bluuebunny/crossref_metadata_2025 huggingface dataset:
Stress Relaxation Testing as a Basis for Creep Analysis and Design of Silicon Nitride
Authors: Woodford David A. , Wereszczak Andrew A. , Bakker Wate T.
Published: July 2002

A new approach to tensile creep testing and analysis based on stress relaxation is described for sintered silicon nitride. Creep rate data covering up to five orders of magnitude were generated in tests lasting less than one day. Tests from various initial stresses at temperatures from 1250°C to 1350°C were analyzed and compared with creep rates measured during conventional constant load testing. It was shown that at least 40 percent of the creep strain accumulated under all test conditions was recoverable, and that the deformation could properly be described as viscoelastic/plastic. Tests were conducted to establish the level of repeatability and the effects of various thermomechanical histories. It was shown that none of the prior exposures led to significant impairment in creep strength. The results were used for three different grades to establish the value of the accelerated test to compare creep strengths for acceptance and for optimization. Several useful correlations were obtained between stress and creep rate. The systematic creep rate dependence as a function of loading strain prior to relaxation provided a possible basis for design in terms of a secant modulus analysis. [S0742-4795(00)02302-4]
A General Velocity Field for Shape Rolling of a V-Sectioned Sheet
Authors: Hwang Yeong-Maw , Lin Hung-Jiun , Chen J. R.
Published: July 2002

A general kinematically admissible velocity field has been proposed in this work to examine the plastic deformation behavior of the sheet at the roll gap during shape rolling of a V-sectioned sheet. This velocity field is employed to examine the geometry of the rolled product, which are effected by various rolling conditions such as the sizes of the raw sheet and the vacancy, thickness reduction, etc. Furthermore, experiments on cold shape rolling of aluminum sheet have also been conducted. The rolling forces and the shape of the rolled product were measured to compare with the analytical values. Through the comparisons between them, the validity of this newly proposed velocity field was verified. [S1087-1357(00)71301-3]
Contact Mechanics of Superfinishing
Authors: Chang Shih-Hsiang , Farris Thomas N. , Chandrasekar Srinivasan
Published: July 2002

Superfinishing is an abrasive finishing process in which a smooth work surface is produced by simultaneously loading a bonded abrasive stone against a rotating workpiece surface and oscillating (reciprocating) the stone. The surface topography of a 600 grit aluminum oxide stone used for superfinishing is quantitatively described using scanning phase-shift interferometry. A bounded three-parameter lognormal distribution is found to provide a more accurate representation of cutting edge height distribution than a bounded normal distribution, especially in fitting the upper tail end of data. Moreover, the stone surface characteristics are nearly constant throughout stone life suggesting that superfinishing is a self-dressing process. This stone surface geometry is used to develop a contact mechanics model of the superfinishing process. The model estimates the number of cutting edges involved in material removal, the load distribution on these edges, and the resulting surface roughness of the superfinished surface. The effect of contact pressure on these estimated values has been studied. Only a very small percentage (less than 0.16 percent) of the cutting edges, which are comprised of the large cutting edges occurring in the tail end of distribution, are actively engaged in material removal. Further, the arithmetic average surface roughness, Ra, is found to be related to the average depth of penetration while the peak-to-valley surface roughness, Rt or Rtm, is related to the maximum depth of penetration. The prediction of surface roughness made with this model is found to agree reasonbly well with experimental results for superfinishing of hardened steel surfaces. [S0742-4787(00)00302-7]
A Detailed Analysis of Film Cooling Physics: Part IV— Compound-Angle Injection With Shaped Holes
Authors: Brittingham R. A. , Leylek J. H.
Published: July 2002

The flow physics of film cooling with compound-angle shaped holes is documented for realistic gas turbine parameters. For the first time in the open literature, the combined effects of compound-angle injection and hole shaping are isolated and the dominant mechanisms are examined. Results provide valuable insight into the valuable insight into the flowfield of this class of film-cooling jets. Computational and experimental results are presented for a row of holes injected at 35 deg on a flat plate with three distinct geometric configurations: (1) streamwise injected cylindrical holes (reference case); (2) 15 deg forward-diffused holes injected at a 60 deg compound angle; and (3) 12 deg laterally diffused holes injected a 45 deg compound angle. Detailed field and surface data, including adiabatic effectiveness (η) and heat transfer coefficient (h), of the two compound-angle shaped holes are provided and compared to: (i) the references streamwise cylindrical case; (ii) results from Part II detailing the compound-angle flowfield for cylindrical holes; (iii) results of Part III detailing the streamwise injected shaped-hole flowfield; and (iv) experimental data. The 60 deg compound-angle forward-diffused holes provided excellent lateral coolant distribution, but suffered from crossflow ingestion at the film-hole exit plane. The 45 deg compound-angle lateral-diffused hole and had much steeper lateral effectiveness variations. A previously documented and validated computational methodology was utilized. Computations were performed using a multiblock, unstructured-adaptive grid, fully implicity pressure-correction Navier–Stokes code with multigrid and underrelaxation type convergence accelerators. All simulations had fixed length-to-diameter ratio of 4.0, pitch-to-diameter ratio of 3.0, nominal density ratio of 1.55 and film-hole Reynolds number of 17,350, which allowed isolation of the combined effects of compound-angle injection and hole shaping for nominal blowing ratios of 1.25 and 1.88. The results demonstrate the ability of the prescribed computational methodology to predict accurately the complex flowfield associated with compound-angle shaped-hole film-cooling jets. [S0889-504X(00)01501-4]
Iron oxide thin films prepared by ion beam induced chemical vapor deposition: Structural characterization by infrared spectroscopy
Authors: Yubero F. , Ocaña M. , Justo A. , Contreras L. , González-Elipe A. R.
Published: July 2002

Iron oxide thin films as hematite (α-Fe2O3) have been prepared by ion beam induced chemical vapor deposition. Very compact and dense films are obtained by this procedure. The thin films have been grown by bombardment of the substrate surfaces with O2+ ions or mixtures of O2+ and Ar+ ions, while a volatile precursor of iron [i.e., Fe(CO)5] is dosed onto the substrate surface. In the latter case, Ar atoms are incorporated within the iron oxide lattice. Atomic force microscopy, Rutherford backscattering spectroscopy, and x-ray photoelectron spectroscopy were utilized to characterize the films’ surface morphology, stoichiometry and chemical state. The film structure has been analyzed by grazing angle x-ray diffraction (XRD) and infrared spectroscopies. In particular, infrared spectroscopy has permitted a thorough structural characterization of the films, even in the cases where XRD does not provide information about the structure. Thus, when O2+ ions are used for the synthesis, iron oxide thin films grow with a hematite structure with the c axis of the crystallites perpendicular to the film surface. However, when an Ar+/O2+ ion mixture is used, the thin films have a hematite structure with the c axis of the crystallites oriented parallel to the film surface.
SnO2 Nanocrystalline Thin Films by XPS
Authors: Barreca Davide , Garon Simona , Tondello Eugenio , Zanella Pierino
Published: July 2002

SnO2 nanocrystalline thin films are deposited on Al2O3 and SiO2/Si(100) by chemical vapor deposition starting from diethylaminodimethylstannane (IV) [(CH3)2Sn(N(C2H5)2)2]. X-ray photoelectron spectra of the principal core levels for the surface of a SnO2 film on SiO2/Si(100) are presented.
The influence of surface preparation on the bond strength of flame-sprayed aluminium coatings on mild steel
Authors: Apps R. L.
Published: July 2002

The bond strength of sprayed-aluminium coatings on grit blasted steel substrates was shown to be highly dependent on surface preparation. Type and condition of the grit and the angle of blasting markedly influenced bond strength but variations of blasting pressure, blasting speed, and nozzle–substrate distance had no effect. With chilled iron angular grit, failure occurred mainly at the sprayed metal–substrate interface. The level of bond strength was reduced when blunted grit or low blasting angles were used. With alumina grit the bond strength was increased and the failure location moved from the interface to within the spray coating. Examination of grit blasted surfaces with the scanning-electron microscope gave an indication of the cause of the above behavior in terms of surface roughness and surface debris. The work indicates that bonding between flame-sprayed aluminium and steel substrates is of a mechanical rather than metallurgical nature. From the technological viewpoint, the importance of grit condition and blasting angle can be seen and simple rules of surface preparation formulated.
Purification of Vanadium by Vacuum Melting
Authors: Anable W. E. ,   nited
Published: July 2002

The Bureau of Mines compared the purification of two commercially available vanadium samples by three vacuum melting techniques: consumable-electrode arc melting in a conventional deep mold, consumable-electrode arc melting at the top of the mold, and conventional electron-beam melting. Top-of-the-mold (TOM) and electron-beam (EBF) melts were both conducted in the same vessel equipped with a bottom-withdrawal mechanism. Pressures during melting were in the range of 0.10–0.50 mTorr; the pressure in the deep mold could not be measured, but probably exceeded 100–300 mTorr during a typical melt. Arc melting was characterized by melting rates of 500–800 g/min, but electron-beam melts were limited to rates of 20–30 g/min. Forty-nine percent of the oxygen content was removed by double melting vanadium sponge at the top of the mold, and 42% of the oxygen content was removed from electrorefined vanadium treated in the same manner; however, the carbon and nitrogen increased. The purity of samples melted at the TOM approached the purity of samples prepared in the EBF. In some instances, a further decrease in the oxygen and metallic impurity content resulted from remelting selected materials in the electron-beam furnace. Little or no purification resulted from melting vanadium in the conventional deep mold. Purification proceeded faster and more completely on melting vanadium with small additions of yttrium, carbon, or aluminum; aluminum was largely removed on double melting, but carbon and yttrium were retained in the products. Metal or carbon additions tended to stabilize the arc and improve metal recovery from 85 to greater than 90% during a consumable-electrode arc melt. Typical metal hardness ranged from Rhn B-20 to B-30. Mass-spectrometric studies conducted in conjunction with the purification work demonstrated that CO, CO2, Al2O, and AlO were the principal oxides, while Al, Fe, Ti, Mn, Ni, V, Cr, Ca, and Cu were the principal metallics evolved when heating and melting vanadium. The volatilization of VO was slow and incomplete; therefore, sacrificial dissociation was of minor importance in the purification of vanadium.
Mass-Spectrometric Observation of Gaseous Species Evolved in a Vacuum System by Solid-State Electrolysis
Authors: Coburn J. W.
Published: July 2002

The electrolysis of small crystals of CaF2, MgF2, and NaCl has been observed in a high-vacuum system by monitoring the gaseous species evolved with a quadrupole residual gas analyzer. As would be expected the nature of the evolved species is determined by the electrode material. When CaF2 was electrolyzed using carbon electrodes, as many as 20 different carbon fluorides were observed. Atomic fluorine was also generated. The simplicity of the apparatus and the substantial quantity of gas evolved suggest that this technique might be useful for admitting small quantities of unusual and/or reactive gaseous species to a vacuum system in an easily controllable manner.
Plasma Silicon Nitriding and Iron Boriding
Authors: Gifford Fay E.
Published: July 2002

Plasma hardening of silicon and iron surfaces was investigated to determine if such processing can provide any advantage over conventional methods. In particular, can suitably hardened surfaces be achieved at lower temperatures or with shorter process times? On solid silicon a nitride case (∼0.0002 in.) forms when the sample is heated for 2 h at 1420 °C in a nitrogen plasma at about 5 Torr. The rate at which the nitrogen diffuses into the solid silicon is greatly reduced once the case has formed. Boriding experiments on iron showed a 0.003-in. case is formed on compressed 1080 iron powder when treated at 780 °C in a boron trichloride plasma for 4 h. For these results the principal hardened layer appeared slightly below the surface and was predominantly Fe2B, contrary to the results of Lyakhovich et al. [Metal Sci. and Heat Treat. Metals (USSR) 1969]. These results show no advantage for hardening of silicon by plasma nitriding. However, iron may be plasma borided in comparable times at a lower temperature than by conventional means.
Rapid prototyping of active microfluidic components based on magnetically modified elastomeric materials
Authors: Jackson William C. , Tran Hy D. , O’Brien Michael J. , Rabinovich Emmanuil , Lopez Gabriel P.
Published: July 2002

Replica molding of elastomeric materials has proven to be an extremely useful new technology for the formation of complex microfluidic systems. Recent demonstrations of convenient methods for production of such systems by simple, rapid methods that do not require expensive fabrication facilities have enabled the extensive use of microsystems in research and development into a host of new application fields. This report describes a simple new method for fabricating active elastomeric components in microfluidic systems that is based on deformation of elastic materials that have been impregnated or coated with magnetic materials. Computer controlled miniature electromagnets are used to activate switching valves within microfluidics systems. Similar fabrication techniques can be easily extended to construct complex, and potentially completely integrated, microfluidic systems containing active valves, pumps, injectors, mixers, and flow controllers. Preliminary results indicate fabrication of channels approximately 200 μm in width, with valves approximately 5 mm in size (including both valve chamber and valve actuator). The fabrication cycle time is on the order of one day using readily available benchtop equipment, and the valves seal hermetically against a 1.5 kPa back pressure.
Formation and photoluminescence of stacked CdSe quantum dots grown by molecular beam epitaxy
Authors: Murase Yasuhiro , Noma Tsuguki , Maehashi Kenzo , Nakashima Hisao
Published: July 2002

We have investigated formation and optical properties of single-layer and stacked self-assembled CdSe quantum dots (QDs) by reflection high-energy electron diffraction (RHEED), plan-view transmission electron microscope (TEM) image, and photoluminescence (PL) spectra. We have demonstrated a useful technique to control the dot size using the RHEED intensity observation during CdSe growth. The RHEED intensity significantly changes with the increase of CdSe coverage. The TEM observation reveals that the dot structures are formed at the minimum of the RHEED intensity variation. Using this technique, we have fabricated stacked QDs. The excitation power dependence of the PL spectra indicates the vertically coupling effect on thin ZnSe spacer samples.
Application of magnetic neutral loop discharge plasma in deep silica etching
Authors: Chen W. , Sugita K. , Morikawa Y. , Yasunami S. , Hayashi T. , Uchida T.
Published: July 2002

The electron temperature Te is one of the key parameters for process plasma because the decomposition of most reactive gases depends on the kinetic energy of electrons in the plasma. Pressure is another important parameter in the etching process for microelectromechanical systems (MEMS). Low pressure can avoid etch product substrate redepositing by reducing the collision between neutral particles and etch products in the gas phase. Also, low pressure may reduce the scattering of incident ions in the sheath that may reduce the negative taper angle for trench etching. Therefore, this study is focused on low pressure (<0.67 Pa), low Te plasma production for optical MEMS etching processes. To reduce the Te and keep the high density of the plasma, use of a parallel turn antenna was proposed and it was applied in magnetic neutral loop discharge plasma, where the Te is desirably reduced to about 2.5 eV while the density is about 1.2×1011 cm−3 at pressure of 0.2 Pa. With this improvement in plasma production, fused quartz and chemical vapor deposition SiO2 were successfully etched in a trench 5–40 μm deep at a high etch rate of over 500 nm/min. The vertical angles are about 90° and the surface roughness is less than 50 nm as evaluated by a scanning electron microscope picture, where Cr, WSi and Si were used as hard masks of SiO2 in order to achieve the selectivity required.
Comprehensive study of microcrystalline silicon solar cells deposited at high rate using 13.56 MHz plasma-enhanced chemical vapor deposition
Authors: Roschek T. , Repmann T. , Müller J. , Rech B. , Wagner H.
Published: July 2002

In this article we present a comprehensive study of microcrystalline silicon (μc-Si:H) p-i-n solar cells prepared by using plasma-enhanced chemical vapor deposition (PECVD) at 13.56 MHz excitation frequency. In the first step the cell development was performed in a small area PECVD reactor showing the relationship between the deposition process parameters and the resulting solar cell performance. Subsequent up-scaling to a substrate area of 30×30 cm2 confirmed the scalability of optimized deposition parameters to large area reactors. We investigated the deposition regime of high rf power Prf (0.25–0.7 W/cm2) and high deposition pressure pdep (1–11 Torr) for the μc-Si:H i layer. Furthermore, the influence of silane concentration and deposition temperature was studied. A transition between amorphous and microcrystalline growth could be achieved by a variation of either deposition pressure, plasma power, or silane concentration. The best microcrystalline silicon solar cells were prepared close to the transition to amorphous growth. A high deposition pressure was a prerequisite for obtaining high quality material at a high growth rate. The best solar cell efficiencies achieved so far are 8.1% and 6.6% at i-layer growth rates of 5 and 10 Å/s, respectively, for μc-Si:H single junction cells. Applied in a-Si:H/μc-Si:H tandem cells a stabilized efficiency of 10.0% was achieved.
Relationship of CF2 concentration to deposition rates in the pyrolytic chemical vapor deposition process
Authors: Cruden Brett A. , Gleason Karen K. , Sawin Herbert H.
Published: July 2002

Polytetrafluoroethylene films have been deposited for use as low dielectric constant materials in microelectronic chips. Deposition is performed through pyrolysis of hexafluoropropylene oxide on a heated filament array to produce CF2, which can then polymerize and deposit as a thin film. The variation of CF2 concentration as a function of the pressure and filament temperature has been characterized by ultraviolet absorption spectroscopy. The CF2 concentration is seen to approach a constant as filament temperature approaches 400 °C, and an activation energy of 11.9 kcal/mol is measured at lower temperatures. Attempting to develop a specific relationship between the CF2 concentration and deposition rate yields a sticking coefficient of ∼4×10−5, which is consistent with what has been measured in a CF2 beam experiment. However, this result is not sufficient to explain deposition properties observed in other related work. This implies that it is possible for other properties of the deposition process to affect the sticking coefficient. A consistent alternative picture is also developed in which gas phase polymerization can produce (CF2)n species that are responsible for deposition.
Tailoring mid- and long-wavelength dual response of InAs quantum-dot infrared photodetectors using InxGa1−xAs capping layers
Authors: Kim Eui-Tae , Chen Zhonghui , Ho Max , Madhukar Anupam
Published: July 2002

We report on the tailoring of detection bands of InAs quantum-dot infrared photodetectors (QDIPs) using InxGa1−xAs capping layers and on the realization of voltage-tunable two-color QDIPs for mid-wavelength infrared (MWIR) and long-wavelength infrared (LWIR) detection. QDIPs having 2.0 ML InAs QDs capped by 20 ML In0.15Ga0.85As layer show bias-dependent photocurrent peak positions in the LWIR regime (∼8–9 μm) which are redshifted with respect to those (∼5–7 μm) in the counterpart QDIPs without InxGa1−xAs capping layers. QDIPs having 2.5 ML InAs QDs capped by a 30 ML In0.15Ga0.85As layer have a bimodal QD size distribution and show voltage-tunable MWIR (∼5.5–6 μm) and LWIR (∼9–11 μm) photoresponse. At low bias, MWIR photoresponse is dominant whereas with increasing bias, the LWIR photoresponse becomes dominant.
Arc generation from sputtering plasma-dielectric inclusion interactions
Authors: Wickersham C. E. , Poole J. E. , Fan J. S.
Published: July 2002

Arcing during sputter deposition and etching is a significant cause of particle defect generation during device fabrication. In this article we report on the effect of aluminum oxide inclusion size, shape, and orientation on the propensity for arcing during sputtering of aluminum targets. The size, shape, and orientation of a dielectric inclusion plays a major role in determining the propensity for arcing and macroparticle emission. In previous studies we found that there is a critical inclusion size required for arcing to occur. In this article we used high-speed videos, electric arc detection, and measurements of particle defect density on wafers to study the effect of Al2O3 inclusion size, shape, and orientation on arc rate, intensity, and silicon wafer particle defect density. We found that the cross-sectional area of the inclusion exposed to the sputtering plasma is the critical parameter that determines the arc rate and rate of macroparticle emission. Analysis of the arc rate, particle defect density, and the intensity of the optical emission from the arcing plasma indicates that the critical aluminum oxide inclusion area for arcing is 0.22±0.1 mm2 when the sputtering plasma sheath dark-space λd, is 0.51 mm. Inclusions with areas greater than this critical value readily induce arcing and macroparticle ejection during sputtering. Inclusions below this critical size do not cause arcing or macroparticle ejection. When the inclusion major axis is longer than 2λd and lies perpendicular to the sputter erosion track tangent, the arcing activity increases significantly over the case where the inclusion major axis lies parallel to the erosion track tangent.
Surface composition and morphology vs secondary-electron yield of Be–Cu dynodes
Authors: Ruttenberg F. E. , Haas T. W.
Published: July 2002

Auger electron spectroscopic techniques were used to monitor the surface composition of a beryllium–copper alloy upon heating and oxidation to determine the surface composition necessary for maximum secondary-electron yield. A 500–1000 Å BeO layer on the surface was found to give rise to the maximum secondary-electron yield. Surface morphology was also found to play an important role. A wide range of oxygen pressures was found to produce the same surface condition and this fact was used in regeneration studies of fatigued Be–Cu electron multipliers.
Composition variations as a function of ejection angle in sputtering of alloys
Authors: Olson R. R. , Wehner G. K.
Published: July 2002

Auger electron spectroscopy has been used to analyze the composition of sputtered deposits as a function of ejection angle from Fe–Ni and Ni–Cu alloy targets. The sputtering was performed with 1-keV Hg+ or Ar+ multibeamlet ion beam (from a NASA thruster) impinging on the target at normal incidence. It was found that the composition varies substantially with ejection angle. In Fe–Ni the material which is ejected normal to the target surface shows up to 30% enrichment in Ni. Under very oblique ejection angles, one finds the corresponding Ni deficiency. In Ni–Cu it is again the Ni which becomes enriched (up to 30%) normal to the target surface. The effect has far-reaching implications in film deposition as well as in SIMS analysis.
End-point determination of aluminum reactive ion etching by discharge impedance monitoring
Authors: Ukai K. , Hanazawa K.
Published: July 2002

In reactive ion etching, it is found that CCl4 discharge impedance is reduced during aluminum etching and changes markedly at the final aluminum interface. This phenomenon was monitored by measuring the target electrode voltage with a 2-in. aluminium-coated Si wafer. This measurement is compared with the 261.6-nm Al–Cl optical emission spectrum and verified with SEM photographs of the etched wafer. As a result the end points detected by these two methods are consistent with each other and discharge impedance monitoring is applicable as an in-process monitoring method.
Enhanced ARE apparatus and TiN synthesis
Authors: Yoshihara Hideo , Mori Hidefumi
Published: July 2002

To apply the activated reactive evaporation (ARE) process to coatings for telecommunication components, the deposition rate must be less than 0.1 μm/min. To accomplish this slow rate, an electron emitting electrode was attached to the ARE apparatus. Electrons emitted from the electrode ’’enhanced’’ the ARE process. In the enhanced ARE process, the generation of plasma and evaporation of metal can be controlled independently. Therefore, the deposition rate can be controlled widely, and resistance heating and laser heating can be used for evaporation instead of electron beam heating. The enhanced ARE process was tested by synthesizing titanium nitride. Since N2 gas pressure can be varied widely in the enhanced ARE process, the chemical composition of the Ti–N films is more easily controlled than with the ARE process. Ti2N film synthesized by the enhanced ARE process showed a maximum hardness of Hv:2824 kg/mm2.
Study of surfaces and interfaces using quantum chemistry techniques
Authors: Goddard III William A. , McGill T. C.
Published: July 2002

There are a number of difficulties in elucidating the microscopic details of the electronic states at surfaces and interfaces. The first step should be to determine the structure at the surface or interface, but this is difficult experimentally even for the clean, ordered surface and extremely difficult for cases with impurity atoms (e.g., nonordered oxide layers). The theoretical study of such geometries and energy surfaces is the subject of quantum chemistry. We present a review of some of the theoretical techniques from quantum chemistry that are being applied to surfaces. The procedure consists of treating a finite piece of the surface or interface as a molecule. Ab initio calculations are then carried out on the molecule using the generalized valence bond (GVB) method (with additional configuration interaction), thereby incorporating the dominant many-body effects. The reliability of these techniques is discussed by giving some examples from molecular chemistry and the surfaces of solids. The strengths and weaknesses of this approach are compared with more traditional band theory related methods and are illustrated with various examples.
Growth of single-crystal metastable InSb1−xBix and (GaSb)1−xGex semiconducting films
Authors: Cadien K. C. , Zilko J. L. , Eltoukhy A. H. , Greene J. E.
Published: July 2002

Epitaxial metastable InSb1-xBix alloys with InBi concentrations up to 12 mol % and (GaSb)1−xGex alloys with compositions across the pseudobinary phase diagram have been grown on GaAs substrates by multitarget rf sputtering. The InSb1−xBix film were n-type while the (GaSb)1−xGex films were p-type. Polycrystalline films from both alloy systems grown on Corning 7059 glass substrates exhibited strong (220) preferred orientation with lattice constants obeying Vegard’s law. Annealing experiments showed that the InSb1−xBix films were metastable in two directions on the In–Sb–Bi ternary phase diagram—the solid solubility of tetragonal InBi in zinc blende structure InBi was increased by more than a factor of 4 and the width of the InSb–InBi pseudobinary ’’line compound’’ phase field was increased to ?0.5%. Both InSb1−xBix and (GaSb)1−xGex films were found to be stable to decomposition during long anneals which, in the case of InSb1−xBix, were within 100°C of the equilibrium liquidus temperature. Annealing studies carried out on (GaSb)0.38Ge0.62 showed that such films transform from the as-deposited (220) oriented alloy to GaSb–rich and Ge–rich phases in which the solute concentrations continuously decrease until an equilibrium two phase alloy is obtained. The activation energy for this process is 3.1 eV.
A continuous x-ray study of the interfacial reaction in Au–Al thin-film couples
Authors: Vandenberg J. M. , Hamm R. A.
Published: July 2002

The intermetallic compound formation in gold–aluminum thin-film couples is monitored as a continuous function of time by photographic x-ray analysis during in situ annealing in the temperature range 35°–350 °C. A copper rotating anode x-ray machine gave high enough intensities to allow phase changes to be detected in a matter of minutes. The experimental procedure will be presented. It was found that Au5Al2 is the dominant crystalline phase in the initial stage of the reaction. The order of formation of the various intermetallic compounds is discussed.
Transformation of the diamond (110) surface
Authors: Pepper S. V.
Published: July 2002

The diamond surface undergoes a transformation in its electronic structure by a vacuum anneal ∠900 °C. The transformation is characterized by the appearance of a feature in the band gap region of the energy loss spectrum. The kinetics of the transformation on the (110) surface have been studied by observing the growth of this feature with time and temperature. It is found that the transformation is consistent with first order kinetics with an activation energy of 4.8 eV. It is also found that the band gap feature could be removed by exposing the transformed surface to excited hydrogen. These results are consistent with the polished diamond (110) surface being covered with hydrogen which removes the band gap states and can be thermally desorbed at ∠900 °C.
Sputtering negative carbon ions from cesiated graphite surfaces
Authors: Pargellis A. , Seidl M.
Published: July 2002

The sputtering of negative carbon ions from graphite targets bombarded with Cs+ ions has been studied. The energy of the Cs+ ions has been varied from 200 V to 20 kV. The targets studied were polycrystalline, pyrolytic and vitreous graphite. The negative ion yield strongly depends on the amount of cesium adsorbed on the surface and intercalated into the bulk of the graphite. The optimum C− ion yield is 0.5 to 0.6 C− ions per incident Cs+ ions for a bombarding energy of 10 keV and for a target temperature of 200 °C. The yield is independent of the graphite structure. In addition to C− ions, negatively charged clusters of carbon ions up to C−19 were sputtered from polycrystalline and pyrolytic graphite. Sputtering from vitreous graphite produces only light clusters, up to C−4.
Analysis of the rate of vaporization of CuCl for solar cell fabrication
Authors: Brestovansky D. F. , Baron B. N. , Rocheleau R. E. , Russell T. W. F.
Published: July 2002

A mathematical model for the rate of CuCl vaporization was developed based on the laws of mass and energy conservation and constitutive relationships describing low pressure gas flows. This model was needed for the design of a unit operations scale system to be used in solar cell fabrication. This system continuously produces a Cu2S film on a moving CdS substrate by a solid state reaction. Experimental verification of the model was carried out using laboratory scale experiments. Over a range in vaporization rates that are useful for unit operations scale experimentation 0.225 to 5.66×10−6 kg CuCl/s, model behavior is in good agreement with experimental observation. Over the major portion of this range calculated and observed rates agree within 10%. Agreement is no worse than 18.5% over the entire range. Aspects of the model relevant to commercial scale design are discussed.
Unoccupied surface state and conduction band critical points of GaP(110): A high resolution inverse photoemission study
Authors: Straub D. , Skibowski M. , Himpsel F. J.
Published: July 2002

We report the first angle-resolved, high-resolution inverse photoemission study of the cleaved (110) surface of GaP. The experiment was performed at normal electron incidence for electron energies between 11.6 and 18.6 eV. We are able to resolve the unoccupied dangling bond surface state in the band gap of GaP at 0.3 eV below the conduction band minimum. The maximum of the Γ1 X1 band is found at about 4.5 eV.
Rolling contact fatigue behavior of Cu and TiN coatings on bearing steel substrates
Authors: Hochman R. F. , Erdemir A. , Dolan F. J. , Thom R. L.
Published: July 2002

In this study the characteristics of film morphology, thickness, microstructure, and chemistry of sputter deposited and ion plated films have been studied in relation to their rolling contact fatigue (RCF) properties. Coatings were prepared on standard RCF samples of 440C and AMS 5749 bearing steels. Films were deposited in a range of thicknesses from approximately 2000 Å to 2 μm. Copper was chosen to evaluate the potential of a soft metal coating, and the TiN was used as an example of an ultrahard material. The rolling contact fatigue was markedly improved for pure copper tested on 440C but was degraded for copper on AMS 5749. The thinner titanium nitride films (2000 Å) were found to behave favorably on these bearing steels at RCF stress levels of 786 ksi. Scanning electron microscopy (SEM) was used to characterize the ‘‘as-plated’’ coatings, and the wear tracks following rolling contact fatigue tests. Chemical characterization of the films was performed by x-ray diffraction (XRD) and electron spectroscopy for chemical analysis (ESCA).
Thickness dependence of a direct current breakdown field in stearic acid films
Authors: Huang C. H. , Agarwal V. K.
Published: July 2002

Stearic acid films in the thickness range of 180–2000 Å were deposited by thermal evaporation in vacuum. The sandwich-type structures, Al–film–Al, were first self-healed by applying voltages lower than the breakdown voltages, and then their direct current (dc) breakdown fields (FB) were derived from the current–voltage characteristics. A power law dependence FB∝d−α, where d is the films thickness, and α≂0.5 and 1.0 have been found to fit the data in the respective thickness ranges of 600–2000 Å and 180–600 Å. The results have been discussed qualitatively in terms of the breakdown theories. The power law dependence FB∝d−α appears to be common to a wide variety of insulating thin films but α varies considerably depending on the insulator material, film thickness range, film deposition process and the testing method. The existing breakdown theories cannot explain the variation in α because they do not take into account the density of weak spots in the films.
Static SIMS applications—From silicon single crystal oxidation to DNA sequencing
Authors: Benninghoven A.
Published: July 2002

Static secondary ion mass spectrometry is a hydrogen-, isotope-, and compound-sensitive technique for monolayer analysis. Originally it was applied mainly for the determination of surface composition in surface reaction studies and for the investigation of the secondary ion formation process itself. More recently it has been shown that static SIMS allows high sensitivity detection identification, and structural analysis of large and thermally labile organic molecules such as, e.g., oligopeptides, -nucleotides, and -saccharides. This opens new fields of applications in the life sciences and many related areas.
Spectroscopic examination of clean glass surfaces at elevated temperatures
Authors: Kelso J. F. , Pantano C. G.
Published: July 2002

Glass melt surfaces have been analyzed at elevated temperatures in situ with ion scattering spectroscopy (ISS). The surface composition of alkali trisilicate glasses is found to be dependent upon the relative fluxes of alkali ions out of the surface due to evaporation and to the surface due to bulk diffusion. At temperatures within and below the glass transition range Tg, the surface composition is very sensitive to time and temperature. However, at temperatures greater than Tg, the bulk diffusion flux replenishes the alkali surface sites rapidly. Thus, the surface composition of the liquid surface is relatively insensitive to time and temperature.
The quadrupole: System design and residual gas analyzer performance
Authors: Dawson P. H.
Published: July 2002

The relationship of the system design to the performance of quadrupole residual gas analyzers is reviewed with the emphasis on those factors that may influence stability and reproducibility. It is important to recognize the four operating regimes—source limited, analyzer limited, length limited, and imperfection limited—when making comparisons of performance or seeking to improve the system design.
Evaluation of substrates for growth of HgCdTe by molecular beam epitaxy
Authors: Dinan J. H. , Qadri S. B.
Published: July 2002

Spectral transmission, reflection high-energy electron diffraction, x-ray diffraction, and photoluminescence have been measured for several wafers and wafer/buffer layer combinations suitable for use as substrates for epitaxy of HgCdTe. Structural properties of wafers of Si, GaAs, and InSb were found to be superior to those of CdZnTe. Luminescent properties of thin epitaxial layers of CdZnTe grown on either GaAs or InSb are found to be excellent. We suggest that the combination of a III–V substrate and CdZnTe buffer layer may be ideal for subsequent growth of HgCdTe.
Effect of energetic neutralized noble gas ions on the structure of ion beam sputtered thin metal films
Authors: Kay E. , Parmigiani F. , Parrish W.
Published: July 2002

Energetic ion bombardment of a sputtering target often results in a significant fraction of incident ions being reflected as energetic neutrals in the direction of the growing film. Experiments are described which test the degree to which bombardment by these energetic backscattered neutrals can influence the microstructure of a growing film. As anticipated, microstructural changes of the film are influenced by the reflection coefficient and energy exchange of a given energetic gas ion at the sputtering target which in turn depends on the mass ratio of the sputtering gas to that of the target. Whereas the sputtered metal species leave the target with a near cosine distribution, evidence for a strong noncosine reflection preference in the forward direction for the energetic backscattered neutrals will be given. Very careful x-ray diffraction studies show that films grown in a Ne/Pd system give rise to lattice dilation in the (111) lattice planes resulting in a 1% increase in the lattice parameter over Pd bulk values. On the other hand, in the Xe/Cu system no significant changes from bulk unit cell dimensions were observed. Data are also presented to show lattice distortions induced by deliberate energetic ion bombardment during film growth involving normalized energies much greater than that obtainable by energetic neturals. X-ray data show that lattice distortions and preferred crystallographic orientation induced by equivalent energetic particle bombardment differs significantly for different metals.
Photon stimulated desorption from a vacuum chamber at the National Synchrotron Light Source
Authors: Kobari T. , Halama H. J.
Published: July 2002

In our search for surfaces exhibiting the lowest photon stimulated desorption, we have exposed a 3-m-long beam tube to photons from the vacuum ultraviolet ring of the National Synchrotron Light Source having critical energy of ∼500 eV. Desorption of H2, CH4, CO, and CO2, which are the main gas species, was studied as a function of the beam dose for the following surface treatments: standard chemical cleaning, Ar 10% O2 glow discharge, N2 glow discharge, and radio frequency glow discharge using O2 disassociation. In addition, we measured the desorption as a function of vertical collimator position. N2 glow discharge treatment yielded the lowest desorption.
Tunneling microscopy on various carbon materials
Authors: Elings V. , Wudl F.
Published: July 2002

Scanning tunneling microscopy images of the surfaces of graphite, glassy carbon, pyrolyzed perylene tetracarbolic acid dianhydride, pyrolyzed C5Br6, and hydrogenated carbon were made. A new periodic structure was found on graphite whose size was ∼240 Å on a side and whose height was 7 Å. The structure is made of an integral number of surface waves whose wavelength is 15 Å. The glassy carbon and carbon films had graphitelike regions extending up to 20 Å and round structures were observed on the pyrolyzed C5Br6 film. The hydrogenated carbon films showed a filamentlike structure with essentially no graphitelike regions.
Tunneling microscopy of silicon and germanium: Si(111)7×7, SnGe(111)7×7, GeSi(111)5×5, Si(111)9×9, Ge(111)2×8, Ge(100)2×1, Si(110)5×1
Authors: Becker R. S. , Swartzentruber B. S. , Vickers J. S.
Published: July 2002

The tunneling microscope has been used to study the low-index faces of silicon and germanium. Si(111) 7×7 and 9×9, GeSi(111) 5×5, and SnGe(111) 7×7 are discussed in the light of the dimer–adatom–stacking fault structural model. Ge(111) 2×8 is compared to Si(111), Ge(100) is shown and compared to Si(100), and new structures on the Si(110) 5×1 surface are shown.
Reconstruction on rows and steps of Si(112) and Si(223)
Authors: Berghaus Th. , Brodde A. , Neddermeyer H. , Tosch St.
Published: July 2002

We have investigated Si(112) and Si(223) by using scanning tunneling microscopy and low-energy electron diffraction. A well-developed two-dimensional long-range order of atomic structures in the corresponding macroscopic orientations could not be observed in the present experiment. Instead, the surfaces exhibited large facets of 7×7 reconstructed Si(111) and various modes of local reconstructions, which predominantly occurred on rows and steps in the [1̄10] direction. A frequently observed doubling of periodicity could in either case be explained by dimerization of atoms or by the presence of adatoms. On Si(223) a fivefold periodicity of the ideal atomic distance along [1̄10] was found in addition.
The chemical interaction of Mn with the MoS2(0001) surface studied by high-resolution photoelectron spectroscopy
Authors: Lince Jeffrey R. , Stewart Thomas B. , Fleischauer Paul D. , Yarmoff Jory A. , Taleb-Ibrahimi Amina
Published: July 2002

The interface produced by vapor deposition of Mn on the MoS2(0001) surface has been studied in situ by high-resolution photoelectron spectroscopy using synchrotron radiation. The evolution of the Mo 3d, Mn 3p, and S 2p core levels and of the valence-band spectra during growth of thin films (10–58 Å) is consistent with partial conversion of the Mn overlayer to MnS via the overall reaction 2Mn+MoS2→2MnS+Mo. The persistence of the substrate components of the Mo 3d and S 2p spectra for thicknesses >35 Å are consistent with the Volmer–Weber growth mode. Annealing a 58-Å film to 770 K resulted in an overlayer film consisting mostly of MnS coexisting with some metallic Mn. Analysis of the Mo 3d core levels indicates the production of a MoS2(0001) surface with S vacancy defects. Annealing to temperatures between 850 and 1040 K drove the reaction to completion (as shown by the valence band and Mn 3p core level spectra). Annealing of the sample to 1130 K resulted in uncovering the MoS2(0001) surface due to breakup of the reacted layer. In addition, low-energy electron diffraction indicated the formation of (0001)–2×2 regions on the surface. This surface structure is interpreted in terms of an ordered, MoS2−x sulfur vacancy defect structure rather than a Mn–Mo–S compound.
CO diffusion on Pt(111) by time-resolved surface infrared spectroscopy
Authors: Reutt-Robey J. E. , Chabal Y. J. , Doren D. J. , Christman S. B.
Published: July 2002

The mobility of CO chemisorbed on Pt(111) has been measured using a technique that synchronizes pulsed molecular-beam dosing with fast scanning infrared interferometry. The method is based on the observation that molecules are generally more tightly bound at defects (e.g., steps) where they exhibit a different internal vibrational frequency to that associated with the same molecule adsorbed on the low-index terrace site. On a stepped Pt(111) surface, a low coverage (θ∼0.006 monolayer) of CO is deposited in a random spatial distribution (in 600 μs). The time evolution of the infrared spectrum is then recorded with ≥5-ms resolution as the CO diffuses to the steps. A simple kinetic model makes it possible to extract the statistical microscopic hopping rates for CO diffusion on the (111) plane over the range of temperature from 95 to 195 K.
The use of a linear piezoelectric actuator for coarse motion in a vacuum compatible scanning tunneling microscope
Authors: Stupian Gary W. , Leung Martin S.
Published: July 2002

Coarse adjustment of the distance between the tunneling tip and the specimen is a major concern in the design of scanning tunneling microscopes (STMs). We present an STM design that uses a piezoelectric actuator to move a tubular piezoelectric scanning assembly and an attached tunneling tip perpendicular to the sample. The linear actuator employs piezoelectric elements driven at their resonant frequency to move a steel bar in steps. The smallest actuator step is much less than the roughly 1 μm total extension of the tubular scanning assembly. The actuators are compact and provide for tip motion from macroscopic distances to within the range of the scanning assembly without the need for additional lever or gear mechanisms. The stepper actuator assembly has the advantage of ultrahigh vacuum (UHV) compatibility when compared to other devices for achieving small linear motions such as motorized micrometers.
Scanning tunneling spectroscopy study of adsorbed molecules
Authors: Mizutani W. , Shigeno M. , Sakakibara Y. , Kajimura K. , Ono M. , Tanishima S. , Ohno K. , Toshima N.
Published: July 2002

Adsorbed molecules of copper phthalocyanine (CuPc) and liquid crystals on graphite were measured by scanning tunneling microscopy (STM) and spectroscopy (STS) in air. The islands of molecules of CuPc were detected by STM. Tunneling spectra taken simultaneously with STM showed characteristic peaks correlated with local topographic features. In the observation of a nematic liquid crystal on graphite, one reproducible molecular pattern was found, for which a model of molecular ordering is proposed. Ordinary spectroscopy was found to be difficult due to a large polarization current caused by the liquid surrounding the tip. Bias voltage dependent images of the molecules which demonstrate electronic structure effects were obtained.