bluuebunny/crossref_metadata_2025 huggingface dataset:
Chemical bonding and reaction at metal/polymer interfaces
Authors: Ho P. S. , Hahn P. O. , Bartha J. W. , Rubloff G. W. , LeGoues F. K. , Silverman B. D.
Published: July 2002

A combination of surface spectroscopy and microanalytical techniques have been used to investigate the chemical and material characteristics of interfaces formed between metal and a high temperature polymer, polyimide. Results reveal significant chemical reactivity at the interface, as manifested by intermixing and cluster formation. The extent of the material reaction is strongly influenced by the bonding characteristics between metal and the polyimide. Results on Cu and Al are reviewed to illustrate the chemical trend due to increasing reactivity.
Low temperature adsorption of CO and O2 on Ni(100) and Ni(111): Evidence for precursors
Authors: Shayegan M. , Glover R. E. , Park Robert L.
Published: July 2002

Studies of the adsorption of O2 and CO on different faces of single crystal Ni held at T≂6 K are reported which provide direct evidence for a precursor adsorption preceding chemisorption. Values of the work function were obtained using the field-emission retarding potential method as Ni surfaces held at 6 K were exposed to O2 and CO and, subsequently, as the gas covered surfaces were annealed. Comparison with results for chemisorbed surfaces formed by gas exposure at 77 K indicates stabilized precursor adsorption phases at 6 K for O/Ni(111), O/Ni(100), and CO/Ni(111). Starting at temperatures on the order of 20 K, these convert at appreciable rates to the usual chemisorption phases. Analysis of the temperature and time dependence of the reaction rates indicates activation energies EA of approximately 13, 6, and 4 meV for O/Ni(111), O/Ni(100), and CO/Ni(111), respectively. Precursor adsorption was not observed for CO/Ni(100). Presumably the activation energy, if it exists, is too small for effective stabilization at 6 K.
Calibration and characterization of Bayard–Alpert gauges operating in high magnetic fields
Authors: Pickles W. L. , Hunt A. L.
Published: July 2002

Standard Bayard–Alpert gauges have been successfully operated for several months in 0.3–0.7 T magnetic fields at eleven locations near the plasma edge of the Tandem Mirror Experiment-Upgrade (TMX-U). After individual calibration in the local TMX-U magnetic field, the gauges clearly measure gas density. One of these eleven gauges has been studied extensively and has maintained calibration within 12% during this period of operation. All gauge filaments are tungsten and are heated with direct current. The gauge housing allows operation in the low density plasma outside the limiter radius by thermalizing the neutral gas that enters the gauge and by preventing plasma from entering the gauge. Changing the orientation of the gauge with respect to the magnetic field changes the gauge calibration, or effective sensitivity, by as much as a factor of 100. Only some orientations of the filament collector plane with respect to the magnetic field direction allow calibrated operation as a pressure gauge. This range of angles is approximately from 20° to 50°. Each of the eleven gauges was oriented to produce a usable sensitivity, then calibrated for the magnetic field effects at that position. After initial operation in the magnetic field, a small recalibration of less than 10% for permanent filament distortion was necessary for the unshielded gauge. For D2, CH4, Xe and Kr gas, the measured recalibration factor to the gauge sensitivity in the same high magnetic field varied only 16% rms about the average of 9.7 for the unshielded gauge. Repeated measurement of the magnetic recalibration for each of the species over a 1 month period showed less than 12% variation.
A review of recent advances in solid film lubrication
Authors: Spalvins T.
Published: July 2002

Thin, adherent sputtered MoS2 and ion plated metallic (Au, Ag, Pb) lubricating films are primarily used in precision contacting triboelement surfaces where wear debris formation is critical and high reliability requirements have to be satisfied. Detailed structural and compositional characterization of solid film lubricants is of prime importance. It is this information from the nano–micro–macro level which is needed to interpret and improve the frictional behavior and assure long endurance lives. The purpose of this paper is to summarize in a concise review the solid lubricant film structure and morphology and their effects on the tribological properties of the lubricant systems. The tribological performance of thin lubricating films has significantly advanced through progressive understanding of the film parameters such as adhesion, cohesion, interface formation, nucleation and microstructural growth, critical film thickness and substrate finish, and temperature. Sputtered MoS2 and ion plated Au, Ag, and Pb films are separately discussed and evaluated in terms of the above film parameters to establish the most desirable film structures and thicknesses in order to achieve effective lubrication.
Methods in semiconductor surface chemistry
Authors: Bozack M. J. , Muehlhoff L. , Russell J. N. , Choyke W. J. , Yates J. T.
Published: July 2002

Methods for studying semiconductor surface chemistry are presented. It is shown that adsorption and desorption kinetic measurements, when combined with Auger spectroscopy, can give useful insights into fundamental elementary surface kinetic processes which are important in understanding the behavior of complex chemical vapor deposition, plasma vapor deposition, or reactive ion etching processes. Techniques for crystal preparation, mounting, temperature control, and reaction kinetic measurements are given using examples from the adsorption and reaction of propylene with Si(100). An illustration of the manipulation of active site availability on Si(100) is described.
Adhesion and toughness of protective coatings
Authors: Laugier M. T.
Published: July 2002

Coatings must be both tough and adherent to afford mechanical protection under tribological conditions. Adhesion energies of TiN protective coatings on cemented carbides produced by chemical vapor deposition and physical vapor deposition techniques are determined using an energy formulation of the scratch test. Toughness of the coatings is determined from Hertzian indentation with flat punches; behavior of coatings under sliding Hertzian loads is considered.
Energy distribution of primary backscattered electrons in Auger electron spectroscopy
Authors: Jousset D. , Langeron J. P.
Published: July 2002

One of the major problems for the quantification of Auger electron spectroscopy is the accurate subtraction of the background under the Auger peaks. Although many studies have been done on the energy distribution of electrons emitted by the true secondary or Auger internal sources, the shape of the primary backscattered electron distribution has yet been completely reproduced only for aluminum with Monte Carlo calculations. We develop a simple transport model where elastic and inelastic scattering are separated, following Tougaard and Sigmund [Phys. Rev. B 25, 4452 (1982)], and which gives the shape of the energy spectrum in the off-peak region with a diffusion approximation. This allows a measurement of the influence of physical parameters, like elastic and inelastic mean free paths and stopping power. Concurrently, we compare calculations with experimental spectra of copper, and propose to fit the primary induced background with an exponential law.
Ion enhanced reactive etching of tungsten single crystals and films with XeF2
Authors: Bensaoula A. , Strozier J. A. , Ignatiev A. , Yu J. , Wolfe J. C.
Published: July 2002

The etching of W(100) single crystals and sputter-deposited tungsten films by XeF2 has been investigated with and without inert gas ion bombardment. The surface fluorine was measured by Auger electron spectroscopy as a function of pressure (from low 10−8 to 10−4 Torr), and temperature (80–1300 K). The fluorine coverage was found to be near one monolayer at 170 K and decreased to 4% coverage at 1300 K. The pressure dependence showed a maximum coverage for sputter-deposited films at 6×10−6 Torr. Quartz-crystal microbalance measurements of etch rates of sputter-deposited W films under different ion fluxes, XeF2 pressures, ion beam angles, and temperatures have been measured and are consistent with a kinetic model of the etch process. The model, which is damage driven, reproduces well both the surface fluorine concentration and the measured etch rates with and without ion bombardment.
High-coverage surface phases of tellurium on Ni(111)
Authors: Samanta P. , Unertl W. N.
Published: July 2002

The complex surface phases formed when tellurium is adsorbed to high coverage (>0.4 monolayer) on Ni(111) have been studied using a mirror electron microscope–low-energy electron diffraction apparatus and Auger electron spectroscopy. The unit meshes of the complex overlayer structures all have one side along the [1,−1] surface direction with length equal to the Te–Te nearest-neighbor spacing in the (√3×√3)R30 structure and one side along the [11] direction with lengths of 10, 11, 13, 14, and 16 Ni–Ni nearest-neighbor spacings. These one-dimensional coincidence meshes can be described in terms of ordered dislocation structures in a compressed hexagonal Te unit mesh. Two intermediate phases with unequal diffraction beam spacings are also observed and transform with a small hysteresis into phases with equal spot spacings.
The tribological properties of MoS2 coatings in vacuum, low relative humidity, and high relative humidity environments
Authors: Panitz J. K. G. , Pope L. E. , Lyons J. E. , Staley D. J.
Published: July 2002

We have rf-sputter deposited MoS2 coatings onto stainless-steel plates using two extreme combinations of deposition conditions. Raman spectroscopy indicates that there is a small but significant difference in the number of sulfur–sulfur bonds and the amount of amorphous material present in the two types of coatings. The friction and wear properties were evaluated within five days of deposition and after being stored for 150 days in 35%–45% relative humidity followed by over 75 days in (1) 2% or (2) 98% relative humidity environments. The more crystalline material had a coefficient of friction of 0.085±0.017 in lab air and 0.06±0.005 in ultrahigh vacuum. For lab air testing the coefficient of friction increased with wet storage to 0.10±0.01, and the wear life decreased by a factor of 3 for dry storage and by a factor of 10 for wet storage. The MoS2 material with the larger amount of amorphous material has a coefficient of friction of 0.10±0.013 which increased to 0.14±0.04 for storage in the wet environment. The wear life of the MoS2 coating with the greater amount of amorphous material improved significantly (by 100%) for storage in the wet environment. These results are consistent with the observations of others who noted that water vapor promotes the conversion of MoS2 to MoO3.
Ion bombardment of polyimide films
Authors: Bachman B. J. , Vasile M. J.
Published: July 2002

Surface modification techniques such as wet chemical etching, oxidizing flames, and plasma treatments (inert ion sputtering and reactive ion etching) have been used to change the surface chemistry of polymers and improve adhesion. With an increase in the use of polyimides for microelectronic applications, the technique of ion sputtering to enhance polymer-to-metal adhesion is receiving increased attention. For this study, the argon-ion bombardment surfaces of pyromellitic dianhydride and oxydianiline (PMDA–ODA) and biphenyl tetracarboxylic dianhydride and phenylene diamine (BPDA–PDA) polyimide films were characterized with x-ray photoelectron spectroscopy (XPS) as a function of ion dose. Graphite and high-density polyethylene were also examined by XPS for comparison of C 1s peak width and binding-energy assignments. Results indicate that at low ion doses the surface of the polyimide does not change chemically, although adsorbed species are eliminated. At higher doses the chemical composition is altered and is dramatically reflected in the C 1s spectra where graphiticlike structures become evident and the prominent carbonyl peak is reduced significantly. Both polyimides demonstrate similar chemical changes after heavy ion bombardment. Atomic composition of PMDA–ODA and BPDA–PDA polymers are almost identical after heavy ion bombardment.
The effect of a valence-band offset on potential and current distributions in HgCdTe heterostructures
Authors: Kraut E. A.
Published: July 2002

A simplified model of current transport in diffusion limited abrupt mercury cadmium telluride (MCT) pn heterojunctions is used to show that n-type doping should be preferred for the narrow-band-gap detector layer in a pn-heterojunction photodiode because most of the difference in the energy band gaps between narrow- and wide-band-gap MCT alloys occurs as a discontinuity at the conduction-band edges. Although p-type doping for the narrow-band-gap layer would result in a smaller dark current, the large conduction-band barrier that reduces the dark current also impedes the collection of light generated minority-carrier photoelectrons. For diodes operating in the drift-diffusion regime, an examination of D* shows that the reduction in minority-carrier photocurrent due to the large conduction-band barrier more than offsets the gain in R0A due to the reduced dark current. This indicates that holes should be used as the minority photocarriers because of the small valence-band offset. The resulting current transport will be essentially like that for a homojunction.
Surface photovoltage on Si(111)-(7×7) probed by optically pumped scanning tunneling microscopy
Authors: Hamers R. J. , Markert K.
Published: July 2002

Scanning tunneling microscopy (STM) is combined with optical excitation techniques to probe spatially resolved, nonequilibrium electronic transport processes at Si(111)-(7×7) surface. Photoexcited carriers separate in the subsurface space-charge region, producing a surface photovoltage which is detected using the STM tip as a potentiometer. While the photovoltage is uniform on well-ordered regions of Si(111)-(7×7), strong decreases are observed near virtually all defects. Differences in the functional dependence of the photovoltage on the illumination intensity are also observed. The spatial dependence of the photovoltage primarily results from spatial variations in the local surface recombination rate.
Electron energy-loss spectral analysis of diamond and diamond-like carbon films
Authors: Wang Yaxin , Hoffman R. W. , Angus John C.
Published: July 2002

The characteristic electron energy-loss features of hydrogenated diamond-like carbon materials (a-C:H) and crystalline diamond films have been studied. The a-C:H films were grown by radio-frequency self-bias plasma-enhanced chemical vapor deposition from methane. The a-C:H films had hydrogen concentrations from 28 to 44 at. % and mass densities from 1.45 to 1.68 g/cm3. We find that in the a-C:H samples, increasing hydrogen content increases the fraction of carbon sp3 sites. The crystalline diamond films were grown by hot-filament-assisted chemical vapor deposition and the hydrogen concentration in these samples is less than 1 at. %. The electron energy-loss spectra showed the diamond films were a mixed phase material containing both a diamond-like phase and crystalline diamond. The main energy-loss peaks for the diamond-like component are caused by π and (π+σ) electron plasma resonances in the ranges from 3.3 to 4.4 eV and from 21.1 to 23.2 eV, respectively. The mass density of the diamond-like component in the crystalline diamond films as determined from the energy of the (π+σ)- plasmon is approximately 1.9 g/cm3. The characteristic energy loss features of crystalline diamond are the band-gap transition of about 5 eV and the surface and bulk plasmon energy losses at 23 and 34 eV, respectively. A σ-electron interband transition peak from the valence band to the conduction band in the energy range from 14–17 eV has been observed from both diamond-like and crystalline diamond films.
Low resistivity indium–tin oxide transparent conductive films. I. Effect of introducing H2O gas or H2 gas during direct current magnetron sputtering
Authors: Ishibashi S. , Higuchi Y. , Ota Y. , Nakamura K.
Published: July 2002

When an inline sputtering system is used to make conductive transparent ITO film by the direct current (dc) magnetron sputtering method, it was found that the partial gas pressure of H2O affected the properties of deposited films. When the substrate temperature is at or below 200 °C, the control of H2O partial gas pressure is especially important. Using room temperature substrates, an addition of 2×10−5 Torr of H2O in the sputtering process could form ITO films with good repeatability at a low resistivity of 6.0×10−4 Ω cm. By adding H2O gas, it was possible to solve the issue of increased resistivity in thicker films. The films with added H2O gas have H element immersed into the film and have high carrier concentration. Film transmittance stayed constant with or without H2O gas addition. Similar effect was observed by adding H2 gas instead of H2O gas.
Vacuum particle generation and the nucleation phenomena during pumpdown
Authors: Chen Degang , Hackwood Susan
Published: July 2002

This paper explores the source of an unexpectedly large number of particles found while examining the rough pumping cycles of a vacuum system. It is proposed that these particles are generated through nucleation of moisture onto fine particles during pumpdown, and that turbulence enhances this process. A brief discussion about the particle monitor used for data acquisition and a review of previous experimental results on the dependency of particle generation on turbulence is included. The body of the paper contains experimental results supporting the nucleation hypothesis, and a discussion on the effects and prevention of particle nucleation. The experimental results include a comparison of particle generation for two gases of similar original particle content but different humidity levels, reduction of particle count using a molecular sieve to remove the moisture in the chamber, and a systematic change of the relative humidity (by adding or removing moisture) in the chamber.
The anodic vacuum arc and its application to coating
Authors: Ehrich H. , Hasse B. , Mausbach M. , Müller K. G.
Published: July 2002

A steady vacuum arc discharge is obtained by a special design of the electrodes. This new type of arc discharge is ignited in vacuum and is sustained by metal vapor produced at a consumable anode. The new discharge generates a gas- and droplet free metal vapor plasma expanding into the ambient vacuum (10−4 mbar) and producing thin metallic films at the surface of substrates. An analysis of the metal–plasma at the position of a possible substrate for different materials (Al, Cu, and Ag) and arc currents >20 A leads to the following results: electron densities, 1015 –1017 /m3 ; electron temperatures, 0.2–1 eV; degree of ionization, 1%–25%; ion energies, 5 eV. Coatings are generated with deposition rates up to 100 nm/s and show the following properties: purity 99.9 %, polycrystalline structure with grain sizes between a few and some 100 nm, within 2% density of the respective bulk material, good optical properties, and an electrical conductivity rather close to that of the bulk material. The coatings show good adhesion, which can be enhanced by accelerating the ions towards the substrate.
High-resolution electron microscope observation of ‘‘atomic bridge’’ formation between two interacting gold particles
Authors: Murooka Ken-ichi , Mitome Masanori , Tanishiro Yasumasa , Takayanagi Kunio
Published: July 2002

Structures of two interacting fine particles are observed at atomic level ‘‘in situ’’ by high-resolution, ultrahigh vacuum, electron microscopy. When a small particle is distant from the surface of a large particle by several atomic distances, atoms at the surface of the small cluster are attracted toward the surface of the large particle, and form a ‘‘bridge’’ between the two. This observation indicates that the interaction between two surfaces apart can be strong enough to modify their structure locally.
Low temperature (∼400 °C) growth of polycrystalline diamond films in the microwave plasma of CO/H2 and CO/H2/Ar systems
Authors: Muranaka Yasushi , Yamashita Hisao , Miyadera Hiroshi
Published: July 2002

In order to elucidate the growth conditions for pure diamond of good crystallinity, the correlation of the properties of deposited films and gas phase species in microwave plasma of CO/H2 and CO/H2/Ar systems was investigated through film characterization and optical emission spectroscopic measurements. It was found that the increase of gas phase atomic hydrogen and the suppression of gas phase acetylene were effective for the growth of pure diamond of good crystallinity. Low temperature growth was proposed to realize these growth conditions. It was confirmed that diamond films with good crystallinity and optical transparency could be synthesized at 410 °C (diamond film growth was possible even at 365 °C). The growth rate was accelerated in a CO/H2/Ar system (0.33 μm/h at 410 °C), which was several times faster than that obtained in a CO/H2 system (0.14 μm/h at 450 °C).
Space simulation for the study of material outgassing
Authors: Gordon Lloyd B. , Little Jon C. , Phillips Robert G.
Published: July 2002

The design of a system to study the outgassing characteristics of materials under a simulated space environment is described. A vacuum chamber simulates the pressure experienced by spacecraft in earth orbit and on the lunar surface. The samples are mounted on a cold/hot surface whose temperature can be varied between −200 and +200 °C. Windows allow the application of ultraviolet radiation. The pressure in the chamber and the material temperatures are monitored, and the outgassing products are analyzed with a quadrupole mass spectrometer. A specially designed sampling system allows the mass spectrometer to automatically measure gases in the simulation chamber for a wide range of dynamically varying pressures. Applications of the space simulation chamber to dielectric-material outgassing characterization under the space environment conditions are discussed.
Collimated magnetron sputter deposition
Authors: Rossnagel S. M. , Mikalsen D. , Kinoshita H. , Cuomo J. J.
Published: July 2002

A technique to deposit films compatible with lift-off patterning techniques and hole filling has been developed for large magnetron sputter deposition systems. This technique allows the patterned sputter deposition of Cu films, as well as other relevant metal or alloy systems, using conventional lift-off lithography techniques. To overcome the gas scattering effects which are prevalent in the normal range of magnetron operation and which would prohibit lift-off of a photoresist mask by coating the sides of the mask, a hollow cathode electron source has been implemented near the magnetron cathode which allows operation (i.e., sputtering) of the cathode at full power in the low 10−4 Torr range. At this pressure, the mean free path for the sputtered atoms greatly exceeds the typical cathode-to-sample throw distance of 5–7 cm. To overcome the broadness of the sputtering target and the cosine-like distribution of the emitted, sputtered atoms, an array of collimating tubes is placed just above the sample to restrict the depositing flux to normal incidence ±5°. Atoms whose trajectory is more than 5° from normal are deposited on the inner surfaces of the collimators. The collimators are water cooled and grounded, which significantly reduces the thermal load on the samples due to electron bombardment. The lift-off samples must be backed and moved behind the collimators so as to eliminate shadowing and nonuniformity effects. Measured deposition rates for Cu are several hundred angstroms per minute at 1.5 kW discharge power for a 15 cm diam magnetron at 10−4 Torr using a 4:1 aspect ratio collimator. No degradation of the lift-off mask is observed, and the resulting, patterned films have little if any debris from deposition on the sides of the mask structures. Hole filling at aspect ratios up to 3.0 has been observed. The technique scales to virtually any size cathode, and has been tested on manufacturing scale systems with cathode diameters up to 30 cm and at powers approaching 30 kW.
Properties of (Ti1−xAlx)N coatings for cutting tools prepared by the cathodic arc ion plating method
Authors: Tanaka Y. , Gür T. M. , Kelly M. , Hagstrom S. B. , Ikeda T. , Wakihira K. , Satoh H.
Published: July 2002

(Ti,Al)N coatings with several Ti/Al ratios were deposited on Si and WC–Co substrates by the cathodic arc ion plating method. The crystal structure was found to be cubic B1 type, which is isostructural with the titanium-based nitrides. Morphology of the (Ti0.4Al0.6)N and TiN films was investigated, using transmission and scanning electron microscopy. The films seemed to have a less columnar structure than expected. The (Ti,Al)N films containing less than 75 mol % AlN had higher hardness than for the pure TiN films. Similarly, (Ti,Al)N coatings displayed superior oxidation resistance at elevated temperatures. Overall, (Ti,Al)N coated cutting tools offer significantly better performance characteristics compared to the tools with TiN coatings.
GaAs deposition on the (100) and (110) planes of gold by electrochemical atomic layer epitaxy: A low-energy electron diffraction, Auger electron spectroscopy, and scanning tunneling microscopy study
Authors: Villegas Ignacio , Stickney John L.
Published: July 2002

Preliminary studies on the deposition of GaAs by electrochemical atomic layer epitaxy (ECALE) were performed. ECALE is based on the alternated underpotential deposition (UPD) of atomic layers of different elements to form a compound. Oxidative UPD of As and reductive UPD of Ga on the low-index planes of gold were studied using Auger electron spectroscopy (AES), low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), and coulometry. AES and LEED were performed in an ultrahigh vacuum (UHV) surface analysis instrument interfaced to an electrochemical cell in an antechamber. This instrument configuration allowed the electrochemical treatment of the samples and their subsequent analysis in UHV without the need to transfer the samples through air. STM was performed under nitrogen at atmospheric pressure. AES and coulometry were used for surface composition analysis while LEED and STM provided structural information. The substrate was a gold single-crystal electrode with three oriented faces, each to a different low-index plane. Oxidative UPD of arsenic was observed only on the (100) and (110) faces. The resulting structures were a Au(100)(2×2)-As at 1/4 coverage and an Au(110)c(2×2)-As at 1/2 coverage. Reductive UPD of Ga was observed on all three faces, although it resulted in disordered layers of Ga oxide upon removal of the substrate from solution, due to partial oxidation of the Ga in contact with water in the absence of potential control. Stoichiometric coverages of Ga and As were obtained on the (100) and (110) surfaces when Ga was underpotentially deposited on the As covered surfaces [Au(100)(2×2)-As at 1/4 coverage and Au(110)c(2×2)-As at 1/2 coverage]. Structures displaying (2×2) and c(2×2) LEED patterns were observed on the (100) and (110) faces, respectively.
Role of substrate excitation in the photochemistry of dioxygen on Ag(110)
Authors: Hatch S. R. , Campion Alan
Published: July 2002

The rates of O2 photodissociation and photodesorption on Ag(110) under UV irradiaton have been measured with temperature programmed desorption and high-resolution electron energy loss spectroscopy. The alignment of O2 adsorbed on Ag(110) permits polarization measurements at normal incidence. The rates are found to be independent of the azimuthal orientation of the electric field of the light. Dependences on angle of incidence are consistent with the angle dependence of metal absorption predicted by Fresnel’s equations. These observations rule out direct intra-adsorbate excitation and suggest a substrate mediated mechanism. Similar photoexcitation thresholds suggest that both channels are activated by a common process. A model is proposed whereby substrate charge transfer induces dissociation. Dissociating adatoms, in competition with molecular oxygen for adsorption sites, induce molecular desorption. This model reproduces the dependences on initial O2 coverage and extent of irradiation for both channels and allows calculation of the photodissociation cross section.
Reactive ion etching (CF4+O2 plasma) induced deep levels in metal–oxide–semiconductor devices
Authors: Misra D.
Published: July 2002

A reduction in device dimensions requires more accurate etching procedures. Reactive ion etching (RIE) provides many of the needed improvements. The energetic ions and photons produced by the glow discharge plasma of RIE, individually or in combination, can create lattice damage thereby forming trapping centers for electrons and holes at the Si–SiO2 interface, as well as in the bulk silicon. In this work the capacitance–voltage (C–V) measurement techniques and deep level transient spectroscopy (DLTS) were used to investigate the interface trapping sites and the bulk defect centers at or near to the Si–SiO2 interface region, produced by the energetic ions and/or photons present in the reactive ion etching. An electron trap level, ascribed to a bulk defect, was detected using the DLTS technique. In this study two types of metal–oxide–semiconductor (MOS) test structures were used to investigate the origin of damage. It has been observed that a major source of RIE damage in MOS structures and to the underlying silicon substrate can be energetic photons.
Effect of orientation on the Schottky barrier height of thermodynamically stable epitaxial metal/GaAs structures
Authors: Palmstro/m C. J. , Cheeks T. L. , Gilchrist H. L. , Zhu J. G. , Carter C. B. , Wilkens B. J. , Martin R.
Published: July 2002

The use of thermodynamically stable epitaxial metal/GaAs contacts fabricated by molecular-beam epitaxy has enabled detailed studies of Schottky barrier formation on well characterized and controlled structures. The effects of lattice mismatch, annealing and substrate orientation on the barrier height of Sc1−xErxAs semimetal contacts on n-GaAs are studied. The barrier height could be varied from ∼1.03 eV for Sc1−xErxAs films grown at 350–400 °C and annealed at ∼600 °C on (100) GaAs to ∼0.63 eV for films grown at ∼600 °C on (1̄1̄1̄) GaAs.
Measurements of the Cl atom concentration in radio-frequency and microwave plasmas by two-photon laser-induced fluorescence: Relation to the etching of Si
Authors: Ono Kouichi , Oomori Tatsuo , Tuda Mutumi , Namba Keisuke
Published: July 2002

Atomic chlorine concentrations in Cl2 plasmas have been measured by two-photon laser-induced fluorescence (LIF). Experiments were performed over a wide pressure range in rf, rf magnetron, and microwave electron cyclotron resonance (ECR) discharges. Absolute calibration was achieved by generating Cl atoms through UV photolysis of CCl4 with the same laser radiation. The LIF measurements showed that in the respective discharges, the Cl concentrations decreased and the corresponding Cl fractions increased with decreasing pressure: the measured fractions ranged from 0.3% to 0.7% in rf discharges, from 0.8% to 8% in magnetron, and from 1% to 2% in ECR. These results, together with electrical measurements of ion and electron energies and densities, demonstrated that the ratio of neutral Cl flux to ion flux toward the substrate decreased from 400:1 to 1:1, almost linearly with decreasing pressure in the three discharges. These results of plasma diagnostics are compared with the etching characteristics of heavily P-doped polycrystalline Si obtained.
Metal overlayers on organic functional groups of self-organized molecular assemblies. II. X-ray photoelectron spectroscopy of interactions of Cu/CN on 12-mercaptododecanenitrile
Authors: Jung D. R. , King D. E. , Czanderna A. W.
Published: July 2002

The interaction of evaporated copper overlayers, from 0.03 to 0.4 nm thick, with specific terminal functional groups of an organized molecular assembly (OMA) of HS(CH2)11CN formed on gold has been studied by x-ray photoelectron spectroscopy. For average copper coverages above 0.1 nm, the peak intensities show fair agreement with a model that assumes an increasing fraction of each increment of the deposited copper penetrates the OMA and resides at the OMA/Au interface. For lower coverages, a weak Cu(CN) interaction is indicated by shifts of the N 1s level and the C 1s high binding energy (HBE) shoulder to lower binding of as well as by the presence of a Cu 2p HBE shoulder.
Role of oxygen in the electron cyclotron resonance plasma-assisted chemical vapor deposition of diamond films
Authors: Youchison D. L. , Eddy C. R. , Sartwell B. D.
Published: July 2002

The effects of oxygen on the electron cyclotron resonance plasma-assisted chemical vapor deposition of diamond films on Si(100) substrates have been investigated in the CH4:O2:H2 system at 1.33 Pa and a substrate temperature of 500 °C. Various [O]/[C] volume fractions ranging from 0.5 to 2.0 as determined by partial pressures were investigated while maintaining a constant [C]/[H2] volume fraction of 0.67 for all depositions. Plasmas for each [O]/[C] ratio were characterized with optical emission spectroscopy. The quality of the diamond films was evaluated with micro-Raman spectroscopy, x-ray diffraction (XRD), and scanning electron microscopy. It was discovered that microcrystalline graphite and nanocrystalline diamond in a cauliflowerlike morphology were produced at 0.5<[O]/[C]<0.7. Pronounced 〈111〉 faceting (∼0.3 μm grain size) with positive micro-Raman and XRD results were obtained for 0.7<[O]/[C]<1.2. For [O]/[C]≳1.2, a fewer number of larger grained (∼0.5–0.8 μm) crystallites formed in a matrix of fine-featured, renucleated diamond. Correlations between plasma and diamond film characteristics for various [O]/[C] ratios are presented. An empirical model which describes the production of hydrogen and atomic oxygen in an electron cyclotron resonance source from the dissociation of CH4 and O2, respectively, is also presented.
Electrophoretic deposition of pure MoS2 dry film lubricant coatings
Authors: Panitz Janda K. G. , Dugger M. T. , Peebles D. E. , Tallant D. R. , Hills C. R.
Published: July 2002

Electrophoresis can be employed to deposit a wide variety of materials including MoS2 coatings that exhibit properties comparable to the properties of sputtered MoS2 coatings used as lubricants for vacuum applications. Coatings which display coefficients of friction as low as 0.03 can be deposited from an aqueous suspension containing approximately 2.5 wt %, micrometer-sized MoS2 particles stablized with approximately 500 ppm of a nonionic surfactant. Uniform coatings with appropriate thicknesses can be deposited on nonplanar surfaces in minutes with minimal equipment. The morphology of the as-deposited coatings suggest that MoS2 is electrophoretically active as a result of a net positive surface charge along the basal plane.
Effects of O2, air, and CF4 plasmas on poly(etherketone) surfaces
Authors: Onyiriuka E. C.
Published: July 2002

The effects of molecular oxygen, air, and CF4 plasma treatments on the surface chemistry of poly(etherketone) have been studied by x-ray photoelectron spectroscopy. Oxygen or ambient air plasma treatment led to oxidation producing mainly surface ether, and carbonyl groups. The reaction with CF4 plasma resulted primarily in the formation of surface carbonates, CF2–CF2, and CF3 with CF2–CF2 as the dominant species. For the reaction with CF4 plasma, the experimental data indicated that cleavage of the polymer aromatic structure is extensive.
Chemical composition of electron-beam evaporated TiO2 films
Authors: Rao K. Narasimha , Mohan S. , Hegde M. S. , Balasubramanian T. V.
Published: July 2002

Chemical composition and optical properties of TiO2 films depend on deposition conditions. A detailed investigation has been made on the influence of deposition parameters, such as starting material, substrate temperature, and post deposition heating in air on the chemical composition of TiO2 films deposited by electron-beam evaporation of TiO and TiO2 in neutral and ionized oxygen. The chemical composition of the films has been analyzed by x-ray photoelectron spectroscopy and Auger electron spectroscopy. The composition of TiO2 films deposited in neutral oxygen were found to contain lower oxides of titanium in addition to TiO2 whereas films prepared in ionized oxygen were found to be stoichiometric TiO2.
Neutral pressure studies with a fast ionization gauge in the divertor region of the DIII-D tokamak
Authors: Klepper C. C. , Evans T. E. , Haas G. , Jackson G. L. , Maingi R.
Published: July 2002

An ionization gauge, specially designed to operate in the high magnetic fields of present-day tokamaks (1–6 T) and with electronics designed for fast time response and high noise rejection, was installed and operated in the new pumping plenum in the divertor region of DIII–D. This plenum, formed by a toroidally symmetric baffle, is used to compress neutrals to high pressures (≳1 mTorr) to allow for high particle removal rates when a pump is added inside the plenum. Pressures of 2–20 mTorr were measured with the fast gauge under the baffle, compared to less than 1 mTorr measured by a similar gauge also installed in the divertor but outside the baffle. A detailed description of the fast gauge, its operation, and its calibration is provided.
Nonstable behavior of widely used ionization gauges
Authors: Arnold P. C. , Borichevsky S. C.
Published: July 2002

This is the first in a set of related reports on (1) nonstable behavior of widely used ionization gauges, (2) causes of nonstability and nonreproducibility in widely used Bayard-Alpert (BA) gauges, and (3) a stable and reproducible BA gauge design with approximately a tenfold improvement in both stability of gauge calibration and reproducibility gauge-to-gauge compared to older ionization gauge designs. Thirteen widely used BA gauges and inverted magnetron gauges (IMGs) of eight different designs from five manufacturers were operated along with 29 BA gauges of a new design for thousands of hours each and periodically calibrated against a reference standard traceable to the National Institute of Standards and Technology. The older design BA gauges exhibited changes in calibration ranging from −57 to 72% relative to their initial calibration during the first 4000 h of operation and varied within this range over total operating periods of up to 14 000 h. The IMGs showed changes ranging from −90 to 148% relative to their initial calibration during the first 4000 h. A set of five glass BA gauges, nominally identical except for two different port diameters, differed by −20 to 32% from the average of their initial calibration values after a minimum of 48 h operation, and by −18 to 55% from their individual initial calibration values during 3500 h of operation. Because the new design gauges did not exhibit such nonstability using the same apparatus and calibration procedures and the same operating procedures except for the frequency of degas, our results demonstrate that these older design gauges significantly change calibration during long term use.
Photoemission study of evaporated CuInS2 thin films. II. Electronic surface structure
Authors: Scheer R. , Lewerenz H. J.
Published: July 2002

The electronic surface structure of evaporated CuInS2 films with different stoichiometries was investigated by photoelectron spectroscopy [x-ray and ultraviolet (XPS and UPS, respectively)]. The Fermi level position is observed to vary from EF−EV=1.3 eV for the In-rich to EF−EV=0.0 eV for the Cu-rich films. Valence band spectra of In-rich films can be interpreted according to theoretical band structure calculations in the literature. The electronic surface structure of Cu-rich films is determined by a CuS phase segregation which is displayed by an additional valence band emission structure. This phase is responsible for the semimetallic character of the Cu-rich films. A comparison of the energy level positions of Cu-rich and In-rich films is given according to a simple model. The removal of CuS by a KCN treatment is indicated by the complete recovery of the CuInS2 valence band structure. As a consequence highly efficient solar-to-energy conversion can be obtained from CuInS2 films of a wide as-deposited Cu-rich composition range.
Model for water outgassing from metal surfaces. II
Authors: Li Minxu , Dylla H. F.
Published: July 2002

The outgassing rate from an electropolished stainless steel (type 304) surface is measured after the surface is exposed to H2O vapor at pressures (p0) of 10−3–10 Torr for exposure periods (t0) of 3–600 min. The system is kept at 310, 350, or 390 K during H2O exposures and subsequent outgassing measurements. Our data show that the outgassing rate is proportional to pn0, where n=0.3, 0.26, 0.25 for T=310, 350, 390 K, respectively. The adsorption rate, defined as the quantity of H2O being adsorbed during exposures per unit time, is proportional to 1/t0. Continuing the previous work [Li and Dylla, J. Vac. Sci. Technol. A 11, 1702 (1993)] on correlating the outgassing with the source distribution of sorbed gas, we prove that the practical expression for the outgassing rate, Q(t)=Q10/tα, can be derived from a H2O concentration falling as (1/x)2α−1 with the spatial variable x defined as the distance away from the surface. The observed dependence of the outgassing rate on the exposure conditions is consistent with the predictions of this simple model.
Turbomolecular pump with an ultimate pressure of 10−12 Torr
Authors: Ishimaru Hajime , Hisamatsu Hiromi
Published: July 2002

An ultimate pressure of the order of 10−12 Torr using a turbomolecular pump was realized. The ultimate pressure of a turbomolecular pump with magnetic bearings is mainly limited by outgassing from heat generation of the rotor. The rotor temperature in operation is about 60 °C due to eddy-current loss in the magnetic suspensions. The rotor temperature was measured by thermovideo camera through an optical window. To reduce thermal outgassing of the rotor, the rotor must be cooled by radiation. The lower half of the rotor and the opposite stators were coated with SiO2 to a thickness of about 10 μm. This ceramic surface has high emissivity and good thermal heat exchange. The suspended rotor temperature during operation then dropped to about 25 °C. Also, the SiO2 coating enabled the rotor to be baked with more efficiency. The upper half of the rotor and the stators, and aluminum alloy housing were finished using a clean machining method known as the EL process, which helped reduce outgassing. These processes were applied by Seiko–Seik and Osaka Vacuum. Ultimate pressure of the turbomolecular pumps with turbobacking were of the order of 10−12 Torr, measured by a Leybold extractor gauge; best pressure was less than 2×10−12 Torr.
Friction and energy dissipation at the atomic scale: A review
Authors: Singer I. L.
Published: July 2002

Discussions of energy dissipation during friction processes have captured the attention of engineers and scientists for over 300 years. Why then do we know so little about either dissipation or friction processes? A simple answer is that we cannot see what is taking place at the interface during sliding. Recently, however, devices such as the atomic force microscope have been used to perform friction measurements, characterize contact conditions, and even describe the ‘‘worn surface.’’ Following these and other experimental developments, friction modeling at the atomic level—particularly molecular dynamics (MD) simulations—has brought scientists a step closer to ‘‘seeing’’ what takes place during sliding contact. With these investigations have come some answers and new questions about the modes and mechanisms of energy dissipation at the sliding interface. This article will review recent theoretical and experimental studies of friction processes at the atomic scale. Theoretical treatments range from simple, analytical models of two-dimensional, coupled ball-spring systems at 0 K, to more complex MD simulations of three-dimensional arrays of hydrogen- and hydrocarbon-terminated surfaces at finite temperatures.

Results are presented for the simplest yet most practical cases of sliding contact: sliding without wear. Sliding without friction is seen in weakly interacting systems. Simple models can easily explain the energetics of such friction processes, but MD studies are needed to explore the dynamics (excitation modes, energy pathways,...) of thermally excited atoms interacting in three-dimensional fields. These studies provide the first atomic-scale models for anisotropic friction and boundary lubrication. Friction forces at atomic interfaces must ultimately be measured at the macroscopic level; these measurements, which depend on the mechanical properties of the measuring system, are discussed. Two rather unique experimental studies of friction are also reviewed. The first employs a ‘‘surface force apparatus’’ to measure adhesion and friction between surfactant monolayers. The correlation of adhesion hysteresis and friction provides a new mechanism of friction; moreover, the interpretation for the effect—hysteresis from entanglement of the molecular chains during a phase transformation—implies that the dynamics are taking place at an accessible time scale (seconds to minutes). The second study extends the time domain at which friction can be measured to the nanosecond scale. A quartz-crystal oscillator is used to monitor the viscosity of monolayer liquids and solids against solid surfaces. Interfaces slip angstroms in nanoseconds. Modelers have suggested a variety of mechanisms for this atomic-scale friction process, from defect-mediated sliding to electron drag effects. The article ends by identifying the vast, barely charted time-space domain (micro-to-pico time and length scales) in which experiments are needed to further understand the dynamic aspects of friction processes.
Electron-stimulated and thermal desorption study of trimethylsilane from Si(100)
Authors: Campbell J. H. , Ascherl M. V. , Craig J. H.
Published: July 2002

The adsorption and decomposition of trimethylsilane, HSi(CH3)3, on Si(100) has been studied at T∼120 K for a variety of trimethylsilane exposures. The trimethylsilane molecule is not observed by quadrupole mass spectrometry during temperature programmed desorption from the Si(100) sample, but various fragments of trimethylsilane can be seen. The primary species seen desorbing during electron bombardment of the Si(100) surface were the H+, H−, and CH+3 ions. Both H+ and H− KEDs exhibit bimodal kinetic energy peaks, most likely due to hydrogen bound in multiple states. The bimodal H+ and H− kinetic-energy distributions (KEDs) exhibit an interesting reversal of intensities that suggests that the state giving rise to the low-energy peak in one KED gives rise to the high-energy peak in the other KED, and vice versa. Kinetic energy distributions for the CH+3 ions consisted of only one peak, indicating a high probability that the CH+3 originates from only one surface state. Our results indicate that electron-simulated desorption can be used as an adsorption state sensitive probe of chemical species on semiconductor surfaces.
Role of ions in reactive ion etching
Authors: Coburn J. W.
Published: July 2002

Energetic ion bombardment is responsible for the anisotropic etching which can be obtained in reactive ion etching. This has been recognized for many years but the detailed mechanisms involved in this process are still not well understood. In this paper, the various phenomena resulting from ion bombardment of a surface in a reactive gas glow discharge will be summarized. The discussion will be limited to chemical dry etching environments, that is, the products of the reactive gas-surface interaction are volatile at or slightly above room temperature. The phenomena which will be discussed are chemical sputtering, ion-induced mixing, ions as a source of reactants, physical sputtering, and the effect of prior ion bombardment on selected gas-surface reactions.