bluuebunny/crossref_metadata_2025 huggingface dataset:
An Extended Pattern Search Algorithm for Three-Dimensional Component Layout
Authors: Yin Su , Cagan Jonathan
Published: July 2002

An extended pattern search algorithm is introduced for efficient component layout optimization. The algorithm is applicable to general layout problems, where component geometry can be arbitrary, design goals can be multiple and spatial constraint satisfactions can be of different types. Extensions to pattern search are introduced to help the algorithm to converge to optimal solutions by escaping inferior local minima. The performance on all of the test problems shows that the algorithm runs one-to-two orders of magnitude faster than a robust simulated annealing-based algorithm for results with the same quality. The algorithm is further extended to solve a concurrent layout and routing problem, which demonstrates the ability of the algorithm to apply new pattern strategies in search and to include different objective functions in optimization. [S1050-0472(00)01901-2]
Ship Capsize Risk in a Seaway Using Fitted Distributions to Roll
Maxima
Authors: McTaggart Kevin A.
Published: July 2002

This paper presents an efficient method for determining capsize risk for a given seaway and ship operational condition using time domain simulations. The risk of capsize during 1 h exposure to a given seaway is dependent on the wave process realization, which is determined by a seed number and resulting random wave phases. The dependence of maximum roll angle on wave process can be modeled by fitting a suitable distribution to maximum roll angles from a moderate number of simulations. Sample computations for a naval frigate demonstrate that a Gumbel distribution provides a very good fit to maximum roll angles from different wave realizations. [S0892-7219(00)00402-7]
A Self-Calibration Method for Robotic Measurement System
Authors: Gong Chunhe , Yuan Jingxia , Ni Jun
Published: July 2002

Robot calibration plays an increasingly important role in manufacturing. For robot calibration on the manufacturing floor, it is desirable that the calibration technique be easy and convenient to implement. This paper presents a new self-calibration method to calibrate and compensate for robot system kinematic errors. Compared with the traditional calibration methods, this calibration method has several unique features. First, it is not necessary to apply an external measurement system to measure the robot end-effector position for the purpose of kinematic identification since the robot measurement system has a sensor as its integral part. Second, this self-calibration is based on distance measurement rather than absolute position measurement for kinematic identification; therefore the calibration of the transformation from the world coordinate system to the robot base coordinate system, known as base calibration, is not necessary. These features not only greatly facilitate the robot system calibration, but also shorten the error propagation chain, therefore, increase the accuracy of parameter estimation. An integrated calibration system is designed to validate the effectiveness of this calibration method. Experimental results show that after calibration there is a significant improvement of robot accuracy over a typical robot workspace. [S1087-1357(00)01301-0]
The Origin of Turbulent Spots
Authors: Johnson M. W. , Dris A.
Published: July 2002

It has been suggested that a turbulent spot is formed when a transient separation occurs in the laminar boundary layer and this criterion has been successfully used by Johnson and Ercan (1996, ASME Paper No. 96-GT-44; 1997, ASME Paper No. 97-GT-475) to predict bypass transition for boundary layers subjected to a wide range of free-stream turbulence levels and streamwise pressure gradients. In the current paper experimental results are presented that support the premise that the formation of turbulent spots is associated with transient separation. Near-wall hot-wire signals in laminar and transitional boundary layers are analyzed statistically to produce probability distributions for signal level and trough frequency. In the laminar period the signal level is normally distributed, but during the inter-turbulent periods in the transitional boundary layer, the distribution is truncated at the lower end, i.e., the lowest velocity periods in the signal disappear, suggesting that these are replaced during transition by the turbulent periods. The number of these events (troughs) also correlates with the number of turbulent spots during early transition. A linear perturbation theory is also used in the paper to compute the streamlines through a turbulent spot and its associated calmed region. The results indicate that a hairpin vortex dominates the flow and entrains a low-momentum fluid stream from upstream with a high-momentum stream from downstream and then ejects the combined stream into the turbulent spot. The hairpin can only exist if a local separation occurs beneath its nose and the current results suggest that this separation is induced when the instantaneous velocity in the near-wall signal drops below 50 percent of the mean. [S0889-504X(00)01001-1]
Evaluation of the Integrity of PWR Bimetallic Welds
Authors: Devaux Josette , Mottet Ge´rard , Bergheau Jean-Michel , Bhandari Surender K. , Faidy Claude
Published: July 2002

This paper presents the state of the art and the progress made in the numerical simulation of the stress state in a complex multi-material structure, using not only sophisticated finite element tools, but also the simplified engineering methods. A comparison of the numerical results concerning residual stresses is made with those measured using X-ray diffraction method and incremental hole-drilling technique. Finally, an example is given on the analysis of a fully circumferential crack in a typical bimetallic weld under pressure, thermal, and residual stresses. [S0094-9930(00)00703-4]
Recent Advances in Acoustic Microscopy for Nondestructive Evaluation
Authors: Miyasaka C. , Tittmann B. R.
Published: July 2002

Driven by new demands from industry, the field of acoustic imaging is rapidly evolving new approaches to meet the demands. The current trend toward micro and nano-technology has been pushing the operating frequency of scanning acoustic microscopes (SAM), from MHz to GHz. To become a useful tool for nondestructive evaluation (NDE), the SAM must give high resolution and also maintain reasonable depth of field below the sample surface, while overcoming the effects of surface roughness. A recent trend of needs for the SAM is to enhance resolution for detecting defects (e.g., microcracks, inclusions, debondings, delaminations), and develop a capability and an accuracy for obtaining quantitative data (e.g., velocities of waves, attenuation) for measuring residual stress, anisotropy, thickness of thin films, or the like. Furthermore, the SAM is to be modified to use in various environments. In this paper, a principle and some applications for both a practical shear wave lens and a noncontact lens will be summarized. [S0094-9930(00)02503-8]
Damping Effect of Winding on the Lateral Vibrations of Axially Moving Tapes
Authors: Garziera B. , Amabili M.
Published: July 2002

The lateral vibrations of winding tapes are investigated by using a second order linear model, where lateral indicates the direction parallel to the reel rotation axis. A boundary condition describing the winding of tapes on the reel considering a perfect reel-tape adhesion is applied. This condition imposes zero lateral velocity of the string as measured by a fixed observer and has a significant damping effect on the lateral vibrations. Both natural and forced vibrations are investigated. A boundary excitation is assumed in the forced vibration analysis. Numerical results show the effect of the parameters on the system dynamics. The present model is applicable to a class of tapes travelling in manufacturing machines. [S0739-3717(00)00901-6]
Experimental Application of Feedback Control to Localize Vibration
Authors: Shelley F. J. , Clark W. W.
Published: July 2002

The purpose of this study is to apply feedback control to a physical system in order to localize structural vibration. This is accomplished using an eigenstructure placement technique called eigenvector scaling. Active eigenvector scaling mimics one of the properties of passive mode localization, namely the confinement of vibrational energy, by re-forming or scaling portions of all the system mode shapes. This produces areas of localization, with relatively large amplitudes and high vibrational energy levels, and areas of isolation, with relatively small amplitudes and little vibrational energy. Because all mode shapes are scaled in the same fashion, the system response reflects this vibration confinement regardless of the type of disturbance input. In this paper, the above statements are supported using control law development and analysis as well as experimental application and numerical simulations. [S0739-3717(00)70402-8]
Characterization of Ni2O3⋅6H2O by XPS
Authors: Mansour A. N. , Melendres C. A.
Published: July 2002

We report x-ray photoemission spectra (XPS) of hydrated nickelic oxide (Ni2O3⋅6H2O). 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 Ni2O3⋅6H2O sample was obtained commercially from Alfa. Our XPS results show that the near surface region consists of a large proportion of Ni(OH)2. In addition, the sample contains Na and Cl in small quantities. The presence of Na and Cl is probably an artifact of sample preparation procedures.
Palladium Oxide (PdO) by XPS
Authors: Militello Maria C. , Simko Steven J.
Published: July 2002

X-ray photoelectron spectroscopy (XPS) spectra of palladium oxide (PdO) are presented. Clean, ground PdO powder was pressed into In foil and analyzed with a Surface Science Instruments SSX-101 M-Probe ESCA instrument using monochromatized Al Kα x rays. Spectra include a survey scan, the Pd 3d, 3p, 3s, 4s, 4p regions, the O 1s, and valence band regions, and the O KLL, Pd MNN and MNV Auger transitions.
Epitaxially Grown Fe3O4 Thin Films: An XPS Study
Authors: Anderson J. F. , Kuhn Markus , Diebold Ulrike
Published: July 2002

Magnetite is a technologically important material with interesting magnetic and electronic properties. The applications of this oxide include, but are not limited to, magnetic storage media, as a catalyst in the plastics industry, electronic circuit applications, and may have important future applications in the micro-electronics industry as well. Since the transition between different iron oxide phases can be easily achieved, characterization of well-defined materials with XPS is quite important. We report XPS measurements of a 1 μm thick Fe3O4 thin film on a MgO(001) substrate. The film was grown using plasma-assisted MBE, and was characterized in situ with RHEED which indicated a well ordered surface. A companion sample was characterized ex situ with XRD and SQUID which showed it to be single-crystalline, stoichiometric Fe3O3. The sample was transported under argon atmosphere and introduced into the XPS chamber under flowing nitrogen. The sample was then cleaned by annealing in a 2 × 10−6 oxygen at 620 K until XPS indicated no carbon present. The x-ray source is a non-monochromated Al Kα and Mg Kα, and the resulting spectra were analyized using a cylindrical sectional analyzer (CSA) with entrance lens (Omicron Vakuumphysic Ges.m.b.H). Survey scans, Fe 2p, and O 1s transitions are presented.
Aluminum Metaphosphate (Al(PO3)3) by XPS
Authors: Rotole John A. , Sherwood Peter M. A.
Published: July 2002

The XPS spectra of aluminum metaphosphate were collected with a VSW HA150 using monochromatic Al Kα x-radiation. Monochromatic radiation provides a distinct clarity to the rich peak structure in the valence band of aluminum metaphosphate due to the absence of interfering x-ray satellites from the intense O 2s region. The valence band, survey, and the Al 2s, Al 2p, O 1s, and C 1s core levels are reported. The valence band region of metaphosphate is significantly different from that of phosphate.
Influence of Oxygen on the B 1s and La 3d Line Shapes of a Lanthanum Hexaboride (100) Surface
Authors: Perkins C. L. , Singh R. , Trenary M. , Tanaka T. , Otani S.
Published: July 2002

X-ray photoelectron spectroscopy was used to investigate the initial stages of adsorption on the (100) surface of a single crystal of lanthanum hexaboride. Numerous previous studies had not resolved the issue of whether oxygen adsorbs at lanthanum sites, boron sites, or both. We find that oxygen adsorption produces new peaks in the La 3d region, whereas the B 1s peak is unaffected. The La 3d3/2 peak at a binding energy of 854.8 eV on the clean surface splits into two components at 855.2 and 852.1 eV after a 10 L O2 exposure at room temperature. Annealing the surface to 600 °C and then to 700 °C produces sharp c(2 × 2) and p(2 × 1) LEED patterns, respectively. The La 3d peaks still show two components for both LEED patterns indicating oxygen bonding to La in both oxygen overlayer structures whereas the B 1s region remains unaffected. Thus while the XPS data clearly reveal oxygen adsorption at La sites, there is no indication of adsorption at boron sites for low O2 exposures. More extensive oxidation at higher temperatures shows formation of both boron and lanthanum oxides.
Molecular beam epitaxy system at an undergraduate institution
Authors: Celinski Z.
Published: July 2002

We describe a relatively inexpensive molecular beam epitaxy system built at our undergraduate institution to study novel magnetic structures. The system consists of two main chambers, growth and analysis, a sophisticated manipulator, and a loadlock chamber. It is pumped by a series of ion pumps (400, 140, 60, and 2 l/s), a cryopump, and a turbomolecular pump system that reach basic pressure of 10−10 Torr. The 8 ports for K cells, surrounded by a nitrogen cryoshroud, and a multipocket e-gun allow us to evaporate 12 different materials onto a substrate 1 in. in diameter. The system is equipped with a series of analytical techniques, such as reflection high energy electron diffraction (RHEED), low energy electron diffraction, and Auger electron spectroscopy (AES). The total cost of our system is $160,000, excluding the RHEED gun, AES system, and about $50,000 worth of used parts that were available in our department.
Laterally graded multilayers and their applications
Authors: Liu Chian , Macrander A. , Als-Nielsen J. , Zhang K.
Published: July 2002

Laterally graded multilayers consisting of uniform W layers and wedge-shaped C layers have been made at the Advanced Photon Source deposition lab for tunable x-ray double-monochromator applications. The double monochromator has two identical graded multilayers in series, as in the conventional double-crystal monochromator arrangement. By letting the x-ray beam hit slightly different (bilayer) d spacing on each multilayer, one can adjust the bandpass and peak energy of the transmitted beam. Also, since the Bragg angles of the two multilayers are not constrained to be the same, the angle of the transmitted beam can be varied in the vertical plane. This option may be an attractive alternative to the conventional way of studying liquid surfaces in reflectivity and grazing-incidence diffraction measurements. The graded multilayer comprised 60 bilayers of W and C on 100×25×3 mm float glass with a d spacing varying from 35 to 60 Å and an average gradient of 0.27 Å/mm in the long direction. The films were made by dc magnetron sputtering with the sputtered atoms passing a contoured mask while the substrate was moving. Two different masks were designed to produce either a uniform (for W) or graded (for C) thickness profile. The multilayer and graded multilayers have many other novel applications. Potential applications in x-ray fluorescence detection and x-ray standing wave experiments will be discussed.
Structural and optical properties of thin lead oxide films produced by reactive direct current magnetron sputtering
Authors: Venkataraj S. , Geurts Jean , Weis Hansjörg , Kappertz Oliver , Njoroge Walter K. , Jayavel R. , Wuttig Matthias
Published: July 2002

The structural and optical properties of thin lead oxide films were studied. Thin films were prepared by reactive dc magnetron sputtering of lead (Pb) targets in an Ar/O2 mixture. The structure has been determined by x-ray diffraction measurements, which show that crystalline lead oxide films of different composition (PbO, PbO1.44, Pb2O3, and PbO2) have been formed upon increasing oxygen flow (partial pressure). This result is confirmed by Raman spectroscopy. The effect of postdeposition annealing on the structural properties of PbO films reveals that the film structure is governed by both energetics and kinetics. X-ray reflectivity measurements were used to determine the thickness, density, and roughness of the films. The calculated film density values are almost equal to the bulk density of the material, showing that compact, nearly void free films are formed. The optical properties of the films have been studied from the reflectance and transmittance spectra recorded by optical spectroscopy measurements from 10 000 (1.24 eV) to 50 000 (6.21 eV) cm−1. From these data we have determined optical properties such as the dielectric function, the optical band gap Eg and the refractive index n as well as the film thickness.
Characterization of fluoropolymers for 157 nm chemically amplified resist
Authors: Itani Toshiro , Toriumi Minoru , Naito Takuya , Ishikawa Seiichi , Miyoshi Seiro , Yamazaki Tamio , Watanabe Manabu
Published: July 2002

Fluoropolymers were characterized for 157 nm lithography resist. We obtained superior optical transparencies, with absorption coefficient of 0.01–2 μm−1 at 157 nm wavelength. The resists based on the fluoropolymers characterized exhibited suitable dissolution behavior into alkaline developer of 0.26 N tetramethylammonium hydroxide solution. Dry-etching resistance of the resist film showed the almost equivalent to conventional ArF resist based on an acrylic polymer. The lithographic evaluation showed that high sensitivities of 1.0–10.0 mJ/cm2 for 157 nm exposure, and high dissolution contrast. Furthermore, the resolution capability of 95 nm lines and spaces was obtained with proper pattern profiles. These results indicate that 157 nm resist based on fluoropolymers we characterized have enough potential for practical use of 157 nm lithography.
Effect of substrate–film lattice mismatch in La0.7Ba0.3MnO3−δ thin films for transport properties
Authors: Hayashi K. , Ohta E. , Wada H.
Published: July 2002

In this study, we explore the use of La0.7Ba0.3MnO3−δ (LBMO) for use in uncooled infrared bolometers. To obtain a high temperature coefficient of resistance (TCR) (defined as 1/R dR/dT) at near-room temperature, thin films were deposited on SrTiO3 (100), LaAlO3 (100) and MgO (100) substrates by a laser ablation method. The substrate–film lattice mismatch between these substrates and LBMO films caused misfit stress which changed the surface structure of the films and influenced their temperature dependence of resistivity. The microstructures of films were characterized by x-ray diffraction and atomic force microscope. As a result, the LBMO film deposited on SrTiO3 (the LBMO/STO film) had crystallinity like LBMO bulk and showed high orientation of the substrate. And its temperature dependence of resistivity agreed with LBMO bulk. Near 300 K the LBMO/STO film showed high TCR values, about 4%/K. In addition, the TCR values of the LBMO/STO films were over 2%/K over a wide temperature range centered near 300 K. These results suggest that LBMO/STO films are possible for use as an uncooled infrared bolometer material.
Importance of fluorine surface diffusion for plasma etching of silicon
Authors: Verdonck P. , Goodyear A. , Mansano R. D. , Barroy P. R. J. , St. J. Braithwaite N.
Published: July 2002

Dry etching of silicon is an important process in the manufacturing of integrated circuits and micromachined devices. Traditionally, the etch rate limiting step for an isotropic silicon etching process is considered to be the arrival of fluorine atoms directly from the gas phase onto the silicon surface, and the mechanism to promote anisotropy is the prevention of lateral etching by the formation of an inhibiting layer on the vertical walls. Furthermore, isotropic dry etching is considered to etch features in the same way as isotropic wet etching. Conventional mechanisms cannot explain, however, the perfect anisotropic etching of silicon with pure SF6, when no polymer is formed. Neither can it be understood how a deep (>50 μm), isotropic, dry etching process applied to silicon can result in structures with a pinched neck and sharp ridges, in contrast with a wet etching process, where the corners are rounded and no pinching of the neck is observed. It is proposed that long-range diffusion of fluorine atoms can precede the eventual binding to a silicon atom. The rate of binding increases if the silicon is bombarded with high energy ions. Tests were performed to corroborate this model which is also consistent with the findings of others.
Nucleation and Initial Growth of Single-Crystal Films
Authors: Adamsky Robert F. , LeBlanc Robert E.
Published: July 2002

The mechanism of epitaxial growth has been investigated by the study of the nucleation process and early growth stages of single-crystal gold and silver films in (100) and (111) orientations. Films were grown by evaporation on vacuum-cleaved NaCl and mica cleavage planes, and on single-crystal NaCl films deposited on fresh mica cleavage surfaces. In the earliest observable period of growth, nuclei have been found to be as small as 5 Å in size. These nuclei, which contain 10–20 atoms, strongly indicate that growth proceeds continuously from initial nuclei consisting of only a few atoms. In subsequent stages of growth, coalescence processes occur which are governed by mobility of atoms and clusters on the substrate material. Mobility is highest on the evaporated film substrates, and leads to a decrease in nucleation density as a function of time because of rapid coalescence of the mobile nuclei. Nucleation rates have been measured as a function of substrate temperature and activation energies determined for the nucleation process.
Effects of accumulated film layers on the accuracy of quartz film thickness monitors
Authors: Heyman J. S. , Miller W. E.
Published: July 2002

The effect of accumulation layers on the accuracy of quartz thin-film thickness monitors is evaluated. Use of an expanded plane wave ultrasonic propagation theory correctly accounts for observed experimental data. The magnitude of the maximum errors calculated for simply reversing the order of a series of aluminum gold deposits is on the order of 5%. If one totally neglects intervening layers, multiple film propagation and nonlinearity can produce errors greater than 50%.
Performance of a cryopump–ion pump system
Authors: de Rijke J. E.
Published: July 2002

In a cryopump, hydrogen is pumped through cryosorption using solid sorbents. At temperatures at which the pump operates, the vapor pressure of hydrogen exceeds the pressure that has to be obtained. The cryopump therefore, has a limited capacity for hydrogen. The capacity, and the pumping speed, will be dependent on the pressure at which the system operates and on the comtamination of the sorbent. The speed of a cryopump for hydrogen has been measured as a function of pressure in the range between 10−4 and 10−8 Torr(10−3–10−6 Pa). Also the speeds for nitrogen and argon have been measured. Gauge constants for the various gases were used to obtain ’’true’’ pressures for each gas type. To determine the dependence of system performance on sorbent contamination, the speed for hydrogen has been measured as a function of the number of times the system has been cycled from atmosphere. To augment the performance of the cryopump–ion pumps have been used. Speed performance as a function of system pressure and as a function of the number of times the system has been cycled, is compared to the use of a cryopump alone.
Combination analysis of metal oxides using ESCA, AES, and SIMS
Authors: Conner G. R.
Published: July 2002

Combination ESCA, AES, and SIMS analyses have been conducted on high purity metal foils of Fe, Ni, Cr, and Mo to investigate oxides formed on sputter-cleaned surfaces. Results are given for the controlled oxidation of Fe and Ni metals and the rapid sequential analysis by the three techniques. Oxygen signals from the three methods are shown to have identical dependence on oxygen dosage during the initial stages of oxidation for these two metal-oxygen systems. ESCA and SIMS results of both systems are in agreement with divalent oxide formation at oxygen dosages up to 60 L for Fe and 50 L for Ni. Preliminary results for Cr-O and Mo-O systems are also reported.
Technology of ion beam sources used in sputtering
Authors: Kaufman Harold R.
Published: July 2002

The technology of broad-beam ion sources is reviewed from the viewpoint of the sputtering–deposition user. This review includes a short description of the development of discharge chambers, accelerator systems, and cathodes; the present alternatives for these components and the expected future improvements.
Intermolecular forces and kinetics of adsorption into a c (2×2) overlayer on (100) surface: H2S, C2H2, and C2H4 on Pt(100)
Authors: Fischer T. E. , Kelemen S. R.
Published: July 2002

Pt(100) surfaces, either in the 1×1 or the 5×20 structure, held at various temperatures were exposed to H2S, acetylene or ethylene gas in the 10−5 Pa (10−7 Torr) pressure range and the surface coverage ϑ was determined from the size of the C or S Auger signal as a function of exposure to the gas ε=ℱpdt. Asymptotic saturation, ϑ=1 in the case o9f acetylene, was measured to correspond to 1 molecule/2 Pt surface atoms. Coadsorption measurements and LEED measurements justify the use of the same molecule density for ϑ=1 in the case of ethylene adsorption. All adsorbates formed a variously developed C (2×2) superstructure. The adsorption of acetylene and dissociation of H2S followed the Langmuir isotherm ϑ=1−exp(Sε) or dϑ/dE=S(1−ϑ). When the surfaces are exposed to ethylene, the adsorbed species in C2Hx, where the value of x depends on experimental condition. Exposure to ethylene yields the adsorption kinetics (1=ϑ) =constxε−1/3, or dϑ/dε=S(1−ϑ)4. We show that the adsorption kinetics of ethylene is a simple consequence of the c (2×2) overlayer formed by the absorbate and interpret the coexistence of Langmuir kinetics and a c (2×2) structure of the adsorbate layer in terms of the interlay of attraction to the surface and repulsion for adsorbed molecules.
LEED–Auger study of the (11̄0) surface of a 1% Si–Fe single crystal
Authors: Viljoen P. E. , Roux J. P. , Boonstra E. G.
Published: July 2002

An optimal procedure involving ion bombardment at elevated temperatures for surface cleaning is described. The observed LEED pattern basically consists of the ideal (11̄0) surface of a bcc structure together with extra spots indicating additional periodicity in the 〈001〉 direction. A possible explanation is proposed. Intensity profiles for different beams and their temperature dependence are discussed. An effective surface Debye temperature of 300 K and a predicted bulk value of about 420 K are deduced. Annealing at temperatures above 780° C leads to diffusion of sulfur atoms from the bulk and to ordering on the surface. The resulting LEED pattern is described in terms of a rationally related lattice with a unit net [(16/3)1/2× (8/3)1/2] with respect to the basic (11̄0) -surface p lattice of a bcc crystal.
Thermal noise in balances and its significance for physical measurements
Authors: Poulis J. A. , Hooge F. N.
Published: July 2002

The fundamental limits to the accuracy of automated balances are discussed in connection with application of those balances. The applications concerned are manometers, magnetic susceptibility measurements, measurements of the De Haas–Einstein effect, and measurements of gravitational constant. In the last three applications the fundamental thermal noise accompanying the use of the balance is shown to be the limiting factor.
MBE-grown insulating oxide films on GaAs
Authors: Ploog K. , Fischer A. , Trommer R. , Hirose M.
Published: July 2002

The technique of molecular beam epitaxy (MBE) has been used to grow two types of insulating oxide films on the surface of GaAs active layers; (i) a native oxide and (ii) an amorphous aluminium oxide, respectively. Native oxides on (100) GaAs obtained by thermal oxidation at 400°C under MBE conditions were found to be suitable for masking purposes and pattern generation because of their favorable mechanical and interface properties. Insulating amorphous aluminium oxide films were grown by molecular beam reaction on an intermediate AlxGa1−xAs layer, in order to preserve the stoichiometry of the GaAs active layer surface. The initial measurements on Al/Al2O3/Al0.35Ga0.65As/GaAs MOS capacitors have shown that favorable mechanical and insulating behavior can be obtained with Al2O3 layers grown at low temperatures and that the properties are sufficiently promising to investigate the MOS device potential of these Al2O3/AlxGa1−xAs/GaAs heterostructures.
Optical properties of reactively sputtered Ta2O5 films
Authors: Rubio F. , Albella J. M. , Denis J. , Martinez-Duart J. M.
Published: July 2002

The optical properties of reactively sputtered Ta2O5 thin films are investigated in the 0.25–2.5 μm wavelength range. The dispersion curves for the refraction and absorption indices are obtained from the reflectance and transmittance spectra. From the absorption data, one electronic transition at 4.07 eV and another about 4.5 eV are obtained. Finally, the optical transitions in Ta2O5 are discussed.
Extended-fine-structure analysis of oxygen on titanium
Authors: Morar John F. , Park Robert L.
Published: July 2002

Problems with overlapping extended fine structure inhibit the study of many interesting adsorbate systems, including oxygen, on nearly all of the transition metals. Using conventional techniques, the proximity of the titanium 2p levels at 455 eV and the oxygen 1s level at 535 eV produces a spectrum in which the fine structure above the Ti 2p overlaps fine structure above the oxygen 1s, rendering analysis of the fine structure above either unreliable. In contrast, the Auger-monitored extended-fine-structure (AMEFS) technique monitors excitation of each core level individually, therefore providing separate spectra of the extended fine structure above the Ti 2p3/2 and the oxygen 1s levels. In AMEFS, detection of core excitations is accomplished with a standard single-pass cylindrical mirror analyzer tuned to the Auger transition energy. Core excitations are produced with incident electrons provided by the CMA’s integral electron gun. The only modification to the standard commercially available equipment was in the electronics.
Development of a coating technique for inertial confinement fusion plastic targets
Authors: Kubo Uichi , Tsubakihara Hiroshi
Published: July 2002

Deuterated polystyrene as a target material offers several advantages over other polymers because of the following: (1) it is chemically and physically stable at ordinary conditions, (2) it can be easily formed into spherical shells, and (3) it has a very high fraction of D2/H2 (above ∼99%). As in our previous studies, the fabrication method was basically a utilization of the emulsion technique. This method is well suited to mass-producing the polymer targets without microprocessing techniques. We have developed a fabrication method for single shell targets and an extension of this technique also enables us to fabricate double shell targets. This new method is faster and less labor intensive than previous techniques. The development of ICF experiments requires multilayer structure targets; we have developed, moreover, a new fabrication technique called the multicoating method. The polymer coating can be fabricated by the application of an emulsion technique. On the other hand, with metal coating, a nonelectroplating method was used, and nickel was employed as the coating metal. The thickness of the polymer coating layer can be controlled with the rotational speed of a stirrer in the emulsion. In the case of nickel coating, it is achieved by controlling the plating bath temperature and immersion time during the plating process. The experiment resulted in the development of a new technique for the fabrication of multilayer targets and low density, thick polymer-layer-coated targets.
Real-time study of self-sustained oscillations in the CO oxidation rate on Pt
Authors: Burrows V. A. , Sundaresan S. , Chabal Y. J.
Published: July 2002

The driving mechanism for self-sustained oscillations in the rate of some catalytic oxidations under steady-state conditions has remained unexplained despite numerous theoretical and experimental studies since the early 1970s. We have used reflection–absorption infrared spectroscopy to perform the first real-time analysis of a Pt foil surface during constant temperature oscillations in CO oxidation. The CO absorption capacity of the surface is shown to vary periodically during oscillations. Inverse correlation of the CO adsorption capacity with surface carbon concentration (measured with Auger spectroscopy), and demonstration that (1) carbon can diffuse from the bulk to the surface, (2) oxygen can remove surface carbon from the surface, and (3) CO can block carbon diffusion, all at oscillation temperatures, indicate that variation in surface carbon concentration may be driving the oscillations. Modeling of the phenomenon is found to account for all observations.
Development of a direct current reactively sputtered black chromium oxide coating for use in a high-resolution color cathode-ray tube application
Authors: Kulkarni Sudhakar , Miller Paul , Wagner Michael
Published: July 2002

A dc reactive sputtering technique was developed to deposit 4 kÅ of CrOx followed by 1 kÅ of Cr onto a glass substrate. Optimized deposition parameters produce a CrOx film with minimum reflectance and transmission through the glass and at the same time avoid discoloration (other than black). An electron spectroscopy for chemical analysis of the CrOx film suggested that the bulk of the oxide was CrO2. To achieve an acceptable quality of etching to form a black matrix, a lower chromium-to-oxygen ratio at the interface of the film and substrate was employed. The appearance of discolored oxide film was quantified by calculating chromaticity and using the Commission Internationale de l’Eclariage
Inelastic background removal in x-ray excited photoelectron spectra from homogeneous and inhomogeneous solids
Authors: Tougaard S.
Published: July 2002

We investigate formulas for the deconvolution of inelastic background signal from measured electron spectra of both homogeneous and inhomogeneous solids. It is found that for noble metals ∼ (1)/(3) of the measured intensity 10–30 eV below a peak energy is intrinsic in origin. A new formula valid for the situation where electron emitters are located at a certain depth x0 underneath the sample surface is found. All formulas require a detailed knowledge of the differential inelastic electron scattering cross section K(E,T) for an electron of energy E to lose energy T. Attention is paid to recent progress in ways of determining K(E,T). In particular, it is found that for noble and transition metals K(E,T) is sufficiently similar, that it makes sense to approximate K(E,T) by a universal function. Then for this class of metals, as well as for inhomogeneous alloys within the class, a very simple and fast procedure for background removal in electron spectra can be defined. Finally, examples of the use of the deconvolution formulas are given and the limits of validity discussed.
High spatial resolution secondary ion mass spectrometry with parallel detection system
Authors: Nihei Y. , Satoh H. , Tatsuzawa S. , Owari M. , Ataka M. , Aihara R. , Azuma K. , Kammei Y.
Published: July 2002

High-resolution secondary ion mass spectrometry is constructed by combining focused liquid metal ion beam and simultaneous detection mass spectrometer. A beam diameter on the sample is estimated to be less than 0.1 μm with the current of 100 pA, when the accelerating voltage is 35 kV. The detector is composed of a microchannel plate, and a multianode–multiamplifier–multicounter system controlled by a personal computer. The prototype multichannel detector covers the 1:2 mass range of m/e dispersion with a 120-channel parallel counting system. By using a multichannel parallel detection scheme, a spectral data acquisition rate several tens of times larger than that of the single-channel scheme was achieved. An ion-induced secondary electron image, a total secondary ion image, and mass-analyzed ion images (element maps) were obtained. In the individual analysis of a small particle, rapid and distinctive intensity changes for multiple elements were observed. This indicates that our detecting system is suitable for the accurate analysis of small-volume samples.
X-ray photoelectron spectroscopic comparison of sputtered Ti, Ti6Al4V, and passivated bulk metals for use in cell culture techniques
Authors: Sodhi R. N. S. , Weninger A. , Davies J. E. , Sreenivas K.
Published: July 2002

In view of the reported differences in biological bone tissue reactions to Ti and Ti6Al4V the aim of the work described herein was to establish whether direct-current magnetron sputtered films would be realistic models of these materials which could then be used for in vitro studies of bone cell behavior. X-ray photoelectron spectroscopy (XPS) was used to compare the surface chemistries of bulk-passivated metals and the sputtered films. In the bulk passivated samples the predominant Ti oxide phase was 4+. However, Ti in its lower oxidation states was evident though closer to the bulk–oxide interface as seen by angle-resolved XPS. The Al content of the passivated alloy oxide film was seen to be greatly enhanced (26 wt. %) over that of the stoichiometric alloy while V was reduced (1 wt. %). The surfaces of the sputtered films were very similar to their bulk passivated counterparts. Although there was indication that the distribution of the various Ti oxide phases within the film differed to that in the passivated oxide layer, it was concluded that the sputtered films may be developed as realistic substrata to model bone cell reactions to bulk passivated metals.
High orientation CdS thin films grown by pulsed laser and thermal evaporation
Authors: Dai C. M. , Horng L. , Hsieh W. F. , Shih Y. T. , Tsai C. T. , Chuu D. S.
Published: July 2002

Undoped CdS films have been grown by pulsed laser evaporation (PLE) and thermal evaporation (TE) techniques on Corning’s 7059 glass at a substrate temperature between room temperature and 250 °C. The deposition rates are 0.07 Å/s for PLE and 60 Å/s for the TE technique. These as-deposited films have high (002) preferred orientation by both techniques even without preheating the substrate. However, films deposited by PLE have more preferred orientation and larger grain size. These features make the PLE films have sharper Raman peaks, smaller Raman shift of surface mode and more overtones of longitudinal optical phonon mode observed than those in TE films. The transparency of PLE or TE films for wavelengths which are larger than that of absorption edge is around 90% on average.
Schottky barrier height control at epitaxial NiAl/GaAs(001) interfaces by means of variable band gap interlayers
Authors: Chambers Scott A.
Published: July 2002

This article discusses recent developments in the use of semiconducting interlayers to tailor the Schottky barrier height (SBH) at a metal/GaAs interface. We have used AlAs, GaSexAs1−x, n++-Ge, and n++-Si interlayers between n- and p-GaAs(001) substrates and epitaxial NiAl metallic overlayers to see if a variable SBH is achievable. The interlayers were grown by molecular beam epitaxy and metal organic chemical vapor deposition, while the NiAl overlayers were grown by molecular beam epitaxy. X-ray photoelectron spectroscopy was used to follow the chemistry of interface formation, as well as band offsets and SBH values. Low-energy electron diffraction and x-ray photoelectron diffraction were used to determine structural properties of both the interlayer and overlayer. It was found that thermally stable SBH values ranging from ∼0.5 eV for n++-Si interlayers to ∼1.2 eV for AlAs interlayers are readily achievable on n-GaAs. Different mechanisms were found to be responsible for these two extrema in the SBH. For instance, charge transfer from the n++-Si interlayer to the depletion region of the substrate was found to compensate the space-charge region, thereby lowering the band bending and the resulting SBH. In contrast, Fermi-level pinning rather deep in the gap, combined with a substantial conduction band offset at the heterojunction, created a high SBH when AlAs interlayers were used. n++-Ge interlayers, while causing a similar SBH reduction as n++-Si were not found to be thermally stable. Disruption of the anion sublattice and Fermi-level pinning deep in the gap nullified the band flattening effect of the GaSexAs1−x interlayer. Using these fundamental interface science results, we propose an application to complementary digital GaAs circuit design that may significantly reduce gate leakage relative to what can be achieved with conventional metallization schemes.
Controlling the plasma chemistry of silicon nitride and oxide deposition from silane
Authors: Smith Donald L.
Published: July 2002

We have studied the chemistry of glow discharge plasma-enhanced chemical vapor deposition (PECVD) by using vibrating quartz crystal deposition rate monitoring at 200–300 °C and line-of-sight mass spectrometry of orifice-sampled reactive neutral species. In the deposition of dielectric films from silane plus a large excess of oxidant (NH3, N2, or N2O), the key process factor is the ratio of plasma power to silane supply rate. When enough of the oxidant is activated by the plasma, it completely converts the silane to films which have no excess Si and no Si–H bonding. The critical ratio can be detected by the disappearance of Si2H6 byproduct or by the presence of excess activated oxidant. Nitride deposited from N2 is electrically leaky due to porous microstructure even when deposited using excess activated oxidant. Conversely, nitride deposited from NH3 is nonporous, and when deposited using excess activated oxidant it has a surprisingly low electron trapping rate which is at least as low as that achievable in PECVD oxide. Deposition using N2 involves no formation of gas-phase precursor molecules; but using NH3, •Si(NH2)3, and Si(NH2)4 were the dominant precursors. SiO2 deposition from N2O involved a minor contribution from Si(OH)4. High reactant partial pressure or excess rf power can lead to particle formation and deposition rate loss, especially in SiO2 deposition, due to gas-phase reaction among precursors. Partial pressure reduction either by He dilution or by total pressure reduction suppressed these problems with equal effectiveness in SiO2 deposition. No other effects of He could be detected either in the plasma chemistry or in the bulk film trapping rate.
Silicon oxycarbide formation on SiC surfaces and at the SiC/SiO2 interface
Authors: Önneby C. , Pantano C. G.
Published: July 2002

Amorphous and single-crystal α-SiC were exposed to various oxygen sources at room temperature. The oxygen sources included the residual gas in an ultrahigh vacuum environment, ambient air, ozone, and oxygen plasma. X-ray photoelectron spectroscopy (XPS) was used to follow changes in the surface composition and to determine the local bonding environment of the Si atoms. It was found that silicon oxycarbide species are formed when these SiC materials are initially exposed to oxygen. With extended exposure to ambient air, a SiO2 layer is subsequently formed over the silicon oxycarbide. However, the native oxide on the single-crystal SiC consists mainly of silicon oxycarbide species. The thicknesses of these native oxides were calculated using the XPS data.
Epitaxial growth of Cu on Si by magnetron sputtering
Authors: Jiang H. , Klemmer T. J. , Barnard J. A. , Payzant E. A.
Published: July 2002

Epitaxial Cu films were grown on H-terminated Si(100), Si(110) and Si(111) substrates by magnetron sputtering. The epitaxial orientation relationships and microstructural characteristics of the Cu films were studied by x-ray diffraction (XRD) including the conventional θ-2θ mode, rocking curve and pole figures, as well as by transmission electron microscopy. The results of both pole figure and electron diffraction reveal the epitaxial orientation relationship of the Cu/Si epitaxial system is as follows: Cu(100)/Si(100) with Cu[010]//Si[011]; Cu(111)//Si(110) with Cu[1̄10]//Si[001] and Cu[11̄0]//Si[001] which are twin related; and for the Cu/Si(111) system the Cu film grows primarily in the epitaxial relationship of Cu(111)/Si(111) with Cu[11̄0]//Si[2̄11]. It is shown by XRD that Si(110) is a more favorable substrate than Si(111) for the epitaxial growth of Cu(111). An ultrathin Cu(111) film (up to 2.5 nm) with high epitaxial quality can be grown on Si(110). The epitaxial relationships of the Cu/Si are discussed on the basis of geometrical lattice matching, including the invariant-line criterion and the superlattice area mismatch rule.
Expanding microwave plasma for steel carburizing: Role of the plasma impinging species on the steel surface reactivity
Authors: Jauberteau I. , Cinelli M. J. , Cahoreau M. , Jauberteau J. L. , Aubreton J.
Published: July 2002

A steel carburizing treatment using (Ar–CH4) gas mixtures with low CH4 contents is performed in an expanding microwave plasma reactor, where the distance between the discharge center and the substrate is choosen as a critical parameter to select the impinging plasma species. A 2 μm thick zone oversaturated in carbon is identified by secondary ion mass spectometry measurements at the steel surface after a 15 min treatment in an (Ar–5%CH4) gas mixture. The amount of carbon in this zone increases as the distance between the center of the discharge and the substrate decreases. After carburizing at a distance close to the center of the discharge, where CHx<3 and CxHy+ plasma species are numerous, almost no oxygen is detected. So, the plasma species improve the infusion of carbon partly by removing the oxides from the steel surface. Based on Fick’s second law, a carbon diffusion coefficient of 10−11 cm2 s−1 is found in the 2 μm thick zone, whereas at a depth larger than 2 μm, the classical carbon diffusion coefficient in austenite of 10−7 cm2 s−1 is obtained. So, the storage of carbon in a thin zone close to the steel surface can be seen as an additional key stage in the plasma carburizing process.