bluuebunny/crossref_metadata_2025 huggingface dataset:
Stress-Modulated Growth, Residual Stress, and Vascular Heterogeneity
Authors: Taber Larry A. , Humphrey Jay D.
Published: July 2002

A simple phenomenological model is used to study interrelations between material properties, growth-induced residual stresses, and opening angles in arteries. The artery is assumed to be a thick-walled tube composed of an orthotropic pseudoelastic material. In addition, the normal mature vessel is assumed to have uniform circumferential wall stress, which is achieved here via a mechanical growth law. Residual stresses are computed for three configurations: the unloaded intact artery, the artery after a single transmural cut, and the inner and outer rings of the artery created by combined radial and circumferential cuts. The results show that the magnitudes of the opening angles depend strongly on the heterogeneity of the material properties of the vessel wall and that multiple radial and circumferential cuts may be needed to relieve all residual stress. In addition, comparing computed opening angles with published experimental data for the bovine carotid artery suggests that the material properties change continuously across the vessel wall and that stress, not strain, correlates well with growth in arteries.
Computerized Method for Preliminary Structural Design of Composite Wind Turbine Blades
Authors: Bir Gunjit S.
Published: July 2002

A computerized method has been developed to aid preliminary design of composite wind turbine blades. The method allows for arbitrary specification of the chord, twist, and airfoil geometry along the blade and an arbitrary number of shear webs. Given the blade external geometry description and its design load distribution, the Fortran code uses ultimate-strength and buckling-resistance criteria to compute the design thickness of load-bearing composite laminates. The code also includes an analysis option to obtain blade properties if a composite laminates schedule is prescribed. These properties include bending stiffness, torsion stiffness, mass, moments of inertia, elastic-axis offset, and center-of-mass offset along the blade. Nonstructural materials—gelcoat, nexus, and bonding adhesive—are also included for computation of mass. This paper describes the assumed structural layout of composite laminates within the blade, the design approach, and the computational process. Finally, an example illustrates the application of the code to the preliminary design of a hypothetical blade and computation of its structural properties.
Scale Effect of Cavitation Inception on a 2D Eppler Hydrofoil
Authors: Amromin E. L.
Published: July 2002

Cavitation inception on an E817 hydrofoil issued from an inverse calculus for ideal fluid has been numerically analyzed for speeds and scales inherent to both model test and full-scale marine conditions. The computations have been carried out with account to the Reynolds number effect on hydrofoil lift and combined effect of the Reynolds number and Weber number on the equilibrium of sheet cavities in the hydrofoil boundary layer. Different levels of scale effects for cavitation inception on suction and pressure sides of E817 hydrofoil are shown. Comparison with the scale effect of cavitation inception on conventional NACA-0012 hydrofoil has helped to explain this difference. Issues in blade design with sections similar to E817 are discussed.
A Noncontact, Nondestructive Method for Quantifying Intratissue Deformations and Strains
Authors: Bey M. J. , Song H. K. , Wehrli F. W. , Soslowsky L. J.
Published: July 2002

The function of soft connective tissues is frequently characterized by quantifying tissue strain (e.g., during joint motion). Conventional techniques for quantifying tendon and ligament strain typically provide surface measures, using markers, stain lines or instrumentation that may influence the tissue. An alternative approach is to quantify intratendinous strain by applying texture correlation analysis to magnetic resonance (MR) images. This paper reports the accuracy and reproducibility of this approach by (1) assessing the reproducibility of MR images, (2) assessing texture correlation accuracy using simulated displacements, and (3) comparing texture correlation measures of displacement and strain from MR images to conventional techniques.
Average Flow Model of Rough Surface Lubrication: Flow Factors for Sinusoidal Surfaces
Authors: Letalleur N. , Plouraboue´ F. , Prat M.
Published: July 2002

The effects of lubricant film flow, pressurized and sheared between two parallel sinusoidal wavy surfaces in sliding motion is studied analytically. Results are presented using a flow factor model which provides an average description of the surfaces roughness impact. Two distinct cases are studied in order to compare stationary or time dependent local aperture configurations. Flow factors are computed respectively for each case through spatial or spatio-temporal average, revealing striking differences. The results shed light on the relevance of the composite roughness concept. Special attention is paid to the flow factor analytical behavior when surfaces are near contact.
The DISS Project: Direct Steam Generation in Parabolic Trough Systems. Operation and Maintenance Experience and Update on Project Status
Authors: Zarza Eduardo , Valenzuela Loreto , Leo´n Javier , Weyers H.-Dieter , Eickhoff Martin , Eck Markus , Hennecke Klaus
Published: July 2002

The DISS (DIrect Solar Steam) project is a complete R+TD program aimed at developing a new generation of solar thermal power plants with direct steam generation (DSG) in the absorber tubes of parabolic trough collectors. During the first phase of the project (1996-1998), a life-size test facility was implemented at the Plataforma Solar de Almerı´a (PSA) to investigate the basic DSG processes under real solar conditions and evaluate the unanswered technical questions concerning this new technology. This paper updates DISS project status and explains O&M-related experience (e.g., main problems faced and solutions applied) with the PSA DISS test facility since January 1999.
Failure of a Ductile Adhesive Layer Constrained by Hard Adherends
Authors: Ikeda Toru , Yamashita Akira , Lee Deokbo , Miyazaki Noriyuki
Published: July 2002

The evaluation of a fracture from a thin layer constrained by a hard material is important in relation to the structural integrity of adhesive joints and composite materials. It has been reported that the fracture toughness of a crack in a ductile adhesive joint depends on the bond thickness, but the mechanism has not yet been elucidated clearly. In this study, the J-integral and the near-tip stress of a crack in an adhesive joint are investigated. It is determined that a decrease of the bond thickness increases the stress ahead of a crack rip, which results in the decrease of fracture toughness. [S0094-4289(00)01201-9]
Damage of Short-Fiber-Reinforced Metal Matrix Composites Considering Cooling and Thermal Cycling
Authors: Zhou Chuwei , Yang Wei , Fang Daining
Published: July 2002

Mechanical properties and damage evolution of short-fiber-reinforced metal matrix composites (MMC) are studied under a micromechanics model accounting for the history of cooling and thermal cycling. A cohesive interface is formulated in conjunction with the Gurson-Tvergaard matrix damage model. Attention is focused on the residual stresses and damages by the thermal mismatch. Substantial stress drop in the uniaxial tensile response is found for a computational cell that experienced a cooling process. The stress drop is caused by debonding along the fiber ends. Subsequent thermal cycling lowers the debonding stress and the debonding strain. Micromechanics analysis reveals three failure modes. When the thermal histories are ignored, the cell fails by matrix damage outside the fiber ends. With the incorporation of cooling, the cell fails by fiber end debonding and the subsequent transverse matrix damage. When thermal cycling is also included, the cell fails by jagged debonding around the fiber tops followed by necking instability of matrix ligaments. [S0094-4289(00)01202-0]
Investigation of Transition From Annular to Intermittent Flow in Pipes
Authors: Serdar Kaya Avni , Tom Chen X. , Sarica Cem , Brill James P.
Published: July 2002

A new unified model is proposed for the transition from annular to intermittent flow patterns for the entire range of pipe inclination angles. Experimentally, it has been observed that the transition from annular flow takes place at a critical void fraction. To obtain a transition boundary equation, conservation of momentum equations for gas and the liquid film are combined and solved with the critical void fraction. The new model captures the correct transition characteristics, agrees favorably with experimental flow pattern data, and performs the best when compared with previous transition models. [S0195-0738(00)00601-4]
Flutter Mechanisms in Low Pressure Turbine Blades
Authors: Nowinski M. , Panovsky J.
Published: July 2002

The work described in this paper is part of a comprehensive research effort aimed at eliminating the occurrence of low pressure turbine blade flutter in aircraft engines. The results of fundamental unsteady aerodynamic experiments conducted in an annular cascade are studied in order to improve the overall understanding of the flutter mechanism and to identify the key flutter parameters. In addition to the standard traveling wave tests, several other unique experiments are described. The influence coefficient technique is experimentally verified for this class of blades. The beneficial stabilizing effect of mistuning is also directly demonstrated. Finally, the key design parameters for flutter in low pressure turbine blades are identified. In addition to the experimental effort, correlating analyses utilizing linearized Euler methods demonstrate that these computational techniques are adequate to predict turbine flutter. [S0742-4795(00)01301-6]
Analysis of In-Flight Oxidation During Reactive Spray Atomization and
Deposition Processing of Aluminum
Authors: Delplanque J.-P. , Lavernia E. J. , Rangel R. H.
Published: July 2002

This work defines a model to predict the characteristics of materials processed using reactive spray atomization and deposition. The materials considered are aluminum alloys while target dispersoids are primarily oxides. These may be obtained by the reaction of oxygen-containing atomization gas mixtures with molten alloy droplets. Droplet position and velocity histories are obtained from the numerical solution of the one-dimensional equation of motion. The energy equation inside the droplet is solved numerically using finite differences to predict the spatially resolved temperature field. The solid/liquid interface progression rate is estimated using a power law while an oxidation rate expression based on the Mott-Cabrera theory is used for the oxide thickness. Such a model should prove very valuable in determining the parameters controlling the volume fraction and the size distribution of the dispersoids for various systems. [S0022-1481(00)02901-7]
Two- and Three-Dimensional Path Optimization for Production Machinery
Authors: Khan W. A. , Hayhurst D. R.
Published: July 2002

Path optimization is desirable in many problem instances occurring in discrete manufacturing and pick and place technology. The problem may refer to applications ranging from two-dimensional movements such as in milling processes to three-dimensional movements required in many robotic operations. The optimal path can be found using tour construction techniques, sub tour elimination techniques and tour to tour improvement techniques. The limits to which these solution methodologies can be applied are restricted to a certain number of nodes. The optimal path for two- and three-dimensional TSP is determined using a stochastic search procedure based on a tour improvement technique. An optimal solution is presented for 500 node TSP in two dimensions. A procedure for finding optimal path for an even larger number of nodes is outlined. The optimal path in three dimensions is also presented using nodes distributed along the periphery of three-dimensional primitives. [S1087-1357(00)71601-7]
A Deformation Formula for Circular Crowned Roller Compressed Between Two Flat Plates
Authors: Horng T. L. , Ju S. H. , Cha K. C.
Published: July 2002

The main purpose of this paper is to develop a deformation equation for the circular crowned roller compressed between two plates. First, the roller is divided into three parts, two crowned parts and one cylindrical part. The superposition method is then introduced to obtain the roller stiffness. The stiffness contribution of the crowned parts is calculated by the classical Hertzian contact solution and the stiffness contribution of the noncrowned part is obtained by the Hoeprich’s formula. Comparisons with various finite element results indicate that the deformation equation derived in this paper can be a good deformation formula for the circular crowned roller. [S0742-4787(00)01502-2]
Steady-State Frictional Sliding of Two Elastic Bodies With a Wavy Contact Interface
Authors: Nosonovsky M. , Adams G. G.
Published: July 2002

Dry frictional sliding of two elastic bodies, one of which has a periodic wavy surface, is considered. Such a model represents the frictional sliding of two nominally flat surfaces, one of which has periodically spaced asperities. The dependence of the true contact area on loading is analyzed by using the plane strain theory of elasticity. Fourier series and integral transform techniques are applied to reduce the problem to an integral equation which is solved using a series of Jacobi polynomials. For steady-state dynamic frictional sliding with given values of the friction coefficient, materials constants, and sliding velocity, the dependence of the contact zone length on the remotely applied tractions is determined. The results indicate a decrease of the minimum applied traction required to close the gap between the bodies, with an increase of the friction coefficient and/or the sliding velocity. A resonance exists as the sliding velocity approaches the Rayleigh wave speed of the flat body. [S0742-4787(00)01403-X]
Creep Modeling of Welded Joints Using the Theta Projection Concept and Finite Element Analysis
Authors: Law M. , Payten W. , Snowden K.
Published: July 2002

Modeling of welded joints under creep conditions with finite element analysis was undertaken using the theta projection method. The results were compared to modeling based on a simple Norton law. Theta projection data extends the accuracy and predictive capability of finite element modeling of critical structures operating at high temperature and pressure. In some cases analyzed, it was found that the results diverged from those gained using a Norton law creep model. [S0094-9930(00)00601-6]
Elemental Lead by XPS
Authors: Bozack Michael J. , Bryant Kenneth W.
Published: July 2002

An XPS spectrum of elemental lead (Pb) is presented. The Pb foil was supplied commercially (Goodfellow Corp.) as a 0.1 mm thick specimen of quoted purity 99.95%. The BE range 1000–0 eV is documented.
Epitaxial Aluminum Nitride Film on Silicon(111) Grown by Reactive DC Magnetron Sputter Deposition
Authors: Militello Maria C. , Gaarenstroom Stephen W. , Simko Steven J.
Published: July 2002

An Auger electron spectrum of an aluminum nitride thin film is presented. The film was prepared by reactive dc magnetron sputter deposition onto a silicon wafer substrate. The film was grown epitaxially on the Si(111) substrate. The film was also characterized using electron probe microanalysis, x-ray diffraction, and transmission electron microscopy.
Magnesium Aluminate (MgAl2O4) by XPS
Authors: Strohmeier Brian R.
Published: July 2002

The XPS spectra of materials containing both magnesium and aluminum can exhibit a number of spectral artifacts when using a Mg Kα x-ray source. These artifacts are easily observed in XPS spectra of magnesium aluminate (MgAl2O4, also known as magnesium aluminum oxide), which are presented in this article. For example, the Al 2p peak is overlapped by the Mg Kα x-ray satellites from the Mg 2s peak, and the Mg Kα x-ray induced Mg KLL Auger peak. In addition, the Mg 2p peak can be overlapped by a C 1s x-ray ghost line caused by stray Al Kα x-ray radiation when using a dual Mg/Al x-ray source. Because of these artifacts, the amounts of Mg and Al in such samples should be quantified (when using a Mg Kα x-ray source) using the Mg 2s and Al 2s peaks, respectively, which are free of these artifacts.
Gamma-Alumina (γ-Al2O3) by XPS
Authors: Strohmeier Brian R.
Published: July 2002

This article presents the main core lines and the valence band x-ray photoelectron (XPS) spectra obtained for a commercial gamma-alumina (γ-Al2O3) powder. The electronic record includes the Al 2p, Al 2s, O 1s, O 2s, C 1s, and valence band spectra. Although it is usually difficult to distinguish among the various forms of aluminum oxide [Al2O3], oxyhydroxide [AlO(OH)] and hydroxide [Al(OH)3] based on the core XPS binding energies, the valence band spectra for many of these materials are unique. The valence band spectrum for γ-Al2O3 shows two broad distinct peaks that are separated by about 3.3 eV.
R-cut Sapphire Surface Spectra by XPS and UPS: Clean Surface and Ultra-thin Mg Films
Authors: Yu Yan , Lad R. J.
Published: July 2002

Sapphire wafers (single crystal α-Al2O3) are important optically transparent substrates used in microelectronics and are also useful model surfaces for studying the surface properties of polycrystalline α-alumina ceramics. The R-cut (1012¯) surface of sapphire can easily be prepared to have a stoichiometric composition and exhibit a (1×1) surface mesh by annealing a mechanically polished surface to 1123 K in 7 × 10−4 Pa O2. This surface preparation yields a distribution of single atomic height steps and flat terraces (typically 40 nm wide) as revealed by atomic force microscopy. In this article, XPS and UPS spectra are reported for the clean α-Al2O3 (1012¯) surface which were acquired with a PHI 15-255G double-pass CMA. We also present XPS spectra of ultra-thin Mg films (<20 monolayers) deposited on the α-Al2O3 (1012¯) surface at room temperature.
Effects of gap states on scanning tunneling spectra observed on (110)- and (001)-oriented clean surfaces and ultrathin Si layer covered surfaces of GaAs prepared by molecular beam epitaxy
Authors: Hasegawa Hideki , Negoro Noboru , Kasai Seiya , Ishikawa Yasuhiko , Fujikuwa Hajime
Published: July 2002

In an attempt to understand and control Fermi level pinning on GaAs surfaces, an ultrahigh vacuum (UHV) scanning tunneling spectroscopy (STS) study was made on (110) and (001) clean surfaces and Si covered (001) surfaces of n-type GaAs prepared by molecular beam epitaxy. Normal STS spectra showing conductance gaps corresponding to GaAs energy gap and anomalous spectra showing much larger gaps coexisted on all samples. The rate of finding normal spectra was very low on the initial surfaces, but it greatly increased after Si deposition particularly on the c(4×4) surface. A previous explanation of the gap anomaly by tip-induced electrostatic bend bending change is invalid. A new model based on a band bending change due to tip-induced local charging of surface states is presented where tunneling proximity makes occupancy of surface states in equilibrium with the scanning tunneling microscopy (STM) tip. Spots with anomalous spectra correspond to Fermi level pinning centers where the tip directly “writes” or “erases” single or a few electrons to and from the surface states. Away from the pinning center, such charge transfer does not take place, and normal STS spectra are obtained with Fermi level positions consistent with macroscopic band bending measured by x-ray photoelectron spectroscopy and by an UHV contactless capacitance–voltage system. No direct one-to-one correlation existed between the pinning center and any specific visual STM defect features such as vacancies, dimer-desorbed holes, dimer kinks, step etc. Pinning centers make up inhomogeneous distributions of spatially extended pinning areas of universal nature surrounding any kind of structural disorder. Si deposition is shown to be very effective in reducing the number, spatial extension and state density of such pinning areas, particularly on the initially c(4×4) reconstructed surface.
Mosaic structure of various oriented grains in CoSi2/Si(001)
Authors: Kang Tae Soo , Je Jung Ho , Kim Gi Bum , Baik Hong Koo , Lee Sung-Man
Published: July 2002

We investigated the mosaic structure of CoSi2/Si(001) film in a synchrotron x-ray scattering experiment. The CoSi2 film, formed by thermal reaction of a 120 Å Co film on Si(001), was composed largely of epitaxial grains of various orientations. In particular, the twin oriented (B-type) CoSi2(111) grains were grown epitaxially on the Si{111} facets that were generated during annealing. Two distinct mosaic structures were observed in the CoSi2 grains; the epitaxial grains of the same orientation with the Si substrate, such as the CoSi2(001) [the CoSi2(111)] grains lying on the Si(001) [the Si{111} facets], showed a small mosaicity of ∼0.5° full width at half maximum (FWHM), while those of different orientations demonstrated a rather broad mosaicity of ∼2.5° FWHM. We attributed the smaller mosaicity of the epitaxial grains of the same orientation to the reduced interfacial energy due to higher coincidence site density.
Investigation of Hot-Filament and Hollow-Cathode Electron-Beam Techniques for Ion Plating
Authors: Wan C. T. , Chambers D. L. , Carmichael D. C.
Published: July 2002

The ion plating process has been generally limited to low-melting materials in past coating applications. In this study, several electron-beam melting techniques have been investigated which provide methods for melting various high-melting-point materials within a glow discharge atmosphere. The magnetically focused hot-filament and the cold-hollow-cathode electron sources have been experimentally studied to evaluate their operational and evaporation-deposition characteristics for the ion plating process. The hollow-cathode electron source emits an intense electron beam and is capable of delivering very high beam power. The gun is made of high melting-point sheets or screens formed into a hollow cylinder or sphere having an aperture to allow the emittance of electrons. It operates in an inert-gas, glow discharge environment such as that of ion plating. Gas pressure is a key processing variable in controlling the mode of operation; the hot-cathode mode operates at high pressures with excellent stability and the cold-cathode mode operates at low pressure and is sensitive to gas pressure variation. The operational characteristics of conventional hot-filament electron-beam guns are also described for this type of application. Evaporation-deposition parameters and techniques for each type of electron source have been determined using various materials. Type 304 stainless steel, titanium, iron chromium-aluminum-yttrium, and other alloys and metals have been successfully deposited and the coatings evaluated. The uniformity and adhesion of the coatings were experimentally investigated and are reported for various source and process conditions.
Relationship between Substrate Temperature, Structure, and Superconducting Properties of Reactively Sputtered Niobium Nitride Thin Films
Authors: Spitzer Hermann J.
Published: July 2002

Niobium nitride thin films have been reactively sputtered at substrate temperatures of 300 ° and 700 °C. The background pressure was in the low 10−7-Torr range, total sputtering pressure was kept at 2×10−3 Torr and partial pressures of argon and nitrogen were monitored and controlled with a residual gas analyzer. The structure was examined by reflection electron diffraction and Jc-H characteristics were measured using a pulsed field and pulsed current technique. Substrate temperature and Ar/N2 partial-pressure ratio strongly influenced the crystallographic structure which in turn determined the superconducting properties of the films. Consequently, a clear relationship between deposition parameters, particular nitride phases and their mixtures and superconducting properties has been established. The highest Tc of 14.9 K has been observed for a film deposited at 700 °C which exhibited the δ NbN phase.
Plasma cleaning of metal surfaces
Authors: O'Kane D. F. , Mittal K. L.
Published: July 2002

Mild plasma cleaning of metal surfaces was shown to be effective in removing organic contaminants. Auger electron spectroscopy and surface wettability measurements were used to evaluate the plasma cleaning procedure and to provide a comparison with conventional solvent cleaning methods.
X-Ray Lithography: A Complementary Technique to Electron Beam Lithography
Authors: Smith Henry I. , Spears D. L. , Bernacki S. E.
Published: July 2002

X-ray lithography provides a means of replicating, in a single large-area exposure, submicron linewidth patterns made by scanning electron beam lithography. The technique is complementary to existing electron beam technology, and provides a number of unique advantages: (i) it is simple and inexpensive; (ii) the penetrating character of x-rays makes it relatively insensitive to contamination; (iii) both positive and negative type resists can be used; and (iv) because of the absence of backscattering effects, both positive and negative type patterns can be made with equal facility. Exposure times of seven minutes have been achieved for 3 μ mask-sample gaps. This can be decreased to less than one minute by using a rotating anode, or by reducing the mask-sample gap. The most recent results in x-ray lithography are reported, including the fabrication of surface wave devices. The elements of a multiple-mask alignment system are described. This system should permit the rapid and automatic superposition on a substrate of patterns from several different masks, to a precision of 1/10 μ.
Soft x-ray appearance potential spectroscopy
Authors: Park Robert L. , Houston J. E.
Published: July 2002

The total soft x-ray emission of an electron-bombarded surface exhibits abrupt changes at the threshold potentials for the excitation of core levels of surface atoms. These features represent the excitation probabilities of core states superimposed on a smoothly increasing bremsstrahlung background. The threshold potentials can be sensitively detected by differentiating the current from an x-ray photocathode with respect to sample potential. This technique represents the highest resolution core-level spectroscopy available. We discuss the principles underlying the design and operation of soft x-ray appearance potential spectrometers and review their application to the study of surface composition, electron binding energies, chemical shifts, and band structure.
The role of dc self-bias potential in the control of rf sputtering
Authors: Lamont Lawrence T. , Turner Frederick T.
Published: July 2002

For rf, as with dc sputtering, the deposition rate may be uniquely related to the power delivered to the target electrode. The power delivered to the electrode is less than the power delivered by the rf generator by an amount equal to the rf losses in the system. These losses can be substantial and quite variable, even when a good match is indicated at the generator. It is shown that an important source of such losses is seemingly insignificant amounts of series inductance between the matching network and the powered electrode. Deposition rate cannot then, in general, be related reproducibly to the power delivered by the generator. Data are presented which show that, for a given discharge mode, the dc self-bias potential is uniquely related to the power delivered to the electrode and hence to the deposition rate. Implications of this observation as they relate to control of the sputtering process are discussed.
Incorporation and behavior of helium in co-deposited films
Authors: Berg R. S. , Kominiak G. J. , Mattox D. M.
Published: July 2002

Mixtures of normally insoluble helium and gold have been formed by co-deposition using both sputter deposition and e-beam (electron-beam) evaporation in a helium discharge for the purpose of studying the behavior of various amounts of helium in gold. Thin films containing 10–30 at.% helium (inferred) formed by these techniques were examined by transmission electron microscopy. It is shown that for sputter-deposited films on water-cooled substrates the helium is either dispersed atomically or in void nuclei smaller than the resolution of the analytical technique. For e-beam-deposited films and heated, continuous sputter-deposited films, internal voids are found which grow with subsequent heating. It is proposed that the sputter co-deposition technique may be a useful technique for fabricating insoluble gas-metal alloys and that the sputter deposition and evaporation techniques may be useful for stimulating radiation effects of inert gases in reactor materials. An ultraclean vacuum system suitable for recycling discharge gases is described.
Fabrication of quantum point contacts by imprint lithography and transport studies
Authors: Martini Ingo , Kuhn Silke , Kamp Martin , Worschech Lukas , Forchel Alfred , Eisert Dominik , Koeth Johannes , Sijbesma Rint
Published: July 2002

This article demonstrates the integration of imprint lithography into nanoelectronic device fabrication. We present a quantum point contact (QPC) with split gates patterned by imprint lithography. The semiconductor substrate is a modulation-doped GaAs/AlGaAs heterostructure with the two-dimensional electron gas located about 90 nm below the surface. A Si mold with a split-gate pattern is embossed into a poly(methylmethacrylate) film located on top of the semiconductor. The Schottky gates are fabricated by metal evaporation and liftoff. The gate tip separation ranges from 120 to 600 nm. Transport studies performed at T=2 K show conductance quantization with varying gate voltages. Measurements performed on a reference QPC with gates defined by electron beam lithography show similar results. This indicates that the imprint does not affect the electronic performance of the semiconductor.
Control of the radio-frequency wave form at the chuck of an industrial oxide-etch reactor
Authors: Berry Lee , Maynard Helen , Miller Paul , Moore Tony , Pendley Michael , Resta Victoria , Sparks Dennis , Yang Qingyun
Published: July 2002

Radio frequency (rf) power is commonly applied to the chuck of a high-density plasma reactor in order to extract ions and to control the energy of the ions used for the fabrication of microelectronic devices. In many cases, the temporal shape of the rf wave form largely determines the shape of the spectrum of those extracted ions, thereby strongly affecting feature evolution. Using auxiliary rf circuits, we successfully made major changes to the rf-potential wave form at the chuck of an Applied Materials 5300 HDP Omega reactor without affecting the normal functioning of the reactor’s control systems. This work established the practical feasibility of techniques for modifying the ion energy distribution functions of industrial reactors.
Deposition of Fe clusters on Si surfaces
Authors: Upward M. D. , Cotier B. N. , Moriarty P. , Beton P. H. , Baker S. H. , Binns C. , Edmonds K.
Published: July 2002

We have used an ultrahigh vacuum scanning tunneling microscope to investigate the deposition of mesoscopic iron clusters from a gas aggregation source. The size of the clusters was found to be in the range 1–7 nm. The effect of exposure of the iron clusters to the atmosphere results in a significant increase in cluster size, which we believe is consistent with total oxidation of the clusters. A specially designed quadrupole mass filter is incorporated inside the cluster source. We have investigated the sizes of the clusters deposited using different quadrupole settings and find that it is possible to size select the clusters prior to deposition. Finally we have studied the effect of sample surface reactivity and annealing on cluster distribution.
Field emission properties of nanocomposite carbon nitride films
Authors: Alexandrou I. , Baxendale M. , Rupesinghe N. L. , Amaratunga G. A. J. , Kiely C. J.
Published: July 2002

A modified cathodic arc technique has been used to deposit carbon nitride thin films directly on n+ Si substrates. Transmission electron microscopy showed that clusters of fullerene-like nanoparticles are embedded in the deposited material. Field emission in vacuum from as-grown films starts at an electric field strength of 3.8 V/μm. When the films were etched in an HF:NH4F solution for 10 min, the threshold field decreased to 2.6 V/μm. The role of the carbon nanoparticles in the field emission process and the influence of the chemical etching treatment are discussed.
In situ determination of growth rate by pyrometric interferometry during molecular-beam epitaxy: Application to the growth of AlGaN/GaN quantum wells
Authors: Ng H. M. , Chu S. N. G. , Cho A. Y.
Published: July 2002

In this article, we report on the application of pyrometric interferometry to monitor the growth rate of (Al)GaN in situ during molecular-beam epitaxy. Since the growth rate of III-nitrides is very sensitive to the nitrogen flux, it is important to monitor the variation in growth rate from run to run. Using this method, we grew GaN/AlxGa1−xN quantum-well structures with well thicknesses between 10 and 40 Å. The thicknesses of the quantum wells were confirmed by cross-sectional transmission electron microscopy measurements and found to be in good agreement with the corresponding growth rate determined in situ during the growth process.
Pulsed dc magnetron discharge for high-rate sputtering of thin films
Authors: Musil Jindřich , Leština Jan , Vlček Jaroslav , Tölg Tomáš
Published: July 2002

This article analyzes a pulsed magnetron discharge. Main attention is devoted to the specific behavior of the pulsed discharge. The time development of pulsed discharge is composed of three regimes of operation: (1) plasma buildup, (2) stationary plasma, and (3) decaying plasma when the pulse power is off. The duration of individual regimes strongly depends on the pulse length t1, the repetition frequency fr of pulses, the power delivered into the discharge, and the operating pressure. The proportion of duration of the regime of plasma buildup to the regime of stationary plasma in the pulse dramatically influences the I–V characteristics of the pulsed discharge and the deposition rate of sputtered films. The I–V characteristics of an unbalanced round planar magnetron with a Cu target 100 mm in diameter are shown. The deposition rate of Cu films sputtered with the pulsed magnetron is also given.
Surface science with nanosized particles in a carrier gas
Authors: Keller A. , Fierz M. , Siegmann K. , Siegmann H. C. , Filippov A.
Published: July 2002

The dynamics of nanoparticles in a carrier gas are governed by the physical and chemical nature of the surface. The total surface area can be divided into an “active” and a “passive” part. The active surface is the surface on which transfer of momentum, energy, and mass from the gas to the particle takes place. The experiments show that the active surface may be determined in physically very different in situ experiments such as measuring the mobility b, the diffusion constant D, or the mass transfer coefficient K of the particle. The concept of the active surface manifests itself in scaling laws Kb=const, KD=const, and Yb=const, found valid over a large range of particle shapes and sizes. Y is the yield of low energy photoelectrons from the particles upon irradiating the carrier gas with light of energy below the ionization energy of the carrier gas molecules but above the photoelectric threshold of the particles. While K, D and b are independent of the chemical nature of the particles as far as we know today, the simultaneous measurement of Y provides a chemical fingerprint of the particles and allows one to observe, in combination with pulsed lasers as sources of light, the dynamical changes of the active surface while the nanoparticle is interacting with the carrier gas.
Preparation and properties of transparent conductive aluminum-doped zinc oxide thin films by sol–gel process
Authors: Alam M. J. , Cameron D. C.
Published: July 2002

Highly conductive and transparent aluminum-doped zinc oxide thin films have been prepared from the solution of zinc acetate and aluminum nitrate in ethanol by the sol–gel process. The effect of changing the aluminum-to-zinc ratio from 0 to 5 at. % and annealing temperature from 0 °C to 700 °C in air has been investigated. The resistivities of thin films were measured as a function of annealing temperature and also as a function of aluminum dopant concentration in the solution. As-deposited films have high resistivity and high optical transmission. Annealing of the as-deposited films in air leads to a substantial reduction in resistivity. The films have a minimum value of resistivity of 1.5×10−4 Ω cm for 0.8 at. % aluminum-doped zinc oxide and a maximum transmission of about 91% when deposited on glass substrates. X-ray diffraction measurements employing Cu Kα radiation were performed to determine the crystallinity of the ZnO:Al films which showed that the films were polycrystalline with a hexagonal structure when annealed at 500 °C.
Synthesis of carbon nanotubes by chemical vapor deposition for field emitters
Authors: Yoon Young Joon , Baik Hong Koo
Published: July 2002

We synthesized highly aligned carbon nanotubes by thermal decomposition of acetylene gas using metal catalyst island. The alignment technique in this experiment is a very efficient method because it does not require any treatments before and after catalyst metal deposition, and can be achieved directly during the reaction process in the chemical vapor deposition chamber. Alignment of nanotubes was dominated by the uniform diameter and the high density of metal catalysts. In the field emission test, the comparative study progressed with aligned nanotubes and nonaligned nanotubes via the analysis of emission patterns on phosphor screen.
Fluorinated–chlorinated SiO2 films prepared at low temperature by remote plasma-enhanced chemical-vapor deposition using mixtures of SiF4 and SiCl4
Authors: Alonso J. C. , Pichardo E. , Rodrı́guez-Fernandez L. , Cheang-Wong J. C. , Ortiz A.
Published: July 2002

Fluorine-chlorine-doped silicon-dioxide films have been deposited at 200 °C by the remote plasma-enhanced chemical-vapor-deposition technique using SiF4 and SiCl4 as silicon precursors in combination with O2/He/H2 mixtures. The behavior of the deposition rate and structural properties of the films as a function of SiF4 ratio, R=SiF4/(SiF4+SiCl4), was studied for two O2 flow rates by means of ellipsometry, chemical etch rate measurements, and infrared (IR) spectroscopy. Due the higher reactivity of SiCl4 compared with that of SiF4, films deposited with R<0.8 have high deposition rates (400–1410 Å/min), high refractive indices (1.46–1.59), and contain more chlorine than fluorine. On the contrary, films prepared using high SiF4 ratios (R>0.8) are deposited at lower rates (38–400 Å/min), have low refractive indices (1.43–1.46), and contain more fluorine. Etch rate and IR measurements indicate that all fluorinated–chlorinated SiO2 films deposited with an O2 flow rate of 130 sccm do not contain Si–OH or Si–H bonds and are more resistant to being chemically attacked than films deposited with 40 sccm of this gas. In this study, I–V and C–V measurements were used to compare the dielectric properties of stable fluorinated–chlorinated films prepared with an O2 flow rate of 130 sccm and the two highest SiF4 ratios; R=0.9 and R=1. The fluorine content measured by resonant nuclear reactions with the F19(p,αγ)16O nuclear reaction is 2.6 at. % for the film deposited with R=0.9 and 5.9 at. % for that deposited with R=1. The dielectric constants are 3.8 and 3.7, respectively. Although the deposition rate is higher for the former film (190 Å/min) than for the latter (38 sccm), both films have a leakage current density lower than 1×10−7 Å/cm2 and their dielectric breakdown occurs at electric fields higher than 8.2 MV/cm. These results indicate that the use of SiCl4 in combination with SiF4 is a good approximation to prepare and to increase the deposition rate of hydrogen-free fluorinated–chlorinated SiO2 films with low dielectric constants and good electrical integrity.
Defect structure of epitaxial ZnO films on (0001) sapphire studied by transmission electron microscopy
Authors: Lim S.-H. , Shindo D. , Kang H.-B. , Nakamura K.
Published: July 2002

Defects and structural characteristics (threading dislocations and angles of rotational disorder in the subgrain) of wurtzite-type ZnO films grown by electron cyclotron resonance-assisted molecular beam epitaxy on (0001) c-plane sapphire have been investigated extensively using conventional transmission electron microscopy and high-resolution electron microscopy (HREM). Through the cross-sectional and plan-view observations, the existence of threading dislocations in the ZnO film and the basic crystallographic orientation relationship of (0001)ZnO∥(0001)sapphire and [21̄1̄0]ZnO∥[11̄00]sapphire were clarified. The line directions of most threading dislocations were found to be normal to the interface. The density of the threading dislocations in ZnO film was estimated to be 1.9×1011 cm−2 and the subgrains being accompanied by the threading dislocations and Burgers vectors of 1/3〈112̄0〉 were clearly observed. It was found that the size of the subgrains ranges from 15 to 150 nm and the subgrains are rotated by 1°–5° with respect to the ZnO film. The overlapping manner of the ZnO film and the sapphire substrate in the subgrains was discussed taking into account the moiré fringes of HREM images.
Axisymmetrical particle-in-cell/Monte Carlo simulation of narrow gap planar magnetron plasmas. I. Direct current-driven discharge
Authors: Kondo Shuji , Nanbu Kenichi
Published: July 2002

An axisymmetrical particle-in-cell/Monte Carlo simulation is performed for modeling direct current-driven planar magnetron discharge. The axisymmetrical structure of plasma parameters such as plasma density, electric field, and electron and ion energy is examined in detail. The effects of applied voltage and magnetic field strength on the discharge are also clarified. The model apparatus has a narrow target-anode gap of 20 mm to make the computational time manageable. This resulted in the current densities which are very low compared to actual experimental results for a wider target-anode gap. The current–voltage characteristics show a negative slope in contrast with many experimental results. However, this is understandable from Gu and Lieberman’s similarity equation. The negative slope appears to be due to the narrow gap.
Atomic-order thermal nitridation of Si(100) and subsequent growth of Si
Authors: Watanabe T. , Sakuraba M. , Matsuura T. , Murota J.
Published: July 2002

Atomic-order nitridation by NH3 on Si(100) and subsequent Si growth by SiH4 were investigated using an ultraclean low-pressure chemical vapor deposition system with a Xe flash lamp. In thermal nitridation on Si(100), it is found that nitridation occurs even at 260 °C with flash heating, and the N atom concentration tends to saturate to about 2.4×1015 cm−2. In Si deposition on the ultrathin Si nitride, it is found that N desorption from the Si nitride films hardly occurs, and Si grew on Si nitride at 385 °C in an SiH4 environment with and without the flash lamp light irradiation. An incubation period of Si growth is observed and increases with increasing N atom concentration of the Si nitride film. On Si with N atom concentration of about 2×1014 cm−2, the incubation period is hardly observed and the reflection high energy electron diffraction patterns indicates that Si epitaxially grew. Layer-by-layer growth control of Si nitride is proposed by combining atomic-order nitridation on Si and atomic-layer growth of Si on the Si nitride.
Formation of Si–Si bonds and precipitation of Si nanocrystals in vacuum-ultraviolet-irradiated a-SiO2 films
Authors: Akazawa Housei
Published: July 2002

Decomposition of the Si–O–Si bulk network and the composition change in vacuum ultraviolet (hν>100 eV) irradiated SiO2 films have been investigated by spectroscopic ellipsometry and transmission electron microscopy. Real-time monitoring the dielectric function revealed that the irradiated SiO2 film initially evaporates while accumulating Si–Si bonds and that when the evaporation stops, further volume loss is primarily due to the formation of oxygen vacancies. Finally a steady-state composition is reached because the increased valence electrons made available as a result of the formation of Si–Si bonds efficiently quench the electronically excited state. At irradiation temperatures lower than 300 °C, the Si–Si bond units are distributed randomly within the SiO2 matrix. Between 470 °C and 690 °C phase separation of SiOx into Si and SiO2 domains yields Si nanocrystals embedded in the SiO2 matrix. This results in the volume fraction of SiO2 being between 80% and 0%. Above 700 °C, the SiO2 domains disappear, leaving Si crystalline islands at the surface.
Surface states on n-type Al0.24Ga0.76As characterized by deep-level transient spectroscopy
Authors: Choi K. J. , Lee J.-L.
Published: July 2002

Surface states on n-type Al0.24Ga0.76As were studied using capacitance deep-level transient spectroscopy (DLTS). Two types of hole-like traps (labeled as H1 and H2 in this work) were observed in a Al0.24Ga0.76As/In0.22Ga0.78As pseudomorphic high-electron-mobility transistor with a multifinger gate. But, no hole-like traps were observed in the fat field-effect transistor (FATFET) having a negligible ratio of the ungated surface to the total area between the source and the drain. This provides evidence that the hole-like trap peaks in the DLTS spectra originated from surface states at the ungated Al0.24Ga0.76As regions exposed between gate and source/drain electrodes. The activation energies for both surface states were determined to be 0.50±0.03 and 0.81±0.01 eV. The comparison of activation energies of the two surface states with the Schottky barrier height 0.66±0.01 eV suggests that H1 and H2 are deeply related to the Fermi energy pinning levels at the Al0.24Ga0.76As surface.
Growth of HgCdTe for long-wavelength infrared detectors using automated control from spectroscopic ellipsometry measurements
Authors: Phillips Jamie , Edwall Dennis , Lee Don , Arias Jose
Published: July 2002

Hg 1−x Cd x Te is the leading material for high-performance long-wavelength (λ∼10–20 μm) infrared detectors. At these wavelengths, highly accurate compositional control (Δx⩽0.002) is required to achieve a particular device cutoff and the detector’s performance characteristics. Spectroscopic ellipsometry has proven to be a highly accurate technique of measuring the HgCdTe composition during epitaxial growth. Here we present the growth of HgCdTe by molecular beam epitaxy using an automated control program using real-time feedback from spectroscopic ellipsometry measurements. Excellent control is demonstrated for more than 50 growth runs with a standard deviation of Δx=0.0004 observed for the error between the composition measured by ellipsometry and the target growth composition.
Fluorinated amorphous carbon thin films: Analysis of the role of the plasma source frequency on the structural and optical properties
Authors: Valentini L. , Braca E. , Kenny J. M. , Lozzi L. , Santucci S.
Published: July 2002

Different types of fluorinated amorphous carbon (a-C:H:F) thin films were grown by CH4/CF4/Ar mixtures using a 13.56 MHz radio frequency (rf) and a 13.56 MHz rf −2.45 GHz microwave hybrid plasma source. The optical properties of films were carried out by ellipsometric measurement, while x-ray photoelectron spectroscopy (XPS) and Raman spectroscopy were exploited to study their structural and vibrational properties. XPS spectra showed that the fluorine incorporation increased with the CF4 partial pressure while fluorine-poorer films were deposited with the rf-microwave hybrid technique. Raman measurements also suggested that with increasing fluorine content, the film microstructure changed from diamond-like to polymer-like. The mechanism of the a-C:H:F refractive index dependency on the plasma source frequency is investigated in terms of the amount of fluorine incorporation in the films produced.