bluuebunny/crossref_metadata_2025 huggingface dataset:
Sliding Mode Control of Magnetic Bearings: A Hardware Perspective
Authors: Maslen E. , Montie D.
Published: July 2002

The physical hardware of magnetic bearing systems has a very strong impact on the application of sliding mode control to this technology. Finite current slew rates affect the character of achievable reaching conditions; flexible rotors demand the use of state observers which then affect achievable robustness; finite controller throughput and use of switching power amplifiers has substantial impact on how chatter should be addressed. This paper formulates the sliding mode control problem for realistic rotor/magnetic actuator systems considering rotor flexibility and finite amplifier voltages. The structure of the resulting class of controllers is examined for both rigid and for flexible rotors. It is demonstrated that, fundamentally, these controllers are conventional linear state observer-based controllers acting through high-speed switching amplifiers as in conventional magnetic bearing technology.
An Evaluation of Three-Dimensional Diarthrodial Joint Contact Using Penetration Data and the Finite Element Method
Authors: Dunbar, W. L. , U¨n K. , Donzelli P. S. , Spilker R. L.
Published: July 2002

We have developed an approximate method for simulating the three-dimensional contact of soft biphasic tissues in diarthrodial joints under physiological loading. Input to the method includes: (i) kinematic information describing an in vitro joint articulation, measured while the cartilage is deformed under physiological loads, (ii) geometric properties for the relaxed (undeformed) cartilage layers, obtained for the analyses in this study via stereophotogrammetry, and (iii) material parameters for the biphasic constitutive relations used to represent cartilage. Solid models of the relaxed tissue layers are assembled in physiological positions, resulting in a mathematical overlap of the cartilage layers. The overlap distribution is quantified and converted via the biphasic governing equations into applied traction boundary conditions for both the solid and fluid phases for each of the contacting layers. Linear, biphasic, three-dimensional, finite element analysis is performed using the contact boundary conditions derived for each of the contacting layers. The method is found to produce results consistent with the continuity requirements of biphasic contact. Comparison with results from independent, biphasic contact analyses of axisymmetric problems shows that the method slightly underestimates the contact area, leading to an overestimation of the total traction, but yields a good approximation to elastic stress and solid phase displacement.
Assessment of Muneer’s Luminous Efficacy Models in Madrid and a Proposal for New Models Based on His Approach
Authors: Ruiz Enrique , Soler Alfonso , Robledo Luis
Published: July 2002

From luminous efficacy models, illuminance can be estimated if irradiance is known or can be estimated. In the present paper, Muneer’s models for the luminous efficacy of global and diffuse radiation, useful for illumination engineers, are statistically assessed using data obtained at Madrid during a seven-year period. Several other models inspired on the simple approach proposed by Muneer are developed and statistically assessed. Some of those model the luminous efficacy of global or diffuse solar radiation, while others directly model the global or the diffuse illuminance. It is shown that for diffuse illuminance estimation the ratio of diffuse to extraterrestrial irradiance is to be preferred as independent variable to the ratio of global to extraterrestrial irradiance proposed by Muneer. Some models that estimate global illuminance from global irradiance and solar elevation, or diffuse illuminance from diffuse irradiance and solar elevation, perform practically on a par with the corresponding luminous efficacy models. It is also concluded that the striking difference between global luminous efficacy between the United Kingdom and Japan observed by Muneer is not due to a latitude effect.
Combined Methodology for Analysis of Rotary Systems
Authors: Huang Yuan Mao , Wang Chin-Ming
Published: July 2002

This study develops a numerical method for analyzing the unbalanced effect of rotary systems by combining the finite element method, the transfer matrix method, the time marching numerical integration method and the Houbolt numerical method. Previous studies of the individual effects associated with the rotary inertia, gyroscopic phenomenon, shear deformation, axial loading and internal damping on the dynamic behavior of rotary systems are all incorporated and examined in this study. The calculated transient and steady displacements of components in two systems are comparable with the available data. The results show that maximum displacements occur in the transient states at some critical speeds to assure the importance for analyzing the unbalanced effect of the rotary systems. Compared with existing methods, this presently combined methodology provides a faster converging speed. In addition, this model should improve the predicted results for the transient dynamic analysis of rotary systems than those obtained from existing models.
Mapping of Permeability Damage Around Perforation Tunnels
Authors: Ozgen Karacan C. , Grader Abraham S. , Halleck Phillip M.
Published: July 2002

We have investigated porosity and permeability damage around perforations using a combination of transient analysis and X-ray CT. The method applied allowed us to perform the entire experiments on samples under simulated in-situ stress conditions and to map variations in permeability along the length of the core as well as with radial distance from the perforation. Berea (10.2-cm (4-in.) dia) cores saturated with low-viscosity silicone oil were perforated using conventional-shaped charges (6-g HMX) and API RP43 procedures by using 6.88-MPa (1000-psi) effective stress and 5.16-MPa (750-psi) and 2.61-MPa (350-psi) underbalance. Low-permeability Torrey Buff Sandstone was also perforated using 5.16-MPa (750-psi) underbalance. After sufficiently flowing the perforations, higher-viscosity silicone oil was injected. The movement of fluids was tracked using X-ray CT to measure the local velocity of the viscous fluid front at different locations along the perforation. Results of these tests were compared in terms of permeability and porosity damage. Quantitative analysis on Berea cores show, for the specific charge and test conditions used, that damage extends approximately 2 cm (0.78 in.) from the center of the perforation. Comparison of tests performed with 2.41-MPa (350-psi) and 5.16-MPa (750-psi) underbalance show a clear increase in permeability near the tunnel wall at the higher underbalance. A zone of somewhat-reduced permeability exists at approximately 1.7 cm from the perforation center in the latter case. Porosity profiles calculated show that porosity is almost uniform out from the tunnel and there is no compacted zone near the tunnel wall in liquid-saturated cores. However, there is a high-porosity zone from the tunnel wall out about 2 mm. This may be due to a region of circumferential partings and small cracks that lead to high porosity or due to the possible artifacts discussed in the paper. Qualitative results have also been obtained for a tight sandstone for which underbalance was insufficient to remove debris from the perforation tunnel. CT images reveal that the plugged tunnel acts as a conduit for fluid flow, showing that the plugging material has significantly higher permeability than the surrounding rock.
Virus Transmission Through Compromised Synthetic Barriers: Part II—Influence of Pore Geometry
Authors: Das Bigyani , Myers Matthew R.
Published: July 2002

When stressed during normal use, synthetic barriers such as gloves and condoms can develop tears that are undetectable by the user. It is of considerable public-health importance to estimate the quantity of virus transmitted through the tear, in the event of viral contamination of the fluid medium. A mathematical model that accounts for virus adsorption to the barrier material was used to compute the quantity of virus transmitted through defects of various geometries. Slits were modeled as cylinders of elliptic cross section, and upper and lower bounds for the transmission rate of HIV and Hepatitis B virus (HBV) were calculated for barrier-use scenarios such as coitus and gripping of surgical instruments. For a 1-μm high slit, HIV transmission was found to be negligible for all likely use scenarios. HIV transmission became potentially significant for a 5-μm slit. Due to its high titer, HBV transmitted at potentially important levels even through the 1-μm slit. The dependence of the transmission rate upon pore aspect ratio was determined and found to be very strong for high-adsorption situations and near-circular pores. Numerical predictions of virus transport through a laser-drilled hole in a condom matched experimental measurements well, even when the tapered nature of the geometry is ignored.
A New Wave Dispersion Equation: Effects of Soil Characteristics
Authors: Jeng D. S.
Published: July 2002

The evaluation of wave characteristics has been widely studied by ocean engineers in the past. However, conventional investigations for determining wave characteristics have been focused on the nonlinear wave effects in a rigid seabed. On the other hand, most previous investigations for the wave-induced seabed response in a porous seabed have been only concerned with the soil response after wave pressure penetrate into seabed. In this paper, employing a complex wave number, the whole wave-seabed interaction problem will be re-examined. Based on the new closed-form analytical solution, a new wave dispersion equation is derived, including the seabed characteristics. The numerical results indicate that the wave characteristics (such as the wavelength, wave pressure and wave profile) are affected by the soil permeability and shear modulus in a shallow water.
On the Growth of Wind-Generated Waves in a Swell-Dominated Region in the South Atlantic
Authors: Violante-Carvalho Nelson , Parente Carlos Eduardo , Robinson Ian S. , Nunes Luis Manoel P.
Published: July 2002

The growth of surface gravity waves is investigated in an open sea region dominated by swell. An extensive database was collected by the Brazilian Oil Company during the South Atlantic Deep Water Program (PROCAP) in Campos Basin, off coast of Rio de Janeiro. This is the most important petrolic basin in Brazil where tens of drilling platforms are located. The data set contains over 5800 directional wave spectra measured by a heave-pitch-roll buoy in conjunction with meteorological data. A spectral approach is applied in a novel method for the partitioning of sea from swell and for the adjustment of the spectral parameters. The wave growth is investigated and the regression laws of the windsea extracted from the swell-contaminated spectra are compared to earlier works in sheltered areas. It is shown that, on the grounds of the equilibrium range theory, the high-frequency spectral level (the alpha parameter) scale with the reciprocal wave age in the same manner as in unimodal swell-free spectra.
A New Troughlike Nonimaging Solar Concentrator
Authors: Rinco´n Eduardo A. , Osorio Fidel A.
Published: July 2002

A new two-dimensional concentrator for solar energy collection has been developed. The concentrator has the following advantages, when compared with the classic Compound Parabolic Concentrators invented by Roland Winston, W. T. Welford, A. Rabl, Baranov, and other researchers: 1) It allows the use of parabolic mirrors, which have a reflecting area much smaller for a given concentration ratio and acceptance angle. 2) Between the mirror and the absorber, there is a large gap so that conduction losses are reduced. Convection losses can be reduced, too, if the absorber is enclosed within a glass tube. 3) It can be easily manufactured. Instead of seeking the shape of the mirrors for a given shape of the absorber, we have made the inverse statement of the problem, and we have obtained the optimal shapes of the absorbers with a prescribed acceptance angle, for parabolic mirrors, assuming that the intercept factor is unity, the mirrors are perfect, and the absorber surfaces are convex. The concentrator should be east-west oriented, and could be seasonal or monthly tilt adjusted. This concentrator could have many practical applications, such as fluid heating, steam generation, etc.
Normal Stresses on the Surface of a Rigid Body in an Oldroyd-B Fluid
Authors: Patankar N. A. , Huang P. Y. , Joseph D. D. , Hu H. H.
Published: July 2002

In this note we present a proof showing that the contribution from the extra stress tensor to the normal component of the stress on the surface of a moving rigid body in an incompressible Oldroyd-B fluid is zero.
A Viscoplastic Constitutive Model for 63Sn37Pb Eutectic Solders
Authors: Yi Sung , Luo Guangxing , Chian Kerm Sin
Published: July 2002

In the present study, a new constitutive model for eutectic solders (63Sn37Pb) is proposed. Grain sizes and phase sizes are considered as the coarsening is one of the main reasons for failure of solder joints. The present model has been developed based on the combination of grain boundary sliding and matrix dislocation deformation mechanisms in order to describe a thermo-mechanical behavior of eutectic solders. Internal stress tensors are also introduced to describe the transient behaviors during the tensile test and first stage creep. A series of tensile, creep, and creep recover tests were conducted at temperature range from −10 to 100°C. The specimens with two different phase sizes were tested. Good agreements were obtained between the experimental results and the model.
Theoretical Analysis of Fluid Forces on an Open-Type Centrifugal Impeller in Whirling Motion
Authors: Hiwata Akira , Tsujimoto Yoshinobu
Published: July 2002

For turbomachines operating at supercritical shaft speed, it is important to understand the characteristics of unsteady fluid forces on the impeller that occur due to shaft vibration. The present paper treats the forces on an open-type centrifugal impeller in whirling motion using unsteady potential flow theory. The whirling forces obtained agree reasonably with experimental results and show a destabilizing region at small positive whirl. It was found that the destabilizing force is due to the forces on the hub caused by temporal change in the thickness of the flow channel, with minor contribution of tip leakage on the destabilization.
Application of Type Synthesis Theory to the Redesign of a Complex Surgical Instrument
Authors: Lim Jonas J. B. , Erdman Arthur G.
Published: July 2002

Surgical instruments consist of basic mechanical components such as gears, links, pivots, sliders, etc., which are common in mechanical design. This paper describes the application of a method in the analysis and design of complex surgical instruments such as those employed in laparoscopic surgery. This is believed to be the first application of type synthesis theory to a complex medical instrument. Type synthesis is a methodology that can be applied during the conceptual phase of mechanical design. A handle assembly from a patented laparoscopic surgical stapler is used to illustrate the application of the design method developed. Type synthesis is applied on specific subsystems of the mechanism within the handle assembly where alternative design concepts are generated. Chosen concepts are then combined to form a new conceptual design for the handle assembly. The new handle assembly is improved because it has fewer number of parts, is a simpler design and is easier to assemble. Surgical instrument designers may use the methodology presented here to analyze the mechanical subsystems within complex instruments and to create new options that may offer improvements to the original design.
Estimation of in Situ Elastic Properties of Biphasic Cartilage Based on a Transversely Isotropic Hypo-Elastic Model
Authors: Garcia J. J. , Altiero N. J. , Haut R. C.
Published: July 2002

Articular cartilage is known to behave nonlinearly for large deformations. Mechanical properties derived from small strain experiments yield excessively large deformations in finite element models used in the study of severe blunt impact to joints. In this manuscript, a method is presented to determine the nonlinear elastic properties of biphasic cartilage based on a transversely isotropic hypo-elastic model. The elastic properties were estimated by fitting two force-displacement curves (in rapid loading and at equilibrium) obtained from large deformation indentation relaxation tests on cartilage using a nonporous spherical indentor. The solid skeleton of the cartilage was modeled as a transversely isotropic hypo-elastic material and a commercial finite element program was employed to solve the problem of a layer indented by a rigid sphere. Components of the hypo-elasticity tensor were made dependent on deformation according to the variations defined by a transversely isotropic hyperelastic formulation given earlier by others. Material incompressibility was assumed during the initial stage of rapid loading. The analysis was utilized for the determination of in situ properties of rabbit retropatellar cartilage at large deformations. The model was able to fit the material response to rapid loading and equilibrium indentation test data to approximately 50 percent strain. This material model suggested even higher percentage of stress supported by the fluid phase of cartilage than given earlier by small deformation theories of biphasic cartilage. [S0148-0731(00)01401-1]
Residual Stress Reduction and Fatigue Strength Improvement by Controlling Welding Pass Sequences
Authors: Mochizuki Masahito , Hattori Toshio , Nakakado Kimiaki
Published: July 2002

The effects of residual stress on fatigue strength at a weld toe in a multi-pass fillet weld joint were evaluated. The residual stresses in the weld joints were varied by controlling the sequence of welding passes. The residual stress at the weld toe was 80 MPa in the specimen whose last welding pass was on the main plate side, but it was 170 MPa in the specimen whose last pass was on the attachment side. The fatigue strength was nearly the same at high stress amplitude for both specimens, but the fatigue strength of the specimen whose last weld pass on the main plate was higher than that of the other specimen at low stress amplitude. This difference is due to the magnitude of the initial residual stress and the relaxation of the residual stress under fatigue cycling. The effects of the residual stress were shown in a modified Goodman diagram, in which residual stress is treated as a mean stress. [S0094-4289(00)01701-1]
Form Error Estimation Using Spatial Statistics
Authors: Yang Tai-Hung , Jackman John
Published: July 2002

Form error estimation is an essential step in the assessment of product geometry created through one or more manufacturing processes. We present a new method using spatial statistics to estimate form error. Using large sets of uniform sample points measured from five common machined surfaces, we compare the form error estimates using individual points and fitted surfaces obtained through spatial statistical methods. The results show that spatial statistics can provide more accurate estimates of form error under certain conditions. [S1087-1357(00)01701-9]
Fatigue-Strength-Reduction Factors for Welds in Pressure Vessels and Piping
Authors: Jaske Carl E.
Published: July 2002

Fatigue-strength-reduction factors (FSRFs) are used in the design of pressure vessels and piping subjected to cyclic loading. This paper reviews the background and basis of FSRFs that are used in the ASME Boiler and Pressure Vessel Code, focusing on weld joints in Class 1 nuclear pressure vessels and piping. The ASME Code definition of FSRF is presented. Use of the stress concentration factor (SCF) and stress indices are discussed. The types of welds used in ASME Code construction are reviewed. The effects of joint configuration, welding process, cyclic plasticity, dissimilar metal joints, residual stress, post-weld heat treatment, the nondestructive inspection performed, and metallurgical factors are discussed. The current status of weld FSRFs, including their development and application, are presented. Typical fatigue data for weldments are presented and compared with the ASME Code fatigue curves and used to illustrate the development of FSRF values from experimental information. Finally, a generic procedure for determining FSRFs is proposed and future work is recommended. The five objectives of this study were as follows: 1) to clarify the current procedures for determining values of fatigue-strength-reduction factors (FSRFs); 2) to collect relevant published data on weld-joint FSRFs; 3) to interpret existing data on weld-joint FSRFs; 4) to facilitate the development of a future database of FSRFs for weld joints; and 5) to facilitate the development of a standard procedure for determining the values of FSRFs for weld joints. The main focus is on weld joints in Class 1 nuclear pressure vessels and piping. [S0094-9930(00)02703-7]
Argon Implanted into Graphite, by XPS
Authors: Crist B. Vincent
Published: July 2002

Argon ions (Ar+) were implanted into a substrate of natural graphite (crystal) by 4 kV acceleration for a period of 5 min using a VG EX05 ion gun. (The surface plane of the substrate was perpendicular to the flight path of the argon ions.) No attempt was made to maximize the argon concentration within the graphite. The resulting concentration of argon within the graphite surface was approximately 4.0 at. %. The BE for Ar 2p3 is 241.7 eV which is similar to the 241.9 eV obtained by Perkin Elmer [see J. F. Moulder, W. F. Stickle, P. E. Sobol, and K. O. Bomben, Handbook of X-ray Photoelectron Spectroscopy, 2nd ed. (Perkin-Elmer Corporation, Eden Prairie, MN, 1992), p. 65].
Sputter-Induced Modifications of IrO2 During XPS Measurements
Authors: Bozack Michael J.
Published: July 2002

We have characterized sputter-induced modifications of IrO2 during low-energy Ar+ bombardment. The O 1s peak contains at least two components whose intensity drops by a factor of 2 after 10 min of sputtering at 2.5 kV. The relative peak areas of the Ir 4d5/2–7/2 features are altered and their binding energies shift downward by −0.4 eV after sputtering. The unusual Ir 4d5/2–7/2 ratio before sputtering may indicate higher oxidation states and/or poor preparation from the metal chloride; however, the Ir 4f7/2 BE of 61.5 eV is consistent with a principal IrO2 composition. The drop in O 1s intensity and lower binding energy indicate that reduction to Ir metal occurs durng Ar+ irradiation.
Core Level and Valence Band Spectra of PbO2 by XPS
Authors: Rondon Sonia , Sherwood Peter M. A.
Published: July 2002

Core and valence band spectra were obtained from a PbO2 sample. The XPS data were collected with a VSW HA150 spectrometer equipped with a monochromatic Al Kα x-ray source and a multichannel detector. This report includes the Pb 4f, Pb 5d, Pb 4d, O 1s, C 1s, and valence band photoemission peaks. The XPS analysis showed the presence of small amounts of adventitious carbon, adsorbed water, and hydroxide on the surface of the sample. The valence band spectrum of PbO2 collected with achromic radiation provides limited information because of overlapping with the Mg Kα3/4 satellites associated with the intense Pb 5d and O 2s peaks. The use of monochromatic x-radiation allows one to collect a high resolution valence band spectrum without the interference of these satellite features. This is of particular interest in the study of lead oxides because their XPS valence band spectra present features that can be used successfully to distinguish the different oxide forms.
Analysis of a 20% Magnesium Silicate Filled Poly(propylene) Polymer by XPS
Authors: Lannon John M. , Meng Qingru
Published: July 2002

We report x-ray photoemission spectra for a 20% magnesium silicate (talc) filled poly(propylene) (PP) polymer. XPS spectra were acquired with a SSI model SSX-100 instrument using monochromated Al Kα x-rays. We present the survey spectrum (binding energy 0–1000 eV) and a narrow spectrum of the C 1s and O 1s photoelectron peaks.
Crack formation in tensile InGaAs/InP layers
Authors: Natali M. , De Salvador D. , Berti M. , Drigo A. V. , Lazzarini L. , Salviati G. , Rossetto G. , Torzo G.
Published: July 2002

A systematic investigation of crack formation has been performed in tensile InxGa1−xAs/InP layers with indium composition ranging from x=0.2 up to x=0.35 and thicknesses ranging from 8 nm to 2 μm. It has been found that cracks form after growth and on a characteristic timescale of several days. The formation of cracks has been found to occur in a well defined thickness interval correlated to the residual strain during growth. Crack formation is favored along the [110] in-plane direction in samples with low indium composition. The results can be rationalized within a model which explicitly takes into account the fact that cracks form after growth.
Wear resistant coatings for reactor components in liquid sodium environments
Authors: Johnson R. N. , Schrock S. L. , Whitlow G. A.
Published: July 2002

Rubbing surfaces of critical components for the coming generation of the nation's liquid–metal-cooled fast-breeder reactors must withstand severe environments of high temperature, liquid–metal corrosion, and nuclear irradiation. For some component requirements, the use of the better known bearing materials and hardfacings has been shown to be inadequate or impractical. For several applications, bulk (> 25-μ thick) coatings have provided the only successful solution to friction problems in high-temperature sodium. Coating processes that have been or are being evaluated include plasma spray, detonation gun, spark-discharge, sputtering, and diffusion coating processes. Testing included friction and wear tests in up to 650 °C sodium, sodium corrosion tests for up to one year, thermal cycling, bond strength tests, and irradiation tests in a fast reactor. For one particularly severe application, a specially modified commercial coating of chromium carbide in a 15 vol% nichrome binder, applied by a commercial detonation gun process, has so far been found to be most acceptable in meeting the friction, corrosion, and irradiation damage criteria. Much of the test data reported is on this coating and its antecedent modifications.
Relation of Measured Outgassing Pressures to Surface Adsorption in Satellite Borne Pressure Gauges
Authors: Silverman Peter J. , Newton George P.
Published: July 2002

Two different pressure gauges were mounted in the Explorer 32, a spin stabilized, aeronomy satellite, in such a way that they were alternately exposed to a beam of atmospheric gas and to a nearly total vacuum. During exposure to the nearly total vacuum, it was possible to measure the pressure in the gauge enclosure produced by gas desorbed from the gauge surfaces. This outgassing pressure was found to depend in a fixed way upon the ambient atmospheric density and the elapsed time since the satellite was last at perigee. The main features of the variation of outgassing pressure with time near perigee were reproduced using a Langmuir model of surface adsorption, with an adsorption probability near 10−4 and a desorption rate from a surface covered with one monolayer of gas near 1013 particles per sq cm per sec. The results of this study show that the adsorption-desorption phenomena have a component that occurs during times comparable to an orbit period (100 min).
Vacuum Heat Treatment of Tool Steels
Authors: Reynoldson R. W. , Harris K. C.
Published: July 2002

The heat treatment of tools and dies in vacuum furnaces is discussed, together with the major problems of dimensional changes in tool steels, and methods of controlling such changes in the equipment available today.
Degassing Kinetics of Molten Metals in Vacuum
Authors: Winkler Otto
Published: July 2002

A brief review of the theoretical and experimental work on the kinetics of the vacuum degassing of liquid metals is given. This review is limited to the case usually encountered where the transport in the melt alone is rated determining, i.e., where desorption processes at the melt surface and the transport in the gas phase may be neglected. Different models describing the mass transfer from the interior of the melt to the interface are also discussed. The course of degassing of a melt pool without bubble formation, based on the mathematical treatments of Kraus (see Refs. 1 and 2) and Machlin (see Ref. 3) is described. In the model of Kraus—which may be applied, for instance, to ladle degassing—convection currents in the interior of the melt develop by density differences caused by the heat loss of the freely radiating melt surface. The calculations of Machlin refer to inductively stirred melts. Formulas for the mass transfer coefficients for these two cases are given. If layers of surface active elements or slags accumulate at a melt surface, the rate of degassing may be largely reduced. There is also an examination of how far the model of Kraus is applicable to degassing in electron-beam and vacuum-arc melting with consumable electrodes. Most technical degassing processes rely on the formation of bubbles, for only with them are the high rates required for economical degassing obtained. Also shown are the conditions under which bubble nuclei may exist and growth of the bubbles in a melt pool or in stream degassing is possible. Reference is made to the calculations of the gas pick-up of ascending CO bubbles in a steel melt made by Kraus (see Refs. 1 and 2), which also permit the calculation of the mass transfer coefficient if, in this case, a surplus of nuclei in the melt exists. If the gas content is too low for spontaneous bubble nucleation, the use of a neutral scavenging gas is advantageous. Computations of its purging effect have been made by Bradshaw and Richardson (see Ref. 4) as well as by Lange et al. (see Ref. 5). Stream degassing is not accessible to an exact mathematical treatment. However, an estimation of the degassing rates of droplets and experimental results show that the removal of hydrogen probably takes place mainly by diffusion from the external surfaces of metal droplets and bubbles, whereas nitrogen and oxygen removal depends more on the bubble formation in the metal stream and melt pool.
Theory, Design, and Selection of Vacuum Metallurgical Processing Equipment
Authors: Durant John H.
Published: July 2002

Process advantages of vacuum are compared with conventional and inert gas atmospheres with respect to purity, repeatability, and operating cost. Recognition of vapor pressures of workloads, containers, and furnace hot zone parts is essential to predicting system performance parameters, maintenance schedules, and pumping equipment selection. Cooling requirements of batch equipment are evaluated with respect to quench characteristics, equipment turn-around time, and work-piece surface quality. Design features of system details are evaluated for such factors as heat removal (jacketing vs traced cooling); safety (one-piece electrode design); integrity at full vacuum and partial pressure operation. Typical systems are examined for conformity to design criteria established.
Use of the Photoemission Electron Microscope as a High-Vacuum Hot-Stage Microscope for Temperatures up to 2000°C
Authors: Dannöhl H.-D. , Wegmann L.
Published: July 2002

When studying vacuum-treated materials at high temperatures, the specimen must be kept at a low pressure, which is at least of the same magnitude as that used during the metallurgical treatment, to avoid contamination by gases. The pressure obtainable in most commercial hot-stage microscopes is not low enough, resolution at the higher temperatures is poor, and contamination of the optics often affects longtime studies. Progress has been made with the emission electron microscope using kinetic and thermionic emission; however, electron emission at low temperatures was possible only with kinetic emission or by coating the specimen with thin films to lower the work function. Surface conditions were then uncontrollably altered. These disadvantages are not present in the photoemission electron microscope. Using powerful vacuum pumps, continuous observations at gas pressures within the normal working range of 5 × 10−7 Torr and 10−3 Torr are possible. With liquid helium cryopumping, pressures of 10−8 Torr are obtainable. Gas treatments at higher pressure are possible, but without simultaneous observation of the specimen. In the temperature range up to the onset of thermionic emission, a resolution of 150 Å can be obtained from polished samples. When thermionic emission occurs, contrast is not altered and the limit of resolution is unaltered. This type of microscope is now available for studying materials in excellent vacuum with high resolution in the range from room temperature to 2000 °C. Special devices prevent contamination of the sample so that long-term studies can be made over several hours or days with continuous observation. Several accessories attached to the preparation chamber, which is directly connected to the observation chamber and pumped with the same vacuum pumps, allow different treatments such as specimen coating, quenching, cleaning by ion-bombardment, and ion etching. A comparison of the photoemission electron microscope and the scanning electron microscope is made on flat specimens. The results show that only the photoemission electron microscope works at all temperatures with excellent contrast and resolution. Several examples are used to illustrate the potential application of the photoemission electron microscope in the fields of recrystallization, diffusion, precipitation, and transformation studies.
Co-Deposited Aluminum Alloy Films
Authors: Reith T. M. , Peressini P. P.
Published: July 2002

The addition of small amounts of copper to aluminum metallurgy significantly increases the electromigration resistance of aluminum stripes. A reproducible technique for co-evaporating these and other binary and ternary alloy films has been developed using a theoretical model as a guide to its design. The technique, which utilizes up to three evaporation sources, is extremely versatile. Films of controlled and predictable composition are routinely generated facilitating study and optimization of the alloy film properties. The effect of various concentrations of copper on stripe lifetime and resistivity is presented. Also, the effect of small amounts of silicon added to Al-Cu lands in contact with silicon devices to retard junction penetration is discussed. Analysis data on Al-Cu and Al-Cu-Si films are given.
Optical Properties of Thin Films of Zirconium Diboride
Authors: Linton Roger C. , Mookherji T. K.
Published: July 2002

The optical constants of the intermetallic compound ZrB2 were obtained at different angle of incidences over the wavelength range 100–600 nm. These were calculated using a computer code based on the Fresnel equations which solves for n and k from reflectance at two angles of incidence and by the well-known Kramers-Kronig relation. Opaque thin films of about 3000 Å were deposited on quartz substrates employing electron-beam melting technique under a vacuum of 10−7 Torr. The material used was very high-purity ZrB2 powder. Although the samples were exposed to air briefly before measurement, precautions were taken to observe the growth, if any, of an oxide-type layer on the ZrB2 films. No such layer growth was observed. The real and imaginary parts of the dielectric constant, and the energy loss function were calculated from n and k. The significant features of the dispersion curves and the energy loss function are discussed.
Vacuum System for Stanford Storage Ring, SPEAR
Authors: Cummings U. , Dean N. , Johnson F. , Jurow J. , Voss J.
Published: July 2002

Due to its unusual geometry and gas load, the SPEAR vacuum system incorporates several unique design features. The system consists of an aluminum chamber in the form of a 200-ft-diam ring which must achieve a pressure in the 10−9 Torr range with a large gas load due to synchrotron-radiation-induced desorption. Since the system is conductance limited, it was necessary to develop distributed sputter-ion pumps located within the chamber proper. A large number of aluminum-stainless-steel interfaces required the development and testing of various flange arrangements which would withstand a bakeout to 200 °C.
Mass spectrum of dynamite effluent
Authors: Hobbs J. R. , Barrington A. E. , Cline J. E.
Published: July 2002

In order to determine the utility of a portable mass spectrometer equipped with a membrane separator as a detector of concealed explosives, the mass spectrum of dynamite effluent recorded by such an instrument has been identified. Necessary steps in this work were an analysis of the composition of the effluent and an examination of membrane penetration by oxides of nitrogen.
Residual gas analysis studies during sputtering of reactive metals
Authors: Meyer Donald E.
Published: July 2002

Presence of residual gases in a sputtering discharge can alter the properties of sputtered films of molybdenum, titanium, palladium, titanium-tungsten, chromium, and similar reactive metals. Of particular interest are hydrogen and water vapor. In this article, equipment and methods are described and discussed which permit direct and real time analysis of residual gases during sputtering processes. In a production system argon may constitute as little as 59% of a total pressure of 10 μ. Two major sources of residuals are dirty systems and poorly manufactured targets. Diffusion pump, turbopump, and ion-pump systems were monitored.
Measurements of adsorption isotherms and pumping speed of helium on molecular sieve in the 10−11−10−7 Torr range at 4.2 K
Authors: Halama H. J. , Aggus J. R.
Published: July 2002

The experimental data on helium adsorption isotherms for molecular sieve have been extended from 10−7 to 10−11 Torr. A commercially available cryopump CVR 1008 made by Excalibur was used for this investigation. It was found that, in general, the experimental points fall on a curve predicted by the Dubinin and Radushkevich theory down to 1×10−10 Torr. Below this pressure the slope gets steeper and possible causes for this behavior are being studied. When compared with bare copper surfaces, a 1.8-mm-thick layer of bonded molecular sieve 5A adsorbs almost 108 times more helium per unit area. The pumping speed remains high for leaks Q<1×10−6 Torr liters/sec with coverages of 10 cm3 (STP)/cm2 adsorbent. Cryosorption looks very attractive for pumping large amounts of helium at low pressures and is therefore suitable for superconducting storage rings where the pumps have to operate inside superconducting magnet Dewars.
Master replication into thermosetting polymers for nanoimprinting
Authors: Schulz H. , Lyebyedyev D. , Scheer H.-C. , Pfeiffer K. , Bleidiessel G. , Grützner G. , Ahopelto J.
Published: July 2002

Replication of the e-beam master into thermosetting polymers was investigated for low cost working stamp fabrication for nanoimprint lithography (NIL). Negative as well as positive replicas from a master were fabricated in a thermal replication step from duroplastic material. Without any further treatment these working stamps were able to imprint thermoplastic polymers. To demonstrate the procedure we used the custom polymers mr-I-8130 and mr-I-9030 as well as PMMA for comparison. All replications were done in a NIL process. The replication quality is excellent when a suitable imprint procedure is used.
Lithographic performance of thin dendritic polymer resists
Authors: Williamson Mike , Neureuther Andy
Published: July 2002

A dendritic polymer resin lithographic resist is evaluated for surface and line edge roughness, and feasibility to enter the manufacturing environment. This novel resin demonstrates superb surface smoothness; linewidth variation is 5.1 Å and surface roughness is 12.9 Å. Most of the key concerns in the manufacturing environment are adequate, if not excellent. This resist shows excellent potential for processes where very small and smooth features are required, such as gate level definition.
Low resistance transparent electrodes for large area flat display devices
Authors: Laverty S. J. , Maguire P. D.
Published: July 2002

The dynamic performance of large area, high-resolution flat panel displays is contingent upon the conductivity of the transparent electrode. Electroplated copper and vacuum deposited aluminum bus bars attached to the sidewalls of conventional SnO2 electrodes offer theoretical improvements in conductivity while maintaining the electrode transmittivity. In association with a reactive ion etching process for delineating the tin oxide, auto registration methods for attaching copper by electroplating and aluminum by a resist lift off process are described, together with the achieved enhancement factors. A contact resistance between the aluminum and the tin oxide was found to significantly reduce the enhancement. The sidewall contact resistance lies between 0.4 and 4.0×104 Ω μm2, considerably lower than that previously reported for contacts to the tin oxide top surface. The enhancement factor for aluminum lies between two and three. The application of copper did not suffer from a contact resistance and an order of magnitude enhancement was obtained. We also report excellent adhesion, typically greater than 200 kg/cm2, of the metals to the tin oxide and identify the parametric space for achieving this.
Properties of aluminum-doped zinc oxide films deposited by high rate mid-frequency reactive magnetron sputtering
Authors: Malkomes N. , Vergöhl M. , Szyszka B.
Published: July 2002

Aluminum-doped zinc oxide films are promising candidates for economic transparent conducting oxide (TCO) applications. To reach high deposition rates (about 7 nm/s at 4.5 W/cm2) in combination with optimum TCO properties by using the reactive mid-frequency sputtering technique, the process window must be precisely controlled, especially for unheated substrates. To overcome the typical hysteresis problem, the process was stabilized by plasma impedance control for ease of use; this enabled the stabilization of the deposition process at any setpoint on the S-curve of the corresponding hysteresis loop. Hence in contrast to former work [B. Szyszka, Thin Solid Films 351, 164 (1999)], wherein a flow control at fixed power restricted the stabilization either to the metallic mode or to the oxide mode, respectively, the samples were prepared at various deposition parameters (setpoint, pressure, and temperature) also within the transition mode. It turns out that for certain process parameters optimum TCO properties were achieved only within this transition mode, which was not accessible without control. Electrical measurements indicated that the optimum resistivity of ZnO:Al films deposited on unheated substrates was about 2.5 times higher than at a substrate temperature of 200 °C. In the latter case, an improved value of 290 μΩ cm at 1.2 mTorr total pressure and of 250 μΩ cm at 13.2 mTorr, respectively, could be reached. Due to band-gap widening, which follows the Burstein–Moss theory, the optimum films showed a neutral color. For those samples, the ellipsometric spectra could be well modeled without using interface layers, indicating the dense structure of the films. The process state on the stabilized S-curves was characterized by partial pressure measurements and optical emission spectroscopy (OES). These investigations show that it is also possible to stabilize the process at fixed flow with a modified OES control using the process power as the control variable, and using the ratio of an oxygen and a metal emission line as the controlled variable.
Characteristic structures of the Si(111)-7×7 surface step studied by scanning tunneling microscopy
Authors: Miyake K. , Okawa S. , Takeuchi O. , Futaba D. N. , Hata K. , Morita R. , Yamashita M. , Shigekawa H.
Published: July 2002

Contrary to previous results concluding that all 7×7 boundaries in the down step edge were complete, 5×5 faulted half units were found to be introduced in part when the transition region was narrow. In addition, the formation characteristic of the 5×5 faulted half units was strongly influenced by the type of step configuration (nF or nU) and by the structure of the upper step edge (complete or incomplete). Even when the step configuration was the same, the difference in the upper step edge structures strongly affected introduction of 5×5 units.
Plasma diagnostics in large area plasma processing system
Authors: Leonhardt D. , Walton S. G. , Blackwell D. D. , Amatucci W. E. , Murphy D. P. , Fernsler R. F. , Meger R. A.
Published: July 2002

A series of plasma diagnostic have been carried out in our large area plasma processing system which is based on a modulated electron-beam produced plasma. These discharges were created in both electrically conducting and insulated vacuum chambers operated in 30–120 mTorr of pure gases (argon, oxygen, and nitrogen). Langmuir probes, microwave transmission, mass spectrometry, and external current sensors show robust discharges were made over fairly wide parameter ranges resulting in plasma densities of 1–4×1011 cm−3 and temperature ranging from 0.2 eV for the molecular gases and 1.4 eV for argon. The effects of various experimental techniques, parameters, and contamination issues are discussed in detail.
High reflectivity symmetrically strained ZnxCdyMg1−x−ySe-based distributed Bragg reflectors for current injection devices
Authors: Maksimov O. , Guo S. P. , Fernandez F. , Tamargo M. C. , Peiris F. C. , Furdyna J. K.
Published: July 2002

Distributed Bragg reflectors (DBRs) with different numbers of periods were grown by molecular beam epitaxy from ZnxCdyMg1−x−ySe-based materials on InP substrates. The alternating ZnCdSe/ZnCdMgSe layers were symmetrically strained to the InP substrate greatly simplifying the growth process and increasing the uniformity. High crystalline quality was also achieved in these structures. A maximum reflectivity of 99% was obtained for a DBR with 24 periods. Chlorine doped (n-type) DBRs were grown and their electrical and optical properties were investigated. Electrochemical capacitance–voltage profiling indicated that the doping concentrations of the ZnCdSe and ZnCdMgSe layers were 4×1018 and 2×1018 cm−3, respectively. The reflectivity of the doped DBR structures was comparable to that of the undoped ones.
Modification of polycarbonate and polypropylene surfaces by argon ion cluster beams
Authors: Biederman H. , Slavinska D. , Boldyreva H. , Lehmberg H. , Takaoka G. , Matsuo J. , Kinpara H. , Zemek J.
Published: July 2002

Impacts of energetic argon ion clusters on surfaces of inorganic solids have shown modification of the respective surface properties. Polymeric samples such as (PC) polycarbonate and (PP) polypropylene were irradiated by argon ion clusters (average size of 3000 atoms) accelerated to 10 and 20 keV at doses ranging from 109 to 1014 cluster/cm2. The irradiated surfaces were investigated by surfometer (profilometer), atomic force microscope, contact angle measurements and x-photoelectron spectroscopy. Measurements using these techniques show that the smoothing effect and the postirradiation oxidation of the surface take place. The direct evidence was obtained in case of PP that the irradiation dose 1011 cluster/cm2 produces the smoothest surface as measured by surfometer. In the case of PC the same conclusion is suggested indirectly.