bluuebunny/crossref_metadata_2025 huggingface dataset:
Flow and Stress Induced Cavitation in a Journal Bearing With Axial Throughput
Authors: Pereira A. , McGrath G. , Joseph D. D.
Published: July 2002

The problem of predicting flow between rotating eccentric cylinders with axial throughput is studied. The system models a device used to test the stability of emulsions against changes in drop size distribution. The analysis looks for the major variation in flow properties which could put an emulsion at risk due to coalescence or breakage and finds the most likely candidate in the pressure gradient defined as the ratio of the difference between the maximum and minimum pressure to the arc length between the difference. The axial throughput is modeled by flow driven by a constant pressure gradient. The flow is calculated from the Navier-Stokes equation using the code SIMPLER (Patankar 1980). The effects of inertia at values typical for the device are studied. Several eccentricities and different rotational speeds are computed to sample the changes in flow and stress parameters in the idealized device for typical conditions. The numerical analysis is validated against the lubrication approximation in the low Reynolds number case. Conditions for stress induced cavitation are evaluated. The flow is completely determined by a Reynolds number, an eccentricity ratio and a dimensionless pressure gradient and all computed results are either presented or can be easily expressed in terms of these dimensionless parameters. The effect of inertia is to shift the eddy or re-circulation zone which develops in the more open region of the gap toward the region of low relative pressure; the zero of the relative pressure migrates away from the center and the distribution breaks the skew symmetry of the Stokes flow solution. The state of stress in the journal bearing is analyzed and a cavitation criterion based on the maximum tensile stress is compared with the traditional criterion based on pressure.
Active Control of Periodic Structures
Authors: Baz A.
Published: July 2002

Conventional passive periodic structures exhibit unique dynamic characteristics that make them act as mechanical filters for wave propagation. As a result, waves can propagate along the periodic structures only within specific frequency bands called the “Pass Bands” and wave propagation is completely blocked within other frequency bands called the “Stop Bands.” In this paper, the emphasis is placed on providing the passive structures with active control capabilities in order to tune the spectral width and location of the pass and stop bands in response to the structural vibration. Apart from their unique filtering characteristics, the ability of periodic structures to transmit waves, from one location to another, within the pass bands can be greatly reduced when the ideal periodicity is disrupted resulting in the well-known phenomenon of “Localization.” In the case of passive structures, the aperiodicity (or the disorder) can result from unintentional material, geometric and manufacturing variability. However, in the case of active periodic structures the aperiodicity is intentionally introduced by proper tuning of the controllers of the individual substructure or cell. The theory governing the operation of this class of Active Periodic structures is introduced and numerical examples are presented to illustrate their tunable filtering and localization characteristics. The examples considered include periodic/aperiodic spring-mass systems controlled by piezoelectric actuators. The presented results emphasize the unique potential of the active periodic structures in controlling the wave propagation both in the spectral and spatial domains in an attempt to stop/confine the propagation of undesirable disturbances.
Influence of a Honeycomb Facing on the Flow Through a Stepped Labyrinth Seal
Authors: Schramm V. , Willenborg K. , Kim S. , Wittig S.
Published: July 2002

This paper reports numerical predictions and measurements of the flow field in a stepped labyrinth seal. The theoretical work and the experimental investigations were successfully combined to gain a comprehensive understanding of the flow patterns existing in such elements. In order to identify the influence of the honeycomb structure, a smooth stator as well as a seal configuration with a honeycomb facing mounted on the stator wall were investigated. The seal geometry is representative of typical three-step labyrinth seals of modern aero engines. The flow field was predicted using a commercial finite volume code with the standard k-ε turbulence model. The computational grid includes the basic seal geometry as well as the three-dimensional honeycomb structures.
Autofrettaged Cylindrical Vessels and Bauschinger Effect: An Analytical Frame for Evaluating Residual Stress Distributions
Authors: Livieri Paolo , Lazzarin Paolo
Published: July 2002

The paper reports analytical solutions valid for residual stresses in cylindrical pressure vessels subjected to autofrettage. The material behavior is thought of as obeying a generic monotonic σ−ε curve and exhibiting the Bauschinger effect during the unloading phase. Under linear and power-hardening conditions, the solution is given in an explicit form. The circumstances under which it is possible to apply the superposition principle also in the presence of localized plasticity are clearly identified. When possible, the final stresses can be obtained by using in an appropriate manner the stress expressions related to the loading phase. Finally, the influence on residual stresses, both of the hardening law and of the shape of the unloading σ−ε curve, is discussed.
Effect of Vessel Compliance on the In-Vitro Performance of a Pulsating Respiratory Support Catheter
Authors: Garcia Monica Y. , Hattler Brack G. , Federspiel William J.
Published: July 2002

Intravena caval respiratory support (or membrane oxygenation) is a potential therapy for patients with acute respiratory insufficiency. A respiratory support catheter is being developed that consists of a bundle of hollow fiber membranes with a centrally positioned pulsating balloon to enhance gas exchange. This study examined the influence of vessel compliance on the gas exchange performance of the pulsating respiratory support catheter. Polyurethane elastic tubes were fabricated with compliance comparable to that measured in bovine vena cava specimens. The gas exchange performance of the respiratory catheter was studied in an in-vitro flow loop using either the model compliant tube or a rigid tube as a “mock” vena cava. Balloon pulsation enhanced gas exchange comparably in both rigid and model compliant vessels up to 120 bpm pulsation frequency. Above 120 bpm gas exchange increased with further pulsation in the rigid tube, but no additional increase in gas exchange was seen in the compliant tube. The differences above 120 bpm may reflect differences in the compliance of the elastic tube versus the natural vena cava.
Efficient Adaptive Meshing of Parametric Models
Authors: Sheffer Alla , U¨ngo¨r Alper
Published: July 2002

Parametric modeling is becoming the representation of choice for most modern solid modelers. However, when generating the finite-element mesh of the model for simulation and analysis, most meshing tools ignore the parametric information and use only the boundary representation of the model for meshing. This results in re-meshing the model basically from scratch each time a parametric change is instantiated, which happens numerous times throughout the design process. In this paper we look at ways to use the parametric information during the meshing procedure to prevent unnecessary re-meshing. The paper examines existing meshing techniques developed for other purposes, which can be applied to this problem. It also suggests several new mesh modification techniques specifically designed for efficient mesh adjustment after parametric model changes.
Predicting Local Cell Deformations in Engineered Tissue Constructs: A Multilevel Finite Element Approach
Authors: Breuls Roel G. M. , Sengers Bram G. , Oomens Cees W. J. , Bouten Carlijn V. C. , Baaijens Frank P. T.
Published: July 2002

A multilevel finite element approach is applied to predict local cell deformations in engineered tissue constructs. Cell deformations are predicted from detailed nonlinear FE analysis of the microstructure, consisting of an arrangement of cells embedded in matrix material. Effective macroscopic tissue behavior is derived by a computational homogenization procedure. To illustrate this approach, we simulated the compression of a skeletal muscle tissue construct and studied the influence of microstructural heterogeneity on local cell deformations. Results show that heterogeneity has a profound impact on local cell deformations, which highly exceed macroscopic deformations. Moreover, microstructural heterogeneity and the presence of neighboring cells leads to complex cell shapes and causes non-uniform deformations within a cell.
DSG Under Two-Phase and Stratified Flow in a Steel Receiver of a Parabolic Trough Collector
Authors: Almanza Rafael , Jime´nez Gustavo , Lentz Alvaro , Valde´s Alberto , Soria Alberto
Published: July 2002

The bending of a receiver tube in two-phase flow under stratified conditions when water is first introduced to the hot steel receiver of a 14.5-m long parabolic trough concentrator is presented in this paper. Thermal gradients were observed on the absorber wall at the inlet of the receiver tube during the boiling of water, at low mass flow of 1.6×10−5m3/sec (1 liter/min), and low pressure 4×102kPa. It should be noted that the solar concentrator was focused on the receiver tube, which contained static air before the water was introduced. The introduction of the water produced a change in the temperature difference between the upper and lower sides of the receiver, from 40-60 K to much lower temperatures, in about 45 seconds. The bending of the steel receiver tube occurred when the two-phase flow began. Maximum deflection was observed when the thermal gradient reached a minimum value. We conclude that, when the flow of steam, water, and air exist in a stratified pattern, the combination of these three elements produces the bending phenomenon. The theoretical model, developed to evaluate the experimental data, confirms that the change in temperature gradient produces the bending of the steel receiver tube during this transient stage.
On the Original Publication of the General Canonical Functional of Linear Elasticity
Authors: Felippa C. A.
Published: July 2002

The general canonical functional of linear elastostatics is associated with the names of Hu and Washizu, who published it independently in 1955. This note discusses how that functional, in a generalized four-field form, had been derived by B. M. Fraeijs de Veubeke in a 1951 technical report. This report presents five of the seven canonical functionals of elasticity. In addition to the general functional, it exhibits what is likely the first derivation of the strain-displacement dual of the Hellinger-Reissner functional. The tour of five variational principles takes only a relatively small portion of the report: 8 pages out of 56. The bulk is devoted to the use of energy methods for analysis of wing structures. The title, technology focus, and limited dissemination may account for the subsequent neglect of this original contribution to variational mechanics. [S0021-8936(00)00401-3]
A Sensitivity Study on Optimum Delayed Feedback Vibration Absorber
Authors: Jalili Nader , Olgac Nejat
Published: July 2002

A sensitivity analysis is presented for a novel tuned vibration absorber. The active tuning of the absorber is achieved using partial state feedback with a controlled time delay. The final structure, which is named Delayed Feedback Vibration Absorber (DFVA), is optimized to yield minimum Mpeak of the primary system involved for a given wide band of excitation frequencies. The optimization is performed over the absorber’s structural properties and the feedback control parameters. An optimal tuning over optimally designed passive absorber is conducted first, and separately a collective optimization over both the absorber structure and the control is studied. The assurance of the stability of the time-delayed system, which forms a critical constraint on the optimization, is also discussed. Regardless of the nature of the optimal operation, the parametric variations in the structure can influence the vibration absorption performance significantly. This concern is addressed via a sensitivity analysis. Primarily, the variations on the absorber stiffness and damping properties are studied. The findings of this effort provide tools for determining the acceptable tolerance limits of the absorber properties. [S0022-0434(00)02202-4]
Simplifying the Development and Usage of Fixtures for Sheet Metal and Composite Aircraft Parts
Authors: Walczyk Daniel F. , Raju Vinay
Published: July 2002

Based on a survey of small- to medium-sized companies that supply sheet metal parts to the major aircraft manufacturers, there is a need for a more simplified, flexible and inexpensive method to design, fabricate and register part fixtures used for CNC post forming operations (e.g., trimming, drilling). Consequently, a method has been developed that bases fixture development completely on the CAD model, eliminates the need for datum surfaces and registration features on the CNC machine workbed, and makes fixture fabrication as easy and inexpensive as possible while still maintaining high geometrical accuracy. Practical implementation of this simplified method and an actual case study are discussed. [S1087-1357(00)00102-7]
A Two-Dimensional Numerical Investigation of Transient Heat Flux Gage Performance in Short-Duration Facilities
Authors: Kim J. , Sakamoto H. , Dunn M. G.
Published: July 2002

[S0889-504X(00)02101-2]
Characterization of LiF Using XPS
Authors: Ro Chul-un , Linton Richard W.
Published: July 2002

A commercial LiF powder sample was investigated using x-ray photoelectron spectroscopy. Sample preparation included washing in acetone and methanol, pressing into indium foil and gold decoration for charge correction. Measured binding energies were very similar to those previously reported. [See W. E. Morgan, J. R. Van Wazer, and W. J. Stec, J. Amer. Chem. Soc. 95, 751 (1973); K. Hamrin, G. Johansson, U. Gelius, C. Nordling, and K. Siegbahn, Phys. Scr. 1, 277 (1970); C. D. Wagner, W. M. Riggs, L. E. Davis, J. F. Moulder, and G. E. Muilenberg, Handbook of X-ray Photoelectron Spectroscopy (Physics Electronics Division, Perkin Elmer, Eden Prarie, MN, 1979).] Because F is commonly used as a reference element for tabulated sensitivity factors, data in this paper are useful in evaluating empirical relative sensitivity factors for a specific instrument, in this instance, a Perkin Elmer-Physical Electronics Model 5400 XPS.
Si(111)2×1 by XPS
Authors: Poirier D. M. , Weaver J. H.
Published: July 2002

XPS spectra were recorded for the (111) cleavage surface of Si. For comparison, one surface was cleaved in situ (Accession #00099) and a second was cleaved in air and exposed for 90 min before it was inserted into the vacuum chamber (Accession #00100). Si 2p, 2s, and valence band spectra are included.
Native Oxide Chemistry of Amorphous Al90Fe7Ce3 Alloy by Angle Resolved XPS
Authors: Mansour Azzam N. , Poon S. J. , He Y. , Shiflet G. J.
Published: July 2002

X-ray photoemission spectra of the core and valence band levels for an amorphous Al90Fe7Ce3 ribbon are presented. Survey scan and high resolution multiplexes of the C 1s, O 1s, F 1s, Al 2p, Al 2s, Fe 2p, and Ce 3d photoelectron lines and the valence band region were collected on a Perkin-Elmer/Physical Electronics model # 5400 photoelectron spectrometer using monochromatized Al x rays. Angle resolved spectra of the O 1s, Al 2p, and Al 2s photoelectron lines for emission angles of 5°, 15°, 25°, 35°, 45°, 55°, 60°, 65°, 70°, 75°, 78°, and 80° relative to sample normal were also collected to aid in identifying the chemistry of the native oxide. The material, 25 μm thick amorphous ribbon, was prepared by rapid solidification of the metallic components from the liquid phase using the melt-spinning method. The material is of technological importance due to its extremely high strength, low density, and anticipated high corrosion resistance. Analysis of XPS data reveals the following conclusions: (i) the chemistry of the native oxide is similar to that of an aluminum oxyhydroxide chemistry namely, AlOx(OH)y, (ii) the oxygen 2s line consists of low (~531.2 eV) and high (~532.4 eV) binding energy peaks corresponding to ionic O and OH chemistries in AlOx(OH)y, respectively, with the ratio of the mole fraction of OH to that of O decreasing with decrease in electron emission angle, (iii) both the aluminum 2p and 2s lines consist of low and high binding energy peaks corresponding to Al in AlOx(OH)y and Al in Al90Fe7Ce3, respectively, (iv) both Fe and Ce are present in metallic forms as in Al90Fe7Ce3 with no indication of any segregation of oxidized species into the native oxide region, (v) F is present in small quantities as a surface impurity, and (vi) the presence of a native oxide coating of AlOx(OH)y may enhance the corrosion resistance of such a class of amorphous alloys.
Hysteresis and mode transitions in a low-frequency inductively coupled plasma
Authors: Xu S. , Ostrikov K. N. , Luo W. , Lee S.
Published: July 2002

Global electric properties, distributions of the induced electromagnetic fields, electron density, temperature, and plasma potential in the 500 kHz planar-coil inductively coupled plasma source have been investigated. The transitions between the two (E and H) discharge operating regimes with variation of input power and operating gas pressure have been demonstrated. It has been shown that the E↔H transitions are accompanied by the resonant minima in the rf power reflection coefficient, which are characteristic for mode jumps in electron cyclotron resonance and microwave slot-excited discharges. The optical emission spectra of argon atoms and ions together with global power balance arguments suggest that the step-wise ionization via the excited states of argon atoms and ions is presumably a mechanism which is responsible for hysteresis. The achieved high plasma density with a high homogeneity level, and low electron temperature and plasma potential imply that the studied plasma source is promising for industrial applications.
The deposition behavior of SiO2–TiO2 thin film by metalorganic chemical vapor deposition method
Authors: Lee Si-Moo , Park Jeong-Hoon , Hong Kug-Sun , Cho Woon-Jo , Kim Dong-Lae
Published: July 2002

SiO 2 –TiO 2 thin films were deposited by metalorganic chemical vapor deposition using an alkoxide source. At 680 °C, the deposition rate curve showed parabolic behavior and the refractive index increased linearly from 1.45 to 2.35 with increasing titanium tetraisopropoxide: Ti(OC3H7)4(TTIP) ratio. Each oxide component in the film was separated analytically and its effective deposition rate, in the composite thin film, was calculated to analyze the deposition mechanism of the mixed sources. A Lorentz–Lorenz model was used to attain the composition of the film for each component separation. Effective SiO2 deposition from tetraethylorthosilicate: Si(OC2H5)4(TEOS) showed parabolic behavior with increasing TTIP ratio, while the effective TiO2 deposition did not. In addition, TTIP lowered the apparent activation energy of SiO2 deposition significantly from ∼40 to ∼10 Kcal/mol. From this, it was concluded that TTIP enhanced the TEOS decomposition, which results in the anomalous deposition behavior in composite films. A more reactive TTIP molecule acting as a “free radical reaction initiator” was suggested as a mechanism for enhancement of the process.
Dependence of optical properties on structural and compositional parameters in CuGaSe2
Authors: Dı́az R. , Martı́n T. , Merino J. M. , León M. , Rueda F.
Published: July 2002

The dielectric constant of CuGaSe2 as a function of stoichiometric deviations has been obtained from photomodulated spectral ellipsometry measurements. Optical gaps have been computed by fitting experimental and differentiated data of the imaginary part of the dielectric constant to function ε2 of the Lorentz model and to the second derivative of ε2. In each sample, three transition energy values have been found in the 1.65–1.72, 1.83–1.95, and 2.97–3.14 eV ranges. The presence of point defects reduces the energy gap values. For nonstoichiometric samples, changes in the first energy gap values have been analyzed as a function of the displacement of the position of the anion in the unit cell. The shifts in the valence band structure have been analyzed and it is concluded that the difference between the first and second transition energies, (Eg2−Eg1), is also affected by stoichiometric deviations, so that the Γ5v(2) level in samples with point defects is closer to Γ4v(2) level than in stoichiometric ones. Changes in (Eg3−Eg2) and (Eg3−Eg1) are related to Se position.
Mechanical properties of TiC/metal multilayers synthesized by ion beam sputtering technique
Authors: Wang Jing , Li Wen-Zhi , Li Heng-De
Published: July 2002

Artificially modulated TiC and a series of metals with modulation wavelength λ from 1.8 to 25.0 nm and the metallic content fraction from 10 to 50 vol % were prepared by ion beam sputtering technique at ambient temperature. Low-angle x-ray diffraction and x-ray diffraction were used to analyze their periodicity and structural properties. It was found that sharp interfaces were formed between individual layers. With the modulation parameters properly adjusted, the multilayer was even harder than its hard component (TiC). The maximum hardness of the multilayers was about a 120% enhancement above the rule-of-mixture values of TiC/Cr multilayers, and was achieved at λ=9.0 nm, with the metallic content of 50%. The possible mechanism for hardening is discussed.
Fabrication of molybdenum carbide and hafnium carbide field emitter arrays
Authors: Wei Yi , Chalamala Babu R. , Rossi Gene , Palmer Kathleen , Smith Bruce G. , Reuss Robert H.
Published: July 2002

We report on a process for the fabrication of Mo2C and HfC refractory metal carbide field emitter arrays using a modified Spindt tip fabrication process. Measurements of the aspect ratios of emitter cones showed that Mo2C tip structures have an aspect ratio similar to Mo field emitter tips. Where as with HfC, tip structures with a higher aspect ratio than either Mo or Mo2C were obtained. The measured aspect ratios for Mo, Mo2C, and HfC tips were 1.09, 1.10, and 1.20, respectively. While the target materials to fabricate the arrays were the appropriate carbides, x-ray photoelectron spectroscopy of the carbide films showed evidence for the presence of significant amount of oxygen throughout the films, mostly in the form of oxycarbides. The primary purpose of this report is to describe materials and processes suitable for large area field emission display applications. However, we also provide preliminary electrical results which demonstrate the feasibility of fabrication of metal carbide field emitters and identify important details to be addressed to achieve successful electrical performance.
Comparison of pulsed laser deposition CNx films grown from organic and inorganic targets
Authors: González P. , Soto R. , León B. , Pérez-Amor M.
Published: July 2002

A comparative study of CNx films grown by pulsed laser ablation from organic and inorganic targets has been reported. An ArF excimer laser (193 nm) was used to ablate pure glassy graphite (>99, 95%) and guanazole (3,5 diamino 1,2,4 triazol) targets in a reactive atmosphere of ammonia. Changes in thickness and properties of the CNx films were studied by profilometry, Fourier transform infrared and energy dispersive x-ray spectroscopies. Additional information on the film bonding configuration was obtained by a controlled thermal effusion system. The role of the target materials on the CNx film growth rate, composition and bonding configuration was investigated. We find that the ablation of organic targets in a NH3 atmosphere leads to films with nitrogen content near to stoichiometric values (57 at. %) and a wider variety of carbon–nitrogen bonds. Also, the formation of C–N single bonds is promoted and the thermal desorption spectra give interesting information about film structural changes. Finally, the thermal stability of the films grown from both compounds is discussed.
Preparation of site specific transmission electron microscopy plan-view specimens using a focused ion beam system
Authors: Langford R. M. , Huang Y. Z. , Lozano-Perez S. , Titchmarsh J. M. , Petford-Long A. K.
Published: July 2002

A new technique for the preparation of site specific plan-view specimens using a focused ion beam system is presented. The technique consists of milling a wedge shaped piece of material which is free from the substrate, lifting this out using a micromanipulator and needle, and orientating it on the substrate with the original surface vertical. The plan-view specimen is then milled from this piece of material using an approach based on the “lift-out” technique for the preparation of a cross-section specimen. Advantages of this technique over current methods based on the “lift-out” and the “trench” techniques are that the plan-view specimens are site specific, the surrounding substrate is left intact, and numerous plan-view specimens can be prepared in close proximity to one another.
Analysis of Cerium–Zirconium Mixed Metal Oxides by Auger Electron Spectroscopy
Authors: Nelson A. E. , Schulz Kirk H.
Published: July 2002

Auger electron spectra of cerium–zirconium mixed metal oxides over a kinetic energy range of 50–1200 eV are presented. The cerium–zirconium metal oxides were prepared via co-precipitation of nitrate precursors. The precipitate compositions were confirmed to ± 5 at. % with x-ray fluorescence and the crystalline structures were determined with x-ray diffraction. The precipitates were formed into 0.1 mm thick specimens and analyzed in wafer form.
Model for an inductively coupled Ar/c-C4F8 plasma discharge
Authors: Rauf Shahid , Ventzek Peter L. G.
Published: July 2002

This article describes a two-dimensional model for an inductively coupled Ar/c-C4F8 plasma discharge, which is widely used in the microelectronics industry for dielectric etching and polymerization. The chemical mechanism for c-C4F8 incorporates known information about electron impact dissociation, ionization, and attachment processes. Unknown details such as neutral dissociation byproducts have been empirically inferred using energetics analysis or diagnostic experiments. The mechanism also considers electron impact processes for neutral radicals (e.g., CF, CF2, CF3) and stable molecules (e.g., C2F4) produced in a c-C4F8 plasma. It is demonstrated in the article that the resulting neutral species densities, ion flux to the wafer, and electron characteristics are in good agreement with experiments in the Gaseous Electronics Conference reference cell. The validated model is used to understand the dynamics of an inductively coupled Ar/c-C4F8 plasma discharge, and the impact of various control parameters on plasma characteristics. Results indicate that CF2 is the dominant CFx radical in the c-C4F8 discharge and the plasma is mildly electronegative. Enhanced ionization and dissociation of c-C4F8 with increasing inductive power deposition leads to an increase in electron and CFx radical densities, and total ion flux to the wafer. Enhanced dissociative attachment at higher gas pressure decreases the electron density and increases the negative ion density. The plasma becomes more electropositive with decreasing c-C4F8 concentration in the gas mixture, which increases the total positive ion flux to the wafer.
Electromigration performance of AlCu/Ti and AlCu/Ti/TiN/Ti metallization
Authors: Kamoshida Kazuyoshi
Published: July 2002

The electromigration (EM) lifetimes of top-TiN/Ti/Al-0.5%Cu/Ti-bottom and top-TiN/Ti/Al-0.5%Cu/Ti/TiN/Ti-bottom stacked structures were investigated using five-level Al-alloy interconnections with tungsten-filled vias. TiN/Ti/AlCu /Ti stacked structures had an EM lifetime ten times longer than TiN/Ti/AlCu/Ti/TiN/Ti ones. This longer EM lifetime is probably due to the small grain-boundary diffusivities for the bamboo microstructure. In the TiN/Ti/AlCu/Ti structure, a localized Al3Ti intermetallic compound layer was formed by the reaction between Al and Ti at the AlCu/Ti interface. On the other hand, in the TiN/Ti/AlCu/Ti/TiN/Ti structures, an almost uniform Al3Ti intermetallic compound layer was formed at the AlCu/Ti interface. In the initial nucleation process in Al, the Al grain growth increased on Ti/SiO2 compared with Ti/TiN/Ti/SiO2 according to atomic force microscopy observation. Using the optimum Ti thickness (10 nm) made it possible to form long-EM-lifetime multilevel interconnections without using many metal stacked structures.
Redistribution and electrical activation of ultralow energy implanted boron in silicon following laser annealing
Authors: Whelan S. , Privitera V. , Italia M. , Mannino G. , Bongiorno C. , Spinella C. , Fortunato G. , Mariucci L. , Stanizzi M. , Mittiga A.
Published: July 2002

The electrical activation of B in Si following excimer laser annealing has been investigated with transmission electron microscopy (TEM) and spreading resistance profiling. Ultrashallow profiles, extending to a depth of 35 nm, have formed in Si following laser annealing. The lateral distribution of the implanted B following laser annealing has been studied with two-dimensional measurements using selective etching and cross-sectional TEM on samples where the implanted dopant was confined within an oxide mask. The results show that there is substantial lateral diffusion of B under the oxide mask when melting occurs in this region. However it is shown in this article that the melting of the Si under the masked region can be controlled by the oxide thickness. Dopant diffusion into the bulk was observed after a combination of laser and rapid thermal annealing (RTA). The TEM results suggest that there is considerable lattice strain at the liquid–crystal interface after regrowth of the layer, which was subsequently removed following a RTA process step.
Open boat evaporation of low arsenic−selenium alloys
Authors: Sigai A. G.
Published: July 2002

The open boat evaporation of low arsenic−selenium alloys has been investigated to determine the feasibility of depositing compositionally uniform films. Although a thermochemical analysis is presented which indicates that congruent evaporation should occur in this system, experimentally determined arsenic profiles reveal that unfractionated films cannot be obtained by this technique. In situ measured evaporation rates using a quartz crystal oscillator demonstrate that this is a consequence of the low−thermal transfer from the boat to the alloy, relative to the high evaporation rate of the melt, causing the required congruent evaporation temperature to be unattainable.
Structure–property relationships in xerographic selenium-alloy films
Authors: Schottmiller John C.
Published: July 2002

The properties of vitreous selenium–arsenic films important for xerographic application are reviewed in terms of direct and inferred knowledge of their structure. Charge transport properties in particular are sensitive to factors affecting the ring and chain arrangement of atoms characteristic of selenium polymorphs. Composition, purity, evaporation–deposition conditions, and aging influence structure and are critical in determining xerographic performance.
Canadarm and the space shuttle
Authors: Aikenhead Bruce A. , Daniell Robert G. , Davis Frederick M.
Published: July 2002

‘‘Canadarm’’ is the remote manipulator system (RMS) given by Canada to NASA for installation on the shuttle orbiter. The RMS is to be used for deployment, retrieval, and handling of payloads up to 65 000 lb mass, 15 ft in diameter and 60 ft in length. Controllability, operating constraints, flight environments, safety, reliability, volume, weight, and power allocations were factors which influenced the design. The system uses brushless dc servomotors to drive the six joints and the end effector of the 50 ft arm in a variety of control modes, which provide both manual and automatic control of arm functions. In describing the system, this paper concentrates on the various mechanical devices which are required to operate in the orbital environment and discusses some of the problems encountered during their development. SPAR Aerospace Ltd., under contract to the National Research Council of Canada, designed, developed, manufactured, tested, and delivered the system, which at the time of this writing has been successfully demonstrated on two flights of the orbiter ‘‘Columbia.’’
Metal-derived band gap states: Ti on GaAs(110)
Authors: Ludeke R. , Straub D. , Himpsel F. J. , Landgren G.
Published: July 2002

The emergence of filled and empty Ti-derived interface states in the band gap of GaAs has been observed for coverages as low as 0.03 monolayer with synchrotron radiation excited photoemission (XPS) and inverse photoemission (IPS) spectroscopies. The onset of the photoelectron threshold for filled states in the valence band spectra and of the IPE photon threshold for the empty states follow directly the position of the surface Fermi level in the band gap. The origin of these states is associated with the rehybridization of the Ti-3d electrons with the valence electrons of the Ga and As atoms of the interface. This notion is supported by XPS core level studies, which show the occurrence of exchange reactions between the Ti and Ga, and the out-diffusion of As and its reaction with Ti. Chemical rebonding at the interface, which produces bonding (filled) and nonbonding (empty) states, is thus the first demonstrable mechanism for Fermi level pinning and Schottky barrier formation.
Quartz friction vacuum gauge for pressure range from 0.001 to 1000 Torr
Authors: Ono M. , Hirata M. , Kokubun K. , Murakami H. , Hojo H. , Kawashima H. , Kyogoku H.
Published: July 2002

A quartz friction vacuum gauge (QF gauge) is based on the fact that the resonance impedance of a quartz oscillator is proportional to the frictional force of ambient gas. The first model of the QF gauge, which was developed by the authors as a wide range pressure monitor, has the minimum measuring pressure of 0.01 Torr with an accuracy of the order of 10%. To lower the minimum measurable pressure, we developed a sensing head consisting of a tuning fork oscillator with higher sensitivity fixed on a temperature-stabilized metal rod and a digital readout circuit. The performance of the gauge was evaluated from results of measurement of pressure dependence, temperature variations, and fluctuations of the gauge output, which is proportional to the resonance current of the oscillator. It was confirmed that an error in measurement by the gauge is within ±10% for pressure from 0.001 to 1000 Torr.
High-rate reactive sputter deposition of zirconium dioxide
Authors: Jones Fletcher
Published: July 2002

Using an improved reactive sputter deposition technique, zirconium dioxide is deposited on cooled and uncooled substrates at low, medium, and high rates of 51.7, 95.4, and 152.4 nm/min, respectively. The films are deposited by sputtering a Zr target in an oxygen–argon plasma. The Zr target remains in the metallic state. The films are characterized by measuring the stoichiometry, refractive index, optical transmission, stress, and crystallinity as a function of deposition rate. Films deposited on (100) N-type silicon substrates were annealed at temperatures ranging from 200 to 500 °C in steps of 50 °C. X-ray diffraction patterns show that the ‘‘as-deposited’’ films contain polycrystalline and amorphous phases of various amounts depending on the deposition rate and substrate temperature. Amorphous components crystallize into the cubic phase as the annealing temperature increases. At deposition rates of 95.4 and 152.4 nm/min, the refractive index and optical transmission (at 820 nm) of the unannealed, as-deposited films are not affected by the quantity of material in the amorphous state and are also independent of substrate temperature.
Ruthenium impregnation of plasma grown alumina films
Authors: Halverson D. E. , Cocke D. L.
Published: July 2002

This investigation centers around the impregnation of plasma grown alumina films using the incipient wetness technique for introduction of ruthenium chloride to the surface. The modeling of bulk alumina catalysts by use of planar alumina films necessitates investigation of the impregnation of these films. It has been found that very different products are formed by slight changes in the process used for impregnation. The impregnation was found to yield a product ranging from a highly dispersed ruthenium species to the dispersion of relatively large metal islands on the surface of the alumina. Characterization by x-ray photoelectron spectroscopy, scanning electron microscopy, and energy dispersive spectroscopy indicates that the products containing highly dispersed metal are suitable for further investigation in the modeling of bulk ruthenium catalysts.
Thermal stabilization of device quality films deposited at low temperatures
Authors: Fitch J. T. , Kim S. S. , Lucovsky G.
Published: July 2002

The effects of postdeposition furnace annealing, at temperatures typical of metal–oxide semiconductor (MOS) fabrication processes, on gate oxides formed by remote plasma-enhanced chemical vapor deposition (remote PECVD) are discussed. SiO2 films were prepared by (1) remote PECVD at substrate temperatures of 200 and 400 °C, and (2) by thermal oxidation of silicon at temperatures from 850 to 1150 °C. Postdeposition thermal processing was carried out in industrial-type diffusion furnaces in both N2/O2 and N2/H2 ambients over a temperature range of 400–1050 °C. Film properties were studied by infrared spectroscopy, ellipsometry, and by measurements of capacitance voltage (C–V) characteristics in MOS device structures. Postdeposition thermal processing at temperatures of 400 °C and above was shown to modify both the structure and electrical properties of deposited SiO2 films. It is shown that changes in the as-deposited film properties occur by two different relaxation mechanisms, one of which is operative in the temperature range up to 750 °C and the other from 750 to 1050 °C, and both of which are different from the viscoelastic relaxation process observed in thermally grown SiO2.
Formation of Cu3Si and its catalytic effect on silicon oxidation at room temperature
Authors: Stolt L. , Charai A. , D’Heurle F. M. , Fryer P. M. , Harper J. M. E.
Published: July 2002

Copper forms three silicides which are stable at room temperature, with compositions of Cu5Si, Cu15Si4, and Cu3Si. The sequence of formation of these phases in Cu–Si bilayers is described. Cu3Si is always the first phase formed by annealing to 200 °C, and is the stable phase on bulk Si. We show that Cu3Si has a dramatic effect on the oxidation of (100) silicon.While thermal oxidation of Si is normally carried out at temperatures above 700 °C, the process described here produces a thick layer of SiO2 at room temperature. The SiO2 layer grows spontaneously to over one micrometer in thickness in several weeks in air, beneath most of the original Cu3Si layer. Analysis by Rutherford backscattering, Auger electron spectroscopy, cross-sectional transmission electron microscopy, and scanning electron microscopy reveals the presence of Cu3Si particles at the buried SiO2/Si interface. These Cu3Si particles catalyze the room temperature oxidation of silicon.
Measurement of CO pressures in the ultrahigh vacuum regime using resonance-enhanced multiphoton-ionization time-of-flight mass spectroscopy
Authors: Looney J. Patrick , Harrington Joel E. , Smyth Kermit C. , O’Brian Thomas R. , Lucatorto Thomas B.
Published: July 2002

An evaluation is made of measurements of CO pressures in the UHV regime using resonance-enhanced multiphoton ionization coupled with time-of-flight mass spectroscopy (REMPI-TOFMS). It has been found that once the REMPI-TOFMS system has been calibrated, quantitative measurement of CO pressures as low as 10−10 Pa is possible, even in overwhelming N2 backgrounds. With compensation for laser pulse energy variations, we find measurements with uncertainties of 10%–15% are possible for pressures down to 10−7 Pa, and an ultimate detection limit for CO pressures of 10−10 Pa for our measurement system. In this study, the REMPI-TOFMS system was calibrated using a pressure division technique along with a spinning rotor gage. The ionization of CO is achieved using 230 nm radiation to excite the B 1Σ+ state of CO at 10.8 eV via a two-photon absorption and then ionizing some of the excited state molecules by the absorption of an additional photon from the laser beam.
Investigation of roughened silicon surfaces using fractal analysis. II. Chemical etching, rapid thermal chemical vapor deposition, and thermal oxidation
Authors: Spanos L. , Liu Q. , Irene E. A. , Zettler T. , Hornung B. , Wortman J. J.
Published: July 2002

Fractal analysis was applied to images of rough silicon surfaces which were acquired with an atomic force microscope. Spectroscopic ellipsometry was also used to extract roughness information using an optical model and the Bruggeman effective-medium approximation. Different rough silicon surfaces were examined from three microelectronics processes; rapid thermal chemical vapor deposition, chemical etching, and thermal oxidation. The fractal nature of the surfaces and the correlation between fractal, optical, and topographic parameters were explored.
Enhanced adherence of area-selective electroless metal plating on insulators
Authors: Shafeev G. A. , Themlin J.-M. , Bellard L. , Marine W. , Cros A.
Published: July 2002

We describe a simple way of producing adherent metal films (Cu or Ni) on insulator surfaces [SiO2, glass, or polyphenylquinoxaline (PPQ), an insulating polymer] by electroless growth on a thermally activated palladium acetylacetonate [Pd(acac)2] seeding layer. Using this process, we produced tiny metal patterns on insulators by localized laser pyrolysis (using either a pulsed Cu vapor or a cw Ar+ laser) of the spun-on seeding layer. A tensile stress test applied to a Ni deposit on SiO2 reveals bonding strengths as high as 2 N/mm2. The mechanisms of such an increased adherence have been studied using x-ray photoemission spectroscopy (XPS). The critical role of the chemical environment of the Pd clusters obtained by pyrolytic decomposition of the Pd(acac)2 seeding layer is shown. In particular, XPS reveals that most of the Pd atoms left at the surface after thermal decomposition still remain bonded to an organic aromatic species identified as one of the two acetylacetonate ‘‘wings’’ of the parent molecule. A wear-resistant metal deposit on insulators can only be formed when these remaining ligands are removed by an additional acetic acid treatment.
Oxygen plasma asher contamination: An analysis of sources and remedies
Authors: Synowicki R. A. , Hale Jeffrey S. , McGahan William A. , Ianno N. J. , Woollam John A.
Published: July 2002

The low Earth orbit (LEO) environment is commonly simulated using oxygen plasma ashers to determine the effects of LEO on spacecraft materials. However, plasma ashers can also contaminate samples during plasma exposure, making them less than ideal for space simulation. This study results from attempts to minimize or eliminate contamination. Optical methods of variable angle spectroscopic ellipsometry and reflectance spectrophotometry were used to quantify contaminant stoichiometry and deposition rate. Auger electron spectroscopy identified deposited contaminants and their surface coverage. Contamination results from etching of the rubber chamber seals by the plasma. The deposited contaminant was nearly indistinguishable from fully stoichiometric SiO2. Contaminant deposition rates up to 0.27 nm/min have been observed, and these layers effectively passivate the surface by depositing an overcoat of SiOx. Placing metal into the path of the plasma before it can reach the chamber seals greatly reduces contamination. A newly designed chamber confines the plasma to a small volume away from the chamber seals. For fluences as high as 3.5×1022 atoms/cm2, equivalent to 7.5 years of space exposure for the International Space Station, the redesigned asher showed less than one monolayer of deposited contaminant.
Influence of strain on semiconductor thin film epitaxy
Authors: Fitzgerald E. A. , Samavedam S. B. , Xie Y. H. , Giovane L. M.
Published: July 2002

Under typical growth conditions, strain levels greater than or equal to 10−4 are shown to influence thin film surface morphology and strain relaxation pathways. Misfit and threading dislocations in relaxed heterostructures produce long wavelength undulations on the surface and shallow depressions, respectively. Threading dislocation densities greater than ∼105–106 cm−2 in relaxed heterostructures must be due to increased impediments to dislocation motion, which in turn originate from the effect of the misfit dislocations on the surface morphology. Under typical growth conditions, the origin of strain-induced surface features can be identified by recognizing the length scale at which the features occur.
Multilayer film deposition of TiN/AlN on a rotating substrate holder from reactive sputtering of elemental targets of titanium and aluminum
Authors: Jensen H. , Sobota J. , Sorensen G.
Published: July 2002

(Ti,Al)N x coatings have previously been deposited by reactive sputtering from (TiAl) targets. This article will report on a multilayer approach, where a substrate is rotating successively through sputter zones with targets of elemental Ti and Al. In reactive sputtering of these elements the well-known hysteresis curves of total pressure versus reactive gas flow for constant Ar flow were observed. It was then possible to select certain flow values of nitrogen and to maintain a constant sputtering pressure by using a PC process control. By variation of the substrate holder velocity a multilayer TiNx/AlNx system, with bilayer thicknesses from 1 to 8 nm, was studied. The multilayer film was characterized by the acoustic-emission scratch technique used in adhesion studies. Consistency between the various critical load values were achieved, and adhesion values between 40 and 80 N were measured; wear was also found to depend on the number of multilayers.
Time dependence and spatial distribution of the deposition rate of YBa2Cu3O7 thin films in 90° off-axis sputtering
Authors: Quigley P. G. , Rao R. A. , Eom C. B.
Published: July 2002

We have examined the time dependence and spatial distribution of the deposition rate of YBa2Cu3O7 (YBCO) thin films in 90° off-axis radio frequency planar magnetron sputtering throughout the life of a target. We have found that although the amount of YBCO sputtered from the target is constant, the amount of YBCO deposited on the substrate decreases linearly over time. Furthermore, the time dependence of the deposition rate changes at different positions on the substrate. The changes in the deposition rate at any point along the substrate as a function of time can be explained by the change in the angular distribution of the sputtered particles that is caused by changes in the target erosion groove geometry, and the decrease in the kinetic energy of sputtered particles that is indicated by the decrease in the self-bias voltage over time.