R. J. Nemanich

Arizona State University, Phoenix, Arizona, United States

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Publications (537)841.22 Total impact

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    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 · 2.14 Impact Factor
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    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 · 1.57 Impact Factor
  • Sean W. King, Robert J. Nemanich, Robert F. Davis
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    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 · 1.39 Impact Factor
  • Source
    Anna M Zaniewski, Christie J Trimble, Robert J Nemanich
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    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 · 3.52 Impact Factor
  • Brianna S. Eller, Jialing Yang, Robert J. Nemanich
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    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 · 1.68 Impact Factor
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    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; DOI:10.1021/nn505356g · 12.03 Impact Factor
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    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 similar to 5 x 10(-5) A/cm(2) at 500 degrees C. In contrast, the initial TE current density of a film aged for 18 months was similar to 1.8 x 10(-9) A/cm(2) at 500 degrees 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 x 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 degrees C, the surface exhibited a stable emission current density of similar to 23 x 10(-5) A/cm(2) (an increase by a factor of similar to 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 x 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 to molecular hydrogen. During exposure at 400 degrees C the surface oxygen was substantially reduced, the TEED cut-off energy, which indicates the effective work function, decreased by similar to 200 meV, and the TE intensity increased by a factor of similar to 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 · 1.57 Impact Factor
  • Sean W. King, Robert J. Nemanich, Robert F. Davis
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    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 · 1.61 Impact Factor
  • Jialing Yang, Brianna S. Eller, Robert J. Nemanich
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    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 · 2.19 Impact Factor
  • Source
    Sean W. King, Robert F. Davis, Robert J. Nemanich
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    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 · 2.14 Impact Factor
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    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 · 3.66 Impact Factor
  • Sean W. King, Robert J. Nemanich, Robert F. Davis
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    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 · 3.52 Impact Factor
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    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 · 5.07 Impact Factor
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    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 · 1.57 Impact Factor
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    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 · 2.14 Impact Factor
  • M. C. Zeman, R. J. Nemanich, A. Sunda-Meya
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    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 · 2.31 Impact Factor
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    ABSTRACT: Vanadium dioxide (VO2) is a narrow band gap material that undergoes a metal-insulator phase transition at similar to 343 K with evidence of an electric-field induced transition at T<343 K. In this study, a sandwich-type dielectric structure is prepared consisting of two similar to 1.5 nm hafnium oxide (HfO2) layers with a similar to 1.0 nm VO2 interlayer grown on an oxidized n-type silicon substrate. The electronic properties of the sample were characterized by in-situ x-ray and ultraviolet photoelectron spectroscopy after each layer was deposited. The band alignment was analyzed after each growth step. The SiO2/HfO2 interface valence band offset is found to be 0.7 eV, and the HfO2/VO2 interface valence band offset is determined to be 3.4 eV. (C) 2014 American Vacuum Society.
    Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society 01/2014; 32(1):011203-011203-6. DOI:10.1116/1.4832341 · 1.36 Impact Factor
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    ABSTRACT: Hydrogen terminated, nitrogen doped diamond thin films have been the focus of recent research for application in thermionic energy conversion devices and possibly in solar cells. Nitrogen doped diamond films can attain negative electron affinity (NEA) through treatment with hydrogen plasma, which also produces a very low work function surface. Photoemission and thermionic emission spectroscopy measurements confirm a work function of approximately 2 eV for such films. The research presented here includes results from imaging these thin films with photo-electron emission microscopy (PEEM) and thermionic electron emission microscopy (ThEEM), in addition to spectroscopic studies using ultraviolet photoelectron spectroscopy (UPS). From the images it can be concluded that the photo- and thermionic emission are spatially uniform and do not originate from different isolated emission sites. This observation holds true up to the highest resolution and for all temperatures investigated (300–800 K). While relatively uniform, the emission is found to be influenced by the surface morphology and film microstructure. The spatial intensity distributions of the PEEM and ThEEM images are very similar, as reflected by the structure present in both of these images. This observation indicates that both emission processes are enabled by the low work function of the film.
    Diamond and Related Materials 11/2013; 40:12–16. DOI:10.1016/j.diamond.2013.09.009 · 1.57 Impact Factor
  • Brianna S. Eller, Jialing Yang, Robert J. Nemanich
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    ABSTRACT: GaN and AlGaN have shown great potential in next-generation high-power electronic devices; however, they are plagued by a high density of interface states that affect device reliability and performance, resulting in large leakage current and current collapse. In this review, the authors summarize the current understanding of the gate leakage current and current collapse mechanisms, where awareness of the surface defects is the key to controlling and improving device performance. With this in mind, they present the current research on surface states on GaN and AlGaN and interface states on GaN and AlGaN-based heterostructures. Since GaN and AlGaN are polar materials, both are characterized by a large bound polarization charge on the order of 1013 charges/cm2 that requires compensation. The key is therefore to control the compensation charge such that the electronic states do not serve as electron traps or affect device performance and reliability. Band alignment modeling and measurement can help to determine the electronic state configuration. In particular, band bending can determine how the polarization bound charge is compensated; however, the band bending is extremely sensitive to the specific processing steps such as cleaning, dielectric or metal deposition, postdeposition or postmetallization treatments, which affect oxygen coverage, carbon contamination, structural defects, bonding configurations, defect states, absorbates, and Fermi pinning states. In many cases, the specific effects of these treatments on the surface and interface states are not entirely clear as the nature of the electronic states has been obscured in complexity and subtlety. Consequently, a more systematic and methodical approach may be required.
    Journal of Vacuum Science & Technology A Vacuum Surfaces and Films 09/2013; 31(5):050807-050807-29. DOI:10.1116/1.4807904 · 2.14 Impact Factor
  • Xin Liu, Sean W. King, Robert J. Nemanich
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    ABSTRACT: The thermal stability of 7 nm Ti, Pt, and Ru interfacial adhesion layers between Cu film (10 nm) and a Ta barrier layer (4 nm) has been investigated. The barrier properties and interfacial stability have been evaluated by Rutherford backscattering spectrometry (RBS). Atomic force microscopy was used to measure the surfaces before and after annealing, and all the surfaces are relatively smooth which excludes islanding or dewetting phenomena as a cause of the instability. The RBS showed no discernible diffusion across the adhesion layer/Ta and Ta/Si interfaces which provides a stable underlying layer. For a Ti interfacial layer, RBS indicates that during 400 °C annealing, Ti interdiffuses through the Cu film and accumulates at the surface. For the Pt/Cu system, Pt interdiffusion is detected which is less evident than Ti. Among the three adhesion layer candidates, Ru shows negligible diffusion into the Cu film indicating thermal stability at 400 °C.
    Journal of Vacuum Science & Technology B Microelectronics and Nanometer Structures 01/2013; 31(2):2205-. DOI:10.1116/1.4792523 · 1.36 Impact Factor

Publication Stats

12k Citations
841.22 Total Impact Points


  • 2007–2014
    • Arizona State University
      • Department of Physics
      Phoenix, Arizona, United States
  • 1986–2014
    • North Carolina State University
      • • Department of Materials Science and Engineering
      • • Department of Physics
      Raleigh, North Carolina, United States
  • 2006
    • Dongguk University
      Sŏul, Seoul, South Korea
  • 2004–2005
    • Duke University
      • Department of Chemistry
      Durham, NC, United States
  • 1992–1996
    • Duke Raleigh Hospital
      Raleigh, North Carolina, United States
  • 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
  • 1978–1986
    • Palo Alto Research Center
      Palo Alto, California, United States
    • Massachusetts Institute of Technology
      Cambridge, Massachusetts, United States
  • 1984
    • Xerox Corporation
      Norwalk, Connecticut, United States
  • 1977
    • University of Illinois at Chicago
      • Department of Physics
      Chicago, IL, United States
  • 1976–1977
    • University of Chicago
      • James Franck Institute
      Chicago, IL, United States