_reitmeier_davis_pandarinath_rodriguez_nemanich_2005, title={Preparation and characterization of atomically clean, stoichlometric surfaces of AIN(0001)}, volume={23}, ISSN={["0734-2101"]}, DOI={10.1116/1.1830497}, abstractNote={In situ exposure of the (0001) surface of AlN thin films to flowing ammonia at 1120 °C and 10−4Torr removes oxygen∕hydroxide and hydrocarbon species below the detectable limits of x-ray photoelectron spectroscopy and decreases the Al∕N ratio from 1.3 to 1.0. The positions of the Al2p and the N1s core level peaks acquired from the cleaned surfaces were 75.0±0.1eV and 398.2±0.1eV, respectively, which were similar to the values determined for the as-loaded samples. The cleaning process left unchanged the (1×1) low energy electron diffraction pattern, the step-and-terrace microstructure, and the root mean square roughness values observed for the surfaces of the as-loaded samples; i.e., the surface structure and microstructure were not changed by the high-temperature exposure to ammonia at low pressures. Vacuum annealing under 10−7Torr at 1175 °C for 15 min removed all detectable hydrocarbons; however, it did not remove the oxygen∕hydroxide species.}, number={1}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A}, author={Mecouch, WJ and Wagner, BP and Reitmeier, ZJ and Davis, RF and Pandarinath, C and Rodriguez, BJ and Nemanich, RJ}, year={2005}, pages={72–77} }
 @article{rodriguez_yang_nemanich_gruverman_2005, title={Scanning probe investigation of surface charge and surface potential of GaN-based heterostructures}, volume={86}, ISSN={["1077-3118"]}, DOI={10.1063/1.1869535}, abstractNote={Scanning Kelvin probe microscopy (SKPM) and electrostatic force microscopy (EFM) have been employed to measure the surface potentials and the surface charge densities of the Ga- and the N-face of a GaN lateral polarity heterostructure (LPH). The surface was subjected to an HCl surface treatment to address the role of adsorbed charge on polarization screening. It has been found that while the Ga-face surface appears to be unaffected by the surface treatment, the N-face surface exhibited an increase in adsorbed screening charge density (1.6±0.5×1010cm−2), and a reduction of 0.3±0.1V in the surface potential difference between the N- and Ga-face surfaces.}, number={11}, journal={APPLIED PHYSICS LETTERS}, author={Rodriguez, BJ and Yang, WC and Nemanich, RJ and Gruverman, A}, year={2005}, month={Mar} }
 @article{wieser_wurz_nemanich_fuselier_2005, title={Secondary electron emission of chemical-vapor-deposited diamond by impact of slow H+, D+, H-2(+), C+, O+, and O-2(+) ions}, volume={98}, ISSN={["0021-8979"]}, DOI={10.1063/1.1996855}, abstractNote={We report on the measurements of the secondary electron yield of chemical-vapor-deposited diamond upon the reflection of primary H+, D+, H2+, C+, O+, and O2+ ions in an energy range of 50–1000 eV per atom at a 60° angle of incidence to the surface normal. Depending on the species and energy, a secondary electron yield between 0.1 and 2 was observed and remained unchanged over weeks without further periodic reconditioning of the surface and in spite of the moderate vacuum environment of 10−7mbar. Semiempirical fit functions were found with a dependence on the inverse velocity and the square root of the atomic number of the projectiles.}, number={3}, journal={JOURNAL OF APPLIED PHYSICS}, author={Wieser, M and Wurz, P and Nemanich, RJ and Fuselier, SA}, year={2005}, month={Aug} }
 @article{fitting_ware_haywood_walter_nemanich_2005, title={Self-organized nanoscale Ge dots and dashes on SiGe/Si superlattices}, volume={98}, ISSN={["1089-7550"]}, DOI={10.1063/1.1993751}, abstractNote={This study explores the self-organization of Ge nanostructures on SiGe/Si superlattices grown on Si substrates with the surface normal tilted from (001) towards (111) by up to 25°. Prior studies found two-dimensional ordering of Ge dots on nominally flat Si(001) surfaces with a very homogeneous size distribution. Our results show that the Ge islands are less ordered for tilted Si(001) substrates. For substrates with a miscut of 25°, Ge dots nucleate on top of the ripples that form approximately perpendicular to the [1-10]Si direction, i.e., perpendicular to the step direction. Additionally, we observe the formation of Ge dashes, which align preferentially along the [1-10]Si direction.}, number={2}, journal={JOURNAL OF APPLIED PHYSICS}, author={Fitting, L and Ware, ME and Haywood, JR and Walter, JJH and Nemanich, RJ}, year={2005}, month={Jul} }
 @article{coppa_fulton_kiesel_davis_pandarinath_burnette_nemanich_smith_2005, title={Structural, microstructural, and electrical properties of gold films and Schottky contacts on remote plasma-cleaned, n-type ZnO{0001} surfaces}, volume={97}, ISSN={["1089-7550"]}, DOI={10.1063/1.1898436}, abstractNote={Current–voltage measurements of Au contacts deposited on ex situ cleaned, n-type ZnO(0001) [(0001¯)] surfaces showed reverse bias leakage current densities of ∼0.01(∼0.1)A∕cm2 at 4.6 (3.75) V reverse bias and ideality factors >2 (both surfaces) before sharp, permanent breakdown (soft breakdown). This behavior was due primarily to the presence of (1.6–2.0)±0.1[(0.7–2.6)±0.1] monolayers (ML) of hydroxide, which forms an electron accumulation layer and increases the surface conductivity. In situ remote plasma cleaning of the (0001) [(0001¯)] surfaces using a 20vol%O2∕80vol%He mixture for the optimized temperatures, times, and pressure of 550±20°C(525±20°C), 60 (30) min, and 0.050 Torr reduced the thickness of the hydroxide layer to ∼0.4±0.1ML and completely eliminated all detectable hydrocarbon contamination. Subsequent cooling of both surfaces in the plasma ambient resulted in the chemisorption of oxygen and a change from 0.2 eV of downward band bending for samples cooled in vacuum to 0.3 eV of upward band bending indicative of the formation of a depletion layer of lower surface conductivity. Cooling in either ambient produced stoichiometric ZnO{0001} surfaces having an ordered crystallography as well as a step-and-terrace microstructure on the (0001¯) surface; the (0001) surface was without distinctive features. Sequentially deposited, unpatterned Au films, and presumably the rectifying gold contacts, initially grew on both surfaces cooled in the plasma ambient via the formation of islands that subsequently coalesced, as indicated by calculations from x-ray photoelectron spectroscopy data and confirmed by transmission electron microscopy. Calculations from the current–voltage data of the best contacts revealed barrier heights on the (0001) [(0001¯)] surfaces of 0.71±0.05(0.60±0.05)eV, a saturation current density of (4±0.5)×10−6A∕cm2(2.0±0.5×10−4A∕cm2), a lower value of n=1.17±0.05(1.03±0.05), a significantly lower leakage current density of ∼1.0×10−4A∕cm2(∼91×10−9A∕cm2) at 8.5 (7.0) V reverse bias prior to sharp, permanent breakdown (soft breakdown). All measured barrier heights were lower than the predicted Schottky–Mott value of 1.0 eV, indicating that the interface structure and the associated interface states affect the Schottky barrier. However, the constancy in the full width at half maximum of the core levels for Zn 2p(1.9±0.1eV) and O 1s(1.5±0.1eV), before and after sequential in situ Au depositions, indicated an abrupt, unreacted Au∕ZnO(0001) interface. Transmission electron microscopy confirmed the abruptness of an epitaxial interface. Annealing the contacts on the (0001) surface to 80±5 and 150±5°C resulted in decreases in the ideality factors to 1.12±0.05 and 1.09±0.05 and increases in saturation current density to 9.05 and 4.34μA∕cm2, the barrier height to 0.82±0.5 and 0.79±0.5eV, and in the leakage current densities to ∼2×10−3A∕cm2 at 6 V and ∼20×10−3A∕cm2 at 7 V, respectively.}, number={10}, journal={JOURNAL OF APPLIED PHYSICS}, author={Coppa, BJ and Fulton, CC and Kiesel, SM and Davis, RF and Pandarinath, C and Burnette, JE and Nemanich, RJ and Smith, DJ}, year={2005}, month={May} }
 @article{fulton_lucovsky_zhang_zou_nemanich_ade_whitten_2005, title={Studies of the coupling of final d*-states in mixed Hf and Ti oxides (HfO2)(x)(TiOx)(1-x) and other complex oxides}, volume={144}, ISSN={["1873-2526"]}, DOI={10.1016/j.elspec.2005.01.098}, abstractNote={Abstract X-ray absorption spectroscopy and vacuum ultra-violet spectroscopic ellipsometry are used to study the electronic structure of complex oxides comprised of mixed TM/TM and TM/RE oxides. Experimental spectra for HfTiO 4 and Gd(Dy)ScO 3 indicate multiple d-state features in the O K 1 edge. These are compared with the empirical models for atomic d-state mixing. It is concluded that a mean field, virtual alloy model does not apply, and that the effects associated with the differences in atomic coordination and deviations from ideal octahedral or cubic bonding play a determinant role in d-state atom mixing. The results are applied band edge engineering options for high- k dielectric applications.}, journal={JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA}, author={Fulton, CC and Lucovsky, G and Zhang, Y and Zou, Y and Nemanich, RJ and Ade, H and Whitten, JL}, year={2005}, month={Jun}, pages={913–916} }
 @article{koeck_nemanich_2005, title={Sulfur doped nanocrystalline diamond films as field enhancement based thermionic emitters and their role in energy conversion}, volume={14}, ISSN={["0925-9635"]}, DOI={10.1016/j.diamond.2005.09.001}, abstractNote={Sulfur doped nanocrystalline diamond films, like other nanostructured carbon films, exhibit electron emission characterized by a spatial non-uniformity of the field enhancement factor. While field emission effects are observed at room temperature, an increase in emitter temperature is accompanied by an amplified emission current with a simultaneous drop in the threshold field. At low extraction fields a fit of the emission current to the Richardson equation indicates a material work function of ∼2.5 eV. The Schottky formula describes thermionic emission at a moderate field and is utilized to determine the work function at an electric field of 0.8 V/μm with a value of ∼1.7 eV and a concurrently reduced Richardson constant. This significant difference in the work function of 2.5 and 1.7 eV for 0.5 and 0.8V/μm, respectively can be attributed to field enhancement effects.}, number={11-12}, journal={DIAMOND AND RELATED MATERIALS}, author={Koeck, FAM and Nemanich, RJ}, year={2005}, pages={2051–2054} }
 @article{monteiro-riviere_inman_wang_nemanich_2005, title={Surfactant effects on carbon nanotube interactions with human keratinocytes}, volume={1}, ISSN={["1549-9642"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-33745481652&partnerID=MN8TOARS}, DOI={10.1016/j.nano.2005.10.007}, abstractNote={Interactions of multiwalled carbon nanotubes (MWCNTs) with human epidermal keratinocytes (HEKs) were studied with respect to the effect of surfactant on dispersion of MWCNT aggregates and cytotoxicity. Our earlier studies had shown that the unmodified MWCNTs were localized within the cytoplasmic vacuoles of HEKs and elicited an inflammatory response. However, MWCNTs in solution tend to aggregate and, therefore, cells are exposed to large MWCNT aggregates. The purpose of this study was to find a surfactant that prevents the formation of large aggregates of MWCNTs without being toxic to the HEKs. HEKs were exposed to serial dilutions (10% to 0.1%) of L61, L92, and F127 Pluronic and 20 or 60 Tween for 24 hours. HEK viability, proportional to surfactant concentration, ranged from 27.1% to 98.5% with Pluronic F127; viability with the other surfactants was less than 10%. Surfactants dispersed and reduced MWCNT aggregation in medium. MWCNTs at 0.4 mg/mL in 5% or 1% Pluronic F127 were incubated with HEKs and assayed for interleukin 8 (IL-8). MWCNTs were cytotoxic to HEKs independent of surfactant exposure. In contrast, MWCNT-induced IL-8 release was reduced when exposed to 1% or 5% Pluronic F127 (P < .05). However, both MWCNTs and surfactant, alone or in combination, increased IL-8 release compared with control exposures at 12 and 24 hours. These results suggest that the surfactant-MWCNT interaction is more complex than simple dispersion alone and should be investigated to determine the mode of interaction.}, number={4}, journal={NANOMEDICINE-NANOTECHNOLOGY BIOLOGY AND MEDICINE}, author={Monteiro-Riviere, Nancy A. and Inman, Alfred O. and Wang, Yunyu Y. and Nemanich, Robert J.}, year={2005}, month={Dec}, pages={293–299} }
 @article{castro-colin_donner_moss_islam_sinha_nemanich_metzger_bosecke_shulli_2005, title={Synchrotron x-ray studies of vitreous SiO2 over Si(001). I. Anisotropic glass contribution}, volume={71}, ISSN={["1098-0121"]}, DOI={10.1103/physrevb.71.045310}, abstractNote={While numerous investigations of the structure and interface of amorphous SiO{sub 2} thermally grown on Si, theoretical as well as experimental, have been carried out over the years, a definitive picture of this thin gate oxide and its interface remains lacking. We have explored this issue using synchrotron x rays in grazing incidence geometry. In this geometry a fourfold modulation in the first sharp diffraction peak (FSDP) from thin vitreous SiO{sub 2} of 100 and 500 A thickness can be observed. While the FSDP exhibits a modulation throughout the entire film, this modulation decays away from the interface. Reflectivity measurements were also performed, which reveal an interfacial layer of 3% density increase in the SiO{sub 2} film over the bulk (film) density.}, number={4}, journal={PHYSICAL REVIEW B}, author={Castro-Colin, M and Donner, W and Moss, SC and Islam, Z and Sinha, SK and Nemanich, R and Metzger, HT and Bosecke, P and Shulli, T}, year={2005}, month={Jan} }
 @article{castro-colin_donner_moss_islam_sinha_nemanich_2005, title={Synchrotron x-ray studies of vitreous SiO2 over Si(001). II. Crystalline contribution}, volume={71}, ISSN={["1098-0121"]}, DOI={10.1103/physrevb.71.045311}, abstractNote={Thermally oxidized thin films grown on Si(001) were analyzed with synchrotron x rays. By looking at crystal truncation rod (CTR) profiles we were able to observe, as have others, a crystalline peak, nominally along the (1 1 L) rod, together with Laue oscillations matching the film thickness. These oscillations are evidence of a crystalline component present throughout the entire film that vanishes away from the interface with the silicon substrate. A model consisting of distorted coesite is proposed to explain the results.}, number={4}, journal={PHYSICAL REVIEW B}, author={Castro-Colin, M and Donner, W and Moss, SC and Islam, Z and Sinha, SK and Nemanich, R}, year={2005}, month={Jan} }
 @article{garguilo_koeck_nemanich_xiao_carlisle_auciello_2005, title={Thermionic field emission from nanocrystalline diamond-coated silicon tip arrays}, volume={72}, ISSN={["2469-9969"]}, DOI={10.1103/physrevb.72.165404}, abstractNote={Thermionic field emission properties of nitrogen doped ultrananocrystalline diamond (UNCD) coated silicon tip arrays are examined using thermionic field emission electron microscopy (TFEEM). Nitrogen doping has been shown to enhance the emission properties of diamond by the introduction of a donor level $1.7\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ below the conduction band minimum. The field enhancing geometry of the films initiates accelerated electron emission at the tipped structures which may be beneficial to thermionic energy converter design where space charge effects can significantly limit attainable current densities. Two temperature regimes of electron emission are observed; $600--800\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$, where the emission is enabled because of the H passivation and $900--1100\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$, where the emission is attributed to tunneling from nitrogen related states through the barrier of a clean diamond surface.}, number={16}, journal={PHYSICAL REVIEW B}, author={Garguilo, JM and Koeck, FAM and Nemanich, RJ and Xiao, XC and Carlisle, JA and Auciello, O}, year={2005}, month={Oct} }
 @article{hinkle_fulton_nemanich_lucovsky_2004, title={A novel approach for determining the effective tunneling mass of electrons in HfO2 and other high-K alternative gate dielectrics for advanced CMOS devices}, volume={72}, ISSN={["1873-5568"]}, DOI={10.1016/j.mee.2003.12.047}, abstractNote={There has been a search for alternative dielectrics with significantly increased dielectric constants, K, which increases physical thickness in proportion to K, and therefore would significantly reduce direct tunneling. However, increases in K to values of 15–25 in transition metal and rare earth oxides are generally accompanied by decreases in the conduction band offset energy with respect to Si, EB, and the effective electron tunneling mass, meff, which mitigate gains from increased thickness. A novel technique, based on stacked dielectrics, is used to obtain the tunneling mass-conduction band offset energy product. When combined with optical measurements of tunneling barriers, this yields direct estimates of the tunneling mass.}, number={1-4}, journal={MICROELECTRONIC ENGINEERING}, author={Hinkle, CL and Fulton, C and Nemanich, RJ and Lucovsky, G}, year={2004}, month={Apr}, pages={257–262} }
 @article{ware_nemanich_gray_hull_2004, title={Analysis of a nonorthogonal pattern of misfit dislocation arrays in SiGe epitaxy on high-index Si substrates}, volume={95}, DOI={10.1063/1.1630362}, abstractNote={We have investigated the formation of misfit dislocations resulting from the growth of partially strained Si0.7Ge0.3 epitaxial films on Si substrates with surface normals rotated off of the [001] axis toward [110] by 0°, 13°, and 25°. Transmission electron microscopy has shown that the dislocations form in a modified cross-hatch pattern for samples grown on the off-axis substrates. This modified cross hatch consists of three arrays along which the dislocations align. This is in contrast to the two orthogonal arrays found on the on-axis (001) substrates. These dislocations correspond well with the intersection of the (111) slip planes with the respective surfaces. We present a simple analysis of the amount of relaxation due to probable Burger’s vectors for these dislocations, which reveals the most likely directions for these vectors and shows that the density of dislocations only accounts for a fraction of the total film relaxation as measured by Raman peak shifts. These studies form the basis for the use of high index surfaces as components in modern devices, and provide pathways to possible templates for use in the growth of nanostructures.}, number={1}, journal={Journal of Applied Physics}, author={Ware, M. E. and Nemanich, R. J. and Gray, J. L. and Hull, R.}, year={2004}, pages={115–122} }
 @article{kock_garguilo_nemanich_2004, title={Direct correlation of surface morphology with electron emission sites for intrinsic nanocrystalline diamond films}, volume={13}, ISSN={["1879-0062"]}, DOI={10.1016/j.diamond.2004.01.008}, abstractNote={Abstract Field emission properties of nanocrystalline diamond films show low turn-on fields resulting in significant electron emission at low applied fields originating from individual sites with an emission site density of ∼104/cm2. We have employed a high resolution electron emission microscope operating in field emission mode to image the spatial distribution of emission sites for intrinsic nanocrystalline diamond thin films. The location of individual emission sites has been directly correlated to the surface morphology probed by scanning electron microscopy. Surface topography measurements show fine structured features consisting of micron and submicron domains separated by grain boundaries. No preferred topographic features that would account for field emission can be detected suggesting that the electronic structure of the grains and their boundaries under a high electric field has to be considered in order to account for the observed emission characteristics.}, number={4-8}, journal={DIAMOND AND RELATED MATERIALS}, author={Kock, EM and Garguilo, JM and Nemanich, RJ}, year={2004}, pages={1022–1025} }
 @article{hinkle_fulton_nemanich_lucovsky_2004, title={Enhanced tunneling in stacked gate dielectrics with ultra-thin HfO2 (ZrO2) layers sandwiched between thicker SiO2 layers}, volume={566}, ISSN={["1879-2758"]}, DOI={10.1016/j.susc.2004.06.084}, abstractNote={There has been a search for alternative dielectrics with significantly increased dielectric constants, K, which increases in physical thickness proportional to K, and therefore would significantly reduce direct tunneling. However, increases in k to values of 15–25 in transition metal and rare earth oxides are generally accompanied by decreases in the conduction band offset energy with respect to Si, EB, and the effective electron tunneling mass, meff, which mitigate gains from increased thickness. A novel technique, based on stacked dielectrics, is used to obtain the tunneling mass-conduction band offset energy product. When combined with optical measurements of tunneling barriers, this yields direct estimates of the tunneling mass.}, journal={SURFACE SCIENCE}, author={Hinkle, CL and Fulton, C and Nemanich, RJ and Lucovsky, G}, year={2004}, month={Sep}, pages={1185–1189} }
 @article{hinkle_fulton_nemanich_lucovsky_2004, title={Enhanced tunneling in stacked gate dielectrics with ultra-thin HfO2 layers sandwiched between thicker SiO2 layers}, volume={234}, DOI={10.1016/j.apsusc.2004-05.076}, number={37990}, journal={Applied Surface Science}, author={Hinkle, C. L. and Fulton, C. and Nemanich, R. J. and Lucovsky, G.}, year={2004}, pages={240–245} }
 @article{wang_tang_koeck_brown_garguilo_nemanich_2004, title={Experimental studies of the formation process and morphologies of carbon nanotubes with bamboo mode structures}, volume={13}, ISSN={["0925-9635"]}, DOI={10.1016/j.diamond.2004.01.009}, abstractNote={Carbon nanotubes (CNT) were synthesized by microwave plasma chemical vapor deposition, and the formation process and morphologies of bamboo mode structures were systematically analyzed. Thin films of Fe on Si substrates were used as the catalyst, and the CNT films were characterized with electron microscopy, Raman spectroscopy, and Auger electron spectroscopy. For growth up to 15 min, the films grow with vertically aligned CNT with evidence of amorphous carbon at the top surface. For longer growth times the films exhibit a layer of amorphous carbon and a CNT mat on top of the aligned carbon nanotube ‘forest.’ Transmission electron microscopy measurements displayed multiwalled CNT with bamboo structure and encapsulated tips some of which contained catalyst particles. Two kinds of bamboo mode structures were observed: cone shaped, and cylindrical. The results indicate that the CNT growth is predominantly of the base growth mode, and the formation of the compartments was attributed to the difference in the bulk and surface diffusion of carbon species at the catalyst.}, number={4-8}, journal={DIAMOND AND RELATED MATERIALS}, author={Wang, YY and Tang, GY and Koeck, FM and Brown, B and Garguilo, JM and Nemanich, RJ}, year={2004}, pages={1287–1291} }
 @article{garguilo_davis_buddie_kock_nemanich_2004, title={Fibrinogen adsorption onto microwave plasma chemical vapor deposited diamond films}, volume={13}, ISSN={["1879-0062"]}, DOI={10.1016/j.diamond.2003.10.008}, abstractNote={This study investigates the haemocompatibility of diamond films and attempts to correlate the results to structural characteristics and surface termination. The samples evaluated consisted of polycrystalline and nanocrystalline diamond films, single crystal diamond, titanium and silicon. Raman spectroscopy detailed the sp3 and sp2 bonding configurations while surface morphology was imaged using atomic force microscopy. Initial contact angles of deionized water were obtained using the sessile drop method. Samples exposed to a hydrogen plasma, and thus hydrogen terminated, became more hydrophobic while samples oxidized by a nitric acid etch became more hydrophilic. The adsorption process of the human protein fibrinogen was then studied on each of the samples. The water contact angle for the MPCVD and single crystal diamond samples did not change, indicating little protein adsorption. Titanium and silicon samples became more hydrophilic as a result of adhered fibrinogen protein.}, number={4-8}, journal={DIAMOND AND RELATED MATERIALS}, author={Garguilo, JM and Davis, BA and Buddie, M and Kock, FAM and Nemanich, RJ}, year={2004}, pages={595–599} }
 @article{coppa_fulton_hartlieb_davis_rodriguez_shields_nemanich_2004, title={In situ cleaning and characterization of oxygen- and zinc-terminated, n-type, ZnO{0001} surfaces}, volume={95}, ISSN={["1089-7550"]}, DOI={10.1063/1.1695596}, abstractNote={A layer containing an average of 1.0 monolayer (ML) of adventitious carbon and averages of 1.5 ML and 1.9 ML of hydroxide was determined to be present on the respective O-terminated (0001̄) and Zn-terminated (0001) surfaces of ZnO. A diffuse low-energy electron diffraction pattern was obtained from both surfaces. In situ cleaning procedures were developed and their efficacy evaluated in terms of the concentrations of residual hydrocarbons and hydroxide and the crystallography, microstructure, and electronic structure of these surfaces. Annealing ZnO(0001̄) in pure oxygen at 600–650 °C±20 °C reduced but did not eliminate all of the detectable hydrocarbon contamination. Annealing for 15 min in pure O2 at 700 °C and 0.100±0.001 Torr caused desorption of both the hydrocarbons and the hydroxide constituents to concentrations below the detection limits (∼0.03 ML=∼0.3 at. %) of our x-ray photoelectron spectroscopy instrument. However, thermal decomposition degraded the surface microstructure. Exposure of the ZnO(0001̄) surface to a remote plasma having an optimized 20% O2/80% He mixture for the optimized time, temperature, and pressure of 30 min, 525 °C, and 0.050 Torr, respectively, resulted in the desorption of all detectable hydrocarbon species. Approximately 0.4 ML of hydroxide remained. The plasma-cleaned surface possessed an ordered crystallography and a step-and-terrace microstructure and was stoichiometric with nearly flat electronic bands. A 0.5 eV change in band bending was attributed to the significant reduction in the thickness of an accumulation layer associated with the hydroxide. The hydroxide was more tightly bound to the ZnO(0001) surface; this effect increased the optimal temperature and time of the plasma cleaning process for this surface to 550 °C and 60 min, respectively, at 0.050 Torr. Similar changes were achieved in the structural, chemical, and electronic properties of this surface; however, the microstructure only increased slightly in roughness and was without distinctive features.}, number={10}, journal={JOURNAL OF APPLIED PHYSICS}, author={Coppa, BJ and Fulton, CC and Hartlieb, PJ and Davis, RF and Rodriguez, BJ and Shields, BJ and Nemanich, RJ}, year={2004}, month={May}, pages={5856–5864} }
 @article{fulton_cook_lucovsky_nemanich_2004, title={Interface instabilities and electronic properties of ZrO2 on silicon (100)}, volume={96}, ISSN={["1089-7550"]}, DOI={10.1063/1.1776313}, abstractNote={The interface stability of Zr-based high-k dielectrics with an oxide buffer layer was explored with x-ray (hυ=1254eV) and ultraviolet (hυ=21.2eV) photoemission spectroscopy. Zirconium oxide films were grown and characterized in situ in a stepwise sequence to explore their chemical stability and electronic properties as a function of film thickness and processing conditions. The buffer layers serve to lower the interface state density and to address the high temperature instabilities of ZrO2 in direct contact with Si. This research addresses three issues: (1) the development of the band offsets and electronic structure during the low temperature (T<300°C) growth processes, (2) variations in the band structure as effected by process conditions and annealing (T<700°C), and (3) the interface stability of Zr oxide films at high temperatures (T>700°C). Annealing the as-grown films to 600°C results in an ∼2eV shift of the ZrO2-Si band alignment, giving a band offset that is, favorable to devices, in agreement with predictions and in agreement with other experiments. We propose that the as-grown films contain excess oxygen resulting in a charge transfer from the Si substrate to the internal (ZrO2-SiO2) interface and that annealing to 600°C is sufficient to drive off this oxygen. Further annealing to 900°C, in the presence of excess Si at the surface, results in decomposition of the oxide to form ZrSi2.}, number={5}, journal={JOURNAL OF APPLIED PHYSICS}, author={Fulton, CC and Cook, TE and Lucovsky, G and Nemanich, RJ}, year={2004}, month={Sep}, pages={2665–2673} }
 @article{koeck_garguilo_nemanich_2004, title={On the thermionic emission from nitrogen-doped diamond films with respect to energy conversion}, volume={13}, ISSN={["0925-9635"]}, DOI={10.1016/j.diamond.2004.06.027}, abstractNote={Thermionic energy converters utilize thermal energy and efficiently transform it into more useful electrical energy. A key aspect in thermionic energy conversion is the emission of electrons at elevated temperatures, where the electron emitter is separated from the collector by a vacuum gap and a voltage is generated due to the temperature difference between the emitter and collector. In this study, nitrogen-doped diamond films with a negative electron affinity surface have been synthesized with plasma-assisted chemical vapor deposition, and the electron emission has been imaged using high-resolution electron emission microscopy. This study reports the measurement of a thermovoltage and current, i.e. energy conversion, at temperatures considerably less than 1000 °C.}, number={11-12}, journal={DIAMOND AND RELATED MATERIALS}, author={Koeck, FAM and Garguilo, JM and Nemanich, RJ}, year={2004}, pages={2052–2055} }
 @misc{samokhvalov_garguilo_yang_edwards_nemanich_simon_2004, title={Photoionization threshold of eumelanosomes determined using UV free electron laser - Photoelectron emission microscopy}, volume={108}, ISSN={["1520-5207"]}, DOI={10.1021/jp046701q}, abstractNote={The application of UV-free electron laser photoelectron emission microscopy (UV-FEL PEEM) to measure the threshold photoelectron spectrum and photoionization potential for human eumelanosomes is described. The origin of potential artifacts and the limitations of the technique are discussed and their potential effects on the measured photoionization potential are quantified. The UV-FEL-PEEM images collected on human eumelanosomes isolated from black hair show that the organelle is photoionized by UV-B radiation. The photoionization threshold is determined to be 4.6 ± 0.2 eV. This result provides new insight into the origin of the differences between the photoionization and oxygen photoconsumption action spectra for eumelanins.}, number={42}, journal={JOURNAL OF PHYSICAL CHEMISTRY B}, author={Samokhvalov, A and Garguilo, J and Yang, WC and Edwards, GS and Nemanich, RJ and Simon, JD}, year={2004}, month={Oct}, pages={16334–16338} }
 @article{yang_rodriguez_gruverman_nemanich_2004, title={Polarization-dependent electron affinity of LiNbO3 surfaces}, volume={85}, ISSN={["1077-3118"]}, DOI={10.1063/1.1790604}, abstractNote={Polar surfaces of a ferroelectric LiNbO3 crystal with periodically poled domains are explored using UV-photoelectron emission microscopy (PEEM). Compared with the positive domains (domains with positive surface polarization charges), a higher photoelectric yield is found from the negative domains (domains with negative surface polarization charges), indicating a lower photothreshold and a corresponding lower electron affinity. The photon-energy-dependent contrast in the PEEM images of the surfaces indicates that the photothreshold of the negative domains is ∼4.6eV while that of the positive domains is greater than ∼6.2eV. We propose that the threshold difference between the opposite domains can be attributed to a variation of the electron affinity due to opposite surface dipoles induced by surface adsorbates.}, number={12}, journal={APPLIED PHYSICS LETTERS}, author={Yang, WC and Rodriguez, BJ and Gruverman, A and Nemanich, RJ}, year={2004}, month={Sep}, pages={2316–2318} }
 @article{fulton_lucovsky_nemanich_2004, title={Process-dependent band structure changes of transition-metal (Ti,Zr,Hf) oxides on Si (100)}, volume={84}, ISSN={["1077-3118"]}, DOI={10.1063/1.1639944}, abstractNote={In this study, we have deposited Ti, Zr, and Hf oxides on ultrathin (∼0.5 nm) SiO2 buffer layers and have identified metastable states which give rise to large changes in their band alignments with respect to the Si substrate. This results in a potential across the interfacial SiO2 layer, significant band bending, and large shifts of the high-k valence band. The magnitude of the shift differs for the three materials and is dependant on both the SiO2 buffer layer thickness and annealing temperature. We propose a model where excess oxygen accumulates near the high-k-SiO2 interface providing electronic states, which are available to electrons that tunnel from the substrate.}, number={4}, journal={APPLIED PHYSICS LETTERS}, author={Fulton, CC and Lucovsky, G and Nemanich, RJ}, year={2004}, month={Jan}, pages={580–582} }
 @article{prawer_nemanich_2004, title={Raman spectroscopy of diamond and doped diamond}, volume={362}, ISSN={["1364-503X"]}, DOI={10.1098/rsta.2004.1451}, abstractNote={The optimization of diamond films as valuable engineering materials for a wide variety of applications has required the development of robust methods for their characterization. Of the many methods used, Raman microscopy is perhaps the most valuable because it provides readily distinguishable signatures of each of the different forms of carbon (e.g. diamond, graphite, buckyballs). In addition it is non-destructive, requires little or no specimen preparation, is performed in air and can produce spatially resolved maps of the different forms of carbon within a specimen. This article begins by reviewing the strengths (and some of the pitfalls) of the Raman technique for the analysis of diamond and diamond films and surveys some of the latest developments (for example, surface-enhanced Raman and ultraviolet Raman spectroscopy) which hold the promise of providing a more profound understanding of the outstanding properties of these materials. The remainder of the article is devoted to the uses of Raman spectroscopy in diamond science and technology. Topics covered include using Raman spectroscopy to assess stress, crystalline perfection, phase purity, crystallite size, point defects and doping in diamond and diamond films.}, number={1824}, journal={PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY OF LONDON SERIES A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES}, author={Prawer, S and Nemanich, RJ}, year={2004}, month={Nov}, pages={2537–2565} }
 @article{wang_gupta_nemanich_2004, title={Role of thin Fe catalyst in the synthesis of double- and single-wall carbon nanotubes via microwave chemical vapor deposition}, volume={85}, ISSN={["0003-6951"]}, DOI={10.1063/1.1796529}, abstractNote={Synthesis of vertically aligned small diameter (single- and double-wall) carbon nanotube films on thermally oxidized n+-Si(001) wafers, with acetylene diluted with ammonia gas mixture using a microwave plasma-assisted chemical vapor deposition technique, is reported. Experiments show that by continuous reduction in the thickness of the iron catalyst film to ∼0.3–0.5nm, or alternately, smaller catalyst particles produces hollow concentric tubes with a fewer number of walls. Double- and single-wall carbon nanotubes with diameters ranging from 1 to 5nm were identified using transmission electron microscopy and Raman spectroscopy. A relatively higher deposition temperature (∼850°C) in conjunction with a controlled catalyst and rapid growth (<40s) allowed for the growth of well-graphitized, high areal density (∼1012-1013∕cm2) nanotubes with reduced amorphous carbon and iron. Our results also indicate that the base growth is the most appropriate model to describe the growth mechanism for the nanotube films.}, number={13}, journal={APPLIED PHYSICS LETTERS}, author={Wang, YY and Gupta, S and Nemanich, RJ}, year={2004}, month={Sep}, pages={2601–2603} }
 @article{yang_ade_nemanich_2004, title={Shape stability of TiSi2 islands on Si (111)}, volume={95}, ISSN={["1089-7550"]}, DOI={10.1063/1.1636526}, abstractNote={The evolution of the shape and size of TiSi2 islands on Si (111) surfaces is explored with real time ultraviolet photoelectron emission microscopy. During continuous deposition of Ti at elevated temperatures, individual islands in a dilute surface distribution grow larger without island–island interactions. As they increase in size, symmetric islands transform into elongated shaped islands with high length-to-width aspect ratios. An extremely elongated island shows a ratio of 85:1 and is ∼17 μm long and ∼0.2 μm wide. The individual elongated islands have different widths regardless of their length. The width of the growing islands is determined at the initial transition stage and remains essentially constant with increasing length. We propose that the various widths of the elongated islands are determined by the degree of strain relaxation, possibly through the nucleation of dislocations at the island interface. In addition, it is found that the elongated islands display a prism-like shape or a truncated prism-like shape. We propose that the shape evolution of the elongated islands is related to both strain relaxation and growth kinetics.}, number={3}, journal={JOURNAL OF APPLIED PHYSICS}, author={Yang, WC and Ade, H and Nemanich, RJ}, year={2004}, month={Feb}, pages={1572–1576} }
 @inbook{burnette_himmerlich_nemanich_2004, title={Silicide contacts for Si/Ge devices}, DOI={10.1049/pbep005e_ch7}, abstractNote={The development of ohmic or rectifying contacts to the semiconducting Si/Ge layers is a critical step in the development of the device technologies. Understanding the formation and electronic states of contacts to Si/Ge semiconducting layers begins with the clean surfaces. The formation and stability of the contacts will depend on the interface chemistry, and for Si/Ge, the system shows significant complexity in comparison to silicide contacts to silicon surfaces. Finally, the device operation will depend on the electrical properties of the interface. This chapter presents summaries of the current understanding of each of these areas, focusing on: (1) surface properties of Si1-xGex/Si(100) and Si1-xGex-Si(111) surfaces and stoichiometry of Si1-xGex surfaces, (2) interface thermodynamics, formation and stability of Ti(Si/Ge) on Si/Ge, CoSi2 on Si/Ge, NiSi on Si/Ge, and other metal silicide or germanosilicide thin films on Si/Ge, and lastly (3) Schottky barrier properties of silicide contacts on Si/Ge.}, booktitle={Silicide technology for integrated circuits}, publisher={London: Institution of Electrical Engineers}, author={Burnette, J. E. and Himmerlich, M. and Nemanich, R. J.}, year={2004} }
 @article{lucovsky_hong_fulton_zou_nemanich_ade_scholm_freeouf_2004, title={Spectroscopic studies of metal high-k dielectrics: transition metal oxides and silicates, and complex rare earth/transition metal oxides}, volume={241}, ISSN={["1521-3951"]}, DOI={10.1002/pssb.200404938}, abstractNote={Abstract}, number={10}, journal={PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS}, author={Lucovsky, G and Hong, JG and Fulton, CC and Zou, Y and Nemanich, RJ and Ade, H and Scholm, DG and Freeouf, JL}, year={2004}, month={Aug}, pages={2221–2235} }
 @article{yang_ade_nemanich_2004, title={Stability and dynamics of Pt-Si liquid microdroplets on Si(001)}, volume={69}, ISSN={["2469-9969"]}, DOI={10.1103/physrevb.69.045421}, abstractNote={The formation and dynamics of Pt-Si liquid droplets on Si (001) surfaces are explored with real-time ultraviolet photoelectron emission microscopy. PtSi islands of micrometer lateral diameter begin to melt and are transformed into molten Pt-Si alloy islands below the melting point of bulk PtSi. In particular, at ∼1100 °C surface migration of the liquid microdroplets is observed, where the droplets move directionally from the cold to the hot regions of the surface following the temperature gradient across the substrate. It is proposed that the droplet surface migration is due to dissolution-diffusion-deposition flow of Si through the droplet driven by the Si concentration difference in the droplet. In addition, the migration rate of the droplet is measured as a function of temperature and droplet diameter. Above a minimum diameter, the migration velocity is independent of the droplet size, which indicates that Si diffusivity through the droplet is the primary factor determining the rate of migration. The activation energy for the Si diffusion in the droplet is found to be ∼0.57 eV. We conclude that the thermal and chemical stability of the droplet-substrate interface significantly affects the evolution and dynamics of the liquid island on the surface.}, number={4}, journal={PHYSICAL REVIEW B}, author={Yang, WC and Ade, H and Nemanich, RJ}, year={2004}, month={Jan} }
 @article{rodriguez_gruverman_kingon_nemanich_cross_2004, title={Three-dimensional high-resolution reconstruction of polarization in ferroelectric capacitors by piezoresponse force microscopy}, volume={95}, ISSN={["1089-7550"]}, DOI={10.1063/1.1638889}, abstractNote={A combination of vertical and lateral piezoresponse force microscopy (VPFM and LPFM, respectively) has been used to map the out-of-plane and in-plane polarization distribution, respectively, of (111)-oriented Pb(Zr,Ti)O3-based (PZT) ferroelectric patterned and reactively-ion-etched capacitors. While VPFM and LPFM have previously been used to determine the orientation of the polarization vector in ferroelectric crystals and thin films, this is the first time the technique has been applied to determine the three-dimensional polarization distribution in thin-film capacitors and, as such, is of importance to the implementation of nonvolatile ferroelectric random access memory. Sequential VPFM and LPFM imaging have been performed in poled 1×1.5 μm2 PZT capacitors. Subsequent quantitative analysis of the obtained piezoresponse images allowed the three-dimensional reconstruction of the domain arrangement in the PZT layers of the capacitors. It has been found that the poled capacitors, which appear as uniformly polarized in VPFM, are in fact in a polydomain state as is detected by LPFM and contain 90° domain walls. Despite the polycrystallinity of the PZT layer, regions larger than the average PZT grain size are found to have the same polarization orientation. This technique has potential for clarifying the switching behavior and imprint mechanism in micro- and nanoscale ferroelectric capacitors.}, number={4}, journal={JOURNAL OF APPLIED PHYSICS}, author={Rodriguez, BJ and Gruverman, A and Kingon, AI and Nemanich, RJ and Cross, JS}, year={2004}, month={Feb}, pages={1958–1962} }
 @article{lucovsky_hong_fulton_zou_nemanich_ade_2004, title={X-ray absorption spectra for transition metal high-kappa dielectrics: Final state differences for intra- and inter-atomic transitions}, volume={22}, ISSN={["2166-2746"]}, DOI={10.1116/1.1771670}, abstractNote={This article applies x-ray absorption spectroscopy to a study of the electronic structure of the high-k gate dielectrics, TiO2, ZrO2, and HfO2. Qualitative and quantitative differences are identified between intra-atomic transitions such as the Zr 3p-state, M2,3 core state absorptions which terminate in TM 4d*- and 5s*-states, and inter-atomic transitions such as the Zr 1s- and O 1s-state K1 absorptions which terminate in Zr 4d*- and 5s*-states that are mixed with O atom 2p* states through nearest neighbor bonding interactions. Differences between the spectral peak energies of the lowest d*-features in the O K1 spectra are demonstrated to scale with optical band gap differences for TiO2, ZrO2, and HfO2, providing important information relevant to applications of TM oxides as high-κ gate dielectrics in advanced Si devices. This is demonstrated through additional scaling relationships between (i) conduction band offset energies between Si and the respective dielectrics, and the optical band gaps, and (ii) the conduction band offset energies, and the electron tunneling masses as well.}, number={4}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B}, author={Lucovsky, G and Hong, JG and Fulton, CC and Zou, Y and Nemanich, RJ and Ade, H}, year={2004}, pages={2132–2138} }
 @article{yang_zeman_ade_nemanich_2003, title={Attractive migration and coalescence: A significant process in the coarsening of TiSi2 islands on the Si(111) surface}, volume={90}, ISSN={["0031-9007"]}, DOI={10.1103/physrevlett.90.136102}, abstractNote={The dynamics and coarsening of TiSi2 islands on Si(111) surfaces are studied in real time with photoelectron emission microscopy. A significant fraction of events are observed in which nearby islands move attractively toward each other and subsequently coalesce. It is proposed that attractive island migration is due to the growth-decay flow of the island edges driven by a nonuniform surface concentration around the islands. The local surface concentration is induced by the neighboring islands. This coarsening mechanism should significantly affect the evolution of the island distribution.}, number={13}, journal={PHYSICAL REVIEW LETTERS}, author={Yang, WC and Zeman, M and Ade, H and Nemanich, RJ}, year={2003}, month={Apr} }
 @article{cook_fulton_mecouch_davis_lucovsky_nemanich_2003, title={Band offset measurements of the GaN (0001)/HfO2 interface}, volume={94}, DOI={10.1063/1.1618374}, number={11}, journal={Journal of Applied Physics}, author={Cook, T. E. and Fulton, C. C. and Mecouch, W. J. and Davis, R. F. and Lucovsky, G. and Nemanich, R. J.}, year={2003}, pages={7155–7158} }
 @article{cook_fulton_mecouch_davis_lucovsky_nemanich_2003, title={Band offset measurements of the Si3N4/GaN (0001) interface}, volume={94}, ISSN={["0021-8979"]}, DOI={10.1063/1.1601314}, abstractNote={X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy were used to measure electronic states as Si3N4 was deposited on clean GaN (0001) surfaces. The n-type (2×1018) and p-type (1×1017) GaN surfaces were atomically cleaned in NH3 at 860 °C, and the n-and p-type surfaces showed upward band bending of ∼0.2±0.1 eV and downward band bending of 1.1±0.1 eV, respectively, both with an electron affinity of 3.1±0.1 eV. Layers of Si (∼0.2 nm) were deposited on the clean GaN and nitrided using an electron cyclotron resonance N2 plasma at 300 °C and subsequently annealed at 650 °C for densification into a Si3N4 film. Surface analysis was performed after each step in the process, and yielded a valence band offset of 0.5±0.1 eV. Both interfaces exhibited type II band alignment where the valence band maximum of GaN lies below that of the Si3N4 valence band. The conduction band offset was deduced to be 2.4±0.1 eV, and a change of the interface dipole of 1.1±0.1 eV was observed for Si3N4/GaN interface formation.}, number={6}, journal={JOURNAL OF APPLIED PHYSICS}, author={Cook, TE and Fulton, CC and Mecouch, WJ and Davis, RF and Lucovsky, G and Nemanich, RJ}, year={2003}, month={Sep}, pages={3949–3954} }
 @article{hartman_roskowski_reitmeier_tracy_davis_nemanich_2003, title={Characterization of hydrogen etched 6H-SiC(0001) substrates and subsequently grown AlN films}, volume={21}, ISSN={["0734-2101"]}, DOI={10.1116/1.1539080}, abstractNote={Wafers of n-type, 6H–SiC(0001) with (ND–NA)=(5.1–7.5)×1017 and 2.5×1018 were etched in a flowing 25%H2/75%He mixture within the range of 1500–1640 °C at 1 atm. Equilibrium thermodynamic calculations indicated that the presence of atomic hydrogen is necessary to achieve etching of SiC. Atomic force microscopy, optical microscopy, and low energy electron diffraction of the etched surface revealed a faceted surface morphology with unit cell and half unit cell high steps and a 1×1 reconstruction. The latter sample also exhibited a much larger number of hexagonal pits on the surface. Annealing the etched samples under ultrahigh vacuum (UHV) at 1030 °C for 15 min resulted in (1) a reduction of the surface oxygen and adventitious hydrocarbons below the detection limit of Auger electron spectroscopy, (2) a (√3×√3)R30° reconstructed surface and (3) a Si-to-C peak-to-peak height ratio of 1.2. By contrast, using a chemical vapor cleaning (CVC) process consisting of an exposure to 3000 Langmuir (L) of silane at 1030 °C for 10 min under UHV conditions resulted in a (3×3) surface reconstruction, a Si-to-C ratio of 3.9, and islands of excess silicon. Continued annealing of the latter material for an additional 10 min at 1030 °C resulted in a (1×1) LEED pattern with a diffuse ring. Films of AlN grown via MOCVD at a sample platter temperature of 1274 °C for 15 min on hydrogen etched wafers having a doping concentration of 8.7×1017 cm−3 and cleaned via annealing had a rms roughness value of ≈0.4 nm.}, number={2}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A}, author={Hartman, JD and Roskowski, AM and Reitmeier, ZJ and Tracy, KM and Davis, RF and Nemanich, RJ}, year={2003}, pages={394–400} }
 @article{tracy_hartlieb_einfeldt_davis_hurt_nemanich_2003, title={Electrical and chemical characterization of the Schottky barrier formed between clean n-GaN(0001) surfaces and Pt, Au, and Ag}, volume={94}, ISSN={["0021-8979"]}, DOI={10.1063/1.1598630}, abstractNote={Platinum, gold, and silver formed abrupt, unreacted, smooth, and epitaxial metal–semiconductor interfaces when deposited from the vapor onto clean, n-type GaN(0001) films. The Schottky barrier heights, determined from data acquired using x-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, capacitance–voltage, and current–voltage measurements agreed to within the experimental error for each contact metal and had the values of 1.2±0.1, 0.9±0.1, and 0.6±0.1 eV for Pt, Au, and Ag, respectively. The band bending and the electron affinity at the clean n-GaN surface were 0.3±0.1 and 3.1±0.1 eV, respectively. The barrier height is proportional to the metal work function, indicating that the Fermi level is not pinned at the GaN surface. However, discrepancies to the Schottky–Mott model were found as evidenced by a proportionality factor of 0.44 between the work function of the metal and the resulting Schottky barrier height. The sum of these discrepancies constitute the interface dipole contributions to the Schottky barrier height which were measured to be ∼1.4, 1.3, and 0.7 eV for Pt, Au, and Ag, respectively.}, number={6}, journal={JOURNAL OF APPLIED PHYSICS}, author={Tracy, KM and Hartlieb, PJ and Einfeldt, S and Davis, RF and Hurt, EH and Nemanich, RJ}, year={2003}, month={Sep}, pages={3939–3948} }
 @article{lucovsky_raynor_zhang_fulton_nemanich_appel_ade_whitten_2003, title={Electronic structure of transition metal high-k dielectrics: interfacial band offset energies for microelectronic devices}, volume={212}, ISSN={["0169-4332"]}, DOI={10.1016/S0169-4332(03)00055-2}, abstractNote={Transition metal silicates, (ZrO2)x(SiO2)1� x, have dielectric constants k > 10 that make them attractive for advanced Si devices. Band offset energies relative to Si are an important factor in determining tunneling leakage current, and internal photoemission. Studies by X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and X-ray absorption spectroscopy (XAS) are combined with ab initio calculations to identify the compositional variation of the band-gap, and valence and conduction band offset energies of Zr silicate alloys with respect to Si. The minimum conduction band offset, due to}, number={2003 May 15}, journal={APPLIED SURFACE SCIENCE}, author={Lucovsky, G and Raynor, GB and Zhang, Y and Fulton, CC and Nemanich, RJ and Appel, G and Ade, H and Whitten, JL}, year={2003}, month={May}, pages={563–569} }
 @article{kobashi_tachibana_yokota_kawakami_hayashi_yamamoto_koga_fujiwara_gotoh_nakahara_et al._2003, title={Fibrous structures on diamond and carbon surfaces formed by hydrogen plasma under direct current bias and field electron-emission properties}, volume={18}, ISSN={["2044-5326"]}, DOI={10.1557/JMR.2003.0042}, abstractNote={Polycrystalline diamond films, single crystal bulk diamonds, and diamond powder were treated in microwave plasma of hydrogen at 1.6 torr under a negative direct-current bias of −150 to −300 V without metal catalyst. It was found that fibrous structures, uniformly elongated along the direction normal to the specimen surface, were formed on the diamond surfaces. Similar experiments for glasslike carbon resulted in conical structures with frizzy fibers at the tops. Transmission electron microscopy measurements indicated that the fibers formed on diamond consisted of randomly oriented diamond nanocrystals with diameters of less than 10 nm, while the conical structures formed on glasslike carbon consisted of graphite nanocrystals. Field emission measurements of the fibrous specimens exhibited better emission efficiency than untreated ones. The field emission electron microscopy of the fibrous glasslike carbon showed a presence of discrete electron emission sites at a density of approximately 10,000 sites/cm2.}, number={2}, journal={JOURNAL OF MATERIALS RESEARCH}, author={Kobashi, K and Tachibana, T and Yokota, Y and Kawakami, N and Hayashi, K and Yamamoto, K and Koga, Y and Fujiwara, S and Gotoh, Y and Nakahara, H and et al.}, year={2003}, month={Feb}, pages={305–326} }
 @article{coppa_davis_nemanich_2003, title={Gold Schottky contacts on oxygen plasma-treated, n-type ZnO(000(1)over-bar)}, volume={82}, ISSN={["0003-6951"]}, DOI={10.1063/1.1536264}, abstractNote={Reverse bias current–voltage measurements of ∼100-μm-diameter gold Schottky contacts deposited on as-received, n-type ZnO(0001̄) wafers and those exposed for 30 min to a remote 20% O2/80% He plasma at 525±20 °C and cooled either in vacuum from 425 °C or the unignited plasma gas have been determined. Plasma cleaning resulted in highly ordered, stoichiometric, and smooth surfaces. Contacts on as-received material showed μA leakage currents and ideality factors >2. Contacts on plasma-cleaned wafers cooled in vacuum showed ∼36±1 nA leakage current to −4 V, a barrier height of 0.67±0.05 eV, and an ideality factor of 1.86±0.05. Cooling in the unignited plasma gas coupled with a 30 s exposure to the plasma at room temperature resulted in decreases in these parameters to ∼20 pA to −7 V, 0.60±0.05 eV, and 1.03±0.05, respectively. Differences in the measured and theoretical barrier heights indicate interface states. (0001) and (0001̄) are used in this letter to designate the polar zinc- and oxygen-terminated surfaces, respectively.}, number={3}, journal={APPLIED PHYSICS LETTERS}, author={Coppa, BJ and Davis, RF and Nemanich, RJ}, year={2003}, month={Jan}, pages={400–402} }
 @article{patten_fesperman_kumar_mcspadden_qu_lance_nemanich_huening_2003, title={High-pressure phase transformation of silicon nitride}, volume={83}, ISSN={["0003-6951"]}, DOI={10.1063/1.1632031}, abstractNote={We provide evidence for a high-pressure phase transformation (HPPT) in the ceramic material silicon nitride. This HPPT is inferred by a high-pressure diamond anvil cell, Raman spectroscopy, scanning/transmission electron microscopy, and optical and acoustic microscope inspection. In the case of silicon nitride, the HPPT involves a ductile or metallike behavior that is observed in severe deformation processes, such as nanoindentation and micromachining. This pressure-induced plasticity is believed to be similar to that found in silicon and germanium with its origin in the high-pressure metallic β-Sn phase formation.}, number={23}, journal={APPLIED PHYSICS LETTERS}, author={Patten, J and Fesperman, R and Kumar, S and McSpadden, S and Qu, J and Lance, M and Nemanich, R and Huening, J}, year={2003}, month={Dec}, pages={4740–4742} }
 @article{fitting_zeman_yang_nemanich_2003, title={Influence of strain, surface diffusion and Ostwald ripening on the evolution of nanostructures for erbium on Si(001)}, volume={93}, ISSN={["1089-7550"]}, DOI={10.1063/1.1557787}, abstractNote={This study explores the evolution of nanoscale islands and wire structures during deposition and surface ripening. Ultraviolet photoelectron emission microscopy has been employed to study the real time growth process of individual erbium silicide nanostructures on Si(001) surfaces at temperatures up to 1050 °C. During the initial island formation process compact islands form and some undergo a shape transition to elongated islands oriented along the 〈110〉 directions of the Si substrate. The initial island formation is driven by the surface and interface energies of the silicide/Si structure. The widths of the growing islands remain essentially constant while the lengths increase. The observed elongated islands are ∼150 nm wide, which is larger than the width of prior reported erbium silicide nanowire structures. We propose that the ∼150 nm elongated islands are partially relaxed, possibly through the formation of misfit dislocations. The results indicate a temperature regime where island growth is mainly governed by surface diffusion of the deposited Er adatoms and a higher temperature regime where Ostwald ripening contributes to the island morphology.}, number={7}, journal={JOURNAL OF APPLIED PHYSICS}, author={Fitting, L and Zeman, MC and Yang, WC and Nemanich, RJ}, year={2003}, month={Apr}, pages={4180–4184} }
 @article{cook_fulton_mecouch_tracy_davis_hurt_lucovsky_nemanich_2003, title={Measurement of the band offsets of SiO2 on clean n- and p-type GaN(0001)}, volume={93}, ISSN={["0021-8979"]}, DOI={10.1063/1.1559424}, abstractNote={The band alignment at the SiO2-GaN interface is important for passivation of high voltage devices and for gate insulator applications. X-ray photoelectron spectroscopy and ultraviolet photoemission spectroscopy have been used to observe the interface electronic states as SiO2 was deposited on clean GaN(0001) surfaces. The substrates, grown by metallorganic chemical vapor deposition, were n- (1×1017) and p-type (2×1018) GaN on 6H-SiC(0001) with an AlN(0001) buffer layer. The GaN surfaces were atomically cleaned via an 860 °C anneal in an NH3 atmosphere. For the clean surfaces, n-type GaN showed upward band bending of 0.3±0.1 eV, while p-type GaN showed downward band bending of 1.3±0.1 eV. The electron affinity for n- and p-type GaN was measured to be 2.9±0.1 and 3.2±0.1 eV, respectively. To avoid oxidizing the GaN, layers of Si were deposited on the clean GaN surface via ultrahigh vacuum e-beam deposition, and the Si was oxidized at 300 °C by a remote O2 plasma. The substrates were annealed at 650 °C for densification of the SiO2 films. Surface analysis techniques were performed after each step in the process, and yielded a valence band offset of 2.0±0.2 eV and a conduction band offset of 3.6±0.2 eV for the GaN-SiO2 interface for both p- and n-type samples. Interface dipoles of 1.8 and 1.5 eV were deduced for the GaN-SiO2 interface for the n- and p-type surfaces, respectively.}, number={7}, journal={JOURNAL OF APPLIED PHYSICS}, author={Cook, TE and Fulton, CC and Mecouch, WJ and Tracy, KM and Davis, RF and Hurt, EH and Lucovsky, G and Nemanich, RJ}, year={2003}, month={Apr}, pages={3995–4004} }
 @article{gruverman_rodriguez_kingon_nemanich_tagantsev_cross_tsukada_2003, title={Mechanical stress effect on imprint behavior of integrated ferroelectric capacitors}, volume={83}, ISSN={["0003-6951"]}, DOI={10.1063/1.1593830}, abstractNote={Stress-induced changes in the imprint and switching behavior of (111)-oriented Pb(Zr,Ti)O3 (PZT)-based capacitors have been studied using piezoresponse force microscopy. Visualization of polarization distribution and d33-loop measurements in individual 1×1.5-μm2 capacitors before and after stress application, generated by substrate bending, provided direct experimental evidence of stress-induced switching. Mechanical stress caused elastic switching in capacitors with the direction of the resulting polarization determined by the sign of the applied stress. In addition, stress application turned capacitors into a heavily imprinted state characterized by strongly shifted hysteresis loops and almost complete backswitching after application of the poling voltage. It is suggested that substrate bending generated a strain gradient in the PZT layer, which produced asymmetric lattice distortion with preferential polarization direction and triggered polarization switching due to the flexoelectric effect.}, number={4}, journal={APPLIED PHYSICS LETTERS}, author={Gruverman, A and Rodriguez, BJ and Kingon, AI and Nemanich, RJ and Tagantsev, AK and Cross, JS and Tsukada, M}, year={2003}, month={Jul}, pages={728–730} }
 @article{yang_rodriguez_park_nemanich_ambacher_cimalla_2003, title={Photoelectron emission microscopy observation of inversion domain boundaries of GaN-based lateral polarity heterostructures}, volume={94}, DOI={10.1063/1.1618355}, abstractNote={An intentionally grown GaN film with laterally patterned Ga- and N-face polarities is studied using in situ UV-photoelectron emission microscopy (PEEM). Before chemical vapor cleaning of the surface, the emission contrast between the Ga- and N-face polarities regions was not significant. However, after cleaning the emission contrast between the different polarity regions was enhanced such that the N-face regions exhibited increased emission over the Ga-face regions. The results indicate that the emission threshold of the N-face region is lower than that of the Ga face. Moreover, bright emission was detected from regions around the inversion domain boundaries of the lateral polarity heterostructure. The PEEM polarity contrast and intense emission from the inversion domain boundary regions are discussed in terms of the built-in lateral field and the surface band bending induced by the polarization bound surface charges.}, number={9}, journal={Journal of Applied Physics}, author={Yang, W. C. and Rodriguez, B. J. and Park, M. and Nemanich, R. J. and Ambacher, O. and Cimalla, V.}, year={2003}, pages={5720–5725} }
 @article{tracy_mecouch_davis_nemanich_2003, title={Preparation and characterization of atomically clean, stoichiometric surfaces of n- and p-type GaN(0001)}, volume={94}, ISSN={["1089-7550"]}, DOI={10.1063/1.1596369}, abstractNote={It is demonstrated that in situ exposure of the (0001) surface of n- and p-type GaN thin films to flowing ammonia at 860 °C and 10−4 Torr removes hydrocarbon and oxygen/hydroxide species below the detectable limits of x-ray and ultraviolet photoelectron spectroscopies (UPS) and decreases the Ga/N ratio from 1.3 to 1.0. Additional indications of the efficacy of this ammonia-based chemical vapor cleaning (CVC) process were the shifts in the Ga 3d and the N 1s core level positions from the as-loaded to the CVC surfaces of the n-type samples from 21.0±0.1 to 20.6±0.1 eV and from 398.3±0.1 to 398.0±0.1 eV, respectively, and the change in the UPS measured low energy spectrum turn on from 3.9±0.1 (as-loaded samples) to 3.0±0.1 eV (cleaned samples) below the Fermi level. Analogous changes in the p-type samples were from 19.6±0.1 to 18.9±0.1 eV and from 397.1±0.1 to 396.3±0.1 eV for the Ga 3d and the N 1s core levels, and from 3.0±0.1 to 1.1±0.1 eV for the UPS valence band maximum (VBM). The VBM values of the CVC samples indicate band bending of ∼0.3 eV upward on n type and ∼0.8 eV downward on p type. Electron affinities of 2.8±0.1 and 2.6±0.1 eV were determined for the clean n-type and p-type surfaces, respectively. Irrespective of doping, the CVC process left unchanged the (1×1) low energy diffraction pattern, the terraced microstructure, and the root mean square roughness observed for the surfaces of the as-loaded samples, i.e., the surface microstructure was not damaged during the high temperature exposure to ammonia at low pressure.}, number={5}, journal={JOURNAL OF APPLIED PHYSICS}, author={Tracy, KM and Mecouch, WJ and Davis, RF and Nemanich, RJ}, year={2003}, month={Sep}, pages={3163–3172} }
 @article{kobashi_nishibayashi_yokota_ando_tachibana_kawakami_hayashi_inoue_meguro_imai_et al._2003, title={R&D of diamond films in the Frontier Carbon Technology Project and related topics}, volume={12}, ISSN={["1879-0062"]}, DOI={10.1016/S0925-9635(02)00298-4}, abstractNote={R&D activities on diamond chemical vapor deposition (CVD) and field emission in the Frontier Carbon Technology Project are presented. The topics are (1) morphology control of diamond films grown by a 60-kW, 915-MHz microwave plasma CVD reactor, (2) growth technology of large single crystal diamond with a low density of defects, (3) heteroepitaxial growth technology of diamond films on Pt, (4) fabrication of sharp emitter tips on single crystal diamond, (5) field emission study from diamond particles, and (6) intense field emission from ion implanted homoepitaxial diamond layer. Research results of field emission obtained by Kyoto University and North Carolina State University are also described.}, number={3-7}, journal={DIAMOND AND RELATED MATERIALS}, author={Kobashi, K and Nishibayashi, Y and Yokota, Y and Ando, Y and Tachibana, T and Kawakami, N and Hayashi, K and Inoue, K and Meguro, K and Imai, H and et al.}, year={2003}, pages={233–240} }
 @article{hartlieb_roskowski_davis_platow_nemanich_2003, title={Response to "Comment on 'Pd growth and subsequent Schottky barrier formation on chemical vapor cleaned p-type GaN surfaces' [J. Appl. Phys. 91, 732 (2002)]"}, volume={93}, ISSN={["0021-8979"]}, DOI={10.1063/1.1542911}, number={6}, journal={JOURNAL OF APPLIED PHYSICS}, author={Hartlieb, PJ and Roskowski, A and Davis, RF and Platow, W and Nemanich, RJ}, year={2003}, month={Mar}, pages={3679–3679} }
 @article{kock_garguilo_nemanich_gupta_weiner_morell_2003, title={Spatial distribution of electron emission sites for sulfur doped and intrinsic nanocrystalline diamond films}, volume={12}, ISSN={["1879-0062"]}, DOI={10.1016/S0925-9635(02)00365-5}, abstractNote={We have investigated high sp2 content intrinsic and sulfur doped nanocrystalline diamond films to study field emission properties by electron emission microscopy operated in different modes. Electron emission microscopy enables real time imaging of the electron emission from a surface with a lateral resolution of ∼15 nm. The nanocrystalline intrinsic diamond films exhibit electron emission at room temperature from localized emission sites with weak temperature dependence, and a density of ∼103–104/cm2. In contrast, sulfur doped diamond films show similar emission characteristics at room temperature, but at elevated temperatures the emission significantly increases from the localized regions and a thermionic component is identified in the I/V dependence. We discuss the role of S-donor states to explain the enhanced emission of the S-doped nanocrystalline diamond.}, number={3-7}, journal={DIAMOND AND RELATED MATERIALS}, author={Kock, FAM and Garguilo, JM and Nemanich, RJ and Gupta, S and Weiner, BR and Morell, G}, year={2003}, pages={474–480} }
 @article{gruverman_rodriguez_kingon_nemanich_cross_tsukada_2003, title={Spatial inhomogeneity of imprint and switching behavior in ferroelectric capacitors}, volume={82}, ISSN={["0003-6951"]}, DOI={10.1063/1.1570942}, abstractNote={Piezoresponse force microscopy has been used to perform nanoscale characterization of the spatial variations in the imprint and switching behavior of (111)-oriented Pb(Zr,Ti)O3-based capacitors on Pt electrodes. Mapping of polarization distribution in the poled capacitors as well as local d33–V loop measurements revealed a significant difference in imprint and switching behavior between the peripheral and inner parts of the capacitors. It has been found that the inner regions of the capacitors are negatively imprinted (with the preferential direction of the normal component of polarization upward) and tend to switch back after application of the positive poling voltage. On the other hand, switchable regions at the edge of the integrated capacitors generally exhibit more symmetric hysteresis behavior. Application of an ac switching voltage, contrary to what was expected, resulted in an increase of the negatively imprinted regions. The observed effect has been explained by incomplete or asymmetric switching due to the mechanical stress conditions existing in the central parts of the capacitors.}, number={18}, journal={APPLIED PHYSICS LETTERS}, author={Gruverman, A and Rodriguez, BJ and Kingon, AI and Nemanich, RJ and Cross, JS and Tsukada, M}, year={2003}, month={May}, pages={3071–3073} }
 @article{park_sakhrani_maria_cuomo_teng_muth_ware_rodriguez_nemanich_2003, title={Wavelength-dependent Raman scattering of hydrogenated amorphous silicon carbon with red, green, and blue light excitation}, volume={18}, ISSN={["2044-5326"]}, DOI={10.1557/JMR.2003.0106}, abstractNote={This study presents results of wavelength-dependent Raman scattering from amorphous silicon carbon (a-Si:C:H). The a-Si:C:H films were produced by radio-frequency plasma-enhanced chemical vapor deposition. Prior results with amorphous carbon indicate that laser excitation selectively probes clusters with differing sizes. Our measurements with a-Si:C:H indicate that when using red (632.8 nm), green (514.5 nm), and blue (488.0 nm) excitation, the Raman D and G peaks shift to higher wave numbers as the excitation energy increases. The higher frequency is associated with smaller clusters that are preferentially excited with higher photon energy. It appears that photoluminescence occurs due to radiative recombination from intracluster transitions in Si-alloyed sp2-bonded carbon clusters}, number={4}, journal={JOURNAL OF MATERIALS RESEARCH}, author={Park, M and Sakhrani, V and Maria, JP and Cuomo, JJ and Teng, CW and Muth, JF and Ware, ME and Rodriguez, BJ and Nemanich, RJ}, year={2003}, month={Apr}, pages={768–771} }
 @article{jeon_won_kim_lee_nemanich_2002, title={Analysis of Ti-silicide formation with a thin Ta interlayer on Si (100)}, volume={40}, number={5}, journal={Journal of the Korean Physical Society}, author={Jeon, H. and Won, H. and Kim, Y. and Lee, J. and Nemanich, R. J.}, year={2002}, pages={903–907} }
 @article{hartlieb_roskowski_davis_nemanich_2002, title={Chemical, electrical, and structural properties of Ni/Au contacts on chemical vapor cleaned p-type GaN}, volume={91}, ISSN={["1089-7550"]}, DOI={10.1063/1.1471578}, abstractNote={Chemical vapor cleaned, Mg-doped, p-type GaN(0001) surfaces and Ni/Au contacts deposited on these surfaces have been studied using several characterization techniques. Stoichiometric surfaces without detectable carbon and an 87% reduction in the surface oxygen to 2±1 at. % were achieved. The binding energies of the Ga 3d and N 1s core level photoelectron peaks were reduced by 0.5±0.1 eV following the chemical vapor clean. The band bending at the clean surface was measured to be 0.8±0.1 eV. As-deposited Ni/Au contacts on chemical vapor cleaned surfaces exhibited significantly less rectification in the low voltage region (<2 V) compared to identical contact structures on conventional HCl treated surfaces. The specific contact resistance of these contacts deposited on chemical vapor cleaned surfaces and subsequently annealed at 450 °C for 30 seconds was 3±2 Ω cm2. Improved ohmic behavior and a specific contact resistance of 4±2 Ω cm2 was obtained for contacts deposited on HCl treated surfaces and annealed using the same schedule. The formation of Au:Ga and Au:Ni solid solutions was observed for contacts on HCl treated surfaces following the 450 °C anneal. There were significantly less interfacial reactions for annealed contacts on chemical vapor cleaned surfaces. The values of specific contact resistance, sheet resistance, and transfer length of the annealed contacts deposited on both chemical vapor cleaned and HCl treated surfaces and measured from room temperature to 140 °C did not change during three successive thermal cycles within this range.}, number={11}, journal={JOURNAL OF APPLIED PHYSICS}, author={Hartlieb, PJ and Roskowski, A and Davis, RF and Nemanich, RJ}, year={2002}, month={Jun}, pages={9151–9160} }
 @article{oh_nemanich_2002, title={Current-voltage and imaging of TiSi2 islands on Si(001) surfaces using conductive-tip atomic force microscopy}, volume={92}, ISSN={["1089-7550"]}, DOI={10.1063/1.1499545}, abstractNote={Using conducting tip atomic force microscopy (c-AFM), we have measured the current–voltage (I–V) characteristics of individual submicron islands of TiSi2 on Si(100) surfaces, and we have developed an imaging approach that distinguishes the electrical properties of the islands. The Schottky barrier height (SBH) of the submicron TiSi2 islands was deduced from the I–V measurements. The results indicate that there is a significant variation of SBH among the islands on the same surface. The measurements employ a conventional AFM with a heavily B-doped diamond tip to obtain the current–voltage relations. In contact mode AFM, electrical signals are extracted independently from the topographic image. In addition, we have modified the imaging method to probe the local electrical properties of a surface with regions of different conductivity. Using a lock-in technique both phase and amplitude images were obtained, and the resultant image is essentially a map of the differential surface conductivity. Using this method, TiSi2 islands on a Si(100) surface were imaged. This approach can be readily extended to other materials systems.}, number={6}, journal={JOURNAL OF APPLIED PHYSICS}, author={Oh, J and Nemanich, RJ}, year={2002}, month={Sep}, pages={3326–3331} }
 @article{preble_tracy_kiesel_mclean_miraglia_nemanich_davis_albrecht_smith_2002, title={Electrical, structural and microstructural characteristics of as-deposited and annealed Pt and Au contacts on chemical-vapor-cleaned GaN thin films}, volume={91}, ISSN={["0021-8979"]}, DOI={10.1063/1.1432127}, abstractNote={Schottky contacts of Pt(111) and Au(111) were deposited on chemical-vapor-cleaned, n-type GaN(0001) thin films. The growth mode of the deposition, as determined by x-ray photoelectron spectroscopy analysis, followed the two-dimensional Frank–van der Merwe growth model. The resulting as-deposited metal films were monocrystalline and epitaxial with a (111)//(0002) relationship with the GaN. Selected samples were annealed for three minutes at 400 °C, 600 °C or 800 °C. The rectifying behavior of both contacts degraded at 400 °C; they became ohmic after annealing at 600 °C (Au) or 800 °C (Pt). High-resolution transmission electron micrographs revealed reactions at the metal/GaN interfaces for the higher temperature samples. X-ray diffraction results revealed an unidentified phase in the Pt sample annealed at 800 °C. A decrease in the room temperature in-plane (111) lattice constant for both metals, ranging from −0.1% to −0.5%, was observed as the annealing temperature was increased from 400 to 800 °C. This plastic deformation was caused by tensile stresses along the [111] direction that exceeded the yield strength as a result of the large differences in the coefficients of thermal expansion between the metal contacts and the GaN film.}, number={4}, journal={JOURNAL OF APPLIED PHYSICS}, author={Preble, EA and Tracy, KM and Kiesel, S and McLean, H and Miraglia, PQ and Nemanich, RJ and Davis, RF and Albrecht, M and Smith, DJ}, year={2002}, month={Feb}, pages={2133–2137} }
 @article{fulton_lucovsky_nemanich_2002, title={Electronic states at the interface of Ti-Si oxide on Si(100)}, volume={20}, ISSN={["1071-1023"]}, DOI={10.1116/1.1493785}, abstractNote={The requirement for high K dielectrics for Si devices includes both a low interface state density and a band alignment that blocks both electrons and holes. Titanium dioxide materials are known to exhibit dielectric constants of 80 or higher depending on the crystal structure and, as such, are prime candidates for gate dielectrics. We employ an ultrathin layer of SiO2 prior to the formation of a Ti oxide to limit the density of defect states. The electronic structure is observed during the stepwise growth of the oxide using x-ray and ultraviolet photoemission spectroscopy. Measurements indicate Ti oxide states at approximately 2 eV below the Si valence band maximum suggesting that the TiO2 conduction band aligns with the Si conduction band. The results indicate nearly flat bands in the silicon consistent with a low interface state density.}, number={4}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B}, author={Fulton, CC and Lucovsky, G and Nemanich, RJ}, year={2002}, pages={1726–1731} }
 @article{kock_garguilo_brown_nemanich_2002, title={Enhanced low-temperature thermionic field emission from surface-treated N-doped diamond films}, volume={11}, ISSN={["1879-0062"]}, DOI={10.1016/S0925-9635(02)00006-7}, abstractNote={Nitrogen-doped diamond films have been synthesized for application as a low-temperature thermionic field-emission cathode. The critical result of this study is the observation of uniform electron emission from UV photo-excitation and from thermionic field emission for films terminated with hydrogen or a 0.3-nm Ti layer. The samples were imaged with photoelectron emission microscopy (PEEM) and thermionic field-emission electron microscopy (T-FEEM) at temperatures up to 900 °C, and the electron emission current was recorded vs. the applied voltage. Hydrogen-passivated films show enhanced electron emission, but become unstable at elevated temperatures, while Ti-terminated films showed similar enhanced emission at temperatures up to 950 °C. Temperature-dependent I/V measurements show strongly increased electron emission at higher temperatures, suggesting that electron emission originates from the conduction band. These results indicate a promising new material for the production of low-temperature, high-brightness electron sources.}, number={3-6}, journal={DIAMOND AND RELATED MATERIALS}, author={Kock, FAM and Garguilo, JM and Brown, B and Nemanich, RJ}, year={2002}, pages={774–779} }
 @article{gruverman_rodriguez_nemanich_kingon_2002, title={Nanoscale observation of photoinduced domain pinning and investigation of imprint behavior in ferroelectric thin films}, volume={92}, ISSN={["1089-7550"]}, DOI={10.1063/1.1497698}, abstractNote={Piezoresponse force microscopy has been used to investigate the nanoscale mechanism of imprint behavior of ferroelectric PbTiO3 thin films by studying the photoinduced changes in the hysteresis loops of individual grains. Illumination of the film with UV light resulted in a voltage shift opposite to that observed in ferroelectric thin film capacitors. This effect is attributed to the generation of an electric field within the surface dielectric layer as a result of the interaction between photoinduced charges and polarization charges. Application of a small nonswitching bias to the film with simultaneous UV illumination resulted in domain pinning in the grains where the polarization direction coincided with the direction of the applied field, in agreement with the proposed model. Domain pinning was also observed in grains with polydomain structure suggesting that charge entrapment at the existing domain boundaries in the bulk of the film contributes to the suppression of switchable polarization. However, a symmetric character of hysteresis loops observed in such grains implies that charge entrapment in the bulk of the film does not cause the voltage shift. It has been suggested that a thin high-dielectric interfacial layer can improve the imprint behavior of ferroelectric capacitors.}, number={5}, journal={JOURNAL OF APPLIED PHYSICS}, author={Gruverman, A and Rodriguez, BJ and Nemanich, RJ and Kingon, AI}, year={2002}, month={Sep}, pages={2734–2739} }
 @article{hartlieb_roskowski_davis_platow_nemanich_2002, title={Pd growth and subsequent Schottky barrier formation on chemical vapor cleaned p-type GaN surfaces}, volume={91}, ISSN={["1089-7550"]}, DOI={10.1063/1.1424060}, abstractNote={Characterization of chemical vapor cleaned, Mg-doped, p-type GaN(0001) surfaces and Pd contacts sequentially deposited on these surfaces has been conducted using x-ray and ultraviolet photoelectron spectroscopies and low-energy electron diffraction. The band bending and the electron affinity at the cleaned p-GaN surface were 1.4±0.1 eV and 3.1±0.1 eV, respectively. A previously unidentified band of surface states was observed at ∼1.0 eV below the Fermi level on this surface. The Pd grew epitaxially on the cleaned surface in a layer-by-layer mode and formed an abrupt, unreacted metal–semiconductor interface. The induced Fermi level movement with Pd deposition has been attributed to a complex interaction between extrinsic and intrinsic surface states as well as metal induced gap states. The final Schottky barrier height at the Pd/p-GaN interface was 1.3±0.1 eV; the interface dipole contribution was 0.4±0.1 eV.}, number={2}, journal={JOURNAL OF APPLIED PHYSICS}, author={Hartlieb, PJ and Roskowski, A and Davis, RF and Platow, W and Nemanich, RJ}, year={2002}, month={Jan}, pages={732–738} }
 @article{rodriguez_gruverman_kingon_nemanich_2002, title={Piezoresponse force microscopy for piezoelectric measurements of III-nitride materials}, volume={246}, ISSN={["0022-0248"]}, DOI={10.1016/S0022-0248(02)01749-9}, abstractNote={Piezoelectric constants and polarity distributions of epitaxial AlN and GaN thin films are investigated by piezoresponse force microscopy (PFM). The magnitude of the effective longitudinal piezoelectric constant d33 is determined to be 3±1 and 2±1 pm/V for wurtzite AlN and GaN/AlN layers grown by organo-metallic vapor phase epitaxy on SiC substrates, respectively. Simultaneous imaging of surface morphology as well as the phase and magnitude of the piezoelectric response is performed by PFM on a GaN film with patterned polarities on a c-Al2O3 substrate. We demonstrate that the polarity distribution of GaN based lateral polarity heterostructures can be deduced from the phase image of the piezoresponse with nanometer scale spatial resolution. We also present images of AlN/Si samples with regions of opposite piezoresponse phase, which indicate the presence of antiphase domains. We discuss the potential application of this technique for determination of the orientation of bulk crystals.}, number={3-4}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Rodriguez, BJ and Gruverman, A and Kingon, AI and Nemanich, RJ}, year={2002}, month={Dec}, pages={252–258} }
 @article{rodriguez_gruverman_kingon_nemanich_ambacher_2002, title={Piezoresponse force microscopy for polarity imaging of GaN}, volume={80}, ISSN={["1077-3118"]}, DOI={10.1063/1.1483117}, abstractNote={The polarity distribution of GaN based lateral polarity heterostructures is investigated by piezoresponse force microscopy (PFM). Simultaneous imaging of surface morphology, as well as the phase and magnitude of the piezoelectric response, is performed by PFM on a GaN film with patterned polarities on a c-Al2O3 substrate. We demonstrate that the polarity distribution of GaN based lateral polarity heterostructures can be deduced from the phase image of the piezoresponse with nanometer scale spatial resolution.}, number={22}, journal={APPLIED PHYSICS LETTERS}, author={Rodriguez, BJ and Gruverman, A and Kingon, AI and Nemanich, RJ and Ambacher, O}, year={2002}, month={Jun}, pages={4166–4168} }
 @article{oh_meunier_ham_nemanich_2002, title={Single electron tunneling of nanoscale TiSi2 islands on Si}, volume={92}, ISSN={["0021-8979"]}, DOI={10.1063/1.1499531}, abstractNote={Nanoscale TiSi2 islands are formed by electron beam deposition of a few monolayers of titanium on an atomically clean silicon surface followed by in situ annealing at high temperatures (800–1000 °C). The lateral diameter of typical islands are ∼5 nm, and they form a nanoscale metal–semiconductor interface. Direct probing of the electrical characteristics of these islands on both p- and n-type Si substrates was performed using ultrahigh vacuum scanning tunneling microscopy and scanning tunneling spectroscopy. With the vacuum between the tip and the island as a second tunnel junction, we thus form a double-junction system for observation of single electron tunneling (SET) effects. Moreover, the small dimensions of the system allow room temperature observation. The results showed features in the I–V spectra attributed to single electron tunneling. Features were more evident when the island–Si junction was in reverse bias. For substrates with a thin epitaxial layer of intrinsic Si, the tunneling related features were enhanced for both doping types. The experimental results are compared with the standard theory and numerical values from the fitting are in agreement with the experimental structures. The results indicate that the nanoscale Schottky barrier of the island–substrate interface can be employed as a tunnel barrier in SET structures.}, number={6}, journal={JOURNAL OF APPLIED PHYSICS}, author={Oh, J and Meunier, V and Ham, H and Nemanich, RJ}, year={2002}, month={Sep}, pages={3332–3337} }
 @article{popov_kyotani_nemanich_koga_2002, title={Superhard phase composed of single-wall carbon nanotubes}, volume={65}, ISSN={["2469-9969"]}, DOI={10.1103/physrevb.65.033408}, abstractNote={Single-wall carbon nanotubes (SWNT's) have been studied under pressure up to 55 GPa. We report experimental data on irreversible changes of mechanical and structure properties of SWNT under pressure. The new superhard phase (SP-SWNT) composed of single-wall carbon nanotubes has been studied which exhibits a bulk modulus exceeding or comparable with diamond and hardness belongs to the range between cubic BN and diamond. The SP-SWNT were synthesized by applying a shear deformation under load in a diamond-anvil cell; the procedure of stress tensor variation. After intermediate phase transitions, single-wall carbon nanotubes are transformed to SP-SWNT at pressure of 24 GPa. The transformation is accompanied by irreversible changes in the Raman spectra. The nanotubes do not collapse at least up to pressure 55 GPa (maximum pressure of the study). Bulk modulus of 462 to 546 GPa was found out for SP-SWNT from the comparative study of pressure dependence of the Raman modes of SP-SWNT (high-energy mode ∼1590 cm - 1 ) and diamond (1333 cm - 1 ), This value exceeds the bulk modulus of diamond (420 GPa for single diamond crystal). Hardness measurements were performed using nanoindentation technique. Hardness of SP-SWNT (62 to 150 GPa) was found out from comparative study of SP-SWNT, diamond and cubic BN.}, number={3}, journal={PHYSICAL REVIEW B}, author={Popov, M and Kyotani, M and Nemanich, RJ and Koga, Y}, year={2002}, month={Jan} }
 @article{platow_oh_nemanich_sayers_hartman_davis_2002, title={TiC nanoisland formation on 6H-SiC(0001)(Si)}, volume={91}, ISSN={["0021-8979"]}, DOI={10.1063/1.1465121}, abstractNote={Spontaneous formation of titanium carbide nanoislands on silicon carbide substrates has been studied with scanning tunneling microscopy and x-ray absorption near-edge spectroscopy. Scratch-free and atomically flat 6H–SiC(0001)Si substrates were prepared by high temperature hydrogen etching. The surfaces were subsequently cleaned by in situ ultrahigh vacuum annealing. Titanium carbide nanoislands were formed by titanium deposition and annealing at 950 °C. The average width (10–50 nm) and separation of the Ti islands was controlled by varying the titanium coverage (0.1–0.3 nm) and the annealing time (1–20 min). At the lowest coverage, the islands were uniformly distributed over the surface, while at higher coverage the islands tended to collect at the substrate step edges.}, number={9}, journal={JOURNAL OF APPLIED PHYSICS}, author={Platow, W and Oh, J and Nemanich, RJ and Sayers, DE and Hartman, JD and Davis, RF}, year={2002}, month={May}, pages={6081–6084} }
 @article{park_maria_cuomo_chang_muth_kolbas_nemanich_carlson_bumgarner_2002, title={X-ray and Raman analyses of GaN produced by ultrahigh-rate magnetron sputter epitaxy}, volume={81}, ISSN={["0003-6951"]}, DOI={10.1063/1.1506781}, abstractNote={Thick films of GaN were studied by x-ray diffraction and Raman spectroscopy. The GaN thick films were deposited on (0001) sapphire using ultrahigh-rate magnetron sputter epitaxy with typical growth rates as high as 10–60 μm/min. The width of the x-ray rocking curve from the (0002) reflection for the sample produced by this technique is ∼300 arcsec, which is unprecedented for GaN produced by a sputtering-type process. Our recent sample shows an x-ray rocking curve width of 240 arcsec. Only allowed modes were observed in the polarized Raman spectra. The background free carrier concentration is lower than 3×1016 cm−3. The phonon lifetime of the Raman E2(2) mode of the sputtered GaN was comparable to that of bulk single crystal GaN grown by sublimation. The quality of the film was uniform across the wafer. The film was thermally stable upon annealing in N2 ambient. The x-ray and Raman analyses revealed that the sputtered GaN films are of high crystalline quality.}, number={10}, journal={APPLIED PHYSICS LETTERS}, author={Park, M and Maria, JP and Cuomo, JJ and Chang, YC and Muth, JF and Kolbas, RM and Nemanich, RJ and Carlson, E and Bumgarner, J}, year={2002}, month={Sep}, pages={1797–1799} }
 @article{platow_wood_tracy_burnette_nemanich_sayers_2001, title={Formation of cobalt disilicide films on (root 3 x root 3)6H-SiC(0001)}, volume={63}, ISSN={["1550-235X"]}, DOI={10.1103/physrevb.63.115312}, abstractNote={This paper presents a detailed study of thin Co films grown directly, sequentially, and by codeposition with Si on the $(\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3})\ensuremath{-}R30\ifmmode^\circ\else\textdegree\fi{}$ surface of $6H\ensuremath{-}\mathrm{SiC}(0001).$ The structure, chemistry, and morphology of the films were determined using x-ray absorption fine structure, x-ray photoelectron spectroscopy, Auger electron spectroscopy, and atomic force microscopy. For directly deposited Co films (1--8 nm) graphite layers form on top of the film surface during annealing, whereas Co stays mainly unreacted over a temperature range of 300--1000 \ifmmode^\circ\else\textdegree\fi{}C. The formation of ${\mathrm{CoSi}}_{2}$ is achieved by sequential and codeposition of Co and Si. Films annealed at 550 \ifmmode^\circ\else\textdegree\fi{}C are polycrystalline and further annealing to 650 \ifmmode^\circ\else\textdegree\fi{}C causes no C segregation, but there is islanding of the films. Attempts to improve film morphology and homogeneity including applying a template method and varying growth temperature are also reported.}, number={11}, journal={PHYSICAL REVIEW B}, author={Platow, W and Wood, DK and Tracy, KM and Burnette, JE and Nemanich, RJ and Sayers, DE}, year={2001}, month={Mar} }
 @article{platow_nemanich_sayers_hartman_davis_2001, title={Growth of epitaxial CoSi2 on 6H-SiC(0001)(Si)}, volume={90}, ISSN={["1089-7550"]}, DOI={10.1063/1.1412842}, abstractNote={Epitaxial growth of (111)-oriented CoSi2 has been achieved on a scratch-free 6H-SiC(0001)Si substrate. The surface was prepared using atmospheric hydrogen etching and ultrahigh vacuum Si cleaning. A high-quality CoSi2 thin film was obtained by a modified template method and co-deposition of Co and Si at 550 °C. The structure and morphology of the film is studied by means of reflection high electron energy diffraction, x-ray absorption fine structure, x-ray diffraction, and atomic force microscopy.}, number={12}, journal={JOURNAL OF APPLIED PHYSICS}, author={Platow, W and Nemanich, RJ and Sayers, DE and Hartman, JD and Davis, RF}, year={2001}, month={Dec}, pages={5924–5927} }
 @article{kock_garguilo_nemanich_2001, title={Imaging electron emission from diamond film surfaces: N-doped diamond vs. nanostructured diamond}, volume={10}, ISSN={["1879-0062"]}, DOI={10.1016/S0925-9635(01)00401-0}, abstractNote={Abstract This study reports direct imaging of electron emission from two different classes of diamond containing films that were prepared by microwave plasma chemical vapor deposition. These are N-doped, and nanostructured diamond containing films. The electron emission is excited by UV light (photoemission) or by an applied field (field emission). The photo electron emission microscopy (PEEM) of the N-doped films exhibited uniform emission, and upon heating to ∼700°C, field electron emission microscopy (FEEM) of the films showed similar uniform emission. In contrast, FEEM of the nanostructured films showed high brightness, localized emission sites at room temperature. The results indicate different processes for electron emission from nanostructured and N-doped diamond films.}, number={9-10}, journal={DIAMOND AND RELATED MATERIALS}, author={Kock, FAM and Garguilo, JM and Nemanich, RJ}, year={2001}, pages={1714–1718} }
 @article{park_teng_sakhrani_mclaurin_kolbas_sanwald_nemanich_hren_cuomo_2001, title={Optical characterization of wide band gap amorphous semiconductors (a-Si : C : H): Effect of hydrogen dilution}, volume={89}, ISSN={["1089-7550"]}, DOI={10.1063/1.1332421}, abstractNote={The effect of hydrogen dilution on the optical properties of a wide band gap amorphous semiconductor (a-Si:C:H) was investigated. The samples were prepared by glow discharge decomposition of tetramethylsilane and were characterized primarily by optical techniques: spectroscopic ellipsometry, Raman scattering, infrared absorption, spectrophotometry, and UV photoluminescence. The deposition rate decreased with hydrogen dilution, while the silicon to carbon ratio remained constant with the addition of hydrogen. The optical band gap of this material increased as the hydrogen flow rate increased. Infrared absorption studies show that the concentration of hydrogen which is bonded to carbon decreases systematically upon hydrogen dilution. Hydrogen dilution appears to reduce the size and concentration of sp2 bonded carbon clusters, possibly caused by the etching of sp2 clusters by atomic hydrogen. The result was also supported by the shift of the Raman G peak position to a lower wave number region. Room temperature photoluminescence in the visible spectrum was observed with UV excitation.}, number={2}, journal={JOURNAL OF APPLIED PHYSICS}, author={Park, M and Teng, CW and Sakhrani, V and McLaurin, MB and Kolbas, RM and Sanwald, RC and Nemanich, RJ and Hren, JJ and Cuomo, JJ}, year={2001}, month={Jan}, pages={1130–1137} }
 @article{dutta_alexson_bergman_nemanich_dupuis_kim_komirenko_stroscio_2001, title={Phonons in III–V nitrides: Confined phonons and interface phonons}, volume={11}, ISSN={1386-9477}, url={http://dx.doi.org/10.1016/S1386-9477(01)00217-X}, DOI={10.1016/S1386-9477(01)00217-X}, abstractNote={Phonons in III–V nitrides are examined experimentally for dimensionally confined systems and for alloys of InGaN with a view towards understanding the phonon modes of these systems. Results are compared with the predictions of Loudon's model for uniaxial semiconductors. The modes of the InGaN system are compared with those of the AlGaN ternary alloy. The first Raman measurements of interface phonons in binary GaN–AlN superlattices are presented.}, number={2-3}, journal={Physica E: Low-dimensional Systems and Nanostructures}, publisher={Elsevier BV}, author={Dutta, M and Alexson, D and Bergman, L and Nemanich, R.J and Dupuis, R and Kim, K.W and Komirenko, S and Stroscio, M}, year={2001}, month={Oct}, pages={277–280} }
 @article{ballarotto_siegrist_phaneuf_williams_yang_nemanich_2001, title={Photon energy dependence of contrast in photoelectron emission microscopy of Si devices}, volume={78}, ISSN={["0003-6951"]}, DOI={10.1063/1.1376151}, abstractNote={We investigate the variation in doping-induced contrast with photon energy in photoelectron emission microscopy images of Si pn devices using a free-electron laser as a tunable monochromatic light source. Photoyield is observed from p-doped regions of the devices for photon energies as low as 4.5 eV. Band tailing is the dominant effect contributing to the low energy photoyield from the heavily doped p regions. The low intensity tail from the n regions, however, may be from surface states.}, number={22}, journal={APPLIED PHYSICS LETTERS}, author={Ballarotto, VW and Siegrist, K and Phaneuf, RJ and Williams, ED and Yang, WC and Nemanich, RJ}, year={2001}, month={May}, pages={3547–3549} }
 @article{gracin_bogdanovic_borjanovic_jaksic_pastuovic_dutta_vlahovic_nemanich_2001, title={Quantitative analysis of a-Si1-xCx : H thin films by vibrational spectroscopy and nuclear methods}, volume={61}, ISSN={["0042-207X"]}, DOI={10.1016/S0042-207X(01)00134-8}, abstractNote={Thin amorphous hydrogenated silicon–carbon films, a-Si1−xCx : H were deposited by magnetron sputtering on glass and mono-crystalline substrates with carbon content from x=0.2 to 1, wide variation of hydrogen concentration and different degrees of structural ordering. The obtained films were investigated by Fourier transform infra-red (FTIR) spectroscopy, Raman spectroscopy, Rutherford backscattering (RBS) and elastic recoil detection analysis (ERDA). The results of the quantitative analyses obtained by the above-mentioned techniques were compared. It has been concluded that the applied vibrational methods can be used quantitatively which enables estimation of the degree of chemical ordering in the analysed samples.}, number={2-4}, journal={VACUUM}, author={Gracin, D and Bogdanovic, I and Borjanovic, V and Jaksic, M and Pastuovic, Z and Dutta, JM and Vlahovic, B and Nemanich, RJ}, year={2001}, month={May}, pages={303–308} }
 @article{gracin_borjanovic_vlahovic_sunda-meya_patterson_dutta_hauger_pinayev_ware_alexson_et al._2001, title={Selective bond breaking in amorphous hydrogenated silicon by using Duke FEL}, volume={475}, ISSN={["0168-9002"]}, DOI={10.1016/S0168-9002(01)01578-9}, abstractNote={In order to study the possibility of influencing the phase containing predominantly Si–H bonds, while having minimal influence on the surrounding materials, samples of a-Si were exposed to Duke-FEL Mark III radiation. The wavelength of the radiation was selected to fit the absorption maximum of stretching vibrations of Si–H bonds (5 μm). By varying the wavelength in the vicinity of 5 μm, the illumination time and the power density, different types and degrees of structural ordering, of Si–H bonds and Si–Si bonds were obtained, and monitored by Raman spectroscopy. By increasing the energy density, at certain level the crystallization occurs. We were able to demonstrate a direct correlation between short and intermediate range ordering and the wavelength and intensity of the radiation. Using 5 μm at 10 kW/cm2 leads to increase in structural disordering. However, increasing power to 60 kW/cm2 improves both short and intermediate order in a-Si : H, as demonstrated by Raman spectroscopy. Further increasing power density by an order of magnitude results in crystallization of the sample.}, number={1-3}, journal={NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT}, author={Gracin, D and Borjanovic, V and Vlahovic, B and Sunda-Meya, A and Patterson, TM and Dutta, JM and Hauger, S and Pinayev, I and Ware, ME and Alexson, D and et al.}, year={2001}, month={Dec}, pages={635–639} }
 @article{alexson_bergman_nemanich_dutta_stroscio_parker_bedair_el-masry_adar_2001, title={Ultraviolet raman study of A(1)(LO) and E-2 phonons in InxGa1-xN alloys}, volume={89}, ISSN={["0021-8979"]}, DOI={10.1063/1.1330760}, abstractNote={We report on ultraviolet Raman spectroscopy of InxGa1−xN thin films grown on sapphire by metal-organic chemical vapor deposition. The A1(LO) and E2 phonon mode behavior was investigated over a large compositional range (0<x<0.50). Compelling evidence is presented for one-mode behavior for the A1(LO) phonon, and data suggestive of two-mode behavior are presented for the E2 phonon.}, number={1}, journal={JOURNAL OF APPLIED PHYSICS}, author={Alexson, D and Bergman, L and Nemanich, RJ and Dutta, M and Stroscio, MA and Parker, CA and Bedair, SM and El-Masry, NA and Adar, F}, year={2001}, month={Jan}, pages={798–800} }
 @article{platow_wood_burnette_nemanich_sayers_2001, title={XAFS studies of the formation of cobalt silicide on (root 3 x root 3) SiC(0001)}, volume={8}, ISSN={["0909-0495"]}, DOI={10.1107/S0909049500017921}, abstractNote={Thin Co films (1-8 nm) were directly, sequentially, and co-deposited with Si (3.6-29.2 nm) on the (31/2 × 31/2)-R30° reconstruction of 6H-SiC(0001). The films were annealed over a temperature range of 823-1373K and investigated with XAFS, XPS, AES and AFM. After annealing up to 1373K directly deposited Co films do not transform entirely to cobalt disilicide and C segregation is observed on the surface of the films. On the other hand, sequentially and co-deposited films do form cobalt disilicide after annealing at 823K, but also show islanding after annealing at 923K.}, journal={JOURNAL OF SYNCHROTRON RADIATION}, author={Platow, W and Wood, DE and Burnette, JE and Nemanich, RJ and Sayers, DE}, year={2001}, month={Mar}, pages={475–477} }
 @article{nemanich_2000, title={Advancing the science and technology of diamond, diamond-like carbon, silicon carbides and Group 3 nitride materials}, volume={9}, number={1}, journal={Diamond and Related Materials}, author={Nemanich, R. J.}, year={2000}, pages={vii} }
 @article{jeon_jung_kim_yang_nemanich_2000, title={Effects of a Ta interlayer on the phase transition of TiSi2 on Si(111)}, volume={88}, DOI={10.1063/1.1286725}, abstractNote={This study examines the effects of a thin Ta interlayer on the formation of TiSi2 on Si(111) substrate. The Ta interlayer was introduced by depositing Ta and Ti films sequentially on an atomically clean Si(111) substrate in an ultrahigh vacuum (UHV) system. Samples of 100 Å Ti with 5 and 10 Å Ta interlayers were compared to similar structures without an interlayer. After deposition, the substrates were annealed for 10 min, in situ, at temperatures between 500 and 750 °C in 50 °C increments. The TiSi2 formation with and without the Ta interlayer was analyzed with an X-ray diffractometer, Auger electron spectroscopy (AES), Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and a four-point probe. The AES analysis data showed a 1:2 ratio of Ti:Si in the Ti-silicide layer and indicated that the Ta layer remained at the interface between TiSi2 and the Si(111) substrate. The C 49–C 54 TiSi2 phase transition temperature was lowered by ∼200 °C. The C 49–C 54 TiSi2 phase transition temperature was 550 °C for the samples with a Ta interlayer and was 750 °C for the samples with no Ta interlayer. The sheet resistance of the Ta interlayered Ti silicide showed lower values of resistivity at low temperatures which indicated the change in phase transition temperature. The C 54 TiSi2 displayed different crystal orientation when the Ta interlayer was employed. The SEM and TEM micrographs showed that the TiSi2 with a Ta interlayer significantly suppressed the tendency to islanding and surface agglomeration.}, number={5}, journal={Journal of Applied Physics}, author={Jeon, H. and Jung, B. and Kim, Y. D. and Yang, W. C. and Nemanich, R. J.}, year={2000}, pages={2467–2471} }
 @article{balkas_sitar_bergman_shmagin_muth_kolbas_nemanich_davis_2000, title={Growth and characterization of GaN single crystals}, volume={208}, ISSN={["0022-0248"]}, DOI={10.1016/S0022-0248(99)00445-5}, abstractNote={Up to 3 mm long GaN single crystals were grown by sublimation of cold pressed GaN pellets or evaporation of gallium (Ga) metal under an ammonia (NH3) flow in a dual heater, high-temperature growth system. A growth rate of 500 μm/h along the [0 0 0 1] direction was achieved using a source temperature of 1200°C, a total pressure of 760 Torr, and an NH3 flow rate of 50 sccm. The resulting crystals were transparent, possessed low aspect ratios and well-defined growth facets. The only impurity present at high concentrations was oxygen (3×1018 atoms/cm3). Photoluminescence studies conducted at 77 K showed a sharp emission peak centered at 359 nm. Time-dependent photoluminescence measurements revealed optical metastability in bulk GaN. Raman spectroscopy yielded narrow peaks representing only the modes allowed for the wurtzite structure. All characterization studies confirmed excellent crystalline and optical quality of the obtained single crystals.}, number={1-4}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Balkas, CM and Sitar, Z and Bergman, L and Shmagin, IK and Muth, JF and Kolbas, R and Nemanich, RJ and Davis, RF}, year={2000}, month={Jan}, pages={100–106} }
 @article{sowers_ward_english_nemanich_2000, title={Measurement of field emission from nitrogen-doped diamond films}, volume={9}, ISSN={["1879-0062"]}, DOI={10.1016/S0925-9635(00)00304-6}, abstractNote={This study explores issues related to the measurement of the field emission properties of nitrogen-doped diamond grown by microwave plasma chemical vapor deposition (CVD). Growth conditions have been optimized to produce films with a low concentration of sp2-bonded carbon which results in high electrical resistance. Field emission characteristics were measured in an ultrahigh vacuum with a variable distance anode technique. For samples grown with gas phase [N]/[C] ratios less than 10, damage from micro-arcs occurred during the field emission measurements. Samples grown at higher [N]/[C] content could be measured prior to an arcing event. The occurrence of a micro-arc is related to the film properties. The measurements indicate relatively high threshold fields (>100 V μm−1) for electron emission.}, number={9-10}, journal={DIAMOND AND RELATED MATERIALS}, author={Sowers, AT and Ward, BL and English, SL and Nemanich, RJ}, year={2000}, pages={1569–1573} }
 @article{bilbro_nemanich_2000, title={Nongeometric field enhancement in semiconducting cold cathodes and in metal-insulator-semiconductor structures}, volume={76}, ISSN={["0003-6951"]}, DOI={10.1063/1.125620}, abstractNote={We extend the usual one-dimensional equilibrium theory of the surface space charge region that screens a semiconductor from an external electric field in order to admit perturbations in three dimensions and time. We identify a class of perturbations of the one-dimensional equilibrium that grow exponentially in time at least until our first-order perturbation theory fails. The resulting spontaneous field enhancement may explain enhancement factors observed in electron emission from semiconducting cathodes and may similarly contribute to gate leakage in metal–oxide–semiconductor field effect transistors.}, number={7}, journal={APPLIED PHYSICS LETTERS}, author={Bilbro, GL and Nemanich, RJ}, year={2000}, month={Feb}, pages={891–893} }
 @article{hartman_naniwae_petrich_ramachandran_feenstra_nemanich_davis_2000, title={Photo-emission electron microscopy (PEEM) of cleaned and etched 6H-SiC(0001)}, volume={338-3}, ISBN={["*************"]}, ISSN={["0255-5476"]}, DOI={10.4028/www.scientific.net/msf.338-342.353}, journal={SILICON CARBIDE AND RELATED MATERIALS - 1999 PTS, 1 & 2}, author={Hartman, JD and Naniwae, K and Petrich, C and Ramachandran, V and Feenstra, RM and Nemanich, RJ and Davis, RF}, year={2000}, pages={353–356} }
 @article{ml o'brien_koitzsch_nemanich_2000, title={Photoemission of the SiO2-SiC heterointerface}, volume={18}, ISSN={["1071-1023"]}, DOI={10.1116/1.591471}, abstractNote={Photoelectron spectroscopy has been performed on SiC surfaces to investigate the valence band characteristics during SiO2 formation. Various stages of the oxide development were investigated. The √3×√3R30° surface is used as the initial surface for the oxidation experiments. The substrates were exposed to a succession of a 30 s oxygen exposure, two 30 s oxygen plasmas, and finally, a plasma-enhanced chemical vapor deposition SiO2 deposition. Ultraviolet photoemission spectroscopy was employed to measure the valence band discontinuity for the oxide on n-type 6H and n-type 4H SiC substrates for each step in the oxidation process. X-ray photoemission spectroscopy was used to confirm the valence band offset. The valence band discontinuity was determined to be 2.0 eV. Furthermore, the location of the valence band maximum of the SiC to the conduction band minimum of the SiO2 is determined to be a constant (∼7.0 eV) between 6H and 4H SiC. Band bending effects are directly measured from ultraviolet photoemission spectroscopy (UPS) and x-ray photoemission spectroscopy. From the UPS measurements of the band bending effects, the interface state density is determined to be ∼5×1012 cm−2.}, number={3}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B}, author={ML O'Brien and Koitzsch, C and Nemanich, RJ}, year={2000}, pages={1776–1784} }
 @article{bergman_dutta_stroscio_komirenko_nemanich_eiting_lambert_kwon_dupuis_2000, title={Photoluminescence and recombination mechanisms in GaN/Al0.2Ga0.8N superlattice}, volume={76}, ISSN={["0003-6951"]}, DOI={10.1063/1.126225}, abstractNote={A detailed study of photoluminescence (PL) of GaN(1 nm)/Al0.2Ga0.8N(3.3 nm) twenty periods superlattice grown via metal-organic chemical vapor deposition is presented. The dependence of the PL emission energy, linewidth, and intensity on temperature, in the low temperature regime, is consistent with recombination mechanisms involving bandtail states attributed to a small degree of interfacial disorder. The activation energy of the nonradiative centers in our superlattice agrees well with the value we derive for the width of the tail-state distribution. Moreover, we find that the average phonon energy of the phonons that control the interband PL energy at high temperatures is larger for the superlattice than for a high-quality GaN film. This observation is consistent with model calculations predicting the phonon mode properties of GaN–AlN-based wurtzite heterostructures.}, number={15}, journal={APPLIED PHYSICS LETTERS}, author={Bergman, L and Dutta, M and Stroscio, MA and Komirenko, SM and Nemanich, RJ and Eiting, CJ and Lambert, DJH and Kwon, HK and Dupuis, RD}, year={2000}, month={Apr}, pages={1969–1971} }
 @article{ward_hartman_hurt_tracy_davis_nemanich_2000, title={Schottky barrier height and electron affinity of titanium on AIN}, volume={18}, ISSN={["1071-1023"]}, DOI={10.1116/1.1303733}, abstractNote={Approximately 100 or 1000 Å of AlN was deposited on the (0001)Si-face of on-axis n-type 6H–SiC. The surfaces were examined by ultraviolet photoemission spectroscopy (UPS) utilizing the He I α (21.2 eV) and the He II α (40.8 eV) excitation. Experimental difficulties are discussed. Titanium was deposited on the clean surface of in situ grown AlN. The titanium–AlN interface was also characterized with UPS. Two approaches are presented to identify the valence band maximum (VBM) and the electron affinity χ of the clean surface of AlN was found to be either 0 to 1 eV depending upon the position of the valence band edge. The same assumptions were applied to the analysis of the Ti/AlN interface and, for the case of χ=0 eV, the position of the valence band maximum is 3.4 eV below the position of the Fermi level. For the case of χ=1 eV, the position of the valence band maximum is 4.4 eV below the position of the Fermi level. Therefore, the p-type Schottky barrier height of titanium on AlN is measured to be 3.4±0.2 or 4.4±0.2 eV for χ=0 eV and χ=1 eV, respectively. Independent of the selection of the valence band maximum, the observed Schottky barrier differed from that predicted by the Schottky–Mott model by 1.5±0.2 eV.}, number={4}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B}, author={Ward, BL and Hartman, JD and Hurt, EH and Tracy, KM and Davis, RF and Nemanich, RJ}, year={2000}, pages={2082–2087} }
 @article{christman_kim_maiwa_maria_rodriguez_kingon_nemanich_2000, title={Spatial variation of ferroelectric properties in Pb(Zr-0.3, Ti-0.7)O-3 thin films studied by atomic force microscopy}, volume={87}, ISSN={["0021-8979"]}, DOI={10.1063/1.373492}, abstractNote={Imaging of the phase and magnitude of the piezoelectric strain in Pb(Zr0.3, Ti0.7)O3 (PZT) capacitors is performed with an atomic force microscope. The imaging reveals a significant spatial dependence of the ferroelectric properties of both fatigued and unfatigued PZT films. We propose that the variation is related to the domain structure of the PZT. Through the measurement of local piezoelectric hysteresis loops and imaging of the piezoelectric strain, areas are observed in fatigued PZT that exhibit hysteresis loops shifted along the polarization axis. In some regions of fatigued samples, the hysteresis loops are shifted such that both remanent points of the hysteresis curve have the same polarization direction. These results have important implications for the scalability of nonvolatile ferroelectric random access memory to higher device densities.}, number={11}, journal={JOURNAL OF APPLIED PHYSICS}, author={Christman, JA and Kim, SH and Maiwa, H and Maria, JP and Rodriguez, BJ and Kingon, AI and Nemanich, RJ}, year={2000}, month={Jun}, pages={8031–8034} }
 @article{carter_hauser_nemanich_2000, title={Surface residue island nucleation in anhydrous HF/alcohol vapor processing of Si surfaces}, volume={147}, ISSN={["0013-4651"]}, DOI={10.1149/1.1393929}, abstractNote={Anhydrous HF/methanol vapor-phase chemistries were employed to etch SiO 2 /Si surfaces at low pressure (5-50 Torr) and ambient temperature. The oxides on Si were formed from the following: (1) RCA chemical cleaning and (ii) UV-ozone treatment. Atomic force microscopy (AFM) and lateral force microscopy (LFM) were used to analyze the HF vapor-cleaned Si surfaces. AFM/LFM displayed residue islands distributed randomly upon the Si surface as a result of vapor-phase cleaning. As a result of etching RCA chemical oxides, the average lateral dimension of the residue islands is 40 nm and the average height of the islands is 6 nm. As a result of etching UV-ozone oxides, the average lateral dimension of the residue islands is 30 nm, and the average height of the islands is 3.5 nm. A decrease in residue island density is observed after the removal of a UV-ozone oxide compared to RCA chemical oxide removal. Secondary ion mass spectroscopy was used to characterize chemical impurities (O, C, F, and N) in the SiO 2 films and and the Si surface after HF vapor-phase cleaning. The constituents of the residue islands have been attributed to nitrogen impurities and silicon atoms imbedded in the passivating oxides. Results indicate that condensation of methanol vapor onto the bare Si surface, after oxide removal, is necessary for residue island formation. We suggest a model in which residue island nucleation occurs from nonvolatile N-Si complexes that form hydrogen bonds with methanol molecules and diffuse into the adsorbed alcohol layer. The molecular impurities then interact and form residue islands.}, number={9}, journal={JOURNAL OF THE ELECTROCHEMICAL SOCIETY}, author={Carter, RJ and Hauser, JR and Nemanich, RJ}, year={2000}, month={Sep}, pages={3512–3518} }
 @article{kim_kim_lee_park_kingon_nemanich_im_streiffer_1999, title={An optimized process for fabrication of SrBi2Ta2O9 thin films using a novel chemical solution deposition technique}, volume={14}, ISSN={["0884-2914"]}, DOI={10.1557/JMR.1999.0594}, abstractNote={Ferroelectric SrBi2Ta2O9 (SBT) thin films on Pt/ZrO2/SiO2/Si were successfully prepared by using an alkanolamine-modified chemical solution deposition method. It was observed that alkanolamine provided stability to the SBT solution by retarding the hydrolysis and condensation rates. The crystallinity and the microstructure of the SBT thin films improved with increasing annealing temperature and were strongly correlated with the ferroelectric properties of the SBT thin films. The films annealed at 800 °C exhibited low leakage current density, low voltage saturation, high remanent polarization, and good fatigue characteristics at least up to 1010 switching cycles, indicating favorable behavior for memory applications.}, number={11}, journal={JOURNAL OF MATERIALS RESEARCH}, author={Kim, SH and Kim, DJ and Lee, KM and Park, M and Kingon, AI and Nemanich, RJ and Im, J and Streiffer, SK}, year={1999}, month={Nov}, pages={4395–4401} }
 @article{king_kern_benjamin_barnak_nemanich_davis_1999, title={Chemical vapor cleaning of 6H-SiC surfaces}, volume={146}, ISSN={["0013-4651"]}, DOI={10.1149/1.1392494}, abstractNote={The techniques (temperature range of study) of in situ thermal desorption (500-1100°C) and chemical vapor cleaning (CVC) via exposure to SiH 4 and/or C 2 H 4 (750-1100°C) have been investigated for preparing 6H SiC [(0001) Si , (0001) C , (1120), and (1010)] surfaces suitable for epitaxial growth of SiC and III-nitride films, and are compared with regard to surface purity, stoichiometry, and structural order. Oxide removal below the detection limits of Auger electron spectroscopy was achieved for all orientations via annealing in 200 L SiH 4 at 850-900°C or 200° lower than necessary by thermal desorption. No non-SiC carbon was detected on the surface by X-ray photoelectron spectroscopy. An approximately one-tenth of a monolayer of oxygen coverage and significant quantities of non-SiC carbon were detected for all 6H-SiC surfaces prepared by thermal desorption. In contrast to the predominantly non-SiC carbon-rich surfaces prepared by thermal desorption, the stoichiometry of the SiC surfaces prepared by CVC could be manipulated from Si-rich to C-rich without non-SiC carbon formation by either extending the SiH 4 exposures or by following with C 2 H 4 exposure. The latter surfaces also had lower concentrations of both oxygen and non-SiC carbon and increased surface order.}, number={9}, journal={JOURNAL OF THE ELECTROCHEMICAL SOCIETY}, author={King, SW and Kern, RS and Benjamin, MC and Barnak, JP and Nemanich, RJ and Davis, RF}, year={1999}, month={Sep}, pages={3448–3454} }
 @article{porto_boyanov_sayers_nemanich_1999, title={Cobalt suicide formation on 6H silicon carbide}, volume={6}, ISSN={["0909-0495"]}, DOI={10.1107/S0909049599001326}, abstractNote={Cobalt films (1, 25 and 100 A) have been directly deposited on top 6H-SiC(0001) wafers by molecular beam epitaxy and annealed at 500-800°C in UHV. The structure of the metal-semiconductor interface was investigated by XAFS. The results show that Co-Si bonds were preferentially formed in the 1 A Co films. In the 25 and 100 A Co films only Co-Co bonds were identified. The XRD pattern of the 100 A Co film exhibits a Co (200) peak confirming the presence of unreacted metal even after annealing at 800°C.}, journal={JOURNAL OF SYNCHROTRON RADIATION}, author={Porto, AO and Boyanov, BI and Sayers, DE and Nemanich, RJ}, year={1999}, month={May}, pages={188–189} }
 @article{alexson_bergman_dutta_kim_komirenko_nemanich_lee_stroscio_yu_1999, title={Confined phonons and phonon-mode properties of III–V nitrides with wurtzite crystal structure}, volume={263-264}, ISSN={0921-4526}, url={http://dx.doi.org/10.1016/S0921-4526(98)01423-9}, DOI={10.1016/s0921-4526(98)01423-9}, abstractNote={Stimulated by the recent interest in the use of nitride-based III–V wurtzite structures for optoelectronic and electronic devices, this paper reports on the application of the Loudon model for uniaxial crystals to derive the Fröhlich interaction Hamiltonian as well as the electron–optical-phonon scattering rate in wurtzite crystals. This paper also presents experimental analyses of the mode behavior of phonons in wurtzite crystals.}, journal={Physica B: Condensed Matter}, publisher={Elsevier BV}, author={Alexson, D and Bergman, Leah and Dutta, Mitra and Kim, K.W and Komirenko, S and Nemanich, Robert J and Lee, B.C and Stroscio, Michael A and Yu, SeGi}, year={1999}, month={Mar}, pages={510–513} }
 @article{king_nemanich_davis_1999, title={Dry ex situ cleaning processes for (0001)(Si) 6H-SiC surfaces}, volume={146}, ISSN={["0013-4651"]}, DOI={10.1149/1.1391986}, abstractNote={A completely dry ex situ cleaning process based on UV/O 3 oxidation and HF vapor exposure for removal of residual C and oxide, respectively, from (0001) Si [the silicon-terminated surface of SiC] 6H-SiC surfaces to levels equivalent to or better than conventional wet chemical ex situ processing has been demonstrated. X-ray photoelectron spectroscopy (XPS) of surfaces exposed to UV-generated ozone revealed the formation of carbon and silicon oxides, as indicated by the broad Si-O Si 2p peak at 102.4 eV (full width at half-maximum = 2.1 eV) and a shift in the surface C 1s peak from 283.6 to 284.2 eV, respectively. Evidence for a reduction in the amount of surface C was shown by an increase in the ratio of the SiC C peak to the surface C peak from 0.8 to 2.7 after the UV/O 3 treatment. Removal of the UV/O 3 silicon oxide via exposure to the vapor from a 10:1 buffered HF solution was indicated by the absence (below the XPS detection limit) of the Si-O Si 2p peak at 102.4 eV. However, this last process results in a F-terminated surface.}, number={7}, journal={JOURNAL OF THE ELECTROCHEMICAL SOCIETY}, author={King, SW and Nemanich, RJ and Davis, RF}, year={1999}, month={Jul}, pages={2648–2651} }
 @article{park_sowers_rinne_schlesser_bergman_nemanich_sitar_hren_cuomo_zhirnov_et al._1999, title={Effect of nitrogen incorporation on electron emission from chemical vapor deposited diamond}, volume={17}, ISSN={["2166-2746"]}, DOI={10.1116/1.590630}, abstractNote={Two different types of the nitrogen-doped chemical vapor deposited (CVD) diamond films were synthesized with N2 (nitrogen) and C3H6N6 (melamine) as doping sources. The samples were analyzed by scanning electron microscopy, Raman scattering, photoluminescence spectroscopy, and field-emission measurements. More effective substitutional nitrogen doping was achieved with C3H6N6 than with N2. The diamond film doped with N2 contained a significant amount of nondiamond carbon phases. The sample produced with N2 exhibited a lower field emission turn-on field than the sample produced with C3H6N6. It is believed that the presence of the graphitic phases (or amorphous sp2 carbon) at the grain boundaries of the diamond and/or the nanocrystallinity (or microcrystallinity) of the diamond play a significant role in lowering the turn-on field of the film produced using N2. It is speculated that substitutional nitrogen doping plays only a minor role in changing the field emission characteristics of CVD diamond films.}, number={2}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B}, author={Park, M and Sowers, AT and Rinne, CL and Schlesser, R and Bergman, L and Nemanich, RJ and Sitar, Z and Hren, JJ and Cuomo, JJ and Zhirnov, VV and et al.}, year={1999}, pages={734–739} }
 @article{sowers_ward_english_nemanich_1999, title={Field emission properties of nitrogen-doped diamond films}, volume={86}, ISSN={["1089-7550"]}, DOI={10.1063/1.371316}, abstractNote={This study explores the field emission properties of nitrogen-doped diamond grown by microwave plasma chemical vapor deposition. Over 70 nitrogen-doped diamond samples were grown on silicon and molybdenum under varying process conditions. Under certain conditions, films can be grown which exhibit photoluminescence bands at 1.945 and 2.154 eV that are attributed to single substitutional nitrogen. Photoelectron emission microscopy with UV free electron laser excitation indicated a 0 or negative electron affinity. Field emission characteristics were measured in an ultrahigh vacuum with a variable distance anode technique. For samples grown with gas phase [N]/[C] ratios less than 10, damage from microarcs occurred during the field emission measurements. Samples grown at higher [N]/[C] content could be measured prior to an arcing event. Contrary to other reports on nitrogen-doped diamond, these measurements indicate relatively high threshold fields (>100 V/μm) for electron emission. We suggest that the nitrogen in these films is compensated by defects. A defect-enhanced electron emission model from these films is discussed.}, number={7}, journal={JOURNAL OF APPLIED PHYSICS}, author={Sowers, AT and Ward, BL and English, SL and Nemanich, RJ}, year={1999}, month={Oct}, pages={3973–3982} }
 @article{goeller_boyanov_sayers_nemanich_myers_steel_1999, title={Germanium segregation in the Co/SiGe/Si(001) thin film system}, volume={14}, ISSN={["0884-2914"]}, DOI={10.1557/JMR.1999.0592}, abstractNote={Cobalt disilicide contacts to silicon–germanium alloys were formed by direct deposition of pure cobalt metal onto silicon–germanium films on Si(001) substrates. Segregation of germanium was observed during the reaction of the cobalt with the silicon–germanium alloy. The nature of the Ge segregation was studied by transmission electron microscopy, energy dispersive spectroscopy, and x-ray diffraction. In the case of cobalt films deposited onto strained silicon–germanium films, the Ge segregation was discovered to be in the form of Ge-enriched Si1−xGex regions found at the surface of the film surrounding CoSi and CoSi2 grains. In the case of cobalt films deposited onto relaxed silicon–germanium films, the Ge segregation was dependent on formation of CoSi2. In samples annealed below 800 °C, where CoSi was the dominant silicide phase, the Ge segregation was similar in form to the strained Si1−xGex case. In samples annealed above 800 °C, where CoSi2 was the dominant silicide phase, the Ge segregation was also in the form of tetrahedron-shaped, Ge-enriched, silicon–germanium precipitates, which formed at the substrate/silicon– germanium film interface and grew into the Si substrate. A possible mechanism for the formation of these precipitates is presented based on vacancy generation during the silicidation reaction coupled with an increased driving force for Ge diffusion due to silicon depletion in the alloy layer.}, number={11}, journal={JOURNAL OF MATERIALS RESEARCH}, author={Goeller, PT and Boyanov, BI and Sayers, DE and Nemanich, RJ and Myers, AF and Steel, EB}, year={1999}, month={Nov}, pages={4372–4384} }
 @article{boyanov_goeller_sayers_nemanich_1999, title={Growth of epitaxial CoSi2 on SiGe(001)}, volume={86}, ISSN={["0021-8979"]}, DOI={10.1063/1.370894}, abstractNote={A technique for achieving epitaxial growth of (001)-oriented CoSi2 on strained epitaxial layers of Si1−xGex(001) is described. The technique is based on a variation of the template method, and is designed to control the local environment of Co atoms at the CoSi2/SiGe interface. The effects of the Co–Ge interactions on the interfacial reaction and the epitaxial orientation and the morphology of the silicide film were investigated. This reaction was found to cause pitting in (001)-oriented CoSi2 films, and to stabilize the (221¯) orientation for films codeposited under conditions where CoSi2(001) growth is achieved on Si(001) substrates. The (221¯)-oriented CoSi2 films were islanded after annealing at 700 °C. The islands were terminated by (1¯11) and (110) facets inclined at 15.8° and 19.5°, respectively, from CoSi2 [221¯] towards CoSi2 [114]. These results were interpreted in terms of reduction of interfacial and surface energies, and geometric effects. Silicide films up to 730-Å-thick were deposited and annealed up to 900 °C. The films were stable against agglomeration, and retained tensile stress in the CoSi2 layer after annealing at 700 °C. The rms roughness of the CoSi2 films was comparable to that of the Si(001) substrate—less than 15 Å over areas as large as 20×20 μm2. Films annealed at 900°C were severely agglomerated.}, number={3}, journal={JOURNAL OF APPLIED PHYSICS}, author={Boyanov, BI and Goeller, PT and Sayers, DE and Nemanich, RJ}, year={1999}, month={Aug}, pages={1355–1362} }
 @article{somashekhar_ying_smith_aldrich_nemanich_1999, title={Hydrogen plasma removal of post-RIE residue for backend processing}, volume={146}, ISSN={["0013-4651"]}, DOI={10.1149/1.1391933}, abstractNote={Reactive ion etching of a patterned silicon dioxide layer leaves behind a uniform fluorocarbon layer which must subsequently be removed. Both surface and via polymeric residues form during the reactive ion etch step and their removal using H 2 -based plasma clean processes is reported here. X-ray photoelectron spectroscopy was used to determine the composition of the residue. Scanning electron microscope images were taken before and after the dry clean treatment to determine the effectiveness of the residue removal process. A radio-frequency-generated hydrogen plasma was used in the dry clean experiments. Power, temperature, and pressure were varied while gas flow was kept constant at 75 sccm and the process time was 5-10 min. The surface residue (on the oxide) was most efficiently removed at 400 W, 450°C, and 15 mTorr when exposed to the plasma for 10 min. The in-via residue was best removed following a 5 min plasma exposure at 100 W, 450°C and 15 mTorr.}, number={6}, journal={JOURNAL OF THE ELECTROCHEMICAL SOCIETY}, author={Somashekhar, A and Ying, H and Smith, PB and Aldrich, DB and Nemanich, RJ}, year={1999}, month={Jun}, pages={2318–2321} }
 @article{nemanich_english_hartman_sowers_ward_ade_davis_1999, title={Imaging electron emission from diamond and III-V nitride surfaces with photo-electron emission microscopy}, volume={146}, ISSN={["0169-4332"]}, DOI={10.1016/S0169-4332(99)00021-5}, abstractNote={Wide bandgap semiconductors such as diamond and the III–V nitrides (GaN, AlN, and AlGaN alloys) exhibit small or even negative electron affinities. Results have shown that different surface treatments will modify the electron affinity of diamond to cause a positive or negative electron affinity (NEA). This study describes the characterization of these surfaces with photo-electron emission microscopy (PEEM). The PEEM technique is unique in that it combines aspects of UV photoemission and field emission. In this study, PEEM images are obtained with either a traditional Hg lamp or with tunable UV excitation from a free electron laser. The UV-free electron laser at Duke University provides tunable emission from 3.5 to greater than 7 eV. PEEM images of boron or nitrogen (N)-doped diamond are similar to SEM of the same surface indicating relatively uniform emission. For the N-doped samples, PEEM images were obtained for different photon energies ranging from 5.0 to 6.0 eV. In these experiments, the hydrogen terminated surface showed more intense PEEM images at lower photon energy indicating a lower photothreshold than annealed surfaces which are presumed to be adsorbate free. For the nitrides, the emission properties of an array of GaN emitter structures is imaged. Emission is observed from the peaks, and relatively uniform emission is observed from the array. The field at the sample surface is approximately 10 V/μm which is sufficient to obtain an image without UV light. This process is termed field emission electron microscopy (FEEM).}, number={1-4}, journal={APPLIED SURFACE SCIENCE}, author={Nemanich, RJ and English, SL and Hartman, JD and Sowers, AT and Ward, BL and Ade, H and Davis, RF}, year={1999}, month={May}, pages={287–294} }
 @article{bergman_alexson_nemanich_dutta_stroscio_balkas_davis_1999, title={Phonon dynamics and lifetimes of AlN and GaN crystallites}, volume={4S1}, DOI={10.1557/s1092578300003422}, abstractNote={The quasi-LO and quasi-TO modes of AlN crystallite were investigated. The analysis indicates that the Raman mode behavior concurs with Loudons’ model of mode-mixing in wurtzite (WZ) structure crystals which is due to the long-range electrostatic field. Phononlifetimes of GaN and AlN crystallites were studied via Raman lineshape. It was found that the low energy E2 mode lifetime is about an order of magnitude longer than that of the other modes, and that impurities impact significantly the phonon-lifetimes.}, number={G6.65}, journal={MRS Internet Journal of Nitride Semiconductor Research}, author={Bergman, L. and Alexson, D. and Nemanich, R. J. and Dutta, M. and Stroscio, M. A. and Balkas, C. and Davis, R. F.}, year={1999} }
 @article{park_mcgregor_bergman_nemanich_hren_cuomo_choi_zhirnov_1999, title={Raman analysis and field emission study of ion beam etched diamond films}, volume={17}, ISSN={["2166-2746"]}, DOI={10.1116/1.590622}, abstractNote={Discontinuous diamond films were deposited on silicon using a microwave plasma chemical vapor deposition system. The diamond deposits were sharpened by argon ion beam etching. Raman spectroscopy was carried out to study the structural change of the diamond after ion beam bombardment. It was found that amorphous sp2 carbon is produced as diamond is being sputtered by the Ar ion beam. The field emission turn-on field was also drastically lowered after sharpening, which, it is speculated, is caused by field enhancement due to change in geometry and/or structural changes (such as amorphization of crystalline diamond into graphitic or amorphous sp2 carbon) by Ar ion irradiation.}, number={2}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B}, author={Park, M and McGregor, DR and Bergman, L and Nemanich, RJ and Hren, JJ and Cuomo, JJ and Choi, WB and Zhirnov, VV}, year={1999}, pages={700–704} }
 @article{bergman_alexson_murphy_nemanich_dutta_stroscio_balkas_shin_davis_1999, title={Raman analysis of phonon lifetimes in AlN and GaN of wurtzite structure}, volume={59}, ISSN={["1550-235X"]}, DOI={10.1103/physrevb.59.12977}, abstractNote={Raman analyses of the lifetimes of phonons in GaN and AlN crystallites of wurtzite structure are presented. In order to ensure the accuracy of the measurement of the phonon lifetimes, an experimental procedure to eliminate the broadening due to the finite slit width was performed. The lifetime analyses indicate that the phonon lifetimes in AlN as well as in GaN fall into two main time regimes: a relatively long time of the ${E}_{2}^{1}$ mode and much shorter times of the ${E}_{2}^{2},$ $E1(\mathrm{TO}),$ and $A1(\mathrm{TO})$ modes. The lifetimes of the ${E}_{2}^{1},$ ${E}_{2}^{2},$ $E1(\mathrm{TO}),$ $A1(\mathrm{TO}),$ and $A1(\mathrm{LO})$ modes of an high-quality AlN crystallite are 4.4, 0.83, 0.91, 0.76, and 0.45 ps, respectively. Moreover, the lifetime of the $A1(\mathrm{LO})$ mode found in this study is consistent with the current phonon-decay model of that mode in wurtzite structure materials. The lifetimes of ${E}_{2}^{1},$ ${E}_{2}^{2},$ $E1(\mathrm{TO}),$ and $A1(\mathrm{TO})$ of a GaN crystallite were found to be 10.1, 1.4, 0.95, and 0.46 ps, respectively. The $A1(\mathrm{LO})$ mode in the GaN was not observed and its absence is attributed to plasmon damping. The lifetime shortening due to impurities was also studied: the lifetimes of the Raman modes of an AlN crystallite, which contains about two orders of magnitude more Si and C impurities relative to the concentration of the high-quality crystallite were found to be 50% shorter.}, number={20}, journal={PHYSICAL REVIEW B}, author={Bergman, L and Alexson, D and Murphy, PL and Nemanich, RJ and Dutta, M and Stroscio, MA and Balkas, C and Shin, H and Davis, RF}, year={1999}, month={May}, pages={12977–12982} }
 @article{bergman_dutta_balkas_davis_christman_alexson_nemanich_1999, title={Raman analysis of the E1 and A1 quasi-longitudinal optical and quasi-transverse optical modes in wurtzite AlN}, volume={85}, ISSN={["0021-8979"]}, DOI={10.1063/1.369712}, abstractNote={This article presents a study of the quasi-longitudinal optical and quasi-transverse optical modes in wurtzite AlN which originate from the interaction of phonons belonging to the A1 and E1 symmetry groups. In order to analyze the allowed quasi as well as pure Raman modes, the modes were observed in a rotating crystallographic coordinate system, and the Raman tensors of the wurtzite crystal structure were calculated as a function of the crystallographic rotation. The frequencies of the quasimodes of wurtzite AlN were also analyzed in terms of the interaction of the polar phonons with the long range electrostatic field model. The experimental values of the Raman frequencies of the quasiphonons concur with these expected from the model, implying that the long range electrostatic field dominates the short range forces for polar phonons in AlN.}, number={7}, journal={JOURNAL OF APPLIED PHYSICS}, author={Bergman, L and Dutta, M and Balkas, C and Davis, RF and Christman, JA and Alexson, D and Nemanich, RJ}, year={1999}, month={Apr}, pages={3535–3539} }
 @article{park_camphausen_myers_barletta_sakhrani_bergman_nemanich_cuomo_1999, title={Raman scattering of tetrahedrally-bonded amorphous carbon deposited at oblique angles}, volume={41}, ISSN={["1873-4979"]}, DOI={10.1016/S0167-577X(99)00135-4}, abstractNote={Amorphous carbon (txa-C1−x) films were prepared by filtered cathodic arc deposition (FCAD). The films were deposited on p-type Si (111). The angle of beam incidence was varied from 0° to 75° with respect to the substrate normal. Micro-Raman spectroscopy, electron energy loss spectroscopy (EELS), and transmission electron microscopy (TEM) were carried out for sample analysis. It was found that the position of the G peak shifts to a higher wave number region as the angle of incidence increases. This means that the sp2/sp3 ratio increases with increasing angle. This conclusion is supported by EELS. The film deposited at an angle of 75° exhibits a columnar structure with alternating high and low carbon density regions.}, number={5}, journal={MATERIALS LETTERS}, author={Park, M and Camphausen, SM and Myers, AF and Barletta, PT and Sakhrani, V and Bergman, L and Nemanich, RJ and Cuomo, JJ}, year={1999}, month={Dec}, pages={229–233} }
 @article{jung_kim_jeon_yang_nemanich_1999, title={Reduction of the transition temperature of C54TiSi(2) through a Ta interlayer}, volume={35}, number={1999 Dec.}, journal={Journal of the Korean Physical Society}, author={Jung, B. and Kim, Y. D. and Jeon, H. and Yang, W. and Nemanich, R. J.}, year={1999}, pages={S769–773} }
 @article{maillard-schaller_boyanov_english_nemanich_1999, title={Role of the substrate strain in the sheet resistance stability of NiSi deposited on Si (100)}, volume={85}, ISSN={["1089-7550"]}, DOI={10.1063/1.369774}, abstractNote={In order to study the influence of strain on the formation and stability of NiSi, Ni has been deposited on strained and relaxed Si(100) n-type substrates. Strained Si substrates have been produced by depositing a pseudomorphic silicon film onto a 3000 Å thick relaxed Si0.8Ge0.2 film. Raman spectroscopy has established that the silicon film is strained. The presence of a characteristic cross-hatch pattern has been identified by atomic force microscopy. Measurements show that the sheet resistance (Rs) of the silicide formed on strained silicon remains stable up to 700 °C while the Rs of the silicide formed on bulk silicon (100) shows a significant increase at 600 °C . X-ray photoelectron spectroscopy shows that the NiSi–NiSi2 phase transition occurs at a higher temperature and is, therefore, not responsible for the Rs instability. Scanning electron microscopy measurements indicate that islanding occurs in the temperature region of the resistivity increase. Photoelectron emission microscopy has been employed to observe the surface morphology during annealing, and islanding is not observed until a higher annealing temperature for the NiSi on strained Si. The increase in Rs is apparently correlated to the islanding of NiSi which appears at lower temperature on the bulk silicon substrate than on the strained silicon substrate. The stability of the NiSi film on the strained Si substrate is related to the strain induced by thermal expansion and the increased lattice constant of the strained Si.}, number={7}, journal={JOURNAL OF APPLIED PHYSICS}, author={Maillard-Schaller, E and Boyanov, BI and English, S and Nemanich, RJ}, year={1999}, month={Apr}, pages={3614–3618} }
 @article{boyanov_goeller_sayers_nemanich_1999, title={The effect of germanium on the Co-SiGe thin-film reaction}, volume={6}, ISSN={["0909-0495"]}, DOI={10.1107/S0909049599000060}, abstractNote={Ge Co Germanium was found to have a strong influence on the path and products of the Co-SiGe reaction, and on the interfacial stability and crystallographic orientation of the silicide film. The segregation of Ge that occurs during the reaction of blanket Co films with SiGe results in thickness effects not present in the reaction of Co with Si. The thickness effect was modelled in terms of the energy cost of Ge segregation, and good agreement with experimental results was obtained. In s i tu EXAFS experiments on sub-monolayer Co films annealed on SiGe substrates indicate a strong preference for the formation of Co-Si bonds at the silicide-SiGe interface. The implications of these results for the stability of the interface and the epitaxial orientation of co-deposited cobalt disilicide (CoSi2) films will be discussed.}, journal={JOURNAL OF SYNCHROTRON RADIATION}, author={Boyanov, BI and Goeller, PT and Sayers, DE and Nemanich, RJ}, year={1999}, month={May}, pages={521–523} }
 @article{wolfe_hinds_wang_lucovsky_ward_xu_nemanich_maher_1999, title={Thermochemical stability of silicon-oxygen-carbon alloy thin films: A model system for chemical and structural relaxation at SiC-SiO2 interfaces}, volume={17}, ISSN={["0734-2101"]}, DOI={10.1116/1.581745}, abstractNote={Alloy thin films of hydrogenated silicon–oxygen–carbon (Si,C)Ox x<2, were deposited and analyzed in terms of changes in structure and bonding as a function of rapid thermal annealing between 600 and 1100 °C using a combination of Fourier transform infrared spectroscopy, Raman scattering and high-resolution transmission electron microscopy. Results showed that three structural/chemical transformations took place upon annealing. The initial reaction (600–800 °C) involved the loss of hydrogen bonded to both silicon and carbon. At intermediate temperatures (900–1000 °C) a Si–O–C type bond was observed to form, and subsequently disappear after annealing to 1050 °C. The formation of ordered amorphous-SiC regions, nanocrystalline-Si regions, and stoichiometric, thermally relaxed SiO2 accompanied the disappearance of the Si–O–C bond at the 1050 °C annealing temperature. Using this alloy as a model system, important information is obtained for optimized processing of SiC–SiO2 interfaces for device applications.}, number={4}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A-VACUUM SURFACES AND FILMS}, author={Wolfe, DM and Hinds, BJ and Wang, F and Lucovsky, G and Ward, BL and Xu, M and Nemanich, RJ and Maher, DM}, year={1999}, pages={2170–2177} }
 @article{king_davis_ronning_nemanich_1999, title={Valence band discontinuity of the (0001) 2H-GaN/(111) 3C-SiC interface}, volume={28}, ISSN={["0361-5235"]}, DOI={10.1007/s11664-999-0145-4}, number={12}, journal={JOURNAL OF ELECTRONIC MATERIALS}, author={King, SW and Davis, RF and Ronning, C and Nemanich, RJ}, year={1999}, month={Dec}, pages={L34–L37} }
 @article{king_davis_ronning_benjamin_nemanich_1999, title={Valence band discontinuity, surface reconstruction, and chemistry of (0001), (000(1)over-bar), and (1(1)over-bar-00) 2H-AlN/6H-SiC interfaces}, volume={86}, ISSN={["0021-8979"]}, DOI={10.1063/1.371391}, abstractNote={A detailed examination of the valence band discontinuity (ΔEv) formed at the (0001), (0001̄), and (11̄00) interfaces between 2H–AlN and 6H–SiC has been conducted using x-ray and UV photoelectron spectroscopies. The ΔEv was observed to range from 0.6–2.0 eV depending on the growth direction (i.e., AlN on SiC vs SiC on AlN), as well as the crystallographic orientation, cut of the SiC substrate (i.e., on versus off axis), and SiC surface reconstruction and stoichiometry. A ΔEv of 1.4–1.5 eV was observed for AlN grown on (3×3) (0001)Si6H–SiC on-axis substrates; a ΔEv of 0.9–1.0 eV was observed for off-axis substrates with the same surface reconstruction. The values of ΔEv for AlN grown on (√3×√3)R30°(0001) 6H–SiC on-and-off-axis substrates were 1.1–1.2 eV. A larger valence band discontinuity of 1.9–2.0 eV was determined for 3C–SiC grown on (0001) 2H–AlN. Smaller values of ΔEv of 0.6–0.7 and 0.8–0.9 eV were observed for AlN grown on on-axis (0001̄)C and (11̄00)6H–SiC substrates, respectively.}, number={8}, journal={JOURNAL OF APPLIED PHYSICS}, author={King, SW and Davis, RF and Ronning, C and Benjamin, MC and Nemanich, RJ}, year={1999}, month={Oct}, pages={4483–4490} }
 @article{king_nemanich_davis_1999, title={Wet chemical processing of (0001)(Si) 6H-SiC hydrophobic and hydrophilic surfaces}, volume={146}, ISSN={["0013-4651"]}, DOI={10.1149/1.1391864}, abstractNote={The wetting characteristics of polished or polished and thermally oxidized, on- and off-axis (0001) Si 6H-SiC [the silicon-terminated surface of SiC] surfaces in selected acids and bases have been determined and compared with that of (111)Si. Auger electron and X-ray photoelectron spectroscopies and low energy electron diffraction were used to characterize the chemical state and order of these surfaces. The oxidized SiC surfaces were hydrophilic after oxide removal with a 10:1 HF solution and were terminated with approximately a monolayer containing OH, CO, CH, and F species. The same effects were observed for the similarly treated (0001) C [the carbon-terminated surface of SiC], (1120), and (1010) surfaces. The as-polished SiC surfaces were hydrophobic and covered with a thin (5-10 A) contamination layer composed primarily of C-C, C-F, and Si-F bonded species. Removal of this layer using an RCA SC etch or Piranha clean resulted in a disordered hydrophilic SiC surface. A 20 A amorphous Si capping layer both passivated the SiC surfaces and provided a better alternative to the aforementioned contamination layer for producing hydrophobic surfaces on this material.}, number={5}, journal={JOURNAL OF THE ELECTROCHEMICAL SOCIETY}, author={King, SW and Nemanich, RJ and Davis, RF}, year={1999}, month={May}, pages={1910–1917} }
 @article{king_carlson_therrien_christman_nemanich_davis_1999, title={X-ray photoelectron spectroscopy analysis of GaN/(0001)AlN and AlN/(0001)GaN growth mechanisms}, volume={86}, ISSN={["0021-8979"]}, DOI={10.1063/1.371564}, abstractNote={The mechanisms of growth of GaN on AlN and AlN on GaN via gas source-molecular beam epitaxy with NH3 as the nitrogen source have been investigated using x-ray photoelectron spectroscopy, low energy electron diffraction, and Auger electron spectroscopy. The growth of GaN on AlN at low temperatures (650–750 °C) occurs via a Stranski–Krastanov 2D→3D type mechanism with the transition to 3D growth occurring at ≈10–15 Å. The mechanism changes to Frank van der Merwe (FM)/layer-by-layer growth above 800 °C. The growth of AlN on GaN occurred via a FM layer-by-layer mechanism within the 750–900 °C temperature range investigated. We propose a model based on the interaction of ammonia and atomic hydrogen with the GaN/AlN surfaces which indicates that the surface kinetics of hydrogen desorption and ammonia decomposition are the factors that determine the GaN growth mechanism.}, number={10}, journal={JOURNAL OF APPLIED PHYSICS}, author={King, SW and Carlson, EP and Therrien, RJ and Christman, JA and Nemanich, RJ and Davis, RF}, year={1999}, month={Nov}, pages={5584–5593} }
 @article{ade_yang_english_hartman_davis_nemanich_litvinenko_pinayev_wu_madey_1998, title={A free electron laser-photoemission electron microscope system (FEL-PEEM)}, volume={5}, ISSN={["0218-625X"]}, DOI={10.1142/S0218625X98001596}, abstractNote={ We report first results from our effort to couple a high resolution photoemission electron microscope (PEEM) to the OK-4 ultraviolet free electron laser at Duke University (OK-4/Duke UV FEL). The OK-4/Duke UV FEL is a high intensity source of tunable monochromatic photons in the 3–10 eV energy range. This tunability is unique and allows us to operate near the photoemission threshold of any samples and thus maximize sample contrast while keeping chromatic berrations in the PEEM minimal. We have recorded first images from a variety of samples using spontaneous radiation from the OK-4/ Duke UV FEL in the photon energy range of 4.0–6.5 eV. Due to different photothreshold emission from different sample areas, emission from these areas could be turned on (or off) selectively. We have also observed relative intensity reversal with changes in photon energy which are interpreted as density-of-state contrast. Usable image quality has been achieved, even though the output power of the FEL in spontaneous emission mode was several orders of magnitude lower than the anticipated full laser power. The PEEM has achieved a spatial resolution of 12 nm. }, number={6}, journal={SURFACE REVIEW AND LETTERS}, author={Ade, H and Yang, W and English, SL and Hartman, J and Davis, RF and Nemanich, RJ and Litvinenko, VN and Pinayev, IV and Wu, Y and Madey, JMJ}, year={1998}, month={Dec}, pages={1257–1268} }
 @article{baumann_nemanich_1998, title={Characterization of copper-diamond (100), (111), and (110) interfaces: Electron affinity and Schottky barrier}, volume={58}, ISSN={["1550-235X"]}, DOI={10.1103/physrevb.58.1643}, abstractNote={In this study ultraviolet photoemission spectroscopy was employed to correlate the electron affinity and Schottky barrier height of Cu films on type-IIb ($p$-type) diamond (100), (111), and (110) surfaces. Furthermore, field emission measurements were correlated with the effective electron affinity of the samples. Prior to deposition the diamond samples were cleaned by various annealings and plasma treatments in ultrahigh vacuum. Annealing the diamond substrates to 1150 \ifmmode^\circ\else\textdegree\fi{}C resulted in adsorbate-free surfaces with a positive electron affinity. A negative electron affinity (NEA) was induced after depositing 1 \AA{} of Cu on the clean surface. The Schottky barrier heights for the clean surfaces ranged from 0.30 eV for the (111) surface to 0.70 eV for the (100) surface. Depositing Cu onto H-terminated surfaces exhibiting a NEA still resulted in a NEA on all surfaces. However, the Schottky barrier heights were larger, ranging from 0.50 eV for the (111) surface to 0.90 eV for the (100) and (110) surfaces. The metal-induced NEA has been found to be stable to exposure to air. Following a 500 \ifmmode^\circ\else\textdegree\fi{}C annealing an oxygen-terminated (100) surface with a positive electron affinity was obtained. Cu deposition resulted in a positive electron affinity and the largest Schottky barrier height with 1.60 eV. A field emission threshold field of 79 V/\ensuremath{\mu}m was obtained for an oxygen-terminated diamond (100) surface. Values of 20, 25, and 53 V/\ensuremath{\mu}m were measured for Cu on clean, H- and O-terminated surfaces, respectively. Based on these experiments, it is suggested that chemisorbed species such as H or O on diamond surfaces cause an increase in the Schottky barrier as well as in the field emission threshold field after Cu deposition.}, number={3}, journal={PHYSICAL REVIEW B}, author={Baumann, PK and Nemanich, RJ}, year={1998}, month={Jul}, pages={1643–1654} }
 @article{nemanich_baumann_benjamin_english_hartman_sowers_ward_1998, title={Characterization of electron emitting surfaces of diamond and III-V nitrides}, volume={8}, number={4}, journal={Diamond Films and Technology}, author={Nemanich, R. J. and Baumann, P. K. and Benjamin, M. C. and English, S. L. and Hartman, J. D. and Sowers, A. T. and Ward, B. L.}, year={1998}, pages={211–223} }
 @article{king_barnak_bremser_tracy_ronning_davis_nemanich_1998, title={Cleaning of AlN and GaN surfaces}, volume={84}, ISSN={["0021-8979"]}, DOI={10.1063/1.368814}, abstractNote={Successful ex situ and in situ cleaning procedures for AlN and GaN surfaces have been investigated and achieved. Exposure to HF and HCl solutions produced the lowest coverages of oxygen on AlN and GaN surfaces, respectively. However, significant amounts of residual F and Cl were detected. These halogens tie up dangling bonds at the nitride surfaces hindering reoxidation. The desorption of F required temperatures >850 °C. Remote H plasma exposure was effective for removing halogens and hydrocarbons from the surfaces of both nitrides at 450 °C, but was not efficient for oxide removal. Annealing GaN in NH3 at 700–800 °C produced atomically clean as well as stoichiometric GaN surfaces.}, number={9}, journal={JOURNAL OF APPLIED PHYSICS}, author={King, SW and Barnak, JP and Bremser, MD and Tracy, KM and Ronning, C and Davis, RF and Nemanich, RJ}, year={1998}, month={Nov}, pages={5248–5260} }
 @article{goeller_boyanov_sayers_nemanich_1998, title={Co-deposition of cobalt disilicide on silicon-germanium thin films}, volume={320}, ISSN={["0040-6090"]}, DOI={10.1016/S0040-6090(97)00941-3}, abstractNote={The formation of CoSi2 on strained epitaxial Si0.8Ge0.2/Si(100) films has been studied as a function of the deposition method and annealing temperature. Two types of deposition processes were used: a direct method, where 5 nm of pure Co metal were deposited at room temperature onto a strained 80 nm thick Si0.8Ge0.2 layer; and a co-deposition method, where 5 nm Co and 18.2 nm Si were simultaneously deposited in a 1:2 ratio onto a strained Si0.8Ge0.2 layer at 450°C. Samples were then annealed at temperatures ranging from 500 to 800°C. Extended X-ray absorbance fine structure spectroscopy (EXAFS) and X-ray diffraction (XRD) were used to characterize the structure of the resulting films. It was found that the samples prepared via the direct deposition method did not convert to CoSi2 at any annealing temperature up to 800°C, while the co-deposited samples formed epitaxial CoSi2 at even the lowest annealing temperature of 500°C. These results are discussed in terms of proposed reaction mechanisms of the different deposition methods, based on consideration of the Co–Si–Ge ternary phase diagram.}, number={2}, journal={THIN SOLID FILMS}, author={Goeller, PT and Boyanov, BI and Sayers, DE and Nemanich, RJ}, year={1998}, month={May}, pages={206–210} }
 @article{king_ronning_davis_benjamin_nemanich_1998, title={Dependence of (0001) GaN/AlN valence band discontinuity on growth temperature and surface reconstruction}, volume={84}, ISSN={["0021-8979"]}, DOI={10.1063/1.368355}, abstractNote={X ray and ultraviolet photoelectron spectroscopies have been used to determine the heterojunction valence band discontinuity at the (0001) GaN/AlN interface. Type I discontinuity values of 0.5±0.2 eV were determined for GaN grown on AlN at 650 °C and 0.8±0.2 eV for GaN grown on AlN at 800 °C. These values are critically evaluated with respect to film quality, the results of other experimental studies, and theory.}, number={4}, journal={JOURNAL OF APPLIED PHYSICS}, author={King, SW and Ronning, C and Davis, RF and Benjamin, MC and Nemanich, RJ}, year={1998}, month={Aug}, pages={2086–2090} }
 @article{baumann_nemanich_1998, title={Electron affinity and Schottky barrier height of metal-diamond (100), (111), and (110) interfaces}, volume={83}, ISSN={["0021-8979"]}, DOI={10.1063/1.366940}, abstractNote={The electron emission properties of metal–diamond (100), (111), and (110) interfaces were characterized by means of UV photoemission spectroscopy (UPS) and field-emission measurements. Different surface cleaning procedures including annealing in ultrahigh vacuum (UHV) and rf plasma treatments were used before metal deposition. This resulted in diamond surfaces terminated by oxygen, hydrogen, or free of adsorbates. The electron affinity and Schottky barrier height of Zr or Co thin films were correlated by means of UPS. A negative electron affinity (NEA) was observed for Zr on any diamond surface. Co on diamond resulted in NEA characteristics except for oxygen-terminated surfaces. The lowest Schottky barrier heights were obtained for the clean diamond surfaces. Higher values were measured for H termination, and the highest values were obtained for O on diamond. For Zr, the Schottky barrier height ranged from 0.70 eV for the clean to 0.90 eV for the O-terminated diamond (100) surface. Values for Co ranged from 0.35 to 1.40 eV for clean- and O-covered (100) surfaces, respectively. The metal-induced NEA proved to be stable after exposure to air. For the oxygen-terminated diamond (100) surface a field-emission threshold of 79 V/μm was measured. Zr or Co deposition resulted in lower thresholds. Values as low as 20 V/μm were observed for Zr on the clean diamond (100) surface. Results for Zr or Co on H- or O-terminated surfaces were higher. H or O layers on diamond tend to cause an increase in the Schottky barrier height and the field-emission threshold field of Zr– and Co–diamond interfaces. The value of the electron affinity and Schottky barrier were correlated with work function and different initial surface preparation. The results were largely consistent with a model in which the vacuum level was related to the metal work function and the measured Schottky barrier.}, number={4}, journal={JOURNAL OF APPLIED PHYSICS}, author={Baumann, PK and Nemanich, RJ}, year={1998}, month={Feb}, pages={2072–2082} }
 @article{ward_nam_hartman_english_mccarson_schlesser_sitar_davis_nemanich_1998, title={Electron emission characteristics of GaN pyramid arrays grown via organometallic vapor phase epitaxy}, volume={84}, ISSN={["0021-8979"]}, DOI={10.1063/1.368775}, abstractNote={Selective growth of arrays of silicon-doped GaN (Si:GaN) pyramids for field emitter applications has been achieved. The electron emission characteristics of these arrays has been measured using techniques such as field emission, field emission energy distribution analysis (FEED), photoemission electron microscopy (PEEM), and field emission electron microscopy (FEEM). The field emission current–voltage (I–V) results indicate an average threshold field as low as 7 V/μm for an emission current of 10 nA. It is suggested that the low threshold field value is a consequence of both the low work function of Si:GaN and the field enhancement of the pyramids. The results of the FEEM and FEED measurements indicate agreement with the field emission I–V characteristics. The FEED results indicate that the Si:GaN pyramids are conducting, and that no significant ohmic losses are present between the top contact to the array and the field emitting pyramids. The PEEM and FEEM images show that the emission from the arrays is uniform over a 150 μm field of view.}, number={9}, journal={JOURNAL OF APPLIED PHYSICS}, author={Ward, BL and Nam, OH and Hartman, JD and English, SL and McCarson, BL and Schlesser, R and Sitar, Z and Davis, RF and Nemanich, RJ}, year={1998}, month={Nov}, pages={5238–5242} }
 @article{baumann_nemanich_1998, title={Electron emission from metal-diamond (100), (111) and (110) interfaces}, volume={7}, ISSN={["0925-9635"]}, DOI={10.1016/S0925-9635(97)00256-2}, abstractNote={Electron emission characteristics of Cu, Co or Zr films on diamond (100), (111) and (110) surfaces were measured by employing ultraviolet photoemission spectroscopy (UPS) and field emission measurements. Prior to metal deposition, the diamond substrates were terminated with oxygen, hydrogen or were free of adsorbates. Deposition of thin Cu or Co films induced a NEA on clean and H-terminated surfaces. A positive electron affinity was observed for Cu or Co on oxygenated surfaces, and depositing thin Zr films resulted in a NEA on all surfaces considered. UPS can be used to correlate the electron affinity and Schottky barrier height. Schottky barriers of metals on clean surfaces were the lowest, whereas they were the highest on oxygen-covered surfaces. Values for the Schottky barrier height ranged from 0.70 eV to 1.60 eV for Cu, 0.35 eV to 1.40 eV for Co and 0.70 eV to 0.95 eV for Zr. A field emission threshold of 79 V μm−1 was measured for oxygenated (100) surfaces. The lowest value of 20 V μm−1 was observed for Zr on the clean (100) surface. For all the metals studied, it was found that a lower Schottky barrier height results in a lower electron affinity, and a lower electron affinity results in a lower field emission threshold.}, number={2-5}, journal={DIAMOND AND RELATED MATERIALS}, author={Baumann, PK and Nemanich, RJ}, year={1998}, month={Feb}, pages={612–619} }
 @article{nemanich_baumann_benjamin_nam_sowers_ward_ade_davis_1998, title={Electron emission properties of crystalline diamond and III-nitride surfaces}, volume={130}, ISSN={["0169-4332"]}, DOI={10.1016/s0169-4332(98)00140-8}, abstractNote={Wide bandgap semiconductors have the possibility of exhibiting a negative electron affinity (NEA) meaning that electrons in the conduction band are not bound by the surface. The surface conditions are shown to be of critical importance in obtaining a negative electron affinity. UV-photoelectron spectroscopy can be used to distinguish and explore the effect. Surface terminations of molecular adsorbates and metals are shown to induce an NEA on diamond. Furthermore, a NEA has been established for epitaxial AlN and AlGaN on 6H–SiC. Field emission measurements from flat surfaces of p-type diamond and AlN are similar, but it is shown that the mechanisms may be quite different. The measurements support the recent suggestions that field emission from p-type diamond originates from the valence band while for AlN on SiC, the field emission results indicate emission from the AlN conduction band. We also report PEEM (photo-electron emission microscopy) and FEEM (field electron emission microscopy) images of an array of nitride emitters.}, number={1998 June}, journal={APPLIED SURFACE SCIENCE}, author={Nemanich, RJ and Baumann, PK and Benjamin, MC and Nam, OH and Sowers, AT and Ward, BL and Ade, H and Davis, RF}, year={1998}, month={Jun}, pages={694–703} }
 @article{boyanov_goeller_sayers_nemanich_1998, title={Film thickness effects in the Co-Si1-xGex solid phase reaction}, volume={84}, ISSN={["0021-8979"]}, DOI={10.1063/1.368872}, abstractNote={The thickness dependence of the reaction of cobalt with epitaxial silicon–germanium alloys (Si1−xGex) has been studied. The reaction products of Co with (100)-oriented Si0.79Ge0.21 after annealing at 800 °C depended on the thickness of the Co film. Complete conversion to CoSi2 occurred only when the thickness of the Co layer exceeded 350 Å. Interface reactions with Co layers thinner than 50 Å resulted in CoSi formation, while a mixture of CoSi and CoSi2 was formed at intermediate thicknesses. X-ray diffraction and extended x-ray absorption fine structure measurements indicated no measurable incorporation of Ge had occurred in either the CoSi or CoSi2. The threshold thickness for nucleation of CoSi2 on (100)-oriented Si1−xGex was determined in the range 0⩽x⩽0.25. The threshold thickness increased superlinearly with the Ge concentration x, and did not depend on the doping of the Si(100) substrate or the strain state of the Si1−xGex film. The observed thickness effect was attributed to preferential Co–Si bonding in the reaction zone and the energy cost of Ge segregation, which accompanies the formation of CoSi and CoSi2 during the reaction of Co with Si1−xGex.}, number={8}, journal={JOURNAL OF APPLIED PHYSICS}, author={Boyanov, BI and Goeller, PT and Sayers, DE and Nemanich, RJ}, year={1998}, month={Oct}, pages={4285–4291} }
 @article{sayers_goeller_boyanov_nemanich_1998, title={In situ studies of metal-semiconductor interactions with synchrotron radiation}, volume={5}, ISSN={["0909-0495"]}, DOI={10.1107/S0909049597015240}, abstractNote={The capabilities and performance of a UHV system for in situ studies of metal–semiconductor interactions are described. The UHV system consists of interconnected deposition and analysis chambers, each of which is capable of maintaining a base pressure of approximately 1 × 10−10 torr. The deposited materials and their reaction products can be studied in situ with RHEED, XAFS, AES, XPS, UPS and ARUPS. Results from a study of the reaction of 0.7- and 1.7-monolayer-thick films of cobalt with strained silicon–germanium alloys are presented. The signal-to-noise ratio obtained in these experiments indicates that the apparatus is capable of supporting in situ EXAFS studies of ∼0.1-monolayer-thick films.}, journal={JOURNAL OF SYNCHROTRON RADIATION}, author={Sayers, DE and Goeller, PT and Boyanov, BI and Nemanich, RJ}, year={1998}, month={May}, pages={1050–1051} }
 @article{christman_woolcott_kingon_nemanich_1998, title={Piezoelectric measurements with atomic force microscopy}, volume={73}, ISSN={["0003-6951"]}, DOI={10.1063/1.122914}, abstractNote={An atomic force microscope (AFM) is used to measure the magnitude of the effective longitudinal piezoelectric constant (d33) of thin films. Measurements are performed with a conducting diamond AFM tip in contact with a top electrode. The interaction between the tip and electric field present is a potentially large source of error that is eliminated through the use of this configuration and the conducting diamond tips. Measurements yielded reasonable piezoelectric constants of X-cut single-crystal quartz, thin film ZnO, and nonpiezoelectric SiO2 thin films.}, number={26}, journal={APPLIED PHYSICS LETTERS}, author={Christman, JA and Woolcott, RR and Kingon, AI and Nemanich, RJ}, year={1998}, month={Dec}, pages={3851–3853} }
 @article{ronning_banks_mccarson_schlesser_sitar_davis_ward_nemanich_1998, title={Structural and electronic properties of boron nitride thin films containing silicon}, volume={84}, ISSN={["0021-8979"]}, DOI={10.1063/1.368752}, abstractNote={The incorporation of silicon into boron nitride films (BN:Si) has been achieved during ion beam assisted deposition growth. A gradual change from cubic boron nitride (c-BN) to hexagonal boron nitride (h-BN) was observed with increasing silicon concentration. Ultraviolet photoelectron spectroscopy, field emission, and field emission electron energy distribution experiments indicated that the observed electron transport and emission were due to hopping conduction between localized states in a band at the Fermi level for the undoped c-BN films and at the band tails of the valence band maximum for the BN:Si films. A negative electron affinity was observed for undoped c-BN films; this phenomenon disappeared upon silicon doping due to the transformation to h-BN. No shift of the Fermi level was observed in any BN:Si film; thus, n-type doping can be excluded.}, number={9}, journal={JOURNAL OF APPLIED PHYSICS}, author={Ronning, C and Banks, AD and McCarson, BL and Schlesser, R and Sitar, Z and Davis, RF and Ward, BL and Nemanich, RJ}, year={1998}, month={Nov}, pages={5046–5051} }
 @article{baumann_nemanich_1998, title={Surface cleaning, electronic states and electron affinity of diamond (100), (111) and (110) surfaces}, volume={409}, ISSN={["0039-6028"]}, DOI={10.1016/S0039-6028(98)00259-3}, abstractNote={The effects of cleaning natural type IIb diamond (100), (111) and (110) samples by annealing and hydrogen – or deuterium plasma exposure were investigated by means of ultraviolet photoemission spectroscopy (UPS). Different wet chemical cleaning processes (a conventional chromic acid clean and an electrochemical etch) and a H plasma exposure have been employed to clean natural type IIb semiconducting diamond C(100) wafers. The effects of these processes on the diamond surface have been assessed and compared. As evidenced by Auger electron spectroscopy (AES), an oxygen free surface could be obtained following vacuum annealing to 900°C for the electrochemical process compared to 1050°C for the chromic acid etch. In addition, the technique of atomic force microscopy demonstrated the presence of oriented pits on the surface of samples that were electrochemically etched for long times at high currents. After a H plasma exposure the negative electron affinity (NEA) peak in the UPS spectra doubled in intensity. An anneal to 1100°C resulted in the removal of the sharp NEA feature. A second H plasma treatment resulted in the reappearance of the NEA peak similar to that after the first H plasma exposure. A (2×1) reconstructed low energy electron diffraction pattern was observed subsequent to the anneals as well as the H plasma treatments. The fact that a NEA can be induced or removed repeatedly by means of a H plasma exposure or annealing at 1100°C, respectively, provides evidence to correlate the appearance of a NEA with the presence of a monohydride terminated surface. Corresponding effects were found for (111) and (110) surfaces. A NEA could be induced by a H plasma and removed by annealing at 900 or 800°C for diamond (111) or (110) surfaces, respectively. Following a deuterium plasma exposure the diamond surfaces exhibited a NEA like the ones treated by a hydrogen plasma. Higher annealing temperatures were necessary to remove the NEA for deuterium due to the isotope effect. Values of 79 and 81 V μm−1 were measured for the field emission threshold of the oxygen terminated C(100) and C(110) surfaces, respectively. A value of 25 V μm−1 was determined for the hydrogen terminated C(110) surface.}, number={2}, journal={SURFACE SCIENCE}, author={Baumann, PK and Nemanich, RJ}, year={1998}, month={Jul}, pages={320–335} }
 @article{king_ronning_davis_busby_nemanich_1998, title={X-ray photoelectron diffraction from (3X3) and (root 3X root 3)R30 degrees (001)(Si) 6H-SiC surfaces}, volume={84}, ISSN={["1089-7550"]}, DOI={10.1063/1.368879}, abstractNote={High-resolution (±1°) x-ray photoelectron diffraction (XPD) patterns were obtained along high symmetry azimuths of the (3×3) and (√3×√3)R30° reconstructed (0001)Si 6H–SiC surfaces. The data were compared to XPD patterns obtained from (7×7) Si (111) as well as to models proposed for the (3×3) and (√3×√3)R30° 6H–SiC reconstructions. Forward scattering features similar to those observed from the (7×7) Si (111) were also observed from the (√3×√3)R30° 6H–SiC (0001)Si surface. Additional structures were found and attributed to the substitution of carbon atoms for silicon. Unlike (1×1) and (7×7) Si (111) surfaces, the XPD patterns of (3×3) and (√3×√3)R30° SiC (0001)Si surfaces are different which is due to the presence of an incomplete bilayer of Si on the (3×3) surface. The most significant difference with the Si system is the equivalence of the [101̄0] and [011̄0] azimuths in the (3×3) structure. These results are consistent with a faulted Si bilayer stacking sequence which was proposed based on scanning tunneling microscopy observations.}, number={11}, journal={JOURNAL OF APPLIED PHYSICS}, author={King, SW and Ronning, C and Davis, RF and Busby, RS and Nemanich, RJ}, year={1998}, month={Dec}, pages={6042–6048} }
 @article{wang_goeller_boyanov_sayers_nemanich_1997, title={An integrated growth and analysis system for in-situ XAS studies of metal-semiconductor interactions}, volume={7}, ISSN={["1155-4339"]}, DOI={10.1051/jp4/1997096}, abstractNote={A UHV system for in-situ studies of metal-semiconductor interactions has been designed and assembled at North Carolina State University and recently installed and tested at the NSLS. The UHV system consists of interconnected deposition and analysis chambers, each of which is capable of maintaining a base pressure of approximately 1 x 10 -10 Torr. Up to three materials can be co-deposited on 25 mm wafers by electron-beam evaporation. Substrate temperature can be controlled in the range 30-900 °C during deposition, and the growth process may be monitored with RHEED. The deposited materials and their reaction products can be studied in-Situ with a variety of technique: XAFS, AES, XPS, UPS and ARXPS/UPS. We describe the capabilities of the system and present our first EXAFS results on the stabilization of Co + 2 Si films co-deposited on Si 0.8 Ge 0.2 alloys. Preliminary results indicate that Co + 2Si forms a stable film on Si 0.8 Ge 0.2 with a CoSi 2 -like reaction path. As is the case with CO/Si 0.8 Ge 0.2 , silicide formation is complete at 700 °C. However, the Co+2Si/Si 0.8 Ge 0.2 system does not undergo a Cosi → CoSi 2 transition when annealed at 500-700 °C, and exhibits only weak CoSi features in this temperature range.}, number={C2}, journal={JOURNAL DE PHYSIQUE IV}, author={Wang, Z and Goeller, PT and Boyanov, BI and Sayers, DE and Nemanich, RJ}, year={1997}, month={Apr}, pages={561–564} }
 @article{baumann_bozeman_ward_nemanich_1997, title={Characterization of metal-diamond interfaces: Electron affinity and Schottky barrier height}, volume={6}, ISSN={["0925-9635"]}, DOI={10.1016/S0925-9635(96)00601-2}, abstractNote={In this study, the electron affinity and Schottky barrier height of thin Cu and Zr films on diamond (100) substrates were correlated by means of UV photoemission spectroscopy (UPS) measurements. Prior to metal deposition the diamond crystals were cleaned by a 1150°C or 500°C anneal in UHV, and the surfaces were characterized by AES and AFM. This resulted in surfaces terminated with oxygen or free of chemisorbed species. By means of UPS it was found that whether a metal did induce a negative electron affinity (NEA) on a diamond surface was dependent on the surface preparation before metal deposition and on the metal work function. In particular, the Schottky barrier height for clean surfaces was lower than for surfaces terminated by oxygen. Metal-diamond interfaces exhibiting a NEA had a lower Schottky barrier height than those exhibiting a positive electron affinity. These effects were attributed to different interfacial layers. Field emission measurements were performed before and after metal deposition. For all cases a reduction in the threshold electric field was observed upon metal overgrowth.}, number={2-4}, journal={DIAMOND AND RELATED MATERIALS}, author={Baumann, PK and Bozeman, SP and Ward, BL and Nemanich, RJ}, year={1997}, month={Mar}, pages={398–402} }
 @article{baumann_nemanich_1997, title={Comparison of electron affinity and Schottky barrier height of zirconium and copper-diamond interfaces}, volume={15}, DOI={10.1116/1.589444}, abstractNote={In this study, the evolution from diamond surfaces to metal–diamond interfaces has been examined. The electron affinity and the Schottky barrier height of a few Å thick films of Zr and Cu deposited in ultrahigh vacuum (UHV) onto IIb substrates were correlated. Prior to metal deposition, the diamond surfaces have been cleaned by different anneals and plasma treatments in UHV, and the surfaces were characterized by Auger electron spectroscopy and atomic force microscopy. The initial surfaces were terminated with oxygen, or free of chemisorbed species. Ultraviolet photoemission spectroscopy was employed to determine whether the samples exhibited a positive electron affinity or a negative electron affinity (NEA) before and after metal deposition. For Zr, the Schottky barrier height was found to change very little with the presence or absence of chemisorbed species at the interface. A NEA was observed for Zr on diamond independent of the surface termination. However, for Cu, the surface cleaning prior to metal deposition had a more significant effect. The Schottky barrier height changed strongly depending on the chemical species at the interface. A NEA was only detected for Cu on clean diamond surfaces. The differences between Zr on the one hand and Cu on the other are correlated with differences in interface chemistry and structure.}, number={4}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B}, author={Baumann, PK and Nemanich, RJ}, year={1997}, pages={1236–1240} }
 @article{yang_jedema_ade_nemanich_1997, title={Correlation of morphology and electrical properties of nanoscale TiSi2 epitaxial islands on Si (001)}, volume={308}, ISSN={["1879-2731"]}, DOI={10.1016/S0040-6090(97)00431-8}, abstractNote={The morphology and electrical properties of nanoscale epitaxial islands of TiSi2 are explored. The TiSi2 islands are prepared by ultra-high vacuum (UHV) deposition of ultra-thin Ti (0.3–2 nm) on both smooth and roughened Si (001) substrates. The roughened substrates are prepared by etching with atomic H produced in a plasma. The island formation is initiated by annealing to 800–1000°C. The morphologies of the substrate before and after island formation are examined by atomic force microscopy (AFM). In particular, the influence of surface-roughness on both the formation of islands and the size distribution of islands is investigated. Islands with a lateral dimension of ~35 nm and a vertical dimension of ~2.5 nm on a roughened substrate (RMS=12 nm) were observed, with a uniform distribution of 120 nm spacing between the islands. It was found that for similar processing conditions the size distribution of islands formed on a rough surface was smaller than islands formed on smooth surfaces. The results are discussed in terms of surface energy, diffusion and the strain field around the islands. The island structures can affect the electrical characteristics of the interface and the Schottky barrier was obtained from diodes formed with a Pt layer deposited over the islanded interface. The Schottky barrier was lowest for interfaces with the smaller TiSi2 islands.}, number={1997 Oct. 31}, journal={THIN SOLID FILMS}, author={Yang, W and Jedema, FJ and Ade, H and Nemanich, RJ}, year={1997}, month={Oct}, pages={627–633} }
 @article{jeon_yoon_nemanich_1997, title={Dependence of the C49-C54 TiSi2 phase transition temperature on film thickness and Si substrate orientation}, volume={299}, ISSN={["0040-6090"]}, DOI={10.1016/S0040-6090(96)09042-6}, abstractNote={The C49 to C54 phase transition and the surface and interface morphologies were examined for titanium silicides formed on atomically clean Si substrates. The properties were explored as a function of the Ti film thickness, deposition temperature and Si substrate orientation. Ti films of thicknesses between 5 nm and 40 nm were deposited at elevated temperatures from 500 °C to 900 °C in increments of 100 °C onto Si(100) and Si(111) wafers. The titanium silicides are analyzed with X-ray diffraction, Raman, scanning and transmission electron microscopy for phase identification and measurement of the surface and interface morphologies. The C49 to C54 TiSi2 phase transition is observed to occur between 600 °C and 700 °C for the thickest films on (100) wafers, but the transition temperature is observed to increase as the film thickness is decreased or for films formed on Si(111) substrates. For a 20 nm Ti film deposited onto Si(100), the transition temperature occurs between 600 °C and 700 °C. However, for the same thickness of Ti on Si(111), the transition temperature is found between 700 °C and 800 °C. This retardation of the phase transition is discussed in terms of surface and volume free-energy considerations.}, number={1-2}, journal={THIN SOLID FILMS}, author={Jeon, H and Yoon, G and Nemanich, RJ}, year={1997}, month={May}, pages={178–182} }
 @article{wang_aldrich_nemanich_sayers_1997, title={Electrical and structural properties of zirconium germanosilicide formed by a bilayer solid state reaction of Zr with strained Si1-xGex alloys}, volume={82}, ISSN={["0021-8979"]}, DOI={10.1063/1.366043}, abstractNote={The effects of alloy composition on the electrical and structural properties of zirconium germanosilicide (Zr–Si–Ge) films formed during the Zr/Si1−xGex solid state reaction were investigated. Thin films of Zr(Si1−yGey) and C49 Zr(Si1−yGey)2 were formed from the solid phase reaction of Zr and Si1−xGex bilayer structures. The thicknesses of the Zr and Si1−xGex layers were 100 and 500 Å, respectively. It was observed that Zr reacts uniformly with the Si1−xGex alloy and that C49 Zr(Si1−yGey)2 with y=x is the final phase of the Zr/Si1−xGex solid phase reaction for all compositions examined. The sheet resistance of the Zr(Si1−yGey)2 thin films was higher than the sheet resistance of similarly prepared ZrSi2 films. The stability of Zr(Si1−yGey)2 in contact with Si1−xGex was investigated and compared to the stability of Ti(Si1−yGey)2 in contact with Si1−xGex. The Ti(Si1−yGey)2/Si1−xGex structure is unstable when annealed for 10 min at 700 °C, with Ge segregating from Ti(Si1−yGey)2 and forming Ge-rich Si1−zGez precipitates at grain boundaries. In contrast, no Ge segregation was detected in the Zr(Si1−yGey)2/Si1−xGex structures. We attribute the stability of the Zr-based structure to a smaller thermodynamic driving force for germanium segregation and stronger atomic bonding in C49 Zr(Si1−yGey)2. Classical thermodynamics were used to calculate Zr(Si1−yGey)2–Si1−xGex tie lines in the Zr–Si–Ge ternary phase diagram. The calculations were compared with previously calculated Ti(Si1−yGey)2–Si1−xGex tie lines.}, number={5}, journal={JOURNAL OF APPLIED PHYSICS}, author={Wang, Z and Aldrich, DB and Nemanich, RJ and Sayers, DE}, year={1997}, month={Sep}, pages={2342–2348} }
 @article{nam_bremser_ward_nemanich_davis_1997, title={Growth of GaN and Al0.2Ga0.8N on patterened substrates via organometallic vapor phase epitaxy}, volume={36}, ISSN={["0021-4922"]}, DOI={10.1143/JJAP.36.L532}, abstractNote={ 
   The selective growth of GaN and  Al0.2Ga0.8N has been achieved on stripe and circular patterned    GaN/AlN/6H-SiC(0001) multilayer substrates. Growth morphologies on the stripe patterns were a    function of the widths of the stripes and the flow rate of triethylgallium. No ridge growth was    observed along the top edges of the truncated stripe patterns. Smooth (0001) top facets formed on    stripes ≥5 µ m wide. Uniform hexagonal pyramid arrays of undoped GaN and Si-doped GaN    were successfully grown on 5 µ m circular patterns. Field emission measurements of a Si-doped    GaN hexagonal pyramid array exhibited a turn-on field of 25  V/µ m for an emission current of 10.8 nA at an anode-to-sample distance of 27 µ m. 
   }, number={5A}, journal={JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS}, author={Nam, OH and Bremser, MD and Ward, BL and Nemanich, RJ and Davis, RF}, year={1997}, month={May}, pages={L532–L535} }
 @article{shen_shmagin_koch_kolbas_fahmy_bergman_nemanich_mcclure_sitar_quan_1997, title={Photoluminescence from mechanically milled Si and SiO2 powders}, volume={55}, ISSN={["0163-1829"]}, DOI={10.1103/physrevb.55.7615}, abstractNote={The photoluminescence (PL) in as-received and milled Si and SiO2 powder is reported. The Si and SiO2 powder is characterized by chemical analysis, Raman scattering, x-ray photoelectron spectra, infrared absorption, x-ray diffraction, and differential thermal analysis. The results indicate that the Si powder has amorphous Si oxide and suboxide surface layers. The milling of Si powder results in the formation of nanocrystalline/amorphous Si components. An amorphous SiO2 component is formed by milling crystalline SiO2. The PL spectra for as-received Si, milled Si, and SiO2 powder exhibit similar peak shapes, peak maxima, and full width at half maximum values. For both the as-received and the milled Si powder, experimental results appear to exclude mechanisms for PL related to an amorphous Si component or Si-H or Si-OH bonds, or the quantum confinement effect. Similarly, for milled SiO2 powder mechanisms for PL do not appear related to Si-H or Si-OH bonds. Instead the greatly increased intensity of PL for milled SiO2 can be related to both the increased volume fraction of the amorphous SiO2 component and the increased density of defects introduced in the amorphous SiO2 upon milling. It is suggested that the PL for as-received Si, milling-induced nanocrystalline/amorphous Si, and milled SiO2 results from defects, such as the nonbridging oxygen hole center, in the amorphous Si suboxide and/or SiO2 components existing in these powder samples. The PL measurement for milled SiO2 is dependent on air pressure whereas that for as-received SiO2 is not, suggesting that new emitting centers are formed by milling.}, number={12}, journal={PHYSICAL REVIEW B}, author={Shen, TD and Shmagin, I and Koch, CC and Kolbas, RM and Fahmy, Y and Bergman, L and Nemanich, RJ and McClure, MT and Sitar, Z and Quan, MX}, year={1997}, month={Mar}, pages={7615–7623} }
 @article{boyanov_goeller_sayers_nemanich_1997, title={Preferential Co-SI bonding at the Co/SiGe(100) interface}, volume={71}, DOI={10.1063/1.119436}, abstractNote={The initial stages of the reaction of Co with Si0.79Ge0.21(100) were studied in situ with extended x-ray absorption fine structure spectroscopy and reflection high energy electron diffraction. The Si:Ge ratio in the first coordination shell of Co in sub-monolayer Co films was found to increase with film thickness and annealing temperature, indicating preferential formation of Co–Si bonds. The impact of the observed preference for Co–Si bonding on the morphology of epitaxial CoSi2/Si1−xGex heterostructures is discussed.}, number={21}, journal={Applied Physics Letters}, author={Boyanov, B. I. and Goeller, P. T. and Sayers, D. E. and Nemanich, R. J.}, year={1997}, pages={3060–3062} }
 @article{bergman_bremser_perry_davis_dutta_nemanich_1997, title={Raman analysis of the configurational disorder in AlxGa1-xN films}, volume={71}, ISSN={["0003-6951"]}, DOI={10.1063/1.119367}, abstractNote={Raman analysis of the E2 mode of AlxGa1−xN in the composition range 0⩽x⩽1 is presented. The line shape was observed to exhibit a significant asymmetry and broadening toward the high energy range. The spatial correlation model is discussed, and is shown to account for the line shape. The model calculations also indicate the lack of a long-range order in the chemical vapor deposition alloys. These results were confirmed by x-ray scattering: the relative intensity of the superlattice line was found to be negligible. The line broadening of the E2 mode was found to exhibit a maximum at a composition x≅0.5 indicative of a random disordered alloy system.}, number={15}, journal={APPLIED PHYSICS LETTERS}, author={Bergman, L and Bremser, MD and Perry, WG and Davis, RF and Dutta, M and Nemanich, RJ}, year={1997}, month={Oct}, pages={2157–2159} }
 @article{goeller_boyanov_sayers_nemanich_1997, title={Structure and stability of cobalt-silicon-germanium thin films}, volume={133}, ISSN={["0168-583X"]}, DOI={10.1016/S0168-583X(97)00458-8}, abstractNote={The phase formation and stability of CoSi2 on strained epitaxial Si0.80Ge0.20Si (0 0 1) thin films has been investigated. Silicide films prepared via direct deposition of cobalt (CoSiGe), and via co-deposition of silicon and cobalt (Co+2SiSiGe), were compared. EXAFS, XRD, and sheet-resistance measurements indicated that co-deposited Co+2Si films annealed at 400–700°C exhibit the expected low-resistivity CoSi2 structure but were susceptible to roughening, pinhole formation, and agglomeration. In contrast, the CoSiGe structure formed CoSi2 only after annealing at 700°C and silicide formation was accompanied by Ge segregation in the contact region. In situ RHEED experiments indicated that growth of CoSi2 co-deposited on SiGe at 400–500°C results in immediate island formation. Template methods, which are often used to enhance the quality of co-deposited Co+2SiSi structures, did not lead to two-dimensional growth in the Co+2SiSiGe system. In situ EXAFS measurements of 2 Å Co films deposited on SiGe substrates and annealed at 450°C suggested that the failure to achieve two-dimensional growth may be due to preferential bonding of Co to Si atoms at the interface, which prevents the formation of a continuous CoSi2 template.}, number={1-4}, journal={NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS}, author={Goeller, PT and Boyanov, BI and Sayers, DE and Nemanich, RJ}, year={1997}, month={Dec}, pages={84–89} }
 @article{balkas_sitar_zheleva_bergman_nemanich_davis_1997, title={Sublimation growth and characterization of bulk aluminum nitride single crystals}, volume={179}, ISSN={["0022-0248"]}, DOI={10.1016/S0022-0248(97)00160-7}, abstractNote={Single crystalline platelets of aluminum nitride (AlN) ⩽ 1 mm thick have been grown within the temperature range of 1950–2250°C on 10 × 10 mm2 α(6H)-silicon carbide (SiC) substrates via sublimation-recondensation in a resistively heated graphite furnace. The source material was sintered AlN. A maximum growth rate of 500 μm/h was achieved at 2150°C and a source-to-seed separation of 4 mm. Growth rates below 2000°C were approximately one order of magnitude lower. Crystals grown at high temperatures ranged in color from blue to green due to the incorporation of Si and C from the SiC substrates; those grown at lower temperatures were colorless and transparent. Secondary-ion mass spectroscopy (SIMS) results showed almost a two order of magnitude decrease in the concentrations of these two impurities in the transparent crystals. Plan view transmission electron microscopy (TEM) of these crystals showed no line or planar defects. Raman spectroscopy and X-ray diffraction (XRD) studies indicated a strain free material.}, number={3-4}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Balkas, CM and Sitar, Z and Zheleva, T and Bergman, L and Nemanich, R and Davis, RF}, year={1997}, month={Aug}, pages={363–370} }
 @article{mccormick_jackson_nemanich_1997, title={The characterization of strain, impurity content, and crush strength of synthetic diamond crystals}, volume={12}, ISSN={["0884-2914"]}, DOI={10.1557/JMR.1997.0033}, abstractNote={This study addresses the correlation of the macroscopic and microscopic characteristics of synthetic diamond crystals produced by high pressure, high temperature conditions. Microscopic properties were characterized using Raman spectroscopy, birefringence, and photoluminescence (PL). Macroscopic properties characterized included inclusion content and crush force. Raman measurements detected measurable stress shifts in only two samples. The PL measurements indicated an increased presence of the H3 center in areas of high strain. The absence of the H3 center and the presence of the N-V PL center was correlated to lower average crush force. A hierarchy has been developed that relates microscopic properties to average crush force.}, number={1}, journal={JOURNAL OF MATERIALS RESEARCH}, author={McCormick, TL and Jackson, WE and Nemanich, RJ}, year={1997}, month={Jan}, pages={253–263} }
 @article{sowers_christman_bremser_ward_davis_nemanich_1997, title={Thin films of aluminum nitride and aluminum gallium nitride for cold cathode applications}, volume={71}, DOI={10.1063/1.120052}, abstractNote={Cold cathode structures have been fabricated using AlN and graded AlGaN structures (deposited on n-type 6H-SiC) as the thin film emitting layer. The cathodes consist of an aluminum grid layer separated from the nitride layer by a SiO2 layer and etched to form arrays of either 1, 3, or 5 μm holes through which the emitting nitride surface is exposed. After fabrication, a hydrogen plasma exposure was employed to activate the cathodes. Cathode devices with 5 μm holes displayed emission for up to 30 min before failing. Maximum emission currents ranged from 10–100 nA and required grid voltages ranging from 20–110 V. The grid currents were typically 1 to 104 times the collector currents.}, number={16}, journal={Applied Physics Letters}, author={Sowers, A. T. and Christman, J. A. and Bremser, M. D. and Ward, B. L. and Davis, R. F. and Nemanich, R. J.}, year={1997}, pages={2289–2291} }
 @inproceedings{balkas_sitar_zheleva_bergman_shmagin_muth_kolbas_nemanich_davis_1996, title={Growth of bulk AIN and GaN single crystals by sublimation}, booktitle={III-V nitrides: symposium held December 2-6, 1996, Boston, Massachusetts, U.S.A.  (Materials Research Society symposia proceedings ; v. 449)}, publisher={Pittsburgh, Pa.: Materials Research Society}, author={Balkas, C. M. and Sitar, Z. and Zheleva, T. and Bergman, L. and Shmagin, I. K. and Muth, J. F. and Kolbas, R. M. and Nemanich, R. and Davis, R. F.}, year={1996}, pages={41–46} }
 @misc{humphreys_nemanich_das_1993, title={High temperature rectifying contact}, volume={5212401}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Humphreys, T. P. and Nemanich, R. J. and Das, K.}, year={1993} }
 @misc{high temperature refractory silicide rectifying contact_1992, volume={5155559}, publisher={Washington, DC: U.S. Patent and Trademark Office}, year={1992} }
 @article{shroder_nemanich_glass_1990, title={ANALYSIS OF THE COMPOSITE STRUCTURES IN DIAMOND THIN-FILMS BY RAMAN-SPECTROSCOPY}, volume={41}, ISSN={["2469-9969"]}, DOI={10.1103/physrevb.41.3738}, abstractNote={Ces films ont des structures cristallines composites de types diamant amorphe/graphite. Les composantes de cette structures qui contribuent a la diffusion Raman sont etudiees en termes de rapport des hybridations sp 2 et sp 3}, number={6}, journal={PHYSICAL REVIEW B}, author={SHRODER, RE and NEMANICH, RJ and GLASS, JT}, year={1990}, month={Feb}, pages={3738–3745} }
 @article{nemanich_glass_lucovsky_shroder_1988, title={RAMAN-SCATTERING CHARACTERIZATION OF CARBON BONDING IN DIAMOND AND DIAMONDLIKE THIN-FILMS}, volume={6}, ISSN={["1520-8559"]}, DOI={10.1116/1.575297}, abstractNote={The atomic bonding configurations of carbon bonding in diamond and diamondlike thin films are explored using Raman scattering. The general aspects of Raman scattering from composites are presented. Effects are discussed due to crystalline or amorphous structures, large versus microcrystalline domains, and strong optical absorption and transparent regions. The Raman scattering from diamondlike films shows several features which are attributed to microcrystalline graphitelike structures which all originate from the same region in the sample. In contrast, the spectra of diamond films show features attributed to different components of a composite film. Components identified are crystalline diamond, and disordered and microcrystalline graphitic structures. The presence of precursor microcrystalline or amorphous diamond structures is also suggested.}, number={3}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A}, author={NEMANICH, RJ and GLASS, JT and LUCOVSKY, G and SHRODER, RE}, year={1988}, pages={1783–1787} }