bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling the Air-Cooled Gas Turbine: Part 1—General Thermodynamics
Authors: Young J. B. , Wilcock R. C.
Published: July 2002

This paper is Part I of a study concerned with developing a formal framework for modeling air-cooled gas turbine cycles and deals with basic thermodynamic issues. Such cycles involve gas mixtures with varying composition which must be modeled realistically. A possible approach is to define just two components, air and gas, the latter being the products of stoichiometric combustion of the fuel with air. If these components can be represented as ideal gases, the entropy increase due to compositional mixing, although a true exergy loss, can be ignored for the purpose of performance prediction. This provides considerable simplification. Consideration of three idealized simple cycles shows that the introduction of cooling with an associated thermal mixing loss does not necessarily result in a loss of cycle efficiency. This is no longer true when real gas properties and turbomachinery losses are included. The analysis clarifies the role of the cooling losses and shows the importance of assessing performance in the context of the complete cycle. There is a strong case for representing the cooling losses in terms of irreversible entropy production as this provides a formalized framework, clarifies the modeling difficulties, and aids physical interpretation. Results are presented that show the effects on performance of varying cooling flowrates and cooling losses. A comparison between simple and reheat cycles highlights the ro^le of the thermal mixing loss. Detailed modeling of the heat transfer and cooling losses is discussed in Part II of this paper.
Floquet Theory Based Approach for Stability Analysis of the Variable Speed Face-Milling Process
Authors: Sastry Sridhar , Kapoor Shiv G. , DeVor Richard E.
Published: July 2002

This paper presents a new method for stability analysis of the variable spindle speed face milling process whose dynamics are described by a set of differential-difference equations with periodic coefficients and time varying time delay. Fourier analysis and Floquet theory applied to the system equations result in a characteristic equation of infinite order with constant coefficients. Its truncated version is used to determine the limit of stability by employing standard techniques of control theory. Analytically predicted stability boundaries are compared with lobes generated by time domain simulations. Experimental results are also presented that validate the proposed analytical method for chatter stability analysis. Finally, an example is presented that demonstrates the advantage of using spindle speed variation when machining a workpiece having multiple modes of vibration.
Dynamics of a Large Scale Hydraulic Capsule Pipeline System
Authors: Du Hongliu , Nair Satish S.
Published: July 2002

The dynamics of a booster station, which is critical for the control of a novel, long distance, hydraulic capsule pipeline, is simulated mathematically for design studies and control of the hydraulic transients caused by the valve actuators in the system. Several modifications to the pump bypass station configuration of the booster station have been studied. With the objective of eliminating column separation and reducing flow reversals, a configuration with several centrifugal pumps connected in series, and a carefully sized air chamber is found to be a viable design. A valve control method is designed to eliminate column separation and the design results in acceptable flow reversal levels in the main pipe. The simulation results match with trends in limited experimental studies performed on a small scale experimental capsule pipeline system.
A Virtual Sensing Method for Tonal ANVC Systems
Authors: Tran Chau M. , Southward Steve C.
Published: July 2002

Virtual Sensing (VS) is considered to be an extension for feedforward Active Noise and Vibration Control (ANVC) systems when, for example, it is desired to minimize the response at one or more spatial locations where it is either physically impossible or undesirable to place an actual error sensor. In this context, VS is an estimation technique for predicting the appropriate system response using available measurements and a dynamic system model. A hybrid adaptive feedforward observer is proposed which has the ability to overcome the limitations of conventional dynamic observer designs. The hybrid observer utilizes a conventional dynamic observer augmented with an adaptive feedforward element for estimating the effect of the persistent disturbance. For simplicity, we restrict this development to a single tonal disturbance for which a coherent reference is assumed available. It will be appreciated that this technique may be extended to handle disturbances that contain multiple tones as well as broadband noise, as long as suitable reference signals are available. Numerical simulations and real-time experiments were performed on a one-dimensional acoustic duct. The results demonstrate that the hybrid adaptive feedforward observer is an effective method for predicting the virtual sensor response in an ANVC system.
Surface Roughness Effects on Turbulent Boundary Layer Structures
Authors: Keirsbulck L. , Labraga L. , Mazouz A. , Tournier C.
Published: July 2002

A turbulent boundary layer structure which develop over a k-type rough wall displays several differences with those found on a smooth surface. The magnitude of the wake strength depends on the wall roughness. In the near-wall region, the contribution to the Reynolds shear stress fraction, corresponding to each event, strongly depends on the wall roughness. In the wall region, the diffusion factors are influenced by the wall roughness where the sweep events largely dominate the ejection events. This trend is reversed for the smooth-wall. Particle Image Velocimetry technique (PIV) is used to obtain the fluctuating flow field in the turbulent boundary layer in order to confirm this behavior. The energy budget analysis shows that the main difference between rough- and smooth-walls appears near the wall where the transport terms are larger for smooth-wall. Vertical and longitudinal turbulent flux of the shear stress on both smooth and rough surfaces is compared to those predicted by a turbulence model. The present results confirm that any turbulence model must take into account the effects of the surface roughness.
The Impact of Data Accuracy on the POT Estimates of Long Return Period Design Values
Authors: Naess A. , Clausen P. H.
Published: July 2002

The main focus of this paper is an investigation of the effect which the accuracy of data representation may have on the results obtained by using standard peaks-over-threshold (POT) methods. It is shown that this effect may lead to a substantial shift in the resulting predictions of long return period extreme values for specific types of estimators combined with the POT method. A brief discussion of the implication for the estimation of confidence intervals on the various estimates will also be given.
Concentration Measurements in a Pressurized and Heated Gas Mixture Flow Using Laser Induced Fluorescence
Authors: Guibert Philippe , Perrard William , Morin Ce´line
Published: July 2002

The fuel concentration in a pressurized and heated gas mixture flow was measured by LIF (laser induced fluorescence) technique. Diacetyl was used as the fluorescence tracer of fuel and was excited at a wavelength of 355 nm. Influent parameters on the LIF intensity among the equivalence ratio, the environment temperature and pressure, the flow velocity were determined from a parametric study. The technique of plans of experiments with statistical tests and analysis was investigated to determine exactly the preponderant parameters and their influence on the LIF intensity. For the experimental conditions explored in this work, the value of the LIF intensity was calculated by developing a quadratic model. By inversion of the transfer function, the equivalence ratio was deduced with a low mean relative error.
Stress Intensity Factors for Finite Interface Cracks Between a Special Pair of Transversely Isotropic Materials
Authors: Boniface V. , Banks-Sills L.
Published: July 2002

An infinite bimaterial system made of two dissimilar, transversely isotropic materials bonded together (with the lower material being mathematically degenerate) and subject to remote loads is considered. An analytical expression for the complex stress intensity factor of a finite crack along the interface between these two materials is obtained. This result is extended to the case of an infinite array of collinear cracks along a similar interface. Next, the finite element method is employed to analyze these geometries for specific material properties. An area M-integral is used to extract stress intensity factors from the finite element results, which compare well with those obtained from the analytic expressions. Different types of loads are considered.
Synthesis of Universal Motion Curves in Generalized Model
Authors: Cheng Wen-Teng
Published: July 2002

The universal motion curve is synthesized in a generalized model. The acceleration curve is divided into seven intervals of which the curve shapes on varying-acceleration intervals can be prescribed by arbitrary functions. The characteristics of the motion curve are controlled completely by four shape functions of acceleration and seven time increments. To simplify the synthesis derivation, normalized function and symmetric function are defined to represent these shape functions. The displacement, velocity, acceleration, and jerk curves are derived in piecewise function forms and the peak values of velocity and acceleration are also expressed in explicit parametric forms. The designers can quickly construct the motion curves according to the synthesis formulas and the step-by-step procedures. The helpfulness and convenience of these formulas are demonstrated by three examples in symbolic or numerical solution.
Detached-Eddy Simulations Over a Simplified Landing Gear
Authors: Hedges L. S. , Travin A. K. , Spalart P. R.
Published: July 2002

The flow around a generic airliner landing-gear truck is calculated using the methods of Detached-Eddy Simulation, and of Unsteady Reynolds-Averaged Navier-Stokes Equations, with the Spalart-Allmaras one-equation model. The two simulations have identical numerics, using a multi-block structured grid with about 2.5 million points. The Reynolds number is 6×105. Comparison to the experiment of Lazos shows that the simulations predict the pressure on the wheels accurately for such a massively separated flow with strong interference. DES performs somewhat better than URANS. Drag and lift are not predicted as well. The time-averaged and instantaneous flow fields are studied, particularly to determine their suitability for the physics-based prediction of noise. The two time-averaged flow fields are similar, though the DES shows more turbulence intensity overall. The instantaneous flow fields are very dissimilar. DES develops a much wider range of unsteady scales of motion and appears promising for noise prediction, up to some frequency limit.
Ill-Posedness in a Thermomechanically Consistent Constrained Theory for Materials With Prescribed Temperature-Dependent Density
Authors: Wang Q.
Published: July 2002

We examine the local dynamics of nonisothermal viscous flows in the neighborhood of the constant equilibria using the thermomechanically consistent constrained theory for materials with prescribed temperature-dependent density developed by Cao et al.. We discover that the linearized growth rate of small length scale, infinitesimal disturbances near the equilibria is proportional to the reciprocal of their wave length, a classical phenomenon known as the Hadamard instability, indicating the local ill-posedness of the constrained theory. Therefore, the use of the theory to model transient flow phenomenon is not advised. [S0021-8936(00)01901-2]
Effects of Heat-Induced Damage on the Radial Component of Thermal Diffusivity of Bovine Aorta
Authors: Davis, Sean E. , Doss, David J. , Humphrey, Jay D. , Wright Neil T.
Published: July 2002

The extent of the change in thermal diffusivity of soft tissues due to heat-induced damage is not well known. Reported here are the results of using the flash method to measure the through-the-wall component of thermal diffusivity of bovine aorta before and after the tissue has undergone two hours of heating at 75°C. The measurements indicate a 10.1 percent increase in the thermal diffusivity of the tissue post-heating. While this change may not result in a significant change in the tissue temperature profile, further study is needed to quantify the thermal diffusivity in other coordinate directions, as well as the mechanisms by which this change in properties occurs. [S0148-0731(00)01103-1]
Measurement of the Axial Residual Stresses Using the Initial Strain Approach
Authors: Cheng Weili
Published: July 2002

Traditionally, the unknown variables to be estimated in residual stress measurement are based on the approximation of the stresses. In this paper an alternative approach is presented, in which the initial strain is used as the unknown variable to be estimated in the measurement. A useful feature of the approach is that it does not require the measurement to be made on the original part if the stress is uniform in the axial direction. Instead, the original residual stress can be computed once the initial strains are obtained from a specimen removed from the original part. This approach is incorporated into two recently developed methods: the crack compliance method and the single-slice method for measurement of the axial stress in plane strain. Experimental validation shows that the approach based on initial strains leads to a result that agrees very well with the analytical prediction. [S0094-4289(00)02101-0]
Pressure Loss/Gain Boundary of Gas-Liquid Downward Flow in Inclined and Vertical Pipes
Authors: Chen X. Tom , Zhang Hong-Quan , Redus Clifford L. , Brill James P.
Published: July 2002

Gas-liquid downward flow is frequently encountered in hilly-terrain pipelines, downcomer pipes extending from offshore production platforms to sea floors, and steam injection wells in thermal enhanced recovery operations. Since the gravitational and frictional terms in the total pressure gradient equation for downward flow have opposite signs, gas-liquid downward flow in inclined and vertical pipes may experience either pressure loss or pressure gain, depending on flow rates, pipe geometry, and fluid properties. A mechanistic model for the pressure loss/gain boundary of gas-liquid downward flow in inclined and vertical pipes is developed in this work and is verified with available experimental results. The effects of pipe inclination angle, inside diameter, wall roughness, and fluid physical properties on the pressure loss/gain boundary are presented. [S0195-0738(00)00302-2]
Electrohydrodynamically Enhanced Convective Boiling: Relationship Between Electrohydrodynamic Pressure and Momentum Flux Rate
Authors: Bryan J. E. , Seyed-Yagoobi J.
Published: July 2002

The relationship between the mean radial electrohydrodynamic (EHD) pressure and the rate of the axial momentum flux and its influence on heat transfer enhancement and pressure drop in EHD-enhanced convective boiling of R-134a in a horizontal smooth tube was investigated in detail. A simple theory, which included the characteristics of two-phase flow, was developed to determine the mean radial EHD pressure. It was shown that the amount of heat transfer enhancement and the pressure drop penalty were dependent upon the size of the mean radial EHD pressure relative to the rate of the axial momentum flux. The influence of the mass flux, change in quality, and saturation temperature on the mean radial EHD pressure relative to the rate of the axial momentum flux was also studied. This study has provided a greater understanding of EHD enhancement of the convective boiling heat transfer. [S0022-1481(00)01802-8]
Machining-Induced Residual Stress: Experimentation and Modeling
Authors: Jacobus Kurt , DeVor R. E. , Kapoor S. G.
Published: July 2002

Controlled orthogonal and controlled oblique machining of annealed AISI 4340 have been undertaken in a design of experiments framework to investigate the machining-induced residual stresses resulting from these processes. The experimentation demonstrates significant simplifications in the machining-induced residual stress problem when the stresses are expressed in a coordinate system fixed in the tool and also indicates that the directions along the cutting edge and normal to the cutting edge of the tool are principal directions of the machining-induced residual stresses. Based on the experimental results, a plane strain thermoelastoplastic model of metal flow under the flank of a cutting tool is developed to predict the full in-plane biaxial residual stress profiles existing at and beneath the newly created surface. Calibrated results show favorable agreement with the experimental machining-induced residual stresses in annealed AISI 4340. [S1087-1357(00)00201-X]
High Speed Grinding of Silicon Nitride With Electroplated Diamond Wheels, Part 1: Wear and Wheel Life
Authors: Hwang T. W. , Evans C. J. , Whitenton E. P. , Malkin S.
Published: July 2002

An investigation is reported on high speed grinding of silicon nitride using electroplated single-layer diamond wheels. This article is concerned with wheel wear and wheel life, and a second paper (ASME J. Manuf. Sci. Eng., 122, pp. 42–50) deals with wheel topography and grinding mechanisms. It has been suggested that grinding performance may be enhanced at higher wheel speeds due to a reduction in the undeformed chip thickness. Grinding experiments were conducted at wheel speeds of 85 and 149 m/s with the same removal rate. Contrary to expectations, the faster wheel speed gave no improvements in surface finish, grinding ratio, or wheel life. Microscopic observations of the wheel surface revealed dulling of the abrasive grains by attritious wear, thereby causing a progressive increase in the forces and energy until the end of the useful life of the wheel. For all grinding conditions, a single-valued relationship was found between the wheel wear and the accumulated sliding length between the abrasive grains and the workpiece. A longer wheel life and improved grinding performance can be obtained when the operating parameters are selected so as to reduce the abrasive sliding length per unit volume of material removal. [S1087-1357(00)00301-4]
An FFT-Based Transient Flash Temperature Model for General Three-Dimensional Rough Surface Contacts
Authors: Gao Jianqun , Lee Si C. , Ai Xiaolan , Nixon Harvey
Published: July 2002

A transient flash temperature model was developed based on a Fast Fourier Transform method. An analytical expression for the heat partition function was obtained. Together, these substantially increase the speed of flash temperature calculations. The effect of surface topography on the flash temperature was examined. According to the simulation results, the surface with a longitudinal roughness produced a noticeably higher flash temperature than the surface with a transverse roughness. The simulation results also indicate that there is a significant cross-heating activity between the asperities; the temperature profiles appeared surprisingly gradual although their contact pressures had extremely sharp peaks. [S0742-4787(00)04002-9]
Simulations of the Unsteady Flow Through the Fastrac Supersonic Turbine
Authors: Griffin Lisa W. , Dorney Daniel J.
Published: July 2002

Analysis of the unsteady aerodynamic environment in the Fastrac supersonic turbine is presented. Modal analysis of the turbine blades indicated possible resonance in crucial operating ranges of the turbopump. Unsteady computational fluid dynamics (CFD) analysis was conducted to support the aerodynamic and structural dynamic assessments of the turbine. Before beginning the analysis, two major problems with current unsteady analytical capabilities had to be addressed: modeling a straight centerline nozzle with the turbine blades and exit guide vanes (EGVs), and reducing run times significantly while maintaining physical accuracy. Modifications were made to the CFD code used in this study to allow the coupled nozzle/blade/EGV analysis and to incorporate Message Passing Interface (MPI) software. Because unsteadiness is a key issue for the Fastrac turbine [and future rocket engine turbines such as the Reusable Launch Vehicle (RLV)], calculations were performed for two nozzle-to-blade axial gaps. Calculations were also performed for the nozzle alone, and the results were imposed as an inlet boundary condition for a blade/EGV calculation for the large gap case. These results are compared to the nozzle/blade/EGV results. [S0889-504X(00)02902-0]
Effects of Creep on Modulus of Elasticity Determination of Wood
Authors: Divo´s F. , Tanaka T.
Published: July 2002

[S0739-3717(00)01401-X]
Three-Dimensional Vibrations of Thick, Circular Rings with Isosceles Trapezoidal and Triangular Cross-Sections
Authors: Kang Jae-Hoon , Leissa Arthur W.
Published: July 2002

A three-dimensional (3-D) method of analysis is presented for determining the free vibration frequencies and mode shapes of thick, circular rings with isosceles trapezoidal and triangular cross-sections. Displacement components us,uz, and uθ in the meridional, normal, and circumferential directions, respectively, are taken to be sinusoidal in time, periodic in θ, and algebraic polynomials in the ϕ and z directions. Potential (strain) and kinetic energies of the circular ring are formulated, and upper bound values of the frequencies are obtained by minimizing the frequencies. As the degree of the polynomials is increased, frequencies converge to the exact values. Novel numerical results are presented for the circular rings with isosceles trapezoidal and equilateral triangular cross-sections having completely free boundaries. Convergence to four-digit exactitude is demonstrated for the first five frequencies of the rings. The method is applicable to thin rings, as well as thick and very thick ones. [S0739-3717(00)00702-9]
GaP(110) by XPS
Authors: Poirier D. M. , Weaver J. H.
Published: July 2002

XPS spectra were recorded for a GaP single crystal that was cleaved in situ to expose the (110) plane (Accession #00118). For comparison, a (110) surface exposed to air for 1 h (Accession #00119) was also examined. The electronic record includes the Ga 3d, P 2p, Ga LMM, Ga 2p, and valence band regions.
Characterization of α-Ni(OH)2 by XPS
Authors: Mansour A. N. , Melendres C. A.
Published: July 2002

We report x-ray photoemission spectra (XPS) of hydrated nickel hydroxide, α-Ni(OH)2, with composition 3Ni(OH)2 2H2O as determined by thermogravimetry. XPS spectra were measured with the Physical Electronics Model 5400 x-ray photoelectron spectrometer using unmonochromatized Mg Kα x rays at two pass energy settings corresponding to analyzer energy resolutions of 1.34 and 0.54 eV. We present the survey spectrum (binding energy range of 0–1100 eV) measured at an analyzer energy resolution of 1.34 eV. Multiplexes of the C, O, and Ni photoemission lines, valence band region, as well as the Ni LVV Auger line were measured at an analyzer energy resolution of 0.54 eV. The α-Ni(OH)2 sample was prepared chemically by reacting Ni(NO3)2 with NaOH.
Characterization of the Surface of FeO Powder by XPS
Authors: Mansour A. N. , Brizzolara Robert A.
Published: July 2002

We report x-ray photoemission spectra of the surface of iron oxide (FeO) particles. The research grade high purity FeO sample was commercially obtained from Alfa/AESAR. The XPS spectra were measured with the Physical Electroncs Model 5400 x-ray photoelectron spectrometer using unmonochromatized Mg Kα x-rays at two pass energy settings corresponding to analyzer resolutions of 1.34 and 0.54 eV. We present the survey spectrum (binding energy range of 0–1100 eV) measured at an analyzer energy resolution of 1.34 eV. Multiplexes of the C 1s, O 1s and 2s, and Fe 2p and 3p photoemission lines, valence band region as well as the Fe LVV Auger line were measured at an analyzer energy resolution of 0.54 eV. The XPS data indicate that the surface of FeO powdered material consists mainly of Fe2O3 with small quantities of FeOOH, oxidized carbon, and hydrocarbon as contaminants.
CuSO4 by XPS
Authors: Vasquez R. P.
Published: July 2002

X-ray photoemission measurements of CuSO4 are presented.
Experimental and theoretical study of a differentially pumped absorption gas cell used as a low energy-pass filter in the vacuum ultraviolet photon energy range
Authors: Mercier B. , Compin M. , Prevost C. , Bellec G. , Thissen R. , Dutuit O. , Nahon L.
Published: July 2002

In order to separate the fundamental synchrotron radiation from the high harmonics emitted by an undulator, a low photon energy-pass filter has been designed and built, ensuring a high spectral purity on the vacuum ultraviolet (VUV) SU5 beamline at Super-ACO. It consists of an absorption cell filled with rare gases and separated from the ultrahigh vacuum of the storage ring and of the beamline by a double differential pumping obtained with thin capillaries. Its conception has been optimized by numerical computation of pumping speed. Admission pressures in the range of 100 Pa in the central part of the filter have been used without any degradation of the upstream or downstream ultrahigh vacuum. The measured attenuation factors above the energy cutoff are above 105 and 102 (and certainly above 103 with ultimate pressure of Ne) for argon and neon absorbing gases, respectively, with no measurable attenuation of fundamental radiation. A sophisticated numerical simulation of the pressure distribution, taking into account the geometry of the whole absorption cell including the first pair of capillaries, has been developed. The corresponding calculated attenuation factors are in very good agreement with the measurements, and thus allow reliable predictions of the expected attenuation factors for any given configuration of the filter.
Observation of fine structures of nanodomains in donor-modified Pb(Zr,Ti)O3 ferroelectrics
Authors: Tan Qi , Li Jianxing
Published: July 2002

A nanodomain morphology comprising fine structures of less than 5 nm spacing was observed in oxygen deficient lead zirconate titanates modified by La, Ca, and Sr. Oxidation of samples can eliminate the fine structures and facilitate polarization switching. Although grain growth after high temperature annealing results in normal domain morphology and complete polarization switching, irregular and fragmented domains remain. These fine domain structures were explained in terms of local polarization pinning due to oxygen vacancies and antisite substitutents.
Residual stress formation in multilayered TiN/TaNx coatings during reactive magnetron sputter deposition
Authors: Nordin M. , Larsson M. , Joelsson T. , Birch J. , Hultman L.
Published: July 2002

Multilayered physical vapor deposited TiN/TaNx coatings were deposited on cemented carbide substrates using a dual target magnetron sputtering system. The coatings were investigated with respect to the influence of nitrogen partial pressure during deposition on the residual stress developed in the coatings. Furthermore, the fracture strength of the material, i.e., the magnitude of the tensile stress that the coating can support without cracking, was evaluated. It was found that, by increasing the nitrogen partial pressure, it is possible to change the stress from compressive to tensile. The highest tensile stress was about 3.6 GPa. Despite this high stress, the coating displayed no cracking. This implies that it is possible to grow TiN/TaNx multilayered coatings with high tensile fracture strength using dual magnetron sputtering and a high deposition temperature (about 680 °C).
Secondary-ion mass analysis: Instrumentation, data interpretation, and applications
Authors: Phillips Bradway F.
Published: July 2002

The field of secondary-ion mass analysis is discussed starting with the historical events leading up to present-day instrumentation. The two principal types of instruments are described in some detail, as well as anticipated new developments. Problems in data interpretation and quantitative treatment of data are discussed as a background for the presentation of several examples of the technique's usefulness.
Three-dimensional nanostructure fabrication by focused-ion-beam chemical vapor deposition
Authors: Matsui Shinji , Kaito Takashi , Fujita Jun-ichi , Komuro Masanori , Kanda Kazuhiro , Haruyama Yuichi
Published: July 2002

Three-dimensional nanostructure fabrication has been demonstrated by 30 keV Ga+ focused ion beam assisted deposition using a aromatic hydrocarbon precursor. The characterization of deposited film on a silicon substrate was performed by a transmission microscope and Raman spectra. This result indicates that the deposition film is a diamondlike amorphous carbon. Production of three-dimensional nanostructure is discussed. Microcoil, drill, and bellows with 0.1 μm dimension were fabricated as parts of the microsystem. Furthermore, microstructure plastic arts is advocated as a new field using microbeam technology, presenting one example of a microwine glass with 2.75 μm external diameter and 12 μm height.
Behavior of zirconium surfaces in the presence of oxygen, nitrogen, and hydrogen containing adsorbates
Authors: Kang Y. C. , Clauss D. A. , Ramsier R. D.
Published: July 2002

As part of an effort to address questions related to corrosion passivation in zirconium alloys, low energy electron diffraction (LEED) and temperature programmed desorption (TPD) techniques have been applied to the adsorption of water and ammonia on Zr(0001). Water adsorption at 180 K results in water desorption in a broad TPD feature near 625 K. Ammonia exposure at 150 and 180 K results in the unexpected production of water during TPD near 625 and 525 K, respectively, and the formation of complex residual LEED patterns. Auger electron spectroscopy indicates that nitrogen remains at or near the surface following ammonia adsorption and TPD. A phenomenological explanation involving a temperature-dependent dissociation probability for ammonia and nitrogen/oxygen exchange between the surface and subsurface regions is presented to qualitatively account for these findings.
Surface processing with gas-cluster ions to improve giant magnetoresistance films
Authors: Fenner D. B. , Hautala J. , Allen L. P. , Tetreault T. G. , Al-Jibouri A. , Budnick J. I. , Jones K. S.
Published: July 2002

The reduction of roughness, without introducing damage, of thin-film surfaces in giant magnetoresistance (GMR) applications will be essential in the development of advanced devices. Tools and methods to accomplish this are limited at present. Gas-cluster ion beam (GCIB) technology shows promise as a dry, low-temperature process that can provide substantial improvement, and can be integrated into GMR-film deposition-and-etch tools. In this work, we describe recent GCIB technique developments and processes for tantalum, alumina, permalloy, and other relevant materials. With argon GCIB it is possible to reduce the roughness of many films to well below a nanometer (root-mean-square), with the roughness falling exponentially with cluster dose. Prototype magnetic films for evaluation were fabricated on GCIB-smoothed alumina gap layers. Transmission electron microscopy revealed changes in roughness and grain morphology that may be correlated with magnetic properties.
Photon-stimulated ion desorption from mono- and multilayered silicon alkoxide on silicon by core-level excitation
Authors: Baba Y. , Wu G. , Sekiguchi T. , Shimoyama I.
Published: July 2002

Photon-stimulated ion desorption from Si(OCH3)4 [tetramethoxysilane (TMOS)] adsorbed on Si(100) following silicon K-edge excitation has been investigated using monochromatized synchrotron radiation. In order to separate the photochemical process induced by the substrate excitation from that induced by adsorbate excitation, we have prepared well-controlled monolayer, submonolayer and multilayer coverages of TMOS on Si(100). In the x-ray absorption near-edge structure (XANES) spectrum for a multilayer of TMOS, the peak energy of the resonant excitation from the Si 1s to the unoccupied σ* orbitals was shifted to higher energy by 6 eV than that for the silicon substrate. For a thin layer such as the monolayer and submonolayer, the XANES spectra taken by total electron yields were almost the same as those of the silicon substrate. However, the photon-energy dependencies of the CH3+ and Si(OCH3)3+ yields for the monolayer sample did not follow the XANES spectra of silicon but they followed those for multilayered TMOS. This result indicates that the secondary electrons produced in the silicon substrate scarcely contribute to the fragment-ion desorption for thin layers. It was concluded that the core-to-valence resonant excitation in monolayered TMOS is the main trigger of the C–O bond scission and the fragment-ion desorption.
Characterization of Cobalt Silicide Formation by X-ray Photoelectron Spectroscopy. I. CoSi
Authors: Zhao Jin , Poirier Derrick M.
Published: July 2002

X-ray photoelectron spectroscopy (XPS) has been used to characterize the chemical composition and chemical state information of silicide formation in our laboratory and many others. In this work, we report the x-ray photoelectron spectra of CoSi. XPS spectra were measured with the Physical Electronics Quantum2000 system using a monochromatic Al Kα x-ray source. A survey spectrum and multiplex spectra of Co and Si photoemission lines as well as Co Auger lines were recorded.
Characterization of Cobalt Silicide Formation by X-ray Photoelectron Spectroscopy. II. CoSi2
Authors: Zhao Jin , Poirier Derrick M.
Published: July 2002

X-ray photoelectron spectroscopy (XPS) has been used to characterize the chemical composition and chemical state information of silicide formation in our laboratory and many others. In the present work, we report the x-ray photoelectron spectra of CoSi2. XPS spectra were measured with the Physical Electronics Quantum2000 system using a monochromatic Al Kα x-ray source. A survey spectrum and multiplex spectra of Co and Si photoemission lines as well as Co Auger lines were recorded.
Integrated multiscale three-dimensional simulation approach in local interconnect gap-fill optimization
Authors: Sukharev Valeriy , Kumar Kiran , Li Weidan , Zhao Joe , Pyka Wolfgang , McInerney E. Jack , Joh Sooyun
Published: July 2002

An integrated three-dimensional (3D) simulation approach for the optimization of multistep process modules is developed. A link between a 3D finite volume reactor-scale model and a developed 3D cell topography feature-scale model allows the prediction of uniformity distribution for a sequence of process steps on an entire wafer surface. As an example, an across-wafer gap-fill is simulated using a combination of simulation tools to capture a variety of nonuniformities that exist in all steps involved in the local interconnect tungsten-fill process flow. Across-wafer variations in Ti flux density, angular distributions in Ti and TiN physical vapor deposition fluxes, as well as nonuniformities in precursor fluxes in TiN and W chemical vapor deposition are taken into consideration. Across wafer blanket layer thickness variations as well as bottom and sidewall thickness variations inside interconnect features are determined for all deposited layers. Across-wafer metal stack thickness distributions, wafer edge effect, and key-hole formation inside the features are simulated. Experimentally extracted parameters are employed for the calibration of the simulation results.
Combined effect of electrode gap and radio frequency on power deposition and film growth kinetics in SiH4/H2 discharges
Authors: Amanatides E. , Mataras D. , Rapakoulias D. E.
Published: July 2002

The combined effect of the variation of the interelectrode gap (1.3–2.5 cm) and radio frequency (13.56–50 MHz) on the properties of highly diluted silane in hydrogen discharges used for the deposition of microcrystalline silicon thin films is presented. The investigation included electrical and optical discharge measurements as well as the in situ determination of the film growth rate. In the lower frequencies regime, the increase of the interelectrode gap for the same applied voltage results in higher current flows and higher total power dissipation. On the other hand, at 50 MHz the variation of the interelectrode space has only a slight effect on the total power dissipation, due to the low excitation voltage. However, at all frequencies, the increase of the interelectrode space results in a drop of the power dissipation per discharge volume. This is related to the less effective energy transfer to the electrons that is due to the enhancement of the bulk relative to the sheath ohmic heating. The variation of the relative importance of the electron heating modes is reflected in the discharge radical production efficiency and the film growth rate.
Ti diffusion in ion prebombarded MgO(100). I. A model for quantitative analysis
Authors: Lu M. , Lupu C. , Styve V. J. , Lee S. M. , Rabalais J. W.
Published: July 2002

Enhancement of Ti diffusion in MgO(100) prebombarded with 7 keV Ar+ has been observed. Diffusion was induced by annealing to 1000 °C following the prebombardment and Ti evaporation. Such a sample geometry and experimental procedure alleviates the continuous provision of freely mobile defects introduced by ion irradiation during annealing for diffusion, making diffusion proceed in a non-steady-state condition. Diffusion penetration profiles were obtained by using secondary ion mass spectrometry depth profiling techniques. A model that includes a depth-dependent diffusion coefficient was proposed, which successfully explains the observed non-steady-state radiation enhanced diffusion. The diffusion coefficients are of the order of 10−20 m2/s and are enhanced due to the defect structure inflected by the Ar+ prebombardment.
Evaluation of radio-frequency sputter-deposited textured TiN thin films as diffusion barriers between copper and silicon
Authors: Chen G. S. , Guo J. J. , Lin C. K. , Hsu Chen-Sheng , Yang L. C. , Fang J. S.
Published: July 2002

Thin textured titanium nitride (TiN) films with thicknesses under 100 nm were grown on (100) silicon wafers by employing a radio-frequency generator to sputter reactively a Ti target under poisoned modes in mixtures of fixed Ar (3.6×10−1 Pa) and N2 at various partial pressures. The texture of the TiN films can be tailored by appropriately controlling the partial pressure of the reactive nitrogen. (111) textured films can be deposited over a broad range of lower N2 partial pressures from 2.9×10−2 to 1.8×10−1 Pa, while (100) textured films can be deposited in a narrow range of higher nitrogen partial pressures (2.3×10−1 to 3.3×10−1 Pa). The texturing effect is accounted for by a previously described thin film deposition mechanism. Scanning electron and atomic force microscopies demonstrate that the two textured TiN films both exhibit a column-grained structure; the columnar size of the (111) oriented TiN (⩾30 nm) is coarser than that of the (100) oriented TiN (10–20 nm). Evaluations of the textured TiN barriers, based on differences in sheet resistance, surface morphology, and phase transformation induced by annealing Si/TiN(40 nm)/Cu(200 nm) samples, suggest that the (111) TiN is a superior diffusion barrier material for copper than (100) TiN. The difference in barrier effectiveness is attributed to variations in crystallographic packing and microstructure of the textured diffusion barrier.
Etching of organosilicate glass low-kdielectric films in halogen plasmas
Authors: Vitale Steven A. , Sawin Herbert H.
Published: July 2002

The chemistry and kinetics of alternative etching chemistries for low-k dielectric materials are explored to improve the anisotropy of the etching process and to reduce the problems associated with postetch clean-up. Etching rates, selectivities, and etching yields of Black Diamond and Coral organosilicate glasses (OSGs) have been measured. Black Diamond and Coral are etched rapidly in F2, Cl2, and HBr high density plasmas, and Cl2+HBr plasmas have been identified as a viable process chemistry with several advantages over traditional fluorocarbon plasmas. The OSG films are not spontaneously etched by F2, Cl2, HBr molecules, Cl, or Br atoms, however, F atoms etch the OSGs spontaneously. F, Cl, and H atoms extract a substantial amount of carbon from the films, but Cl and H do not attack the OSG oxide matrix. The Coral films are more strongly depleted of carbon after halogen plasma etching than the Black Diamond. In addition, oxygen atoms extract nearly all of the carbon and nitrogen from the OSGs, leaving a stoichiometric SiO2 layer.
Role of surface steps in the arrangement of silicon nano-dots on a vicinal Si(111) surface: Scanning tunneling microscopy investigation
Authors: Ha Jeong Sook , Park Kang-Ho , Ko Young-Jo , Park Kyungwan
Published: July 2002

We have investigated the role of surface steps in the arrangement of silicon nano-dots on a vicinal Si(111) surface by scanning tunneling microscopy. Nanometer sized silicon nitride islands were formed on a vicinal Si(111) surface, which was 1° off toward [1̄1̄2] direction, via thermal nitridation using N2 gas. On the nitrided surface, oxygen gas was dosed to induce a local selective etching of bare silicon using the silicon nitride islands as masks. The resultant surface showed one-dimensional arrangement of silicon nano-dots along the step edges of silicon surface. The lateral size of the dot in the direction perpendicular to the step edges was restricted to the terrace width of the stepped Si(111) surface. We consider that the preferential growth of silicon nitride islands on the edges of single height steps is responsible for the arrangement of silicon nano-dots along the step edges of the 1° off vicinal Si(111) surface.
Some properties of Ni−Cu foils and their behavior when heated in hydrogen
Authors: Morrison Richard A.
Published: July 2002

Nickel foils of nominal thickness 0.1 and 1 μ have been resistively evaporated onto copper−foil substrates of thickness 25 and 2.5 μ. In depositions in which the pressure was as high as 10−5 Torr, the deposited nickel was not shiny and appeared granual in a 100x microscope. Foils evaporated in higher vacuums were shiny, but became granular if heated to 500°C in oxygen at pressures greater than 5×10−6 Torr, or in carbon dioxide at pressures greater than 5×10−7 Torr. This phenomenon has been interpreted as recrystallization. Foils heated to 500°C at pressures of hydrogen above 3×10−4 Torr exhibit cracking characteristic of hydrogen embrittlement. The bimetallic foils curled concave toward the nickel during evaporation, consistent with a connected−island form of film growth.
Investigations of adsorption on metal surfaces by photoelectron spectroscopy, combined with other methods
Authors: Menzel D.
Published: July 2002

A survey is given of the experimental information which can be obtained for adsorbate layers on metals by photoelectron spectroscopy (valence level spectroscopy by UPS, quantitative analysis, and chemical shifts of adsorbate and substrate core levels by XPS), and of the difficulties arising in their interpretation. Three levels of interpretation are distinguished: a qualitative approach using the UPS and XPS spectra as fingerprints, which works best in correlation with other methods, a semiquantitative approach which tries to extract physical insight from the measured data on an intermediate level of sophistication, and as the ultimate aim, a correlation of photoelectron spectra with the spectral density obtained from many−body theories. As examples for the first approach, results for the adsorption of CO on Ru(001) and W(110), and of oxygen on W(100) are described and discussed.
Reactive ion etching of aluminum and aluminum alloys in an rf plasma containing halogen species
Authors: Schaible P. M. , Metzger W. C. , Anderson J. P.
Published: July 2002

An etching method capable of producing vertical-walled high-resolution patterns in aluminum and aluminum alloy films is described. The process consists of rf sputter etching in a plasma containing ion species, which react with the metal to form volatile or easily sputtered compounds. The presence of reactive species greatly enhances the etch rate, while the electric field maintains the directionality inherent in the sputtering process. Halogen ion species, as obtained in rf plasmas containing a partial pressure of Cl2, Br2, HCl, HBr, or CCl4, were used to produce reactive ion etching of Al. The etch rate in a CCl4 plasma at a power input of 0.6 W/cm2 is as high as 5000 Å/min. Variations in reaction rate with rf power, reactant concentration, reactant flow rate, temperature, gas pressure, batch size, and residual gas contamination are discussed. Etch rate data for various materials found suitable for masking are also presented.
Thirty-centimeter-diameter ion milling source
Authors: Robinson Raymond S.
Published: July 2002

A 30 cm beam diameter ion source has been designed and fabricated for micromachining and sputtering applications. An argon ion current density of 1 mA/cm2 at 500 eV ion energy was selected as a design operating condition. The completed ion source met the design criteria at this operating condition with a uniform and well-collimated beam having an average variation in current density of ±5% over the center of 20 cm of the beam. This ion source has a multipole magnetic field that employs permanent magnets between permeable pole pieces. Langmuir probe surveys of the source plasma support the design concepts of a multipole field and a circumferential cathode to enhance plasma uniformity.
Magnetron sputter coating of microspherical substrates
Authors: Lowe A. T. , Hosford C. D.
Published: July 2002

The fabrication of laser fusion targets requires the deposition of various metal and dielectric layers on microspherical substrates (100–500 μm diameter). The continuous motion for uniformly coating these spherical substrates has been accomplished for rf sputtering applications. In one approach, the spheres being coated are bounced and laterally swept across a table as the frequency of vibration of the table is changed continously. In another approach, the sputtering gas is also a levitation gas. The argon is fed through a collimated hole structure and keeps the microsphere both levitated and rotating during the sputter deposition. The uniformity and surface quality of the deposited films obtained by these two techniques are compared.
Measurement and modulation of atomic interdiffusion at Au–Al/GaAs(110) interfaces
Authors: Brillson L. J. , Margaritondo G. , Stoffel N. G. , Bauer R. S. , Bachrach R. Z. , Hansson G.
Published: July 2002

Atomic layers of Al at Au-GaAs(110) interfaces have been used to measure the absolute motion of metal and semiconductor atoms at their intimate contact. This new technique reveals both Au indiffusion and nonstoichiometric outdiffusion during the initial stages of Schottky barrier formation. The Al ’’interlayers’’ at Au–GaAs interfaces also modulate the relative Ga to As diffusion into Au by over an order of magnitude. This new phenomenon at compound semiconductor–metal interfaces reveals a systematic relationship between the local atomic bonding and the extended chemical structure of the interface.
Surface photovoltage spectroscopy with cleaved GaAs (110) surfaces: Spectroscopy of Cr2+
Authors: Mönch W. , Clemens H. J. , Görlich S. , Enninghorst R. , Gant H.
Published: July 2002

Surface photovoltage spectra of clean (110) surfaces cleaved from n-type GaAs crystals doped with Te or Si exhibit two narrow peaks at 0.72 and 0.89 eV superimposed on a broad shoulder extending from h/ω≊0.7 eV to Eg. Both peaks are strongly increased by chemisorption of oxygen and by increasing the band bending. The peak at 0.89 eV is attributed to intra-ion 3d transitions of deep Cr2+ impurities, with the ground state 0.72 eV below the conduction band edge. The presence of chromium in the samples was proven by AES after anneals at 800 K, causing an enrichment of chromium near to the surface. The growth of the 0.89 eV peak proportional to the square of the surface potential is explained by an increase of the net escape probability from the excited state into the conduction band via tunneling.