R. J. Nemanich

North Carolina State University, Raleigh, North Carolina, United States

Are you R. J. Nemanich?

Claim your profile

Publications (552)861.76 Total impact

  • Sean W. King · Satoru Tanaka · Robert F. Davis · Robert J. Nemanich ·
    [Show abstract] [Hide abstract]
    ABSTRACT: 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.
    Journal of Vacuum Science & Technology A Vacuum Surfaces and Films 09/2015; 33(5):05E105. DOI:10.1116/1.4921526 · 2.32 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: 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.
    Journal of Vacuum Science & Technology A Vacuum Surfaces and Films 09/2015; 33(5):05E115. DOI:10.1116/1.4926733 · 2.32 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The possibility of laser induced variation of optical and electrical properties of conductive nanocrystalline diamond (CNCD) films has been demonstrated. The films were produced by microwave plasma chemical vapor de-position (MPCVD) from CH 4 :H 2 :N 2 gas mixtures. The films were irradiated in air with 20 ns pulses of an ArF excimer laser (λ = 193 nm). It was found that low laser pulse intensity (~0.05 J/cm 2), well below film surface graphitization (~0.3 J/cm 2) and nanoablation (~0.08 J/cm 2) thresholds, induces changes of the film properties. The effect requires multiple pulsed irradiation and results in a decrease of the film electrical conductivity, which is accompanied by optical bleaching of the diamond film absorption.
  • Sean W. King · Robert J. Nemanich · Robert F. Davis ·
    [Show abstract] [Hide abstract]
    ABSTRACT: 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.
    Journal of Applied Physics 07/2015; 118(4). DOI:10.1063/1.4927515 · 2.18 Impact Factor
  • Joseph Shammas · Tianyin Sun · Franz A.M. Koeck · Aram Rezikyan · Robert J. Nemanich ·
    [Show abstract] [Hide abstract]
    ABSTRACT: Cubic boron nitride (c-BN) was deposited on silicon substrates using electron cyclotron resonance microwave plasma chemical vapor deposition (ECR MPCVD) employing Ar–He–N2–H2–BF3 gas precursors at 780 °C. In situ X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, and transmission electron microscopy (TEM) measurements indicated that c-BN nucleated and grew on a hexagonal boron nitride (h-BN) layer that initially formed on the substrate. The minimum and maximum bias applied to the sample that yielded c-BN growth was investigated by in situ XPS. Rutherford backscattering spectrometry (RBS), elastic recoil detection (ERD), and XPS were employed to determine the chemical composition of the produced films, while XPS and in situ ultraviolet photoelectron spectroscopy (UPS) were employed to investigate the electronic structure of film surfaces. The bandgap of the c-BN films was estimated to be 6.2 ± 0.2 eV from XPS measurements. In situ UPS measurements indicated that as-deposited c-BN films exhibited a negative electron affinity (NEA). The surface continued to exhibit an NEA after H2 plasma treatment performed at 650 °C and annealing at 780 °C. Analysis of surface bonding using a surface dipole model suggests that H-terminated N surface sites could be responsible for the observed NEA character.
    Diamond and Related Materials 06/2015; 56. DOI:10.1016/j.diamond.2015.04.002 · 1.92 Impact Factor
  • Sean W. King · Robert J. Nemanich · Robert F. Davis ·
    [Show abstract] [Hide abstract]
    ABSTRACT: 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.
    Surface and Interface Analysis 05/2015; 47(7). DOI:10.1002/sia.5781 · 1.25 Impact Factor
  • Source
    Anna M Zaniewski · Christie J Trimble · Robert J Nemanich ·
    [Show abstract] [Hide abstract]
    ABSTRACT: Graphene and metal nanoparticle composites are a promising class of materials with unique electronic, optical, and chemical properties. In this work, graphene is used as a reducing surface to grow gold nanoparticles out of solution-based metal precursors. The nanoparticle formation is found to strongly depend upon the graphene substrate selection. The studied substrates include diamond, p-type silicon, aluminum oxide, lithium niobate, and copper. Our results indicate that the chemical properties of graphene depend upon this selection. For example, for the same reaction times and concentration, the reduction of gold chloride to gold nanoparticles on graphene/lithium niobate results in 3% nanoparticle coverage compared to 20% coverage on graphene/silicon and 60% on graphene/copper. On insulators, nanoparticles preferentially form on folds and edges. Energy dispersive X-ray analysis is used to confirm the nanoparticle elemental makeup.
    Applied Physics Letters 03/2015; 106(12). DOI:10.1063/1.4916567 · 3.30 Impact Factor
  • Brianna S. Eller · Jialing Yang · Robert J. Nemanich ·
    [Show abstract] [Hide abstract]
    ABSTRACT: GaN-based devices are currently limited by reliability issues such as gate leakage and current collapse, where the mechanisms responsible for degradation are closely related to the electronic surface state configuration. Therefore, understanding the electronic surface state configuration of GaN-based materials will help improve device performance. Since GaN has an inherent polarization, these materials are also subject to a bound polarization charge, which influences the electronic state configuration. In this study, the surface band bending of N-face GaN, Ga-face GaN, and Ga-face AlGaN was measured with x-ray photoemission spectroscopy after various cleaning steps to investigate the effects of the polarization. Despite the different surface bound charge on these materials, similar band bending was observed regardless of the magnitude or direction of the charge. Specifically, the band bending varied from -0.1 eV to 0.9 eV on these samples, which supported the models of a Fermi level pinning state at similar to 0.4 eV to 0.8 eV below the conduction band. Based on available literature, we suggest this pinning state is indirectly evident of a nitrogen vacancy or gallium-dangling bond.
    Journal of Electronic Materials 12/2014; 43(12):4560-4568. DOI:10.1007/s11664-014-3383-z · 1.80 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Previous measurements of the electronic conductance of DNA nucleotides or amino acids have used tunnel junctions in which the gap is mechanically adjusted, such as scanning tunneling microscopes or mechanically controllable break junctions. Fixed junction devices have, at best, detected the passage of whole DNA molecules without yielding chemical information. Here, we report on a layered tunnel junction in which the tunnel gap is defined by a dielectric layer, deposited by atomic layer deposition. Reactive ion etching is used to drill a hole through the layers so that the tunnel junction can be exposed to molecules in solution. When the metal electrodes are functionalized with recognition molecules that capture DNA nucleotides via hydrogen bonds, the identities of the individual nucleotides are revealed by characteristic features of the fluctuating tunnel current associated with single-molecule binding events.
    ACS Nano 11/2014; 8(12). DOI:10.1021/nn505356g · 12.88 Impact Factor
  • Sean W. King · Robert F. Davis · Robert J. Nemanich ·
    [Show abstract] [Hide abstract]
    ABSTRACT: 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.
    Journal of Vacuum Science & Technology A Vacuum Surfaces and Films 11/2014; 32(6):061504. DOI:10.1116/1.4894816 · 2.32 Impact Factor
  • Vincenc Nemanič · Marko Žumer · Janez Kovač · Franz A. M. Koeck · Robert J. Nemanich ·
    [Show abstract] [Hide abstract]
    ABSTRACT: Nitrogen doped, hydrogen terminated diamond films have shown a work function of less than 1.5 eV and thermionic electron emission (TE) has been detected at temperatures less than 500 °C. However, ambient exposure or extended operation leads to a deterioration of the emission properties. In this study thermionic electron emission has been evaluated for as-received surfaces and for surfaces after 18 months of ambient exposure. The initial TE current density of the freshly deposited diamond film was ∼5 × 10-5 A/cm2 at 500 °C. In contrast, the initial TE current density of a film aged for 18 months was ∼1.8 × 10-9 A/cm2 at 500 °C. The decreased emission current density is presumed to be a consequence of oxidation, surface adsorption of contaminants and hydrogen depletion from the surface layer. In situ reactivation of the aged film surface was achieved by introducing hydrogen at a pressure of 1.3 × 10-4 mbar and using a hot filament of a nearby ionization gauge to generate atomic and/ or excited molecular hydrogen. After 2 h of exposure with the sample at 500 ° C, the surface exhibited a stable emission current density of ∼2.3 × 10-6 A/cm2 (an increase by a factor of ∼1300). To elucidate the reactivation process thermionic electron energy distribution (TEED) and XPS core level spectra were measured during in situ hydrogen exposure at 5 × 10-8 mbar. During the isothermal exposure it was determined that atomic or excited hydrogen resulted in a much greater increase of the TE in comparison to exposure tomolecular hydrogen. During exposure at 400 ° C the surface oxygen was substantially reduced, the TEED cut-off energy, which indicates the effective work function, decreased by ∼200 meV, and the TE intensity increased by a factor of ∼100. The increase in thermionic emission with hydrogen was ascribed to the reactivation of the surface through the formation of a uniform surface dipole layer and a reduction of the surface work function.
    Diamond and Related Materials 11/2014; 50. DOI:10.1016/j.diamond.2014.10.003 · 1.92 Impact Factor
  • Sean W. King · Robert J. Nemanich · Robert F. Davis ·
    [Show abstract] [Hide abstract]
    ABSTRACT: 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.
    physica status solidi (b) 10/2014; 252(2). DOI:10.1002/pssb.201451340 · 1.49 Impact Factor
  • Jialing Yang · Brianna S. Eller · Robert J. Nemanich ·
    [Show abstract] [Hide abstract]
    ABSTRACT: The effects of surface pretreatment, dielectric growth, and post deposition annealing on interface electronic structure and polarization charge compensation of Ga- and N-face bulk GaN were investigated. The cleaning process consisted of an ex-situ wet chemical NH4OH treatment and an in-situ elevated temperature NH3 plasma process to remove carbon contamination, reduce oxygen coverage, and potentially passivate N-vacancy related defects. After the cleaning process, carbon contamination decreased below the x-ray photoemission spectroscopy detection limit, and the oxygen coverage stabilized at ∼1 monolayer on both Ga- and N-face GaN. In addition, Ga- and N-face GaN had an upward band bending of 0.8 ± 0.1 eV and 0.6 ± 0.1 eV, respectively, which suggested the net charge of the surface states and polarization bound charge was similar on Ga- and N-face GaN. Furthermore, three dielectrics (HfO2, Al2O3, and SiO2) were prepared by plasma-enhanced atomic layer deposition on Ga- or N-face GaN and annealed in N2 ambient to investigate the effect of the polarization charge on the interface electronic structure and band offsets. The respective valence band offsets of HfO2, Al2O3, and SiO2 with respect to Ga- and N-face GaN were 1.4 ± 0.1, 2.0 ± 0.1, and 3.2 ± 0.1 eV, regardless of dielectric thickness. The corresponding conduction band offsets were 1.0 ± 0.1, 1.3 ± 0.1, and 2.3 ± 0.1 eV, respectively. Experimental band offset results were consistent with theoretical calculations based on the charge neutrality level model. The trend of band offsets for dielectric/GaN interfaces was related to the band gap and/or the electronic part of the dielectric constant. The effect- of polarization charge on band offset was apparently screened by the dielectric-GaN interface states.
    Journal of Applied Physics 09/2014; 116(12):123702-123702-12. DOI:10.1063/1.4895985 · 2.18 Impact Factor
  • Source
    Sean W. King · Robert F. Davis · Robert J. Nemanich ·
    [Show abstract] [Hide abstract]
    ABSTRACT: 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.
    Journal of Vacuum Science & Technology A Vacuum Surfaces and Films 09/2014; 32(5):051402. DOI:10.1116/1.4891650 · 2.32 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: This work presents a spectroscopic study of the thermally enhanced photoinduced electron emission from nitrogen-doped diamond films prepared on p-type silicon substrates. It has been shown that photon-enhanced thermionic emission (PETE) can substantially enhance thermionic emission intensity from a p-type semiconductor. An n-type diamond/p-type silicon structure was illuminated with 400-450 nm light, and the spectra of the emitted electrons showed a work function less than 2 eV and nearly an order of magnitude increase in emission intensity as the temperature was increased from ambient to ̃400 °C. Thermionic emission was negligible in this temperature range. The results are modeled in terms of contributions from PETE and direct photoelectron emission, and the large increase is consistent with a PETE component. The results indicate possible application in combined solar/thermal energy conversion devices.
    Physical Review B 08/2014; 90(12). DOI:10.1103/PhysRevB.90.121302 · 3.74 Impact Factor
  • Sean W. King · Robert J. Nemanich · Robert F. Davis ·
    [Show abstract] [Hide abstract]
    ABSTRACT: 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.
    Applied Physics Letters 08/2014; 105(8):081606-081606-4. DOI:10.1063/1.4894010 · 3.30 Impact Factor
  • Robert J. Nemanich · John A. Carlisle · Atsushi Hirata · Ken Haenen ·
    [Show abstract] [Hide abstract]
    ABSTRACT: Diamond is a unique material that often exhibits extreme properties compared to other materials. Discovered about 30 years ago, the use of hydrogen in plasma-enhanced chemical vapor deposition (CVD) has enabled the growth and coating of diamond in film form on various substrate materials. CVD diamond research has been actively continued subsequently to develop new understanding and approaches for the growth and processing of this fascinating material. Currently, the study and development of diamond films has enabled a wide range of applications based on the combination of unique and extreme properties of diamond and the variety of film properties obtainable through tuning the microstructure, morphology, impurities, and surfaces. This issue of MRS Bulletin introduces the latest research, recent applications, and the challenges ahead for CVD diamond films.
    MRS Bulletin 06/2014; 39(06):490-494. DOI:10.1557/mrs.2014.97 · 5.67 Impact Factor
  • Tianyin Sun · Franz A.M. Koeck · Petr B. Stepanov · Robert J. Nemanich ·
    [Show abstract] [Hide abstract]
    ABSTRACT: Nitrogen-doped diamond has been under investigation for its low effective work function, which is due to the negative electron affinity (NEA) produced after surface hydrogen termination. Diamond films grown by chemical vapor deposition (CVD) have been reported to exhibit visible light induced electron emission and low temperature thermionic emission. The physical mechanism and material-related properties that enable this combination of electron emission are the focus of this research. In this work the electron emission spectra of nitrogen-doped, hydrogen-terminated diamond films are measured, at elevated temperatures, with wavelength selected illumination from 340 nm to 450 nm. Through analysis of the spectroscopy results, we argue that for nitrogen-doped diamond films on metallic substrates, photo-induced electron generation at visible wavelengths involves both the ultra-nanocrystalline diamond and the interface between the diamond film and metal substrate. Moreover, the results suggest that the quality of the metal-diamond interface can substantially impact the threshold of the sub-bandgap photo-induced emission.
    Diamond and Related Materials 04/2014; 44. DOI:10.1016/j.diamond.2014.02.008 · 1.92 Impact Factor
  • Jialing Yang · Brianna S. Eller · Manpuneet Kaur · Robert J. Nemanich ·
    [Show abstract] [Hide abstract]
    ABSTRACT: In this research, Al2O3 films were grown by remote plasma-enhanced atomic layer deposition using a nonpyrophoric precursor, dimethylaluminum isopropoxide (DMAI), and oxygen plasma. After optimization, the growth rate was determined to be ∼1.5 Å/cycle within a growth window of 25–220 °C; the higher growth rate than reported for thermal atomic layer deposition was ascribed to the higher reactivity of the plasma species compared with H2O and the adsorption of active oxygen at the surface, which was residual from the oxygen plasma exposure. Both effects enhance DMAI chemisorption and increase the saturation density. In addition, a longer oxygen plasma time was required at room temperature to complete the reaction and decrease the carbon contamination below the detection limit of x-ray photoemission spectroscopy. The properties of the subsequent Al2O3 films were measured for different temperatures. When deposited at 25 °C and 200 °C, the Al2O3 films demonstrated a single Al-O bonding state as measured by x-ray photoemission spectroscopy, a similar band gap of 6.8±0.2 eV as determined by energy loss spectroscopy, a similar index of refraction of 1.62±0.02 as determined by spectroscopic ellipsometry, and uniform growth with a similar surface roughness before and after growth as confirmed by atomic force microscopy. However, the room temperature deposited Al2O3 films had a lower mass density (2.7 g/cm3 compared with 3.0 g/cm3) and a higher atomic ratio of O to Al (2.1 compared with 1.6) as indicated by x-ray reflectivity and Rutherford backscattering spectroscopy, respectively.
    Journal of Vacuum Science & Technology A Vacuum Surfaces and Films 03/2014; 32(2):021514-021514-9. DOI:10.1116/1.4866378 · 2.32 Impact Factor
  • M. C. Zeman · R. J. Nemanich · A. Sunda-Meya ·
    [Show abstract] [Hide abstract]
    ABSTRACT: The growth and coarsening dynamics of dysprosium silicide nanostructures are observed in real-time using photoelectron emission microscopy. The annealing of a thin Dy film to temperatures in the range of 700–1050 °C results in the formation of epitaxial rectangular silicide islands and nanowires on Si(001) and triangular and hexagonal silicide islands on Si(111). During continuous annealing, individual islands are observed to coarsen via Ostwald ripening at different rates as a consequence of local variations in the size and relative location of the surrounding islands on the surface. A subsequent deposition of Dy onto the Si(001) surface at 1050 °C leads to the growth of the preexisting islands and to the formation of silicide nanowires at temperatures above where nanowire growth typically occurs. Immediately after the deposition is terminated, the nanowires begin to decay from the ends, apparently transferring atoms to the more stable rectangular islands. On Si(111), a low continuous flux of Dy at 1050 °C leads to the growth of kinked and jagged island structures, which ultimately form into nearly equilateral triangular shapes.
    Journal of Materials Science 02/2014; 49(4). DOI:10.1007/s10853-013-7869-5 · 2.37 Impact Factor

Publication Stats

14k Citations
861.76 Total Impact Points


  • 1986-2015
    • North Carolina State University
      • • Department of Physics
      • • Department of Materials Science and Engineering
      Raleigh, North Carolina, United States
  • 2007-2014
    • Arizona State University
      • Department of Physics
      Phoenix, Arizona, United States
  • 2006
    • Dongguk University
      Sŏul, Seoul, South Korea
  • 1990
    • University of North Carolina at Chapel Hill
      • Department of Physics and Astronomy
      North Carolina, United States
  • 1989
    • RWTH Aachen University
      • Institute of Semiconductor Electronics
      Aachen, North Rhine-Westphalia, Germany
  • 1977-1986
    • Palo Alto Research Center
      Palo Alto, California, United States
  • 1984
    • Xerox Corporation
      Norwalk, Connecticut, United States
  • 1976-1977
    • University of Chicago
      • • Department of Physics
      • • James Franck Institute
      Chicago, Illinois, United States