@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{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{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{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{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{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{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{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{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{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{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} }
 @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{johnson_yu_brown_koeck_el-masry_kong_edmond_cook_schetzina_1999, title={A critical comparison between MOVPE and MBE growth of III-V nitride semiconductor materials for opto-electronic device applications}, volume={4S1}, DOI={10.1557/s1092578300003100}, abstractNote={A systematic study of the growth and doping of GaN, AlGaN, and InGaN by both molecular beam epitaxy (MBE) and metal-organic vapor phase epitaxy (MOVPE) has been performed. Critical differences between the resulting epitaxy are observed in the p-type doping using magnesium as the acceptor species. MBE growth, using rf-plasma sources to generate the active nitrogen species for growth, has been used for III-Nitride compounds doped either n-type with silicon or p-type with magnesium. Blue and violet light emitting diode (LED) test structures were fabricated. These vertical devices required a relatively high forward current and exhibited high leakage currents. This behavior was attributed to parallel shorting mechanisms along the dislocations in MBE grown layers. For comparison, similar devices were fabricated using a single wafer vertical flow MOVPE reactor and ammonia as the active nitrogen species. MOVPE grown blue LEDs exhibited excellent forward device characteristics and a high reverse breakdown voltage. We feel that the excess hydrogen, which is present on the GaN surface due to the dissociation of ammonia in MOVPE, acts to passivate the dislocations and eliminate parallel shorting for vertical device structures. These findings support the widespread acceptance of MOVPE, rather than MBE, as the epitaxial growth technique of choice for III-V nitride materials used in vertical transport bipolar devices for optoelectronic applications.}, number={G5.10}, journal={MRS Internet Journal of Nitride Semiconductor Research}, author={Johnson, M. A. L. and Yu, Z. H. and Brown, J. D. and Koeck, F. A. and El-Masry, N. A. and Kong, H. S. and Edmond, J. A. and Cook, J. W. and Schetzina, J. F.}, year={1999} }