bluuebunny/crossref_metadata_2025 huggingface dataset:
Challenges in Deep Water Experiments: Hybrid Approach
Authors: Stansberg Carl Trygve , Ormberg Harald , Oritsland Ola
Published: July 2002

An overview of challenges within hydrodynamic verification of deep-water offshore structures is given first. The role of model testing in the verification, as well as a range of relevant measured responses, are discussed. Various solutions for experimental verification of deep-water structures are considered. In particular, the combination of model tests with truncated set-up and computer simulations—the hybrid approach—is discussed. Two basic groups of hybrid methods are identified: Active (on-line) and passive (off-line). Most published works are on passive systems, of which a particular method is described. Case study examples with this procedure are reviewed and discussed, and future challenges are commented.
Dislocation-Stacking Fault Tetrahedron Interactions in Cu
Authors: Wirth B. D. , Bulatov V. V. , de la Rubia T. Diaz
Published: July 2002

In copper and other face centered cubic metals, high-energy particle irradiation produces hardening and shear localization. Post-irradiation microstructural examination in Cu reveals that irradiation has produced a high number density of nanometer sized stacking fault tetrahedra. The resultant irradiation hardening and shear localization is commonly attributed to the interaction between stacking fault tetrahedra and mobile dislocations, although the mechanism of this interaction is unknown. In this work, we present results from a molecular dynamics simulation study to characterize the motion and velocity of edge dislocations at high strain rate and the interaction and fate of the moving edge dislocation with stacking fault tetrahedra in Cu using an EAM interatomic potential. The results show that a perfect SFT acts as a hard obstacle for dislocation motion and, although the SFT is sheared by the dislocation passage, it remains largely intact. However, our simulations show that an overlapping, truncated SFT is absorbed by the passage of an edge dislocation, resulting in dislocation climb and the formation of a pair of less mobile super-jogs on the dislocation.
Recent Developments in Gradient Plasticity—Part II: Plastic Heterogeneity and Wavelets
Authors: Konstantinidis Avraam A. , Aifantis Elias C.
Published: July 2002

Wavelet analysis is used for describing heterogeneous deformation in different scales. Slip step height experimental measurements of monocrystalline alloy specimens subjected to compression are considered. The experimental data are subjected to discrete wavelet transform and the spatial distribution of deformation in different scales (resolutions) is calculated. At the finer scale the wavelet analyzed data are identical to the experimental measurements, while at the coarser scale the profile predicted by the wavelet analysis resembles the shear band solution profile provided by gradient theory in agreement with experimental observations. The different data sets provided by wavelet analysis are used to train a neural network in order to predict the spatial distribution of strain at resolutions higher than those possible by the available experimental probes. In addition, applications of wavelet analysis to interpret size effect data in torsion and bending at the micron scale are examined by deriving scale-dependent constitutive equations which are used for this purpose.
A Study of Burr Formation Processes Using the Finite Element Method: Part I
Authors: Park I. W. , Dornfeld D. A.
Published: July 2002

A finite element model of orthogonal metal cutting including burr formation is presented. A metal-cutting simulation procedure based on a ductile failure criterion is proposed for the purpose of better understanding the burr formation mechanism and obtaining a quantitative analysis of burrs using the finite element method. In this study, the four stages of burr formation, i.e., initiation, initial development, pivoting point, and final development stages, are investigated based on the stress and strain contours with the progressive change of geometry at the edge of the workpiece. Also, the characteristics of thick and thin burrs are clarified along with the negative deformation zone formed in front of the tool edge in the final development stage. [S0094-4289(00)00702-7]
The Linkage Between Microscopic Cavitation Damage and Macroscopic Crack Growth
Authors: Onck P. R. , Nguyen B.-N. , van der Giessen E.
Published: July 2002

This paper is concerned with a recent microstructural approach to model creep crack growth. The model spans three different length scales, from the scale of individual cavities, through the grain scale up to the macroscopic scale of cracks in components and test specimens. In order to study the initial stages of creep crack growth, we consider a near-tip process window in which a large number of grains are represented discretely. This window is surrounded by a standard continuum. Macroscopic specimen dimensions and loading configuration are communicated to this near-tip region by applying boundary conditions in accordance with the asymptotic stress fields for power-law creeping materials. The paper presents some novel results of this type of modeling obtained using remote higher-order crack-tip fields. Specific attention is focused on the effect of random nucleation and grain deformation on nonsymmetric crack growth from either initially sharp or blunt cracks. [S0094-4289(00)00703-9]
Effects of Density and Viscosity in Vertical Zero Net Liquid Flow
Authors: An Hyoung-Jin , Langlinais Julius P. , Scott S. L.
Published: July 2002

An experimental study was conducted to investigate the effects of density and viscosity on zero net liquid flow (ZNLF) in vertical pipes. Predicting liquid holdup under ZNLF conditions is necessary in several types of petroleum industry operations. These include predicting bottomhole pressures in pumping oil wells and the design of compact gas-liquid cylindrical cyclone (GLCC©)1 separators. Models are proposed to predict flow pattern transitions under ZNLF conditions and comparisons are made with commonly used vertical flow pattern transition criteria. Data was collected using a 3-in.-diam, 14-ft-section of transparent vertical pipe. Several different fluids, of differing density and viscosity, were utilized with air flowing at approximately 25 psig. Results are presented showing the liquid holdup and the flow distribution coefficient C0 as a function of density, viscosity, and superficial gas velocity. [S0195-0738(00)00402-7]
Exergy Analysis of Modern Fossil-Fuel Power Plants
Authors: Horlock J. H. , Young J. B. , Manfrida G.
Published: July 2002

The definition of open cycle rational efficiency is unequivocally based on the ratio of the actual shaft work output from a power plant to the maximum work that could be obtained in a reversible process between prescribed inlet and outlet states. However, different constraints may be applied to such an ideal reversible process, and the maximum work obtainable will then vary, as will the value of the rational efficiency. Attention has been drawn to this issue before in the literature and it is discussed further here. In particular, the consequences of defining the outlet state for the ideal process are critical. A further complication occurs when water or steam is injected into a gas turbine plant. Three definitions of rational efficiency are discussed here and some illustrative calculations presented. There are small but significant differences between the values of the three derived efficiencies. [S0742-4795(00)00101-0]
Active Control of Discrete-Frequency Turbomachinery Noise Using a Rotary-Valve Actuator
Authors: Sawyer Scott D. , Fleeter Sanford
Published: July 2002

Turbomachine discrete-frequency tones, a significant environmental concern, are generated by rotor-stator interactions. Specific spatial modes are generated, but not all generated modes propagate to the far field. It is the propagating spatial modes generated by rotor-stator interaction that represent the community-disturbing far field discrete-frequency noise. Fundamental active airfoil source discrete-frequency noise control experiments are performed, with the active airfoil source control optimized to generate propagating spatial modes to cancel the propagating spatial modes generated by the rotor-stator interaction. These experiments demonstrate the viability and effectiveness of rotary-valve discrete-frequency noise control. Specifically, the active noise control system combines the active airfoil source control with in-duct spatial mode measurement. In this unique design, the active airfoils of the stator vane row are driven by a remote centerbody-mounted rotary-valve system. Propagating spatial mode reductions of 5 dB and 9 dB upstream and downstream with negligible modal spillover are demonstrated. [S0742-4795(00)02702-2]
Internal Bearing Chamber Wall Heat Transfer as a Function of Operating Conditions and Chamber Geometry
Authors: Busam Stefan , Glahn Axel , Wittig Sigmar
Published: July 2002

Increasing efficiencies of modern aero-engines are accompanied by rising turbine inlet temperatures, pressure levels and rotational speeds. These operating conditions require a detailed knowledge of two-phase flow phenomena in secondary air and lubrication oil systems in order to predict correctly the heat transfer to the oil. It has been found in earlier investigations that especially at high rotational speeds the heat transfer rate within the bearing chambers is significantly increased with negative effects on the heat to oil management. Furthermore, operating conditions are reached where oil coking and oil fires are more likely to occur. Therefore, besides heat sources like bearing friction and churning, the heat transfer along the housing wall has to be considered in order to meet safety and reliability criteria. Based on our recent publications as well as new measurements of local and mean heat transfer coefficients, which were obtained at our test facility for engine relevant operating conditions, an equation for the internal bearing chamber wall heat transfer is proposed. Nusselt numbers are expressed as a function of non-dimensional parameter groups covering influences of chamber geometry, flow rates and shaft speed. [S0742-4795(00)02202-X]
Closure to “Discussion of ‘Thermal Contact Resistance of Silicone Rubber to AISI 304 Contacts’ ” [ASME J. Heat Transfer, 122, p. 403 (2000)]
Authors: Parihar S. K. , Wright N. T.
Published: July 2002

[S0022-1481(00)02902-9]
Identification of Multiple Feature Representations by Volume Decomposition for 2.5-Dimensional Components
Authors: Sundararajan V. , Wright Paul K.
Published: July 2002

Decomposition of computer-aided design models into features that can be directly manufactured and easily translated from one representation to another has been recognized as a necessity for robust automated process planning systems. The algorithms presented here yield multiple representations of features that can be used to generate plans that are easily and efficiently manufacturable by milling processes. Features are recognized from the faces of a prismatic stock by first identifying missing regions on the external faces of the stock and then recursively descending into the part. Each missing region corresponds to a feature. As the projection of the feature is swept into the part, changes in the cross-section are identified. These denote the beginning of new features which become children of the original feature. This process yields a set of six trees, each of which resembles a depth-first search tree and is a partial ordering of features within a setup. Multiple representations are investigated for those features that are accessible from more than one direction. Corresponding features in the different trees are linked by arcs, thus yielding a feature graph. The feature graph can then be used to generate optimal features for machining depending on design or manufacturing requirements such as fixtures, tolerances, corner radii, and tool accessibility. [S1087-1357(00)01901-8]
A Numerical Procedure Based on the Boundary Element Method Analysis of the Archimedean Spiral Grooved Thrust Oil Bearing
Authors: Zhu Qin , Zhang W. J.
Published: July 2002

This paper presents a study which aims at developing a numerical procedure based on the boundary element method (BEM) to compute performance of a Spiral Grooved Thrust (SGT) oil bearing with varying groove depth. The SGT oil bearing has very complex boundary conditions, which can hinder the effective or sufficient applications of the Finite Difference Method (FDM) and the Finite Element Method (FEM) for the same purpose. In order to apply the BEM, the pressure control equation, i.e., the Reynolds equation, is first transformed into Laplace’s and Poisson’s forms of the equations. Discretization of the SGT oil bearing with a set of boundary elements is thus explained in detail, which also includes the handling of boundary conditions. To verify our method, the Archimedean SGT oil bearing is calculated with our proposed procedure; the results of the calculation are compared with the analytical solutions available in the literature. Moreover, the relationships between the performance and structural and operational parameters are discussed by means of the proposed numerical procedure. These relationships are not discussed elsewhere in the literature. Therefore, the work reported lays a solid foundation for a further work of the optimal design of the SGT oil bearing. [S0742-4787(00)00403-3]
Limit Loads Using Extended Variational Concepts in Plasticity
Authors: Seshadri R.
Published: July 2002

Lower-bound limit load estimates are relevant from a standpoint of pressure component design, and are acceptable quantities for ascertaining primary stress limits. Elastic modulus adjustment procedures, used in conjunction with linear elastic finite element analyses, generate both statically admissible stress distributions and kinematically admissible strain distributions. Mura’s variational formulation for determining limit loads, originally developed as an alternative to the classical method, is extended further by allowing the elastic calculated stress fields to exceed yield provided they satisfy the “integral mean of yield” criterion. Consequently, improved lower-bound values for limit loads are obtained by solving a simple quadratic equation. The improved lower-bound limit load determination procedure, which is designated “the mα method,” is applied to symmetric as well as nonsymmetric components. [S0094-9930(00)01103-3]
Highly Oriented Pyrolytic Graphite by XPS
Authors: Schmieg Steven J. , Belton David N.
Published: July 2002

X-ray photoelectron spectroscopy (XPS) was used to characterize a highly oriented pyrolytic graphite (HOPG) sample. The HOPG was cleaved using scotch tape prior to introduction into an ultrahigh vacuum analytical chamber. No further cleaning was used as no elements other than carbon were detected in XPS survey scans. Electron energy loss spectroscopy (EELS) spectra obtained by x-ray excitation of the C 1s level can be used as a fingerprint for distinguishing graphite from diamond or carbides [see D. N. Belton and S. J. Schiemg, J. Vac. Technol. A 8, 2353 (1990)].
Platinum Disulfide by XPS
Authors: Dembowski J. , Marosi L. , Essig M.
Published: July 2002

It is known from crystallographic investigations that there are two distinct Pt–S modifications, PtS and PtS2 [see R. Collins, R. Kaner, P. Russo, A. Wold, and D. Avignant, Inorg. Chem. 18, 727 (1979); A. Finley, D. Schleich, J. Ackerman, S. Soled, and A. Wold, Mater. Res. Bull. 9, 1655 (1974); S. Soled, A. Wold, and O. Gorochov, ibid. 11, 927 (1976); L. Thomasson, Z. Phys. Chem. Bd. 2, 349; and L. Thomasson, ibid. 4, 277]. They are not commercially available in high grade purity. In the present study the production of pure PtS2 reference materials and its characterization by x-ray photoelectron spectroscopy is presented. The PtS investigation is shown in a second submission. The PtS2 samples were produced by annealing stoichiometric mixtures of elemental platinum (DEGUSSA, grade 99.9%) and sulfur (Riedle de Haen, grade 99.5%). Both powders were blended homogeneously and pressed into pellets. The pellets were annealed for 3 weeks in an evacuated quartz tube (800 °C, 10−4 Pa) and cooled in defined steps to room temperature over 8 days. The materials were investigated by x-ray diffraction. The diffraction spectrum of PtS2 (JCPDS 18-973) shows a minor impurity of PtS (<5). The samples were also characterized by transmission electron microscopy (TEM). The PtS2 material consists of thin flakes. Selected area diffraction (SAD) and energy dispersive x-ray spectroscopy (EDXS) give no indication of impurities in the samples.
Titanium Nitride by XPS
Authors: Milošev Ingrid , Strehblow Hans-Henning , Navinšek Boris , Panjan Peter
Published: July 2002

Titanium nitride (TiN) coatings have been deposited on polished steel substrates by a plasma-beam sputtering technique in a Sputron apparatus (Balzers A. G.) at 200 °C. A thin intermediate layer of Ti (0.08 μm) was deposited between the substrate and the 2.8 μm thick TiN coating. The average roughness, Ra, of the substrate was <0.04 μm, whereas after the deposition Ra values between 0.06 and 0.08 μm were measured for TiN coatings. Coatings exhibit a fine grain structure of the grain size <100 nm. The XPS measurements were performed in an Escalab 200-X spectrometer (VG Instruments) using non-monochromated Al Kα radiation from a twin Mg/Al anode operating at 300 W. The hemispherical energy analyzer was operated in the CAE mode with a constant pass energy of 20 eV. In the present paper the following spectra are presented: survey spectrum, spectra of major elements titanium and nitrogen (Ti 2p and N 1s), spectra of minor elements oxygen and carbon (O 1s and C 1s), and valence band spectrum. Spectra were background subtracted using a Shirley method. Peak positions and widths were determined from least squares fitting procedure.
Properties of nitrogen doped silicon films deposited by low-pressure chemical vapor deposition from silane and ammonia
Authors: Temple-Boyer P. , Jalabert L. , Masarotto L. , Alay J. L. , Morante J. R.
Published: July 2002

Nitrogen doped silicon (NIDOS) films have been deposited by low-pressure chemical vapor deposition from silane SiH4 and ammonia NH3 at high temperature (750 °C) and the influences of the NH3/SiH4 gas ratio on the films deposition rate, refractive index, stoichiometry, microstructure, electrical conductivity, and thermomechanical stress are studied. The chemical species derived from silylene SiH2 into the gaseous phase are shown to be responsible for the deposition of NIDOS and/or (silicon rich) silicon nitride. The competition between these two deposition phenomena leads finally to very high deposition rates (≈ 100 nm/min) for low NH3/SiH4 gas ratio (R≈0.1). Moreover, complex variations of NIDOS film properties are evidenced and related to the dual behavior of the nitrogen atom into silicon, either n-type substitutional impurity or insulative intersticial impurity, according to the Si–N atomic bound. Finally, the use of NIDOS deposition for the realization of microelectromechanical systems is investigated.
Coulomb staircases by lateral tunneling between adjacent nanoclusters formed on Si surfaces
Authors: Park Kang-Ho , Ha Jeong Sook , Yun Wan Soo , Shin Mincheol , Ko Young-Jo
Published: July 2002

We have investigated the oscillatory tunneling current–voltage characteristics on metal nanoclusters formed on Sb-terminated Si(100) surfaces by using scanning tunneling microscopy/spectroscopy. Through the systematic investigation on a variety of cluster configuration environments, we suggest that the lateral tunneling between adjacent clusters dominantly contributes to the occurrence of the single electron tunneling phenomena. In the single clusters formed on Si surfaces, we detected only current oscillations, which must be distinguished from Coulomb staircases. Those results strongly suggest that Coulomb staircases should not originate from the direct conduction of electrons through Schottky junction between the single clusters and Si substrates in contrast to other previous reports.
Epitaxial oxide thin films on Si(001)
Authors: Yu Z. , Ramdani J. , Curless J. A. , Overgaard C. D. , Finder J. M. , Droopad R. , Eisenbeiser K. W. , Hallmark J. A. , Ooms W. J. , Kaushik V. S.
Published: July 2002

Over the years, the development of epitaxial oxides on silicon has been a great technological challenge. Amorphous silicon oxide layer forms quickly at the interface when the Si surface is exposed to oxygen, making the intended oxide heteroepitaxy on Si substrate extremely difficult. Epitaxial oxides such as BaTiO3 (BTO) and SrTiO3 (STO) integrated with Si are highly desirable for future generation transistor gate dielectric and ferroelectric memory cell applications. In this article, we review the recent progress in the heteroepitaxy of oxide thin films on Si(001) substrate by using the molecular beam epitaxy technique at Motorola Labs. Structural, interfacial and electrical properties of the oxide thin films on Si have been characterized using in situ reflection high energy electron diffraction, x-ray diffraction, spectroscopic ellipsometry, atomic force microscopy, Auger electron spectroscopy, x-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, high-resolution transmission electron energy loss spectroscopy, capacitance–voltage and current–voltage measurement. We also present the transistor results and address the impact of the epitaxial oxide films on future generation metal-oxide-semiconductor field effect transistors.
The Kinetics of the Hydrogen–Titanium Reaction
Authors: Reichardt J. W.
Published: July 2002

The rate of the hydrogen-titanium reaction has been measured at 75 °C and at hydrogen pressures between 10−4 and 10−2 Torr. Thin films of titanium were deposited on Kovar substrates at room temperature and mechanically transferred in vacuum to a reaction chamber where the rate of the reaction was measured using the flow technique. The rate of the reaction is linearly dependent on the hydrogen pressure and independent of the quantity of gas absorbed for hydrogen to titanium atomic ratios between 0.15 and 1.5.
Electrical Properties of rf Sputtered Bismuth Telluride Thin Films
Authors: McCulley M. J. , Neudeck G. W. , Liedl G. L.
Published: July 2002

The resistivity, Hall coefficient, and composition of thin films prepared by rf sputtering from a sintered cathode of stoichiometric Bi2Te3 were measured. Sputtering parameters were varied and affected both composition and resistivity. The polycrystalline films exhibited a strong (101̄5) fiber texture. Resistivity varied from 0.60 mΩ cm to 9.0 mΩ cm over a composition range from 25 wt % Te to 49 wt % Te with the maximum resistivity near Bi2Te3. High carrier concentration and low ionization energies indicate metallic characteristics.
Measuring Hydrocarbon Gas Pressure with an Ionization Gauge
Authors: Young J. R.
Published: July 2002

The sensitivity of an ionization gauge for CH4, C2H4, C2H6, C6H6, and C6H5CH3 has been determined. Results obtained indicate an almost linear increase in sensitivity for these hydrocarbons with the number of electrons per molecule. A reduction in ionization gauge sensitivity was observed after several hours of operation in a hydrocarbon atmosphere. Results obtained here indicate the reduction in sensitivity is due to a high electrical resistance layer formation on the small wire probe ion collector of the Bayard-Alpert ionization gauge. The sensitivity can be restored by electron bombardment of the collector or operating the gauge for several hours in an O2 atmosphere near 10−4 Torr. The high resistance layer buildup can be prevented for many hours by operating the gauge at 250 °C.
Third-Order Aberration Coefficients of Electron Lenses. II
Authors: Kuyatt C. E. , DiChio D. , Natali S. V.
Published: July 2002

In the standard treatments of aberration coefficients of electron lenses, deviations from perfect imagery are expressed as power series of the ray coordinates in the object and aperture planes. The resulting aberration coefficients depend on the object and aperture positions, and a complete description of the aberrations of an electron lens would require a doubly infinite set of aberration coefficients for each voltage ratio of the lens. Hawkes has carried out a general treatment of the third-order aberrations of electron lenses which is independent of object and aperture positions. Six quantities are sufficient to specify the third-order aberration properties of an electron lens. We have derived equations for these six quantities in the form of integrals, involving derivatives of the axial potential no higher than the second, and using our previously calculated potentials have computed aberration coefficients for the two-tube electrostatic lens.
Some aspects of the use of carbon materials in field electron emission cathodes
Authors: Bobkov A. F. , Davidov E. V. , Zaitsev S. V. , Karpov A. V. , Kozodaev M. A. , Nikolaeva I. N. , Popov M. O. , Skorokhodov E. N. , Suvorov A. L. , Cheblukov Yu. N.
Published: July 2002

A detailed analysis has been carried out of the advantages and disadvantages of using carbon fibers and flat graphite structures with activated surfaces as materials for field electron emission cathodes. In this article we present the results of original experimental studies on the elementary composition of carbon materials and on the effect of thermal annealing on their structure and emission properties and on the reduction of the work function when cesium is implanted into these materials. We also assess the potential of irradiation techniques for producing flat field emission cathodes with activated surfaces, and discuss a method for predicting how the shape of the emitting surface changes as a result of bombardment by low-energy residual-gas ions. Suggestions are made about the best design of field electron emission cathodes for various practical purposes.
Anisotropic etching of polymer films by high energy (∼100s of eV) oxygen atom neutral beams
Authors: Panda Siddhartha , Economou Demetre J. , Chen Lee
Published: July 2002

An inductively coupled high density plasma source was used to generate an energetic (100s of eV), high flux (equivalent of ∼10s mA/cm2) oxygen atom neutral beam. Positive ions were extracted from the plasma and neutralized by a metal grid with high aspect ratio holes. High rate (up to 0.6 μm/min), microloading-free, high aspect ratio (up to 5:1) etching of polymer with straight sidewalls of sub-0.25 μm features was demonstrated. The polymer etch rate increased with power and showed a shallow maximum with plasma gas pressure. The etch rate increased roughly as the square root of the boundary voltage (which controls neutral beam energy), and was independent of substrate temperature. The latter observation suggests that spontaneous etching did not occur. The degree of neutralization of the extracted ions was estimated to be greater than 99% at the base case conditions used in this work.
Formation of macroparticles in arc ion-plated nitride coatings
Authors: Shiao Ming-Hua , Shieu Fuh-Sheng
Published: July 2002

On the basis of transmission electron microscope analysis, a model describing the formation of macroparticles in arc ion-plated nitride coatings is proposed. While emitting from the cathode, the metal droplets react with nitrogen during their travel to the substrate and form a thin layer of nitrides on the surface of the droplets, resulting in a core-shell structure. The flattened torus voids are gradually produced beneath each droplet upon impact on the substrate, which causes shadowing of the ion flux during deposition. Subsequent growth of the nitride coating on the droplets follows the orientation of the nitride nuclei in the outer shell to form a radial type of structure, until coalescence with the regular nitride columns growing perpendicular to the substrate surface occurs.
Spatial distribution of carbon species in laser ablation of graphite target
Authors: Ikegami T. , Ishibashi S. , Yamagata Y. , Ebihara K. , Thareja R. K. , Narayan J.
Published: July 2002

We report on the temporal evolution and spatial distribution of C2 and C3 molecules produced by KrF laser ablation of a graphite target using laser induced fluorescence imaging and optical emission spectroscopy. Spatial density profiles of C2 were measured using two-dimensional fluorescence in various pressures of different ambient (vacuum, nitrogen, oxygen, hydrogen, helium, and argon) gases at various ablation laser fluences and ablation area. A large yield of C2 is observed in the central part of the plume and near the target surface and its density and distribution was affected by the laser fluence and ambient gas. Fluorescent C3 was studied in Ar gas and the yield of C3 is enhanced at higher gas pressure and longer delay times after ablation.
Stress-induced failure of Si3N4 metal-insulator-metal capacitors fabricated by plasma enhanced chemical vapor deposition
Authors: Suh Dongwoo , Kang Jin-Yeong
Published: July 2002

Microstructural and in turn functional failure of Si3N4 metal-insulator-metal (MIM) capacitors fabricated by plasma enhanced chemical vapor deposition was investigated using cross-sectional transmission electron microscopy and residual stress analysis. As a result it was manifested that the failure of the Si3N4 MIM capacitors was caused by microvoids formed over the Si3N4 dielectric and the TiN interlayer adopted for the use of diffusion barrier. The microvoid having occurred at the MIM capacitor with very thin Si3N4–less than 50 nm thick in the present article caused it to leak out much of the current to the extent of a few microamperes even at bias of 3 V. The microvoid, one of the important constraints in the fabrication of high capacitive Si3N4 MIM capacitors, was explained by the residual stress of the constituent layers. The stress analysis showed that the absolute stress normalized by the thickness of the Si3N4 layer should be less than 30 MPa/nm to avoid microvoiding. In this research we noted that the stress state of not only the dielectric but also the interlayer should be taken into account for the successful design of high capacitive Si3N4 MIM capacitors.
Titanium Filaments for Sublimation Pumps
Authors: McCracken G. M. , Pashley N. A.
Published: July 2002

The performance of an alloy of 85% Ti 15%Mo as a filament material for subliming titanium in getter pumps is described. Using 2.1-mm-diam filaments, evaporation rates of up to 1 mg/cm/min have been achieved at filament currents of 57A. The upper limit in the evaporation rate is caused by filament failure which is attributed to crystal growth, but at values below this limit the evaporation is extremely uniform and reproducible. Comparison has been made between the performance of this alloy and a number of filaments of the type in which titanium is wrapped over a tungsten or tantalum core. The alloy was found to compare favorably in terms of peak evaporation rate and efficiency, and to be considerably better in terms of expense, reproducibility, and mechanical strength.
Vacuum System of Ion-Microprobe Mass Spectrometer
Authors: Barrington A. E. , Herzog R. F. K. , Poschenrieder W. P.
Published: July 2002

A mass spectrometer in which atoms from a 0.1-mm2 surface of a target are sputtered and ionized under bombardment by a beam of inert-gas ions has been perfected. To exploit the capabilities of this analytical tool for the detection of trace elements in solids, a drastic reduction of the instrumental background had to be achieved. This was accomplished by using spectroscopically pure structural material in the ion source and by eliminating all sources of hydrocarbons. In particular, since the presence of pump-oil contamination on the surface under analysis was readily detectable, the resulting cracking pattern obscured a large portion of the atomic-mass scale. A combination of liquid-nitrogen-trapped mercury diffusion pumps, zeolite sorption pumps, and sputter-ion pumps has reduced the instrumental background sufficiently to facilitate the routine parts-per-billion trace analysis of the surface and of the bulk of conducting and nonconducting solids.
Micrometer U-Tube Manometers for Medium-Vacuum Measurements
Authors: Thomas Allan M. , Cross James L.
Published: July 2002

A family of U-tube manometers, suitable for use as standard instruments, has been designed and constructed at the National Bureau of Standards to cover the range of pressures from 100 to 1 × 10−2 Torr. In these instruments the levels of the two liquid surfaces are measured by adjusting micrometers with conical points ground on the ends of the spindles. One hundred-millimeter and 50-mm range mercury manometers, with spindles approaching the liquid surface from above, are used for differential or absolute pressure measurements up to 100 Torr. Pressures less than 3.5 Torr are measured with oil manometers, in which the micrometer spindles approach the surfaces from below. Measurements made with the mercury manometer have an uncertainty of about 4 × 10−3 Torr plus 8 parts in 105 of the reading. Measurements made with the oil manometer have an uncertainty of about 4 × 10−4 Torr plus 1 part in 104 of the reading.
Deformation of Optical Surfaces by Film Stress
Authors: Scheuerman Richard J.
Published: July 2002

The development of stress in evaporated dielectric and metal films used as optical coatings has been investigated experimentally by two interferometric techniques. Stress data on a number of materials commonly used in the coating of reflective optics are presented, and the stress behavior in coatings deposited on stationary substrates at normal incidence is compared to those deposited on rotating substrates at high angles of incidence. Analysis of the effect of film stress upon the figure of optical surfaces is given, and examples are presented illustrating how this effect may be minimized.
An ion gun with relatively high yield at low pressure (<10−3 Pa)
Authors: Kornelsen E. V.
Published: July 2002

An ultrahigh-vacuum ion gun is described which is designed specifically for operation at pressures ?1.0×10−3 Pa. It produces mass analyzed ion beams at voltages 100 V to 10 kV and currents up to ∠1×10−7 A. For pressures ?1×10−5 Pa, 0.2 A Torr−1 of argon ions can be focused onto a 0.4-cm-diameter target 45 cm from the source. The gun operates without differential pumping in a system having a background pressure of 4.0×10−9 Pa. With the source in continuous operation at 30 mA electron emission, the partial pressures of H2 and CO within the source are each ∠1×10−9 Pa, and the total apparent source pressure is 11×10−9 Pa (equiv.N2). At a beam energy of 1 keV,ion energy spread (FWHM) is 0.6 eV and the beam divergence half-angle at the source is 0.4°.
Factors contributing to the Si L23V
V, Si L1L23V and O K
V
V Auger lineshape in SiO2
Authors: Ramaker D. E. , Murday J. S.
Published: July 2002

A comparison of the measured Si L23VV, Si L1L23V, and O KVV Auger lineshapes in SiO2 with calculated lineshapes has been reported previously. In this work we carefully examine several of the factors entering the calculated lineshape: the assumed atomic Auger matrix elements, possible contributions due to Auger satellites, and the effects of possible Si 3d electron contributions in the upper valence molecular orbitals. Significantly better agreement between the measured and calculated lineshapes is achieved.
Magnetron-sputtered metal carbide solar selective absorbing surfaces
Authors: Harding G. L. , Craig S.
Published: July 2002

A range of magnetron reactively sputtered metal carbide interference filters has been deposited onto sputtered copper on glass substrates and aged in vacuum at elevated temperature. These films show considerable promise as selective surfaces for incorporation in all glass vacuum insulated solar energy collectors. Surfaces produced by depositing homogeneous metal carbide films have solar absorptances α∠80% and emittances ε∠2.0% at 300 K. Solar absorptances above 90% and emittances 3.0%–4.0% at 300 K are obtained for multilayer metal carbide films fabricated by varying the reactive gas flow rate in steps during the deposition. Ageing experiments show that the reflectances of the multilayer films alter due to interdiffusion between the layers, resulting in a slow degradation of solar absorptance. Some diffusion coefficients for carbon in stainless steel and titanium films have been evaluated. Surfaces fabricated using chromium, molybdenum, and stainless steel carbides are superior to titanium carbide surfaces. Magnetron sputtering technology offers the possibility of more rapid and efficient deposition of these selective surfaces compared with the high pressure diode deposition technique utilized in previous work.
Measurement of interface defect states at oxidized silicon surfaces by constant-capacitance DLTS
Authors: Johnson N. M. , Bartelink D. J. , McVittie J. P.
Published: July 2002

The interface-state distribution for the as-oxidized surface on single-crystal silicon is dominated by a broad peak centered ∠0.3 eV above the Si valence-band maximum. Theoretical studies by Laughlin, Joannopoulos, and Chadi suggest that this peak is due to a trivalent silicon defect at the Si–SiO2 interface. Constant-capacitance DLTS and the quasistatic capacitance–voltage technique were used to characterize this defect on (100) - and (111) -oriented silicon surfaces. It is shown here that: (1) the characteristic defect is present at the Si–SiO2 interface on both n-type and p-type silicon, (2) the density of the defect is higher on (111) -oriented than on (100) -oriented silicon for identically prepared specimens, and (3) the defect density can be reduced by a high-temperature, postoxidation anneal in either an argon or nitrogen ambient.
Auger lineshape analysis of molecules and solids
Authors: Jennison Dwight R.
Published: July 2002

Considerable recent theoretical work has shown that core–valence–valence Auger lineshape analysis may often be successfully made in terms of the molecular orbital structure of the molecule or the band structure of the solid. This approach assumes a priori that the final state hole motion is uncorrelated. Limitations to this approach include the highly correlated final states observed in ionic and narrow band solids (as Cu). Complications to this approach include the initial state valence screening of the core hole which affects the Auger decay probabilities. However, much useful information about the local density of states (local chemical environment) may be extracted in covalent and metallic materials. Examples from molecular (CH4, C2H4, C2H6, and C3H8) and solid state (Cu and Be) spectra are presented and the state of our understanding of lineshape analysis is summarized.
Electronic and atomic structure of Si(111) Al, Ag, and Ni metal overlayer induced surface reconstructions
Authors: Hansson G. V. , Bachrach R. Z. , Bauer R. S. , Chiaradia P.
Published: July 2002

The electronic structure of the ordered metal overlayers Si(111) √3× √3: Al and √3×√3: Ag and Si(111) √19×√19: Ni prepared from Si(111)7×7 surfaces has been studied with angle-resolved photoelectron spectroscopy. On all these surfaces we find dangling bond derived bands which for Al and Ag overlayers have a dispersion of 0.4 eV. We also report a new Si(111) √7×√7: Al structure at ?0.5 monolayer coverage of Al. A new structural model for the √19×√19: Ni surface is proposed.
Thermal nitridation of Si(111) by nitric oxide
Authors: Wiggins M. D. , Baird R. J. , Wynblatt P.
Published: July 2002

Clean Si(111) surfaces were thermally nitrided at various temperatures by exposure to low pressures (1×10−6 Torr) of NO in a UHV system. The nitridation process was monitored by multiple surface analytical techniques including AES, XPS, UPS, LEED, and thermal desorption. At substrate temperatures below 800°C a silicon oxynitride was formed in which the nitrogen to oxygen ratio increased with increasing reaction temperature. These oxynitride films were converted to nitride films by loss of O and SiO when heated to temperatures greater than 850°C in vacuum. Exposure of the clean Si to NO at temperatures greater than 1000°C produced an oxygen-free nitride film. The nitride films formed by either route gave the ’’doublet’’ LEED pattern which has previously been associated with the formation of a two domain epitaxial α-Si3N4 layer. Due to the high reactivity of NO, the presence of 20%–30% C on the Si surface was not necessary for nucleation sites as had been reported for nitridation by NH3.
Core to surface excitations on GaAs(110)
Authors: Swarts C. A. , Goddard W. A. , McGill T. C.
Published: July 2002

We have carried out ab initio calculations of surface core excitations on finite cluster models of the GaAs(110) surface. For the Ga core excitation we find a localized excited state involving excitation into the empty Ga-4p orbital and bound with respect to the conduction band minimum (CBM) by 0.7 eV. This is in reasonable agreement with experiment (binding energy ≳0.8 eV). This transition, which is not analogous to bulk core excitations, is termed a core surfaston to emphasize the character of the state. We find that the As core surfaston is above the CBM by 1.0 eV and hence should be difficult to observe.
Photoemission investigation of Si(111)–Cu interfaces
Authors: Abbati I. , Grioni M.
Published: July 2002

The formation of Si(111)–Cu interfaces has been studied systematically with photoelectron spectroscopy (hν = 21.2 eV, 16.8 eV, 10.2 eV). The samples were prepared by depositing increasing Cu thicknesses up to ten monolayers onto Si(111) held at liquid nitrogen temperature (LNT). The evolution of the photoelectron spectra due to the heating to room temperature (RT) has been studied. The coverage and temperature dependence give spectroscopic evidence of the intermixing taking place in the interface region; this causes a narrowing and a shift of the 3d Cu peak towards higher binding energies with respect to the bulk metal. In the interface intermixed region a considerable concentration gradient is present; approximately five monolayers separate the Cu-rich and the Si-rich side of the interface. This concentration gradient is higher than in the Si–Au case, and we present some speculations to explain this behavior: in this connection some preliminary LEED results on Si(111)–Cu are also used.
Electron stimulated desorption of excited alkali atoms from alkali halide surfaces
Authors: Pian T. R. , Tolk N. , Kraus J. , Traum M. M. , Tully J. , Collins W. E.
Published: July 2002

We have measured the alkali resonance photon intensity due to electron stimulated desorption of excited particles from NaCl and KCl targets as a function of incident electron energy (20 to 1000 eV) and sample temperature (room temperature to 300 °C). The energy dependence data suggest a correlation between excited Na and K desorption thresholds and substrate core levels. These are the first experimental correlations of the desorption of neutral atoms, specifically excited neutral atoms, with the creation of core holes. The intensity of emitted radiation is observed to rise sharply and then saturate with increasing temperature.
Changes in tokamak plasma properties during impurity injection
Authors: Cohen S. , Cecchi J. , Daughney C. , Davis S. , Dimock D. , Efthimion P. , Finkenthal M. , Fonck R. , Hinnov E. , Hulse R. , Johnson D. , Manos D. , McNeill D. , Medley S. , Meservey E. , Mueller D. , Schivell J. , Silver E. , Suckewer S. , Timberlake J. , Von Goeler S.
Published: July 2002

Certain applications of laser blow-off impurity injection, such as ion temperature measurement and spectral line identification, may require the ratio of injected ions-to-plasma electron density to exceed 0.001. To achieve these concentrations we have relied on injection of micron-sized clusters as well as monatomic species. In these cases the injected impurity can no longer be regarded as a nonperturbing trace sourced at the plasma edge. We therefore have studied the variation of plasma parameters in PLT and PDX as a function of the amount of injected impurities, the species mix, and the type of impurity. We find that for ohmically-heated plasmas, impurity injection can increase ?e more than 4×1012 cm−3 without causing disruptions. During Ge-injection experiments where Δne/ne ∠0.05, Te initially rises ∠5% on axis and decreases ∠20% at the edge. The plasma current drops 1–3 % and the loop voltage and radiated power both double. Varying the amount of injected impurities changes the peaking and decay times of both high and low impurity charge states by 10–50 %. Analysis of this in terms of altered temperature profiles, impurity penetration profiles and impurity transport is presented. These studies suggest criteria for performing nonperturbing transport experiments.
The dependence of aluminum nitride film crystallography on sputtering plasma composition
Authors: Aita C. R. , Gawlak C. J.
Published: July 2002

Aluminum–nitrogen films were grown on unheated substrates by rf diode sputtering an aluminum target in Ar/N2 atm. Optical emission spectroscopy was used to monitor excited nitrogen species in the sputtering plasma. X-ray diffraction results, supported by Auger electron spectroscopy for chemical analysis, show that films deposited on Si- and SiO2-coated Si evolve from polycrystalline fcc Al to semiamorphous AlN to basal orientation hcp AlN as the sputtering gas N2 content is increased. The transition from metal to nitride film growth is correlated with a steplike decrease in the growth rate which is characteristic of compound formation at the target, and occurs subsequent to a rapid increase in excited N+2 species in the plasma. This correlation is discussed in terms of processes involving N+2 which produce active N species in the discharge.
Oxygen chemisorption and oxide formation on Si(111) and Si(100) surfaces
Authors: Hollinger G. , Himpsel F. J.
Published: July 2002

We have used photoemission techniques with synchrotron radiation to study the adsorption of oxygen on the Si(111)-(7×7) and Si(100)-(2×1) surfaces at room temperature in the submonolayer and monolayer regimes. High resolution Si 2p core-level spectra, valence-band spectra, work-function, and Fermi-level pinning positions have been measured for exposures between 1 and 1000 L and after annealing at 700 °C. Four oxidation states have been detected for the silicon surface atoms with Si 2p core-level shifts of 0.9, 1.9, 2.6, and 3.4 eV which are assigned to silicon atoms bonded to 1, 2, 3, and 4 oxygen atoms. Both (111) and (100) surfaces are characterized by about the same sticking coefficient, a simple adsorption process for 1-L exposures, the quenching of the surface states after 15 L and a saturation of the amount of oxygen after 100 L. Significant differences exist in the initial bonding geometries for the (111) and (100) surfaces. After 15-L exposure, oxygen atoms are incorporated below the Si (111)-(7×7) surface to form SiO4 units.
Optical absorption edge in Hg0.7 Cd0.3Te
Authors: Mroczkowski J. A. , Nelson D. A. , Murosako R. , Zimmermann P. H.
Published: July 2002

Optical absorption measurements at the fundamental absorption edge in high purity and stochiometrically doped p-type Hg0.7Cd0.3Te show the absorption edge to be significantly influenced by valence band tailing due to native Hg vacancy acceptor defects. The absorption coefficient αe for transitions across the band gap increases as αe=α0 exp k(E−E0); for high purity Hg0.7Cd0.3Te at ambient temperatures k=148 eV−1, this value decreases to k=105 eV−1 at acceptor concentrations of around 2×1016 cm−3.