bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental Investigation of Heat Dispersion Due to Impregnation of Viscous Fluids in Heated Fibrous Porous During Composites Processing
Authors: Hsiao Kuang-Ting , Laudorn Hans , Advani Suresh G.
Published: July 2002

Resin Transfer Molding (RTM) is a composite manufacturing process in which a fibrous preform is placed in a closed mold and a viscous resin is injected into the mold to fill the empty spaces between the stationary network of fibers. The fiber preform and the mold are usually hot and transfer the heat to the moving resin. In this paper, we carried out an experimental investigation to validate the importance of heat dispersion in RTM and the local thermal equilibrium assumption during the non-isothermal mold filling process. In addition, we have developed an expression for the temperature boundary condition at the moving flow front for this moving boundary mold filling process based on volume averaging method and verified it with experiments. The heat dispersion was found to vary linearly with Peclet number and contributed significantly to the temperature distribution in RTM. Using order of magnitude analysis, it was clearly shown that the local thermal equilibrium is a reasonable assumption to model RTM processes and was verified with experimental results. Finally, as many fiber preforms consist of two scales of pore sizes, it is pointed out that further research is necessary in characterization and prediction of heat dispersion in dual scale porous media.
Comparison of the Predictions Relying on Coupled/Uncoupled Damage-Viscoplasticity Models for Creep Test Analyses
Authors: Nicolas L. , Mongabure P. , Le Ber L. , Devos J. , Bhandari S. , Messelier-Gouze C.
Published: July 2002

To enhance the assessment of reactor pressure vessel life under severe accident, a cooperative research program is conducted between CEA, EDF, and Framatome, parts of which are supported by the European Commission. Within the framework of this program, a model based on Lemaitre and Chaboche with predictive capability in the field of viscoplastic flow, material damage, and failure has been generalized and implemented in CASTEM 2000 finite element code. In order to validate the model in mechanical situations featuring the same basic characteristics as the severe accident scenarios, analytical experiments are conducted on the RUPTHER facility: a thin shell tube is loaded with an internal pressure and submitted to an axial thermal gradient with elevated temperatures. The specific question of the interest of the coupled damage approach in the failure prediction is addressed. Comparisons of the predictions relying on coupled and uncoupled damage-viscoplasticity models show that, at higher temperatures, failure could be predicted through uncoupled damage evaluation provided the main nonlinear effects like large displacements and updated pressure are taken into account, while at lower temperatures coupling between damage and deformation is necessary. Examples based on some RUPTHER creep test predictions are given.
Successive Deposition of Metals in Solid Freeform Fabrication Processes, Part 2: Thermomechanical Models of Adjacent Droplets
Authors: Chin R. K. , Beuth J. L. , Amon C. H.
Published: July 2002

Residual stress-induced tolerance losses are a principal barrier for using Solid Freeform Fabrication (SFF) processes to create functional parts out of engineering materials. In Part 1 of this paper, problems of successively deposited layers and droplets deposited in a column are considered for SFF processes. Models of these problems are used to detail thermal and mechanical interactions between existing and newly deposited material as well as their effects on final residual stress distributions on sub-layer (droplet) and multi-layer scales. In the current study, sub-layer interactions are further considered using models of droplets deposited adjacent to one another. As in Part 1, models are applied to a particular SFF process; however, insights and conclusions are relevant to numerous similar SFF processes. Simulations of separated and connected droplets deposited onto a large substrate indicate very limited thermal interactions between adjacently deposited droplets. However, mechanical interactions between droplets can be significant, which is consistent with the directionality of warping observed in experiments. Results from deposition of droplets on a thin substrate demonstrate the importance of process-induced substrate preheating in reducing residual stresses.
Plastic Forming Processes Through Rotating Conical Dies1
Authors: Durban D. , Davidi G. , Lior D.
Published: July 2002

Drawing and extrusion of single-phase and multilayered tubes through rotating conical dies is investigated within the framework of continuum plasticity. Large strain perfectly plastic J2 flow theory models constitutive behavior along with a radial-helical flow pattern. The governing system for a single-layer process is reduced to three coupled nonlinear ordinary differential equations. An approximate solution is developed for long and tapered working zones with low wall friction. That solution is used to simulate the field within each layer in composite tube forming. Exact relations are derived for the n-layered tube and it is shown that wall rotation can considerably reduce the required working loads.

Dedicated to Professor Dietmar Gross on the occasion of his 60th birthday
Sliding Contact Analysis of Layered Elastic/Plastic Solids With Rough Surfaces
Authors: Peng Wei , Bhushan Bharat
Published: July 2002

A three-dimensional numerical model is presented to investigate the quasi-static sliding contact behavior of layered elastic/plastic solids with rough surfaces. The model is applicable for both single-asperity contact and multiple-asperity contacts. The surface deformation is obtained based on a variational principle. The surface and subsurface stresses in the layer and the substrate are determined with a Fast Fourier transformation (FFT) based scheme and von Mises and principal tensile stresses are computed accordingly. Contact statistics, such as fractional contact area, maximum pressure/E2 and relative meniscus force are predicted. The results are used to investigate the effect of the contact statistics on friction, stiction, and wear problems such as debris generation, brittle failure, and delamination of layered media. Optimum layer parameters are identified. It allows the specification of layer properties, according to the contact statistics, to reduce friction, stiction, and wear of materials. A normalization procedure is presented to apply the results on various combinations of surface roughness, material properties, and normal load.
Random Response Analysis of Preisach Hysteretic Systems With Symmetric Weight Distribution
Authors: Ni Y. Q. , Ying Z. G. , Ko J. M.
Published: July 2002

The present study is intended to develop a new method for analyzing nonlinear stochastic dynamic response of the Preisach hysteretic systems based on covariance and switching probability analysis of a nonlocal memory hysteretic constitutive model. A nonlinear algebraic covariance equation is formulated for the single-degree-of-freedom Preisach hysteretic system subjected to stationary Gaussian white noise excitation, from which the stationary mean square response of the system is obtained. The correlation coefficients of hysteretic restoring force with response in the covariance equation are evaluated by using the second moments and switching probabilities that are derived from the disjoint event probability and the mathematical machinery of an exit problem. In recognizing the symmetry of the classical Preisach weighting function, an approximation of equal “up” and “down” switching probabilities is introduced, which greatly simplifies the evaluation of the correlation coefficients. An example of the Preisach hysteretic system with Gaussian distribution weighting function is presented and the analytical results are compared with the digital simulation findings to verify the accuracy of the derived formulas. Computation results show that there exists a sharp drop in the mean square responses with the increase of a hysteresis parameter, and the mean square responses are affected only in a certain range of the Preisach weighting function.
Some Properties of J-Integral in Plane Elasticity
Authors: Chen Y. Z. , Lee K. Y.
Published: July 2002

Some properties of the J-integral in plane elasticity are analyzed. An infinite plate with any number of inclusions, cracks, and any loading conditions is considered. In addition to the physical field, a derivative field is defined and introduced. Using the Betti’s reciprocal theorem for the physical and derivative fields, two new path-independent D1 and D2 are obtained. It is found that the values of Jkk=1,2 on a large circle are equal to the values of Dkk=1,2 on the same circle. Using this property and the complex variable function method, the values of Jkk=1,2 on a large circle is obtained. It is proved that the vector Jkk=1,2 is a gradient of a scalar function Px,y.
Air Film Dynamics for Micro-Textured Flying Head Slider Bearings in Magnetic Hard Disk Drives
Authors: Tagawa Norio , Bogy David B.
Published: July 2002

This paper describes the air film dynamics for micro-textured flying head slider bearings in magnetic hard disk drives and it discusses their ability to increase the air film damping. In order to study the effects of micro-textures on air film dynamic characteristics of flying head slider bearings, two-dimensional micro-textures are modeled as deterministic rectangular models in the transverse and longitudinal directions. Dynamic analysis of these micro-textured flying head slider bearings is carried out by computing the impulse responses of the sliders and applying the modal analysis method to obtain their modal frequencies, damping ratios, and mode shapes. It is found that micro-textures on air bearing surfaces in the transverse direction have very significant effects and increase the air film damping of the slider’s three vibration modes but do not affect the air film stiffness. The same is not true for micro-texture in the longitudinal direction. The effects of transverse micro-textures’ spacing and depth on the air film dynamics are also numerically investigated in detail. The optimum values for high air film damping ratios are obtained. It is found that transverse micro-textures having small spacing are not very effective, being equivalent to the surface roughness effect.
Effects of Distance Between Pads on the Inlet Pressure Build-Up on Pad Bearings
Authors: Kim Jong-Soo , Kim Kyung-Woong
Published: July 2002

Full Navier-Stokes equations are solved numerically for a cavity region between two consecutive pads and a parallel lubricating film. Numerical solutions are obtained for a wide range of Reynolds number and various values of a distance between pads. Numerical results show that the inlet pressure build-up is significantly affected by Reynolds number and the distance between two adjacent pads. A new formula is derived of loss coefficient with Reynolds number and a distance factor, for using it in an extended Bernoulli equation, on the basis of numerical results. Experiments are conducted to investigate the validity of the formula of loss coefficient proposed by authors.
Bifurcations of Flow Through Plane Symmetric Channel Contraction
Authors: Chiang T. P. , Sheu Tony W. H.
Published: July 2002

Computational investigations have been performed into the behavior of an incompressible fluid flow in the vicinity of a plane symmetric channel contraction. Our aim is to determine the critical Reynolds number, above which the flow becomes asymmetric with respect to the channel geometry using the bifurcation diagram. Three channels, which are characterized by the contraction ratio, are studied and the critical Reynolds numbers are determined as 3075, 1355, and 1100 for channels with contraction ratios of 2, 4, and 8, respectively. The cause and mechanism explaining the transition from symmetric to asymmetric states in the symmetric contraction channel are also provided.
Modeling of Irradiation Embrittlement of Reactor Pressure Vessel Steels
Authors: Murakami S. , Miyazaki A. , Mizuno M.
Published: July 2002

A model to describe the change in the inelastic and fracture properties of reactor pressure vessel steels due to neutron irradiation in the ductile region (i.e., irradiation embrittlement) is developed. First, constitutive equations for unirradiated elastic-viscoplastic-damaged materials are developed within the framework of the irreversible thermodynamics theory. To take into account the effect of hydrostatic pressure on the nucleation and growth of microvoids, properly defined dissipation potential is used. Then, the effect of irradiation on the material behavior is incorporated into the proposed model as a function of neutron fluence Φ by taking into account the interaction between irradiation-induced defects and movable dislocations. As regards the damage strain threshold pD, the mechanism of void nucleation due to pile-up of dislocations at the inclusions in the material is proposed first under unirradiated-condition, and then the effect of irradiation on the mechanism is formulated. In order to demonstrate the validity of this model, it is applied to the case of uniaxial tensile loading of a low alloy steel A533B cl. 1 for the pressure vessel use of light-water reactors at 260°C. The resulting model can describe the increase in yield stress and ultimate tensile strength, the decrease in total elongation and strain hardening, and the strain rate dependence of yield stress due to neutron irradiation. [S0094-4289(00)00901-4]
An Experimental Investigation of the Effect of Freestream Turbulence on the Wake of a Separated Low-Pressure Turbine Blade at Low Reynolds Numbers
Authors: Murawski C. G. , Vafai K.
Published: July 2002

An experimental study was conducted in a two-dimensional linear cascade, focusing on the suction surface of a low pressure turbine blade. Flow Reynolds numbers, based on exit velocity and suction length, have been varied from 50,000 to 300,000. The freestream turbulence intensity was varied from 1.1 to 8.1 percent. Separation was observed at all test Reynolds numbers. Increasing the flow Reynolds number, without changing freestream turbulence, resulted in a rearward movement of the onset of separation and shrinkage of the separation zone. Increasing the freestream turbulence intensity, without changing Reynolds number, resulted in shrinkage of the separation region on the suction surface. The influences on the blade’s wake from altering freestream turbulence and Reynolds number are also documented. It is shown that width of the wake and velocity defect rise with a decrease in either turbulence level or chord Reynolds number. [S0098-2202(00)00202-9]
A Photothermal Technique for the Determination of the Thermal
Conductance of Interfaces and Cracks
Authors: McDonald K. R. , Dryden J. R. , Majumdar A. , Zok F. W.
Published: July 2002

The paper describes a phase-sensitive photothermal technique for the determination of the thermal conductance of an interface, a thin interlayer, or crack embedded within a plate. The technique involves sinusoidally modulated heating at one point on the surface using a focused laser beam and measurement of the phase shift of the thermal wave at some other point. The technique is demonstrated using a model system comprising two stainless steel disks, placed either in direct contact with each other or with thin polyethylene sheets between them. The use of the technique for determining the conductance of delamination cracks in fiber-reinforced ceramic matrix composite is also demonstrated. [S0022-1481(00)02801-2]
Vaporization Kinetics During Pulsed Laser Heating of Liquid Hg
Authors: Bennett T. D. , Farrelly M.
Published: July 2002

There is a growing body of experimental evidence showing that the kinetics of nascent vapor produced during pulsed laser heating of metals cannot always be ascribed to the surface thermal conditions. Some investigators have proposed that the discharge of energetic (nonthermal) atoms from metals can involve light coupling to surface plasmons. This requires surface roughness to facilitate wave vector matching of laser light with surface electromagnetic excitation modes. If true, superthermal vaporization kinetics should disappear from time-of-flight measurements when an optically smooth surface is used. Unfortunately, maintaining such an ideal surface is infeasible on a solid target because each laser pulse introduces nanometer sized roughness through the process of melting and resolidification. We have investigated the nature of vaporization from a liquid Hg surface using a nanosecond laser emitting 5 eV photons. Surface tension of the liquid provides an optically smooth surface for this experiment. Nevertheless, we observe superthermal vaporization kinetics from liquid Hg. Yet, the shape of the energy distribution is Boltzmann (the thermal expectation), and the energy distribution does not demonstrate any quanta characteristic of vaporization mediated by an electronic excitation. [S0022-1481(00)01602-9]
Mathematical Model of Universal Hypoid Generator With Supplemental Kinematic Flank Correction Motions
Authors: Fong Zhang-Hua
Published: July 2002

A mathematical model of universal hypoid generator is proposed to simulate virtually all primary spiral bevel and hypoid cutting methods. The proposed mathematical model simulates the face-milling, face-hobbing, plunge cutting, and bevel-worm-shaped hobbing processes with either generating or nongenerating cutting for the spiral bevel and hypoid gears. The supplemental kinematic flank correction motions, such as modified generating roll ratio, helical motion, and cutter tilt are included in the proposed mathematical model. The proposed mathematical model has more flexibility in writing computer program and appropriate for developing the object oriented computer programming. The developed computer object can be repeatedly used by various hypoid gear researchers to reduce the effort of computer coding. [S1050-0472(00)01201-0]
Poly(Amino Acids) by XPS: Analysis of Poly(L-Serine)
Authors: Bartiaux Stéphane , Lhoest Jean-Benoît , Genet Michel J. , Bertrand Patrick , Rouxhet Paul G.
Published: July 2002

Poly(L-serine) was analyzed as a model compound representative of poly(amino acids) with uncharged polar pendant groups. The sample powder was pressed on an indium foil to obtain a relatively smooth surface. The C 1s peak was recorded first, and recorded again at the end; no difference was found between the two records, indicating that poly(L-serine) did not suffer beam damage. The C 1s peak was split in four components. The [O=C_—N] component, characteristic of amide, was fixed at 288.0 eV; a component found at 286.2 eV was attributed to [C_—N] and [C_—OH]. The ratio ([C_—N]+[C_—OH])/[O=C_—N] was 1.85, while the stoichiometric value is 2.00. Two additional peaks were found: one set at 284.8 eV attributed to [C_—(C;H)] of contaminants and one at 289.1 eV attributed to [O=C_—OH] of chain ends and possible contaminants. The O 1s peak was split into two components at 531.4 and 532.6 eV attributed to [O_=C—N] and [C—O_H], respectively, which were not resolved. The ratio between the two peaks ([O_—C]/[C=O_—N=0.95) was close to the stoichiometric value of 1. The N 1s peak at 399.8 eV attributed to the amide nitrogen appeared with a small tail reflecting the presence of traces of protonated nitrogen. The overall N:O:C atomic ratios were 0.30:0.61:1.00 to be compared with the expected value of 0.33:0.66:1.00. These spectra could be used as references for the characterization of polypeptides and proteins.
The role of oxygen in the intrinsic tensile residual stress evolution in sputter-deposited thin metal films
Authors: Misra A. , Nastasi M.
Published: July 2002

The intrinsic tensile stress and oxygen content in thin Cr films sputter deposited at high argon pressure are investigated as a function of negative substrate bias. With increasing bias from 0 to −100 V, the tensile stress increases to a maximum while the oxygen content decreases. At bias higher than −100 V, the tensile stress decreases but no significant change is observed in the oxygen content. A similar trend in stress evolution with bias is also observed in Cr films capped with Al to protect from postdeposition oxidation. It is concluded that, for a given deposition condition, the incorporation of oxygen may lower the magnitude of tensile stress without affecting the trends in stress evolution with increasing substrate bias. These effects are discussed using a model that correlates the film microstructure with long range attractive forces predicted from interatomic potentials.
Strain-induced self-organized growth of nanostructures: From step bunching to ordering in quantum dot superlattices
Authors: Stangl J. , Roch T. , Holý V. , Pinczolits M. , Springholz G. , Bauer G. , Kegel I. , Metzger T. H. , Zhu J. , Brunner K. , Abstreiter G. , Smilgies D.
Published: July 2002

We have investigated the lateral ordering of dot positions in a SiGe/Si multilayer and, for comparison, in a PbSe/PbEuTe dot superlattice using grazing incidence small-angle scattering. The two samples represent two different approaches to achieve an enhanced ordering of dot positions in semiconductor heterostructures: in the SiGe/Si sample, step bunching in the multilayer grown on a vicinal Si substrate was exploited to reduce the fluctuations in lateral dot distances. In the PbSe/PbEuTe sample the strong elastic anisotropy leads to the formation of a three-dimensional dot “lattice,” exhibiting a very narrow distribution of dot distances.
Titanium oxide films on Si(100) deposited by e-beam evaporation
Authors: Jang H. K. , Whangbo S. W. , Choi Y. K. , Chung Y. D. , Jeong K. , Whang C. N. , Lee Y. S. , Lee H-S. , Choi J. Y. , Kim G. H. , Kim T. K.
Published: July 2002

Titanium oxide films with a thickness of a 400 nm were deposited on p-type Si(100) at room temperature by e-beam evaporation, and titanium dioxide was evaporated in oxygen environment at a pressure of 2×10−6–4×10−5 Torr. Effects of oxygen flow rate (FO2) on the properties of the films, such as surface roughness, composition, and chemical states, have been investigated. The root-mean-square surface roughness of the films increased with increasing FO2 up to 20 sccm, and then decreased over 20 sccm. X-ray diffraction patterns show that the titanium oxide films are amorphous. Oxygen resonance backscattering spectroscopy shows that all films are oxygen rich, i.e., relative atomic ratio (CO/CTi) of the films ranged from 2.05 to 2.25. But the x-ray photoelectron spectroscopy (XPS) analysis shows that the titanium oxide films were oxygen deficient. The ratio of oxygen to titanium (CO2/CTi) of the films calculated by XPS ranged from 1.82 to 1.93. XPS shows that there exist only Ti3+ and Ti4+ charge states in the film. Ti4+ states of the films are nearly constant at 0.47 up to O2 flow rate of 20 sccm, and then slightly increase with increasing O2 flow rate. Although rutile TiO2 is used as a starting material, titanium K-edge x-ray absorption near-edge spectroscopy (XANES) spectra show that the structure of the TiO2−x films grown in oxygen environment are amorphous. The Ti K-edge XANES spectra from the films is the same regardless of FO2.
A Simple, Continuously Pumped Field-Ion Microscope
Authors: Murr L. E. , Inal O. T.
Published: July 2002

A simple, demountable glass field-ion microscope design is described which utilizes a series arrangement of liquid nitrogen cooled zeolite pellet sorption traps that actively pump during operation. This scheme allows atomic surface features of etched wire tips to be continuously observed in a clean He image gas environment with good resolution at liquid nitrogen temperature. The complete design details and operational procedures are outlined to allow the results presented to be duplicated with a minimum effort, and for an investment below $3500. Typical results are illustrated with images of W and W-3% Re.
Right Angle Mounted Cold Trap
Authors: Ugiansky Richard J.
Published: July 2002

This paper describes the design of a highly efficient pipe-array right angle mounted cold trap. Space that is normally lost by the use of an empty elbow in it side-pumping vacuum system is utilized in this configuration.
Starting Mode Differences in Triode and Diode Sputter-Ion Pumps
Authors: Snouse Thomas
Published: July 2002

Recent tests are reported comparing the performance of diode vs triode sputter-ion pumps in the starting mode. These measurements indicate that the triode tested has significantly higher relative speed than the diode at pressures in the 10−3−10−2 Torr region. The power demanded by the triode is found to be almost constant in the pressure range of 2×10−4 to 2×10−3 Torr, unlike the diode in which power reaches a maximum at ∼10−4 Torr. In the millitorr pressure range triode powers are thus found to be as much as a factor of three larger than for an equivalent diode. Reasons for the observed differences are discussed, and the practical effects of these characteristics on starting and pumpdown are described.
Diffusion of Metals in Thin Metal Films
Authors: Hörl E. M. , Rieder K. H.
Published: July 2002

Diffusion of a metal A in thin films consisting of a metal B was observed using the following two electron microscopy techniques: (1) observation of the growth of intermetallic phases with increasing concentration of A by the diffraction contrast of transmission micrographs and (2) recording of the distribution of A over the surface of the film by means of electron microprobe analysis. All experiments were carried out using a time dependency of the temperature of the form T(t)=T0(1+bt). The experimental results are interpreted by a simple theoretical diffusion model for the case of copper diffusion into palladium.
Synthesis and Fabrication of High Purity Hafnium Nitride and Hafnium Carbide
Authors: Heestand R. L.
Published: July 2002

The procedures used to prepare kilogram quanties of hafnium nitride and hafnium carbide powders and hot-pressed billets are described. In order to maintain high purity, all steps of the process were conducted in either a vacuum or a high purity atmosphere. Analyses conducted on the starting materials and at various stages of processing indicated that target impurity levels, i.e., less than 100 ppm oxygen, could not be attained but that high levels of contamination could be avoided.
Distribution and Apparent Source Geometry of Electron-Beam-Heated Evaporation Sources
Authors: Graper Edward B.
Published: July 2002

The distribution and apparent source geometry were determined for aluminum evaporation from a 12-kW 270° electron beam gun. The distribution was measured as a function of deposition rate for rates from 1000 to 50 000 Å/min, 20 cm from the hearth. These measured distributions and those from other workers can be described not by a simple cosine relation, as has been assumed, but by a relation of the form (1-A) cosn θ+A, where θ is the angle from the vertical. The coefficient A is the normalized magnitude of an isotropic component, and n is a rate-dependent beaming exponent. The apparent source geometry was measured using a pinhole camera technique. These measurements show the evaporant to originate from the area defined by the visual beam impact point at low-to-moderate rates, and additionally from a larger virtual source at high rates or when a hearth linear is used. The run-to-run stability of the evaporant distribution was also determined.
Normal State Nucleation Times in Superconductors
Authors: Peters Robert , Meissner Hans
Published: July 2002

Both dc and rf currents are passed through a thin narrow film of tin such that the total current exceeds the critical current ic. Lowering the rf frequency from 1 GHz causes, at a reproducible frequency ωc, a step in the rf voltage away from the superconducting state toward the normal state. Increasing the dc increases ωc in accord with the empirical relation: idc+irf exp(−ωcτ)=ic. The time constant τ, which is a measure of the normal state nucleation time, is about 10−9 sec and is a function of temperature and of irf. Second harmonics and phase shifts were observed.
The Study of Periodic Magnetic Structures by Diffraction Analysis
Authors: Ferrier R. P. , Chapman J. N. , Toms N.
Published: July 2002

In trying to determine the nature of the magnetization distribution in thin films having a periodic magnetic structure it is more convenient to work with the “magnetic” small angle diffraction pattern obtained in the electron microscope rather than the Lorentz image. The reasons for this will be discussed and two approaches to the analysis of the diffraction patterns will be described. The first method makes use of models of the magnetization distribution from which theoretical diffraction patterns may be computed for comparison with the observed data. The second method makes use of the Gerchberg-Saxton algorithm which may be applied directly to the intensity distribution in the diffraction pattern. The results of some preliminary studies using this algorithm will be discussed.
Fabrication of 104 Bit Permalloy-First Magnetic Bubble Circuits on Epitaxial Garnet Chips
Authors: Reekstin J. P. , Lehner A. G. , Vratny F. , Kammlott G. W.
Published: July 2002

A major advantage of magnetic bubble devices currently under development is the relatively small number of processing steps involved in device fabrication. With the advent of low defect epitaxial garnet films capable of supporting magnetic bubbles with diameters of 6 μ and less it is now possible to fabricate circuits with a minimum feature size of 3.5 μ and a capacity of 104 bits directly on the epitaxial film with a likelihood of reasonable yields. The major processing problems related to the dielectric layer, permalloy film, and current-carrying conductors are discussed. Processed circuits have been studied with the aid of scanning electron micrographs which reveal etch pattern profiles and composite structural features arising from multiple depositions.
A Thermally Shielded Atmospheric Pressure Standard Leak Calibrator
Authors: Miller J. R.
Published: July 2002

A method is described for the calibration of capillary and permeation standard leaks. The technique utilizes a capacitance manometer to detect the small pressure change in a defined volume caused by the influx of gas from a standard leak. Corrections are derived for the small volume changes which occur during manometer operation. All measurements are made at atmospheric pressure. A double-walled aluminum and copper cylinder design is utilized to decrease temperature related pressure changes. A limiting drift rate of approximately 4×10−8 Torr/sec (Q=3×10−9 std cm3/sec) in the manometer indication was traced to manometer diaphragm “microcreep.” A method to reduce this background to ≃6×10−10 std cm3/sec is described. The unique aspect of the calibrator is its ability to calibrate Freon standard leaks under usage conditions, i.e., using Freon gas with atmospheric pressure on the down-stream side of the leak, down to 10−9 std cm3/sec. Error of measurement ranges from +10% to 15%. Calibration results for several leaks are presented.
Kinetics of solute removal during electron-beam and vacuum-arc melting
Authors: Andreini R. J. , Foster J. S.
Published: July 2002

A steady-state, nondiffusional control model has been derived which describes the kinetics of dilute metallic-solute removal from molten alloys using electron-beam or consumable vacuum-arc-refining techniques. Although the model is developed in terms of a binary alloy, good agreement between theory and experiment was found for the removal of minor components from a complex automotive steel scrap. The model can also be used to predict the melt-stock solute concentration required to attain a desired solute concentration in the final ingot for a given melt rate. Conditions under which calculated results from the model are valid are also discussed.
Electron-probe microanalysis—a capsule survey
Authors: Yakowitz Harvey
Published: July 2002

A brief overview of the way in which electron-probe microanalysis can be used to obtain information from microvolumes comprising 10−12 g or less of specimen material is presented. Elemental identification, distribution, and quantitative analytical procedures are outlined. Energy-resolving detectors and wavelength-dispersive spectrometers are compared; analysis of elements with atomic number < 11 is also briefly considered in this context. An example of the solution of a service failure by means of elemental-distribution mapping is offered. Finally, an indication is given of the accuracy which can be expected from quantitative electron-probe microanalysis.
A technique for the vacuum deposition of alkali metals
Authors: Shiu W. Y. , Ezer S. L. , Young D. J. , Rao B. , Dignam M. J.
Published: July 2002

An ultrahigh vacuum technique for the evaporation of sodium and potassium is described. Metal ions are generated within a gaseous plasma. These migrate through the glass envelope containing the plasma, are then discharged at a gold or platinum film cathode deposited on the far side of the envelope, and enter the vacuum space as a gas. Design and operating characteristics of several units are presented.
Some recent studies of very thin SiO2 films
Authors: van der Meulen Y. J.
Published: July 2002

An overview is given of some recent studies involving characterization of thin SiO2 films. Topics discussed include the stoichiometry of not intentionally contaminated films, the impurity distribution of phosphorus at the Si-SiO2 interface, and some methods of studying these films in a dynamic mode, i.e., while changes occur in their structure or thickness.
Progress on nanostructuring with Nanojet
Authors: Voigt J. , Shi F. , Hudek P. , Rangelow I. W. , Edinger K.
Published: July 2002

Micro- and nanostructuring of a substrate by direct writing of the structures with a localized radical jet using the scanning probe principle is demonstrated. Electrically neutral radicals created in a downstream plasma discharge are pumped through a small nozzle and directed on to the substrate. Due to the small distance between the nozzle and surface of the workpiece, localized interaction is induced. Etched structures with 270 nm resolution produced by a nozzle with a diameter of 250 nm are presented. The etching rates achieved for micro- and nanostructuring are 200 nm/min in photoresist and 400 nm/min in silicon, respectively. It is shown experimentally that the resolution of the process is determined by the diameter of the nozzle, provided that the working distance is small, i.e., less than the diameter of the nozzle. Fundamentals for the development of a tool for direct structuring in the sub-100 nm range, including nanofabrication of a sub-100 nm nozzle, are presented in this work.
Comparative study of self-aligned and nonself-aligned SiGe p-metal–oxide–semiconductor modulation-doped field effect transistors with nanometer gate lengths
Authors: Lu Wu , Koester Steven J. , Wang Xie-Wen , Chu Jack O. , Ma Tso-Ping , Adesida Ilesanmi
Published: July 2002

A self-aligned process used to fabricate p-type SiGe metal–oxide–semiconductor modulation-doped field effect transistors (MOS-MODFET) is described. Self- and nonself-aligned p-type Si0.2Ge0.8/Si0.7Ge0.3 MOS-MODFETs with gate-lengths from 1 μm down to 100 nm were fabricated. The dc and microwave characteristics of these devices are presented. In comparison with nonself-aligned devices, self-aligned devices exhibited higher extrinsic transconductances, lower threshold voltages, higher unity current gain cutoff frequencies fT, and maximum oscillation frequencies fMAX. Self-aligned MOS-MODFETs with a gate length of 100 nm exhibited an extrinsic transconductance of 320 mS/mm, an fT of 64 GHz, and an fMAX of 77 GHz. To our knowledge, these are the highest data ever reported for any MOS-type p-FETs with a SiGe channel. All these excellent performances were measured at very low drain and gate biases.
Model of crystal lattice strained along the preferential direction by anisotropic stress for GaAs heteroepitaxial films grown on vicinal Si(001) and Si(110) substrates by molecular-beam epitaxy
Authors: Yodo T.
Published: July 2002

I estimated anisotropy of stress and strain for GaAs heteroepitaxial films grown on vicinal Si(001) and Si(110) substrates by molecular-beam epitaxy from measurements of in-plane substrate curvatures and components of lattice parameters by a Bond method using x-ray diffraction. It is shown that the GaAs heteroepitaxial film is anisotropically strained through different relaxation processes of stress due to anisotropic dislocations along the [110] and [11̄0] directions. The crystal lattice of the GaAs heteroepitaxial film on Si substrate is qualitatively represented considering the crystal structure elastically strained with the [110]-, [11̄0]-, and [001]-primitive axes as a primitive basis in the orthogonal rhombic system.
Effects of electron-beam irradiation on the properties of CN thin films deposited by direct dual ion beams
Authors: Kim Yong Hwan , Lee Deuk Yeon , Kim In Kyo , Baik Hong Koo
Published: July 2002

We have investigated the effects of electron-beam irradiation on the formation of CN thin films and on the process of direct ion-beam deposition. The properties of CN thin films deposited with and without electron-beam irradiation are compared to verify the charge-enhanced bonding process. The total negative beam of negative-carbon ions and electrons can be induced from the Cs+ ion bombardment on a graphite target. Filtering of the electron beam from the total negative beam was obtained by the transverse magnetic field. The pure negative-carbon-ion beam or the total negative beam was deposited simultaneously with a positive-nitrogen-ion beam. The role of negative charge on the properties of CN thin films and the effects of charged state on the final bonding path of kinetic ion-beam deposition are discussed by comparing the films deposited with and without electron-beam irradiation. The properties of the films were evaluated from the nitrogen content, deconvolution results of N 1s spectra, and plasmon loss energy, which were characterized by x-ray photoelectron spectroscopy and electron energy-loss spectrometry.
Effects of ozone assisted deposition on the dielectric properties of 90° off-axis radio frequency magnetron sputtered SrTiO3
Authors: Gibbons B. J. , Fan Y. , Findikoglu A. T. , Jia Q. X. , Reagor D. W.
Published: July 2002

The low and high frequency dielectric properties of epitaxial SrTiO3 (STO) thin films deposited on LaAlO3 are presented. The effects of in situ ozone annealing during the early stages of deposition were explored. X-ray diffraction results indicated that the ozone treatment resulted in more symmetric and sharper diffraction peaks. In addition, the peaks for the ozone treated samples were shifted in 2θ towards values approaching the bulk. The dielectric constant of the ozone treated samples increased from 275 at room temperature to 1175 at 22 K (measured at 100 kHz). The effective loss tangent of the device remained between 1×10−4 and 1×10−3 down to 100 K, where it began to increase. These properties were far superior to those films deposited without ozone. For high frequency measurements, coplanar waveguide structures with a centerline width of 20 and 40 μm wide gaps were patterned into YBa2Cu3O7 films deposited on top of the 0.5 μm thick STO. For the ozone treated films, Q values of up to 70% greater were achieved at 4 GHz and 75 K with little effect on the frequency modulation (compared to films deposited without ozone).
Enhancement of tribological properties of 9Cr18 stainless steel by dual Mo and S Co implantation
Authors: Zhang Tao , Song Jiaohua , Li Guoqing , Chu Paul K. , Brown Ian G.
Published: July 2002

Mo and S ions were simultaneously implanted into 9Cr18 stainless steel samples. The frictional properties of the implanted samples were assessed using a pin-on-disk tester and the elemental depth profiles were measured by Auger electron spectroscopy. The hardness of the samples was also measured. We find that this dual-element implantation process reduces the coefficient of friction by a factor of 2 and increases the low-friction lifetime by a factor of 4 compared to the 9Cr18 surface with Mo or S implantation alone. This enhancement is related to the synergistic coexistence of the implanted elements at the same place. We have also investigated the process using computer simulation. The simulation results help disclose the characteristics of the modified layer and explain the effects of dual-element ion implantation.
Oxidation of H-covered flat and vicinal Si(111)-1×1 surfaces
Authors: Zhang X. , Chabal Y. J. , Christman S. B. , Chaban E. E. , Garfunkel E.
Published: July 2002

The initial stages of O2 oxidation of H-passivated flat and vicinal Si(111) surfaces are investigated by monitoring the Si–H stretch vibrations with infrared absorption spectroscopy. We find that the incorporation of oxygen into silicon is activated (1.66±0.10 eV on flat surfaces), involving a multistep process. Oxygen molecules are incorporated into Si–Si bonds without removing surface hydrogen and this process is facilitated at steps.
Self-diffusion in ceria
Authors: Perkins Craig L. , Henderson Michael A. , Peden Charles H. F. , Herman Gregory S.
Published: July 2002

Ceria (CeO2) is an oxygen storage material vital to the proper functioning of automobile three-way catalysts and is typically viewed as an anion conductor. Prior experimental work using temperature programmed static secondary ion mass spectrometry (TPSSIMS) has indicated that for rutile TiO2, a prototypical oxide, the mobile species are Ti cations rather than O anions. To further expand on the mobile species in CeO2 we have investigated the diffusion of both cerium and oxygen ions by TPSSIMS. The CeO2(111) film was heteroepitaxially grown by molecular beam epitaxy on a yttria stabilized zirconia substrate. Although high quality low-energy electron diffraction patterns and Auger electron spectroscopy spectra free of impurity signals were obtained after just a few sputtering and annealing cycles, further cleaning was necessary to remove intense alkali and alkaline earth signals observed in SSIMS. The CeO2(111) surface was slightly enriched in O18 by first annealing the film in UHV at 830 K and then exposing the 130 K crystal to O218. TPSSIMS data in conjunction with temperature programmed desorption data demonstrate that surface oxygen atoms begin to exchange with the bulk around 550 K. Physical deposition of submonolayer amounts of isotopically enriched cerium (136Ce) in an O218 background allowed the simultaneous study of the diffusion of both cerium and oxygen ions. Surface cerium cations were found to be immobile with no diffusion into the bulk for temperatures up to 900 K, the highest temperature studied.
Amorphous GexSi1−xOy sputtered thin films for integrated sensor applications
Authors: Clement M. , Iborra E. , Sangrador J. , Barberán I.
Published: July 2002

In this work, we analyze the electrical behavior of amorphous GexSi1−xOy thin films to be used as sensitive layers in integrated bolometers. The GexSi1−xOy films were grown by reactive sputtering of a Ge0.85Si0.15 target using a mixture of argon and oxygen. The films were characterized by measuring the composition, the optical gap, the resistivity, and the activation energy of the electrical conductivity. We analyzed the effects of the sputter gas composition, the rf power applied to the target, and the bias voltage applied to the substrate on the properties of the films. A homogeneous amorphous semiconductor was obtained, in which oxygen is bonded to both silicon and germanium atoms. The optical gap, the resistivity, and the activation energy of the resistivity increase monotonically with the total oxygen content of the films. The application of a bias voltage to the substrate causes slight compositional changes in the films and modifies the band structure of the amorphous semiconductor. As a consequence, the electrical resistivity and the activation energy are reduced with increasing bias. Under optimum experimental conditions, GexSi1−xOy layers with moderate electrical resistivities around 104 Ω cm and thermal coefficients as high as 5% K−1 have been obtained.
Growth and magnetic properties of ultrathin Fe on Pd(110)
Authors: Cuenya Beatriz Roldan , Pearson J. , Yu Chengtao , Li Dongqi , Bader S. D.
Published: July 2002

We have investigated the growth and magnetic properties of 0–3 ML (monolayers) Fe on stepped Pd(110) with reflection high-energy electron diffraction (RHEED), low-energy electron diffraction, and the surface magneto-optic Kerr effect in order to relate the morphology, structure, and magnetic properties in a low-dimensional system. The Fe films grown at 340 K are smooth and pseudomorphic up to 1.5 ML, where three-dimensional growth and lateral lattice relaxation ensues. The in-plane row spacing along the [110] direction decreases by ∼5%–6% at 3 ML. RHEED oscillations with 1 ML period are observed in the (1,0), (2,0), and the center of the (0,0) streak intensity. The tail of the (0,0) streak at low exit angle, however, has a 0.5 ML period oscillation, which suggests step decoration growth. Submonolayer Fe films remain ferromagnetic above ∼0.3 ML. The magnetic easy axis is initially perpendicular to the surface and is in-plane for Fe thickness >1.5 ML. Between 0.9 and 1.2 ML, there appear to be mixed magnetic phases as indicated by an increase in coercivity.
Molecular dynamics study of the interactions of small thermal and energetic silicon clusters with crystalline and amorphous silicon surfaces
Authors: Ramalingam Shyam , Aydil Eray S. , Maroudas Dimitrios
Published: July 2002

An atomic-scale analysis based on molecular dynamics simulations of the interactions of small thermal and energetic SinHm, n>1, clusters observed in various plasmas with crystalline and amorphous Si surfaces is presented. The experimental literature has assumed and employed a unit reaction probability for clusters of various sizes on all Si surfaces in phenomenological models for obtaining hydrogenated amorphous Si film growth rates, while the reaction mechanisms of clusters with the deposition surfaces have remained unexplored. In addition, it is widely speculated that clusters have a detrimental effect on the film quality. Our study shows that the clusters react with high (>85%) probability with crystalline surfaces and with surfaces of amorphous Si films. The structure and energetics of the corresponding adsorbed cluster configurations on these surfaces are analyzed and discussed. Furthermore, the simulations provide insight into possible mechanisms for the formation of defects, such as voids and dangling bonds, in plasma-deposited amorphous Si films through reactions of the clusters with the deposition surfaces.
Metastability of InGaAs/GaAs probed by in situ optical stress sensor
Authors: Beresford R. , Tetz K. , Yin J. , Chason E. , González M. U.
Published: July 2002

Real-time observations of film stress are presented from three growths of strained InGaAs/GaAs layers. The initial metastable growth regime is analyzed to extract the alloy compositions of x=0.136, 0.155, and 0.180. The strain values at the end of the growths (thicknesses 0.791, 1.08, and 0.115 μm, respectively) are then used to deduce the amounts of relaxation γ=0.808, 0.857, and 0.261, respectively. These data obtained from the in situ optical stress sensor are compared with conventional measurements using asymmetric x-ray diffraction. The agreement is good, within 4%–6% for composition, indicating that the in situ sensor is suitable for quantitative study of strain relaxation during film growth.