@article{herro_zhuang_schlesser_sitar_2010, title={Growth of AlN single crystalline boules}, volume={312}, ISSN={["1873-5002"]}, DOI={10.1016/j.jcrysgro.2010.04.005}, abstractNote={We have obtained high-quality, crack-free AlN wafers using a convex thermal field inside the growth chamber. Free-standing AlN boules of 15 mm in height and 15 mm in diameter were grown. The carbon concentration was found to be similar in all parts of the boule (∼8×1018 cm−3) while the initial O concentration was higher (∼1×1019 cm−3) and slightly decreased during growth. It was found that O incorporated differently on different crystallographic faces. High resolution XRD showed a continuous improvement in crystal quality as a function of boule length. The full width at half maximum (FWHM) of the double crystal rocking curves decreased from 78 in at the beginning of growth to 13 in at the growth end. To the best of our knowledge, this is the first report on impurity incorporation on different crystallographic facets obtained from the same boule.}, number={18}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Herro, Z. G. and Zhuang, D. and Schlesser, R. and Sitar, Z.}, year={2010}, month={Sep}, pages={2519–2521} }
 @misc{schlesser_noveski_sitar_2010, title={Seeded growth process for preparing aluminum nitride single crystals}, volume={7,678,195}, number={2010 Mar. 16}, author={Schlesser, R. and Noveski, V. and Sitar, Z.}, year={2010} }
 @misc{schlesser_dalmau_noveski_sitar_2009, title={Dense, shaped articles constructed of a refractory material and methods of preparing such articles}, volume={7,632,454}, number={1999 Dec. 15}, author={Schlesser, R. and Dalmau, R. F. and Noveski, V. and Sitar, Z.}, year={2009} }
 @article{lu_edgar_cao_hohn_dalmau_schlesser_sitar_2008, title={Seeded growth of AlN on SiC substrates and defect characterization}, volume={310}, ISSN={["1873-5002"]}, DOI={10.1016/j.jcrysgro.2008.01.010}, abstractNote={In this study, seeded sublimation growth of aluminum nitride (AlN) on SiC substrates was investigated. Large diameter (15–20 mm) and thick (1–2 mm) AlN layers were demonstrated on Si-face, 3.5° off-axis 6H-SiC (0 0 0 1). A c-axis growth rate of 15–20 μm/h was achieved at 1830 °C, and the surface morphology was highly textured: step features were formed with a single facet on the top of the layer. High-resolution X-ray diffraction (HRXRD), X-ray photoelectron spectroscopy (XPS), and molten KOH/NaOH etching were employed to characterize the AlN layers. The AlN crystals grew highly orientated along the c-axis, however, the impurities of Si (3–6 at%) and C (5.9–8 at%) from the SiC changed the lattice constants of AlN and shifted the AlN (0 0 .2) 2θ value from pure AlN toward SiC. All the growth surfaces had Al-polarity and the dislocation density decreased from 108 to 106 cm−2 as the film thickness increased from 30 μm to 2 mm.}, number={10}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Lu, P. and Edgar, J. H. and Cao, C. and Hohn, K. and Dalmau, R. and Schlesser, R. and Sitar, Z.}, year={2008}, month={May}, pages={2464–2470} }
 @article{cai_zheng_zhang_zhuang_herro_schlesser_sitar_2007, title={Effect of thermal environment evolution on A1N bulk sublimation crystal growth}, volume={306}, ISSN={["0022-0248"]}, DOI={10.1016/j.jcrysgro.2007.04.037}, abstractNote={To obtain a large and thick AlN single crystal during sublimation growth, it is very important to maintain the thermal environment suitable for growth inside the crucible during a long period of time (>50 h). In this paper, an in-house developed integrated model capable of describing inductive, radiative and conductive heat transfer will be used to simulate the transient behavior of thermal environment inside the crucible during a 40-h experiment growth. Effects of graphite insulation degradation on temperature distribution inside the crucible will be investigated. Simulation results will be compared with the experimental data to study the effects of the insulation degradation-induced particle deposition, geometric variation of source material and crystal size enlargement on the temperature distribution in the crucible and the growth rate. The relationship between graphite insulation degradation and power input change of the induction-heated system will be established. The evolution of temperature difference between the source material and crystal, which is the driving force for growth, will be presented. This study will also provide the explanation of mechanism underling substantial reduction of growth rate after a long experiment run.}, number={1}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Cai, D. and Zheng, L. L. and Zhang, H. and Zhuang, D. and Herro, Z. G. and Schlesser, R. and Sitar, Z.}, year={2007}, month={Aug}, pages={39–46} }
 @article{neuburger_aleksov_schlesser_kohn_sitar_2007, title={Electronic high temperature characteristics of AlN}, volume={43}, DOI={10.1049/el:20070275}, abstractNote={The high temperature electronic properties of bulk single crystal AIN were investigated by temperature dependent I-V measurements in the range of R.T. to 1100degC in vacuum. The samples have been highly insulating at R.T. Such isolation properties are mostly obtained by a high defect density and a high oxygen content. Temperature cycling was used to identify carrier activation and heterogeneous conduction paths possibly originating from a dislocation network. Indeed an increase in conductivity with temperature is observed, which can be fitted with an activation energy of 1.3 eV at medium temperatures. The crystals remained stable up to 1100degC. No change of the room temperature conductivity was observed after several cycles. Impedance spectroscopy at medium temperature, where the material behaves like a lossy dielectric, shows only one dominating conduction path. No grain boundary-like heterogeneous transport through a dislocation network could be detected. Thus, the materials' quality as indicated by its Raman spectrum is also mirrored in the electrical high temperature performance}, number={10}, journal={Electronics Letters}, author={Neuburger, M. and Aleksov, A. and Schlesser, R. and Kohn, E. and Sitar, Z.}, year={2007}, pages={592–594} }
 @article{raghothamachar_bai_dudley_dalmau_zhuang_herro_schlesser_sitar_wang_callahan_et al._2006, title={Characterization of bulk grown GaN and AlN single crystal materials}, volume={287}, ISSN={["1873-5002"]}, DOI={10.1016/j.jcrysgro.2005.11.042}, abstractNote={Sublimation method, spontaneously nucleated as well as seeded on SiC substrates, has been employed for growing AlN bulk crystals. For GaN growth, in addition to the sublimation method using sapphire substrates, ammonothermal growth (analogous to the hydrothermal method) on HVPE GaN seeds is also being used. Thick plates/films of AlN and GaN grown by these methods have been characterized by synchrotron white beam X-ray topography (SWBXT) and high resolution X-ray diffraction (HRXRD). Results from a recent set of growth experiments are discussed.}, number={2}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Raghothamachar, B and Bai, J and Dudley, M and Dalmau, R and Zhuang, DJ and Herro, Z and Schlesser, R and Sitar, Z and Wang, BG and Callahan, M and et al.}, year={2006}, month={Jan}, pages={349–353} }
 @article{aleksov_collazo_mita_schlesser_sitar_2006, title={Current-voltage characteristics of n/n lateral polarity junctions in GaN}, volume={89}, ISSN={["1077-3118"]}, DOI={10.1063/1.2244046}, abstractNote={Lateral Si:N-polar/Si:Ga-polar GaN homojunctions were fabricated using metal organic chemical vapor deposition with nitrogen as the carrier and dilution gas. Nominally undoped N-polar areas are n-type conductive, while nominally undoped Ga-polar areas are insulating with carrier densities below 1×1015cm−3. This allows for the fabrication of selectively doped areas within one growth step that can be used to fabricate novel lateral device structures or enhance existing III-N-device structures. In this letter we investigated the electrical properties of the simplest case of these junctions, namely, when both sides are n-type conductive. The results of the IV measurements show a linear characteristic both for the measurement of a N-polar/Si:Ga-polar junction and a N-polar/Si:Ga-polar/N-polar double junction. This result indicates that, as expected, there are no energy barriers between the N-polar and the Ga-polar material and that these structures can be used to achieve laterally selective doped areas in Ga–N for electronic device applications.}, number={5}, journal={APPLIED PHYSICS LETTERS}, author={Aleksov, Aleksandar and Collazo, Ramon and Mita, Seiji and Schlesser, Raoul and Sitar, Zlatko}, year={2006}, month={Jul} }
 @article{collazo_mita_aleksov_schlesser_sitar_2006, title={Growth of Ga- and N- polar gallium nitride layers by metalorganic vapor phase epitaxy on sapphire wafers}, volume={287}, ISSN={["0022-0248"]}, DOI={10.1016/j.jcrysgro.2005.10.080}, abstractNote={Following an already established polarity control scheme for GaN thin films, we developed a process to simultaneously grow Ga- and N-polarity layers side by side on c-plane sapphire. The simultaneous growth is achieved by properly treating the AlN nucleation/buffer layer and subsequent substrate annealing. During this process, the growth is mass-transfer-limited, permitting the same growth rate for both types of polarity domains. Smooth domains of both polarity types (RMS roughness ∼1–2 nm) were obtained.}, number={2}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Collazo, R and Mita, S and Aleksov, A and Schlesser, R and Sitar, Z}, year={2006}, month={Jan}, pages={586–590} }
 @article{zhuang_herro_schlesser_raghothamachar_dudley_sitar_2006, title={Seeded growth of AlN crystals on nonpolar seeds via physical vapor transport}, volume={35}, ISSN={["0361-5235"]}, DOI={10.1007/s11664-006-0141-x}, number={7}, journal={JOURNAL OF ELECTRONIC MATERIALS}, author={Zhuang, D. and Herro, Z. G. and Schlesser, R. and Raghothamachar, B. and Dudley, M. and Sitar, Z.}, year={2006}, month={Jul}, pages={1513–1517} }
 @article{herro_zhuang_schlesser_collazo_sitar_2006, title={Seeded growth of AlN on N- and Al-polar < 0 0 0 1 > AlN seeds by physical vapor transport}, volume={286}, ISSN={["1873-5002"]}, DOI={10.1016/j.jcrysgro.2005.10.074}, abstractNote={We demonstrated seeded growth of AlN on large-area Al- and N-polar <0 0 0 1>-oriented AlN seeds using the physical vapor transport method (PVT). In both cases, crystals having a diameter of 15 mm were obtained from 5 mm seeds. Based on growth step and terrace width analyses, it was found that the N-polar face was suitable for growth within a large window of growth parameters while the Al-polar seeds yielded high-quality crystals only at low supersaturation.}, number={2}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Herro, ZG and Zhuang, D and Schlesser, R and Collazo, R and Sitar, Z}, year={2006}, month={Jan}, pages={205–208} }
 @article{zhuang_herro_schlesser_sitar_2006, title={Seeded growth of AlN single crystals by physical vapor transport}, volume={287}, ISSN={["0022-0248"]}, DOI={10.1016/j.jcrysgro.2005.11.047}, abstractNote={Seeded growth of AlN single crystals was achieved in an induction-heated, high-temperature reactor. The growth process was based on physical vapor transport (PVT), where presintered AlN powder was used as source material. AlN seeds were cut from a boule containing large single crystalline grains, which were grown by natural grain expansion of an initially polycrystalline, self-seeded deposit. Seeded growth was interrupted several times in order to refill the AlN powder source and a dedicated process scheme was used to ensure epitaxial re-growth on the seed surface after each exposure to air. The single crystalline seed expanded laterally at an angle of 45° resulting in an 18 mm large AlN single crystal. The crystal expansion rate, crystalline orientation, as well as growth morphology were characterized by optical microscopy and X-ray diffraction, respectively.}, number={2}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Zhuang, D and Herro, ZG and Schlesser, R and Sitar, Z}, year={2006}, month={Jan}, pages={372–375} }
 @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} }
 @article{schlesser_dalmau_zhuang_collazo_sitar_2005, title={Crucible materials for growth of aluminum nitride crystals}, volume={281}, ISSN={["0022-0248"]}, DOI={10.1016/j.jcrysgro.2005.03.014}, abstractNote={The growth of aluminum nitride (AlN) bulk crystals by sublimation of an AlN source requires elevated temperatures, typically in a range of 1800–2300 °C. These temperature requirements, combined with the chemically aggressive nature of the Al vapor, severely limit the choice of reactor hot-zone materials, and most notably, the selection of reaction crucibles. Aside from refractory elements, potentially promising compound materials include refractory nitrides, carbides, and borides. In this work, TaC crucibles were fabricated using a binderless sintering process and were tested in AlN bulk growth experiments. Elemental analysis of crystals grown in these crucibles revealed extremely low Ta contamination, below the analytical detection limit of 1 ppm by weight and C contamination levels as low as 50 ppm by weight; C contamination likely originated from sources unrelated to the crucible material. Crucibles were re-used in several consecutive growth runs; average crucible lifetimes exceeded 200 h at growth temperatures exceeding 2200 °C.}, number={1}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Schlesser, R and Dalmau, R and Zhuang, D and Collazo, R and Sitar, Z}, year={2005}, month={Jul}, pages={75–80} }
 @article{wu_noveski_zhang_schlesser_mahajan_beaudoin_sitar_2005, title={Design of an RF-heated bulk AlN growth reactor: Induction heating and heat transfer modeling}, volume={5}, ISSN={["1528-7505"]}, DOI={10.1021/cg050014m}, abstractNote={An induction heating and thermal model was developed to design an inductively heated reaction system for bulk AlN crystal growth by powder sublimation. The electromagnetic field and induction heat generation were calculated using the Maxwell equations, and transient temperature distribution was simulated considering conduction and radiation between various components. The complex dependence of the temperature distribution on the radio frequency (RF) coil current and position was demonstrated by numerical studies. A custom-designed high-temperature reactor was constructed and tested. To provide proper temperature control during envisioned sublimation growth, the response of temperature and temperature difference of the bottom and top external surfaces of the growth crucible to power consumption and coil position was measured. The experimental results corresponded well with the simulated temperature responses.}, number={4}, journal={CRYSTAL GROWTH & DESIGN}, author={Wu, B and Noveski, V and Zhang, H and Schlesser, R and Mahajan, S and Beaudoin, S and Sitar, Z}, year={2005}, pages={1491–1498} }
 @article{noveski_schlesser_raghothamachar_dudley_mahajan_beaudoin_sitar_2005, title={Seeded growth of bulk AlN crystals and grain evolution in polycrystalline AlN boules}, volume={279}, ISSN={0022-0248}, url={http://dx.doi.org/10.1016/j.jcrysgro.2004.12.027}, DOI={10.1016/j.jcrysgro.2004.12.027}, abstractNote={Large AlN crystals were grown by powder sublimation in a nitrogen atmosphere at low supersaturation and growth rates of 0.1–0.3 mm/h. The starting deposition surface was a sintered TaC disc. An appropriate adjustment of the system pressure and source-seed temperature gradient during the early stages of growth allowed epitaxial re-growth on AlN seeds that had been exposed to air. Single-crystalline AlN grains of 1 cm in size were achieved through multiple sublimation growth runs conducted at P=500Torr and growth temperatures of 2050–2150 °C. Elemental analysis of impurities in the grown AlN boules confirmed low oxygen contamination levels of ∼1019/cm3. No discontinuities were introduced in the structural defect distribution in the individual single-crystalline grains by the multiple re-growth steps. Absence of preferred growth directions of grains suggest the epitaxial re-growth process is suitable for seeded single-crystal growth in any orientation.}, number={1-2}, journal={Journal of Crystal Growth}, publisher={Elsevier BV}, author={Noveski, V. and Schlesser, R. and Raghothamachar, B. and Dudley, M. and Mahajan, S. and Beaudoin, S. and Sitar, Z.}, year={2005}, month={May}, pages={13–19} }
 @article{chen_skromme_dalmau_schlesser_sitar_chen_sun_yang_khan_nakarmi_et al._2004, title={Band-edge exciton states in AlN single crystals and epitaxial layers}, volume={85}, ISSN={["1077-3118"]}, DOI={10.1063/1.1818733}, abstractNote={The band-edge excitonic properties of AlN are investigated using low-temperature (1.7K) optical reflectance and transmission measurements of samples with various crystal orientations. The A, B, and C excitons are found to have energies of 6.025, 6.243, and 6.257eV in unstrained material, which shift with strain. The results are compared to a calculation of exciton energies and oscillator strengths to yield a crystal-field splitting of −230meV in unstrained AlN, in good agreement with previous ab initio calculations.}, number={19}, journal={APPLIED PHYSICS LETTERS}, author={Chen, L and Skromme, BJ and Dalmau, RF and Schlesser, R and Sitar, Z and Chen, C and Sun, W and Yang, J and Khan, MA and Nakarmi, ML and et al.}, year={2004}, month={Nov}, pages={4334–4336} }
 @article{noveski_schlesser_mahajan_beaudoin_sitar_2004, title={Growth of AlN crystals on AlN/SiC seeds by AlN powder sublimation in nitrogen atmosphere}, volume={9}, DOI={10.1557/s1092578300000375}, abstractNote={AlN single crystals were grown on AlN/SiC seeds by sublimation of AlN powder in TaC crucibles in a nitrogen atmosphere. The seeds were produced by metallorganic chemical vapor deposition (MOCVD) of AlN on SiC crystals. The influence of growth temperature, growth time and source-to-seed distance on the crystallinity and the crystal growth rate were investigated. Crystals were grown in an RF heated sublimation reactor at growth temperatures ranging from 1800-2000°C, at a pressure of 600 Torr, nitrogen flow-rate of 100 sccm and source-to-seed distances of 10 and 35 mm. At 1870°C and a source-to-seed distance of 35 mm, isolated crystals were observed with few instances of coalescence. At 1930°C, a source-to-seed distance of 10 mm and longer growth times (~30 hrs), crystal coalescence was achieved. Above 1930°C, the decomposition of SiC was evidently affecting the growth morphology and resulted in growth of polycrystalline AlN. After an initial nucleation period, the observed growth rates (10-30 µm/hr) were in close agreement with predictions of a growth model that assumed gas-phase diffusion controlled growth. Optical and electron microscope observations revealed step-flow growth, while X-ray diffraction results showed the single crystal nature of the grown material. Single crystalline AlN was grown over surface areas of 200-300 mm2 and was transparent and essentially colorless.}, number={2}, journal={MRS Internet Journal of Nitride Semiconductor Research}, author={Noveski, V. and Schlesser, R. and Mahajan, S. and Beaudoin, S. and Sitar, Z.}, year={2004} }
 @article{noveski_schlesser_mahajan_beaudoin_sitar_2004, title={Mass transfer in A1N crystal growth at high temperatures}, volume={264}, ISSN={["1873-5002"]}, DOI={10.1016/j.jcrysgro.2004.01.028}, abstractNote={A one-dimensional mass transfer model based on equilibrium sublimation and gas phase diffusion was developed for high-temperature sublimation growth of AlN in an RF heated reactor and validated with growth results. The model predicted the apparent activation energy for growth to be close to the energy of sublimation. Using the model-predicted growth conditions, a 25 mm diameter polycrystalline boule was grown at a rate of 1 mm/h. Growth was performed at short source-to-seed distances (∼10 mm), nitrogen pressure of 600 Torr, nitrogen flow-rate of 100 sccm, and source temperatures ranging from 2000°C to 2400°C. Fast grain size development was achieved in the growth direction. The grown material was transparent and virtually colorless.}, number={1-3}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Noveski, V and Schlesser, R and Mahajan, S and Beaudoin, S and Sitar, Z}, year={2004}, month={Mar}, pages={369–378} }
 @article{brenner_schlesser_sitar_dalmau_collazo_li_2004, title={Model for the influence of boron impurities on the morphology of AIN grown by physical vapor transport}, volume={560}, ISSN={["1879-2758"]}, DOI={10.1016/j.susc.2004.05.003}, abstractNote={We propose that the reduction of the Schwoebel barrier by trace B impurities is responsible for the relatively flat c-plane morphology observed in AlN crystals that are deposited via physical vapor transport in BN crucibles relative to crystals grown in boron-free conditions. The model is supported by molecular statics calculations that predict that B substitutional impurities are energetically preferred at steps on the (0 0 0 1) surface, and that these impurities enhance binding and incorporation of growth species onto steps.}, number={1-3}, journal={SURFACE SCIENCE}, author={Brenner, DW and Schlesser, R and Sitar, Z and Dalmau, R and Collazo, R and Li, Y}, year={2004}, month={Jul}, pages={L202–L206} }
 @article{grenko_reynolds_schlesser_hren_bachmann_sitar_kotula_2004, title={Nanoscale GaN whiskers fabricated by photoelectrochemical etching}, volume={96}, ISSN={["0021-8979"]}, DOI={10.1063/1.1788841}, abstractNote={GaN whiskers with nanoscale dimensions have been fabricated by photoelectrochemical (PEC) etching in dilute H3PO4 electrolyte. Etching in lower concentration H3PO4 electrolyte for 1 h or for a short time of 5 min at a higher concentration results in individual whiskers with a density of ∼2×109cm−2 and diameters to 15nm. It is observed that ∼10% of them have formed nearly perfect hexagonal plates on the top of the whiskers, which appear to evolve into flowerlike features upon extended etching to 12 min. Such hexagonal plates have not been reported previously in the PEC etching of GaN. The presence of a dislocation along the central axis of the needles is clearly demonstrated, and the etch pattern is suggested to be related to the growth mechanism for GaN on sapphire. When etched for times >30min, these whiskers are typically arranged in clusters with a density of 2–5×107cm−2 and have ten or more whiskers contributing to the central top of the cluster.}, number={9}, journal={JOURNAL OF APPLIED PHYSICS}, author={Grenko, JA and Reynolds, CL and Schlesser, R and Hren, JJ and Bachmann, K and Sitar, Z and Kotula, PG}, year={2004}, month={Nov}, pages={5185–5188} }
 @article{grenko_reynolds_schlesser_bachmann_rietmeier_davis_sitar_2004, title={Selective etching of GaN from AlGaN/GaN and AlN/GaN structures}, volume={9}, DOI={10.1557/s1092578300000405}, abstractNote={Thick GaN layers as well as AlGaN/GaN and AlN/GaN heterostructures grown by metalorganic vapor phase epitaxy have been photoelectrochemically (PEC) etched in various dilute electrolytes, and bandgap-selective etching has been demonstrated in heterostructures. This result is a significant step forward in the fabrication of group III-nitride devices and one-dimensional photonic bandgap (PBG) structures in the deep UV. Based on initial results from thick GaN layers, a method was developed to achieve self-stopping selective etching of thin GaN layers in AlGaN/GaN and AlN/GaN heterostructures. Selective PEC etching requires the use of a suitable light source with photon energies larger than the bandgap of GaN, but smaller than that of AlGaN or AlN, thus enabling selective hole generation in the GaN layers to be etched. Additionally, it is imperative to use an electrolyte that supports PEC etching of GaN without chemically etching AlGaN or AlN.}, number={5}, journal={MRS Internet Journal of Nitride Semiconductor Research}, author={Grenko, J. A. and Reynolds, C. L. and Schlesser, R. and Bachmann, K. and Rietmeier, Z. and Davis, R. F. and Sitar, Z.}, year={2004} }
 @article{strassburg_senawiratne_dietz_haboeck_hoffmann_noveski_dalmau_schlesser_sitar_2004, title={The growth and optical properties of large, high-quality AlN single crystals}, volume={96}, ISSN={["1089-7550"]}, DOI={10.1063/1.1801159}, abstractNote={The effect of impurities and defects on the optical properties of AlN was investigated. High-quality AlN single crystals of more than 20mm2 size were examined. Different crucible materials and growth procedures were applied to the growth of bulk AlN by physical vapor transport method to vary the defect and the impurity concentrations. The crystalline orientation was investigated by Raman spectroscopy. Glow discharge mass spectrometry was used to determine the trace concentration of the incorporated impurities such as oxygen and carbon. The photoluminescence emission and absorption properties of the crystals revealed bands around 3.5 and 4.3eV at room temperature. Absorption edges ranging between 4.1 and 5.95eV were observed. Since no straight correlation of the oxygen concentration was obtained, a major contribution of oxygen or oxygen-related impurities was ruled out to generate the observed emission and absorption bands in the Ultraviolet spectral range. The carbon-related impurities and intrinsic defects might contribute to the observed optical properties. The absorption coefficient for AlN single crystals has been derived for the spectral range below the band edge.}, number={10}, journal={JOURNAL OF APPLIED PHYSICS}, author={Strassburg, M and Senawiratne, J and Dietz, N and Haboeck, U and Hoffmann, A and Noveski, V and Dalmau, R and Schlesser, R and Sitar, Z}, year={2004}, month={Nov}, pages={5870–5876} }
 @article{collazo_schlesser_roskowski_miraglia_davis_sitar_2003, title={Electron energy distribution during high-field transport in AlN}, volume={93}, ISSN={["0021-8979"]}, DOI={10.1063/1.1543633}, abstractNote={The energy distribution of electrons transported through intrinsic AlN heteroepitaxial films grown on SiC was directly measured as a function of applied field and AlN film thickness. Following the transport, electrons were extracted into vacuum through a semitransparent Au electrode and their energy distribution was measured using an electron spectrometer. Transport through films thicker than 95 nm at an applied field between 200 and 350 kV/cm occurred as steady-state hot electron transport following a Maxwellian energy distribution with a characteristic carrier temperature. At higher fields (470 kV/cm), intervalley scattering was evidenced by a multicomponent energy distribution featuring a second peak at the energy position of the first satellite valley. Velocity overshoot was observed in films thinner than 95 nm and at fields greater than 550 kV/cm. In this case, a symmetric energy distribution centered at an energy above the conduction band minimum was measured, indicating that the drift component of the electron velocity was on the order of the “thermal” component. A transient transport length of less than 80 nm was deduced from these observations.}, number={5}, journal={JOURNAL OF APPLIED PHYSICS}, author={Collazo, R and Schlesser, R and Roskowski, A and Miraglia, P and Davis, RF and Sitar, Z}, year={2003}, month={Mar}, pages={2765–2771} }
 @article{wu_ma_zhang_dudley_schlesser_sitar_2003, title={Growth kinetics and thermal stress in AlN bulk crystal growth}, volume={253}, ISSN={["1873-5002"]}, DOI={10.1016/S0022-0248(03)01044-3}, abstractNote={Group III nitrides, such as GaN, AlN and InGaN, have attracted great attention due to their applications in blue-green and ultraviolet light emitting diodes and lasers. In this paper, an integrated model has been developed based on the conservation of momentum, mass, chemical species and energy together with boundary conditions that account for heterogeneous chemical reactions both at the source and seed surfaces. The predicted temperature profiles have been compared with measurements for different power levels and flow rates in a reactor for AlN crystal growth at the North Carolina State University. We have found that the heat power level affects the entire temperature distribution greatly while the flow rate has insignificant effect on the temperature distribution; the overall thermal stress level is higher than the critical resolved shear stress, indicating that thermal elastic stress can be a major source to induce high dislocation density in the as-grown crystal. The stress level is strongly dependent on the temperature gradient in the as-grown crystal. Results are correlated well with defects showing in an X-ray topograph for the AlN plate crystal.}, number={1-4}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Wu, B and Ma, RH and Zhang, H and Dudley, M and Schlesser, R and Sitar, Z}, year={2003}, month={Jun}, pages={326–339} }
 @article{schlesser_mcclure_sitar_2003, title={Mechanisms limiting electron field emission from diamond}, volume={13}, number={5}, journal={New Diamond and Frontier Carbon Technology}, author={Schlesser, R. and McClure, M. T. and Sitar, Z.}, year={2003}, pages={285–295} }
 @article{collazo_schlesser_sitar_2002, title={Experimental observation of electron velocity overshoot in AlN}, volume={81}, ISSN={["0003-6951"]}, DOI={10.1063/1.1534407}, abstractNote={The energy distribution of electrons transported through intrinsic AlN heteroepitaxial films grown on 6H-SiC was directly measured as a function of the applied electric field. Following the transport, electrons were extracted into vacuum through a semitransparent Au electrode and their energy distribution was measured using an electron spectrometer. Transport through 80-nm-thick layers indicated the onset of quasiballistic transport for fields greater than 510 kV/cm. This was evidenced by a symmetric energy distribution centered at energies above the conduction band minimum. Drifted Fermi–Dirac energy distribution was fitted to the measured energy distribution, with the energy scale referenced to the bottom of the AlN conduction band. The drift energy and the carrier temperature were obtained as fitting parameters. Overshoots as high as five times the saturation velocity were observed and a transient length of less than 80 nm was deduced. In addition, the velocity-field characteristic was derived from these observations.}, number={27}, journal={APPLIED PHYSICS LETTERS}, author={Collazo, R and Schlesser, R and Sitar, Z}, year={2002}, month={Dec}, pages={5189–5191} }
 @article{shin_arkun_thomson_miraglia_preble_schlesser_wolter_sitar_davis_2002, title={Growth and decomposition of bulk GaN: role of the ammonia/nitrogen ratio}, volume={236}, ISSN={["0022-0248"]}, DOI={10.1016/S0022-0248(02)00825-4}, abstractNote={Gallium nitride crystals grown via vapor-phase transport processes that incorporate ammonia as the only source of nitrogen below atmospheric pressures experience significant surface roughening and the eventual cessation of growth. Investigations of these phenomena in this research, and in the context of the discovery of a non-ceasing process route to larger GaN crystals, showed that the RMS values of the surface roughness of single crystal GaN (0 0 0 1) films exposed to pure ammonia flowing at 60 sccm for 2 h at 1130°C increased from the as-received value of 3.7–6.8 nm, 21.4 and 32.6 nm at 100, 430 and 760 Torr, respectively. Quadrupole mass spectrometry revealed that the concentrations of H2 and N2 measurably increased at pressures above 400 Torr. The primary reason for the increased roughness above 430 Torr was the enhanced etching of GaN via reaction with atomic and molecular hydrogen derived from the dissociation of the ammonia. At lower pressures, the decomposition of the GaN via the formation and evaporation of N2 and Ga increased in importance relative to etching for enhancing surface roughness. Dilution with nitrogen reduced the amount of hydrogen generated from the dissociation of the ammonia. The GaN surface annealed at 1130°C and 430 Torr in ammonia diluted with 33 vol% N2 maintained the smoothest surface with a nominal RMS value of 10.4 nm. Mixtures with higher and lower percentages of N2 showed enhanced roughness under the same conditions. Use of this optimum gas mixture also allowed the seeded growth of a 1.5×1.5×2.0 mm3 GaN crystal and a 2.3×1.8×0.3 mm3 thick platelet with neither observable decomposition nor cessation of the growth over periods of 36 and 48 h, respectively.}, number={4}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Shin, H and Arkun, E and Thomson, DB and Miraglia, P and Preble, E and Schlesser, R and Wolter, S and Sitar, Z and Davis, RF}, year={2002}, month={Mar}, pages={529–537} }
 @article{schlesser_sitar_2002, title={Growth of bulk AlN crystals by vaporization of aluminum in a nitrogen atmosphere}, volume={234}, ISSN={["0022-0248"]}, DOI={10.1016/S0022-0248(01)01720-1}, abstractNote={AlN single crystals were grown by vaporization of aluminum in a nitrogen atmosphere. The growth temperature was found to critically influence the crystal morphology, while nitrogen pressure and flow rate had no considerable influence on the growth process. Crystals were grown under quasi-stagnant conditions (nitrogen flow of 100 sccm) at a reactor pressure of 500 Torr. At relatively low temperatures (1800–1900°C), AlN needles were grown at rates up to 10 mm/h along the c-axis. Twinned platelets were observed in a temperature range of 1900–2100°C. At temperatures above 2100°C, AlN c-plates (up to 50 mm2) were grown by spontaneous nucleation within 2 h. Extraordinarily large growth rates of 5 mm/h in the c-plane and 0.2 mm/h along the c-axis were observed. SEM pictures revealed step-flow growth on the c-plane surfaces. Raman spectroscopy indicated a drastic improvement in the crystal quality with growth temperature.}, number={2-3}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Schlesser, R and Sitar, Z}, year={2002}, month={Jan}, pages={349–353} }
 @article{shin_thomson_schlesser_davis_sitar_2002, title={High temperature nucleation and growth of GaN crystals from the vapor phase}, volume={241}, ISSN={["1873-5002"]}, DOI={10.1016/S0022-0248(02)01290-3}, abstractNote={A vapor phase growth process involving the reaction of Ga vapor and ammonia has been used to grow needle- and platelet-shaped single crystals of GaN at 1130°C. Introduction of the NH3 only at high temperatures reduced the nucleation density, minimized the amount of GaN crust on the Ga source and resulted in larger crystals. A processing map has been constructed with respect to ammonia flow rate and total pressure at 1130°C to achieve control of growth in different crystallographic directions. Platelet growth of GaN was favored using low V/III ratios achieved via low ammonia flow rates and/or low total ammonia pressures and/or an increase in the Ga source temperature. Crystals with aspect ratios c/a<1 were obtained at 1130°C, 430 Torr, and 25–75 sccm of ammonia. Raman spectroscopy revealed that the best platelets were grown at 1130°C using ammonia flow rates of 60 sccm and a Ga source temperature of 1260°C. Seeded growth from previously grown needles and platelets at lateral and vertical rates of ∼25 and ∼10 μm/h, respectively, was achieved using these growth parameters.}, number={4}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Shin, H and Thomson, DB and Schlesser, R and Davis, RF and Sitar, Z}, year={2002}, month={Jun}, pages={404–415} }
 @article{collazo_schlesser_sitar_2002, title={Role of adsorbates in field emission from nanotubes}, volume={11}, ISSN={["0925-9635"]}, DOI={10.1016/S0925-9635(01)00585-4}, abstractNote={Two field-emission states of single-walled carbon nanotubes were identified according to their respective emission current levels. The state yielding increased emission current was attributed to the presence of adsorbates on the nanotubes as confirmed by electron emission measurements at different background pressures. Application of high electric fields induced large emission currents and a transition between the two states. During this transition, a current drop to 1/10 of the original value was observed. For the high current state, field-emitted electrons originated from states located below the Fermi level, as was determined by field-emission energy distribution measurements. This suggested that adsorbates introduced a resonant state on the surface that enhanced the tunneling probability of electrons. The adsorbed states are removed at high applied electric fields, presumably due to thermal effects caused by large emission currents. This adsorption/desorption process is completely reversible.}, number={3-6}, journal={DIAMOND AND RELATED MATERIALS}, author={Collazo, R and Schlesser, R and Sitar, Z}, year={2002}, pages={769–773} }
 @article{schlesser_dalmau_sitar_2002, title={Seeded growth of AlN bulk single crystals by sublimation}, volume={241}, ISSN={["0022-0248"]}, DOI={10.1016/S0022-0248(02)01319-2}, abstractNote={AlN bulk single crystals were grown by sublimation of AlN powder at temperatures of 2100–2300°C in an open crucible geometry in a 400 Torr nitrogen atmosphere. Small, single crystalline AlN c-platelets, prepared by vaporization of Al in a nitrogen atmosphere, were used as seeds. Seeded growth occurred preferentially in the crystallographic c-direction, with growth rates exceeding 500 μm/h, while the seed crystals grew only marginally in the c-plane. Transparent, centimeter-sized AlN single crystals were grown within 24 h. Characterization by X-ray diffraction showed that rocking curves around the (0 0 0 2) reflection were very narrow (25 arcsec full-width at half-maximum), thus indicating very high crystalline quality of the material grown on the seeds.}, number={4}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Schlesser, R and Dalmau, R and Sitar, Z}, year={2002}, month={Jun}, pages={416–420} }
 @article{raghothamachar_vetter_dudley_dalmau_schlesser_sitar_michaels_kolis_2002, title={Synchrotron white beam topography characterization of physical vapor transport grown AlN and ammonothermal GaN}, volume={246}, ISSN={["0022-0248"]}, DOI={10.1016/S0022-0248(02)01751-7}, abstractNote={Structural defects in AlN single crystals grown by the sublimation method and GaN single crystals grown by the ammonothermal method are characterized by synchrotron white-beam X-ray topography in conjunction with optical microscopy. AlN platelets are either of (112̄0) or (0 0 0 1) type depending on the growth conditions. Dislocation densities of the order of 103 cm−2 or lower are observed in some crystals. X-ray topographs reveal the presence of growth sector boundaries, inclusions, and growth dislocations that indicate slight impurity contamination. The 2H crystal structure of GaN single crystals obtained by the ammonothermal method was verified by Laue X-ray pattern analysis. GaN crystals grown are of the order of 1 mm in size and are either (0 0 0 1) platelets or [0 0 0 1] prismatic needles. Generally, prismatic needles are characterized by lower degree of mosaicity than (0 0 0 1) platelets.}, number={3-4}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Raghothamachar, B and Vetter, WM and Dudley, M and Dalmau, R and Schlesser, R and Sitar, Z and Michaels, E and Kolis, JW}, year={2002}, month={Dec}, pages={271–280} }
 @article{wolter_schlesser_okuzumi_prater_sitar_2001, title={Angle-dependent reflectometry as a technique for fast assessment of highly oriented diamond film quality}, volume={10}, ISSN={["0925-9635"]}, DOI={10.1016/S0925-9635(01)00487-3}, abstractNote={An expedient technique for assessing the quality of highly oriented diamond films is described. This analysis is based on light reflection from the {111} faces of oriented diamond octahedra as a function of azimuthal sample orientation. Significant light reflection was detected at 90° rotation intervals and the full-width-at-half-maximum of these periodic peaks was determined to be adequate for gauging the upper limit of crystal misorientation. In addition, a two-dimensional surface mapping of the distribution of highly oriented diamond across the sample was determined by analyzing reflectivity properties at equally spaced spots on the surface.}, number={11}, journal={DIAMOND AND RELATED MATERIALS}, author={Wolter, SD and Schlesser, R and Okuzumi, F and Prater, JT and Sitar, Z}, year={2001}, month={Nov}, pages={2092–2095} }
 @article{wolter_schlesser_okuzumi_prater_sitar_2001, title={Process optimization in the low-pressure flat flame growth of diamond}, volume={10}, ISSN={["0925-9635"]}, DOI={10.1016/S0925-9635(00)00477-5}, abstractNote={Abstract The influence of oxy-acetylene gas mixture (O 2 /C 2 H 2 gas ratio — 0.95:1.06) and substrate temperature (ranging from 650 to 850°C) on diamond growth in the low-pressure flat flame is reported. Deconvolution of the Raman spectra was employed to qualitatively estimate the ratio of diamond-to-non-diamond carbon in the film deposits by an area comparison of these discriminate peaks. The diamond crystallinity was assessed quantitatively by a determination of the full-width-at-half-maximum of the 1332 cm −1 Raman line representing sp 3 -bonded carbon. An optimum oxygen/acetylene molar ratio of ∼1.05 and substrate temperature of 650–750°C were observed for limiting both the non-diamond carbon content and a deterioration in the diamond crystallinity. The crystallite morphology was also evaluated as a function of this same parametric regime based on assignment of the parameter α describing growth rate competition between the {100} and {111} faces. The collective data indicates the process conditions required to produce the optimum in film quality according to a desired film morphology.}, number={3-7}, journal={DIAMOND AND RELATED MATERIALS}, author={Wolter, SD and Schlesser, R and Okuzumi, F and Prater, JT and Sitar, Z}, year={2001}, pages={289–294} }
 @article{collazo_schlesser_sitar_2001, title={Two field-emission states of single-walled carbon nanotubes}, volume={78}, ISSN={["0003-6951"]}, DOI={10.1063/1.1361089}, abstractNote={Two field-emission states of single-walled carbon nanotubes have been identified according to their respective emission current levels. The state yielding increased emission current has been attributed to the presence of adsorbates on the nanotubes. It was realized that, by application of high electric fields inducing large emission currents, a transition between the two states could be induced. For the high current state, field-emitted electrons originated from states located 1 eV below the Fermi level, as was determined by field-emission energy distribution measurements. This suggested that adsorbates introduced a resonant state on the surface that enhanced the tunneling probability of the electrons. These states are removed when the nanotubes are cleaned by application of a large electric field, thus, decreasing the field-emitted current.}, number={14}, journal={APPLIED PHYSICS LETTERS}, author={Collazo, R and Schlesser, R and Sitar, Z}, year={2001}, month={Apr}, pages={2058–2060} }
 @article{schlesser_collazo_bower_zhou_sitar_2000, title={Energy distribution of field emitted electrons from carbon nanotubes}, volume={9}, ISSN={["1879-0062"]}, DOI={10.1016/s0925-9635(99)00277-0}, abstractNote={Field emission properties of single-walled carbon nanotubes (SWNTs), deposited on n-type Si substrates, were investigated by a combination of classical I–V characterization and field emission energy distribution (FEED) measurements. I–V characterization showed that current densities on the order of 1 mA/cm2 could be obtained at nominal electric fields as low as 3 V/μm. A current density of up to 25 mA/cm2 was observed, and long-term current stability and reproducibility were excellent. FEED measurements revealed that at low current densities, the field emitted electrons originated from energy levels close to the Fermi level of the Si substrate. At larger applied voltages and larger current densities, I–V characterization of the field emitters showed primarily an ohmic behavior; FEED data taken under the same experimental conditions showed a shift of the main spectral peak toward lower kinetic energies with increasing applied voltages. This energy shift was found to be linear with the applied voltage and emission current over a wide range. Both FEED and I–V data thus indicated that the field emission current was primarily limited by the ohmic resistance of the nanotubes and/or the contact resistance between the nanotubes and the Si substrate; typical measured values for the cathode surface resistances were 100 kΩ cm2.}, number={3-6}, journal={DIAMOND AND RELATED MATERIALS}, author={Schlesser, R and Collazo, R and Bower, C and Zhou, O and Sitar, Z}, year={2000}, pages={1201–1204} }
 @article{collazo_schlesser_roskowski_davis_sitar_2000, title={Hot electron transport in AlN}, volume={88}, ISSN={["0021-8979"]}, DOI={10.1063/1.1318386}, abstractNote={The energy distribution of electrons that were transported through a thin intrinsic AlN film was directly measured as a function of the applied field. The measurements were realized by extracting the electrons into vacuum through a semitransparent Au contact and measuring their energies using an electron spectrometer. At moderate applied fields (100 kV/cm), the energy distribution was found to follow a Maxwellian model corresponding to a temperature of 2700 K and a drift component below the spectrometer resolution. At higher fields, intervalley scattering was evidenced by the presence of a second peak at 0.7 eV. This coincides well with the energy position of the LM valleys in AlN.}, number={10}, journal={JOURNAL OF APPLIED PHYSICS}, author={Collazo, R and Schlesser, R and Roskowski, A and Davis, RF and Sitar, Z}, year={2000}, month={Nov}, pages={5865–5869} }
 @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{yang_wolden_liu_schlesser_davis_prater_sitar_1998, title={Coalesced oriented diamond films on nickel}, volume={13}, ISSN={["0884-2914"]}, DOI={10.1557/JMR.1998.0157}, abstractNote={The growth of coalesced, highly oriented diamond films has been achieved on nickel substrates using a multistep process that consisted of (i) seeding the Ni surface with 0.5 μm diamond powder, (ii) annealing at 1100 °C in a hydrogen atmosphere, and (iii) growth at 900 °C in a mixture of hydrogen and 0.5% methane. Auger depth profile analysis of a sample quenched after the annealing stage showed the presence of significant amounts of carbon (6 at. %) close to the substrate surface and about 3 at.% deeper in the substrate. The loss of carbon into the substrate resulted in relatively low nucleation density. The addition of methane into the gas phase during the annealing stage proved very effective in compensating for the diffusion. An addition of 0.5% methane in the gas phase produced optimum results, as the nucleation density, orientation of diamond particles, and uniformity were substantially improved. Substrates nucleated under these conditions were grown out into coalesced, 30 μm thick films. Both (100) and (111) oriented films showed a high degree of orientation and Raman spectra obtained from these orientations showed intense and narrow diamond signature peaks with FWHM's of 5 and 8 cm-1, respectively.}, number={5}, journal={JOURNAL OF MATERIALS RESEARCH}, author={Yang, PC and Wolden, CA and Liu, W and Schlesser, R and Davis, RF and Prater, JT and Sitar, Z}, year={1998}, month={May}, pages={1120–1123} }
 @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{mccarson_schlesser_mcclure_sitar_1998, title={Electron emission mechanism from cubic boron nitride-coated molybdenum emitters}, volume={72}, ISSN={["0003-6951"]}, DOI={10.1063/1.121492}, abstractNote={The energy distribution of field-emitted electrons from Mo tips coated with intrinsic cubic boron nitride (c-BN) was studied in an effort to determine the origin of the emitted electrons. Voltage-dependent field-emission energy distribution (V-FEED) spectra were collected from the Mo emitters under ultra-high-vacuum conditions both before and after being coated. Emission current at a given voltage increased by as much as two orders of magnitude for the c-BN-coated emitters relative to bare emitters. The energy of field-emitted electrons from the c-BN-coated emitters was linearly dependent upon the applied voltage. Extrapolation of V-FEED data from c-BN-coated emitters to the flatband condition evidenced that the electrons were emitted from the conduction-band minimum of the c-BN coating at the c-BN/vacuum interface.}, number={22}, journal={APPLIED PHYSICS LETTERS}, author={McCarson, BL and Schlesser, R and McClure, MT and Sitar, Z}, year={1998}, month={Jun}, pages={2909–2911} }
 @article{choi_schlesser_wojak_cuomo_sitar_hren_1998, title={Electron energy distribution of diamond-coated field emitters}, volume={16}, number={2}, journal={Journal of Vacuum Science & Technology. B, Microelectronics and Nanometer Structures}, author={Choi, W. B. and Schlesser, R. and Wojak, G. and Cuomo, J. J. and Sitar, Z. and Hren, J. J.}, year={1998}, month={Mar}, pages={716–719} }
 @article{mccarson_schlesser_sitar_1998, title={Field emission energy distribution analysis of cubic-BN-coated Mo emitters: Nonlinear behavior}, volume={84}, ISSN={["1089-7550"]}, DOI={10.1063/1.368496}, abstractNote={Voltage-dependent field emission energy distribution (V-FEED) and current versus voltage measurements were performed on Mo tips coated with intrinsic cubic boron nitride (c-BN) to determine the origin of the field-emitted electrons. Spectra were collected from the Mo emitters under ultrahigh vacuum conditions both before and after being coated. In some instances multiple FEED peaks were observed in the collected spectra. These corresponded to multiple emission sites on the emitter. The energy of the field-emitted electrons from the c-BN-coated emitters usually depended linearly upon the applied voltage and could be explained using a simplified band-bending model. However, at higher voltages the FEED measured from the c-BN-coated emitters departed from this linear behavior. These nonlinearities were attributed to a contact resistance at the Mo/c-BN interface which had a greater influence on the energy distribution of emitted electrons at larger emission currents.}, number={6}, journal={JOURNAL OF APPLIED PHYSICS}, author={McCarson, BL and Schlesser, R and Sitar, Z}, year={1998}, month={Sep}, pages={3382–3385} }
 @article{schlesser_mccarson_mcclure_sitar_1998, title={Field emission energy distribution analysis of wide-band-gap field emitters}, volume={16}, number={2}, journal={Journal of Vacuum Science & Technology. B, Microelectronics and Nanometer Structures}, author={Schlesser, R. and McCarson, B. L. and McClure, M. T. and Sitar, Z.}, year={1998}, pages={689–692} }
 @article{sitar_liu_yang_wolden_schlesser_prater_1998, title={Heteroepitaxial nucleation of diamond on nickel}, volume={7}, ISSN={["0925-9635"]}, DOI={10.1016/S0925-9635(97)00244-6}, abstractNote={Highly oriented diamond has been grown on (100) nickel substrates by the hot filament chemical vapor deposition method. Epitaxial nuclei were obtained by a diamond powder seeding and high temperature annealing process. Since the timing of the process was crucial for the achievement of a high degree of orientation and high density of diamond nuclei, a real-time, in-situ laser reflectometry system was developed to monitor changes in surface morphology observed during the high temperature annealing stage. Characteristic features observed in the intensities of reflected and scattered light were interpreted by comparison with scanning electron micrographs of the samples quenched at sequential stages of the process. It was concluded that the scattered light signal can be effectively used as a process steering parameter. Using this technique, oriented nucleation and growth of diamond on Ni was reproducibly achieved. Auger spectroscopy showed that up to 6 at% of carbon was dissolved in the nickel surface layer. The investigation of interfacial microstructures and phases involved by transmission electron microscopy revealed the formation of Ni4C already in the early stages of nucleation. This phase was manifested as coherent precipitates and is believed to have been the precursor for diamond nucleation. Perfectly epitaxial diamond was grown by this process. The epitaxial relationship was determined by cross-sectional transmission electron microscopy and selected area diffraction analysis.}, number={2-5}, journal={DIAMOND AND RELATED MATERIALS}, author={Sitar, Z and Liu, W and Yang, PC and Wolden, CA and Schlesser, R and Prater, JT}, year={1998}, month={Feb}, pages={276–282} }
 @article{schlesser_mcclure_mccarson_sitar_1998, title={Mechanisms of field emission from diamond coated Mo emitters}, volume={7}, ISSN={["0925-9635"]}, DOI={10.1016/S0925-9635(97)00290-2}, abstractNote={A combination of field emission energy distribution (FEED) and I–V measurements was used to study the field emission mechanisms of tip-shaped molybdenum emitters electrophoretically coated with nominally intrinsic diamond powders. Field-induced band bending was studied as a function of applied voltage and was interpreted in terms of a two-barrier model. Field emitted electrons originated from the conduction band minimum of diamond. Electron injection at the Mo/diamond interface was identified as the dominant field emission current limiting factor. It was concluded that potential negative electron affinity (NEA) properties of diamond did not contribute to a current enhancement. The latter statement was confirmed by the observation that graphite coatings enhanced emission currents in a similar way to diamond coatings.}, number={2-5}, journal={DIAMOND AND RELATED MATERIALS}, author={Schlesser, R and McClure, MT and McCarson, BL and Sitar, Z}, year={1998}, month={Feb}, pages={636–639} }
 @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{yang_liu_schlesser_wolden_davis_prater_sitar_1998, title={Surface melting in the heteroepitaxial nucleation of diamond on Ni}, volume={187}, ISSN={["0022-0248"]}, DOI={10.1016/S0022-0248(97)00854-3}, abstractNote={Surface melting associated with the heteroepitaxial nucleation of diamond on Ni was investigated. Scanning electron microscopy of quenched samples revealed flow patterns and a recrystallized surface morphology. A combination of techniques including in situ optical monitoring, differential thermal analysis, Auger depth profile analysis, and cross-section transmission electron microscopy (TEM) analysis were performed to identify the nature of the molten layer. Data obtained from different experiments were in good mutual agreement. All experimental results strongly indicated that a molten Ni–C–H surface layer was involved in the nucleation process. The presence of both carbon and atomic hydrogen played an important role in the depression of the melting point which was measured to be >300°C less than the melting point of pure Ni.}, number={1}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Yang, PC and Liu, W and Schlesser, R and Wolden, CA and Davis, RF and Prater, JT and Sitar, Z}, year={1998}, month={Apr}, pages={81–88} }
 @article{mcclure_schlesser_mccarson_sitar_1997, title={Electrical characterization of diamond and graphite coated Mo field emitters}, volume={15}, number={6}, journal={Journal of Vacuum Science & Technology. B, Microelectronics and Nanometer Structures}, author={McClure, M. T. and Schlesser, R. and McCarson, B. L. and Sitar, Z.}, year={1997}, pages={2067–2071} }
 @article{collazo_schlesser_sitar, title={Field emission from carbon nanotubes}, volume={13}, number={5}, journal={New Diamond and Frontier Carbon Technology}, author={Collazo, R. and Schlesser, R. and Sitar, Z.}, pages={297–306} }