bluuebunny/crossref_metadata_2025 huggingface dataset:
Enhanced Aluminum Properties by Means of Precise Droplet Deposition
Authors: Orme Melissa , Smith Robert F.
Published: July 2002

The use of molten aluminum droplets is investigated for potential application to precision droplet-based net-form manufacturing (PDM). In the proposed application, final structural components are made from the raw stock in one integrated operation by depositing molten metal droplets, layer after layer, via computer information. This work investigates the feasibility of the proposed technology by investigating the issues associated with generating molten aluminum droplets from capillary stream break-up, and examining the mechanical characteristics of the fabricated aluminum components. New results are presented which illustrate the generation of stable streams of molten aluminum droplets at rates of 24,000 droplets/second for a droplet stream speed of 10.9 m/s, corresponding to throughput rates of 2.3×10−4 kg/s (1.85 lb./hour). The droplets travel 2,500 droplet diameters in an inert environment before impingement with the substrate. Microstructural images are completely devoid of splat boundaries, which have been removed by remelting, and the grain size is approximately uniform throughout the field of view of the image that, in most cases presented, contains easily upwards of 30 splats. Also, it has been found that the presence of aluminum oxide in the melt does not influence the average grain size of the component. An oxide barrier however will encapsulate each grain if the oxides are not removed by filtration in the pre-jetting stage. The presence of aluminum oxide in the melt does not prohibit the removal of the splat boundaries. Mechanical analysis shows that fabrication with molten aluminum droplet deposition results in a 30 percent increase in ultimate tensile strength compared to the raw ingot stock. [S1087-1357(00)02402-3]
Closed-Form Collapse Moment Equations of Elbows Under Combined Internal Pressure and In-Plane Bending Moment
Authors: Chattopadhyay J. , Nathani D. K. , Dutta B. K. , Kushwaha H. S.
Published: July 2002

Elastic-plastic finite element analysis has been carried out to evaluate collapse moments of six elbows with elbow factors varying from 0.24 to 0.6. The loading conditions of combined in-plane closing/opening bending moment and varying degree of internal pressure are considered in the analysis. For each case, collapse moment is obtained by twice elastic slope method from the moment versus end-rotation curve. Based on these results, two closed-form equations are proposed to evaluate the collapse moments of elbows under combined internal pressure and in-plane closing and opening bending moment. [S0094-9930(00)00103-7]
Lead-On-Chip Versus Chip-On-Lead Packages and Solder Failure Criteria
Authors: Mirman Boris
Published: July 2002

High impact of peeling stresses on solder joint reliability, and how to account for these stresses in failure criteria, are discussed. [S1043-7398(00)00803-3]
Closure to “Discussion of ‘On the Development and Application of the Fast-Response Aerodynamic Probe System for Turbomachines—Part 3: Comparison of Averaging Methods Applied to Centrifugal Compressor Measurements’ ” [ASME J. Turbomach., 122, No. 3, p. 527–535 (2000)]
Authors: Kupferschmied Peter
Published: July 2002

[S0889-504X(00)01903-6]
Cell-Level Finite Element Studies of Viscous Cells in Planar Aggregates
Authors: Chen Helen H. , Brodland G. Wayne
Published: July 2002

A new cell-level finite element formulation is presented and used to investigate how epithelia and other planar collections of viscous cells might deform during events such as embryo morphogenesis and wound healing. Forces arising from cytoskeletal components, cytoplasm viscosity, and cell-cell adhesions are included. Individual cells are modeled using multiple finite elements, and cell rearrangements can occur. Simulations of cell-sheet stretching indicate that the initial stages of sheet stretching are characterized by changes in cell shape, while subsequent stages are governed by cell rearrangement. Inferences can be made from the simulations about the forces that act in real cell sheets when suitable experimental data are available. [S0148-0731(00)01404-7]
Computational Simulation of Gas Turbines: Part 2—Extensible Domain Framework
Authors: Reed John A. , Afjeh Abdollah A.
Published: July 2002

This paper describes the design concepts and object-oriented architecture of Onyx, an extensible domain framework for computational simulation of gas turbine engines. Onyx provides a flexible environment for defining, modifying, and simulating the component-based gas turbine models described in Part 1 of this paper. Using advanced object-oriented technologies such as design patterns and frameworks, Onyx enables users to customize and extend the framework to add new functionality or adapt simulation behavior as required. A customizable visual interface provides high-level symbolic control of propulsion system construction and execution. For computationally-intensive analysis, components may be distributed across heterogeneous computing architectures and operating systems. A distributed gas turbine engine model is developed and simulated to illustrate the use of the framework. [S0742-4795(00)02403-0]
Discussion: “On Stability of Time-Varying Multidimensional Linear Systems” [ASME J. Vibr. Acoust., 121, No. 4, pp. 509–511 (1999)]1
Authors: Shahruz S. M.
Published: July 2002

[S0739-3717(00)00604-8]
Economical and Ecological Cryogenic Machining
Authors: Hong Shane Y.
Published: July 2002

To eliminate health and environmental problems caused by using conventional cutting fluid in the machining industry, a new economical and practical approach to cryogenic machining technology was developed. Using micro nozzle jetting to the cutting point locally, this approach minimizes the amount of liquid consumption to levels at which nitrogen costs less than conventional cutting fluid. It reduces tool wear and lengthens tool life up to five times, thereby allowing for high-speed cutting, improving productivity and reducing overall production cost. In addition, this approach reduces the frictional force, improves chip breaking, eliminates build-up edge, and improves surface quality. This paper discloses the new cryogenic machining approach, and assesses the econom- ics of the process in comparison with state-of-the-art conventional emulsion cooling.
Discrete Ordinates Interpolation Method Applied to Irregular Three-Dimensional Geometries
Authors: Cha H. , Song T.-H.
Published: July 2002

[S0022-1481(00)00304-2]
Consideration of Moving Tooth Load in Gear Crack Propagation Predictions
Authors: Lewicki David G. , Handschuh Robert F. , Spievak Lisa E. , Wawrzynek Paul A. , Ingraffea Anthony R.
Published: July 2002

Robust gear designs consider not only crack initiation, but crack propagation trajectories for a fail-safe design. In actual gear operation, the magnitude as well as the position of the force changes as the gear rotates through the mesh. A study to determine the effect of moving gear tooth load on crack propagation predictions was performed. Two-dimensional analysis of an involute spur gear and three-dimensional analysis of a spiral-bevel pinion gear using the finite element method and boundary element method were studied and compared to experiments. A modified theory for predicting gear crack propagation paths based on the criteria of Erdogan and Sih [18] was investigated. Crack simulation based on calculated stress intensity factors and mixed mode crack angle prediction techniques using a simple static analysis in which the tooth load was located at the highest point of single tooth contact was validated. For three-dimensional analysis, however, the analysis was valid only as long as the crack did not approach the contact region on the tooth.
Real-Time Computing in Open Systems for Manufacturing
Authors: Cheng Harry H. , Proctor, Frederick , Michaloski, and John L. , Shackleford William P.
Published: July 2002

This article reviews various mechanisms in languages and operating systems for deterministic real-time computing. Open-architecture systems will be defined and their applications in manufacturing will be addressed. Market directions for open-architecture manufacturing systems will be surveyed. Performance issues based on real-time, reliability, and safety will be discussed relating to manufacturing factory automation designed and implemented with component-based, plug-and-play open-architecture.
Robust Estimation of Inelastic Fracture Energy Release Rate (J ): A Design Approach
Authors: Seshadri R. , Wu S.
Published: July 2002

There are insufficient details during preliminary stages of a pressure component design to warrant a comprehensive inelastic determination of the fracture energy release rate, J. A simplified formulation for estimating J, described in this paper, relies on a knowledge of the linear elastic stress-intensity parameter and the plastic collapse load. Subsequently, an expression for J is provided in terms of the r-node strain, which serves as an upper bound in the elastic-plastic regions for components subjected to mechanical loads. Estimates of J for several standard configurations have been obtained by inelastic FEA, and the comparisons with the corresponding robust estimates are reasonable.
Mechanistic Modeling of the Ball End Milling Process for Multi-Axis Machining of Free-Form Surfaces
Authors: Zhu Rixin , Kapoor Shiv G. , DeVor Richard E.
Published: July 2002

A mechanistic modeling approach to predicting cutting forces is developed for multi-axis ball end milling of free-form surfaces. The workpiece surface is represented by discretized point vectors. The modeling approach employs the cutting edge profile in either analytical or measured form. The engaged cut geometry is determined by classification of the elemental cutting point positions with respect to the workpiece surface. The chip load model determines the undeformed chip thickness distribution along the cutting edges with consideration of various process faults. Given a 5-axis tool path in a cutter location file, shape driving profiles are generated and piecewise ruled surfaces are used to construct the tool swept envelope. The tool swept envelope is then used to update the workpiece surface geometry employing the Z-map method. A series of 3-axis and 5-axis surface machining tests on Ti6A14V were conducted to validate the model. The model shows good computational efficiency, and the force predictions are found in good agreement with the measured data.
Experimental and Theoretical Studies of a Novel Venturi Lean Premixed Prevaporized (LPP) Combustor
Authors: Ro̸kke N. A. , Wilson A. J. W.
Published: July 2002

A new gas turbine engine using a unique layout patented in Norway has a low-emission combustion system under development. The gas generator uses entirely radial rotating components and employs a dual entry LP radial compressor, a radial HP compressor, and a radial HP turbine. The power turbine is of a two-stage axial design, coupled to an epicyclical gear embedded in the exhaust duct. Several combustor concepts have been tested and evaluated during the development of the engine. The engine is targeted for marine, power generation, and train propulsion. For the marine and train application liquid fuel operation is needed, thus the primary focus in the development has been for a lean premixed prevapourised system. An interesting concept utilizing two venturi premixers has been studied intensively. By utilizing venturi premixers the following advantages can be achieved: (1) low overall pressure drop but high injector pressure drop and velocities in the mixing region (throat region), (2) high shear forces and drag imposed on the droplets enhancing droplet shedding and evaporation, and (3) excellent emission behavior at designated load conditions. Although these advantages can benefit gas turbine low-emission combustion, the challenges in using venturi premixers are: (1) venturis are susceptible to separation and thus flame stabilization within the venturi which is detrimental and (2) inlet flow disturbances enhance the tendency for separation in the venturis and must be minimized. Studies were launched to investigate a proposed combustor configuration. These studies included analytical studies, computational fluid dynamics (CFD) calculations of isothermal and combusting flow inside the combustor together with rig tests at atmospheric, medium, and full pressure. Finally, engine tests within the full operating range were conducted with very favorable emission figures for lean premixed prevaporized (LPP) operation. The system was capable of running at below 20 ppm NOx and CO, at elevated power for liquid fuel. Control of part load performance and emissions is by variable fuel staging of the two venturi stages. The paper highlights the features of the venturi combustor development and discusses the characteristics in terms of flow conditions and droplet motion, heat transfer, ignition delay time, and emissions.
Vibration Control Using Parametric Excitation
Authors: Nguyen Phillip H. , Ginsberg Jerry H.
Published: July 2002

A simple pendulum whose pivot executes harmonic motion in the vertical direction is a prototype for systems subjected to parametric excitation. Forced excitation of this system is represented as a harmonically varying torque whose frequency is taken to be arbitrary. The investigation explores whether, for specified values of the natural frequency and the excitation frequency, it is possible to select an amplitude and frequency for the parametric excitation such that the pendulum’s vibratory rotation is reduced. The analysis supplements numerical integration of the equation of motion with a Fourier series analysis suitable to situations where the parametric frequency is a multiple of the forcing frequency. Studies of the behavior for excitation frequencies close to, and far from, the natural frequency lead to a general guideline for selecting the parametric excitation. It is shown that, with judicious selection of the parametric amplitude, a parametric frequency that is very high relative to the highest contemplated excitation frequency can substantially reduce the forced response at any lower excitation frequency.
An Algorithm for Bayes Parameter Identification
Authors: Kulczycki Piotr
Published: July 2002

This paper deals with the task of parameter identification using the Bayes estimation method, which makes it possible to take into account the differing consequences of positive and negative estimation errors. The calculation procedures are based on the kernel estimators technique. The final result constitutes a complete algorithm usable for obtaining the value of the Bayes estimator on the basis of an experimentally obtained random sample. An elaborated method is provided for numerical computations.
Evaluation of Cement Stresses in Finite Element Analyses of Cemented Orthopaedic Implants
Authors: Lennon A. B. , Prendergast P. J.
Published: July 2002

Stress analysis of the cement fixation of orthopaedic implants to bone is frequently carried out using finite element analysis. However, the stress distribution in the cement layer is usually intricate, and it is difficult to report it in a way that facilitates comparison of implants for pre-clinical testing. To study this problem, and make recommendations for stress reporting, a finite element analysis of a hip prosthesis implanted into a synthetic composite femur is developed. Three cases are analyzed: a fully bonded implant, a debonded implant, and a debonded implant where the cement is removed distal to the stem tip. In addition to peak stresses, and contour and vector plots, a stressed volume and probability-of-failure analysis is reported. It is predicted that the peak stress is highest for the debonded stem, and that removal of the distal cement more than halves this peak stress. This would suggest that omission of the distal cement is good for polished prostheses (as practiced for the Exeter design). However, if the percentage of cement stressed above a certain threshold (say 3 MPa) is considered, then the removal of distal cement is shown to be disadvantageous because a higher volume of cement is stressed to above the threshold. Vector plots clearly demonstrate the different load transfer for bonded and debonded prostheses: A bonded stem generates maximum tensile stresses in the longitudinal direction, whereas a debonded stem generates most tensile stresses in the hoop direction, except near the tip where tensile longitudinal stresses occur due to subsidence of the stem. Removal of the cement distal to the tip allows greater subsidence but alleviates these large stresses at the tip, albeit at the expense of increased hoop stresses throughout the mantle. It is concluded that a thorough analysis of cemented implants should not report peak stress, which can be misleading, but rather stressed volume, and that vector plots should be reported if a precise analysis of the load transfer mechanism is required.
Effect of Squealer Geometry Arrangement on a Gas Turbine Blade Tip
Heat Transfer
Authors: Azad Gm Salam , Han Je-Chin , Bunker Ronald S. , Lee C. Pang
Published: July 2002

This study investigates the effect of a squealer tip geometry arrangement on heat transfer coefficient and static pressure distributions on a gas turbine blade tip in a five-bladed stationary linear cascade. A transient liquid crystal technique is used to obtain detailed heat transfer coefficient distribution. The test blade is a linear model of a tip section of the GE E3 high-pressure turbine first stage rotor blade. Six tip geometry cases are studied: (1) squealer on pressure side, (2) squealer on mid camber line, (3) squealer on suction side, (4) squealer on pressure and suction sides, (5) squealer on pressure side plus mid camber line, and (6) squealer on suction side plus mid camber line. The flow condition during the blowdown tests corresponds to an overall pressure ratio of 1.32 and exit Reynolds number based on axial chord of 1.1×106. Results show that squealer geometry arrangement can change the leakage flow and results in different heat transfer coefficients to the blade tip. A squealer on suction side provides a better benefit compared to that on pressure side or mid camber line. A squealer on mid camber line performs better than that on a pressure side.
Role of Out-of-Plane Coefficient of Thermal Expansion in Electronic Packaging Modeling
Authors: Variyam Manjula N. , Xie Weidong , Sitaraman Suresh K.
Published: July 2002

Components in electronic packaging structures are of different dimensions and are made of dissimilar materials that typically have time, temperature, and direction-dependent thermo-mechanical properties. Due to the complexity in geometry, material behavior, and thermal loading patterns, finite-element analysis (FEA) is often used to study the thermo-mechanical behavior of electronic packaging structures. For computational reasons, researchers often use two-dimensional (2D) models instead of three-dimensional (3D) models. Although 2D models are computationally efficient, they could provide misleading results, particularly under thermal loading. The focus of this paper is to compare the results from various 2D, 3D, and generalized plane-deformation strip models and recommend a suitable modeling procedure. Particular emphasis is placed to understand how the third-direction coefficient of thermal expansion (CTE) influences the warpage and the stress results predicted by 2D models under thermal loading. It is seen that the generalized plane-deformation strip models are the best compromise between the 2D and 3D models. Suitable analytical formulations have also been developed to corroborate the findings from the study. [S1043-7398(00)01402-X]
Frictional and Electrical Characteristics of Grooved Fluid Film Bearings for High-Speed Laser Scanner Motor
Authors: Lee Young-Ze , Jeong Seong-Hun , Jeong Kwang-Seob
Published: July 2002

The frictional characteristics of oil-impregnated sintered-metal bearing (OSB) and herringbone-grooved fluid bearing (HFB) with varying loads and speeds were measured, and their electrical properties assembled in the scanner motor were also measured to develop new journal bearings, which could overcome the speed limit of ball bearing. OSB shows very good performance up to 20,000 rpm, and HFB successfully works up to 35,000 rpm. From the endurance tests on start-stop and continuous operating, it was confirmed that those bearings could satisfy the demand for high-rotating technology and could be mass-produced for use on high-speed scanner motor in a laser scanner unit. [S0742-4787(00)02703-X]
Nuclei growth kinetics during the nucleation of gold on UHV-cleaved mica substrates
Authors: Elliot A. Grant
Published: July 2002

The sizes of nuclei obtained during the condensation of gold on UHV-cleaved mica substrates were measured as a function of time of exposure to the incident flux. The size distributions obtained were symmetrical and initially sharply peaked, but flattened and broadened with increasing time of condensation. The mean size, always well defined with a few angstroms, was found to vary approximately as t1/3, provided the number density of nuclei remained nearly constant. When the number density of nuclei increases, the growth rate is suppressed. The time taken to reach a given size increases with increasing temperature when the nuclei are growing as isolated particles. When the nuclei are spaced such that their diffusion fields overlap, then the time taken to reach a given size decreases with increasing temperature. The rms diffusion distance could be defined rather precisely giving (ΔGdes–ΔGsd)=0.5(±0.05) eV.
High-Reflectivity Mirrors for Use at 10.6 μm
Authors: Braunstein A. I. , Braunstein M.
Published: July 2002

The advent of high-efficiency, high-power lasers, operating at various vibrational-rotational transitions of the carbon dioxide molecule in the vicinity of 10 μm, has created a need for mirrors which have high reflectivity in this region. Reflectivities between 98% and 99% can be realized with metallic mirrors of copper, silver, or gold; however, in the case of silver and copper (which have the highest reflectivities) dielectric protective coatings are required to prevent atmospheric degradation of reflectivity and to permit cleaning of the mirror. Reflectivities greater than 99% can be achieved with “enhanced metallic reflectors,” which consist of metals coated with pairs of alternating, quarter-wavelength thick, low and high index of refraction dielectrics or semiconductors. In principal this type of mirror can have a reflectivity approaching 99.9%, as has been achieved for multilayer dielectric mirrors for use at the 0.633-μm He-Ne laser line in the visible. Performance is limited, however, by the difficulty of finding materials which have suitable physical and optical properties when used in quarter-wavelength thicknesses. The present paper includes a discussion of experimental equipment for making accurate and reproducible measurements of absorption in high-reflectivity mirrors at 10.6 μm, of comparative absorption data on a variety of metals produced in different ways, and of the problems involved in producing enhanced dielectric mirrors along with some preliminary results.
Effect of Deposition Temperature on Condensed Phases in Sputtered Ni–Cr Thick Films
Authors: Panzera C. , Krutenat R. C. , Donachie M. J.
Published: July 2002

A modified triode sputtering technique was used to deposit nickel-chromium alloys on pure nickel substrates maintained at temperatures varying from 550 to 1050 °C by controlled, low energy electron bombardment heating. The coatings (110–200 μ thick), deposited at rates between 960 and 1400 Å/min, were evaluated utilizing metallographic, chemical analysis, electron microprobe, x-ray diffraction, and electron diffraction techniques. A new phase, designated ε, was found when Ni-22 at.% Cr was deposited at temperatures above 750 °C. The volume fraction of the new phase increased from 10% at 750 °C to 13% at 1050 °C. Heat treatment for 200 h at 1050 °C showed no change in volume fraction of ε previously deposited at that temperature, indicating that ε is the equilibrium phase. The ε phase containing 87 at.% chromium had a tetragonal structure with a c/a=0.55, and a columnar-plate habit and grew perpendicular to the interface. The alloy target containing 12 at.% chromium condensed as ε+γ between 750 ° and 950 °C but only γ at 1050 °C. A tentative phase diagram section has been proposed showing the relationship between ε and γ, and α phases.
Mechanisms of Stress Relief in Thin Films
Authors: Chaudhari P. , Mader S. , Freedman J. F.
Published: July 2002

The stress required to form a dislocation loop of the size of a grain has been calculated for cases where the loop forms within a grain, at a grain boundary, and in grains adjacent to another grain where a loop is already present. It is shown that in typical polycrystalline films this value of the stress is comparable to the observed stresses in films before plastic flow sets in. In the case of single crystal epitaxial films with a high grown-in dislocation density the plastic strain realizable is shown on the basis of a simple model to be a few percent. The model is based on a simple nearest neighbor dislocation interaction and is shown to explain the tensile behavior of thin single crystal films.
Thermochemistry of Liquid Metal–Gas Crucible Reactions in Vacuum
Authors: Jansson Sven A.
Published: July 2002

Thermochemical analyses are performed for the Ti–O–C, Fe–O–C, Al–O–C, Si–O–C, Mg–O–C, Be–O–C, Y–O–C, Cr–O–C, and U–O–C systems at 1800 K. The role of hydrogen, water vapor, and nitrogen in connection with these systems is exemplified. Log pMexOy vs log pO2 and log pC vs log pO2 diagrams are prepared to illustrate in a simple manner the relations between condensed phases and the equilibrium pressures of gaseous species over the different condensed phases. The diagrams are used to evaluate the correctness or applicability of available thermochemical data, and to predict or interpret reactions in or between the different systems, with particular reference to vacuum metallurgical processes.
Trapping of Rare Gases in Niobium Single Crystals
Authors: Rantanen R. O. , Donaldson E. E.
Published: July 2002

The (100) and the (111) faces of niobium single crystals were bombarded with noble-gas ions having kinetic energies between 100 and 1500 eV. Thermal release spectra were produced [E. V. Kornelsen, Can. J. Phys. 42, 364 (1964)] and characteristic activation energies were inferred as described previously [R. O. Rantanen, A. L. Moen, and E. E. Donaldson, J. Vac. Sci. Technol. 7, 18 (1970)]. These energies were compared with energies for thermally activated processes identified in niobium. Because the trapping probability for ions is greater in cold-worked metal than in an annealed metal, an investigation was made of samples which were annealed and mechanically stressed in vacuum.
Semiconductor Surface Electrostatics
Authors: Greene R. F. , Bixler D. , Lee R. N.
Published: July 2002

Two surface electrostatics problems have been solved assuming linear lattice and electronic response: (a) the screening of the dielectric image potential is calculated for partially degenerate semiconductors; and (b) the bumpiness of the space charge equipotentials produced by discrete surface charges is analyzed. The autocorrelation function of the space charge potential is expressed in terms of the autocorrelation in occupation of surface lattice sites by adions. The significance of these considerations for surface scattering and chemisorption problems is discussed.
Fast Rotation Technique for the Formation of a Thin-Film Intermetallic Compound on a Cylindrical Metallic Substrate
Authors: Meyer C. H. , Merriam Marshal F. , Snowden D. P.
Published: July 2002

A technique has been developed that allows a uniform stoichiometric thin-film compound to be formed on the outer surface of a cylindrical substrate by rapidly rotating the substrate about its longitudinal axis so that the thickness of approximately one lattice constant is deposited per revolution. Niobium and tin were vacuum evaporated simultaneously from separate sources, and bulk quality Nb3Sn films were formed over the complete substrate surface. In addition, samples were prepared of alternate layers of Nb3Sn and a second material with sharp delineation between layers. Some of the technology necessary for this method of film preparation is discussed.
Preparation of Thin-Film Diffusion Microcouples in Ternary Alloys
Authors: Murakami M. , de Fontaine D. , Shipley P. , Rodgers W.
Published: July 2002

A feedback-controlled three-source evaporator system is described. Its purpose is the preparation of multilayered thin-film specimens to be used for the study of diffusion in ternary alloys. It is shown that, with this system, it is possible to prepare thin films representing a variety of binary or ternary diffusion microcouples with specified layer thickness and specified composition ratios of the alloy components. The uniformity of thickness of each layer, essential for diffusion studies, was confirmed by the appearance of satellite intensity maxima around x-ray fundamental reflections from an AgAuPd solid solution alloy in this system.
Electron Stimulated Desorption of Excited Neutrals: CO on W
Authors: Newsham Ivor G. , Hogue James V. , Sandstrom Donald R.
Published: July 2002

A time-of-flight technique is used to study the release of excited neutrals and ions by electron-stimulated desorption ESD for the system CO on W. The method ensures the detection of the excited neutral particles without interference from photons produced by the electron beam. Use of a channel electron multiplier allows the counting of individual particle arrivals, insuring high sensitivity and allowing the use of low electron current densities. Energy distributions are obtained from the flight-time distributions for both kinds of particles, using a (100) single-crystal sample. The release of excited neutrals for this system in the temperature range 130 to 270 K is demonstrated.
Tantalum Films Triode-Sputtered in Mixtures of Argon and Water Vapor
Authors: Westwood W. D. , Willmott D. J. , Wilcox P. S.
Published: July 2002

Tantalum films have been deposited in a triode sputtering system operating at a total pressure of 5×10−4 Torr that was maintained by continuously adding an argon-water vapor mixture. Because of the low operating pressure, a mass spectrometer mounted directly in the chamber was used, without any differential pumping, to monitor mass spectra before, during, and after sputtering. The mass spectra show that the water vapor is dissociated in the discharge, and the resultant oxygen is gettered into the film. The oxygen content of the films was determined from the anodization efficiency, and it increased linearly with the inlet rate of water vapor. Measurements of the electrical properties show that the oxygen is incorporated in the films in the same way for water vapor and oxygen doping. The resistivity is increased from 50 to 1014μΩ cm with increasing oxygen content. The rapid increase in resistivity from 50 to 200 μΩ cm between 4 and 11 at.% is due to the change from bcc to the β-Ta structure. These results show that very low outgassing rates of water vapor may be sufficient to produce β-Ta in many sputtering systems.
Novel uses of the thermo-microbalance in the determination of nonstoichiometry in complex oxide systems
Authors: Holman Robert L.
Published: July 2002

New uses of the thermo-microbalance are possible when studying complex oxide systems such as PbO-La2O3-ZrO2-TiO2 that incongruently and preferentially vaporize a single component. Several vapor phase equilibration procedures are possible when the microbalance is equipped with constant activity multiphase (CAMP) crucibles designed to provide an equilibrium source of, or sink for, PbO vapor. The compositional range of a compound's single-phase stability can be directly determined at temperature. The ionic substitutional lattice site, ionic valence, and resultant charge compensation mechanism that is associated with the solution of an impurity oxide into A-B-O compounds can be inferred from gravimetric data. The methods are applicable to the controlled sintering of these materials. An expanded version of the Knudsen effusion experiment is discussed whereby extensive information of the thermodynamics, phase equilibria, and nonstoichiometry of the oxide system can be generated by a single gravimetric experiment. The binary PbO-TiO2 system is offered as an illustration.
Reactive pulsed magnetron sputtering process for alumina films
Authors: Kelly P. J. , Henderson P. S. , Arnell R. D. , Roche G. A. , Carter D.
Published: July 2002

The pulsed magnetron sputtering (PMS) process is now among the leading techniques for the deposition of oxide films. In particular, the use of pulsed dc power has transformed the deposition of dielectric materials, such as alumina. The periodic target voltage reversals during the PMS process effectively discharge poisoned regions on the target. This significantly reduces the occurrence of arc events at the target and stabilizes the deposition process. Many researchers have now shown that pulsed dc reactive magnetron sputtering can be routinely used to produce fully dense, defect-free oxide films. Despite the success of the PMS process, few detailed studies have been carried out on the role played by parameters such as pulse frequency, duty cycle, and reverse voltage in the deposition process. In this study, therefore, alumina films were deposited by reactive pulsed dc magnetron sputtering. Operating conditions were systematically varied and the deposition process monitored throughout. The aim was to investigate the influence of the pulse parameters on the deposition process, and the interrelationships between the occurrence of arc events and the parameters chosen. As a result of this investigation, optimum conditions for the production of high-quality alumina films under hard arc-free conditions were also identified.
Microstructure and chemical state of Ti1−xYxN film deposited by reactive magnetron sputtering
Authors: Choi W. S. , Hwang S. K. , Lee C. M.
Published: July 2002

A feasibility of using Ti1−xYxN as a hard coating material was investigated. Coatings were made on a Si(100) surface as well as on a steel surface using a dual-target rf-dc reactive magnetron sputtering method with the range of Y varying from x=0 to x=0.16. By x-ray diffraction analysis, it was found that all the coated films were of a single phase with a NaCl structure, with their lattice parameters increasing with Y content. A transmission electron microscopy analysis of the coated film revealed fine columnar grains in the samples containing high NY. This was attributed to Y atoms of low surface mobility and a strong bonding tendency with oxygen. The Y atoms promote the rate of heterogeneous nucleation by easily forming fine oxide particles at the substrate surface. From x-ray photoelectron spectroscopy analysis, it was learned that the binding energies of Y 3d5/2 and N 1s in YN bonding were 157.8 and 397.5 eV, respectively. The optimum combination of microhardness and adhesion strength was obtained in Ti0.928Y0.072N film. In an oxidation resistance test at 800 °C, the TiN films with high Y content performed better than pure TiN film. The oxide scale in this case consisted of rutile TiO2, anatase TiO2, and Y2Ti2O7, in which Y 3d5/2 and O 1s had binding energies of 158.7 and 530.8 eV, respectively. Overall, the present study suggests a good feasibility of utilizing Y in TiN hard coating material.
Maskless deposition of gold patterns on silicon
Authors: Erickson Lynden E. , Schmuki Patrik , Champion Garth
Published: July 2002

We demonstrate that electrochemical metal deposition selectivity may be attained by intentionally introducing defects in a semiconductor surface. The electrolyte–semiconductor surface shows a similar characteristic to a p–n junction, which when reverse biased into (Schottky) breakdown, electrochemical reactions become possible. To achieve electrochemical deposition of metals, a p-type semiconductor must be used. The defects are patterned by focused ion beam silicon ion implantation. Gold was selectively deposited only on the defective surface from a gold containing KCN electrolyte.
Influence of deposition conditions on the thermal stability of ZnO:Al films grown by rf magnetron sputtering
Authors: Haug F.-J. , Geller Zs. , Zogg H. , Tiwari A. N. , Vignali C.
Published: July 2002

The resistivity and the thermal stability of transparent conducting ZnO layers doped with aluminum have been correlated with the conditions of the sputtering process. Layers deposited at low rf power density (∼1.3 to 2.6 W/cm2) exhibit a low resistivity of 9×10−4 Ω cm, predominantly due to a high concentration of intrinsic donor type defects. These donors are compensated during annealing at high temperature in a vacuum; the low resistivity increases and the layers are not thermally stable. At rf power densities of ∼3.2 W/cm2 and more, the deposition conditions yield a high growth rate and the extrinsic aluminum dopant is incorporated on vacant cation sites. These substitutional donors are thermally stable therefore a low resistivity is retained after annealing at 550 °C.
Nanoscale luminescence spectroscopy of defects at buried interfaces and ultrathin films
Authors: Brillson L. J.
Published: July 2002

Low energy electron-excited nano-luminescence (LEEN) spectroscopy provides electronic band gap, confined state, and deep level trap information from semiconductor surfaces and interfaces on a nanometer scale. Correlation of luminescence features with their spatial location inside a growth structure—either depth wise or laterally—also provides information on the physical origin and growth dependence of the electronically active defects that form. LEEN spectroscopy of localized states illustrates this approach for a representative set of III–V nitride interfaces, including metal-GaN Schottky barriers, GaN/InGaN quantum wells, GaN ultrathin films, AlGaN/GaN pseudomorphic heterostructures across a single growth wafer, and GaN/Al2O3 interfaces. In each case, electronic properties are sensitive to the chemical composition, bonding, and atomic structures near interfaces and in turn to the specifics of the growth process.
Photoluminescence characterization of Si-based nanostructured films produced by pulsed laser ablation
Authors: Kabashin A. V. , Meunier M. , Leonelli R.
Published: July 2002

Photoluminescence (PL) properties of nanostructured Si-based films produced by pulsed laser ablation in a residual gas are studied. Two types of PL signals have been identified. Signals of the first type are sensitive to the ablation conditions with the PL peak position depending on the gas pressure during the deposition. Signals of the second type with PL peaks around 1.6–1.7 and 2.2– 2.3 eV are almost independent of the ablation conditions and are mainly determined by the presence of oxygen-related complexes in the film composition. These complexes can be formed through a prolonged natural oxidation or thermal annealing of the films, or through the direct laser ablation in the presence of oxygen. Possible mechanisms of PL signals are discussed.
Vacuum Design Problems of High Current Electron Storage Rings
Authors: Fischer G. E. , Mack R. A.
Published: July 2002

A vacuum of the order of 10−9 Torr is required in the chamber of a proposed 180-ft-diam, 3-BeV, electron-positron storage ring in order to permit beam lifetimes of many hours and to reduce background interaction rates. This pressure must be maintained in the presence of 500 kW of synchrotron radiation with a critical wavelength of 3.2 Å. The rate of radiation-induced gas evolution is investigated. The process is believed to take place via a two-step mechanism—photoelectric emission followed by electron desorption. Experimental results of various investigators are described. A combination ion-getter and titanium sublimation pumping system with total pumping speed of one half million liters per second is proposed to deal wish the problem.
Preparation and Epitaxy of Sputtered Films of Ferroelectric Bi4Ti3O12
Authors: Takei W. J. , Formigoni N. P. , Francombe M. H.
Published: July 2002

Single crystals of ferroelectric Bi4Ti3O12 are known to possess novel optical properties with potential use in optical memory or display applications. There is interest in duplicating these properties in thin films. Suitability of reactive and rf sputtering for preparation of stoichiometric films has been investigated. Films from stoichiometric targets were Bi deficient. Using Bi-rich targets stoichiometric films were obtained by depositing at substrate temperatures (typically in the range of 500 °–700 °C) high enough to prevent inclusion of the more volatile bismuth oxide in excess of the Bi4Ti3O12 composition. Good quality epitaxial growth has been achieved on MgO and epitaxial Pt substrates.
Progress in intense pulsed ion sources
Authors: Humphries Stanley
Published: July 2002

Progress in the development of intense, pulsed ion sources is described. The major impediment, electron breakdown, can be solved by magnetic insulation of the accelerating gap or reflex geometries. Both magnetic insulation and the reflex triode have been used successfully at Cornell to efficiently generate multikiloampere ion fluxes. Scaling of these devices to the range of parameters attained by pulsed electron machings (MA in the MV range) appears feasible. Such ion beams may have applications in plasma heating, ion ring production, thermonuclear pellet compression, and other areas of physical research.
Experimental scanning electron-beam automatic registration system
Authors: Wilson A. D. , Chang T. H. P. , Kern A.
Published: July 2002

An experimental automatic registration system is discussed that is capable of precisely overlaying two or more levels of a microcircuit pattern written by an electron-beam lithographic machine. Because positional information of the registration marks arrives at the detector in the form of random discrete quanta, it is subject to the statistical fluctuations inherent in all such systems. Achievement of a signal-to-noise ratio adequate for precise registrations with inherently noisy backscattered electrons and without overexposure of the resist layers covering the registration mark is accomplished using digital signal enhancement techniques. Manual and computer methods have been developed to correct field size, shift, rotation, and orthogonality. Correlation between manual and automatic registrations and the pattern are excellent because the same basic deflection and electronics systems are used for all three modes of operation. The necessary software to control the registration subsystems and to perform registration computations and edge detection have also been developed. Registration overlays have been made automatically with absolute errors on the order to 100 ppm. For a 2-mm chip, this is a level-to-level error of about ±0.1 μm. Several samples of typical complex microcircuit patterns registered with this experimental automatic system are shown.
Prospects for x-ray fabrication of Si IC devices
Authors: Smith Henry I. , Bernacki S. E.
Published: July 2002

In this paper we report on low-x-ray-attenuation Si vacuum windows for use with Al K x-ray sources and the fabrication of 5.5-cm-diam Si-membrane x-ray masks without supporting ribs. Also discussed are exposure configurations for achieving multilevel pattern superposition on 7.5-cm-diam wafers.
Influence of sputtering parameters on the composition of multicomponent films
Authors: Cuomo J. J. , Gambino R. J.
Published: July 2002

Multicomponent sputtering is examined using as examples amorphous Gd−Co alloys and related ternary systems Gd−Co−Au and Gd−Co−Mo. Film composition was studied as a function of bias voltage, target voltage, pressure, system geometry and target composition. If the sputtering yield, ε, of one constituent is much greater than the yield of the other elements in the system, it is possible to express the film composition as a simple function of the above parameters. For example, in the Gd−Co system εGd ≳ εCo and the Co/Gd ratio in the film is given by (Co/Gd)film = (Co/Gd)target/1 − K (Vb/Vt), where Vb is the effective bias voltage, Vt is the target voltage, and K is a system constant which depends largely on the geometry. The equation involves a number of simplifying assumptions which are only valid in the low bias, low pressure regime. A more complex expression must be used outside of these limits. It has also been shown that there is a simple relationship between sputtering gas incorporation in the film and the effective bias voltage, which provides an independent check on the validity of the sputtering equation.
Nucleation and growth of rf triode-sputtered gold films
Authors: Cornely R. H. , Mumtaz A. , Fuschillo N.
Published: July 2002

The nucleation and growth of rf triode-sputtered gold films, whose electrical and optical properties were previously reported, are described in detail. Electron micrographs show that the rate of formation of nucleated particles is greater than 2×1012 cm−2 sec−1. The resultant island particle density at a nominal film thickness (NFT) of 10 Å is 2×1012 cm−2. Linear alignment (chaining) of tiny nucleated island particles is observed. The growth of the island particles as irregularly shaped flattened platelets is attributed to the influence of electron charge. The islands become completely interconnected by tiny gold bridges when the surface coverage is 50% at a NFT of 30 Å. Diffraction mode and off-axis dark-field microscopy reveal that the island particles are composed of randomly oriented crystallites. Histograms of the crystallite size distribution for a large number of films showed that the crystallite size increases with NFT up to 100 Å; above 100 Å the mean crystallite size remains constant at 85 Å.
Structure and electrical properties of CdS and CdTe thick films for solar cell applications
Authors: Mitchell Kim , Fahrenbruch Alan L. , Bube Richard H.
Published: July 2002

CdTe/CdS heterojunction solar cells show particular promise for large-scale terrestrial use. To evaluate these cells, thick films of CdTe and CdS have been grown and their structure and electrical properties determined. These films have been deposited on both single-crystal and fused-quartz substrates and on each other by close-spaced vapor deposition in H2 and by two-source vacuum evaporation. The influence of growth parameters on epitaxy and crystallite size was determined by scanning electron microscopy, and the electrical transport properties were investigated by conductivity and thermoelectric power measurements. The electrical mobility of the CdTe films on fused quartz shows an exponential dependence on E/kT, indicating that grain boundaries dominate the bulk mobility in the film. To achieve large crystallite sizes and high conductivity in reasonable deposition times, temperature/time profiles have been used to control nucleation and growth of the CdTe films. Post-deposition heat treatments in H2 have been used to increase the conductivity of the CdS films.
Properties of surface carriers at GaAs–native-oxide interfaces
Authors: Stannard J. E. , Kennedy T. A. , McCombe B. D.
Published: July 2002

GaAs MOS structures have been grown using an anodic oxidation process with the electrotype first described by Hasegawa, Forward, and Hartnagel in order to study surface accumulation and inversion carrier properties on n-type material. These native oxide layers have a breakdown strength between 105 and 5×106 V/cm. C–V measurements at 300 K indicate midgap surface state densities of 1012 cm−2 eV−1. Upon cooling the flat band shift increases substantially, indicating a surface state density which is higher near the conduction band edge. The utility of contactless microwave conductance measurements of surface carrier properties in the Si–SiO2 system is shown and their applicability to the GaAs–native-oxide system investigated. The results obtained indicate the conditions under which these techniques may be used.