bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Simulation of Grinding and Drying Performance of a Fluid-Energy Lignite Mill
Authors: Anagnostopoulos J. , Bergeles G. , Epple B. , Stegelitz P.
Published: July 2002

A numerical algorithm is developed for a detailed 3D simulation of the two-phase flow field in fluid-energy mills used for pulverization and drying of fossil fuels in large power plants. The gas phase equations are solved using finite differences and the control volume method, whereas a Lagrangian formulation with a stochastic particle dispersion model is adopted for the particulate phase. Fluid-particle interaction is taken into account to calculate the mass, momentum, and heat transfer between phases. Advanced numerical techniques for partially-blocked cells and local grid refinement have been utilized to achieve an accurate representation of the domain geometry and to enhance the accuracy of the results. Particle collisions, fragmentation mechanism, and moisture evaporation are simulated by corresponding models, whereas the special treatment employed for the rotating fan region provides the capability to solve the two-phase flow simultaneously in the entire rotating and nonrotating mill domain. The flow and the operation characteristics of a recently developed lignite mill are measured, and the numerical algorithm is used to predict the mill performance under various inlet profiles of the fuel mass flow rate. The predicted results are reasonable, and in agreement with the available measurements and observations, thus offering a deeper insight into the complex dynamic and thermal behavior of the two-phase flow in the mill.
Bifurcations of Eigenvalues of Gyroscopic Systems With Parameters Near Stability Boundaries
Authors: Seyranian A. P. , Kliem W.
Published: July 2002

This paper deals with stability problems of linear gyroscopic systems Mx¨+Gx˙+Kx=0 with finite or infinite degrees-of-freedom, where the system matrices or operators depend smoothly on several real parameters. Explicit formulas for the behavior of eigenvalues under a change of parameters are obtained. It is shown that the bifurcation (splitting) of double eigenvalues is closely related to the stability, flutter, and divergence boundaries in the parameter space. Normal vectors to these boundaries are derived using only information at a boundary point: eigenvalues, eigenvectors, and generalized eigenvectors, as well as first derivatives of the system matrices (or operators) with respect to parameters. These results provide simple and constructive stability and instability criteria. The presented theory is exemplified by two mechanical problems: a rotating elastic shaft carrying a disk, and an axially moving tensioned beam.
Dynamic Crack Analysis Under Coupled Thermoelastic Assumption
Authors: Hosseini-Tehrani P. , Eslami M. R. , Daghyani H. R.
Published: July 2002

A boundary element method using Laplace transform in time domain is developed for the analysis of fracture mechanic under coupled thermoelastic assumption. The transient coupled thermoelastic field is solved without need for domain discretization. The singular behavior of the temperature and displacement fields in the vicinity of the crack tip is modeled by quarter-point elements. Thermal dynamic stress intensity factors for mode I are evaluated from computed nodal values, using the well-known displacement and traction formulas. The accuracy of the method is investigated through comparison of the results with the available data in literature. The conditions where the inertia term plays an important role is discussed and variations of the dynamic stress intensity factor is investigated.
Effect of Stress Ratio on Fatigue Crack Growth in 95Pb-5Sn Solder
Authors: Zhao and J. , Mutoh Y. , Ogawa T.
Published: July 2002

The stress ratio effect on the fatigue crack growth behavior of 95Pb-5Sn solder has been investigated. It is found that both ΔJ and ΔK can correlate fatigue crack growth data well, which means that the crack growth behavior of the 95Pb-5Sn solder under the frequency of 10 Hz was dominantly cyclic dependent. The da/dN-ΔJ relationship can be expressed as: da/dN=1.1×10−11s˙ΔJ1.45. Low level of crack closure was found only in the near-threshold region. Except in this region, no crack closure was observed in the present test conditions. Both transgranular and intergranular fractures were observed on fracture surfaces: the former was dominant in most test conditions and the latter was dominant at the high stress ratio of 0.7. Striations and striation-like features were also found. Many slip bands and cavities along the grain boundary were observed on the crack wake and ahead of the crack tip in the high crack growth rate region.
Mixed-Mode Failure of Graphite/Epoxy Composites
Authors: Seif M. A. , Shahjahan M.
Published: July 2002

An experimental study of the crack displacement and failure modes of graphite epoxyplates, having central cracks at different angles with the loading axis, was conducted. Due to this type of loading arrangement, the material was under mixed-mode loading condition (mode I and mode II). In this investigation, Moire´ Interferometry technique was employed to measure Crack Opening Displacement (COD) and Crack Shearing Displacement (CSD). Detailed studies were performed to investigate the effect of the crack angle on the strength reduction ratio, the damage zone, and the critical stress intensity factors. The comparison between the Linear Elastic Fracture Mechanics (LEFM) solution and the results obtained from this investigation showed a fair agreement between the theoretical data and the experimental ones. This confirms the validity of implementing the LEFM model for this type of materials.
Evaluation of Advanced Two-Phase Flow and Combustion Models for Predicting Low Emission Combustors
Authors: Klose G. , Schmehl R. , Meier R. , Maier G. , Koch R. , Wittig S. , Hettel M. , Leuckel W. , Zarzalis N.
Published: July 2002

The development of low-emission aero-engine combustors strongly depends on the availability of accurate and efficient numerical models. The prediction of the interaction between two-phase flow and chemical combustion is one of the major objectives of the simulation of combustor flows. In this paper, predictions of a swirl stabilized model combustor are compared to experimental data. The computational method is based on an Eulerian two-phase model in conjunction with an eddy dissipation (ED) and a presumed-shape-PDF (JPDF) combustion model. The combination of an Eulerian two-phase model with a JPDF combustion model is a novelty. It was found to give good agreement to the experimental data.
Variability of a Three-Dimensional Finite Element Model Constructed Using Magnetic Resonance Images of a Knee for Joint Contact Stress Analysis
Authors: Li Guoan , Lopez Orlando , Rubash Harry
Published: July 2002

Magnetic resonance (MR) imaging has been widely used to evaluate the thickness and volume of articular cartilage both in vivo and in vitro. While morphological information on the cartilage can be obtained using MR images, image processing for extracting geometric boundaries of the cartilage may introduce variations in the thickness of the cartilage. To evaluate the variability of using MR images to construct finite element (FE) knee cartilage models, five investigators independently digitized the same set of MR images of a human knee. The topology of cartilage thickness was determined using a minimal distance algorithm. Less than 8 percent variation in cartilage thickness was observed from the digitized data. The effect of changes in cartilage thickness on contact stress analysis was then investigated using five FE models of the knee. One FE model (average FE model) was constructed using the mean values of the digitized contours of the cartilage, and the other four were constructed by varying the thickness of the average FE model by ±5 percent and ±10 percent, respectively. The results demonstrated that under axial tibial compressive loading (up to 1400 N), variations of cartilage thickness caused by digitization of MR images may result in a difference of approximately 10 percent in peak contact stresses (surface pressure, von Mises stress, and hydrostatic pressure) in the cartilage. A reduction of cartilage thickness caused increases of contact stresses, while an increase of cartilage thickness reduced contact stresses. Furthermore, the effect of variation of material properties of the cartilage on contact stress analysis was investigated. The peak contact stress increased almost linearly with the Young’s modulus of the cartilage. The peak von Mises stress was dramatically reduced when the Poisson’s ratio was increased from 0.05 to 0.49 under an axial compressive load of 1400 N, while peak hydrostatic pressure was dramatically increased. Peak surface pressure was also increased with the Poisson’s ratio, but with a lower magnitude compared to von Mises stress and hydrostatic pressure. In conclusion, the imaging process may cause 10 percent variations in peak contact stress, and the predicted stress distribution is sensitive to the accuracy of the material properties of the cartilage model, especially to the variation of Poisson’s ratio.
Stamping Blank Optimal Layout and Coil Slitting Widths for Single and Multiple Blanks
Authors: Nye T. J.
Published: July 2002

In stamping, operating costs are dominated by raw material costs, which can typically reach 75 percent of total costs in a stamping facility. In this paper, material utilization efficiency is modeled by considering two primary sources of scrap: material cut away from the exterior of each blank on the strip and off-cuts of unusable narrow strips generated when wide master coils are slit into strips for subsequent stamping. Based on these, layout optimization techniques for minimizing raw material usage are described that predict the optimal blank orientation on the strip and the optimum slitting width for the strip. In addition, methods are given for determining optimal common strip widths for multiple parts, both for dependent and independent demand. These algorithms are ideally suited for incorporation into die design CAE systems.
On the Sliding Friction Characteristics of Unidirectional Continuous FRP Composites
Authors: Ning Xinguo , Lovell Michael R.
Published: July 2002

By applying a closed-form analytical solution Hwu and Fan (1998) for an anisotropic half-plane, the contact characteristics of unidirectional continuous fiber-reinforced plastic (FRP) composites are investigated. The particular condition of a rigid parabolic cylinder in normal sliding contact with the composite is evaluated. The influence of FRP composite matrix material, friction coefficient, fiber material, fiber orientation, and fiber volume fraction on the surface contact pressure are determined and evaluated by comparison to published experimental data and results from the finite element method. From the analytical results, several important trends for the contact characteristics of fiber-reinforced plastics are ascertained and discussed with respect to the wear and design-ability of FRP materials.
Accurate 5-Axis Machining of Twisted Ruled Surfaces
Authors: Tsay Der Min , Her Ming Jane
Published: July 2002

Flank cutting can be effectively employed to machine ruled surfaces instead of traditional point cutting. In consideration of reducing discrepancies between designed and machined twisted ruled surfaces, an analytical model is established to account for undercutting incurred in flank milling by the use of cylindrical cutters. Based on the model, the twist angle, the ruling length, and the size of the used cutter relating to the magnitude of undercutting are observed. By flank milling twisted ruled blade surfaces of an impeller, an application example is given to show the developed 5-axis flank milling technique based on a type of a 5-axis machine tool.
Experimental Robot Identification: Advantages of Combining Internal and External Measurements and of Using Periodic Excitation
Authors: Verdonck Walter , Swevers Jan , Samin Jean-Claude
Published: July 2002

This paper discusses the advantages of using periodic excitation and of combining internal and external measurements in experimental robot identification. This discussion is based on the robot identification method developed by Swevers et al., a method that is recognized by industry as an effective means of robot identification that is frequently used, Hirzinger, G., Fischer, M., Brunner, B., Koeppe, R., Otter, M., Grebenstein, M., and Schafer, I, 1999, “Advances is Robotics: The DLR Experiment,” The International Journal of Robotics Research, Vol. 18, No. 11, pp. 1064–1087 [3]. Experimental results on a KUKA IR 361 show that the periodicity of the robot excitation is a key element of this method. Nonperiodic robot excitation complicates the signal processing preceding the parameter estimation, often yielding less accurate parameter estimates. An extension of this identification method combines internal and external measurements, Chenut, X., Samin, J. C., Swevers, J., and Ganseman, C., 2000, “Combining Internal and External robot Models for improved Model Parameter Estimation,” Mechanical Systems and Signal Processing. Vol. 14, No. 5, pp. 691–704 [4], yielding robot models that allow to accurately predict the actuator torques and the reaction forces/torques of the robot on its base plate, which are both important for the path planning. This paper presents and critically discusses the first experimental results obtained with this method.
Dry Patch Stability of Shear Driven Liquid Films
Authors: Penn David G. , Lopez de Bertodano Martin , Lykoudis Paul S. , Beus Stephen G.
Published: July 2002

The breakdown of the liquid film at the wall in annular gas-liquid flow may lead to the formation of a stable dry patch. For the case of heat transfer surfaces this causes a hot spot. Dry patch stability depends on a balance of body and surface forces. In the present study the film is driven by the interfacial shear force and the gravity force is negligible. Hartley and Murgatroyd proposed a model for dry patches of shear driven films based on a balance of surface tension and inertia but the film contact angle had to be adjusted to an unrealistic value to fit the model to experimental data. Murgatroyd later proposed an additional force because the wall and the interfacial shear stresses on the film are unbalanced near the dry patch. The magnitude of the net shear force on the film is determined by a characteristic length, λ, over which this imbalance occurs. However, Murgatroyd did not validate the model with a mathematical solution for the distribution of the shear stresses but determined λ empirically to fit the experimental data. A new computational fluid dynamics (CFD) solution of the flow field in the film around the dry patch has been obtained. The CFD results confirm Murgatroyd’s hypothesis, although the details are more complex. In addition new experimental data for adiabatic upward annular air-water and air-ethylene glycol flows provide further validation for Murgatroyd’s model.
Development and Application to a Real Scenario of a Design for Environment Methodology for Power Plants
Authors: Cedola L. , Stasio G. Di
Published: July 2002

Power plants use burning processes with a heavy environmental impact. Traditional design models aim to optimize economic and thermodynamic performances. Owing to the new sensitivity arising towards the environment, power generation design must respect the environment. Today no standardized design criteria exist; the present work aims to elaborate a specific methodology for power plants consisting of a predictive instrument (the Environmental Impact Evaluation), a management tool (the Environmental Management System), and a series of environmental studies and checks. After showing the methodology, the authors tested it with an application to a real scenario: the heat and electrical power needs of a pharmaceutical firm. Cogeneration seemed to be the best available technology from an economic and environmental point of view. In the proposed case study, all possible impacts have been quantified verifying legislative standards and accomplishing the ISO 14000.
3D FEA Modeling of Hard Turning
Authors: Guo Y. B. , Liu C. R.
Published: July 2002

A practical explicit 3D finite element analysis model has been developed and implemented to analyze turning hardened AISI 52100 steels using a PCBN cutting tool. The finite element analysis incorporated the thermo-elastic-plastic properties of the work material in machining. An improved friction model has been proposed to characterize tool-chip interaction with the friction coefficient and shear flow stresses determined by force calibration and material tests, respectively. A geometric model has been established to simulate a 3D turning. FEA Model predictions have reasonable accuracy for chip geometry, forces, residual stresses, and cutting temperatures. FEA model sensitivity analysis indicates that the prediction is consistent using a suitable magnitude of material failure strain for chip separation, the simulation gives reasonable results using the experimentally determined material properties, the proposed friction model is valid and the sticking region on the tool-chip interface is a dominant factor of model predictions.
Two-Phase Eulerian/Lagrangian Model for Nucleating Steam Flow
Authors: Gerber A. G.
Published: July 2002

This paper describes an Eulerian/Lagrangian two-phase model for nucleating steam based on classical nucleation theory. The model provides an approach for including spontaneous homogeneous nucleation within a full Navier-Stokes solution scheme where the interaction between the liquid and gas phases for a pure fluid is through appropriately modeled source terms. The method allows for the straightforward inclusion of droplet heat, mass, and momentum transfer models along with nucleation within complex flow systems as found, for example, in low pressure steam turbines. The present paper describes the solution method, emphasizing that the important features of nucleating steam flow are retained through comparison with well-established 1-D solutions for Laval nozzle flows. Results for a two-dimensional cascade blade and three-dimensional low pressure turbine stage are also described.
Combined Optimal Design and Control With Application to an Electric DC Motor
Authors: Reyer Julie A. , Papalambros Panos Y.
Published: July 2002

In the design and optimization of artifacts requiring both mechanical and control design, the process is typically divided and performed in separate steps. The physical structure is designed first, a control strategy is selected, and the actual controller is then designed. This article examines how this separation could affect the overall system design and how the combination of the separate problems into a single decision model could improve the overall design, using an electric DC motor as a case study. The combination is challenging since the two problems often have different design criteria, decision objectives, and mathematical model properties. Furthermore, the two problems are often fully coupled in that the physical structure depends on the controller and the controller depends on the physical structure. A Pareto analysis is suggested as a rigorous way to compare a variety of design scenaria.
Computational Design and Experimental Evaluation of Using a Leading Edge Fillet on a Gas Turbine Vane
Authors: Zess G. A. , Thole K. A.
Published: July 2002

With the desire for increased power output for a gas turbine engine comes the continual push to achieve higher turbine inlet temperatures. Higher temperatures result in large thermal and mechanical stresses particularly along the nozzle guide vane. One critical region along a vane is the leading edge-endwall juncture. Based on the assumption that the approaching flow to this juncture is similar to a two-dimensional boundary layer, previous studies have shown that a horseshoe vortex forms. This vortex forms because of a radial total pressure gradient from the approaching boundary layer. This paper documents the computational design and experimental validation of a fillet placed at the leading edge-endwall juncture of a guide vane to eliminate the horseshoe vortex. The fillet design effectively accelerated the incoming boundary layer thereby mitigating the effect of the total pressure gradient. To verify the CFD studies used to design the leading edge fillet, flowfield measurements were performed in a large-scale, linear, vane cascade. The flowfield measurements were performed with a laser Doppler velocimeter in four planes orientated orthogonal to the vane. Good agreement between the CFD predictions and the experimental measurements verified the effectiveness of the leading edge fillet at eliminating the horseshoe vortex. The flow-field results showed that the turbulent kinetic energy levels were significantly reduced in the endwall region because of the absence of the unsteady horseshoe vortex.
Planar Double-Slip Model for Polycrystal Plasticity and Micro Tension Tests of Pure Nickel and Copper
Authors: Hong Hong-Ki , Liu Chein-Shan , Shiao Ya-Po , Shih Bing-Chang
Published: July 2002

Many natural minerals and manmade materials are aggregates of crystals or polycrystalline solids with a nonrandom distribution of grain orientations. Macroscopic behavior in such textured polycrystals depends on directions and is thus anisotropic. In this paper we develop experimental and theoretical procedures for investigating grain orientation evolution and its effect on the tensile stress-strain curve. The micro-tensile experiments were executed in a self-developed micro-forcing-heating device together with a micro-recorder-image analyzer system. In the experiments the 0.1 mm thin foil specimens of pure nickel and copper were gradually loaded toward final failure and the evolution of grain boundaries and slip bands inside grains was observed and recorded digitally via microscope and CCD camera throughout the whole time history. The texture image data were then used in a theoretical micro-macro transformation procedure to simulate the orientation evolutions and the stress-strain curves. The procedure was based on a double-slip model of polycrystal plasticity and on averaging of polycrystalline behavior over all grain orientations weighted by an orientation distribution function. The comparisons made between the simulated and experimental data of orientation evolutions and between the simulated curves and the macro-curves concurrently obtained in the experiments confirm the proposed procedures capable of simulating the considered micro-macro relations.
The Influence of Intrinsic Strain Softening on Strain Localization in Polycarbonate: Modeling and Experimental Validation
Authors: Govaert L. E. , Timmermans P. H. M. , Brekelmans W. A. M.
Published: July 2002

Intrinsic strain softening appears to be the main cause for the occurrence of plastic localization phenomena in deformation of glassy polymers. This is supported by the homogeneous plastic deformation behavior that is observed in polycarbonate samples that have been mechanically pretreated to remove (saturate) the strain softening effect. In this study, some experimental results are presented and a numerical analysis is performed simulating the effect of mechanical conditioning by cyclic torsion on the subsequent deformation of polycarbonate. To facilitate the numerical analysis of the “mechanical rejuvenation” effect, a previously developed model, the “compressible Leonov model,” is extended to describe the phenomenological aspects of the large strain mechanical behavior of glassy polymers. The model covers common observable features, like strain rate, temperature and pressure dependent yield, and the subsequent strain softening and strain-hardening phenomena. The model, as presented in this study, is purely “single mode” (i.e., only one relaxation time is involved), and therefore it is not possible to capture the nonlinear viscoelastic pre-yield behavior accurately. The attention is particularly focused on the large strain phenomena. From the simulations it becomes clear that the preconditioning treatment removes the intrinsic softening effect, which leads to a more stable mode of deformation. [S0094-4289(00)01002-1]
Improvement of the Static and Dynamic Characteristics of Magnetic Head Sliders by Optimum Design
Authors: Hashimoto Hiromu , Hattori Yasuhisa
Published: July 2002

The aim of this paper is to develop a general methodology for the optimum design of magnetic head sliders in improving the spacing characteristics between a slider and disk surface under static and dynamic operating conditions of hard disk drives and to present an application of the methodology to the IBM 3380-type slider design. To generate the optimal design variables, the objective function is defined as the weighted sum of the minimum spacing, the maximum difference in the spacing due to variation of the radial location of the head, and the maximum amplitude ratio of the slider motion. Slider rail width, taper length, taper angle, suspension position, and preload are selected as the design variables. Before the optimization of the head, the effects of these five design variables on the objective function are examined by a parametric study, and then the optimum design variables are determined by applying the hybrid optimization technique, combining the direct search method and successive quadratic programming. From the obtained results, the effectiveness of optimum design on the spacing characteristics of magnetic heads is clarified. [S0742-4787(00)03701-2]
Weld Repair of Aged Cr-Mo Steel Piping—A Review of Literature
Authors: Viswanathan R. , Gandy D.
Published: July 2002

Power plant piping operating at elevated temperatures is subject to several types of service aging-related degradation, such as softening, spheroidization, embrittlement, and creep. When cracks are found in these components, weld repair is often employed to ensure continued operation. The efficacy of the weld repairs in terms of extending the life of the aged components has, however, not been documented quantitatively. The Electric Power Research Institute (EPRI) has recently undertaken a comprehensive study to evaluate weld repairs performed to aged piping. In connection with this study, results from other worldwide activities have been reviewed, leading to significant conclusions regarding weld repair. This review of results from several worldwide studies has confirmed that aged high-temperature piping can be successfully weld repaired to gain additional lives in excess of several decades. The key aspects of successful weld repair include excavation and removal of all prior creep cavitation damage, elimination of external bending stresses, and implementation of good welding practice. From merely a creep rupture point of view, postweld heat treatment (PWHT) has been concluded to be superfluous by several authors. Temperbead repairs appear to offer a promising alternative to PWHT repairs from a creep, tensile, and toughness standpoint. Choice of the repair process ultimately is dictated by many considerations such as toughness, notch sensitivity, residual stresses and hydrogen embrittlement susceptibility. Several reports suggest that gas tungsten arc welding (GTAW) repairs may outperform shielded metal arc welding (SMAW) repairs with or without PWHT. [S0094-9930(00)02001-1]
Corrundum (α-Al2O3) by XPS
Authors: Rotole John A. , Sherwood Peter M. A.
Published: July 2002

The XPS spectra of corrundum were collected with a VSW HA150 using monochromatic Al Kα x-radiation. Monochromatic radiation provides a distinct clarity to the peak structure in the valence band of corrundrum due to the absence of interfering x-ray satellites from the intense O 2s region. Variations in the intensities and peak separation of the two-peak structure in the valence bands of the oxides, hydroxides, and oxyhydroxides of aluminum allow one to distinguish between these compounds. The valence band, survey, and the Al 2s, Al 2p, O 1s, and C 1s core levels are reported.
Effects of chemical etching with hydrochloric acid on a glass surface
Authors: Jang H. K. , Chung Y. D. , Whangbo S. W. , Lyo I. W. , Whang C. N. , Lee S. J. , Lee Seok
Published: July 2002

Glass slides were chemically etched with hydrochloric acid using three different methods. We investigated the effects of chemical etching treatments on such properties as chemical composition, surface roughness, and relative transmittance of the glass. Sodium, calcium, and aluminum atoms at the glass surface were effectively reduced by chemical etching with hydrochloric acid. Boiling the glass in a 36% hydrochloric acid solution for 30 min was more effective in reducing sodium, calcium, and aluminum atoms at the surface of the glass than any of the other etching methods using hydrochloric acid. Surface morphology of the glass was very different with chemical etching treatments with hydrochloric acid etchant. Root-mean-square surface roughness of the bare glass was 0.58 nm, but the roughness of the glass etched with hydrochloric acid ranged from 5.4 to 6.8 nm. The sodium concentration at the glass surface was greatly reduced, from 2.7% to 0.2%. The depth that was affected by chemical etching with hydrochloric acid was about 70 nm.
Surface-enhanced photoemission in Schottky diodes with microrelief interfaces
Authors: Dmitruk N. L. , Mamykin S. V.
Published: July 2002

The internal photoemission current of Au–GaAs Schottky barriers with interfaces like a diffraction grating have been investigated. The surface plasmon-polariton excitation is shown to be an additional mechanism that contributes to an increase in the internal photoemission current. The sharp edges at such interfaces lead to an enhancement of the electric field, which can reach more than ten times that of a flat sample.
Fabrication of masks for electron-beam projection lithography
Authors: Lercel Michael , Magg Chris , Barrett Monica , Collins Kevin , Trybendis Michael , Caldwell Neal , Jeffer Ray , Bouchard Lucien
Published: July 2002

Masks for electron projection lithography (EPL) require the use of thin membranes for either stencil or all membrane scattering masks. The processes of forming the printable patterns before or after the membrane etch step are compared for EPL stencil masks. Image size uniformity and image placement distortions are characterized and indicate, with appropriate process optimization, either process flow is viable for EPL mask manufacture. Image size uniformity within individual membranes has achieved <10 nm (3σ) with the membrane flow process, and the magnitude of process induced image placement distortions is similar for both process flows. Stencil masks have also been fabricated with support rings. The masks with support rings show more repeatable absolute image placement, but the image placement distortion due to patterning is nearly identical for masks with or without a support ring.
Fabrication technology of a Si nanowire memory transistor using an inorganic electron beam resist process
Authors: Tsutsumi Toshiyuki , Ishii Kenichi , Hiroshima Hiroshi , Hazra Sukti , Yamanaka Mitsuyuki , Sakata Isao , Taguchi Hirohisa , Suzuki Eiichi , Tomizawa Kazutaka
Published: July 2002

We report on a novel fabrication technology of a Si nanowire memory transistor using an inorganic SiO2 electron beam (EB) resist process. The inorganic EB resist process technique was put to practical use in Si nanodevice fabrication for the first time. We have successfully demonstrated the 15-nm-wide and 20-nm-thick Si nanowire memory transistor with a Si nanodot less than 10 nm in diameter. In the fabricated Si nanowire nanodot memory transistor, we have observed a large electron memory effect, i.e., a threshold voltage shift ΔVth of 2.2 V at room temperature. It is experimentally shown that the inorganic EB resist process is promising for fabricating various Si nanodevices.
Experimental evaluation of an optimized radiation cooling geometry for ion projection lithography masks
Authors: Torres J. L. , Nounu H. N. , Wasson J. R. , Wolfe J. C. , Lutz J. , Haugeneder E. , Löschner H. , Stengl G. , Kaesmaier R.
Published: July 2002

In this article, we study an optimized radiative cooling geometry for ion projection lithography masks. In this design, a polished infrared mirror guides radiation from the mask to a high-emissivity cooled-cylinder positioned about 0.5 m away. Previous finite element modeling of this system predicts thermal distortion below 1 nm for practical mask designs. This is the first experimental study of the design. We show, by measuring the mean mask stress as a function of cooled cylinder temperature, that radiative cooling balances beam heating, with a power density of 2.15 mW/cm2, when the cooled cylinder is held at 15 °C and the temperature of the mirror and mask frame are at 25 °C. The results agree with finite element modeling.
Outgassing of photoresist materials at extreme ultraviolet wavelengths
Authors: Dentinger Paul M.
Published: July 2002

Outgassing of photoresist materials is a concern for all advanced lithographies. To address this concern, outgassing of photoresist materials exposed at extreme ultraviolet (EUV) wavelengths was studied with a quartz crystal microbalance (QCM) and mass spectrometry and was quantified using the QCM. Mass spectrometry of poly(methylmethacrylate) at 13.4 nm indicated large quantities of hydrogen formed by exposure at EUV wavelengths. QCM studies showed that pure acrylic materials are particularly susceptible to outgassing while pure styrenic materials outgas approximately two orders of magnitude less mass per unit dose. Random copolymers of acrylics and hydroxystyrene, such as found in common 248 nm lithography materials were disproportionately low outgassers. The phenolic moieties randomly introduced into the backbone of acrylics reduced the outgassing by approximately an order of magnitude below what was expected from the pure polymers. It is thought that radical scavenging by phenolic moieties stabilize the acrylic monomers. In addition, judicious selection of the photoacid generator (PAG) is important. It is shown that some PAGs, even at concentrations of 3.8 wt % produce 4 times more volatile mass than the resin itself. The residual solvent left in the film after the postapply bake (PAB) can contribute and even dominate outgassing if the PAB is too low. For the best imaging materials to date, the main sources of outgassing are direct photo/radiolysis of the backbone polymer and the PAG at approximately similar rates, and to a lesser extent, the residual solvent if the PAB is too low. The fate of the outgassed species and their threat to facing optical elements is discussed.
Search for Accuracy in Absolute Calibration
Authors: Gourjault J. D. , Lefevre J. , Choumoff P. S.
Published: July 2002

The need for an absolute calibration facility in metrological studies has resulted in the design and construction of a variable conductance apparatus whose precision has been determined by statistical methods. Absolute manometers have been compared with this apparatus. Particular attention has been given to the exact determination of the error bars, both for the apparatus and for the reference manometers: this comparison yields increased accuracy. The Monte Carlo method appears well adapted to problems of molecular flow in the system and indicates that the diamagnetic suspension molecular gauge (MSD) may be considered absolute between 10−3 and 10−6 Torr. Fruitful comparisons in the 10−4 Torr range have also been made with another absolute device: the differential interferometric manometer (MDI). For instance for absolute pressure differences across the adjustable conductance, calculated value by Monte-Carlo simulation and experimental values measured by MDI and MSD yield a result of 2.25±0.01×10−4 Torr. In the above range of pressure there are now two absolute gauges which renew the calibration method by direct comparison and allows one to avoid the need of a pressure reference transfer, as it is often necessary by using, for instance, a MacLeod gauge.
Pressure Considerations Associated with Ion Sampling from Low-Pressure Glow Discharges
Authors: Coburn J. W. , Kay E.
Published: July 2002

A discussion is presented of the influence of ion–neutral collisions downstream from an orifice through which ions from a glow discharge are being extracted. The effective pressure on the low-pressure side of the orifice is treated as the sum of a static pressure (determined from pumping speed and orifice conductance considerations) and a localized beam pressure which is due to the neutral species effusing through the orifice with the ions. It is shown that in most experimental situations the beam pressure has a much greater influence on a collimated ion beam than does the static pressure. Some experimental results which support this conclusion are presented. These results were obtained using a system which was designed to observe the ionic species in a sputtering glow discharge.
Field Emission Measurements and Electrical Breakdown in Vacuum
Authors: Baker R. J. , Weber A. H.
Published: July 2002

Field emitted current-voltage characteristics were determined experimentally in the range 103–108 A/cm2 in the dc mode. For J>105 A/cm2, deviations from Fowler-Nordheim predictions were found, and Dyke's space charge saturation model was found to be inappropriate. These data were obtained at p≈10−12 Torr, with a demountable, metal bakable uhv system with cryogenic capabilities. The (I,V) form of the data was transformed to the (J,V) form by means of the Charbonnier method, which uses the experimentally determined values of I,V and the slope m of the Fowler-Nordheim plot to determine the current density J. Several of the tips were subjected to a high voltage low impedance vacuum arc, and two tips were viewed in the electron microscope before and after breakdown. Tip end radii were 140 and 340 A, ±10% prior to heat treatment. The breakdown data agree better with Alpert's theory of critical field initiated vacuum breakdown than with Dyke's critical current density theory.
Metal-Dielectric Interference Filter Design
Authors: Bryn Stanley L.
Published: July 2002

The use of the Smith Chart is developed as an aid in the design of metal-dielectric filters. All of the required mathematics for the determination of various parameters such as ψm [P. W. Baumeister, Appl. Opt. 8, 423 (1969)], Xm, and Zm are presented. The use of ψm in the design procedure is analyzed in considerable detail. A step-by-step procedure is outlined for the design of a metal-dielectric filter. This procedure represents a blend of mathematical development and a practical approach Based on the use of the Smith Chart. An actual design for a metal-dielectric filter concludes the paper.
Size Effects and Piezoresistance in Metal Films
Authors: Klokholm E. , Mayadas A. F.
Published: July 2002

Recently, it has been shown that the scattering of electrons by grain boundaries is the major contribution to the electrical resistivity ρ of fine grained metal films. Using this model for the thin film electrical resistivity, the strain coefficient of resistivity, η=Δρ/ρ/ΔL/L [ΔL/L is the longitudinal strain], can be calculated in terms of the film thickness t and a grain size parameter α. The value of η thus obtained decreases with increasing α (i.e., decreasing grain size). For values of α between 0.001 and 0.1, η decreases by about 10%; however, for α from 0.1 to 1, η decreases by about 50%. As α increases from 1, η decreases monotonically towards 0. The effect of film thickness is most apparent for α<0.1 and in the range of film thickness from 10 l0 to l0, a decrease of η of only about 5% occurs. For α>1 the effect of film thickness on η is negligible.
Vacuum System of the Superconducting Linear Accelerator at Karlsruhe
Authors: Flécher P.
Published: July 2002

A 60-MeV superconducting proton accelerator is now being constructed at Karlsruhe as a pilot project for a larger accelerator. This paper discusses vacuum aspects of a superconducting linac in regard to surface contamination, sparking, radiation damage, etc., and presents a brief description of the pilot cryostat and gives some experimental results. Special features of the cryostat are the use of a two vacuum system in which no uhv flange has any contact with superfluid helium and the use of cooled ion pumps as an integral part of the rf structure.
Measurement of Sticking Probabilities of Gases Adsorbed on Metal Films
Authors: Adams Richard O. , Musgrave Larry E.
Published: July 2002

A fundamental measurement in studying adsorption is the probability that a gas molecule striking the surface will stick. Widely varying values of sticking probabilities have been reported for seemingly identical systems indicating the existence of numerous problems in making the measurements. This paper is a discussion of a technique to measure sticking probabilities on metal films that avoids the difficulty of measuring flow rates and/or conductances. The technique is based upon the pressure rise in a closed chamber caused by the admission of gas from a constant pressure reservoir. The amount of gas adsorbed is determined by comparing the rate of increase of pressure with and without an adsorbing surface. Results using this method are compared to results of other workers using other methods.
Analysis of the “Oxygen Pumping Effect” of Tungsten Cathodes in Ionization Gauges and Mass Spectrometers
Authors: Dabiri A. E. , Stickney R. E.
Published: July 2002

The quasiequilibrium treatment of gas-solid reactions (J. C. Batty and R. E. Stickney, J. Chem. Phys. 51, 4475 (1969)] is employed to develop a semiquantitative description of existing experimental data on the “pumping” of O2 by a hot tungsten filament [J. H. Singleton, J. Chem. Phys. 45, 2819 (1966)]. The results indicate that the present analysis provides a useful means for predicting the dependence of the O2 “pumping” speed on the operating conditions (e.g., O2 partial pressure, filament temperature) and on system design (e.g., conductance, pumping speed, wall material). The analysis is applied to estimate the error of an O2 partial pressure measured by a partial pressure analyzer or mass spectrometer having a tungsten cathode. It is also shown that the analysis provides a semiquantitative explanation of existing experimental data on the effects of O2 pressure and filament temperature on the rate of emission of ions (impurities) from a hot tungsten filament [H. F. Winters et al., J. Appl. Phys. 34, 1810 (1963)].
Adsorption of Argon Atoms at Edges and Vertices of Perfect Xenon Crystals
Authors: Pisani C. , Ricca F.
Published: July 2002

Heterogeneity in the adsorption of the Ar atoms has been studied at edges and vertices of perfect unrelaxed cubes and octahedra of solid Xe. The potential field near edges and vertices has been evaluated in the additive pairwise approximation and the quantum states of the adsorbed atom have been determined in the local approximation by a variational method. No special sites are found at the edges, involving atoms from both the converging faces. Instead, well-separated sites are found on each of the limiting surface planes. Due to the small kinetic energy of the localized Ar atom, the majority of the energy is given by the potential energy term which essentially depends on the number of surface atoms directly coordinated to the adsorption site. Only in the case of the cube could surface mobility occur across the edges.
Polymer photochemistry at advanced optical wavelengths
Authors: Fedynyshyn Theodore H. , Kunz Roderick R. , Sinta Roger F. , Goodman Russell B. , Doran Scott P.
Published: July 2002

As lithography is extended to 157 nm, the molecular absorptivity becomes high for most organic polymers. Polymer photochemistry depends on photon absorption, and the higher energy associated with 157 nm light should lead to higher quantum yields of photoproducts. Polymers representative of those commonly employed in 193 or 248 nm resists were selected for this study. A gel permeation chromatography based method was developed to determine quantum yields for chain scission and crosslinking on thin polymers films coated on silicon wafers. This method was applied to determine the ΦS and ΦX of a number of lithographically significant homopolymers and copolymers at both the 157 and 248 nm wavelengths. It was found that polymers containing hydroxystyrene only undergo crosslinking while acrylate and methacrylate polymer only undergo chain scission. The film loss of 157 nm exposed poly-t-butyl acrylate and polymethyl methacrylate was found to be very high and attributed primarily to side chain cleavage of the esters, while no film loss of polyhydroxystyrene was detected. The analysis of outgassing materials showed that ester elimination in poly-t-butyl acrylate was responsible for all outgassed products and that the sum of the quantum yields of all outgassed products exceeded one, implying a reaction mechanism that recycled the initially produced radical. Direct polymer photolysis is significant at 157 nm and must be considered in resist design given the relatively high absorbance of most organic molecules at 157 nm.
Use of an Ion Microprobe in Semiconductor Failure Analysis
Authors: Gerber R. M. , Dzimianski J. W.
Published: July 2002

Causes of high-ohmic contact resistance were explored by analyzing several integrated circuit samples with an ion microprobe. Presence of oxide and dopant depletion at the interface were indicated. Mapping of oxygen vs depth through an oxide revealed that not only the elements present, but also the layered structure of the material could be observed. The possible production of artifacts due to electrostatic charges on the surfaces of a sample was noted.
Aberration Correction for Increased Lines per Field in Scanning Electron Beam Technology
Authors: Owen G. , Nixon W. C.
Published: July 2002

The scanned field performance of probe forming systems has been investigated leading to various methods for increasing the current that may be delivered into an electron probe scanning a square field of 104 lines. Programs for evaluating the third-order aberrations of both lenses and single and double deflection systems have been developed. These have been used to evaluate the performance of a typical pre-lens double deflection probe forming system. It is shown that it is possible to produce much better performance using post-lens deflection coils. Distortion, field curvature and astigmatism can be eliminated, using suitable electronics for dynamic correction, and the remaining third-order aberrations may be reduced by careful design of the deflection coils.
Generation, Transport, and Compression of an Annular Intense Relativistic Electron Beam with Return Current Feedback through the Cathode
Authors: Kelly John G.
Published: July 2002

The properties of an intense annular relativistic electron beam generated by a ring cathode and conical anode have been studied in detail. The beam is injected into a channel between concentric cones (containing a neutral gas for space charge and current neutralization) where it is transported and focused. Half of the return current is then fed back through the cathode to prevent radial pinching of the primary current sheet. On the Sandia Reba accelerator which generated a beam of about 120 kA at 1 MeV an area compression of 10 was achieved with 50% efficiency. The compressability of the beam was found to depend primarily on the azimuthal temperature of the beam as it emerged from the diode and on the diode plasma closure rate.
The effect of substrate bias voltage on the bonding of evaporated silver coatings
Authors: McLeod P. S. , Mah G.
Published: July 2002

Tensile strengths of bonds between evaporated silver coatings have been found to be related to the bias voltage on the substrate during deposition. Silver coatings between 12 and 50 μ thick were deposited by using a hollow cathode evaporator on 304 stainless steel substrates at bias voltages from 0 to −80 V. Tensile strengths up to 3.85×109 dyn cm−2 (56 ksi) have been achieved at relatively low bonding pressures and temperatures.