bluuebunny/crossref_metadata_2025 huggingface dataset:
Disturbance Adaptive Discrete-Time Sliding Control With Application to Engine Speed Control
Authors: Won Mooncheol , Hedrick J. K.
Published: July 2002

This paper presents a discrete-time adaptive sliding control method for SISO nonlinear systems with a bounded disturbance or unmodeled dynamics. Control and adaptation laws considering input saturation are obtained from approximately discretized nonlinear systems. The developed disturbance adaptation or estimation law is in a discrete-time form, and differs from that of conventional adaptive sliding mode control. The closed-loop poles of the feedback linearized sliding surface and the adaptation error dynamics can easily be placed. It can be shown that the adaptation error dynamics can be decoupled from sliding surface dynamics using the proposed scheme. The proposed control law is applied to speed tracking control of an automatic engine subject to unknown external loads. Simulation and experimental results verify the advantages of the proposed control law.
A Quasi-Steady Analytical Solution to Freezing Planar Couette Flow With Viscous Dissipation
Authors: Hall, Carsie A. , Mackie Calvin
Published: July 2002

A quasi-steady analytical solution to freezing planar laminar Couette flow with viscous heating effects is presented. Closed-form expressions for the dimensionless freeze-front location, interface Nusselt number, and dimensionless power density (or dimensionless shear stress) are derived as a function of various dimensionless parameters. Several classical results are obtained in the appropriate asymptotic limits.
Numerical and Experimental Investigations of the Head/Tape Interface in a Digital Linear Tape Drive
Authors: Tan Sanwu , Talke Frank E.
Published: July 2002

Finite element analysis is applied to simulate the head/tape interface in a Digital Linear Tape (DLT) drive. The numerical model was verified by contact spacing measurements using a “three-bump” glass head and three-wavelength interferometry. The effect of tape speed, tension and head contour parameters (island width, island radius, and penetration) on the head/tape spacing is investigated numerically for a three-bump and a five-bump DLT-type head. A “Local Tape Wrap Angle” is defined to characterize the head/tape interface.
Hysteretic Friction for the Transient Rolling Contact Problem of Linear Viscoelasticity
Authors: Chertok D. L. , Golden J. M. , Graham G. A. C.
Published: July 2002

The problem of a smooth rigid indentor under variable loading moving across a viscoelastic half-space in one direction with variable speed is considered. The motion is assumed to be frictionless and the standard linear model is adopted to describe the viscoelastic material response. An integral equation is derived and a numerical algorithm for its solution subject to appropriate subsidiary conditions is constructed. The contact interval length, pressure, and coefficient of hysteretic friction are presented and the results discussed.
An Optimal Container Design for Metal Powder Under Hot Isostatic Pressing
Authors: Chung S. H. , Park H. , Jeon K. D. , Kim K. T. , Hwang S. M.
Published: July 2002

Near-net-shape forming of 316L stainless-steel powder was investigated under hot isostatic pressing. To simulate densification and deformation of a powder compact in a container during hot isostatic pressing, the constitutive model of Abouaf and co-workers was implemented into a finite element analysis. An optimal design technique based on the evaluation schemes of the design sensitivity was used to acquire the desired final shape of a powder compact. Experimental data of 316L stainless steel powder showed that the optimally designed container allowed near-net-shape forming of the desired powder compact during hot isostatic pressing.
A Flexible Rotor on Flexible Bearing Supports: Stability and Unbalance Response
Authors: Va´zquez Jose´ A. , Barrett Lloyd E. , Flack Ronald D.
Published: July 2002

An experimental study of the effects of bearing support flexibility on rotor stability and unbalance response is presented. A flexible rotor supported by fluid film bearings on flexible supports was used with fifteen support configurations. The horizontal support stiffness was varied systematically while the vertical stiffness was kept constant. The support characteristics were determined experimentally by measuring the frequency response functions of the support structure at the bearing locations. These frequency response functions were used to calculate polynomial transfer functions that represented the support structure. Stability predictions were compared with measured stability thresholds. The predicted stability thresholds agree with the experimental data within a confidence bound for the logarithmic decrement of ±0.01. For unbalance response, the second critical speed of the rotor varied from 3690 rpm to 5200 rpm, depending on the support configuration. The predicted first critical speeds agree with the experimental data within −1.7 percent. The predicted second critical speeds agree with the experimental data within 3.4 percent. Predictions for the rotor on rigid supports are included for comparison.
A Theoretical Model of Uniform Flow Distribution for the Admission of High-Energy Fluids to a Surface Steam Condenser
Authors: Wang J. , Priestman G. H. , Wu D.
Published: July 2002

An analytical study is made of the perforated pipe distributor for the admission of high-energy fluids to a surface steam condenser. The results show that for all perforated pipes there is a general characteristic parameter MkD/Lf, which depends on the pipe geometry and flow properties. Four cases are considered based on the value of the characteristic parameter M. (1) When M⩾1/4, momentum controls and the main channel static pressure will increase in the direction of the streamline. (2) When 1/6⩽M<1/4, the momentum effect balances friction losses and the pressure will decrease to a minimum, and then increase in the direction of flow to a positive value. (3) When 0<M<1/6, friction controls and the pressure will decrease to a minimum, then increase slowly, but the total pipe static pressure difference will always be negative. (4) When M=0, a limiting case when the ratio of the length to the diameter is infinite. This analysis is useful not only for the design of perforated pipe distributors for turbine condensers over a wide range of dimensions, fluid properties, and side hole pressure but also for many other technical systems requiring branching flow distribution.
On Saint-Venant’s Problem for an Inhomogeneous, Anisotropic Cylinder—Part III: End Effects
Authors: Lin H. C. , Dong S. B. , Kosmatka J. B.
Published: July 2002

End effects or displacements and stresses of a self-equilibrated state in an inhomogeneous, anisotropic cylinder are represented by eigendata extracted from an algebraic eigensystem. Such states are typical of traction and/or displacement boundary conditions that do not abide by the distributions according to Saint-Venant’s solutions, whose construction were discussed in the first paper of this series of three. This type of analysis of end effects quantitifies Saint-Venant’s principle, and the algebraic eigensystem providing the eigendata is based on homogeneous displacement equations of equilibrium with an exponential decaying displacement form. The real parts of the eigenvalues convey information on the inverse decay lengths and their corresponding eigenvectors are displacement distributions of self-equilibrated states. Stress eigenvetors can be formed by appropriate differentiation of the displacement eigenvectors. The eigensystem and its adjoint system provide complete sets of right and left-handed eigenvectors that are interrelated by two bi-orthogonality relations. Displacement and stress end effects can be represented by means of an expansion theorem based on these bi-orthogonality relations or by a least-squares solution. Two examples, a beam with a homogeneous, isotropic cross section and the other of a two layer beam with a ±30 deg angle-ply composite cross section, are given to illustrate the representation of various end effects.
A Constitutive Description of Aluminum-1% Magnesium Alloy Deformed Under Hot-Working Conditions
Authors: Cabrera E. S. Puchi
Published: July 2002

A constitutive description of the deformation of commercial aluminum-1% magnesium alloy (AA5005) under hot working conditions has been formulated on a rational basis. The strain dependence of the flow stress is described by means of the evolution law earlier advanced by Sah et al. The optimization procedure of the experimental stress-strain data allowed the determination the extrapolated values of the initial flow stress and saturation stress which were subsequently correlated with temperature and strain rate by means of the kinetic model proposed by Kocks. It is shown that the initial work-hardening rate of this alloy is strongly dependent both on temperature and strain rate and that the temperature dependence is much more significant than that explained by the temperature dependence of the shear modulus of aluminum. The best description of the experimental flow stress data is obtained by expressing the initial work-hardening rate as a function of the effective strain rate, in terms of a simple parametric relationship, rather than considering a constant value for this parameter, independent of temperature and strain rate. The accuracy of the constitutive description proposed, regarding the reproduction of both the experimental flow stress and work-hardening rate, makes it reliable for its use in the analysis of hot-working processes involving this material.
Numerical Analysis of the Effect of Coating Microstructure on Three-Dimensional Crack Propagation in the Coating Under Rolling Contact Fatigue Conditions
Authors: Polonsky I. A. , Keer L. M.
Published: July 2002

Hard protective coatings produced by the physical vapor deposition (PVD) processes can potentially be used to prevent rolling contact fatigue (RCF) failures in gears and rolling bearings. Although TiN appears to be an attractive material for such applications, the RCF performance of PVD TiN coatings is limited by their columnar microstructure. One possible solution is to use interlayers interrupting the column growth in TiN to achieve a more equiaxed grain morphology. In this paper, the effect of the coating layer structure on the propagation of a three-dimensional crack through the coating thickness is studied theoretically. Numerical simulations of both planar and kinked three-dimensional cracks under cyclic contact loading are performed using a new numerical approach recently developed by the authors, which is based on a combination of the fast Fourier transform (FFT) technique, the eigenstrain theory, and the conjugate gradient method. The simulation results indicate that high-endurance TiN-based coatings can in principle be produced by alternating relatively thick TiN layers with much thinner interlayers made of another material.
Discussion: “Alternative Models of Turbulence in a Porous Medium, and Related Matters” (D. A. Nield, 2001, ASME J. Fluids Eng., 123, pp. 928–931)
Authors: Travkin V. S.
Published: July 2002

The paper which I authored is mentioned first by Prof. Nield [1]. I would like to make some preliminary comments about that citing in the paper by Nield, because the length of a paper which is presented to a conference like the 3rd ASME/JSME Fluids Engineering Conference in 1999, is usually restricted to 6 pages. That is the reason we could not include discussion or critics of other studies, but focused primarily on our results.
Effect of a Variable Gravity Field on Convection in an Anisotropic Porous Medium With Internal Heat Source and Inclined Temperature Gradient
Authors: Alex Sherin M. , Patil Prabhamani R.
Published: July 2002

The convective instability of a horizontal fluid-saturated anisotropic porous layer, with internal heat source and inclined temperature gradient, subject to a gravity field varying with distance in the layer, is investigated. A linear stability analysis is performed and the resulting eigenvalue problem solved using a Galerkin technique. In the absence of an inclined temperature gradient, an increase in the variable gravity parameter above −1 destabilizes the system. In its presence interesting developments occur. An increase in the heat generation destabilizes the system when the variable gravity parameter is nonnegative. When it is negative the opposite effect is seen.
Investigating the Effect of Crack Shape on the Interaction Behavior of Noncoplanar Surface Cracks Using Finite Element Analysis
Authors: Moussa Walied A. , Bell R. , Tan C. L.
Published: July 2002

In the last two decades, multiple cracks are often found in aging aerospace and mechanical structures. The interaction and coalescence of multiple cracks may significantly affect the service lives of these aging structures. Knowledge of the behavior of interacting cracks is still limited. The calculation of the crack-tip stress intensity factor, SIF, along the interacting crack fronts is considered a major contribution for the application of any linear fracture mechanics model to investigate the growth life of these cracks. In this paper, a parametric study is presented for two parallel surface cracks in an infinite plate subjected to remote tension or to pure bending loads. This study focuses on constructing a finite element (FE) model that combines the submodeling technique with its ability to generate crack submodels of different lengths and depths, and a mesh generator that can build up a mesh grid based on the size, depth, and orientation of the interacting crack sub-models. The stress intensity factors for these cracks are calculated as a function of the crack front position, depth, shape, and plate thickness. In this paper, the values of the studied crack depth to length ratio, a/c, are 0.33, 0.5, 0.67, and 1.0. Where possible, a comparison of the 3-D with 2-D results is also considered.
A Simplified Method to Predict the Steady Cyclic Stress State of Creeping Structures
Authors: Spiliopoulos K. V.
Published: July 2002

Simplified methods have been developed to find the long-term cyclic state of stress for structures that exhibit inelastic creep and are subjected to a short period cyclic loading. In the present work a new simplified method is presented which may be applied to cyclic loads having any period. The method is based on decomposing the residual stress in Fourier series. The various Fourier coefficients are computed, in an iterative way, by satisfying equilibrium and compatibility at a few time points inside the cycle. The whole numerical procedure is formulated within the finite element method and examples of various structures are presented.
Wake Recovery Performance Benefit in a High-Speed Axial Compressor
Authors: Van Zante Dale E. , Adamczyk John J. , Strazisar Anthony J. , Okiishi Theodore H.
Published: July 2002

Rotor wakes are an important source of loss in axial compressors. The decay rate of a rotor wake is largely due to both mixing (results in loss) and stretching (no loss accrual). Thus, the actual loss associated with rotor wake decay will vary in proportion to the amounts of mixing and stretching involved. This wake stretching process, referred to by Smith (1996) as recovery, is reversible and for a 2-D rotor wake leads to an inviscid reduction of the velocity deficit of the wake. It will be shown that for the rotor/stator spacing typical of core compressors, wake stretching is the dominant wake decay process within the stator with viscous mixing playing only a secondary role. A model for the rotor wake decay process is developed and used to quantify the viscous dissipation effects relative to those of inviscid wake stretching. The model is verified using laser anemometer measurements acquired in the wake of a transonic rotor operated alone and in a stage configuration at near peak efficiency and near stall operating conditions. Results from the wake decay model exhibit good agreement with the experimental data. Data from the model and laser anemometer measurements indicate that rotor wake straining (stretching) is the primary decay process in the stator passage. Some implications of these results on compressor stage design are discussed.
Analysis of Damage of Ball Bearings of Aeronautical Transmissions by
Auto-Power Spectrum and Cross-Power Spectrum
Authors: Cavacece Massimo , Introini Alberto
Published: July 2002

Fourier analysis is used as a framework in which to obtain spectral estimates for nonstationary discrete time signals. Analysis of the auto-power spectrum and the cross-power spectrum makes it possible to distinguish between false alarms and real risk situations and, in the latter case, to determine the propagation of any possible damage in its earliest phases. This analysis then allows corrective actions to be taken, such as parts replacement, in order to limit damage and contamination of component parts in fatigue tests and thus shorten machine stoppage times.
Time-Domain Analysis of Floating Bodies with Forward Speed
Authors: Clauss Günther F. , Stutz Katja
Published: July 2002

Broaching, surf-riding, and capsizing of ships and offshore structures are transient wave-structure interactions which imply high risks for crew, vessel and cargo. As nonlinear effects are of great importance, time-domain investigations are indispensable. For unveiling the associated driving mechanism of these critical motions, it is desirable to analyze the cause-reaction chains in detail: Depending on the transient wave elevation, we obtain an instationary pressure distribution on the wetted surface of the cruising vessel. Resulting forces and moments excite vessel motions in six degrees of freedom. Based on the linear panel-method program for transient wave-body interactions, TiMIT [Korsmeyer et al. (1999)], this paper investigates seakeeping characteristics of offshore structures with forward speed. Results are presented in frequency and time domain. The procedure allows to identify critical seaways, and to analyze cause-reaction chains in deterministic wave sequences where critical and steep wave packets are embedded in random seas. The detailed evaluation reveals that large roll and pitch motions are easily reduced by variation of course and speed. For investigating the mechanism of wave/structure interactions, this paper introduces the relevant time-domain methodology, and indicates how nonlinear wave characteristics can be introduced in the time-stepping analysis. In subsequent steps nonlinear wave/structure interactions will also be considered.
Green Water Loading on a FPSO
Authors: Faltinsen O. M. , Greco M. , Landrini M.
Published: July 2002

Green Water Loading in the bow region of a Floating Production Storage and Offloading unit (FPSO) in head sea waves is studied by numerical means. A 2-D method satisfying the exact nonlinear free-surface conditions within potential-flow theory has been developed as a step towards a fully 3-D method. The flow is assumed 2-D in a plane containing the ship’s centerplane. The method is partly validated by model tests. The importance of environmental conditions, 3-D flow effects, ship motions, and hull parameters are summarized. The wave steepness of the incident waves causes important nonlinear effects. The local flow at the bow is, in general, important to account for. It has become popular to use a dam-breaking model to study the propagation of water on the deck. However, the numerical studies show the importance of accounting for the coupled flow between the deck and outside the ship. When the water is propagating on the deck, a suitable distance from the bow can be found from where shallow-water equations can be used. Impact between green water on deck and a vertical deck-house side in the bow area is studied in details. A similarity solution for impact between a wedge-formed water front and a vertical rigid wall is used. Simplified solutions for an impacting fluid wedge with small and large interior angles are developed, both to support the numerical computations and to provide simpler formulas of practical use. It is demonstrated how the local design of the deck house can reduce the slamming loads. The importance of hydroelasticity during the impact is discussed by using realistic structural dimensions of a deck house. This indicates that hydroelasticity is insignificant. On the contrary, first results from an ongoing experimental investigation document blunt impacts against the deck during the initial stage of water shipping, which deserve a dedicated hydroelastic analysis.
Advances in strength theories for materials under complex stress state in the 20th Century
Authors: Yu Mao-hong
Published: July 2002

It is 100 years since the well-known Mohr-Coulomb strength theory was established in 1900. A considerable amount of theoretical and experimental research on strength theory of materials under complex stress state was done in the 20th Century. This review article presents a survey of the advances in strength theory (yield criteria, failure criterion, etc) of materials (including metallic materials, rock, soil, concrete, ice, iron, polymers, energetic material, etc) under complex stress, discusses the relationship among various criteria, and gives a method of choosing a reasonable failure criterion for applications in research and engineering. Three series of strength theories, the unified yield criterion, the unified strength theory, and others are summarized. This review article contains 1163 references regarding the strength theories. This review also includes a brief discussion of the computational implementation of the strength theories and multi-axial fatigue.
Analysis of a Sector Crack in a Three-Dimensional Voronoi Polycrystal With Microstructural Stresses
Authors: Wu M. S. , Guo J.
Published: July 2002

The Mode I stress intensity factor of a sector crack in a three-dimensional Voronoi polycrystal is computed by the body force technique. Microstructural stresses arising from the elastic anisotropy of grains (cubic and hexagonal) and the random grain orientations are estimated using the Eshelby procedure and incorporated in the stress intensity factor calculations. For metallic polycrystals, it is shown that the stress intensity factor depends significantly on the elastic anisotropy ratio, the grain orientations, the remote stress state, and the microstructural stresses. [S0021-8936(00)03401-2]
Biological Activity of rhBMP-2 Released From PLGA Microspheres
Authors: Oldham, J. B. , Lu, L. , Zhu, and X. , Porter B. D. , Hefferan T. E. , Larson D. R. , Currier B. L. , Mikos A. G. , Yaszemski M. J.
Published: July 2002

Human recombinant bone morphogenetic protein-2 (rhBMP-2) has been proven effective in stimulating the regeneration of bone in both skeletal and extraskeletal locations. Through encapsulation within, and release from, biodegradable poly(DL-lactic-co-glycolic acid) (PLGA) microspheres, a proven vehicle for sustained delivery of various proteins, the local concentrations of rhBMP-2 could be maintained at optimal levels to stimulate bone regeneration and remodeling at the site of healing in diverse clinical settings. Thus the purpose of this work was to investigate the encapsulation of rhBMP-2 in PLGA microspheres and its biologic activity upon release. Using in vitro tests in simulated body fluids, the effect of rhBMP-2 released from PLGA microspheres upon osteoblast cell cultures was found to be statistically similar to the effect produced by positive controls consisting of nonencapsulated aqueous rhBMP-2 in simulated body fluids. This clarifies an important step in skeletal tissue engineering strategies aimed at the use of encapsulated rhBMP-2 to stimulate bone regeneration and remodeling. [S0148-0731(00)01303-0]
Stabilization of a Translating Tensioned Beam Through a Pointwise Control Force
Authors: Zhu W. D. , Guo B. Z. , Mote, C. D.
Published: July 2002

A spectral analysis determining asymptotically the distribution of eigenvalues of a constrained, translating, tensioned beam in closed form is the subject of this paper. The constraint is modeled by a spring-mass-dashpot subsystem that is located at any position within the span of the beam. It can represent a feedback controller with a collocated sensor and actuator. The necessary and sufficient condition that ensures a uniform stability margin for all the modes of vibration is determined. Influences of system parameters on the distribution of eigenvalues are identified. The analytical predictions are validated by numerical analyses. The constraint location maximizing the stability margin of the distributed model is predicted through a combined analytical and numerical approach. The implications and utility of the results are illustrated. The methodology developed can be extended to predict stability margins and optimize control parameters for controlled translating beams with other types of boundary conditions and controller structures. [S0022-0434(00)00702-4]
Oblique Wave-Scattering by Thick Horizontal Barriers
Authors: Mandal B. N. , Kanoria Mridula
Published: July 2002

This paper is concerned with scattering of an obliquely incident surface water wave train by an obstacle in the form of a thick horizontal barrier of rectangular cross section present in finite depth water. Four different geometrical configurations of the obstacle are considered. It may be surface-piercing or bottom-standing, or in the form of a submerged block not extending down to the bottom, or in the form of a thick wall with a submerged gap. Multi-term Galerkin approximations involving ultraspherical Gegenbauer polynomials for solving first-kind integral equations are utilized in the mathematical analysis to obtain very accurate numerical estimates for the reflection coefficient, which are depicted graphically against the wave number for each configurations of the thick barrier. [S0892-7219(00)00701-9]
Polystyrene by XPS
Authors: Way Wayne K. , Rosencrance Scott W. , Winograd Nicholas , Shirley David A.
Published: July 2002

X-ray photoelectron spectroscopy was used to analyze a thin film of polystyrene. Spin casting from a 2% by weight solution of polystyrene in toluene was utilized. Film thickness was determined to be 60 nm by ellipsometry. The thin film was examined with a Hewlett Packard 5950A ESCA spectrometer.
Polymethylmethacrylate by XPS
Authors: Rosencrance Scott W. , Way Wayne K. , Winograd Nicholas , Shirley David A.
Published: July 2002

X-ray photoelectron spectroscopy was used to analyze a thin film of polymethylmethacrylate (PMMA) which was spin cast from a 2% weight solution of PMMA in toluene onto a gold substrate. A Hewlett Packard 5950A ESCA spectrometer was used for this investigation.
Characterization of LiNiO2 by XPS
Authors: Mansour A. N.
Published: July 2002

We report x-ray photoemission spectra (XPS) of lithium nickel oxide (LiNiO2). XPS spectra were measured with the Physical Electronics Model 5400 x-ray photoelectron spectrometer using unmonochromatized Mg Kα x rays at two pass energy settings corresponding to analyzer energy resolutions of 1.34 and 0.54 eV. We present the survey spectrum (binding energy range of 0–1100 eV) measured at an analyzer energy resolution of 1.34 eV. Multiplexes of the Li, C, O, and Ni photoemission lines, valence band region, as well as Ni LVV Auger lines were measured at an analyzer energy resolution of 0.54 eV. Our results indicate that the near surface region is highly contaminated with Li2CO3 in agreement with earlier work which showed that even samples of LiNiO2 scraped in vacuum are highly contaminated with Li2CO3 but to a lesser degree. Despite the high degree of contamination, curve fitting analysis was successful in resolving the Li, Ni, and O contributions corresponding to LiNiO2.
Growth, structure, and mechanical properties of CNxHy films deposited by dc magnetron sputtering in N2/Ar/H2 discharges
Authors: Hellgren Niklas , Johansson Mats P. , Hjörvarsson Björgvin , Broitman Esteban , Östblom Mattias , Liedberg Bo , Hultman Lars , Sundgren Jan-Eric
Published: July 2002

Hydrogenated carbon nitride films were deposited by reactive dc magnetron sputtering in mixed Ar/N2/H2 discharges at temperatures of 100 and 350 °C. The total pressure was kept constant at 0.33 Pa and the gas mixtures were varied in order to study the effect of the hydrogen on the resulting film structure and properties. Chemical sputtering effects taking place during deposition were found to be an important factor for the growth and structural evolution. When H2 is mixed into the discharge gas, the growth rate decreases considerably and the films become denser due to desorption of volatile species, like hydrocarbons, NH3 and HCN. For a H2 fraction above 15%, no net film growth takes place. The hydrogen concentration incorporated into the films was highest (up to ∼33 at. %) for low growth temperatures and low nitrogen concentrations. Furthermore, the results indicate that substantial amount of hydrogen are bonded to nitrogen. The incorporation of hydrogen in the structure interrupts the relatively long basal planes in graphite-like structures, and some regions transform into an amorphous structure. Nanoindentation measurements of the film showed decreased elasticity, as well as decreased hardness when incorporating hydrogen. However, fullerene-like films grown at 350 °C in N2/H2 discharges exhibit high elasticity for H2 partial pressures as high as ∼10−3 Pa due to low H incorporation into these films.
Analysis of Accommodation Pumps
Authors: Hobson J. P.
Published: July 2002

Studies on the basic mechanism of accommodation pumping have been continued. Two geometrical replicas of the 28-stage pump were constructed, one with all surfaces of normal smooth Pyrex, the other with all surfaces of leached Pyrex. Step functions of helium gas pressure were applied at each end of all three samples with and without cooling. Analysis of the pressure changes showed that the model of an accommodation pump as a pipe with unequal conductances in two directions was valid.
Evaporation Characteristics of Materials from an Electron-Beam Gun
Authors: Graper Edward B.
Published: July 2002

Measurements have been made of the evaporation characteristics of aluminum, alumina, aluminum nitride, barium titanate, boron carbide, boron nitride, carbon, copper, chromium, gold, iron, inconel, lead, magnesium, magnesium fluoride, molybdenum, nickel, niobium, permalloy, sapphire, silicon, silicon monoxide, silicon dioxide, silver, tantalum, tin, tin oxide, titanium, titanium monoxide, titanium dioxide, tungsten, and zinc. Using a 6-kW, 180 ° bent-beam gun, the deposition rate, required beam power, charge material form, and suitability for evaporation were determined for each material. The evaporation rate is reported in angstroms/minute. Methods of transferring these data to other guns are developed. The beam power limit is discussed and methods of increasing the evaporation rate of power limited materials are explored. Extension of these results to other materials is discussed and examples are given.
Condensation Coefficients of Argon, Krypton, Xenon, and Carbon Dioxide Measured with a Quartz Crystal Microbalance
Authors: Levenson Leonard L.
Published: July 2002

Condensation coefficients were measured by impinging a known flux of gas from a molecular beam onto the surface of a quartz crystal microbalance. The rate of change of the quartz crystal's resonance frequency was used to calculate the condensation rate. The condensation coefficient, which is the ratio of the condensation rate to the impingement rate, was found to be ≥0.95 for Ar, Kr, Xe, and CO2 when surface temperatures are less than 26, 37, 47, and 55 K, respectively, and the gas temperatures are ≤300 K for Ar, Kr, and Xe and ≤200 K for CO2. The condensation coefficients of Ar on Kr and Xe films, Kr on Ar, and Xe on Kr were also determined as a function of surface coverage from about 0.01 to 10 atomic layers.
Comparison of the Pressure Indication of a Bayard–Alpert and an Extractor Gauge
Authors: Beeck U. , Reich G.
Published: July 2002

Previous measurements by Redhead have shown that a main advantage of the extractor gauge (EG) in comparison with the Bayard–Alpert gauge (BAG) is the very much reduced influence of electronic desorption on the pressure indication. Detailed comparative measurements were made and have shown: (1) When pumping a UHV system for the first time, or switching off for a period and re-energizing, the pressure indicated by the EG is 3 to 5 times lower than that indicated by the BAG. (2) After degassing the gauges the pressure readings are almost the same, but higher because of increased gas desorption. The influence of the electronic desorption effect has been quantitatively investigated. The measurements confirmed that the reading of the EG is lower and more correct than the BAG reading under similar conditions.
Application of Various Methods for the Determination of Adsorption Lifetime and Desorption Energy of Oxygen on Tungsten
Authors: Wassmuth H.-W. , Werner H. , Mazumdar A. K.
Published: July 2002

The adsorption lifetime τ and the desorption energy Q of oxygen atoms on a polycrystalline tungsten surface have been determined as functions of the coverage θ by using a uhv mass spectrometer. A method based on contact potential and sticking probability measurements (T=1200–2500 K), a combined study of steady state and transient state desorption processes (T=2000–2600 K), and three different types of flash desorption measurements under single flight detection conditions (T=1900–2600 K) were employed. Satisfactory agreement of the results obtained from the different methods was observed. A compensation effect, depending on the coverage θ, was found between the pre-exponential factor of τ and the desorption energy Q which varies between 6.3 eV at θ=0 to 3.4 eV at θ=1. A further experiment employing a pulsed molecular beam method is in progress.
Epitaxial growth of GaN using reactive neutrals extracted from the nitrogen Helicon wave plasma
Authors: Kim Ki-Sung , Kim Seon-Hyo
Published: July 2002

A GaN epilayer on sapphire (0001) was grown using the N2 Helicon wave plasma assisted evaporation deposition process. Various methods to reduce the N2 ion impingement energy were attempted. The addition of inert gas (Ar, Ne) into the N2 plasma decreased the impingement of N2 ions and generated a higher quantity of activated nitrogen. In addition, the installation of mirror-type magnets effectively reduced the ion impingement energy. Although the ion impingement energy was less than the threshold (∼25 eV) for damaging GaN, the high flux of ion impingement during the growth of GaN induced a considerable strain in the epilayer. GaN film synthesized under direct ion impingement onto the growing surface has poor luminescent properties, despite its relatively good crystallinity. When the neutral nitrogen was utilized for GaN epilayer growth, the crystallinity and luminescent properties were greatly improved. Furthermore, with the decreasing of kinetic energy of fast neutral nitrogen, the in-plane crystallinity of GaN was improved and thus, an enhancement of luminescent properties was attained.
High performance micropane electron beam window
Authors: Dougal Roger A. , Liu Shengyi
Published: July 2002

A silicon disk etched so that it contains a multitude of microscopic and thin window panes (micropanes) can potentially transmit a larger average electron beam current density and absorb a smaller fraction of the beam energy than a common metal foil window. The enhanced performance is achieved by a combination of decreased power loss due to the extremely small window thickness (∼1 μm), and increased conductive cooling due to the small diameter (∼50 μm) of the micropanes and the large cross section of the honeycomb structure that supports the micropanes. Beam current densities up to 34 A/cm2 are permitted within each micropane. When integrated over many micropanes across the face of a window, average current densities up to 1 A/cm2 are permitted—at least three orders of magnitude larger than the <mA/cm2 typical of foil windows. The small mass thickness yields high transparency, even for low energy beams. The transmission efficiency for a 100 keV beam is 99.5.
Modeling of focused ion beam induced surface chemistry
Authors: Edinger Klaus , Kraus Thomas
Published: July 2002

A new macroscopic model for focused ion beam induced surface chemistry is presented. The model consists of two parts. The first part is based on previous work by several authors and assumes a uniform current distribution for the ion beam. In this case an analytical solution for the reaction yield can be obtained. Compared to previous work, the new model shows an improved agreement with experimental data and delivers physically meaningful parameter values. In an extended model a Gaussian beam shape has been used to account for the spatial and temporal variations in the current distribution, which are present in a real focused ion beam system. In this case the analytical solution for the yield dependence has to be solved using a spatially depended ion flux and integrated over the whole area of the pixel, which was done numerically. This model shows very good agreement with experimental data and delivers a consistent set of parameters values. In addition, experimental changes in parameter values such as beam size (defocusing) and pixel step size are accurately reflected in the simulation.
Optimization of a lithographic and ion beam etching process for nanostructuring magnetoresistive thin film stacks
Authors: Walsh Michael E. , Hao Yaowu , Ross C. A. , Smith Henry I.
Published: July 2002

The patterning of multilayer thin-film stacks to create spin valves, with dimensions ∼100 nm, for magnetic-random-access memories presents novel fabrication challenges since the materials commonly used (e.g., Co, Cu, and Ni) do not form volatile compounds, and hence cannot be reactive-ion etched. The consequent necessity of using ion-beam etching (“ion milling”) demands a solution to the twin problems of faceting and redepostion of sputtered material. In addition, antireflection layers are not used during lithography because of the necessity of avoiding high-temperature curing, which would harm the spin valve characteristics. By using a thin SiOx phase-shifting layer under the resist, we obtained adequate resist profiles; and by using a 15-nm-thick W hard mask, no measurable redeposition was observed after ion milling of cobalt. Improved etch selectivity of W relative to Co is achieved by using neon as the ion-milling gas rather than argon. A simple model for the enhanced ion-milling selectivity is presented.
Electrical characteristics of (Pb,Sr)TiO3 thin films for ultra-large-scale-integrated dynamic random access memory capacitors prepared by liquid-source misted chemical deposition
Authors: Chung H. J. , Woo S. I.
Published: July 2002

For the first time, the physical and electrical properties of lead–strontium–titanate (PST) thin films were prepared by liquid-source misted chemical deposition, and are reported. PST thin films were deposited on a platinum-coated Si wafer. Pb acetate, Sr acetate, and Ti isoproxide were used as metallic precursors. These were dissolved in 2-methoxyethnol. A fine mist of metallic precursor solution was carried into a deposition chamber by Ar carrier gas. The crystallization of PST thin film was achieved by heat treatment above 500 °C. The composition and depth profile of PST film, measured by wavelength-dispersive spectroscopy and Auger electron spectroscopy, were uniform. The dielectric constant and dielectric loss of Pb0.36Sr0.64TiO3 films of 80 nm thickness were 376 (equivalent oxide thickness: 0.83 nm) and 0.05, respectively. The electrical properties were improved by postheat treatment under O2 ambient gas after a top electrode Pt was deposited on a PST thin film. It is concluded that PST can be used as a high-capacity material for ultra-large-scale-integrated dynamic random access capacitors.
Effect of thinning a WSiN/WSix barrier layer on its barrier capability
Authors: Hirata Akihiko , Maeda Tomohiko , Machida Katsuyuki , Maeda Masahiko , Yasui Kanji , Kyuragi Hakaru
Published: July 2002

We investigated the effects of tungsten silicon nitride/tungsten silicide (WSiN/WSix) barrier layer thickness on its barrier capability. WSiN was obtained by nitridizing the WSix surface with electron cyclotron resonance nitrogen plasma. The total thickness of the WSiN/WSix barrier layer was reduced by thinning the initial WSix layer. When 5-nm-thick WSix was nitridized, the N and Si contents in the WSiN/WSix layer became smaller than when WSix initial thickness was 20 nm. This barrier layer diffused into the copper (Cu) layer when annealed, and did not act as a barrier layer. On the contrary, a WSiN/WSix barrier layer formed by nitridizing 10-nm-thick WSix showed good barrier capability against Cu diffusion. We evaluated the leakage current between Cu damascene interconnections with this barrier layer and found that this barrier layer formed on the trench side wall prevents Cu diffusion when the thickness on the side wall is over 10 nm.
Lateral correlation of InAs/AlInAs nanowire superlattices on InP(001)
Authors: Li Hanxuan , Daniels-Race Theda , Hasan Mohamed-Ali
Published: July 2002

The appearance of InAs quantum-wire-like morphology on an AlInAs buffer layer grown by molecular-beam epitaxy on nominal InP(001) surfaces is investigated. Lateral composition modulation in the AlInAs buffer layer is suggested to play an important role in the formation of InAs nanowires. For InAs/AlInAs nanowire superlattices, the InAs nanowires are laterally correlated with respect to growth directions. By changing the spacer thickness, no evidence of vertical correlation is observed. The lack of vertical correlation is ascribed to the asymmetrical cross-sectional shape of the nanowires.
Transmission electron microscopy of threading dislocations in ZnO films grown on sapphire
Authors: Lim Sung-Hwan , Washburn Jack , Liliental-Weber Zuzanna , Shindo Daisuke
Published: July 2002

Threading dislocations in wurtzite ZnO films grown on the (112̄0) a plane of sapphire were studied by transmission electron microscopy. A majority of the threading dislocations were found to be of screw or mixed character. Dislocation half loops, elongated along the c axis, were observed. It is likely that they are formed when two screw dislocations of opposite sign attract each other during growth and combine.
Image metrology and system controls for scanning beam interference lithography
Authors: Chen Carl G. , Konkola Paul T. , Heilmann Ralf K. , Pati G. S. , Schattenburg Mark L.
Published: July 2002

We are developing scanning beam interference lithography (SBIL) for writing and reading large gratings with nanometer level distortion. Our distortion goals require fringe locking to a moving substrate with subnanometer spatial phase error while measuring and controlling the fringe period to approximately one part per million. In this article, we describe the SBIL optical system design along with some major subsystems. The design incorporates measurements and controls of the parameters that limit the accuracy of our system. We describe in detail a novel image metrology scheme, which uses interferometry to measure in situ both the period and the phase of the grating image formed by the interference of two laser beams. For a grating period of approximately 2 μm, experiments demonstrate a period measurement repeatability of three parts per ten thousand, one sigma. Phase measurement indicates a slow fringe drift at 0.25 mrad/s. Both the repeatability error and the phase drift are expected to improve by about three orders of magnitude after several improvements including the installation of an environmental enclosure and thermally stable metrology frames.
Fabrication of large area 100 nm pitch grating by spatial frequency doubling and nanoimprint lithography for subwavelength optical applications
Authors: Yu Zhaoning , Wu Wei , Chen Lei , Chou Stephen Y.
Published: July 2002

In this article we report on the fabrication of 100 nm pitch gratings over a large area (∼10 cm2) using a simple, low-cost, fast process. This method includes (1) generation of the grating pattern using interferometric lithography and spatial frequency doubling and (2) pattern replication using nanoimprint lithography. The form birefringence of a 100 nm pitch Si grating was studied using ellipsometry. Measurements show an index difference of Δn>0.9 at a wavelength of 632.8 nm. The experimental data are in good agreement with effective medium theory. This indicates the possibility of using these structures for wave plates and other subwavelength optical devices operating in the visible.
In situ measurement of aspect ratio dependent etch rates of polysilicon in an inductively coupled fluorine plasma
Authors: Lill Th. , Grimbergen M. , Mui D.
Published: July 2002

The etch rate of polysilicon in high aspect ratio structures has been studied in an inductively coupled fluorine based plasma (pure SF6). The change of the silicon etch rate with increasing aspect ratio [aspect ratio dependent etch rate or reactive ion etching (RIE) lag] has been measured in situ by interferometry. The experimental structures as well as the process conditions were chosen such that (i) the interaction of neutral fluorine atoms with the silicon surface determines the etch rate, (ii) the ion energy is minimized, (iii) the mass transport of neutrals is in a molecular flow (Knudsen) regime, and (iv) the interaction of the etch species with the sidewalls can be neglected. Under these conditions, the experimental findings indicate that the RIE lag effect is reduced for higher pressures and lower cathode temperatures, i.e., for higher fluorine atom coverages of the silicon surface. This is in agreement with the Knudsen transport model by Coburn and Winters [W. Coburn and H. F. Winters, Appl. Phys. Lett. 55, 2730 (1989)]. Probabilities for the reaction of fluorine atoms with the silicon surface between 0.03 and 0.11 can be derived when fitting the experimental data with this model. The findings reported in this work are of relevance for the formation of deep trench storage capacitors and polysilicon plugs. In particular, we show that we can control RIE lag and etch rate independently for the given process conditions.
Method for reducing hyperbolic phase in interference lithography
Authors: Walsh Michael E. , Smith Henry I.
Published: July 2002

A new method is proposed for correcting nonlinear spatial phase in gratings produced with spherical beam interference lithography. We suggest that a concave exposure surface can be used to compensate for the variations in interference angle and fringe inclination which lead to hyperbolic phase progression on a flat exposure plane. Experiments are shown using a spherical concave exposure surface that demonstrate the validity of the method.