bluuebunny/crossref_metadata_2025 huggingface dataset:
Scattering of a Rayleigh Wave by an Elastic Wedge Whose Angle is Greater Than 180 Degrees
Authors: Gautesen A. K.
Published: July 2002

The steady-state problem of scattering of an incident Rayleigh wave by an elastic wedge whose angle is greater than 180 degrees is considered. The problem is reduced to the numerical solution of a pair of Fredholm integral equations of the second kind whose kernels consist of elementary functions. Numerical results are given for the amplitude and phase of the Rayleigh waves transmitted and reflected by the corner.
The Dynamics of a Ball-Type Balancer System Equipped with a Pair of Free-Moving Balancing Masses
Authors: Kang Jaan-Rong , Chao Chang-Po , Huang Chun-Lung , Sung Cheng-Kuo
Published: July 2002

This study is devoted to evaluate the performance of a ball-type balancer system that is installed in high-speed optical disk drives. The ball-type balancer system, composed of a circular runway and free-moving balls inside, is designed for reducing radial vibrations induced by the inherent unbalance of the rotating system. A balancer system equipped with a pair of balls is considered in this study for its capability to reach possible near-elimination of radial vibrations as opposed to the serious sizing problem of a single balancing-ball system. A mathematical model is first established to describe the dynamics of the balls and rotor system. Utilizing the method of multiple scales and assuming the smallness of radial vibrations, the system dynamics on the slow time scale is represented by eight first-order autonomous differential equations, which accommodate the radial vibratory motions and ball behaviors. The steady-state solutions of these slow equations are then solved and their stability analyzed to predict settling ball positions. The residual vibrations are computed to evaluate the performance of the balancer system and then the design guidelines are distilled for engineers to design the balancer system.
Impeller Geometry Suitable for Mini Turbo-Pump
Authors: Liu Shuhong , Nishi Michihiro , Yoshida Kouichi
Published: July 2002

The objective of the present study is to investigate the suitable impeller geometry for a mini turbo-pump, which is defined as the size having impeller diameter between around 5 mm and 50 mm. This is treated because those pumps having the above size are regarded as low efficiency machines if efficiency is less than 40 percent or 50 percent. Considering that not only low Reynolds number and tip clearance but the design method are the major causes for low performance, we carried out the performance test experimentally using two semi-open centrifugal impellers: one is named as Impeller B of 36 mm diameter and the other is Impeller C of 34 mm diameter. And the former is designed by a conventional method and the latter is based on the proposed method. In the performance tests, rotational speed was varied between 3000 rpm and 10,000 rpm and the axial clearance at the blade tip of impeller exit was between 0.2 mm and 0.8 mm. It is clearly seen from the results that Impeller C gives the better hydraulic performance. It is also clarified that the effect of tip clearance on Impeller C performance is much smaller than that of the Impeller B. Further, we conducted numerical calculation of impeller performance, where the commercial CFD code named TASCflow was used with k-ω turbulence model. From the results, the turbulent flow analysis is reasonably usable to study the flow in the above mini impellers.
Application of the Radial Return Method to Compute Stress Increments From Mroz’s Hardening Rule
Authors: Tang Sing C. , Xia Z. Cedric , Ren Feng
Published: July 2002

It is well known in the literature that the isotropic hardening rule in plasticity is not realistic for handling plastic deformation in a simulation of a full sheet-metal forming process including springback. An anisotropic hardening rule proposed by Mroz is more realistic. For an accurate computation of the stress increment for a given strain increment by using Mroz’s rule, the conventional subinterval integration takes excessive computing time. This paper proposes the radial return method to compute such stress increment for saving computing time. Two numerical examples show the efficiency of the proposed method. Even for a sheet model with more than 10,000 thin shell elements, the radial return method takes only 40 percent of the overall computing time by the subinterval integration.
Natural Gas Decarbonization to Reduce CO2 Emission From Combined Cycles—Part I: Partial Oxidation
Authors: Lozza G. , Chiesa P.
Published: July 2002

This paper discusses novel schemes of combined cycle, where natural gas is chemically treated to remove carbon, rather than being directly used as fuel. Carbon conversion to CO2 is achieved before gas turbine combustion. Therefore CO2 can be removed from fuel (rather than from exhausts, thus utilizing less demanding equipment) and made available for long-term storage, to avoid dispersion toward the atmosphere and the consequent contribution to the greenhouse effect. The strategy here proposed to achieve this goal is natural gas partial oxidation. The second part of the paper will address steam/methane reforming. Partial oxidation is an exothermic oxygen-poor combustion devoted to CO and H2 production. The reaction products are introduced in a multiple stage shift reactor converting CO to CO2. Carbon dioxide is removed by means of physical or chemical absorption processes and made available for storage, after compression and liquefaction. The resulting fuel mainly consists of hydrogen and nitrogen, thus gas turbine exhausts are virtually devoid of CO2. The paper discusses the selection of some important parameters necessary to obtain a sufficient level of conversion in the various reactors (temperature and pressure levels, methane-to-air or methane-to-steam ratios) and their impact on the plant integration and on the thermodynamic efficiency. Overall performance (efficiency, power output, and carbon removal rate) is predicted by means of a computational tool developed by the authors. The results show that a net efficiency of 48.5 percent, with a 90 percent CO2 removal, can be obtained by combined cycles based on large heavy duty machines of the present technological status, either by using chemical or physical absorption.
Efficient Meshfree Formulation for Metal Forming Simulations
Authors: Yoon Sangpil , Wu Cheng-Tang , Wang Hui-Ping , Chen Jiun-Shyan
Published: July 2002

A stabilized conforming (SC) nodal integration method is developed for elastoplastic contact analysis of metal forming processes. In this approach, strain smoothing stabilization is introduced to eliminate spatial instability in collocation meshfree methods. The gradient matrix associated with strain smoothing satisfies the integration constraint (IC) of linear exactness in the Galerkin approximation. Strain smoothing formulation and numerical procedures for history-dependent problems are introduced. Applications to metal forming analysis are presented, with the results demonstrating a significant improvement in computational efficiency without loss of accuracy.
Axial Strength of Tube-to-Tubesheet Joints: Finite Element and Experimental Evaluations
Authors: Allam M. , Bazergui A.
Published: July 2002

Because of their importance for the integrity of heat exchangers, the strength of tube-to-tubesheet joints, and particularly their axial strength, is of special interest. A finite element model of an expanded tube-to-tubesheet joint is proposed and examined experimentally with the objective of determining numerically its axial strength. Simplified analytical methods that were previously proposed by many authors to predict the joint axial strength are also used in this investigation. Experimental testing shows that the finite element model is highly accurate for calculating the joint axial strength. The experimental investigation also proves that the pull-out strength is overestimated when calculated using a simple analytical solution. A parametric analysis using the finite element results indicates that the pull-out force is normally lower than the push-out load and that both are lower than the estimations of the analytical solution. The results indicate that the pull-out force as given by the finite element model is generally 35 percent lower than that evaluated by the analytical solution. A difference of as much as 10 percent is also found between the push-out and pull-out loads.
Parametric Models for Estimating Wind Turbine Fatigue Loads for Design
Authors: Manuel Lance , Veers Paul S. , Winterstein Steven R.
Published: July 2002

International standards for wind turbine certification depend on finding long-term fatigue load distributions that are conservative with respect to the state of knowledge for a given system. Statistical models of loads for fatigue application are described and demonstrated using flap and edge blade-bending data from a commercial turbine in complex terrain. Distributions of rainflow-counted range data for each ten-minute segment are characterized by parameters related to their first three statistical moments (mean, coefficient of variation, and skewness). Quadratic Weibull distribution functions based on these three moments are shown to match the measured load distributions if the non-damaging low-amplitude ranges are first eliminated. The moments are mapped to the wind conditions with a two-dimensional regression over ten-minute average wind speed and turbulence intensity. With this mapping, the short-term distribution of ranges is known for any combination of average wind speed and turbulence intensity. The long-term distribution of ranges is determined by integrating over the annual distribution of input conditions. First, we study long-term loads derived by integration over wind speed distribution alone, using standard-specified turbulence levels. Next, we perform this integration over both wind speed and turbulence distribution for the example site. Results are compared between standard-driven and site-driven load estimates. Finally, using statistics based on the regression of the statistical moments over the input conditions, the uncertainty (due to the limited data set) in the long-term load distribution is represented by 95% confidence bounds on predicted loads.
Three Dimensional Absolute Nodal Coordinate Formulation for Beam Elements: Implementation and Applications
Authors: Yakoub Refaat Y. , Shabana Ahmed A.
Published: July 2002

This part of these two companion papers demonstrates the computer implementation of the absolute nodal coordinate formulation for three-dimensional beam elements. Two beam elements that relax the assumptions of Euler-Bernoulli and Timoshenko beam theories are developed. These two elements take into account the effect of rotary inertia, shear deformation and torsion, and yet they lead to a constant mass matrix. As a consequence, the Coriolis and centrifugal forces are identically equal to zero. Both beam elements use the same interpolating polynomials and have the same number of nodal coordinates. However, one of the elements has two nodes, while the other has four nodes. The results obtained using the two elements are compared with the results obtained using existing incremental methods. Unlike existing large rotation vector formulations, the results of this paper show that no special numerical integration methods need to be used in order to satisfy the principle of work and energy when the absolute nodal coordinate formulation is used. These results show that this formulation can be used in manufacturing applications such as high speed forming and extrusion problems in which the element cross section dimensions significantly change.
Mechanical Properties of Hardened AISI 52100 Steel in Hard Machining Processes
Authors: Guo Y. B. , Liu C. R.
Published: July 2002

This paper provides an approach using tensile tests at elevated temperatures to estimate mechanical properties of the work material for both elastic and plastic deformations in a broad range of strain, strain rate, and temperature in machining. The proposed method has been applied to estimate mechanical properties of hardened AISI 52100 steel in hard machining. Tensile testing is shown capable of estimating the mechanical properties of both elastic and plastic regions with large strains at elevated temperatures. Flow stresses at high strain rates in machining can be obtained by extrapolating the data from tensile tests by using the velocity-modified temperature. Flow stress data from tensile and cutting tests is consistent with regard to the velocity-modified temperature. Temperature is the dominant factor of mechanical properties of this material, while the effect of strain rate is secondary. Cutting forces and chip geometry predicted by the 3D FEM simulation of hard turning using the material property data obtained from the developed method agree well with the experimental data.
Bubble Behavior and Nucleate Boiling Heat Transfer in Saturated FC-72 Spray Cooling
Authors: Rini Daniel P. , Chen Ruey-Hung , Chow Louis C.
Published: July 2002

Bubble behavior during saturated FC-72 spray cooling was experimentally investigated. A heater previously used for pool boiling was used to allow direct comparison. The results are analyzed to reveal the interaction between bubbles and impinging droplets. The following are presented: (1) the importance of secondary nuclei entrained by impingement droplets, (2) the role of impinging droplets on bubble parameters such as growth, diameter at puncture, lifetime, life cycle and bubble number density, and (3) the relative contribution of nucleation, especially that of secondary nuclei, to the heat transfer. It is concluded that increasing the droplet flux increases the number of secondary nuclei, helps to lower surface temperature for a given heat flux, increases the overall heat transfer coefficient, and increases heat transfer due to both nucleate boiling and enhanced convection. Increasing the droplet flux also shortens the bubble growth time (i.e., resulting in earlier bubble removal) and life cycle. However, increasing the droplet flux (and, therefore, secondary nucleation) for each of the three heat flux values does not affect the percentage of either nucleate or convection heat transfer. This suggests that both the nucleate and convection heat transfer are enhanced, as a result of increased secondary nuclei and turbulent mixing due to the impinging droplets.
Effects of Static Stress on the Mechanical Properties of Cultured Collagen Fascicles From the Rabbit Patellar Tendon
Authors: Yamamoto Ei , Iwanaga Wataru , Miyazaki Hiroshi , Hayashi Kozaburo
Published: July 2002

In-vitro tissue culture experiments were performed to study the effects of static stress on the mechanical properties of collagen fascicles obtained from the rabbit patellar tendon. After collagen fascicles having the diameter of approximately 300 μm were cultured for 1 and 2 wk under static stress between 0 and 3 MPa, their mechanical properties and crimp morphology were determined using a micro-tensile tester and a light microscope, respectively. The tensile strength and tangent modulus of the fascicles were significantly decreased by culture under no load compared to control fascicles. A statistically significant correlation, which was described by a quadratic curve, was observed between applied stress and tensile strength. The maximum tensile strength (16.7 MPa) was obtained at the applied stress of 1.2 MPa; the strength was within a range of control values. There was a similar correlation between applied stress and tangent modulus, and the modulus was maintained at control level under 1.3 MPa stress. The stress of 1.2 to 1.3 MPa is equivalent to approximately 50 percent of the peak stress developed in the intact rabbit patellar tendon by running. Strain at failure of cultured collagen fascicles was negatively correlated with applied stress, and that at 1.2 to 1.3 MPa stress was almost the same as the control value. Crimp morphology in the fascicles cultured under about 1.2 MPa stress was similar to that in control fascicles. These results indicate that cultured collagen fascicles change the mechanical properties and structure in response to static tensile stress. In addition, their mechanical properties and structure are maintained at control level if the static stress of 50 percent of in-vivo peak stress is applied.
Differential Diagnosis of Gear and Bearing Faults
Authors: Antoni J. , Randall R. B.
Published: July 2002

This paper deals with the vibration-based diagnosis of rolling element bearings in the presence of strong interfering gear signals, such as is typical of helicopter gearboxes. The key idea consists in recognizing gear signals as purely periodic, whereas bearing signals experience some randomness and are close to cyclostationary, i.e. with a periodic bivariate autocorrelation function. This assertion is demonstrated by introducing a comprehensive model for the vibration generating process of bearing faults: distinctions are made between localized and distributed faults, between cyclostationary and pseudo-cyclostationary processes, and between additive and multiplicative interactions with gear signals. Finally, an original diagnostic procedure is proposed and its performance illustrated using simulated, experimental and actual cases.
What is the General Form of the Explicit Equations of Motion for Constrained Mechanical Systems?
Authors: Udwadia F. E. , Kalaba R. E.
Published: July 2002

This paper presents the general form of the explicit equations of motion for mechanical systems. The systems may have holonomic and/or nonholonomic constraints, and the constraint forces may or may not satisfy D’Alembert’s principle at each instant of time. The explicit equations lead to new fundamental principles of analytical mechanics.
Linear and Quasi-Linear Viscoelastic Characterization of Ankle Ligaments
Authors: Funk J. R. , Hall G. W. , Crandall J. R. , Pilkey W. D.
Published: July 2002

The objective of this study was to produce linear and nonlinear viscoelastic models of eight major ligaments in the human ankle/foot complex for use in computer models of the lower extremity. The ligaments included in this study were the anterior talofibular (ATaF), anterior tibiofibular (ATiF), anterior tibiotalar (ATT), calcaneofibular (CF), posterior talofibular (PTaF), posterior tibiofibular (PTiF), posterior tibiotalar (PTT), and tibiocalcaneal (TiC) ligaments. Step relaxation and ramp tests were performed. Back-extrapolation was used to correct for vibration effects and the error introduced by the finite rise time in step relaxation tests. Ligament behavior was found to be nonlinear viscoelastic, but could be adequately modeled up to 15 percent strain using Fung’s quasilinear viscoelastic (QLV) model. Failure properties and the effects of preconditioning were also examined. [S0148-0731(00)01001-3]
Erratum: “Joint Surface Modeling With Thin-Plate Splines” [ASME J. Biomech. Eng., 121, pp. 525–532]
Authors: Boyd, S. K. , Ronsky, J. L. , Lichti, D. D. , Sˇalkauskas, and D. , Chapman M. A.
Published: July 2002

[S0148-0731(00)01501-1]
Receding Time Horizon Linear Quadratic Optimal Control for Multi-Axis Contour Tracking Motion Control1
Authors: McNab Robert J. , Tsao Tsu-Chin
Published: July 2002

A receding time horizon linear quadratic optimal control approach is formulated for multi-axis contour tracking problem. The approach employs a performance index with fixed weights on quadratic contouring error, tracking error, and control input over a future finite horizon. The problem is then cast into a standard receding horizon LQ problem with time varying weighting matrices, which are functions of the future contour trajectory within the horizon. The formulation thus leads to a solution of time varying state feedback and finite preview gains. Stability is proven for the linear trajectory case. Experimental and simulated results for an X-Y motion control problem are presented, which demonstrate the effectiveness of the control scheme and the effects of the key controller design parameters. [S0022-0434(00)01202-8]
Turbulent Flow Around Two Interfering Surface-Mounted Cubic Obstacles in Tandem Arrangement
Authors: Martinuzzi Robert J. , Havel Brian
Published: July 2002

The flow around two in-line surface-mounted cubes in a thin laminar boundary layer was experimentally investigated as a function of obstacle spacing for a Reynolds number of 22,000 based on approach velocity and cube height. Mean velocity measurements with Laser Doppler Velocimetry and surface flow patterns, obtained with an oil film technique, show that three distinct mean flow field structures exist based on obstacle spacing. Frequency spectra of velocity and surface pressure fluctuations reveal that these structures are related to three regimes of wake flow periodicity. For small spacings, the shear layer separating from the first cube reattaches on the sides of the second obstacle and wake periodicity can only be detected in the wake of the downstream cube. For a critical spacing range, the fluctuations in the gap and wake lock-in. For larger spacings, a second horseshoe vortex appears at the windward base of the second cube. Observations using dye-injection and smoke-wire techniques are consistent with these results. [S0098-2202(00)02401-9]
Homogeneous, Isotropic Flow in Grid Generated Turbulence
Authors: Tresso Riccardo , Munoz David R.
Published: July 2002

Detailed grid generated turbulent analysis has been completed using a three-dimensional hot-wire anemometer and traversing mechanism to identify a homogeneous, isotropic flow region downstream of a square mesh. The three-dimensional fluctuating velocity measurements were recorded along the centerline of a wind tunnel test section and spatially over the entire wind tunnel cross section downstream of the square mesh. Turbulent intensities for various grid sizes and Reynolds numbers ranged from a minimum of 0.2 percent to a maximum of 2.2 percent in each of the three principal velocity directions. Spatial homogeneity and isotropy were determined for several turbulent flow conditions and downstream positions using the method of covariances. Covariances, in theory, should approach zero asymptotically; however, in practice, this was not achievable. A subjective judgment is required to determine downstream location where the variance of the three covariances reaches a value close to zero. The average standard deviation provides an estimate for defining the limit or subjective threshold needed to determine the onset of homogeneous, isotropic flow. Implementing this threshold, a quantitative method was developed for predicting the streamwise location for the onset of the homogeneous, isotropic flow region downstream of a 25.4 mm square grid as a function of Reynolds number. A comparison of skewness, determined from one-dimensional hot wire anemometer measurements, and covariances, determined from three dimensional hot wire anemometer measurements, indicates a need for caution when relying solely on one-dimensional measurements for determination of turbulence isotropy. The comprehensive three-dimensional characterization also provides an improved understanding of spatial distribution of fundamental turbulence quantities generated by the grid within a low-speed wind tunnel. [S0098-2202(00)02501-3]
Two-Dimensional Transient Analysis of Absorbing Thin Films in Laser
Treatments
Authors: Bianco N. , Manca O.
Published: July 2002

In this paper the transient coupled conductive-radiative field, due to a laser heat source impinging on a thin film deposited on a substrate, has been solved in the hypothesis of one dimensionality of the optical field and of two dimensionality of the thermal field. Results have been obtained with the matrix method for the optical field and the finite volume method for the thermal field. The results show that when the investigation is localized to the center of the spot, the one-dimensional model describes the thermal field quite well. Instead, if knowledge of the temperature is required elsewhere, the two-dimensional model is needed. The investigation herein presented shows that for low-conductivity materials (a–Si) the temperature peaks are placed inside the thin film for the absorption function distribution, determined by interference phenomena. [S0022-1481(00)01301-3]
Calculation of the Stiffness Matrix of Angular Contact Ball Bearings by Using the Analytical Approach
Authors: Hernot X. , Sartor M. , Guillot J.
Published: July 2002

The stiffness matrix of angular contact ball bearings is calculated by using the analytical approach in which the summation of ball-race loads is replaced by an integration. The matrix connected to the conventional model in two degrees of freedom is first presented. A practical application of this formulation is illustrated through the common problem of sizing a two bearings-shaft arrangement. Variations of displacements, axial forces, and bearing fatigue life related to preload are shown to be easily obtained. Then, the matrix connected to the model in five degrees of freedom is given. This may be coupled with finite elements which are generally used to model the shaft or the housing. [S1050-0472(00)01801-8]
An Asperity Contact Model for the Slider Air Bearing
Authors: Huang Weidong , Bogy David B. , Honchi Masayuki
Published: July 2002

As sliders fly closer and closer to the disks, asperity contact is inevitable due to the roughness on the sliders and the disks. A single asperity contact problem was solved using the molecular gas-film lubrication (MGL) model with the no-fly-zone (NFZ) condition, which was discovered with the direct simulation Monte Carlo method (DSMC). It shows that the MGL model can also provide bounded pressure and resultant force in the presence of contact. Moreover, the MGL results agree well with the DSMC results. A database for a single asperity contact force and moment was then created using the MGL model with the NFZ condition. This force and moment was superimposed to the air bearing force calculated by the MGL model calculated by the MGL model when the nominal plane of the slider and the disk are not in contact. The total additional air bearing force due to asperity contact was obtained. Its effect on the slider’s flying attitude was investigated and found to change the flying height and pitch angle up to 20 percent and 10 percent, respectively. [S0742-4787(00)02402-4]
Nonlinear Dynamics and Bifurcations of an Axially Moving Beam
Authors: Pellicano F. , Vestroni F.
Published: July 2002

The present paper analyzes the dynamic behavior of a simply supported beam subjected to an axial transport of mass. The Galerkin method is used to discretize the problem: a high dimensional system of ordinary differential equations with linear gyroscopic part and cubic nonlinearities is obtained. The system is studied in the sub and super-critical speed ranges with emphasis on the stability and the global dynamics that exhibits special features after the first bifurcation. A sample case of a physical beam is developed and numerical results are presented concerning the convergence of the series expansion, linear subcritical behavior, bifurcation analysis and stability, and direct simulation of global postcritical dynamics. A homoclinic orbit is found in a high dimensional phase space and its stability and collapse are studied. [S0739-3717(00)00501-8]
Free Vibration Analysis of Rotating Circular Cylindrical Shells on an Elastic Foundation
Authors: Ng and T. Y. , Lam K. Y.
Published: July 2002

[S0739-3717(00)01301-5]
SnO by XPS
Authors: Stranick Michael A. , Moskwa Anthony
Published: July 2002

Tin and various tin compounds have wide utility in coatings, electronics, and catalysts, as well as having numerous biological applications. Distinguishing between different tin compounds on surfaces is an important aspect of research in many of these disciplines. In this work, x-ray photoelectron spectroscopy has been used to obtain comparison spectra of a SnO powder. The SnO powder was generated by grinding ~150 μm granules of SnO in a mortar and pestle. Grinding is necessary because surface oxidation of the SnO granules occurs producing a SnO2 shell. It has been shown that differences in the valence band spectra provide the most direct method of distinguishing between SnO2 and SnO [see J-M. Themlin, M. Chtaib, L. Henrard, P. Lambin, J. Darville, and J-M. Gilles, Phys. Rev. B 46, 2460 (1992); P. M. A. Sherwood, ibid. 41, 10151 (1990); and C. L. Lau and G. K. Wertheim, J. Vac. Sci. Technol. 15, 622 (1978)]. The separation between the Sn 4d core level line and the most intense Sn valence peak is also characteristic of Sn oxides [see J-M. Themlin, M. Chtaib, L. Henrard, P. Lambin, J. Darville, and J-M. Gilles, Phys. Rev. B 46, 2460 (1992) and P. M. A. Sherwood, ibid. 41, 10151 (1990)]. In the present study, identification of the powder as SnO after grinding was verified by comparison of the measured XPS valence band spectrum with published spectra [J-M. Themlin, M. Chtaib, L. Henrard, P. Lambin, J. Darville, and J-M. Gilles, Phys. Rev. B 46, 2460 (1992) and C. L. Lau and G. K. Wertheim, J. Vac. Sci. Technol. 15, 622 (1978)] and by the XPS Sn:O atomic ratio. The valence band–Sn 4d separation is also consistent with that determined for SnO [see J-M. Themlin, M. Chtaib, L. Henrard, P. Lambin, J. Darville, and J-M. Gilles, Phys. Rev. B 46, 2460 (1992)]. Core level, valence band and x-ray excited Auger spectra for the SnO powder are presented. Data were obtained with a Perkin-Elmer Physical Electronics model 5600 photoelectron spectrometer using monochromatic radiation.
Ag Foil by XPS
Authors: Hoflund Gar B. , Weaver Jason F. , Epling William S.
Published: July 2002

XPS data have been obtained from a polycrystalline Ag foil supplied by AESAR. Initial data indicates a highly contaminated surface region. The foil was heated to 250° C and then sputtered with a 2 keV beam of Ar+ for 35 min. Ion scattering spectroscopy, angle-resolved Auger electron spectroscopy, and x-ray photoelectron spectroscopy data indicate the presence of a small amount of subsurface oxygen which could not be removed by the cleaning procedure used. These spectra will be useful in XPS studies of Ag systems such as alumina-supported silver epoxidation catalysts.
Gamma-Alumina (γ-Al2O3) by XPS
Authors: Rotole John A. , Sherwood Peter M. A.
Published: July 2002

The XPS spectra of gamma-alumina 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 gamma-alumina 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.
Polystyrene Spin Cast Films by XPS
Authors: Burrell Michael C. , Chera John J.
Published: July 2002

A spin cast film of polystyrene (PS) was analyzed by XPS using monochromatic Al Kα excitation. The XPS survey spectrum contained only a trace of oxygen, indicating a minimum of surface contamination. The high resolution spectrum of the C 1s peak is also reported.
Powder formation in germane–silane plasmas
Authors: van Swaaij R. A. C. M. M. , Girwar B. S. , Metselaar J. W.
Published: July 2002

The powder formation in a germane (GeH4)–silane (SiH4) plasma was investigated for a range of deposition parameters used in the processing of amorphous silicon devices, in particular the pressure, p, and the total gas flow, φ. For that purpose the plasma was monitored continuously by measuring the dc self-bias, Vsb, as a function of time. At certain plasma conditions oscillations in the self-bias are observed. In literature these oscillations have been related to the spatial oscillation of the powder-forming region in the plasma and they can be used as an indication of the so-called α–γ′ transition of the plasma, i.e., the moment at which powder formation starts to occur in the plasma. Changes in the plasma are monitored by measuring the amplitude of the oscillations of the self-bias, ΔVsb. It was found that the dependence of ΔVsb on p can be divided into three ranges: (i) low-pressure range in which ΔVsb is small; (ii) medium-pressure range in which ΔVsb varies significantly and powder is formed in the plasma; and (iii) high-pressure range in which the plasma is visually unstable. The pressure at which the transition from range (i) to (ii) occurs is indicative for the α–γ′ transition and appears to depend on the gas composition, in particular the [GeH4]/[SiH4] flow ratio. This ratio also determines the rate of powder formation. We argue that the production of GeH2 radicals is responsible for this formation. In addition we conclude that the α–γ′ transition is determined by the partial pressure of SiH4 plus GeH4 and is not dependent on the residence time of the gas in the reaction chamber.
Luminous efficiency and secondary electron emission characteristics of alternating current plasma display panels with MgO–SrO–CaO protective layers
Authors: Kim Rakhwan , Kim Younghyun , Cho Jinhui , Park Jong-Wan
Published: July 2002

Development of protective layers with a higher secondary electron emission yield than that of the conventional MgO is necessary to attain both a lower driving voltage and a higher luminous efficiency in alternating current plasma display panels. Alkaline earth metal oxides, such as SrO and CaO were added to the pure MgO in order to improve the electrical characteristics of the conventional MgO protective layer. With addition of SrO and CaO to MgO, the intensity of the (111) peak remained unchanged but the (311) peak newly appeared in the x-ray diffraction results. The secondary electron emission yield of Mg1−x−ySrxCayO films was found to be larger than that of the MgO film and in particular, the Mg0.7Sr0.2Ca0.1O films showed the largest secondary electron emission yield among the prepared films of the Mg–Sr–Ca–O system in this work. The luminous efficiency of the panel with the Mg0.7Sr0.2Ca0.1O protective layer was also much higher than that of the panel with the MgO protective layer probably due to its lower discharging voltage. The increase in the luminous efficiency and the decrease in the driving voltage were in good agreement with the results of the secondary electron emission yield as expected.
Characteristics of ZnO:Cr thin films deposited by spray pyrolysis
Authors: Maldonado A. , de la L. Olvera M. , Asomoza R. , Tirado-Guerra S.
Published: July 2002

Chromium-doped zinc oxide thin films were deposited using the spray pyrolysis technique. In all cases 15 at. % of chromium in solution was used. Under diluted HCl, a low etching rate in ZnO:Cr thin films is obtained, as compared to undoped ZnO. As-deposited and vacuum-annealed films show a high resistivity. X-ray diffraction spectra show no extra phases present. A low incorporation efficiency of chromium into the ZnO films is observed, and less than 1 at.% chromium is present in the films and (002) preferential growth is observed in all cases. High transmittance is obtained, which makes films adequate for transparent and protective coatings.
Electron field emission from amorphous carbon nitride synthesized by electron cyclotron resonance plasma
Authors: Liu X. W. , Tsai S. H. , Lee L. H. , Yang M. X. , Yang A. C. M. , Lin I. N. , Shih H. C.
Published: July 2002

Amorphous carbon nitride thin films were synthesized using an electron cyclotron resonance chemical vapor deposition system in which a direct current (dc) bias was applied to the silicon substrate and a mixture of C2H2, H2, and Ar was used as precursors. The films prepared in this way were further treated in an argon plasma to increase their surface roughness thereby creating a more efficient electron emitter. An onset emission field as low as ∼3.5 V μm−1 can be achieved (after Ar+ plasma sputtering for 3 min), significantly lower than other carbon-based electron field emitters. This low value is mainly attributed to the increase of film roughness, decrease of film thickness, and removal of hydrogen from the film. The structural and compositional modification induced by Ar+ plasma post-treatment along with the application of a negative dc bias to the synthesized film were analyzed by Fourier-transformation infrared spectroscopy, Raman spectroscopy, x-ray photoelectron spectroscopy, atomic force microscopy, and field emission scanning electron microscopy.
Mechanism of dopant segregation to SiO2/Si(001) interfaces
Authors: Dabrowski J. , Casali R. A. , Müssig H.-J. , Baierle R. , Caldas M. J. , Zavodinsky V.
Published: July 2002

Dopant atoms segregate to SiO2/Si(001) interfaces and are deactivated there. This can cause problems in fabrication of submicron microelectronic devices. On the basis of ab initio calculations, we propose a mechanism for donor segregation and deactivation. We argue that donor species (P and As) are trapped as threefold-coordinated atoms at interface defect sites (dangling bonds and Si vacancies) and, most significantly, in form of dopant pairs at defect-free interfaces. This pairing will dominate when dopant concentration exceeds approximately 1019 cm−3.
Extreme ultraviolet holographic microscopy and its application to extreme ultraviolet mask-blank defect characterization
Authors: Lee Sang Hun , Bokor Jeffrey , Naulleau Patrick , Jeong Seong Tae , Goldberg Kenneth A.
Published: July 2002

100-nm-resolution at-wavelength holographic microscopy of aerial images produced by extreme ultraviolet (EUV) lithographic optics has recently been demonstrated. It provides a simple and compact method allowing image monitoring without printing in photoresist. Here, the concept of holographic microscopy is extended to the characterizations of defects on EUV multilayer mask blanks. As a proof of principle, defect characterization using the holographic microscope is demonstrated with programmed defects in transmission masks. Amplitude defects as small as 100 nm have been successfully characterized. Extension of this technique to the more relevant reflection mask configuration is also discussed.
A Simple Classical Model for Trapping in Gas–Surface Interactions
Authors: Weinberg W. H. , Merrill R. P.
Published: July 2002

A simple model based on an assumed attractive square well and impulsive repulsive potential is developed to enable the calculation of initial trapping probabilities from thermal accommodation coefficient data. The gas species impinge on a smooth solid surface and are considered to be trapped if they transfer enough energy to the solid to fall into the interatomic potential well. The amount of energy transfer is determined by empirical values of the thermal accommodation coefficient. The model predicts the correct trends with surface and gas temperature when compared with rare gas scattering data and gives values accurate within a factor of 2 or better. Agreement between the model calculations and the sticking coefficient for deuterium adsorption on platinum is also found.
Stress in Vacuum-Deposited Films of Ag, Au, and Cu
Authors: Maki Kunisuke , Nakajima Yuji , Kinosita Koreo
Published: July 2002

The tension per unit width of the film S has been determined for Ag, Au, and Cu films deposited at 10−5 Torr from a few tens of angstroms up to 2000, 1500, and 1000 Å in thickness, respectively. S increases rapidly with the film thickness d until the film attains a thickness dI( = 220/320/160 Å for Ag/Au/Cu films deposited at 2 Å/sec). At dI the mean stress within the film σ ( = S/d) assumes a maximum. With thicker Ag and Cu films S remains nearly constant until at a thickness dII it starts to increase again. With Au films the rapid increase in S below dI is immediately followed by a slower increase with d. The first increase in S below dI is associated with the coalescence of islands. The second increase in S observed at larger thicknesses (d > dII for Ag and Cu, d > dI for Au) is probably due to residual gases. The last view is supported by experiments with Ag films deposited at 10−8 Torr.
The Growth of a GaAs–GaAlAs Superlattice
Authors: Chang L. L. , Esaki L. , Howard W. E. , Ludeke R.
Published: July 2002

An ultra high vacuum epitaxy system is described, including special features such as computer control. The system is capable of preparing sophisticated structures requiring a high degree of precise control. GaAlAs films have been grown and evaluated by various techniques; He-ion backscattering and Raman spectroscopy have been shown to be particularly valuable for periodic structures. A structure with a very narrow period has been made, and its transport properties measured and interpreted by the superlattice mechanism.
Focal Properties of the Two-Tube Electrostatic Lens for Large Voltage Ratios
Authors: Kuyatt C. E. , DiChio D. , Natali S. V.
Published: July 2002

Previous calculations of electron trajectories and first-order focal properties of the two-tube electrostatic lens have been extended to a voltage ratio of 1000. Considerable ultrafocal refraction occurs in these strong lenses, with the result that near the highest voltage ratio studied the two focal points are both on the low-voltage side of the lens and nearly coincident. The results are presented in the form of a table and P-Q (image-object) curves.
A dynamic Knudsen-effusion-torsion balance
Authors: Edwards Jimmie G.
Published: July 2002

A torsion-effusion pendulum which operates dynamically rather than in the usual damped or null mode is described. The pendulum position is observed as a function of time and the equation of motion is solved to obtain the torque exerted by effusing vapor. An iterative statistical technique for including nonideal influences on the pendulum in the solution is given. Tests of the method on the vapor pressure of silver in the temperature range 1160–1360 K are reported. Discovery and treatment of inductive interactions between the pendulum and the furnace which heated the effusion cell are described.
Electrical and magnetic interactions in vacuum-arc remelting and their effect on the metallurgical quality of specialty steels
Authors: Schlatter R.
Published: July 2002

The principal interactions between melting current, self-generated magnetic fields, and structural parts of the vacuum arc furnace, and the effect of unsymmetrical stray fields on arc characteristics, pool behavior, and metallurgical quality are briefly reviewed. Various macrosegregation defects are caused by unbalanced electromagnetic interactions affecting pool rotation and the solidification process. The procedure for measuring magnetic-flux density is described, and the results obtained on a large vacuum arc furnace with different bus-bar arrangements are presented. These results, along with extensive operational observations, strongly pointed out the importance of properly located current connections and coaxial current flow on furnace operation and ingot quality. Corrective actions and modifications of the current transmission system to eliminate nonuniform magnetic stray fields from the arc and melting zone are outlined. A coaxial, electromagnetically “clean” configuration of the entire current circuit to and within the furnace is a most important requirement for consistent consumable-electrode melting operation and reliable avoidance of macrosegregations in specialty steels and alloys. A discussion of controlling electromagnetic interactions by careful engineering of the current supply layout and incorporation of these concepts into an advanced furnace design concludes the paper.
Tunneling in thin MOS structures
Authors: Maserjian J.
Published: July 2002

Recent results on tunneling in thin MOS structures are described. Thermally grown SiO2 films in the thickness range of 22–40 Å have been shown to be effectively uniform on an atomic scale and exhibit an extremely abrupt oxide-silicon interface. Resonant reflections are observed at this interface for Fowler-Nordheim tunneling and are shown to agree with the exact theory for a trapezoidal barrier. Tunneling at lower fields is consistent with elastic tunneling into the silicon direct conduction band and, at still lower fields, inelastic tunneling into the indirect conduction band. Approximate dispersion relations (E-k, E-κ) are obtained over portions of the silicon-dioxide energy gap and conduction band.
CH
4
/H
2
reactive ion etching induced damage of InP
Authors: Neitzert H. C. , Fang R. , Kunst M. , Layadi N.
Published: July 2002

Electrical modifications of InP samples induced by reactive ion etching (RIE) with CH4/H2 have been studied using (a) electrochemical capacitance–voltage measurements, (b) current–voltage characteristics of Schottky diode structures, and (c) transient reflected microwave conductivity measurements. From the capacitance–voltage measurements we confirm a depletion of holes near the surface of the dry-etched p-InP sample and an accumulation of electrons near the surface of the dry-etched n-InP sample. The hole concentration in p-InP sample can be recovered after a 400 °C, 1 min heat treatment in an Ar ambient. From the transient reflected microwave conductivity measurements we reveal new information on the modification of charge carrier mobilities and kinetics caused by dry etching and subsequent annealing procedures on p-InP, n-InP, and semi-insulating (Fe-doped) InP samples. The n-InP sample shows a loss in electron mobility after RIE and annealing; the p-InP sample shows a weakly n-type behavior after RIE and recovers the p-type behavior after annealing.
High density plasma etching of low k dielectric polymers in oxygen-based chemistries
Authors: Fuard D. , Joubert O. , Vallier L. , Bonvalot M.
Published: July 2002

We have studied the etching of low dielectric constant polymers in halogen- and sulfur-free chemistries under various plasma operating conditions. The polymer graphitization phenomenon, which corresponds to the transformation of the aromatic hydrocarbon network into an amorphous carbon backbone, has been fully investigated under several plasma conditions by in situ mass spectrometry and quasi-in situ x-ray photoelectron spectroscopy (XPS). Profile control in high aspect ratio contact holes is obtained thanks to the formation of a passivation layer on the polymer sidewalls preventing the spontaneous chemical attacks by the oxygen reactive species of the plasma. XPS studies show that the passivation layer only forms under conditions where the plasma induces a polymer graphitization. Strong correlations are observed between plasma conditions leading to the polymer graphitization, the presence of heavy carbon byproducts detected in the plasma gas phase, and the passivation layer formation.
Use of microfabricated cold field emitters in sub-100 nm maskless lithography
Authors: Guo G. X. , Tokunaga K. , Yin E. , Tsai F. C. , Brodie A. D. , Parker N. W.
Published: July 2002

We propose a multicolumn and multibeam electron beam direct write lithography scheme using arrays of cold cathode emitters as the electron source. The conceptual design and the requirements for the field emitters in this application will be described. We have fabricated and tested both silicon field emitters and Spindt-type metal field emitters. Tip current stability was improved by pulse conditioning. Patterns with 117 nm feature sizes were written on poly(methylmethacrylate) photo resist.
Improvement of hydrogenated amorphous silicon properties with increasing contribution of SiH3 to film growth
Authors: Kessels W. M. M. , Boogaarts M. G. H. , Hoefnagels J. P. M. , Schram D. C. , van de Sanden M. C. M.
Published: July 2002

From cavity ring down spectroscopy and threshold ionization mass spectrometry measurements in a remote Ar–H2–SiH4 plasma it is clearly demonstrated that the properties of hydrogenated amorphous silicon (a-Si:H) strongly improve with increasing contribution of SiH3 to film growth. The measurements corroborate the proposed dissociation reactions of SiH4 for different plasma settings and it is shown that film growth is by far dominated by SiH3 under conditions for which solar grade quality a-Si:H at deposition rates up to 10 nm/s has previously been reported.