bluuebunny/crossref_metadata_2025 huggingface dataset:
Amorphous silicide formation by thermal reaction: A comparison of several metal–silicon systems
Authors: Holloway Karen , Sinclair Robert , Nathan Menachem
Published: July 2002

At some metal(M)–silicon interfaces, such as in Ti–Si and Ni–Si diffusion couples, an amorphous silicide forms at low annealing temperatures, while such a reaction does not occur at others, such as Mo–Si and Co–Si. As Co–Si and Ni–Si have similar phase diagrams, silicide crystalline structures, and lattice parameters, their differing behavior in this regard has motivated a comparative study. We have used cross-section transmission electron microscopy to investigate interfacial reactions in evaporated Ni–Si and Co–Si four-layer stacks. The structure of the Ni–Si as-deposited films show intermixed amorphous interfacial layers, similar to those observed in sputtered Ti–Si and Mo–Si multilayers. These interlayers grow on rapid thermal annealing at 250 °C for 1 s, forming an amorphous Ni–Si alloy. There are intermixed interfacial layers in the Co–Si stack as well; however, they are partially crystalline. A 250 °C anneal does not change this microstructure; however, the interlayers crystallize more fully during a 10-s anneal at 300 °C. These results are discussed, along with observations in sputtered Ti–Si and Mo–Si multilayers, to clarify the factors which determine the tendency of a M–Si system to undergo amorphization.
A new fast-response Hg vapor source for HgCdTe molecular-beam epitaxy growth
Authors: Wagner B. K. , Benz R. G. , Summers C. J.
Published: July 2002

A new technique is reported for producing a highly stable, fast-response Hg vapor source for high-quality HgTe and HgCdTe growth. The design principles of the Hg furnace are based on the fact that for choked flow conditions across an orifice the gas flow on the low-pressure side is directly proportional to the pressure on the upstream side of the orifice. Measurements show that this system has a response time of 10 s, a dynamic range of 10−6 to 10−3 Torr, and a long-term stability that exceeds our ability to measure with a conventional ion gauge. Additional measurements show a constant flux output for reservoir temperature changes of 20 °C, a stability of 0.1% over >3 h, and setpoint repeatability of 0.1%. Results on HgTe and homogeneous HgCdTe layer growth are presented.
Long-wavelength infrared detectors based on strained InAs–Ga1−xInxSb type-II superlattices
Authors: Mailhiot C. , Smith D. L.
Published: July 2002

We demonstrate that infrared detectors made from strained type-II superlattices consisting of III–V semiconductors can have favorable properties for long-wavelength (λc >10 μm) detection applications. We specifically consider InAs–Ga1−x Inx Sb strained-layer superlattices with x≊0.4 . This is a type-II superlattice where the conduction-band minimum of InAs is lower in energy than the valence-band maximum of Ga1−x Inx Sb. Electrons are localized in the InAs layers while holes are localized in the Ga1−x Inx Sb layers. Generally, in a type-II superlattice such as InAs–GaSb, large absorption coefficients cannot be achieved at the small values of band gap necessary for long-wavelength detection because the localization of electrons and holes in adjacent layers leads to small optical matrix elements. Therefore, small band gaps and large optical matrix elements appear to be two mutually exclusive requirements in the InAs–GaSb superlattice. Here, we show that it is possible to obtain large optical absorption coefficients at the values of band gap required for long-wavelength detection by taking advantage of internal lattice-mismatch induced strains present in InAs–Ga1−x Inx Sb superlattices.

This feature eliminates the principal difficulty associated with type-II superlattices as candidate materials for long-wavelength detection applications. In fact, the near-threshold optical absorption coefficient of the InAs–Ga0.6 In0.4 Sb strained-layer superlattice is found to be as large as that of conventional Hg1−x Cdx Te alloys in the λc ≊ 10–12 μm region. Moreover, the electron effective mass of the InAs–Ga0.6 In0.4 Sb strained-layer superlattice is found to be nearly isotropic and much larger (m*super/m ≊0.05 at λc ≊10 μm) than that of the Hg1−x Cdx Te alloy. This value of the electron effective mass is a favorable feature of the InAs–Ga0.6 In0.4 Sb strained-layer superlattice since it is large enough to lead to small diode tunneling currents, yet it is small enough to lead to large mobilities and diffusivities. As a result, leakage currents are expected to be much less of a problem in infrared detector diodes based on InAs–Ga0.6 In0.4 Sb strained-layer superlattices than they are in conventional Hg1−x Cdx Te-based infrared detectors. Overall, InAs–Ga1−x Inx Sb strained-layer superlattices are expected to have superior materials properties for long-wavelength detection than the Hg1−x Cdx Te alloy.
Low-frequency turbulent transport in magnetron plasmas
Authors: Sheridan T. E. , Goree J.
Published: July 2002

We report the results of an experiment to determine if low-frequency turbulence (frequencies less than the ion plasma frequency) seen in magnetron plasmas is responsible for the transport of electrons across magnetic field lines. This is done by finding the scaling of the electron confinement time τ on the mean-square electric field fluctuation 〈‖δE‖2〉. Turbulent transport models predict the scaling should be τ∝〈‖δE‖2〉−1. Data were taken at a constant pressure of 1.1 Pa of argon and for discharge current densities from 25 to 150 A/m2. Density fluctuations were recorded, and the maximum rms level was <5.2%. Measured values of τ ranged from 0.65 to 0.85 μs as the discharge current density was varied over its full range. Assuming the observed turbulent spectrum is composed of ion acoustic waves, we find that τ∝〈‖δE‖2〉−0.15, quite different from the prediction. We conclude low-frequency turbulence is not responsible for cross-field electron transport.
Temperature effects on structure and optical properties of radio-frequency sputtered VO2
Authors: Razavi A. , Hughes T. , Antinovitch J. , Hoffman J.
Published: July 2002

Vanadium dioxide undergoes a first-order phase transformation near 67 °C. This phase transformation is accompanied by significant changes in optical properties. The most pronounced changes occur between IR wavelengths of 2 and 12 μm; therefore, thin films of this material appear very attractive for uses in IR optical switching devices. By knowing the effects that deposition temperature has on the optical properties and relating these properties to the film microstructure, a process for fabricating films with optimal properties and desired microstructure can be developed. Vanadium oxide films were deposited on sapphire substrates by rf magnetron sputtering. At deposition temperatures of 350 °C, polycrystalline films were observed. X-ray diffraction analysis indicated VO2 and V4O7 to be the phases present, and optical characterization showed a contrast in transmission of <20% between the switched and unswitched states. As the deposition temperature was increased, dendritic growth was observed. Film composition was VO2 and V6O11 when the deposition temperature was 500 °C with improved optical properties at higher deposition temperatures. The changes in optical properties, microstructure, and composition shows the dependence that vanadium oxide has on the deposition temperature.
Stress state of chromium nitride films deposited by reactive direct current planar magnetron sputtering
Authors: Fabis P. M. , Cooke R. A. , McDonough S.
Published: July 2002

Chromium nitride films were deposited on glass substrates using reactive dc planar magnetron sputtering. Film stress-state evaluation permitted a two-level classification into compressive and transition categories. Maximum stress levels in these compressive category films were in the (−) 0.83 to (−) 14.4 GPa range. Sputtering parameter weighting equations indicated the deposition parameters which influenced stress were sputtering pressure, sputtered flux incidence angle, film thickness, and the interactions between these parameters. Subsequent studies indicated substrate bias to be important in the −50 to −250 V interval. Thermal stresses contributed a compressive component of (−) 0.7 GPa which was approximately 4% of the peak compressive stress. Generally, deposition conditions promoting high normalized energies (energetic particle bombardment of the film) produced hard coatings which were highly stressed (compressive) with low resistivities.
Poly(methyl methacrylate) degradation during x-ray photoelectron spectroscopy analysis
Authors: Buchwalter L. P. , Czornyj G.
Published: July 2002

Poly(methyl methacrylate) (PMMA) was chosen as a model lithographic material to study the effect of A1 Kα radiation and the thermal (flood gun) electron flux on polymer surface. The main chemical changes, which can occur in polymers by radiation, are (1) main-chain scission, (2) cross linking, and (3) volatile product formation and cyclization. The data shows that, although the flood gun electrons do not affect the PMMA surface, the x-ray radiation causes degradation in molecular weight by main-chain scission.
Scanning tunneling microscopy and transmission electron microscopy studies of Au and Pd clusters grown on a clean graphite surface
Authors: Humbert A. , Dayez M. , Sangay S. , Chapon C. , Henry C. R.
Published: July 2002

Scanning tunneling microscopy (STM) has been used to image gold and palladium clusters deposited under ultrahigh vacuum (UHV) conditions on clean cleaved surfaces of natural graphite single crystals. Extensive transmission electron microscopy (TEM) studies were performed to determine the growth conditions. Moreover each sample was checked by ex situ TEM after each in situ STM study. The overall shape of the largest isolated clusters imaged by STM (100–200 Å) is consistent with TEM observations: triangular or hexagonal outlines and clusters sitting along surface steps are elongated by coalescence. STM also reveals that they have a height versus diameter ratio about 0.1. Smallest clusters (10–20 Å) are imaged with atomic resolution simultaneously with the graphite lattice. They are close packed and 2–3 atomic layers high. On occasion, two-dimensional Pd islands are observed. They have an hexagonal non-close-packed arrangement.
Performance of thermal cavitation technique for fuel loading in spherical cryogenic foam target for laser fusion
Authors: Katayama H. , Norimatsu T. , Chen C. , Yamanaka T. , Nakai S. , Nishino Y.
Published: July 2002

Examined has been the performance of cryogenic fuel loading into a spherical foam shell target for laser fusion program by means of thermal cavitation technique to nondestructively measure the loaded fuel mass in situ. Experimental results on the loaded mass by means of the thermal cavitation technique ranged from 95% to 135% of the fully saturated fuel mass, which was measured by the resonance elastic vibration technique. In order to discuss the variation in loaded fuel mass, we have analyzed the exact bridge profile formed between the shell and the liquid fuel surface and the capillary binding force. Sublimation of the loaded fuel before the laser irradiation is considered to achieve quantitatively controlled accurate fuel loading, including fuel shrinkage by phase changing and the incoming thermal radiation circumstantially.
Factors affecting the formation, uniformity, and density of misfit and threading dislocation arrays during heteroepitaxial growth
Authors: Rockett A. , Kiely C. J.
Published: July 2002

An improved theory relating the separation of misfit dislocations in a heteroepitaxial thin film undergoing a continuous process of strain relaxation by the introduction of dislocations is presented. Because it provides a quantitative relationship between the dislocation spacing, misfit, total system energy, and film thickness, a number of quantities such as energy gain on formation of the dislocation network as a function of dislocation spacing can be estimated. The model allows calculation of useful thermodynamic quantities such as the compressibility of the misfit array which are useful for determining the average spacing of dislocations, the thickness at which dislocations are introduced (the critical thickness), and the dispersion in dislocation spacings in arrays.
Correlation of interface chemistry, barrier height, and step density for Al on vicinal GaAs(100) surfaces
Authors: Chang S. , Vitomirov I. M. , Brillson L. J. , Rioux D. F. , Kirchner P. D. , Pettit G. D. , Woodall J. M.
Published: July 2002

We have used soft x-ray photoemission spectroscopy to study the chemical and electronic properties of Al on molecular beam epitaxy GaAs(100) vicinal surfaces, specifically with orientations 1°, 2°, and 4° toward [111]B, 2° toward [111]A, as well as 2° and 4° toward [110] surfaces. Our results show that (1) the interface chemistry depends on both the bonding nature of the steps and the degree of misalignment, (2) a monotonic correspondence exists between Schottky barrier and the density of step-related atomic sites, irrespective of the misorientation direction, and (3) a nearly one-to-one functional dependence exists between the density of electronic states and the density of step-related atomic sites. Our results emphasize the key role of local atomic bonding upon interface electronic and chemical properties.
Absolute calibration of a frozen hydrogen pellet mass detector
Authors: Langley R. A. , Qualls A. L. , Wilgen J. B.
Published: July 2002

Fueling of plasma physics experiments by the injection of frozen hydrogenic pellets has been accomplished on many devices, including the Tokamak Fusion Test Reactor (TFTR), the Joint European Torus (JET), Tore Supra, and the Advance Toroidal Facility (ATF). Injection of pellets lead to density increases in the plasma with efficiencies varying from 50% to near 100%. Determination of the fueling efficiency requires knowledge of both the plasma density and the pellet mass. The pellet mass can be determined as the pellet passes through a microwave cavity by the change in power transmitted though the cavity. A one-to-one correspondence between the transmitted power and the pellet mass has been demonstrated, but this system must be calibrated by other techniques. The technique described here is measuring the pellet mass directly by measuring the pressure increase in a vacuum chamber into which the pellet is injected. A high-sensitivity capacitance manometer is used to absolutely measure the pressure profile pulse during pellet injection. Since these fuel pellets are hydrogenic, absorption of hydrogen onto the chamber wall must be accounted for in the calibration procedure. A fast (1 ms response time) pressure manometer allows measurement of the pressure pulse profile from which the absorption can be estimated, thereby allowing a determination of the pellet mass and a calibration of the microwave cavity technique. Results are presented and compared with other pellet size diagnostics.
Hydrogen storage, microstructural properties of, and electromigration effects in Al/Pd/Al films
Authors: Domenicucci A. , Vook R. W.
Published: July 2002

Composite Al/Pd/Al films were thermally evaporated onto SiO2 in an ultrahigh vacuum environment. The thickness of the Pd layer was varied in the range of 0–66 Å. The Pd layer was exposed to various partial pressures of H2 in situ. Secondary ion mass spectrometry showed that the amount of hydrogen dissolved in the Pd layer depended on the thickness of the Pd layer exposed. Transmission electron microscopy revealed that the grain structure of the composite films became more complex with the addition of Pd to the structure. The electromigration resistance of the films increased with the incorporation of even the thinnest of Pd layers. However, no beneficial effect due to the hydrogen dissolved in the Pd layer was evident.
Spatial dependence of composition in ion beam sputter deposited GdTbFe thin films
Authors: Shah S. I. , Carcia P. F.
Published: July 2002

We measured the spatial dependence of chemical composition of ion beam sputtered GdTbFe thin films, which is the recording medium in an erasable magneto-optical disk. We found that films were enriched in Fe, relative to the target composition, directly underneath the target and became increasingly Fe rich as the Ar+ ion energy decreased. We ascribe this characteristic at low incident ion energies to a mass-related sputtering effect, in which the lighter element (Fe) is preferentially sputtered normal to the target surface. At higher incident ion energies we examined the contribution to spatial inhomogeneity from resputtering of Gd and Tb at the growing film by energetic reflected neutrals.
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u chemical analysis in thin film production using soft x-ray emission spectroscopy
Authors: Georgson M. , Bray G. , Claesson Y. , Nordgren J. , Ribbing C.-G. , Wassdahl N.
Published: July 2002

A feasibility study has been made on the use of soft x-ray emission spectroscopy for in situ characterization and on line production monitoring of thin films. Thin films of Ti, TiN, and TiO2 were produced by reactive magnetron sputtering under various conditions. During or directly after deposition the films were subjected to spectral analysis of soft x-ray emission in the 380–550 eV range with the use of a grazing incidence instrument. The experiments showed that, even with a general purpose instrument, it is possible to obtain spectra with sufficient quality to reveal details about the chemical state of the constituents in less than 30 s. The sensitivity of the method allows control of the stoichiometry of the film as well as detection of small amounts of impurities of, e.g., oxygen in TiN.
A magnetically confined and electron cyclotron resonance heated plasma machine for coating and ion surface modification use
Authors: Kidd P.
Published: July 2002

A new coating system which generates a magnetically confined plasma via microwave heating in an electron cyclotron resonance zone has shown much promise in several coating applications. The system is used to produce high density plasmas of gas and/or metals ions. With metal plasmas, many of the deposited coatings are made exclusively from singly ionized, ion depositions. For many metals the system produces fairly high deposition rates (greater than 1 μ a min for many metals) using a sputter plate as the source of neutrals to be ionized. The use of evaporative neutral sources should produce higher densities and deposition rates. The operation of this system and its use in several interesting coating applications is discussed. These applications have included the generation of multilayered coatings for x-ray optics, the effect of surface bias on metal ion depositions, low voltage (50 to 60 eV)/hi current (30 mA/cm2 ) sputter etching, and depositions from metal-reactive gas plasmas.
Using a design of experiments approach for characterization of undoped plasma-enhanced chemical-vapor deposited SiO2 film properties
Authors: Allman D. D. J. , Fuchs K. P. , Cuchiaro J. M.
Published: July 2002

RS/Discover, an experimental software package, was used to construct a Plackett-Burman screening experiment to relate the film properties of a silane-based undoped plasma-enhanced chemical-vapor deposited (PECVD) SiO2 to the deposition parameters in a Novellus PECVD reactor. Temperature, pressure, power, and gas flows were simultaneously varied to study the effects that the deposition parameters had on the physical, chemical, and electrical film characteristics. A linear model was developed from the data collected. The Fourier transform infrared (FTIR) spectra revealed that the asymmetric Si–O–Si peak position correlated to several film parameters including the destructive breakdown voltage, the wet etch rate, and the index of refraction of the deposited oxide. The highest deposition rates (>0.6 μm/min) and film thickness uniformity (<1.0% nonuniformity) were obtained when the Novellus system was operated at high silane flows with low power and pressure values. The particulate level was found to be directly related to the nitrogen carrier gas flow rate.
Modification of optical and mechanical properties of BaF2 bombarded by either Xe or Ar ion
Authors: Scaglione S. , Flori D. , Caneve L. , Emiliani G.
Published: July 2002

Barium fluoride (BaF2 ) material presents a low absorption in a wide range of the spectrum (0.25–15 μm) and a low value of refractive index as well. Typical evaporated thin film of barium fluoride is hygroscopic and presents a low packing density value. The ion assistance by low energy ion beam has been used to improve the mechanical stability and to increase the packing density of evaporated thin films. In this work the BaF2 coatings have been ion bombarded by either Ar ions or Xe ions during the evaporation. The ion beam energy was varied in the range from 300 to 800 eV. The refractive index and the Knoop hardness values of the Xe bombarded samples are higher than the Ar bombarded ones. Besides, the Xe assisted samples present exact stoichiometric values (measured by Rutherford backscattering technique) and their absorption coefficient values (in the UV-VIS region) are lower than those of the Ar assisted samples.
The influence of surface oxygen on uptake and release of deuterium by tantalum
Authors: Wampler W. R.
Published: July 2002

Here we examine the influence of surface oxygen on both the absorption of deuterium (D) from gas into solution in tantalum (Ta) and the release from solution back to the gas. The D uptake rate was proportional to gas pressure with a sticking coefficient of 0.0085±0.0025 for clean Ta surfaces. Exposure to 10 Langmuirs (L) of O2, giving about one monolayer of chemisorbed oxygen, decreased the D uptake rate by about two orders of magnitude. D release was studied using the D(3He,p)α nuclear reaction to measure the concentration of D in the Ta versus time during release at constant temperature. D release was surface-limited and obeyed second-order kinetics for both clean and oxygen-covered Ta surfaces. The second-order kinetics show that D recombines from sites which are not saturated and therefore must have a smaller binding energy than the low-coverage chemisorption sites. Exposure to 106 L of O2 resulted in an additional energy barrier to D recombination of 0.25±0.04 eV/D which greatly reduces the D release rate. This activation barrier should also reduce D dissociation and uptake rates, and this is observed. The measured uptake and release rates are consistent with detailed balance.
Application of computational fluid modeling to the development of semiconductor chemical vapor deposition systems
Authors: Zook M. A. , Runchal A. K.
Published: July 2002

A computational fluid dynamics model was developed to simulate atmospheric pressure chemical vapor deposition of silicate glasses. The model is used to examine chamber geometry and substrate placement effects on fluid flow and temperature profiles. The reaction of tetraethyl orthosilicate (TEOS) and ozonated oxygen to form undoped silicate glass is modeled. Comparison between model predictions and experimental data suggests that ozone is essential for initiating the overall reaction at deposition temperatures between 300 and 550 °C. At deposition temperatures over 300 °C, no ozone is present at the wafer surface. A correlation is found between deposition rate and the time that TEOS is combined with ozone in the gas stream at temperatures below 200 °C.
Dopant diffusion in silicides: Effect of diffusion paths
Authors: Stanis C. , Thomas O. , Cotte J. , Charai A. , LeGoues F. K. , d’Heurle F. M.
Published: July 2002

While dopants implanted in well annealed WSi2 show no lattice diffusion and only limited grain-boundary diffusion at temperatures up to 900 °C, on the contrary, rapid diffusion is observed at temperatures as low as 300 °C when the implantation takes place in the as-deposited amorphous silicide. Diffusion appears to be always accompanied by crystallization, although the inverse is not true: in particular, the diffusion of Sb occurs only at temperatures in excess of what is necessary to cause crystallization. The diffusion coefficients vary in reverse proportion to the size of the diffusing atoms, so that approximately equal coefficients for B, P, As, and Sb require respective temperatures of 350, 400, 450, and 500 °C. The diffusion coefficient of As at 500 °C is estimated at 1 × 10−14 cm2 s−1. The apparent activation energy for grain-boundary diffusion is close to 2.4 eV for P, As, and Sb.
Stacked oxide as trench gate dielectric
Authors: Tsou L. Y. , Kuo D. S. , Egloff R. H. , Mukherjee S.
Published: July 2002

Stacked chemical-vapor-deposition (CVD)-thermal oxide, consisting of a CVD oxide deposited over a thin thermal oxide and followed by a post-deposition anneal in oxygen, is proposed as a gate dielectric in trench technology. In contrast to thermal oxide, it is possible to deposit the CVD oxide uniformly around the trench corners, and low-temperature CVD processes are available. In this report, we discuss the fabrication and characterization of metal–oxide–semiconductor trench capacitors with both thermal and stacked oxides as dielectrics. In addition, planar capacitors are investigated for comparison. It is shown that, in the trench capacitor, the stacked oxide has similar behavior to the thermal oxide in terms of fixed oxide charge and interface state density. There is, however, a dramatic improvement in the charge to breakdown (Qbd) for the stacked oxide in the trench capacitor. Based on the comparison between planar and trench capacitors as well as between stacked and thermal oxides, it is speculated that the much lower Qbd in the thermal oxide may result from a weak spot localized at the trench corners due to high stress generated during thermal oxidation, in addition to the reduced oxide thickness.
Monte Carlo simulation of Auger electron spectroscopy and x-ray photoelectron spectroscopy spectra
Authors: Yoshikawa Hideki , Shimizu Ryuichi
Published: July 2002

A practical model for the Monte Carlo simulation of electron-solid interaction is proposed. This model is based on the use of the dielectric function for describing inelastic scattering and of the differential cross sections derived by partial wave expansion method, often called Mott scattering cross section, for describing elastic scattering. The present approach has been applied to (1) simulation of N(E) spectra with secondary electrons included; (2) the calculation of attenuation length with elastic scattering taken into account; and (3) simulation of x-ray photoelectron spectroscopy spectrum. Very good agreement with the experimental results has been confirmed.
Cathodic arc evaporation in thin film technology
Authors: Vyskočil J. , Musil J.
Published: July 2002

This article analyzes the present status of cathodic arc evaporation. Advantages of this technique are given by some characteristic features of arc metallic plasma, e.g., high ionization degree, multiple ionization, operation up to ultrahigh vacuum conditions, etc. The first part of the paper outlines the development of cathodic arc evaporation and focuses on arc plasma and methods for suppression of macroparticle content in growing films. The second part deals with both theoretical and experimental results of processes during interaction of arc plasma with the substrate and the growing film, mainly for Ti arc plasma in a wide range of ion energy.
Observation of electronic structure at the metal/electrolyte and metal/vacuum interface by second-harmonic generation
Authors: Bradley R. A. , Georgiadis R. , Kevan S. D. , Richmond G. L.
Published: July 2002

The detailed frequency dependence of second-harmonic generation (SHG) from Ag(111) is remarkably similar for the metal/electrolyte and metal/vacuum interface. In both environments, resonant enhancement of the SHG is observed which is attributed to optical transitions at the metal surface consistent with the surface electronic band structure.
Carbon, functionalized carbon, and hydrocarbons studied by valence band photoemission
Authors: Sherwood P. M. A.
Published: July 2002

Hydrocarbons and carbon cannot normally be distinguished by core x-ray photoelectron spectroscopy. Functionalized carbon can be identified by chemical shifts in the C 1s and other core region, but the results are not always unambiguous. A combination of valence band x-ray photoelectron spectroscopy interpreted by Xα calculations can be used to obtain more chemical information. Thus one can distinguish between different hydrocarbons even though the C 1s region is identical. A greater sensitivity to chemical functionality can be obtained for functionalized carbon (such as oxidized carbon). Examples will be provided for oxidized carbon fiber surfaces and for various types of polymer.
Surface lattice dynamics of NiO (001) by inelastic He atom scattering
Authors: Brug W. P. , Chern G. , Duan J. , Bishop G. G. , Safron S. A. , Skofronick J. G.
Published: July 2002

High-resolution inelastic He atom scattering experiments, employing a time-of-flight (TOF) technique, have been carried out on NiO (001) in the 〈100〉 and 〈110〉 high symmetry directions. The targets were prepared by cleaving single-crystal NiO in air and then baking in vacuum. Nearly all of the experiments reported here were carried out at a target temperature of 575 K, which is above the Néel point (TN = 523 K), and with He atom wave vectors in the range of 7–9 Å−1 (25–45 meV). Because of these high temperatures, the peaks in the TOF spectra were found to be somewhat broader and the multiphonon background somewhat higher than in reported spectra from this instrument for alklai halide surfaces. Nonetheless, sufficient data were obtained to allow the determination of the Rayleigh wave almost to the Brillouin zone boundary. The results for this mode are found to be in good agreement with recently published, room-temperature electron energy loss spectroscopy experiments. In contrast, there is a substantial difference between these data and the dispersion data reported for Ni (001) with chemisorbed O atoms [the O-c(2×2) structure]. Experiments that were tried at low temperatures were unsuccessful due to the rapid accumulation of surface contaminants.
An isotope approach to characterization of microwave water plasma modified polyimide surfaces
Authors: Chou N. J. , Marwick A. D. , Goldblatt R. D. , Li Leping , Coleman G. , Heidenreich J. E. , Paraszczak J. R.
Published: July 2002

Water vapor plasma treatment of polymer surfaces has recently gained renewed interest for its potential applications in biomedical science and microelectronics. We have used an isotope technique to characterize the modified polyimide (PI) films by exposing them to microwave H2O and D2O plasmas. Data were obtained showing unambiguously that during treatment the PI surfaces were oxidized and hydroxylated. In situ x-ray photoelectron spectroscopy measurement indicated increased oxygen coverage and formation of carboxylic and possibly hydroxyl bonds on the treated surfaces. Multiple internal reflection Fourier transform infrared spectra confirmed the presence of oxalic acidlike OD stretching band, and demonstrated the propensity of the modified surfaces toward water adsorption. A resonance forward recoil technique was used to monitor the deuterium incorporation in the surfaces after treatment, and the degree of hydroxylation, measured in terms of D uptake, was found to increase monotonically and reach a plateau with prolonged exposure time when the absorbed microwave power and operating pressure were kept constant. A correlation appears to exist between the surface concentration of hydroxyl functionalities and the development of surface morphology during the plasma treatment.
Si/SiO2 interfaces formed by remote plasma-enhanced chemical vapor deposition of SiO2 on plasma-processed Si substrates
Authors: Ma Yi , Yasuda T. , Habermehl S. , Lucovsky G.
Published: July 2002

This paper compares the formation of Si/SiO2 interfaces on Si(100) surfaces by two plasma-assisted processes with different C-atom removal steps: (i) by exposure to plasma-generated atomic H; and (ii) by exposure to plasma-generated atomic O. Studies of electrical characteristics and high-resolution transmission electron microscopy images have established that surface roughening, associated with the H-atom cleaning process, promotes a high midgap trap density through the creation of defect states at approximately 0.35, 0.55, and 0.75 eV above the valence-band edge, whereas exposure to atomic oxygen results in an atomically smoother surface having a lower midgap interfacial trap density, and with a single discrete trapping state at 0.35 eV.
Stacked gates with doped μc-Si electrodes and SiO2 dielectrics, both deposited by remote plasma-enhanced chemical vapor deposition
Authors: Lee D. R. , Ma Y. , Yasuda T. , Björkman C. H. , Lucovsky G.
Published: July 2002

We have developed a new processing sequence for the fabrication of metal–oxide semiconductor capacitors which utilizes remote plasma-enhanced chemical vapor deposition (remote PECVD) techniques to deposit high-quality SiO2 gate dielectrics and highly doped μc-Si gate electrodes. The remote PECVD depositions take place in ultrahigh vacuum compatible systems at temperatures below 350 °C. It was found that: (i) capacitors made with SiO2 deposited by remote PECVD and exposed to a rapid thermal anneal are comparable to capacitors with thermal oxides; (ii) the flatband voltage of these capacitors could be adjusted by changing the doping of the μc-Si film; and (iii) interfacial defect state densities are not degraded with respect to devices with Al electrodes by the use of μc-Si electrodes.
Separation of hydrogen isotopes by selective adsorption with production of high-purity D–T and T2
Authors: Maienschein J. L. , Hudson R. S. , Tsugawa R. T. , Fearon E. M. , Souers P. C. , Collins G. W.
Published: July 2002

Selective adsorption on a solid at 20 K provides the means to separate hydrogen isotopes, and particularly to purify small quantities of molecular D–T or produce pure J=1 T2 for nuclear spin polarization. We develop adsorption isotherms and separation factors for several solids from literature data. Our computational model of adsorption column operation, developed to determine column sensitivity to key parameters, is described. Model results show that column diameter and length, particle diameter, choice of solid, and the fractional void space of the packed solid are all key parameters in determination of total purification capacity of a column. Zeolite 13X is shown to be the optimal adsorbent. Column design and operation is discussed in context of the calculational results. We present experimental data that demonstrate successful operation of an adsorption column in purification of D–T gas by removal of T2, and discuss advantages of this technique over conventional separation means.
Mechanism of carbon incorporation during GaAs epitaxy
Authors: Creighton J. R. , Bansenauer B. A. , Huett T. , White J. M.
Published: July 2002

The use of trimethylgallium (TMGa) as the gallium source during epitaxial growth of GaAs often leads to high levels of carbon incorporation. Using temperature programmed desorption, high-resolution electron energy loss spectroscopy (HREELS), and static secondary ion mass spectroscopy (SSIMS), we have identified a likely carbon incorporation pathway initiated by methyl group dehydrogenation. Methyl group dehydrogenation is evidenced by a small amount of hydrogen evolution around 430 °C. Extended TMGa exposures in this temperature regime yield substantial coverages of methylene (CH2) adsorbate that is detected by HREELS and SSIMS. The CH2 adsorbate undergoes further reaction at higher temperature, yielding acetylene (C2H2), H2, and CH3 radicals as desorption products at ∼550 °C. All of these products can be attributed to a mechanism involving CH2 dehydrogenation, hydrogenation, and recombination reactions. The rate of CH3 dehydrogenation is consistent with carbon doping levels typically obtained by metalorganic molecular beam epitaxy (MOMBE) and related techniques. High temperature exposure to arsine (AsH3) consumes the CH2 adsorbate, apparently by hydrogenating them back to CH3 groups that then desorb. This observation explains why carbon doping is lower during atomic layer epitaxy as compared to MOMBE.
Effects of thin film deposition rates, and process-induced interfacial layers on the optical properties of plasma-deposited SiO2/Si3N4 Bragg reflectors
Authors: Stephens D. J. , He S. S. , Lucovsky G. , Mikkelsen H. , Leo K. , Kurz H.
Published: July 2002

Highly reflecting dielectric multilayer stacks, also designated as Bragg reflectors (BRs) have been fabricated using SiO2 and Si3N4 layers prepared by remote plasma-enhanced chemical-vapor deposition (RPECVD). Departures from the reflectance spectrum of a perfectly periodic bilayer structure with nondispersive dielectric materials results from (i) intrinsic effects associated with dispersion in the dielectric constants of the constituent layers, and (ii) extrinsic effects that are a result of departures from ideal bilayer geometry. Model calculations have shown that extrinsic effects in the optical response of BRs prepared by RPECVD derive from (i) systematic increases in nitride film thickness with increasing stack thickness, and/or (ii) from nonideal optical thicknesses in which the individual layers do not have an optical path length (OPL) equal to one-quarter of the wavelength at the center of the first low photon energy reflectance band, λ/4, but instead maintain a periodic structure in which the sum of the two OPLs equals λ/2.
X-ray standing wave study of the Sb/GaAs(110) interface structure*
Authors: Kendelewicz T. , Woicik J. C. , Herrera-Gomez A. , Miyano K. E. , Cowan P. L. , Karlin B. A. , Pianetta P. , Spicer W. E.
Published: July 2002

The x-ray standing wave technique has been used to determine the geometric structure of the monolayer Sb/GaAs(110) interface. Using the backreflection diffraction geometry, we find the average perpendicular distance of Sb atoms from the (220), (400), and (111) diffracting planes to be 2.27±0.05, 1.60±0.05, and 3.00±0.1 Å, respectively. On the basis of these data, the atomic coordinates of the overlayer have been quantitatively established. The results are in agreement with theoretical calculations for the epitaxial continued layer structure and inconsistent with other models of zigzag chains.
Determination of the geometrical configuration of Bi on GaAs (110) by x-ray standing wave triangulation
Authors: Herrera-Gómez A. , Kendelewicz T. , Woicik J. C. , Miyano K. E. , Pianetta P. , Southworth S. , Cowan P. L. , Karlin B. A. , Spicer W. E.
Published: July 2002

Triangulation from x-ray standing wave applied to three Bragg planes, together with symmetry considerations, have established the geometrical structure of epitaxial Bi overlayers on GaAs (110). Our results are consistent with the epitaxial continued layer structure model. Our analysis is based on prior experimental results that indicate two equally populated Bi sites.
Scanning probe and transmission electron microscopy observations of cobalt naphthalocyanine molecules deposited onto a NaCl substrate
Authors: Nagahara L. A. , Manivannan A. , Yanagi H. , Toriida M. , Ashida M. , Maruyama Y. , Hashimoto K. , Fujishima A.
Published: July 2002

We have used scanning probe microscopy and transmission electron microscopy (TEM) to investigate the molecular orientation of cobalt naphthalocyanine (CoNc) vacuum deposited onto a NaCl substrate. Atomic force microscopy observations taken on CoNc deposited at room temperature reveal mostly amorphous grains with only few regions showing columnar structure. For CoNc films deposited at 250 °C, scanning tunneling microscopy and TEM showed domains of columnar structure arranged in various orientation. The periodicity of the columnar structure was determined to be 1.5 and 0.34 nm from x-ray and electron diffraction and indicates that the molecules are standing with their planes perpendicular to the underlying NaCl substrate surface.
Surface structural study of aniline and hydroxyaniline thin films
Authors: Bowman G. E. , Cornelison D. M. , Caple G. , Porter T. L.
Published: July 2002

The techniques of scanning tunneling microscopy and tunneling spectroscopy were used to study the surface morphological and electronic structural features of electrochemically prepared aniline and hydroxyaniline thin films. The aniline films were found to exhibit a terracedlike structure, with individual large terraces being flat to within a few tens of angstroms. Local density of states features included many intragap maxima, however no evidence of a stable polaron band was observed. Hydroxyaniline films exhibited a nanometer-scale bundle structure, with electronic features similar to the aniline films. A 0.8 eV polaron band was observed for the hydroxyaniline films at approximately 25% of the surface locations examined.
Structural transformations in thin oxide layers on the (211) surface of an Al–Li alloy
Authors: Bottomley D. J. , van Driel H. M. , Timsit R. S.
Published: July 2002

Optical second harmonic generation is used in conjunction with Auger electron spectroscopy to study the evolution with temperature T of oxygen adsorbed at 320 K on the clean, annealed (211) surface of an Al–Li alloy with a bulk Li concentration of 6.5 at. %. The oxygen is chemically bonded to form an oxide. The presence of Li at the clean alloy surface increases the rate of oxygen adsorption by a factor of ∼60 relative to pure Al. The oxygen chemisorption rate is consistent with a sticking coefficient of 1 for O2 on the clean unoxidized surface. For all oxygen exposures, the surface oxide film that is formed undergoes two distinct transformations. A structural transformation occurs between T=450 K and T=860 K, depending on oxygen exposure. This transformation exposes bare Al. Between 860 and 905 K, Li diffuses rapidly to the surface, thus increasing the surface concentration of elemental Li, and the remaining surface oxide becomes predominantly Li2O.
Dynamics of NH3 photodesorption from GaAs(100): Role of electronic quenching
Authors: Zhu X.-Y. , White J. M.
Published: July 2002

A vibration-mediated UV photodesorption (VMPD) model is presented to account for the large isotope effect observed in the nonthermal UV photodesorption of ammonia from GaAs(100). In this mechanism, electronic excitation and deexcitation of the adsorbed molecule results in intramolecular vibrational excitation. The internal vibrational energy can couple to the adsorbate–surface coordinate and lead to desorption. In contrast to the classic Menzel–Gomer–Redhead model, the VMPD model predicts that the isotope effect in desorption is determined by the internal reduced mass of the leaving particle. Both classical Newtonian and semiclassical wave packet formulations are derived.
Real-time scanning tunneling microscopy of phase transition and faceting on a vicinal Si(111) surface
Authors: Suzuki M. , Homma Y. , Hibino H. , Fukuda T. , Sato T. , Iwatsuki M. , Miki K. , Tokumoto H.
Published: July 2002

We have used scanning tunneling microscopy for real-time observation of the (7×7) reconstruction on a Si(111) vicinal surface misoriented by 10° toward [112̄]. The (1×1)–(7×7) reconstruction corresponds to the formation of the (7×7) stripes perpendicular to the misorientation direction, and the width of the stripe is quantized in half units of (7×7) mesh. Moreover the (1×1)–(7×7) transition on the vicinal surface takes place at a temperature about 80° lower than that for the flat surface. As the temperature is decreased, further phase separation takes place, changing the vicinal surface into a (111) facet and a slanting surface. On the (111) facet the (7×7) or (5×5) structure is formed, while the slanting surface becomes a (331) facet that shows (12×1) periodic structure.
Plasma etching: An enabling technology for gigahertz silicon integrated circuits
Authors: Voshchenkov Alexander M.
Published: July 2002

The wide range of plasma-surface interactions, for example balancing competing surface polymer deposition and material removal, provides plasma etching with the flexibility to transfer patterns and tailor their profiles into a wide variety of organic and inorganic films. This has made possible the integration of sophisticated silicon device structures. To achieve the broadband analog and gigahertz rate digital requirements of advanced telecommunication systems, novel device structures and appropriate plasma etching pattern transfer technology had to be developed. Anisotropic reactive ion etching (RIE) with high selectivity and submicron resolution, as well as isotropic RIE etches, were developed for a wide variety of thin films: thermal SiO2, low-pressure chemical vapor deposited Si3N4 and various forms of oxide, plasma deposited oxide and oxynitride, doped and undoped polysilicon, single crystalline and amorphous silicon, and organic polymer planarization materials. In this article the flexibility of RIE to realize several key process modules such as forming fully recessed isolation regions, and a super self-aligned transistor structure, both key elements to multigigahertz performance in silicon, will be described. Circuits fabricated in AT&T’s front-line family of digital bipolar and bipolar complementary metal–oxide–semiconductor, BEST, technologies with 1.5 gbit/s to 10 GHz performance and bit error rates <10−9/s will be discussed briefly.
Electrostatic ion deflection in patterned substrates
Authors: Horwitz C. M. , Puzzer T.
Published: July 2002

Plasma sheaths and radio-frequency target excitation both induce electric fields at substrate surfaces. Where surface topology is pronounced, and ion energies low, electrostatic deflection of incoming ions from normal incidence is possible. Here the field from substrate rf current flow is added to sheath field curvature to obtain analytic relationships between patterning accuracy and sheath properties. Radio-frequency displacement currents arising from the nonlinear rf discharge sheath voltage are shown to be many times larger than ion currents, and larger than current flows calculated from other formalisms. These analytic results are compared with experimental measurements. Sheath fields at a patterned substrate arising from both sheath field curvature and substrate current flow are then calculated, and the resultant ion deviation obtained. The result is expressed as an ‘‘ion isotropy ratio,’’ the fraction of ions bombarding a trench sidewall instead of its bottom. This ratio is equal to [trench depth/ion acceleration distance], multiplied by minor factors including the substrate dielectric constant. Two conclusions arise from this work: (i) At high plasma density, high rf currents through substrates are obtained in the presence of rf bias. Apart from their importance in uniformity control and damage generation, these currents can add to ion deviation. (ii) Ion deviation is significant for small sheath heights or small ion mean free paths—with or without rf bias—and yields a fundamental tradeoff between processing rate, ion directionality, and the ability to decrease ion energies.
Design of large aperture, low mass vacuum windows
Authors: Mapes M. , Leonhardt W. J.
Published: July 2002

Large aperture, low mass, thin vacuum windows are required to minimize beam loss in the beam lines of particle accelerators as the products of nuclear collisions move from upstream targets to downstream detectors. This article describes the design, fabrication, testing, and operating experience of a large rectangular vacuum window, 122 cm×61 cm, and two circular windows of 91.4 and 96.5 cm diam. These window designs utilize a composite Kevlar 29 fabric and Mylar laminate as a window material with a typical combined thickness of 0.35 mm. Data for several material thicknesses are also presented. The windows are usually designed to withstand a pressure differential of two to three atmospheres to achieve the required factor of safety. These windows are typically used in the medium vacuum range of 10−4 Torr. The equations used to predict the behavior of the window material will also be discussed.