bluuebunny/crossref_metadata_2025 huggingface dataset:
Tremper–A Versatile Tool for High-Temperature Chemical Reactivity Studies under Concentrated Solar Radiation
Authors: Frey Th. , Steiner E. , Wuillemin D. , Sturzenegger M.
Published: July 2002

A device for studying the chemical reactivity of condensed phase materials under concentrated solar irradiation has been designed and tested. Heating and cooling rates as well as stagnation temperatures have been calculated and verified experimentally. A key assumption for modelling was that radiation is the prevailing heat transfer mode. Calculated temperatures and those measured by modified pyrometry agree well. The results show that sample temperatures of 2000 K can be reached with heating rates up to 500 Ks−1. Non-forced cooling to ambient occurs with an average rate of about 60 Ks−1. Forced cooling, with calculated rates of 4000 Ks−1, can be achieved with the built-in quench device. Reactivity studies have been initiated on iron oxides and manganese oxide, respectively. The results have shown that chemical analysis of the solid residue provides information for typical reaction times in the range of minutes. On-line gas phase analysis by mass spectrometry has been used to monitor reactions with typical reaction times in the range of several seconds.
An Experimental Investigation of Parametric Rolling in Head Waves
Authors: Francescutto Alberto
Published: July 2002

In this paper, the possibility of excitation of parametric rolling on a ship advancing in head sea condition is studied on an experimental basis. The excitation of parametric rolling was effectively observed in the experimental tests, together with some case of capsizing. The parametric rolling exhibited the typical subharmonic behavior. The use of classical Mathieu equation theory, coupled with hydrostatic calculations in longitudinal waves, accounting for both vertical motions and wave effect on stability, allows a satisfactory explanation of the observed phenomena. In addition, the problem of determination of roll damping dependence on ship speed was solved by using roll decay tests in calm water with forward speed. A simplified nonlinear modeling was proposed to account for the roll motion amplitude above threshold. The comparison with the experimental results is reasonably good.
Numerical Study on the Influence of Radiative Properties in Porous Media Combustion
Authors: Malico Isabel , Pereira Jose´ Carlos F.
Published: July 2002

The importance of radiation and of radiative properties (extinction coefficient, scattering albedo and scattering phase function) in inert porous media combustion was numerically assessed. The two-dimensional mass, momentum, solid and gas energy, and species conservation equations were solved. Emission, absorption and scattering by the porous media were taken into consideration and the S6 approximation was used to solve the radiative transfer equation. The temperature profiles are very sensitive to a perturbation in the radiative coefficients, particularly when the scattering albedo is increased. When compared to the isotropic scattering assumption, using zero, large diffuse spheres’, linear-anisotropic and modified Henyey–Greenstein phase functions leads to an average temperature difference no bigger than 7 percent. When radiation is neglected, the predicted temperature profile is not in agreement with the available experimental values.
On the Improvement of Calibration Coefficients for Hole-Drilling Integral Method: Part I—Analysis of Calibration Coefficients Obtained by a 3-D FEM Model
Authors: Aoh Jong-Ning , Wei Chung-Sheng
Published: July 2002

One of the important factors affecting the accuracy of stress values obtained from the hole-drilling method is the calibration coefficient. A three-dimensional model was established to determine the calibration coefficients for integral method. The constraint conditions and loading conditions during hole-drilling can be simulated more realistically with this method. With this new model, coefficients a¯i,j and b¯i,j could be determined within one computation procedure. The relationship between calibration coefficients and plate thickness was investigated over a wide range of plate thickness. It has been found that the calibration coefficients determined in this work may vary with thickness of plates and the thickness range for thin plates was thus well defined. The calibration coefficients can thus be extended to measure the residual stresses of either thin or thick plates. Comparison of calibration coefficients with those determined by other studies was also conducted.
Optimization Design of Drawbead in Drawing Tools of Autobody Cover
Panel
Authors: Liu Gang , Lin Zhongqin , Bao Youxia
Published: July 2002

In the tooling design of autobody cover panels, design of drawbead will affect the distribution of drawing restraining force along mouth of dies and the relative flowing velocity of the blank, and consequently, will affect the distributions of strain and thickness in a formed part. Therefore, reasonable design of drawbead is the key point of cover panels’ forming quality. An optimization design method of drawbead, using one improved hybrid optimization algorithm combined with FEM software, is proposed in this paper. First, we used this method to design the distribution of drawbead restraining force along the mouth of a die, then the actual type and geometrical parameters of drawbead could be obtained according to an improved drawbead restraining force model and the improved hybrid optimization algorithm. This optimization method of drawbead was used in designing drawing tools of an actual autobody cover panel, and an optimized drawbead design plan has been obtained, by which deformation redundancy was increased from 0% under uniform drawbead control to 10%. Plastic strain of all area of formed part was larger than 2% and the minimum flange width was larger than 10 mm. Therefore, not only better formability and high dent resistance were obtained, but also fine cutting contour line and high assembly quality could be obtained. An actual drawing part has been formed using the optimized drawbead, and the experimental results were compared with the simulating results in order to verify the validity of the optimized design plan. Good agreement of thickness on critical areas between experimental results and simulation results proves that the optimization design method of drawbead could be successfully applied in designing actual tools of autobody cover panels.
Stability Prediction for Low Radial Immersion Milling
Authors: Davies M. A. , Pratt J. R. , Dutterer B. , Burns T. J.
Published: July 2002

Traditional regenerative stability theory predicts a set of optimally stable spindle speeds at integer fractions of the natural frequency of the most flexible mode of the system. The assumptions of this theory become invalid for highly interrupted machining, where the ratio of time spent cutting to not cutting (denoted ρ) is small. This paper proposes a new stability theory for interrupted machining that predicts a doubling in the number of optimally stable speeds as the value of ρ becomes small. The results of the theory are supported by numerical simulation and experiment. It is anticipated that the theory will be relevant for choosing optimal machining parameters in high-speed peripheral milling operations where the radial depth of cut is only a small fraction of the tool diameter.
Friction Factor in U-Type Undulated Pipe Flow
Authors: Popiel C. O. , Wojtkowiak J.
Published: July 2002

Measurements of pressure losses in a U-type undulated hydraulically smooth wall pipe, having constant radius curvature, are presented. The effect of the dimensionless curvature radius 2R/d on the Darcy friction factor was investigated in the range of the Reynolds number from about 50 to 10,000 and for the dimensionless pipe curvature radiuses 2R/d=6.62, 7.95, 11.13, 16.03, 22.58, and 27.85. A smooth transition from laminar to turbulent region in the friction factor versus Reynolds number plot, typical for curved pipe flows, was observed. The experimental data were correlated with the relatively simple equation using new Dean number Den=Re*(Den=Re*d/2R:lnfw*Re/64=a+blnDen2, which is not valid for larger values of Den and 2R/d, e.g., for Den>200 at 2R/d=22.58, and for Den>70 at 2R/d=27.85. The new Dean number, below which the influence of the pipe curvature in comparison to the straight tube was not seen, is Den⩽∼3.[S0098-2202(00)02802-9]
Experimental Investigation of Flow Through an Asymmetric Plane Diffuser
Authors: Buice Carl U. , Eaton John K.
Published: July 2002

[S0098-2202(00)00302-3]
Loop Based Detection of Isomorphism Among Chains, Inversions and Type of Freedom in Multi Degree of Freedom Chain
Authors: Rao A. C. , Prasad Raju Pathapati V. V. N. R.
Published: July 2002

Structural synthesis of kinematic chains usually involves the creation of a complete list of kinematic chains, followed by a isomorphism test to discard duplicate chains. A significant unsolved problem in structural synthesis is the guaranteed precise elimination of all isomorphs. Many methods are available to the kinematician to detect isomorphism among chains and inversions but each has its own shortcomings. Most of the study to detect isomorphism is based on link-adjacency matrices or their modification but the study based on loops is very scanty although it is very important part of a kinematic chain.  Using the loop concept a method is reported in this paper to reveal simultaneously chain is isomorphic, link is isomorphic, and type of freedom with no extra computational effort. A new invariant for a chain, called the chain loop string is developed for a planar kinematic chain with simple joints to detect isomorphism among chains. Another invariant called the link adjacency string is developed, which is a by-product of the same method to detect inversions of a given chain. The proposed method is also applicable to know the type of freedom of a chain in case of multi degree of freedom chains. [S1050-0472(00)70801-4]
Grinding Process Size Effect and Kinematics Numerical Analysis
Authors: Cooper William L. , Lavine Adrienne S.
Published: July 2002

The present work developed numerical codes that simulate steady-state grinding process kinematics. The three-dimensional modeling procedure entails the following: specifying the sizes, shapes, and positions of individual abrasive grains on the wheel surface; geometrically calculating the abrasive grains’ depth of cut distributions along the grinding zone as they pass through the grinding zone (neglecting wheel, abrasive grain, and workpiece deflections); using an empirical relationship to relate the abrasive grains’ geometric depths of cut to the grains’ actual depths of cut; and updating the workpiece surface to account for material removal. The resulting data include the abrasive grains’ average depth of cut distribution along the grinding zone, stock removal depth, stock removal rate, grinding zone shape, grinding zone length, percentage of grains impacting the workpiece, grain-workpiece impact frequency, etc. The calculated grinding zone lengths compare favorably with experimental data. This article examines a number of steady-state grinding processes. [S1087-1357(00)00101-5]
Residual Stress Distribution Depending on Welding Sequence in Multi-Pass Welded Joints With X-Shaped Groove
Authors: Mochizuki Masahito , Hayashi Makoto , Hattori Toshio
Published: July 2002

Residual stress in a large-diameter multi-pass butt-welded pipe joint was calculated for various welding pass sequences by thermal elastic-plastic analysis using the finite element method. The pipe joint used had an X-shaped groove, and the sequences of welding passes were changed. The distribution of residual stress depends on the welding pass sequences. The mechanism that produces residual stress in the welded pipe joint was studied in detail by using a simple prediction model. An optimum welding sequence for preventing stress-corrosion cracking was determined from the residual stress distribution. [S0094-9930(00)00701-0]
Core Level XPS Spectra of Cr and N in Chromium Nitride Films
Authors: Chourasia A. R.
Published: July 2002

Chromium nitride thin films have interesting properties, such as oxidation resistance, corrosion resistance, and wear behavior. In the present investigation, x-ray photoelectron spectroscopy has been employed to record the core levels of Cr and N in chromium nitride (CrNx, x = 0.2, 0.4, 0.8, and 1.0) films. These films have been deposited with varying concentrations of nitrogen on a stainless steel substrate by a dc magnetron sputtering technique. Mg Kα radiation has been employed to record the spectra. The XPS data in the Cr 2p and N 1s regions are presented.
Quartz-crystal microbalance study for characterizing atomic oxygen in plasma ash tools
Authors: Srivastava A. K. , Sakthivel P.
Published: July 2002

This article discusses the measurement of atomic oxygen (AO) concentrations in an oxygen discharge using a quartz-crystal microbalance (QCM). This is a device that has been previously used for monitoring thin-film deposition, among several other applications. The sensor consists of a silver-coated quartz crystal that oscillates at its specific resonant frequency (typically, at about 6 MHz), which is dependent on the mass of the crystal. When exposed to AO, the silver oxidizes rapidly, resulting in a change in its mass, and a consequent change in this frequency. The frequency change is measured with a counter, and when plotted versus time, it may be fit to a standard diffusion-limited oxide-growth model. This model is then used to determine the specific AO flux to the crystal, and by inference, to the wafer. Initial results of QCM measurements in the FusionGemini Plasma Asher (GPL™-standard downstream microwave asher) and FusionGemini Enhanced Strip (GES™-fluorine compatible enhanced strip asher) are presented in this article. The results indicate AO densities of the order of 1012 cm−3 on the wafer. There is a marked increase in AO concentration with addition of nitrogen into the plasma, and a decrease in AO concentration with increasing pressure at constant flow. Effects of increasing the total plasma volume in the enhanced strip tool on AO production are discussed.
Improvements in wafer temperature measurements
Authors: Cardoso A. , Srivastava A. K.
Published: July 2002

Accurate and repeatable wafer temperature measurement and control is critical in many semiconductor processing applications. Many of these applications are done at moderate pressures (0.5–2 Torr) where thermal contact resistance between the wafer and a contact temperature probe is high, and could vary wafer to wafer. The result is an unpredictable difference between the actual wafer temperature and contact measurement probe due to heat transfer across this interface from exothermic reactions, hot plasma gases, or radiant heating. In some applications, this temperature difference is so great that backside helium cooled electrostatic chucks are used to minimize this effect. In many applications, the use of this type of solution is not practical but accurate and repeatable wafer temperature measurement is still required. A new temperature sensor has been developed that utilizes gas injection through a pinhole in a thermocouple pad that creates a “microenvironment” between the pad and the wafer. This results in reduced thermal contact resistance, and more accurate and repeatable temperature measurement. Temperature data on the operation of this probe will be presented, verifying the robustness of this probe. Additionally, diffuse reflectance spectroscopy will be used as a noncontact temperature measurement technique to corroborate data from the new gas-cushion thermocouple.
High quality GaAs grown on Si-on-insulator compliant substrates
Authors: Pei C. W. , Héroux J. B. , Sweet J. , Wang W. I. , Chen J. , Chang M. F.
Published: July 2002

Device quality GaAs epilayers were grown by molecular beam epitaxy using Si-on-insulator (SOI) as a compliant substrate. The density of dislocations is significantly reduced in the GaAs epilayers. Based on the dislocation theory and detailed experiments, a model of compliant growth to reduce dislocation density has been developed. As compared to the conventional growth technique, the advantage of reduction of dislocation density in GaAs epilayers grown on a much thinner compliant Si membrane can be predicted with this model. Our experimental results indicate that compliant growth can improve the crystal quality of epilayers on lattice-mismatched substrates significantly. Utilizing this growth technique, the full width at half-maximum of the x-ray rocking curves is measured to be as low as 128 arcsec for 3-μm-thick GaAs epilayers grown on SOI compliant substrates. Furthermore, structures of AlGaAs/GaAs heterojunction bipolar transistor (HBT) have been grown by compliant growth on SOI substrates. The corresponding I–V characteristics demonstrate good performance of the HBTs.
High-resolution, ion-beam processes for microstructure fabrication
Authors: Seliger R. L. , Kubena R. L. , Olney R. D. , Ward J. W. , Wang V.
Published: July 2002

Ion beams have increased usefulness for high-resolution microstructure fabrication if they are patterned to small dimensions before they strike a target. First, results are presented of maskless micromachining, doping, and resist exposure with a scanning focused gallium ion beam of sub-1000-Å diameter. Secondly, an ion-beam-transmission mask is described, and results are presented showing 1X replicated mask patterns with 0.6-μm features that were exposed in PMMA resist by irradiating the mask with a conventional size 150-kV proton beam. The potentials of ion-beam lithography using masks and focused ion beams are discussed.
Selective etching of SiO2 relative to Si by plasma reactive sputter etching
Authors: Matsuo Seitaro
Published: July 2002

Plasma reactive sputter etching, sputter etching using Freon (CF4, C2F6, etc.) instead of argon as the etching gas, has been investigated. It has been found that there exists an etching reaction caused by energetic ions (CFn+ etc.) different from reactions found in conventional methods. Selective etching of SiO2 and Si3N4 on Si has been realized by enhancing the etching reaction with the effects of etching table materials (Teflon, carbon) and mixing gas (C2H4, CH4, etc.). Pattern transfer from mask to underlying substance, at least in selective SiO2 etching, can be performed uniformly without undercutting and with almost no lateral shift of pattern edges, with higher accuracy than in conventional plasma and sputter etching.
Solid-state processes to produce hemispherical components for inertial fusion targets
Authors: Wise K. D. , Robinson M. G. , Hillegas W. J.
Published: July 2002

The designs proposed for next-generation targets and components for inertial fusion (IF) involve complex multilayer, multishell configurations. Solid-state process technology offers a wide assortment of fabrication techniques useful in the realization of such structures. This paper presents several such processes which are capable of producing freestanding hemishells of a variety of materials.
Molecular secondary ion mass spectrometry (SIMS)
Authors: Colton R. J.
Published: July 2002

Ion beams have been used for a number of years in material analysis. SIMS has been used recently to study the interaction of adsorbed gases on metal surfaces and the molecular structure of organic, inorganic, biologic, and polymeric compounds. This paper reviews the advancing field of molecular SIMS applied in two distinct areas: as an analytical tool for surface analysis and as a sensitive ionization source for nonvolatile and thermally-labile molecules. The present understanding of the molecular ion formation process is illustrated by results of calculation and experiment. Comparison of SIMS with other new ionization methodologies in mass spectrometry such as field, plasma, and laser desorption shows clear spectral similarities. In addition, SIMS demonstrates an extreme surface sensitivity, best detection limits in the picogram range, and high mass capability (≳5000 amu). Ionization of nonvolatile and thermally labile molecules can occur via three separate processes involving cationization/anionization, electron transfer, or direct sputter emission of positive and negative secondary ions. Over 80 papers are referenced.
Electrical properties of SiO2 and Si3N4 dielectric layers on InP
Authors: Meiners L. G.
Published: July 2002

Plasma-enhanced chemical vapor deposition techniques using SiH4 and N2O have been employed to deposit SiO2 insulating layers on n-type InP substrates. Si3N4 layers have been deposited employing the reaction between SiH4 and NH3. Metal-insulator-semiconductor capacitors have been fabricated from these structures and their interfacial properties have been measured using capacitance-voltage techniques. The amount of surface potential modulation achieved using SiO2 layers is process dependent and varied from 0.4 to 1.2 V. The modulation observed using Si3N4 layers was consistently about 0.6 V. The amount of trapped interfacial charge in the SiO2 layers is shown to be given by a fixed charge plus a charge directly proportional to the electric field in the oxide. A compilation of data for SiO2 layers on other semiconductors, including silicon, illustrates that this is apparently a universally-observed phenomenon. It is shown that this charging behavior gives the familiar u-shaped density of states curve. As an alternative to the present method of characterizing interfacial charging behavior, an interfacial quality factor ΔQss/ΔQsc is proposed that is independent of the semiconductor band gap or impurity level.
Organosilicon monomers for plasma-developed x-ray resists
Authors: Taylor G. N. , Wolf T. M. , Moran J. M.
Published: July 2002

A variety of silicon-containing monomers for plasma-developed resists formulated with chlorine-containing host polymers have been prepared and evaluated for use with x-ray lithography. The major design problems encountered were monomer incompatibility, high volatility, and low reactivity. One class of monomers, the bis-acryloxy- and and methacryloxyalkyltetramethyldisiloxanes, satisfies all requirements. A formulation with optimum properties contains 90 parts poly(2,3-dichloro-1-propyl acrylate) (DCPA) and 10 parts bis-acryloxybutyltetramethyldisiloxane (BABTDS). It is very sensitive (30–60 s exposure time), has high resolution (better than 0.5 μm), and can be developed by reactive ion etching which provides extremely uniform developed patterns.
Band structure and electronic properties of mercury chalcogenide alloys containing iron
Authors: Reifenberger R. , Kossut J.
Published: July 2002

Recent results obtained on Fe-based diluted magnetic semiconductors (DMS’s) are reviewed focusing on Hg1−xFexSe, where the Fe ions introduce donor states energetically coincident with the conduction band. These states can pin the Fermi level, producing samples in which the electron concentration is remarkably stable with time. The crystal growth methods and the magnetic properties are briefly presented. A discussion of the band structure and the position in energy of Fe-related donors in Hg1−xFexSe as a function of temperature and alloy composition is also given. Experimental evidence supporting the general picture of the band structure includes synchrotron radiation and ultraviolet photoemission spectroscopies, magnetoreflectivity, Hall effect, and Shubnikov–de Haas and de Haas–van Alphen effects. An anomaly in the low-temperature electron mobility in Hg1−xFexSe (0.0003≤x≤0.01), consistent with low Dingle temperatures seen in quantum oscillatory effects, is also discussed. A hypothetical explanation of the enhanced mobility relies on the spatial ordering of charges within the ionized donor system. Useful new features, related to the independent control over the band gap and Fermi energy in Fe-based DMS’s, are also presented.
The National Bureau of Standards primary high-vacuum standard
Authors: Tilford C. R. , Dittmann S. , McCulloh K. E.
Published: July 2002

The theory, design, operating procedures, and estimated errors are discussed for an orifice-flow-type pressure standard currently in use at the National Bureau of Standards. This standard is used to define pressures between 10−7 and 10−1 Pa. Including the uncertainty of the flowmeter, the estimated total uncertainty varies from 2.6% at the highest pressures, to 1.4% at midrange, and 8.2% at the lowest pressures. Representative calibration results are presented for four different types of hot-cathode ionization gauges.
Infrared spectrum from 400 to 1000 cm−1 of PF3 chemisorbed on the Pt(111) surface
Authors: Agrawal Vijay K. , Trenary Michael
Published: July 2002

We have obtained Fourier transform infrared reflection absorption spectra of phosphorous trifluoride chemisorbed on the Pt(111) surface. The spectra were recorded with an instrumental resolution of 0.25 cm−1 using a silicon bolometer operating at 4.2 K. At the saturation coverage we observe the symmetric P–F stretch at 951 cm−1 with a full width at half-maximum (FWHM) of 1.1 cm−1 and the symmetric PF3 bend at 562 cm−1 with a FWHM of 0.7 cm−1. We do not observe the asymmetric stretch or asymmetric bend which indicates, according to the surface dipole selection rule, that the threefold axis is oriented along the surface normal.
High temperature interfacial reactions of SiC with metals
Authors: Chou T. C. , Joshi A.
Published: July 2002

Interfacial reactions of SiC with selected high temperature metals have been studied at temperatures between 1000 and 1200 °C for various times. The metals include Nb, a strong carbide former, Ni, Co, and stainless steel. Reactions of the metals with SiC in this temperature range were extensive; various metal silicides, metal carbides, ternary metal–silicon–carbides, and unreacted carbon were formed as layered reaction products in the reaction zones. In some systems, massive or localized interfacial melting was observed as a result of metal–silicide formation. The occurrence of interfacial melting resulted in the formation of nonplanar interfaces and fracture beneath the SiC interface, while planar interfaces were generated in the absence of interfacial melting. Reactions of SiC with Ni, Co, and stainless steel resulted in the formation of clustered carbon precipitates with modulated or randomly scattered characters. The nature of the C precipitation behavior depends upon the specific metal system and is a function of distance from the reaction interfaces. In contrast, no unreacted carbon was found in the SiC/Nb system. In all cases, the decomposition of SiC was sluggish. The rate limiting step for the metal/SiC reactions is discussed. Discontinuous decomposition of SiC is proposed to explain the modulation of C precipitates. The effect of interfacial melting on the mechanical properties of metal/SiC composites is addressed.
Study of GaAs and AlGaAs buried structures by differential photoreflectance spectroscopy
Authors: Badakhshan Ali , Sydor M. , Mitchel W. C.
Published: July 2002

Application of the newly developed differential photoreflectance (DPR) technique to study layered GaAs/AlGaAs structures is presented and discussed. We show that in most instances DPR can provide selective photoreflectance (PR) response from layers buried within thin multilayer structures, where such responses may be superimposed on one another in ordinary PR technique. DPR measurement is achieved through alternative modulations from two laser pumps with different penetration depths, so that the modulation has a gradient with respect to the depth within the sample. The application of this technique is demonstrated for a buried heterojunction and buried multiple quantum wells. Comparison is made with ordinary PR. In one case the heterojunction of interest was buried under two highly doped 40-nm-thick GaAs and AlGaAs layers. We show that this heterojunction is barely distinguishable in an ordinary PR measurement. Nevertheless, at room temperature DPR shows distinct peaked signals which correspond to the previously reported PR from a two-dimensional electron gas.
Structure and bonding of tetrahedrally coordinated compound semiconductor cleavage faces
Authors: Duke C. B.
Published: July 2002

The cleavage faces for zinc blende structure compound semiconductors are the (110) surfaces. Those for wurtzite structure compound semiconductors are the (101̄0) and (112̄0) surfaces. The (100) and (112̄0) surfaces consist of chains of equal numbers of anion and cations, each of which exhibits two surface bonds and one back bond. The (101̄0) surface consists of pairs of anions and cations, each of which exhibits one surface and two back bonds. All of these surfaces relax relative to their bulk geometry with the anion moving outward and cation inward until the cation achieves an approximately planar sp2 coordination. These relaxations approximately conserve bond lengths, although surface and back bonds may be altered by a few percent. Second and deeper layer relaxations are predicted but have been confirmed experimentally only in a few cases. The mechanism for the relaxations is the (activationless) lowering in energy of a completely filled band of anion derived surface states as they change from dangling-bond to surface- and back-bonding states. The relaxations are ‘‘universal’’ in that for a given surface all materials exhibit approximately the same structure when distances are measured in units of the bulk lattice constant. A complete set of theoretical predictions, structure determinations, and surface-state eigenvalue spectra is available for the (110) surfaces of GaAs, InP, ZnSe, and CdTe as well as for CdSe (101̄0). Theoretical predictions of the structure and surface state eigenvalue spectra have been given for all common IIII–V and II–VI binary semiconductors. Experimental structure determinations have been reported for their zinc blende (110) surfaces, the (101̄0) surfaces of ZnO and CdSe, and the (112̄0) surfaces of CdS and CdSe. Both the predictions and measurements confirm the notions of the universality of the surface relaxations and the dominant role of surface topology in determining their character.
Growth kinetics of Si hemispherical grains on clean amorphous-Si surfaces
Authors: Sakai Akira , Tatsumi Toru , Ishida Koichi
Published: July 2002

In solid-phase growth on SiO2 layers of amorphous-Si (a-Si) having clean, native oxide-free surfaces under ultrahigh vacuum conditions, a novel mode of crystallization can be observed: upward growth of Si grains resulting in the formation of nearly hemispherical-shaped grains protruding from the flat surface. Kinetics of the grain growth has been studied by measuring the annealing time and temperature dependence of the hemispherical grain size. The growth behavior is well explained by a model based on the crystallization of surface diffusive atoms supplied only from where the edge of the hemispherical grain contacts the a-Si surface. The activation energy for hemispherical grain growth was found to be 2.3±0.1 eV from the temperature dependence of the flux density, defined as the number of atoms crystallized per unit time per unit surface area enclosed by the edge. The atomistic mechanism for the hemispherical shape formation and the origin of the activation energy are also discussed.
Helicon plasma source excited by a flat spiral coil
Authors: Stevens J. E. , Sowa M. J. , Cecchi J. L.
Published: July 2002

We have characterized a new helicon plasma source with an end-launch antenna configuration. Power at 13.56 MHz is coupled via a four-turn flat spiral coil into an m=0 helicon mode with the application of a weak (B≳5 G) axial magnetic field. Plasma parameters were measured with Langmuir probes, and the structure and absorption of the helicon wave fields were determined with magnetic induction probes. Plasma densities of 1011–1012 cm−3 were produced in argon for pressures in the 1–100 mTorr range with a 5–60 G magnetic field. Radio frequency power absorption occurs primarily via collisionless Landau damping for pressures below 5–10 mTorr and collisional damping dominates at higher pressures. Single pass absorption occurs for magnetic fields less than 20 G. This source does not require a separate source chamber, and thus combines the compactness of flat coil inductively coupled sources with the advantages of remote plasma generation found in wave supported sources. The source can be easily optimized for a variety of operating conditions, because the helicon parallel wavelength is not constrained.
Neon ion beam-induced surface reactions of SF6 adsorbed molecules with silicon at low temperature
Authors: Royer J. , Tessier P. Y. , Grolleau B. , Turban G.
Published: July 2002

An x-ray photoelectron spectroscopy study of Ne+ induced interaction between SF6 and monocrystalline silicon at low temperature (123 K≤T≤293 K) is reported. The simultaneous exposure to SF6 gas and 500 eV Ne+ ion beam generates on silicon an interaction layer composed of chemisorbed fluorine and sulfur. The kinetics of the Ne+ activated dissociative chemisorption of SF6 molecules is furthered by the increase in the fraction of the surface sites occupied by physisorbed SF6 molecules (increase in SF6 pressure and/or decrease in substrate temperature). However, above a threshold degree of coverage estimated to a few monolayers, the activated dissociative chemisorption is strongly slowed down because the Ne+ ions do not reach the interface between SF6 adsorbate and silicon substrate.
Comparison of interfacial and electronic properties of annealed Pd/SiC and Pd/SiO2/SiC Schottky diode sensors
Authors: Chen Liang-Yu , Hunter Gary W. , Neudeck Philip G. , Bansal Gaurav , Petit Jeremy B. , Knight Dak
Published: July 2002

Schottky diodes composed of palladium deposited on silicon carbide (Pd/SiC) detect hydrogen and hydrocarbon gases at elevated temperatures with high sensitivity. Previous examination of the properties of the Pd/SiC structure indicated that its forward current responded to the presence of hydrogen even after extended annealing at 425 °C. However, drift in the sensor properties suggested that stabilization of the diode structure was necessary. In this work, we examine the effects of placing a thin layer of silicon dioxide (SiO2) between the Pd and the SiC. Both Pd/SiC and Pd/SiO2/SiC diodes are annealed at 425 °C for 140 h and the electronic and interfacial properties of the annealed diodes are compared. The electronic properties and sensitivity to hydrogen of both diodes change significantly due to the annealing. Scanning electron microscopy and Auger electron spectroscopy indicate that the surface and interfacial properties of the diodes are very different. The Pd/SiC diode has a broad interface region with palladium silicides (PdxSi) distributed throughout the Pd. In contrast, the Pd/SiO2/SiC diode has a sharp interface with significantly less PdxSi formation. A silicon oxide (SiOx) layer has formed in the near surface region of the Pd which likely accounts for the relative insensitivity of the Pd/SiO2/SiC diode to hydrogen. The experimental data suggest that the mechanism for this SiOx formation is likely two-dimensional diffusion between the Pd and the surrounding SiC surface. While the thin SiO2 layer results in a sharp interface between the Pd and SiC, further stabilization of the diode structure is necessary for long term, high temperature sensor operation.
Cyanide intermediates in catalytic reduction of NO by C2H4 on rhodium (111)
Authors: van Hardeveld R. M. , Schmidt A. J. G. W. , van Santen R. A. , Niemantsverdriet J. W.
Published: July 2002

Temperature programmed reaction spectroscopy and secondary ion mass spectrometry (SIMS) have been applied to study reactions of NO and C2H4 coadsorbed on Rh(111). As expected, H2O, CO2, and N2 are the main products at low C2H4 coverages, but at higher coverages H2, HCN, CO, and NO, and even some C2N2 evolve as well. Static SIMS indicates the formation of a large supply of adsorbed CN species, part of which desorbs as HCN, while the remainder decomposes and is responsible for delayed formation of N2. For the highest C2H4 coverages, the majority of the nitrogen atoms in the initially adsorbed NO desorbs as HCN.
Deposition of copper films by an alternate supply of CuCl and Zn
Authors: Juppo Marika , Ritala Mikko , Leskelä Markku
Published: July 2002

Deposition of copper thin films by an alternate supply of CuCl and Zn was examined. Due to a reversible dissolution of Zn into the Cu film, no self-limiting growth characteristic for the atomic layer epitaxy method could be achieved. The resulting films contained about 3 at. % zinc while chlorine residue contents were below 0.5 at. %. The films were polycrystalline consisting of rather coarse grains.
Slip coefficients for binary gas mixtures
Authors: Ivchenko I. N. , Loyalka S. K. , Tompson R. V.
Published: July 2002

A full description of rarefied gas flows requires the solution of the Boltzmann equation. In the near continuum regime, however, the preferred approach is to solve the Navier–Stokes equation subject to appropriate slip boundary conditions. For gas mixtures, the slip coefficients that enter into the conditions are dependent upon a host of parameters. Thus, one desires simple algebraic expressions for these coefficients that are also quite accurate. We describe in this article a study of the slip problems associated with the flow of binary gas mixtures. Using some general conservation laws, we first augment some previously reported expressions for the velocity and diffusion slips with an expression for the thermal slip and then we reduce all of the expressions to very convenient forms. Next, we report results of numerical computations for some specific gas mixtures using Lennard-Jones potentials and show previously unknown dependencies of the slips on the mixture properties. The new slip coefficients should be of interest in all problems dealing with flows of rarefied gases in the slip regime (for example, in aerosol agglomeration and deposition, flow through capillaries, and flow through porous media), as well as in the technologically important processes of physical and chemical vapor deposition.
Etching of Si at low temperatures using a SF6 reactive ion beam: Effect of the ion energy and current density
Authors: Chevolleau T. , Tessier P. Y. , Cardinaud C. , Turban G.
Published: July 2002

Reactive ion beam etching of silicon is performed at low substrate temperature (153<T<300 K). The beam is extracted from a SF6 microwave plasma. The energy of the beam is 100 eV<E<400 eV, the ion current density is 0<J<5 mA cm−2. Energy distribution and composition of the beam have been studied using a mass spectrometer coupled with a cylindric mirror analyzer. The beam can be considered as monoenergetic with a full width at half-maximum about 8 eV. Using SF6 plasma, F+ is the predominant species, a significant proportion of SF+, SF2+, S+, and SF3+ ions is present in the beam. The active neutral flux of fluorine atoms coming from the ion source has been estimated between 6×1016 and 4×1017 cm−2 s−1. When no ion beam strikes the sample, the probability of reaction of neutral F atoms with Si is evaluated between 0.02 and 0.1 at 300 K. The decrease of the substrate temperature has revealed the role of the ion-induced reaction and the ion-stimulated desorption of SFx radicals in the etching process. At relative low power densities (100<E<400 eV and J=0.65 mA cm−2), an increase in the etch yield occurs as the temperature decreases until 220 K because there is an enhancement of the ion-induced reactions. If the energy of the beam is not high enough, the etching is reduced or even blocked by a thick layer of adsorbed molecules at T<220 K. At higher power densities (100<E<400 eV and 2 mA cm−2<J<5 mA cm−2) no significant etch yield enhancement is noted as the temperature decreases because the ion-stimulated desorption becomes predominant. In the case of high current density which corresponds to low values of the ratio of neutral flux over ion flux (a few ten), the etch yield approaches the value of the physical sputtering yield calculated by a model derived from the Sigmund cascade collision.
High-quality Fe(001) single crystal films on MgO(001) substrates for electron spectroscopies
Authors: Bertacco R. , De Rossi S. , Ciccacci F.
Published: July 2002

Fe films have been prepared in ultrahigh vacuum by epitaxial growth on MgO(001) substrates. Spin-resolved inverse photoemission measurements indicate that nonannealed overlayers display lower spectroscopic quality than the corresponding bulk system. Low energy electron diffraction and x-ray photoemission reveal that annealing promotes oxygen surface segregation giving rise to a c(2×2) reconstruction even in several hundred Å thick films. It is found that high-quality Fe(001) single crystal films with clean and well ordered surfaces can be obtained after high temperature annealing (∼600 °C) of relatively thick films (>1000 Å).
X-ray photoelectron spectroscopy investigations of the chemistries of soils
Authors: Barr T. L. , Hoppe E. E. , Hardcastle S. , Seal S.
Published: July 2002

The present study continues our x-ray photoelectron spectroscopy (XPS) or electron spectroscopy for chemical analysis investigations of silicate systems, particularly those in contact with biological materials. In the present case, the investigations are extended to a detailed analysis for a wide variety of soil samples extracted from different locations around the world. The samples were selected from relatively pristine sites, pressed into wafers, and were examined without further modification. All of the materials were insulators and therefore analysis required extensive use of the electron flood gun. Careful XPS chemical shift assignments have been achieved for many silicate minerals. These have been exploited in the present study along with the detailed XPS analysis of organofunctional groups rendered by Beamson and Briggs. As a result, a fairly detailed simultaneous nondestructive description is provided of the surface of both the humus and silt components of these soil samples. Substantial variations in the composition are demonstrated and questions are raised about our classifications of fertility.
Surface diffusion of adsorbed Si atoms on the Si(111)7×7 surface studied by atom-tracking scanning tunneling microscopy
Authors: Sato Tomoshige , Kitamura Shin’ichi , Iwatsuki Masashi
Published: July 2002

The initial adsorption process of Si atoms deposited on a Si(111)7×7 surface has been investigated at 80 to 500 K using a variable-temperature scanning tunneling microscopy. At room temperature, adsorbed Si atoms spontaneously formed tetramers over the center dimers in the dimers adatoms and stacking fault model of a 7×7 structure. Many other adsorbed Si atoms, which were not used for the formation of tetramers, were observed to diffuse within each half of the 7×7 unit cell. The diffusion of Si atoms across the surface was examined directly by using an atom-tracking technique. At low temperatures, the adsorption position of the Si atom was found to depend only on the potential energy. At high temperatures, the activation energy of an Si atom beyond the boundary between the half-unit cells was measured as Ea=1.14 eV.
Real time scanning tunneling microscopy study of the initial stages of oxidation of Ni(111) between 400 and 470 K
Authors: Hildebrandt S. , Hagendorf Ch. , Doege T. , Jeckstiess Ch. , Kulla R. , Neddermeyer H. , Uttich Th.
Published: July 2002

A real-time in situ study of the initial stages of the interaction of oxygen with Ni(111) in a high temperature scanning tunneling microscope (STM) at temperatures between 400 and 470 K is presented. Oxygen adsorption features, in particular the Ni(111)-p(2×2)O reconstruction, were identified in room temperature STM images. The process of oxide formation is investigated in detail at 470 K. Starting from the initial nucleation at the step edges, a gradual transformation of the terrace structure results in the formation of a three-domain NiO(001) layer finally covering the entire terraces as well as forming bulges at the steps due to surface diffusion of excess Ni. Well-resolved local oxide surface structures are discussed on the basis of a thin (001)-oriented NiO layer model on the Ni(111) substrate. Formation of triangular bulk NiO(111) islands is observed for higher oxygen exposures above 25 L.
Formation and properties of the copper silicon(111) interface
Authors: Ringeisen F. , Derrien J. , Daugy E. , Layet J. M. , Mathiez P. , Salvan F.
Published: July 2002

The initial stages of the Cu growth on top of a 7×7 Si(111) surface were monitored with LEED, AES, UPS, and XPS techniques. Results suggest that at room temperature the Cu growth proceeds by a laminar fashion. An intermixing between Si and Cu takes place giving rise to a diffuse interface extending to several first monolayers. This fact is testified by the splitting of the Si LVV transition in AES spectra, by the deviation of the AES and XPS Cu and Si signal plot versus coverage from a perfect layer by layer growth plot, and by a strong diffuse background intensity in LEED diagram. Moreover, at this coverage range, a slight narrowing and a shift (0.7 eV±0.2 eV) of the 3d Cu peak towards higher binding energy as compared with the bulk metal are observed in valence band photoemission spectra. With increasing coverage, a metal rich phase is found displaying an ordered 1×1 Cu(111) planelike structure. No Si enrichment at the topmost metallic layer is observed by XPS. Core level spectroscopy gives similar results showing a noticeable energy shift (0.6 eV±0.2 eV) for the Cu 2p line. A depth profile confirms the interface structure which is rather metastable at room temperature. At high temperature (T>400 °C), an ordered Cu induced pattern is found at θ∼1 monolayer. The diagram resembles a 5×5 superstructure. With increasing coverage, 3D crystallites are growing on top of the first ordered layer. The interface is stable at high temperature.
Applications of Rutherford backscattering spectrometry to refractory metal silicide characterization
Authors: Herman Michael H.
Published: July 2002

Rutherford backscattering spectrometry (RBS) provides a unique combination of sensitivity and accuracy for characterization of thin films. Applications include analyses of composition, contamination levels, and determination of the thickness-density product of both silicide layers and adjacent films. The large mass differences present in refractory metal silicide films make them ideally suited for RBS analysis. Excellent sensitivity, typically to tens of ppm for heavy elements, allows use of RBS for analyses of diffusion of refractory metals into other films, and study of cross-contamination effects. This paper reviews the elements of Rutherford backscattering spectrometry which affect its applicability to refractory metal silicide analysis, and gives specific examples of these applications. The use of RBS analysis for determination of composition and contamination levels is demonstrated, including an estimation of the statistical uncertainty in such calculations. An example of trace refractory metal presence in an adjacent oxide layer is quantitatively calculated to be in the hundred ppm range. Further, the depth resolution generally accessible with normal angle detection is evaluated for various disilicides as a function of depth, and is found to be on the order of tens of nanometers. In addition, the development of two types of automated RBS data analysis is described. One type, a nonlinear least squares data analysis, provides accurate values for the average composition and density-thickness product of multiple films. The value of such a program lies in its general applicability to any laterally uniform sample. The second method takes advantage of the separation of elemental signals, characteristic of thin film refractory metal silicide RBS spectra, to rapidly generate a composition depth profile.