bluuebunny/crossref_metadata_2025 huggingface dataset:
A Nonlinear Dynamics Analysis of Vortex-Structure Interaction Models
Authors: Mureithi N. W. , Goda S. , Kanki H. , Nakamura T.
Published: July 2002

Vortex-structure interaction models are studied in the work presented here. The third- order model by Hartlen and Currie (HC model) can reproduce the correct response amplitude, while a fifth-order model by Landl predicts the observed hysterisis effect. Using concepts from nonlinear dynamics and bifurcation theory, the range of possible dynamics of the models is investigated in parameter space; essentially, a class of nonlinear oscillators deriving “naturally” from the HC model is studied. It is found that perturbations of the HC model in parameter space lead to qualitatively physically meaningful dynamics. Forced excitation of the HC model is the highlight of the work. In this case, it is shown that a subharmonic lock-in predicted by the model may be related to a three-dimensional secondary subharmonic instability of a periodic flow. Experimental results are presented for comparison.
Distribution of Hepatic Venous Blood in the Total Cavo Pulmonary Connection: An In Vitro Study Into the Effects of Connection Geometry
Authors: Walker Peter G. , Oweis Ghanem F. , Watterson Kevin G.
Published: July 2002

The total cavo pulmonary connection, or TCPC, is a surgical correction to congenital heart defects. The geometry of this connection has been shown to determine the fluid power loss as well as the distribution of hepatic fluid that enters through the inferior vena cava. In vitro studies were performed to measure the power loss and hepatic fluid distribution in models of the TCPC with four different geometries. It was found that a zero offset straight geometry provided good hepatic fluid distribution but large power loss. A zero offset flared geometry provided low power loss but poor hepatic fluid distribution. The optimal geometry from those tested was found to be the zero offset cowl geometry whereby an enlargement was made on one side of the inferior and superior vena cava. So long as the cowl was directed toward the pulmonary artery of lowest flow rate, low power loss and relatively good distribution of hepatic flow could be obtained.
Effects of Repair Weld Length on Residual Stress Distribution
Authors: Dong P. , Zhang J. , Bouchard P. J.
Published: July 2002

This paper discusses residual stress distributions induced by repairing a stainless steel girth weld in a 19-mm thick pipe of outer diameter 541 mm. In particular, the effects of repair weld circumferential length are examined using finite element modeling. Results for three different repair lengths are presented having circumferential angular spans of 20 deg (short repair), 57 deg (medium repair), and 114 deg (long repair). A special 3-D shell element model is used which facilitates the simulation of multi-pass welds in 3-D piping components. The results shed light on a number of important 3-D residual stress features associated with repairs. Outer surface axial residual stresses in the weld and adjacent base material are tensile along the length of the repair, reach maxima values near the arc start/stop positions, and then drop into compression beyond the repair ends. The short repair develops the highest axial tensile stresses due to the overlay of start/stop effects. The circumferentially remote residual stresses are unaffected by the repairs. At midlength of the repair, profiles of axial stress along the pipe show tensile peaks at ≈40 mm away from the weld centerline; these peaks decrease in magnitude with increasing repair length. However, the medium repair axial stresses show the greatest range of influence along the pipe. The pre-existing original girth weld residual stresses have very little effect on the repair residual stress characteristics. Finally, residual stress measurements on mock-up components are discussed which confirm the validity of the finite element methods used.
Analytical Solution of a Borehole Problem Using Strain Gradient Plasticity
Authors: Gao X.-L.
Published: July 2002

An analytical solution is presented for the borehole problem of an elasto-plastic plane strain body containing a traction-free circular hole and subjected to uniform far field stress. A strain gradient plasticity theory is used to describe the constitutive behavior of the material undergoing plastic deformations, whereas the generalized Hooke’s law is invoked to represent the material response in the elastic region. This gradient plasticity theory introduces a higher-order spatial gradient of the effective plastic strain into the yield condition to account for the nonlocal interactions among material points, while leaving other relations in classical plasticity unaltered. The solution gives explicit expressions for the stress, strain, and displacement components. The hole radius enters these expressions not only in nondimensional forms but also with its own dimensional identity, unlike classical plasticity-based solutions. As a result, the current solution can capture the size effect in a quantitative manner. The classical plasticity-based solution of the borehole problem is obtained as a special case of the present solution. Numerical results for the plastic region radius and the stress concentration factor are provided to illustrate the application and significance of the newly derived solution.
Effects of Mixed-Mode and Crack Surface Convection in Rapid Crack Growth in Coupled Thermoelastic Solids
Authors: Brock L. M.
Published: July 2002

Two Green’s function problems for rapid two-dimensional steady-state crack growth governed by fully coupled (dynamic) linear thermoelasticity are analyzed. In Problem A, normal and in-plane shear line loads move on the insulated surfaces of a semi-infinite crack growing at a subcritical speed. Problem B involves only normal line loads, but crack surface convection is allowed. Problem A involves, therefore, mixed traction/displacement boundary conditions, while Problem B also exhibits mixed thermal boundary conditions. Robust asymptotic forms based on exact solutions for related problems reduce Problems A and B to coupled sets of integral equations. Both sets exhibit both Cauchy and Abel operators, but are solved exactly. The solutions show that Mode II loading couples the tangential crack face separation and discontinuity in crack-face temperature changes, while crack surface convection enhances thermal response, especially at large distances. [S0021-8936(00)03101-9]
Large Shearing of a Prestressed Tube
Authors: Zidi M.
Published: July 2002

This study is devoted to a prestressed and hyperelastic tube representing a vascular graft subjected to combined deformations. The analysis is carried out for a neo-Hookean response augmented with unidirectional reinforcing that is characterized by a single additional constitutive parameter for strength of reinforcement. It is shown that the stress gradients can be reduced in presence of prestress. [S0021-8936(00)00101-X]
Position Control of a Cylinder Using a Hydraulic Bridge Circuit With ER Valves
Authors: Choi Seung-Bok , Choi Woo-Yeon
Published: July 2002

This paper presents the position control of a double-rod cylinder system using a hydraulic bridge circuit with four electro-rheological (ER) valves. After synthesizing a silicone oil-based ER fluid, a Bingham property of the ER fluid is first tested as a function of electric field in order to determine operational parameters for the ER valves. On the basis of the level of the field-dependent yield stress of the composed ER fluid, four cylindrical ER valves are designed and manufactured. Subsequently, step responses for pressure drops of the ER valve are empirically analyzed with respect to the intensity of the electric field. A cylinder system with a cart is then constructed using a hydraulic bridge circuit with four ER valves, and its governing equation of motion is derived. A neural network control scheme incorporating the proportional-integral-derivative (PID) controller is formulated through the feedback error learning method, and experimentally implemented for the position control of the cylinder system. Both regulating and tracking position control responses for square and sinusoidal trajectories are presented in time domain. In addition, a tracking durability of the control system is provided to demonstrate the practical feasibility of the proposed methodology. [S0022-0434(00)00701-2]
Control of Camless Intake Process—Part II1
Authors: Ashhab M.-S. S. , Stefanopoulou A. G. , Cook J. A. , Levin M. B.
Published: July 2002

A model-based control scheme is designed to regulate the cylinder air charge of a camless multicylinder engine for unthrottled operation. The controller consists of a feedforward and an adaptive feedback scheme based on a control-oriented model of the breathing process of an engine equipped with electro-hydraulic springless valvetrain. The nonlinear control scheme is designed to achieve cylinder-to-cylinder balancing, fast cycle-to-cycle response, and minimization of pumping losses. The algorithm uses conventional sensor measurements of intake manifold pressure and mass air flow to the intake manifold, and intake valve duration measurement. Closed-loop simulation results are shown for a four-cylinder engine. [S0022-0434(00)03001-X]
The Role of Carbon Monoxide in NO2 Plume Formation
Authors: Feitelberg Alan S. , Correa Sanjay M.
Published: July 2002

Through a series of computational studies, carbon monoxide has been identified as an important promoter of NO oxidation to NO2 in combustion turbine exhaust gas at intermediate temperatures (450 to 750°C). NO2 formation is accompanied by enhanced CO burnout at these temperatures. Perfectly stirred reactor and plug flow reactor calculations indicate that concentrations of CO as low as 50 ppmv in exhaust gas containing 25 ppmv NO can result in the conversion of 50 percent of the NO to NO2 in less than 1 s. NO2 concentrations as low as 15 ppmv can result in visible, yellow-brown plumes from large diameter exhaust stacks. If NO2 plumes are to be prevented, then designers of gas turbines and heat recovery steam generators need to be aware of the relationships between time, temperature, and composition which cause NO2 to form in exhaust gas. Reaction path analysis indicates that the mutually promoted oxidation of CO and NO occurs through a self-propagating, three-step chain reaction mechanism. CO is oxidized by OH CO+OH→CO2+H, while NO is oxidized by HO2:NO+HO2→NO2+OH. In a narrow temperature range, the H-atom produced by the first reaction can react with O2 in a three body reaction to yield the hydroperoxy radical needed in the second reaction: H+O2+M→HO2+M, where M is any third body. The observed net reaction is CO+O2+NO→CO2+NO2, which occurs stoichiometrically at temperatures below about 550°C. As the temperature increases, additional reaction pathways become available for H, HO2, and OH which remove these radicals from the chain and eventually completely decouple the oxidation of CO from NO. An abbreviated set of elementary chemical reactions, including 15 species and 33 reactions, has been developed to model CO-enhanced oxidation of NO to NO2. This reaction set was derived from a larger reaction set with more than 50 species and 230 elementary chemical reactions, and was validated by comparison of PSR and PFR calculations using the two sets. [S0742-4795(00)01402-2]
High Accuracy Positioning in SCARA-Type Robot by Sensor-based Decoupling Control
Authors: Shiraishi M. , Sugano S. , Aoshima S.
Published: July 2002

To compensate for the effects of coupling torque and load variations experienced in SCARA-type robots, we propose a new method of sensor-based decoupling control. In this method the plant is first nominalized with the use of a disturbance observer and then nonlinear feedback control is accomplished by this nominalized system based on information from acceleration sensors installed at the end of the robot hand. As a result of high-speed reciprocal motion with a payload of 10 kg mounted on the hand, we were able to achieve satisfactory decoupling using this method. Improvements were also made in steady-state characteristics. [S1087-1357(00)01201-6]
Silver High Energy Auger Transitions
Authors: Landers R. , de Castro S. G. C. , Kleiman G. G.
Published: July 2002

The data presented correspond to the LMM and LMN Auger transitions of silver (some of the LMN transitions involve valence electrons). Differences in screening are clearly seen by the large change in Auger parameter on going from LMM to LMN [see R. Landers, P. A. P. Nascente, S. G. C. de Castro, and G. G. Kleiman, J. Phys. Condens. Matter 4, 5881 (1992); Surf. Sci. 287, 802 (1993)]. Analysis of the LMM data tends to indicate the absence of Coster–Kroning decay from the L2 to L3 initial states, but L1–L2,3 cannot be ruled out [see G. G. Kleiman, R. Landers, and S. G. C. de Castro, J. Electron. Spectrosc. (to be published)]. The relatively poor resolution (2.5 eV FWHM for Au 4f) does not seem to have degraded the spectra appreciably since spectra of the more intense L3M4,5M4,5 line taken with higher resolution (1.5 eV FWHM Au 4f) did not show any additional features. The absolute energy accuracy is probably around ± 1 eV but is difficult to quantify for lack of accurate literature data.
Point defect modification in wide band gap semiconductors through interaction with high-energy electrons: Is reflection high-energy electron diffraction truly benign?
Authors: Myers T. H. , Ptak A. J. , VanMil B. L. , Moldovan M. , Treado P. J. , Nelson M. P. , Ribar J. M. , Zugates C. T.
Published: July 2002

Electron irradiation during reflection high-energy electron diffraction is shown to affect the materials properties of ZnSe and GaN during growth by molecular beam epitaxy. The high-energy electrons produce an electron stimulated desorption effect during growth of ZnSe, which primarily affects adsorbed Se. Se desorption rates under electron irradiation are shown to be significantly larger than thermal desorption rates. Electron irradiation also decreases ZnSe growth rates under Zn-rich conditions. The decrease can be suppressed by either growth under Se-rich conditions or by using high index substrate orientations, in this case (211)B. Electron irradiation also influences growth rates for GaN grown by rf plasma-assisted molecular beam. Characterization using Raman and photoluminescence spectroscopy along with secondary ion mass spectrometry indicate electron irradiation can have a dramatic impact on point defect and impurity content of GaN.
Interfacial scattering of hot electrons in ultrathin Au/Co films
Authors: Lu R. P. , Morgan B. A. , Kavanagh K. L. , Powell C. J. , Chen P. J. , Serpa F. G. , Egelhoff W. F.
Published: July 2002

We have used room-temperature, ballistic electron emission microscopy (BEEM) to measure hot-electron transport through ultrathin Au/Co multilayer structures deposited onto Si. The samples consist of Au/Co/Si or (Au/Co)n/Au/Si diodes, sputter deposited at 175 or 300 K, where n is the number of repeat layers. The thin-film Co attenuation length, λCo, is extracted from the BEEM spectra as a function of Co thickness, in single Co layer samples. Similarly, the interface attenuation number, or the number of Co/Au interfaces required for a 1/e attenuation, is determined from the multi-interface samples. BEEM barrier heights of Au/Co/Si decrease with increasing Co thickness (for thicknesses <1 nm), as the film becomes continuous and develops a Schottky barrier for Co or CoSi2(<0.7 eV). For these diodes, λCo, increases from 0.3 to 0.5 nm, each with an estimated uncertainty of 0.1 nm, when the deposition temperature is decreased from 300 to 175K. This result is associated with decreased silicide formation at the lower deposition temperature. When Co is isolated from the Si with a 2 nm Au layer, the barrier height is stable (0.82 eV), and λCo, increases further to 0.8±0.1 nm. The λCo values are independent of electron energy over the range measurable (1–1.8 eV). The interface attenuation number was 1.8 and 25 interfaces for 0.6 and 1.2 nm total Co thickness, respectively (in structures with a constant total Au thickness of 8 nm). Thus, significant interface scattering is observed in the thinner sample and negligible scattering when the Co thickness was doubled. Further BEEM measurements on similar superlattices are being carried out to understand these results.
Edison’s vacuum coating patents
Authors: Waits Robert K.
Published: July 2002

Among the over one thousand patents bearing Thomas A. Edison’s name are several for vacuum coating processes including chemical vapor deposition, evaporation, and sputter deposition. Beginning in 1880 Edison applied for patents that described carbon deposition processes that would now be called pyrolytic chemical vapor deposition. In 1884 Edison applied for a patent (granted in 1894) that described coating by evaporation in a vacuum by direct resistance heating or arc heating using a continuous current. Edison called the process “electro vacuous deposition.” He prophetically wrote, “the uses of the invention are almost infinite.” Edison also employed sputter deposition and in 1900 applied for a patent on a “Process of Coating Phonograph Records.” Issued in 1902, the patent describes using a “silent or brush electrical discharge” produced by an induction coil. The National Phonograph Company, one of Edison’s many enterprises, used the sputtering process to deposit a thin layer of gold on wax phonograph cylinder masters that could then be electroplated to form molds to mass produce celluloid duplicates. The method was used for 20 years, from 1901 to 1921. It enabled the reproduction of cylinder grooves less than 0.001 in. deep at a density of 200 grooves per in. From 1913 to 1921, 10-in.-diameter Edison Diamond Disc phonograph records were made using the same method. Sputtering was abandoned in 1927, as it could not be scaled up to produce the 12 in. disks that were then introduced.
Mechanical nanofabrication of lignoceric acid monolayer with atomic force microscopy
Authors: Sugihara Hideki , Takahara Atsushi , Kajiyama Tisato
Published: July 2002

Nanometer scale pits have been fabricated in a crystalline fatty acid monolayer by applying weak repulsive force exerted from the cantilever tip of an atomic force microscope. In this method, the shape of fabricated pits was controlled to be circular or rectangular. The minimum diameter of the pit was ∼20 nm. It was demonstrated that the pits could be artificially distributed with different size and surface area density in the organic monolayer.
Imprinted electrically conductive patterns from a polyaniline blend
Authors: Mäkelä T. , Haatainen T. , Ahopelto J. , Isotalo H.
Published: July 2002

Imprinting three-dimensional patterns directly into electrically conductive polymer blends is investigated. Silicon substrates are spin-coated by a polymethylmethacrylate/polyaniline-camphor sulfonic acid mixture dissolved in m-cresol. The patterns are imprinted using a silicon stamp having a 500 nm deep grating with 5 μm wide lines and spaces. The imprinting temperature was 140 °C, pressure 150 bar, and time 10 min. The conductivity of the blend was 1 S/cm prior to imprinting and decreased by a factor of about 2 in the process. Removing the residual film from the grooves by etching in argon/oxygen plasma results in resistance anisotropy larger than 104 perpendicular and parallel to the imprinted polymer ridges.
Silicon-on-insulator processes for the fabrication of novel nanostructures
Authors: Bourland S. , Denton J. , Ikram A. , Neudeck G. W. , Bashir R.
Published: July 2002

In this brief report, we discuss novel single crystal structures for electronic device and microelectromechanical system applications using processes that employ selective epitaxial growth (SEG) and silicon-on-insulator (SOI) wafers. Selective epitaxial growth of silicon is used to provide robust, reliable mechanical and electrical contacts between the SOI layer and the substrate. Subsequent removal of the buried oxide results in single crystal structures suspended in air. The films can then be thinned using wet or dry etching or thinned using sacrificial oxidation steps with the possibility of forming ultrathin SOI layers. Diodes formed at the substrate–SEG junction demonstrate high breakdowns and low leakage indicating good electrical isolation between the SOI layer and the substrate. The silicon on air regions can be used for dual-gate metal–oxide–semiconductor devices, quantum wires, cantilevers, as a substrate for lattice mismatched epitaxy, ultrathin SOIs, and lateral field emission tips.
Effect of container preparation on the growth of protium and methane impurities into tritium gas
Authors: Gill John T.
Published: July 2002

Ten vessels, candidates for the unperturbed storage of analytical calibration gases containing tritium, were investigated. Contamination of 99.7% tritium gas at STP by each container over one year was a function of vessel material and surface preparation. Cylinders of aluminum and stainless steel (SS) could restrict protium ingrowth better than could hydroxyl-rich borosilicate glass. Canister surfaces with the least surface area also allowed the least protium and methane ingrowth: slower exchange of hydrogen isotopes between material and gas, and less occlusion of organic contaminants are likely causes. Protium ingrowth from bulk metal was successfully inhibited by the thin surface oxide or deformed near-subsurface structure present on dry-paper polished SS; gold ion plating such a vessel was no more effective in minimizing protium. Methane could be nearly excluded from tritium by careful cleaning of container material. Borosilicate glass and dry-paper polished SS appeared more effectively cleaned by solvent washing than did electropolished SS or burnished aluminum. Electrocleaning or oxygen discharging procedures removed hydrocarbons effectively, but led to high protium injection to metal. Careful handling of treated container parts is important. Three to four monolayers of adsorbed organics on a surface can cause observable protium and methane impurity in tritium gas.
Measurement of ZnSe–GaAs(110) and ZnSe–Ge(110) heterojunction band discontinuities by x-ray photoelectron spectroscopy (XPS)
Authors: Kowalczyk Steven P. , Kraut E. A. , Waldrop J. R. , Grant R. W.
Published: July 2002

X-ray photoelectron spectroscopy was used to study the growth and energy-band alignment of ZnSe–GaAs(110) and ZnSe–Ge(110) heterojunctions. The ZnSe–GaAs heterojunctions were formed by growing ZnSe on GaAs(110). Growth temperatures were varied to produce both epitaxial and nonepitaxial interfaces. For ZnSe grown at ∠300 °C on GaAs(110), the valence- band discontinuity ΔEv was 0.96 eV; for ZnSe deposited at room temperature and crystallized at ∠300 °C, ΔEv is 1.10 eV. The Ge–ZnSe(110) interfaces were formed by depositing Ge(ZnSe) on ZnSe(Ge)(110) at room temperature, followed by ∠300 °C crystallization. The corresponding ΔEv’s were 1.52 and 1.29 eV, respectively. Our measured ΔEv values for epitaxial heterojunctions are compared with the predictions of theoretical models. Our results demonstrate that substantial interface structure dependent contributions to ΔEv can occur at Ge–ZnSe(110) and GaAs– ZnSe(110) heterojunctions.
Carburization of steel surfaces during implantation of Ti ions at high fluences
Authors: Singer I. L.
Published: July 2002

Auger and nuclear backscattering analyses of ion-implanted steels have shown that surfaces implanted with carbide-forming ions can develop excessively high carbon concentrations well into the implanted layer. A model is presented here in which the residual gases in the vacuum chamber interact with the surface during implantation to carburize the surface. Briefly, (1) implanted Ti ions are ‘‘uncovered’’ by sputtering, (2) they react with residual gases to form surface carbide species, (3) the carbides dissociate, and (4) the carbon atoms diffuse inwards. Composition profiles of steels implanted with Ti ions (5–50×1016/cm2 at 55 and 190 keV) are analyzed and shown to support the model. Carburization occurs at a lower fluence for 55-keV implants than for 190-keV implants, consistent with a nearly energy-independent sputtering yield for Ti into Fe. Implications of the vacuum carburization effects on surface alloy chemistry and mechanical properties are also discussed.
Recent developments in silicon molecular beam epitaxy
Authors: Bean John C.
Published: July 2002

This paper reviews recent advances in silicon molecular beam epitaxy. Discussion includes the following topics: Innovations in the apparatus for increased substrate size, control, uniformity, and versatility; a comparison of work on substrate preparation techniques, such as flash annealing, ion sputtering, and laser irradiation; ion doping experiments; growth, both on and of metals and insulators; device structures; and patterned epitaxy.
Laser annealing of Ni(001)
Authors: McConnell R. P. , Jamison K. D. , Dunning F. B. , Walters G. K.
Published: July 2002

The use of laser annealing in the preparation of a clean, well-ordered Ni(001) surface has been investigated. The surface was cleaned by argon ion bombardment and subsequently irradiated with the fundamental output of a high power, Q-switched ruby laser. The laser treated surface was characterized by use of Auger electron spectroscopy and both conventional and spin-polarized LEED, and the data compared to that from a surface prepared by thermal annealing. Laser irradiation of a sputtered surface at energy densities of ∼0.8 J cm−2 leads to complete removal of residual argon without segregation of carbon or other contaminants at the surface. However, irradiation at an elevated temperature ∼200 °C is required to obtain a well-ordered surface. At elevated temperatures, laser annealing provides a surface with cleanness and surface order comparable to that obtained by conventional thermal annealing.
Local structure of silicon films and silicon carbide by surface extended energy loss fine structure
Authors: Natarajan C. , Abel P. B. , Hoffman R. W.
Published: July 2002

Surface extended energy loss fine structure (SEELFS) has been shown to yield nearest neighbor coordination and bond length for carbon in different structural forms. A standard Auger electron spectrometer(double pass cylindrical mirror analyzer) is used to obtain energy loss spectra in the laboratory. Preliminary work on diamond, graphite and ‘‘Aquadag’’ using spectra in the second derivative mode is now extended to silicon and α- and β-silicon carbide. Silicon has been used as reference for phase and amplitude in the bond length and coordination determination of β-silicon carbide. β-SiC has been used as a standard for α-SiC. The coordination and radius determined agree with known values to within uncertainties estimated. The uncertainties in the determination of bond length and coordination due to the choice of reference phase and amplitude are discussed.
Rate equation modeling of interface width
Authors: Aumann C. E. , Kariotis R. , Lagally M. G.
Published: July 2002

A recently developed rate equation model describing epitaxial growth is described. This method consists of a set of equations that govern the concentration of islands of varying sizes and heights above the substrate. There is one equation for the time rate of change of the number of islands of each possible size at the jth level above the substrate. Diffracted-intensity oscillations can be calculated, as can a qualitatively detailed intensity profile, when combined with some simple arguments from statistical mechanics. The dependence of the interface width (the number of incomplete layers) on temperature, deposition rate, and binding energies is considered. A qualitative criterion is given that determines when an interface is ‘‘rough’’ or ‘‘smooth,’’ and a quantitative restatement of this criterion then allows us to calculate two transition temperatures T1 and T2<TR (where TR is the equilibrium roughening temperature). This result implies that for T1<T<T2, the interface width is bounded, while for temperatures outside this interval, a transition to unbounded growth should be observed. Factors that influence a comparison with diffraction experiments are briefly discussed.
The Auger electron, Rutherford backscattering, secondary neutral mass, and secondary ion mass spectroscopies characterization of a W/TiNy/TiSiz/Si barrier structure for use in 1.0-μm very large scale integrated circuit contacts
Authors: Grove C. L. , Gregory R. B. , Hance R. L. , Sun S. W. , Kelly N.
Published: July 2002

A reliable contact diffusion barrier has been successfully formed by sintering in N2 a physically sputtered W/Ti bilayer. This barrier system is designed for use in 1.0-μm Al/W/TiNy/TiSz/n+ and p+)Si very large scale integrated complementary metal–oxide semiconductor contacts. The structure of this barrier metallization layer has been physically characterized by Auger electron spectroscopy, Rutherford backscattering spectroscopy, secondary neutral mass spectrometry, and secondary ion mass spectrometry.
Flow of a rarefied polyatomic gas between parallel plates
Authors: Lo S. S. , Loyalka S. K.
Published: July 2002

Flow of a rarefied polyatomic gas between parallel plates is considered. The boundary interactions are described by diffuse specular reflection parameter α, and the intermolecular Wang–Chang–Uhlenback collision operator is described by the Hansen–Morse model. Explicit results for the heat and mass flow rates for arbitrary rarefaction and the parameter α are reported. Also included are results for the macroscopic velocity and temperature profiles.
Tin foil reconstruction in a hydrogen plasma
Authors: Chou C. H. , Phillips Jonathan
Published: July 2002

As part of a continuing effort to characterize the influence of plasma environments on metals, tin foil reconstruction in argon, oxygen, and hydrogen plasma afterglows, created with a low power (<250 W) microwave system, was studied. It was found that neither oxygen nor argon plasmas had any apparent impact on the foil morphology. Hydrogen plasma treatments led to a dramatic reconstruction of the foils. Whereas originally the foil samples consisted of large, oriented crystals, following treatment in hydrogen plasmas the foil surfaces became a network of large pores and strings of small randomly oriented crystallites. No weight loss (etching) was observed. Detailed study and modeling work suggested that the reconstruction was the result of the formation of metastable tin hydride and subsequent short range metal transport. In contrast to the etching of other metals, ions, and electrons were found to play no role in the process.
Optimization of primary beam conditions for secondary ion mass spectrometry depth profiling of shallow junctions in silicon using the Perkin–Elmer 6300
Authors: Lee J. J. , Fulghum J. E. , McGuire G. E. , Ray M. A. , Osburn C. M. , Linton R. W.
Published: July 2002

Submicron ULSI designs require the measurement of ultra-shallow junction implants with peak concentrations within 10 nm below the surface of a wafer. Secondary ion mass spectrometry (SIMS) can provide the necessary depth resolution and sensitivity when optimized. The Perkin–Elmer Physical Electronics Model 6300 secondary ion mass spectrometer was used to analyze As and B junctions produced with preamorphization and low-energy ion implantation. Cs+ and O+2 primary ion beams were used for As and B depth profiling, respectively. The primary beam energy and angle of incidence can be independently varied in this instrument. Lower primary energy and shallower angle of incidence reduced the beam broadening effect caused by atomic mixing. Conditions were optimized using a 3 keV primary beam at a 60° angle of incidence for both As and B implanted samples. Lower beam energies resulted in crater edge effects due to poor primary beam focus quality. Other instrumental factors, including electronic ion gating, secondary ion energy, and primary beam current were also evaluated. With a 30° incidence O+2 ion beam, B+ profile distortion was observed and was attributed to SIMS sputter-induced segregation.
Effects of nitrogen pulsing on sputter-deposited beryllium films
Authors: Hsieh E. J. , Price C. W. , Pierce E. L. , Wirtenson R. G.
Published: July 2002

Beryllium films have been used as a ‘‘heat sink’’ layer between the reflective coating of a mirror and its glass substrate to improve the mirror’s radiation resistance to prompt deposition of x rays. Under x-ray irradiation, the beryllium heat sink layer is subjected to tensile stresses caused by differences in thermal expansion coefficients. Test results indicated that the predominant failure mode was the film’s crazing under tensile stress. The inherent columnar structure of the beryllium films deposited under normal conditions is detrimental to the tensile strength of the films and may be responsible for this type of failure. We successfully suppressed the inherent columnar growth in beryllium films by incorporating periodic N2 pulses during sputter deposition. The traditional substrate biasing approach did not seem to be as effective in modifying the grain structure. The results showed that higher N2 pulse rates during deposition were more effective in suppressing the columnar growth. However, we noticed that films deposited with nitrogen pulsing show higher secondary-electron emission in SEM micrographs, which indicates a significant incorporation of contaminants into the beryllium films. Quantitative analyses were conducted for nitrogen and oxygen contamination in the beryllium films using standards prepared by ion implantation. Secondary ion mass spectroscopy (SIMS) depth profiles were obtained for oxygen and nitrogen using mass isotopes 16O and 23(9Be+14N). More than 2% of contaminants was observed in beryllium films at the higher pulse rates that were used. Thus, a minimum pulsing frequency and duration should be selected that provides grain refinement with a minimum amount of contamination.
Mechanisms and kinetics of Si atomic-layer epitaxy on Si(001)2×1 from Si2H6
Authors: Lubben D. , Tsu R. , Bramblett T. R. , Greene J. E.
Published: July 2002

Single-crystal Si films have been grown on Si(001)2×1 substrates by ultraviolet (UV) photostimulated atomic-layer epitaxy (ALE) from Si2H6. The ALE deposition rate R per growth cycle remains constant at 0.4 monolayers (ML), 1 ML=6.8×1014 cm−2, over a wide range of deposition parameters: growth temperature (Ts=180 –400 °C), Si2H6 exposure (peak pressure during gas pulse=0.1–5 mTorr), UV laser energy density (ℰ=250–450 mJ cm−2 where ℰmax is determined by Ts ), and number of UV laser pulses per cycle. A film growth model, based upon the results of the present deposition experiments and Monte Carlo simulations, together with our previous adsorption/desorption measurements, is used to describe the reaction pathway for the process. Si2H6 is dissociatively adsorbed on Si surface dimers as two SiH3 radicals which subsequently dissociate to SiH2 and H. Site blocking during the adsorption and surface dissociation steps limits the surface coverage to 2.9×1014 SiH2 cm−2 (hence, R=0.43 ML per cycle). The H terminated silylene-saturated surface is thermally stable and passive to further Si2H6 exposure. ArF or KrF laser pulses (≊20 ns) are used to desorb H, following a Si2H6 exposure, and the growth cycle is repeated until the desired film thickness is obtained. At Ts<180 °C, the growth process becomes rate limited by the surface dissociation step and R decreases exponentially as a function of 1/Ts with an activation energy of ≊0.5 eV. At Ts>400 °C, H is thermally desorbed and pyrolytic growth competes with ALE. Plan-view and cross-sectional transmission electron micrographs together with selected-area and convergent-beam electron diffraction patterns show that the ALE films are epitaxial layers with no observed extended defects or strain.
Photoemission study of the annealed Pd/GaAs(110) interface
Authors: Kendelewicz T. , Miyano K. E. , Meissner P. L. , Cao R. , Spicer W. E.
Published: July 2002

Chemical reactions on annealed Pd/GaAs(110) interfaces have been studied using soft x-ray core level photoemission spectroscopy. Substantial surface segregation of As and formation of an As-rich ternary phase close to the surface have been observed. Thicker Pd overlayers (22 and 52 Å) annealed to between 250 and 380 °C form reacted interfaces with chemically stable composition. As with the room temperature case, the reaction products due to annealing appear to be As rich close to the surface. Our results are compared with earlier transmission electron microscope studies and sources of some differences are discussed.
Plasma characterization and process control diagnostics
Authors: Hershkowitz N. , Maynard H. L.
Published: July 2002

Diagnostics are needed both for plasma characterization and for plasma processing control. Normally, different diagnostics are employed. Process control relies on the ability to measure data dependent on charged and neutral particle parameters as well as on in situ surface diagnostics. Gas phase diagnostics employed at the University of Wisconsin Engineering Research Center for Plasma-Aided Manufacturing provide examples of both types of diagnostics. Both invasive and noninvasive diagnostics are employed. Invasive diagnostics such as probes are useful for characterizing the plasma but are usually not useful for control. Control is best provided by noninvasive diagnostics. Many noninvasive diagnostics, such as laser induced fluorescence are not suitable for control because they are too finicky or too inconvenient to use. Because monitoring the process in situ usually doesn’t work, it is recommended that characterization be aimed at identifying key parameters to be used for control. The specific problem of controlling the SiO2 etch rate with CF4/O2/CHF3/Ar in an electron cyclotron resonance tool is discussed as an example of this approach. The current status of our attempts at real-time control is given.
Effects of plasma enhancement on the carrier-gas-free metalorganic chemical-vapor deposition of oxide superconducting thin films
Authors: Kanehori Keiichi , Saito Shin’ichiro , Sugii Nobuyuki , Imagawa Kazushige
Published: July 2002

The effect of plasma enhancement on carrier-gas-free metalorganic chemical vapor deposition of superconducting YBa2Cu3Ox films has been investigated based on crystallographic studies, plasma diagnosis, and composition analysis of the gas phase. With plasma enhancement, the oxygen pressure needed for growing thin films with YBa2Cu3Ox structure is reduced from 4.0×10−2 to 2.0×10−2 Pa. YBa2Cu3Ox films grown with plasma-enhancement at oxygen pressure of 4.0×10−2 Pa showed zero resistivity at 86 K and a critical current density of 2×105 A/cm2 at 77 K. Plasma enhancement also was found to increase oxidizing activity by three orders of magnitude during the cooling process. Plasma diagnosis indicated that superconducting properties of grown films are related to plasma density, which can in turn be related to the concentration of active oxygen. Composition analysis of the gas phase indicated that plasma enhancement increases reaction between oxygen and metalorganic sources or their derivatives. The effect of plasma enhancement on oxidizing activity clearly differs between growth and the cooling process, and this difference may be due to the consumption of activated oxygen by metalorganic sources or their derivatives.
Tritium purification via zirconium–manganese–iron alloy getter St 909 in flow processes
Authors: Baker J. D. , Meikrantz D. H. , Pawelko R. J. , Anderl R. A. , Tuggle D. G.
Published: July 2002

A zirconium–manganese–iron alloy, St 909, was evaluated as a purifier in tritium handling, transport, and storage applications. High efficiency removal of CH4, CO, CO2, NH3, and O2 was observed at concentrations of 0.1% to 1% in helium. Gas streams at 100–5000 sccm were passed through getters operated at 600–800 °C. On-getter residence times of two seconds were required to achieve ≳99% removal of these reactive impurities. At this removal efficiency level, the individual impurity capacity of 100 g of St 909 purifier at 800 °C was 0.59, 0.28, 0.19, 0.14, and 0.12 moles of CH4, CO, CO2, O2, and NH3, respectively. Hydrogen containing gasses, CH4 and NH3 were cracked on the purifier and the resultant elemental hydrogen was released. Only 8±2 sccm of H2 were retained on 100 g of St 909 at 800 °C. These features suggest that this alloy can be employed as an efficient purifier for hydrogen isotopes in inert gas, nitrogen, or perhaps even H, D, or T streams.
Outgassing rate of preconditioned vacuum systems after short exposure to the atmosphere: Outgassing rate measurements on Viton-A and copper
Authors: Dayton B. B.
Published: July 2002

When the sorption and desorption rates depend primarily on the diffusion of water vapor and atmospheric gases through the bulk of the sorbent (which may be an elastomer or plastic) and the process is reversible, then by an application of Fick’s law and Duhamel’s theorem equations can be derived for the outgassing rate as a function of time during subsequent pumpdowns in terms of the time of exposure to atmosphere with known relative humidity and the outgassing rate as a function of time during the initial conditioning cycle. Good agreement with the predictions of these equations has been obtained from measurements of repeated pumpdowns of a large-area sample of a Viton-A elastomer. However, similar experiments on copper plates showed relatively poor agreement with the theoretical equations indicating that the sorption–desorption process for water vapor in the oxide layer on metal surfaces may not be exactly reversible or that the process is not strictly controlled by diffusion.
Auger electron spectroscopy characterization of aluminum alloy exposed to synchrotron radiation
Authors: Momose T. , Asano K. , Ohta N. , Kanda Y. , Ishimaru H.
Published: July 2002

The surface of a passivated aluminum alloy exposed to air under synchrotron irradiation in the TRISTAN colliding ring is shown to become carbon free by Auger electron spectroscopy (AES) with a turbomolecular pump and a dry backing pump. In particular, following such exposure, AES detected no carbon on the surface or in the sputter-profiled passivation layer. Furthermore, this surface was stable against carbon contamination while stored for 35 days in a covered glass dish. We attribute this behavior to ozone generated by synchrotron radiation in air, which apparently decarbonized and then oxidized the clean surface. The passivation layer has been shown previously to have a low photodesorption yield surface which, in conjunction with this simple ozone treatment, makes an ideal construction material for storage rings and other extreme high vacuum systems.
Effect of Ni on graphite thin-film formation from organic materials by chemical vapor deposition
Authors: Yudasaka Masako , Kikuchi Rie , Matsui Takeo , Tasaka Kouji , Ohki Yoshimasa , Yoshimura Susumu , Ota Etsuro
Published: July 2002

Two functions of Ni in the process of graphite thin-film formation from organic materials by chemical vapor deposition (CVD) were studied. When dehydrogenation of a certain organic material was enhanced by Ni during CVD at 600 and 700 °C, the graphite thin film could be formed on Ni at these temperatures. On the other hand, a lot of organic materials changed into graphite by CVD on Ni above 800 °C, which corresponds to the obtained result that Ni deposited on disordered graphite changed the disordered graphite to crystalline one by heat treatment above 800 °C.
Preparation of germanium doped plasma polymerized coatings as inertial confinement fusion target ablators
Authors: Brusasco Raymond , Saculla Michael , Cook Robert
Published: July 2002

Targets for inertial confinement fusion experiments at the Lawrence Livermore National Laboratory utilize an organic (CH) ablator coating prepared by plasma polymerization. Some of these experiments require a mid-Z dopant in the ablator coating to modify the opacity of the shell. Bromine had been used in the past, but the surface finish of brominated CH degrades rapidly with time upon exposure to air. This article describes the preparation and characterization of plasma polymer layers containing germanium as a dopant at concentrations of between 1.25 and 2.5 atom percent. The coatings are stable in air and have root-mean-square surface roughness of 7–9 nm (modes 10–1000) which is similar to that obtained with undoped coatings. High levels of dopant result in cracking of the inner mandrel during target assembly. Possible explanations for the observed cracking behavior will be discussed.
In situ wafer temperature monitoring of silicon etching using diffuse reflectance spectroscopy
Authors: Booth J. L. , Beard B. T. , Stevens J. E. , Blain M. G. , Meisenheimer T. L.
Published: July 2002

Real time, in situ temperature measurements during chemical downstream etching of silicon wafers have been performed using a diffuse reflectance spectroscopy based sensor [Weilmeier et al., Can. J. Phys. 69, 422 (1991)]. The spectrometer has a spatial resolution of 1 cm2, updates the temperature every 2 s, and has a temperature resolution of better than 1 °C. The thermal time constant the wafers and the thermally regulated electrostatic chuck (10 °C<T<90 °C) varied between 7 and 30 s depending on clamping and backside gas pressure. The exothermic etch process is accompanied by increases in the silicon wafer temperature consistent with the thermal conductivity conditions and with the etch chemistry. The temperature uniformity across the wafers was better than 2 °C during the entire etch process.
Electronic states of a clean Si(110) 16×2 surface studied by angle resolved photoemission and surface differential reflectivity
Authors: Crincenti A. , Nesterenko B. , Perfetti P. , LeLay G. , Sebenne C.
Published: July 2002

The electronic properties of a clean Si(110)-16×2 surface have been studied by angle resolved ultraviolet photoelectron spectroscopy (ARUPS) and surface differential reflectivity (SDR). Four surface states have been recognized by ARUPS and their dispersions have been mapped along the main symmetry lines in the surface Brillouin zone. SDR experiments revealed transitions between filled and empty surface states at ∼1.8, 2.4, and 2.9 eV. The results have been explained on the basis of a new structural model of the Si(110) 16×2 phase using adatoms, rest atoms and dimers as building blocks similarly to the case of the Si(111) 7×7 dimer-adatom-stacking fault (DAS) model.
Femtosecond time-resolved photoemission of electron dynamics in surface Rydberg states
Authors: Hertel T. , Knoesel E. , Hotzel A. , Wolf M. , Ertl G.
Published: July 2002

Femtosecond time-resolved photoelectron spectroscopy provides a unique tool to study the dynamics of optically excited electrons at surfaces directly in the time domain. We present a new model for two-photon photoelectron spectroscopy from surface and image potential (or Rydberg) states which is based on density matrix theory. The formalism accounts for the influence of both energy and phase relaxation on experimental spectra and thus permits the study of the nature of inelastic and elastic scattering processes at surfaces in more detail. The analysis of experimental data employing the proposed model reveals a new mechanism for optical excitation of electrons to normally unoccupied states at surfaces which is feasible due to the influence of electronic dephasing. We discuss the nature of different relaxation channels with respect to our studies of image state dynamics on the bare and Xe or Kr covered Cu(111) surfaces.
Role of secondary electrons in hot-electron femtochemistry at surfaces using tunnel junctions
Authors: Gadzuk J. W.
Published: July 2002

A theory of resonance-assisted, hot-electron-induced femtochemical processing at surfaces using a tunnel junction device, which has previously been developed in terms of inelastic electron scattering via negative-molecular-ion shape resonances associated with molecules adsorbed on solid surfaces, is extended here to include the effects of secondary electron cascades produced within the device. The potential influence of the secondaries on the proposed control and selectivity of the device is demonstrated and assessed.