bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling of Flow Transition Using an Intermittency Transport Equation
Authors: Suzen Y. B. , Huang P. G.
Published: July 2002

A new transport equation for intermittency factor is proposed to model transitional flows. The intermittent behavior of the transitional flows is incorporated into the computations by modifying the eddy viscosity, μt, obtainable from a turbulence model, with the intermittency factor, γ:μt*=γμt. In this paper, Menter’s SST model is employed to compute μt and other turbulent quantities. The proposed intermittency transport equation can be considered as a blending of two models—Steelant and Dick and Cho and Chung. The former was proposed for near-wall flows and was designed to reproduce the streamwise variation of the intermittency factor in the transition zone following Dhawan and Narasimha correlation and the latter was proposed for free shear flows and a realistic cross-stream variation of the intermittency profile was reproduced. The new model was used to predict the T3 series experiments assembled by Savill including flows with different freestream turbulence intensities and two pressure-gradient cases. For all test cases good agreements between the computed results and the experimental data were observed. [S0098-2202(00)02302-6]
Identification of Dominant Heat Transfer Modes Associated With the Impingement of an Elliptical Jet Array
Authors: Arjocu S. C. , Liburdy J. A.
Published: July 2002

The characteristics of the impinging heat transfer of a three-by-three square array of submerged, elliptic impinging jets was studied. Low Reynolds number conditions, 300 to 1500, are considered for two different elliptic jet aspect ratios, with the impingement distance ranging from 1 to 6 jet hydraulic diameters. A transient thermochromic liquid crystal method was used to map the local heat transfer coefficient distribution. The results are reported for the unit cell under the center jet and detail the mean heat transfer as well as the characteristics of the spatial variation of the heat transfer coefficient. The average heat transfer is found to depend inversely on the elliptic jet aspect ratio at these low Reynolds numbers. Distributions of the heat transfer coefficient, h, are also used to obtain proper orthogonal decompositions of h which are used to identify major spatially distributed features. [S0022-1481(00)02102-2]
Analysis of Variants Within the Porous Media Transport Models
Authors: Alazmi B. , Vafai K.
Published: July 2002

An investigation of variants within the porous media transport models is presented in this work. Four major categories in modeling the transport processes through porous media, namely constant porosity, variable porosity, thermal dispersion, and local thermal nonequilibrium, are analyzed in detail. The main objective of the current study is to compare these variances in models for each of the four categories and establish conditions leading to convergence or divergence among different models. To analyze the effects of variants within these transport models, a systematic reduction and sensitivity investigation for each of these four aspects is presented. The effects of the Darcy number, inertia parameter, Reynolds number, porosity, particle diameter, and the fluid-to-solid conductivity ratio on the variances within each of the four areas are analyzed. It is shown that for some cases the variances within different models have a negligible effect on the results while for some cases the variations can become significant. In general, the variances have a more pronounced effect on the velocity field and a substantially smaller effect on the temperature field and Nusselt number distribution. [S0022-1481(00)02602-5]
Measurement of Eddy Diffusivity of Momentum in Film Cooling Flows With Streamwise Injection
Authors: Kaszeta R. W. , Simon T. W.
Published: July 2002

Measurement of mean velocity and turbulent shear stress are presented for the mixing region of a film cooling situation in which the coolant is streamwise injected with an injection angle of 35 deg. Measurements are performed using triple-sensor anemometry so that all three instantaneous velocity components are documented. The free-stream turbulence intensity level is 12 percent, the ratio of the integral length scale to injection hole diameter is 4.0, the coolant-to-mainstream momentum flux ratio is 1.0, and the density ratio is unity. From these measurements, values for the eddy diffusivities of momentum in the lateral and wall-normal directions are calculated. Additionally, calculated values of the ratio of eddy diffusivity in the spanwise direction to eddy diffusivity in the wall-normal direction are presented, which provide documentation of the anisotropy of turbulent transport in this film cooling flow. [S0889-504X(00)02001-8]
A Detailed Analysis of Film Cooling Physics: Part II—Compound-Angle Injection With Cylindrical Holes
Authors: McGovern K. T. , Leylek J. H.
Published: July 2002

Detailed analyses of computational simulations with comparisons to experimental data were performed to identify and explain the dominant flow mechanisms responsible for film cooling performance with compound angle injection, Φ, of 45, 60, and 90 deg. A novel vorticity and momentum based approach was implemented to document how the symmetric, counterrotating vortex structure typically found in the crossflow region in streamwise injection cases, becomes asymmetric with increasing Φ. This asymmetry eventually leads to a large, single vortex system at Φ=90 deg and fundamentally alters the interaction of the coolant jet and hot crossflow. The vortex structure dominates the film cooling performance in compound angle injection cases by enhancing the mixing of the coolant and crossflow in the near wall region, and also by enhancing the lateral spreading of the coolant. The simulations consist of fully elliptic and fully coupled solutions for field results in the supply plenum, film hole, and crossflow regions and includes surface results for adiabatic effectiveness η and heat transfer coefficient h. Realistic geometries with length-to-diameter ratio of 4.0 and pitch-to-diameter ratio of 3.0 allowed for accurate capturing of the strong three-way coupling of flow in this multiregion flowfield. The cooling configurations implemented in this study exactly matched experimental work used for validation purposes and were represented by high-quality computational grid meshes using a multiblock, unstructured grid topology. Blowing ratios of 1.25 and 1.88, and density ratio of 1.6 were used to simulate realistic operating conditions and to match the experiments used for validation. Predicted results for η and h show good agreement with experimental data. [S0889-504X(00)01301-5]
Mist/Steam Cooling in a Heated Horizontal Tube—Part 2: Results and Modeling
Authors: Guo Tao , Wang Ting , Gaddis J. Leo
Published: July 2002

Experimental studies on mist/steam cooling in a heated horizontal tube have been performed. Wall temperature distributions have been measured under various main steam flow rates, droplet mass ratios, and wall heat fluxes. Generally, the heat transfer performance of steam can be significantly improved by adding mist into the main flow. An average enhancement of 100 percent with the highest local heat transfer enhancement of 200 percent is achieved with 5 percent mist. When the test section is mildly heated, an interesting wall temperature distribution is observed: The wall temperature increases first, then decreases, and finally increases again. A three-stage heat transfer model with transition boiling, unstable liquid fragment evaporation, and dry-wall mist cooling has been proposed and has shown some success in predicting the wall temperature of the mist/steam flow. The PDPA measurements have facilitated better understanding and interpreting of the droplet dynamics and heat transfer mechanisms. Furthermore, this study has shed light on how to generate appropriate droplet sizes to achieve effective droplet transportation, and has shown that it is promising to extend present results to a higher temperature and higher pressure environment. [S0889-504X(00)02502-2]
Thermal Modeling of a Small-Particle Solar Central Receiver
Authors: Miller Fletcher J. , Koenigsdorff Roland W.
Published: July 2002

This paper presents a thermal model of a solar central receiver that volumetrically absorbs concentrated sunlight directly in a flowing gas stream seeded with submicron carbon particles. A modified six-flux radiation model is developed and used with the energy equation to calculate the three-dimensional radiant flux and temperature distributions in a cavity-type particle receiver. Results indicate that the receiver is capable of withstanding very high incident fluxes and delivering high temperatures. The receiver efficiency as a function of mass flow rate as well as the effect of particle oxidation on the temperature profiles are presented. [S0199-6231(00)00201-X]
Characterization of 1,1-Dihydroperfluorooctyl Acrylate (PFOA) by XPS
Authors: Kassis Camille M. , Steehler Jack K. , Linton Richard W.
Published: July 2002

A sample of 1,1-dihydroperfluorooctyl acrylate (PFOA), a low surface energy polymeric material prepared by homogeneous free radical solution polymerization in supercritical CO2, has been investigated by x-ray photoelectron spectroscopy (XPS) using a Perkin-Elmer Physical Electronics Model 5400 spectrometer with monochromatic Al Kα x rays. Knowledge of the surface composition of PFOA is significant since potential applications of this homopolymer include use in polymer blends where this material would be expected to be the surface active species. Controlled surface studies were conducted on a thick polymer film (∼0.5 μm) spun cast from solution onto silicon. Although the F 1s and O 1s regions were structurally straightforward to interpret, the C 1s window showed the expected pattern of functional group components.
Characterization of Poly(2-Hydroxyethyl Methacrylate) (PHEMA) by XPS
Authors: Castner David G. , Ratner Buddy D. , Hirao Akira , Nakahama Seiichi
Published: July 2002

The surface composition of anionic polymerized poly(2-hydroxyethyl methacrylate) (PHEMA) films cast onto glass coverslips was examined with x-ray photoelectron spectroscopy (XPS). The elemental composition determined from a survey scan was 68.3 at. % carbon and 31.7 at. % oxygen. This composition is within experimental error of the composition expected based on the structure of PHEMA (66.7 at. % carbon and 33.3 at. % oxygen). The C 1s spectrum was fit using four components corresponding to C—H/C—C, beta-shifted C—H, C—O, and O=C—O species. The O1s spectrum was fit using three components corresponding to C=O, C—OH, and C—O—C species. The assignment, binding energies, and relative areas are all consistent with the structure of PHEMA and previous XPS studies of methacrylates [D. G. Castner and B. D. Ratner, Surf. Interface Anal. 15, 479 (1990) and G. P. Lopez, D. G. Castner, and B. D. Ratner, 17, ibid. 267 (1991)]. The surface composition of PHEMA after reaction of the hydrdoxyl groups with (CH3Si)2NHSi(CH3)3Cl to produce trimethyl silyated PHEMA (PHEMA-TMS) was also examined with XPS. The elemental composition of PHEMA-TMS determined from a survey scan was 69.2 at. % carbon, 21.9 at. % oxygen, and 8.9 at. % silicon. This composition is within experimental error of the composition expected based on the structure of PHEMA-TMS (69.2 at. % carbon, 23.1 at. % oxygen, and 7.7 at. % silicon). The C 1s spectrum was fit using four components corresponding to C—H/C—C, beta-shifted C—H, C—O, and O=C—O species. The O 1s spectrum was fit using two components corresponding to C=O/C—O—Si and C—O—C species. The assignment, binding energies, and relative areas are all consistent with the structure of PHEMA-TMS and previous XPS studies of methacrylates [D. G. Castner and B. D. Ratner, Surf. Interface Anal. 15, 479 (1990) and G. P. Lopez, D. G. Castner, and B. D. Ratner,17, ibid. 267 (1991)].
UHV-Cleaved NiO (100), CoO (100), and MnO (100) by He II UPS
Authors: McKay Jeffry M. , Henrich V. E.
Published: July 2002

The rocksalt transition-metal oxides whose He II UPS spectra are presented here have the same crystal structure but different cation d-electron configurations: Mn2+ is 3d5; Co2+ is 3d7; and Ni2+ is 3d8. There is currently a great deal of interest in the growth of thin films of these oxides, and it is important to determine the stoichiometry of such films. These UPS spectra are for ultrahigh vacuum-cleaved single-crystal surfaces having bulk stoichiometry. While interpretation of the spectra is complicated by final-state screening effects [V. E. Henrich and P. A. Cox, see The Surface Science of Metal Oxides (Cambridge University Press, Cambridge, 1994)], the increase in the number of occupied 3d orbitals in going from MnO to NiO is clearly visible in the size of the peak at low binding energy (which is the 0 eV reference for the abscissa in the accompanying figure).
Molybdenum Disulfide Single Crystal (0002) Plane XPS Spectra
Authors: Kong Jie , Park Ken T. , Miller A. C. , Klier Kamil
Published: July 2002

Molybdenum disulfide single crystal (0002) plane XPS spectra are presented. The specimen is a natural mineral of graphite-like layered structure. The sample was in situ peeled in the analysis chamber. The spectra include a survey scan, core level Mo 3d5/2, 3d3/2, S 2s, 2p3/2, 2p1/2, 3s, and valence band. The spectra were collected by SCIENTA ESCA-300 High Resolution XPS spectrometer.
Characterization of reactive ion etched surface of GaN using methane gas with chlorine plasma
Authors: Basak D. , Fareed Q. , Nishino K. , Sakai S.
Published: July 2002

Reactive ion etching of GaN has been carried out in two different plasma chemistries using 10Cl2/10Ar and 1CH4/9Cl2/10Ar at various applied radio frequency (rf) power. We have addressed the postetch surface characteristics of GaN, and the effect of CH4 addition to chlorine plasma and the variation of rf power are discussed. Surface contamination, roughness, and stoichiometry have been determined from the results of secondary ion mass spectrometry. It is observed that in the case of plasma with 5% CH4, above 125 W, contamination of carbon is minimal and roughness is similar to that of the as-grown sample. At rf power less than 125 W, the Ga/N ratio of the etched surface is almost unity, whereas at rf power more than 125 W, it is more than unity. When the GaN surface is etched with only chlorine plasma, the surface is Ga excess at all rf power applied. The intensity of the main band-to-band photoluminescence peak is found to decrease when 10Cl2/10Ar is used, and the intensity was a minimum at 200 W. When 5% CH4 is added to the plasma, the intensity at 200 W became almost the same as that of the as-grown sample, indicating minimal damage induced in the surface.
Evacuation and outgassing of vacuum glazing
Authors: Ng N. , Collins R. E.
Published: July 2002

The evacuation and outgassing of vacuum glazing is studied by modeling and experimental methods. A two-dimensional finite difference method of modeling the pumpdown process is validated by comparison with a one dimensional, cylindrically symmetric finite difference method, and with measurements on experimental samples. In the absence of outgassing, the pressure in the glazing decreases linearly with time in the viscous flow region; in the molecular flow region, the pressure decreases exponentially with time. The time taken to evacuate the sample from atmospheric pressure to the transition pressure is approximately equal to one time constant for the subsequent exponential pressure decrease. The time constant associated with the exponential pressure decrease in the molecular flow region can be written τ=V/C, where V is the volume of the sample, and C is the series combination of the conductance associated with the radially inwards gas flow towards the pumpout port, and the conductance of the pumpout tube itself. For very small gaps, τ varies inversely with gap; for large gaps, τ is proportional to gap. The time constant is least for gaps in the range 0.1–0.5 mm, depending on the dimensions of the sample and the pumpout tube. The outgassing rate at elevated temperatures from the internal surfaces of the glazing is shown to decrease slowly, relative to the time constant for pressure reduction in a typical sample. Over a wide pressure range, the outgassing rate is unaffected by the pressure in the sample. The time required to evacuate a sample of vacuum glazing is therefore determined mainly by outgassing, rather than by pumping considerations.
Hot carrier transport effects in Al2O3-based metal-oxide-semiconductor structures
Authors: Ludeke R. , Cuberes M. T. , Cartier E.
Published: July 2002

Over the barrier, hot electron transport across 8 nm thick amorphous Al2O3 layers embedded in metal-oxide-semiconductor (MOS) structures was investigated with ballistic electron emission microscopy (BEEM). The oxide field dependence of the BEEM threshold voltage Vth, which corresponds to the potential maximum of the barrier, was found to be dominated by image force and charge trapping/detrapping effects. The static barrier height at the W–Al2O3 interface ΦB=3.90±0.03 eV and the dynamic dielectric constant εif=1.86±0.1, which reflects the strong image force lowering of the barrier observed at both interfaces. A band offset between the Al2O3 and Si conduction bands of 2.78±0.06 eV was deduced. Electron trap levels at energies overlapping the Si band gap and of densities in the 1012 cm−2 range were deduced to lie in the oxide near the Al2O3–Si interface. Their occupancy is determined by the position of the interface Fermi level. For p-type substrates the traps were empty (filled) for positive (negative) applied bias. Local, electrical stressing increased the interface trap charge for n-type substrates, but had negligible consequences on p-type substrates. The Al2O3 was readily stressed to failure upon injecting sub-nano-Coulomb of charge at electron kinetic energies in the 4–6 eV range.
Influence of Pt underlayer on the magnetic and magneto-optical properties of sputtered Co0.25Pt0.75 alloy films, and the static recording performance
Authors: Zou Z. Q. , Kim K. W. , Lee Y. P. , Li M. , Shen D. F.
Published: July 2002

Influences of a Pt underlayer and the preparing conditions on the magnetic and magneto-optical (MO) properties of Co0.25Pt0.75 alloy films, which were prepared by sputtering using a composite target, were investigated. It was found that a good fcc (111) texture was formed in a Pt underlayer deposited in a sputtering pressure below 2 Pa even without heating the substrate. Co0.25Pt0.75 alloy films subsequently deposited on such a Pt underlayer exhibited an enhanced perpendicular magnetic anisotropy, and the growth temperature for excellent magnetic and MO properties was lowered to 150 °C. Static read–write experiments on the Co0.25Pt0.75 alloy films showed that the static signals could be easily written, at a moderate recording power, in the alloy films without a Pt underlayer, and that the introduction of a relatively thick Pt underlayer was not beneficial to the thermomagnetic writing for the alloy films. The large readout signals of an Al/ZnS/Co0.25Pt0.75/glass trilayer structure suggest that CoxPt1−x alloy films are a promising candidate for the advanced MO recording media.
Characterization of step coverage change in ultraviolet-transparent plasma enhanced chemical vapor deposition silicon nitride films
Authors: Bierner J. , Jacob M. , Schönherr H.
Published: July 2002

Ultraviolet (UV)-transparent silicon nitride films were deposited in a plasma enhanced chemical vapor deposition reactor. The dependence of the film properties on process parameters has been studied. UV transmittance, refractive index, hydrogen content, and step coverage were compared to UV-opaque films. A significant difference in film growth between UV-opaque and UV-transparent SiNx layers has been detected. When film properties shift to an increased UV transparency, step coverage worsens significantly. This phenomenon is suggested to be caused by a strong reduction to Si–Si bonds for films below stoichiometric composition at low SiH4/NH3 gas flow ratios.
Epitaxial Orientation Studies of Gold on uhv-Cleaved Mica during Early Stages of Nucleation and Growth
Authors: Poppa Helmut , Heinemann Klaus , Elliot A. Grant
Published: July 2002

The epitaxial deposition of gold on mica under well-defined deposition and substrate surface conditions was studied in detail. Unconventional electron microscopy methods using newly developed lattice imaging and Bragg reflex-imaging techniques were employed for an in-depth analysis of epitaxial orientational relationships. In addition to the expected parallel and 30 ° rotated {111} orientations of the deposit, a strong genuine {211} orientation (as opposed to a twinned {111} orientation) was found for the first time in very early stages of deposition and hypothetically linked to regional heterogeneities of the actual cleavage structure of the substrate surface. Multiple twinning was found to occur only in later stages of deposition.
Outgassing of Nuclear Rocket Fuel Elements
Authors: Easton D. S. , Clausing R. E.
Published: July 2002

In order to predict the gaseous environment in a nuclear rocket engine before and after operation in space, an apparatus has been developed for measuring the type, quantity, and outgassing rates of gases that are released from graphite fuel elements at various temperatures in vacuum. Data readout from a quadrupole residual gas analyzer (QRGA) and nude Bayard-Alpert type ion gages permit analysis of up to 12 gases simultaneously. The data are processed by a computer program which first calculates the partial pressures of the various gases from a least square fit to a set of 18 simultaneous equations (one for each spectrometer peak) with 12 unknowns (12 separate gases). The coefficients of the unknowns are obtained from the cracking patterns of individual gases. The program then calculates and tabulates the outgassing rate of each gas for each sampling time and produces plots of the outgassing as functions of time or temperature. The computer program also: (a) fits the outgassing rates to an analytical expression, prints out the constants for the equation, and draws the best curve of the specified form through the data points; (b) extrapolates the data to long outgassing times and prints out the outgassing rates and total quantity of each gas at selected times; (c) compiles the data from a number of runs and plots the outgassing rates at preselected times as a function of temperature; and (d) prints out control data such as cracking patterns, calibration constants, and various checks and comparisons to aid in the evaluation of the instrumentation. The experiment not only produces accurate and detailed outgassing data, but also makes possible a more accurate extrapolation of data to long times and other temperatures. The detailed results will also aid in understanding the mechanisms controlling outgassing behavior.
Enhanced Vapor Pressure of Small Clusters
Authors: Behrndt Klaus H.
Published: July 2002

According to the Gibbs-Thomson equation, the vapor pressure pr of clusters of radius r depends on the surface free energy σ. The latter is a function of the number of nearest neighbors of the surface atoms Za. The decrease of Za with cluster size is discussed for several models of Wulff polyhedra. Based on the data for these models, a size-dependent σr is introduced which results in pr,σ≫pr and renders the Gibbs-Thomson equation increasingly inaccurate for r<30 Å. The cluster shape as well as the mode of separation of atoms are affected by the presence of a surface. The consequences of introducing σr, and possibly a size dependent Ωr, into classical nucleation theory are discussed. It is concluded that the atomistic theory describes more reliably the formation of nuclei consisting of only a few atoms.
Recrystallization of (100) Oriented Gold Films onto (111) Orientation
Authors: Feder R. , Mader S.
Published: July 2002

Texture transitions associated with recrystallization and grain growth occur m thin films in different modes from those observed in bulk. As an example, the recrystallization of free standing (100) oriented Au films into (111) films was examined where the overall driving force presumably arises from the anisotropy of the surface energy. The recrystallization took place while heating between 600 ° and 700 °C. Subsequent electron microscope observations showed several stages of the transition mechanism. They include growth of twins inside the (100) oriented regions and a gradual bending and rotation of the twin crystals into the (111) orientation. This leads to (111) films which contain elastic distortions fluctuating on a scale of several microns.
Ac Field Effects in Evaporation of Sodium Chloride, Cadmium Sulfide, and Silver onto Fused Silica
Authors: Sinclair W. R. , Kammlott G. W. , Fastnacht R. A.
Published: July 2002

Ac field effects (i.e., preferred orientation and enhanced crystallite size) have been noted on the structure of evaporated NaCl, CdS, and Ag films on fused silica substrates over a temperature range of −100 ° to +200 °C, a frequency range of 20 Hz–2 MHz and a voltage gradient range of 15–500 V/cm. For each material the effect of frequency at room temperature is greatest at about 104 Hz, but this maximum is rather shallow. The ac field effect on NaCl is greater at −100 °C than at room temperature or 200 °C. Sodium chloride films show greater effects of preferred orientation and crystallite size enhancement at 25 °C than do CdS or Ag.
Magnification of Cracks in Wires Located on the Axis of a Cylindrical Field-Emission Microscope
Authors: Creighton Donald L. , Benedetti Robert L.
Published: July 2002

Previously, only experimental data have been published for the magnification of the cylindrical field-emission microscope in the instance where a depression (i.e., crack) rather than a protuberance is observed. This investigation has resulted in the determination of the theoretical magnification (based on computer-determined field plots and trigonometrical numerical methods) of a cylindrical field-emission microscope, in the axial direction, for “cracks” in wires located on the axis of the microscope; additionally, experimental data on both axial and circumferential magnification have been obtained. Predicted or theoretical magnification is of the correct order of magnitude and follows the same trend as the experimentally measured values. The effect of variation in crack geometries has been studied and the results are discussed.
Metal Surfaces and Their Changes by Chemisorption
Authors: Knor Z.
Published: July 2002

Two basic approaches to the solution of surface problems exist in both theoretical and experimental research on metals. In the first approach, the bulk properties of metals and changes caused by surface processes are studied and the interpretation is based on the nearly-free-electron model of the metal. This approach was successful in the explanation of bulk properties. However, because of the complexity and asymmetry of the system (crystal and gas molecule), one is usually forced to use oversimplified models, which sometimes fail in the elucidation of all the observed effects. Another approach is based on the assumption that the surface interaction (resulting in the formation of a quasichemical compound) concerns a limited number of participants (as in a chemical reaction). In the simplest case: gas particle and a surface atom. New experimental evidence (field-ion-emission microscopy, field-electron-emission microscopy, ion-neutralization spectroscopy) has been found supporting the idea that the properties of a surface atom in the moment of the interaction can be roughly approximated by the properties of an individual atom. The type of approach which should be used in a particular case depends both on the experimental method and on the problems in which we are interested.
Oxidized Silicon Surface
Authors: Gray Peter V.
Published: July 2002

Surface parameters play an important if not dominant role in limiting the performance of many semiconductor devices. The research effort which has been directed toward semiconductor surfaces in recent years has greatly improved our understanding of oxidized silicon and has provided a logical basis for modern semiconductor processing techniques. Relevant surface phenomena include contamination and imperfections in the oxide layer, impurity redistribution in the silicon near the oxide, and additional electronic states at the oxide-silicon interface. The successes of the MOS method of surface characterization will be reviewed.
Physical Factors Influencing Accommodation Pumps
Authors: Hobson J. P. , Pye A. W.
Published: July 2002

An experimental study has been made of a number of simple physical factors which were considered likely to influence the pump ratio of accommodation pumps. Single stage pumps operating between room and liquid nitrogen temperature were used throughout. For most experiments He4 gas was used, but pump ratios greater than unity were also measured with He3, H2, and N2. For the smooth arm of the pump various surfaces were tested: Pyrex after a variety of treatments; various other types of glass; metal films. For the rough arm of the pump various modes of roughening were tested. Geometrical effects were tested by various configurations of pumps. The effect of thermal gradients was examined, as well as the effects of standard vacuum operations. Major conclusions were that vacuum heated Pyrex was the best smooth surface, that several methods of roughening surfaces were equivalent, that Ti was the only metal film tested which was of interest as a smooth surface, that geometrical effects were significant, but the effect of thermal gradients was minor.
Characteristics of rf Sputtered Barium Titanate Films on Silicon
Authors: Salama C. A. T. , Siciunas E.
Published: July 2002

The physical and electrical properties of barium titanate films approximately 1 μm thick, prepared by rf sputtering onto silicon substrates in both pure argon and 95% argon–5% oxygen glow discharges were investigated. The argon-oxygen mixture was used to minimize oxygen deficiencies in the films resulting from the possible decomposition of the barium titanate in the glow discharge. Sputtering was carried out in a standard diode system with a water-cooled target of ceramic BaTiO3 at power densities of up to 1.6 W/cm2, at a gas pressure of 7–8×10−3 Torr, and in a magnetic field of 20 G. The substrate holder could be heated to about 650°C during deposition. The deposition rate was typically 100 Å/min and was dependent on the sputtering power density and the substrate temperature. The films were deposited on clean n-type silicon wafers of approximately 5 and 0.01 Ω⋅cm resistivity. Some samples were subjected to a post-deposition heat treatment in nitrogen or oxygen ambients at 1000°C. The deposition rate, crystal structure, and refractive index of the films were investigated as a function of deposition temperature and sputtering gas. The electrical characteristics of the films, including the dielectric constant, loss tangent, conductivity, insulator bulk charge, charge storage at the BaTiO3–SiO2 interface, and ferroelectricity were also investigated.
U.H.V. Opening Technique for Analyzing Metal Ceramic Vacuum Tubes
Authors: Grady B. I.
Published: July 2002

A method whereby a metal ceramic magnetron tube can be opened on an U.H.V. (ultrahigh vacuum), system and then operated for gas analysis with a mass spectrometer is described. A video tape recorder is employed to record gas evolution during both the tube opening and operation, so that instantaneous gas release can be observed.* Vacuum integrity of the tube, on the system, is kept intact at all times. Preparation of a tube for opening is discussed in detail. Gases evolved due to the opening device piercing the metal tube envelope are also discussed.
The physical interaction of nitrogen with Pyrex, stainless steel, and nickel at very low pressure
Authors: Outlaw R. A. , Brock F. J. , Wightman J. P.
Published: July 2002

The physical adsorption of nitrogen on the surfaces of Pyrex, 347 stainless steel, and polycrystalline nickel was investigated over the pressure range 1×10−12–3×10−7 Torr and for the temperatures 77.4 and 87.4 °K. The metal surfaces were prepared by vacuum firing, by chemical cleaning, and, following bakeout, by electron impact desorption (EID). Work function measurements were used to indicate changes in the surface condition following electron bombardment, and a mass spectrometer was used to monitor gas composition. The isotherms revealed that the stainless surface was very heterogeneous and that the Pyrex surface area had a roughness factor of 1.7. Nitrogen isotherms were also taken on the metal surfaces after they had been exposed to oxygen. Very little change in physical adsorption on the nickel was detected, presumably because the chemisorbed oxygen was incorporated into the bulk. The chemical adsorption of N2 on nickel at room temperature and below was not observed.
Fabrication of experimental Josephson tunneling circuits
Authors: Greiner J. H. , Basavaiah S. , Ames I.
Published: July 2002

A multilevel thin-film process has been developed for fabricating experimental circuits containing Josephson tunneling gates, insulated crossings, superconducting contacts, and terminating resistors. The process utilizes a Nb film for the ground plane and Pb alloy films for overlying superconducting layers. Insulation is achieved through the use of vacuum-deposited SiO films and anodization of the Nb ground plane. An oxide formed by rf sputter-etching in an oxygen plasma is used for forming the tunneling barriers. Photoprocessing techniques are used for patterning. Through use of the process it has been possible to fabricate experimental memory and logic circuits which survive thermal cycling to 4.2 K and intervening storage at room temperature without significant changes in electrical characteristics.
Measurement of beam-gas scattering lifetime in Pohang light source
Authors: Park C. D. , Lee T.-Y. , Bae I. H. , Chung S. M.
Published: July 2002

The beam-gas scattering lifetime of the Pohang light source (PLS) storage ring was studied. To eliminate the dominant Touschek effect for measurements of the beam-gas scattering lifetime, two methods were used separately: vacuum pressure increase by helium injection and very low electron beam density. Then two vertical beam scrapers were used to investigate the dependence of the Coulomb lifetime on the acceptance limiting aperture size. It was possible to obtain the separate ranges of Coulomb and bremsstrahlung lifetimes in the pressure range of normal operation. The results indicate that the vacuum is still an important factor for PLS, especially when small gap undulators are installed.
Study of a mechanically clamped cryo-chuck device in a high density plasma for deep anisotropic etching of silicon
Authors: Hibert C. , Aachboun S. , Boufnichel M. , Ranson P.
Published: July 2002

This article presents a study concerning a cryo-chuck device used in an inductively coupled plasma reactor for deep anisotropic etching of narrow trenches (2 μm wide) in silicon wafers of 5 in. in diameter. Thermal mechanisms in a mechanically clamped cryo-chuck system have been studied. First, wafer deformations have been measured in the chuck device. Deformations occur because of the helium backside pressure allowing thermal transfer to cool the wafer. In a second step, these deformations have been used in calculations considering the heat transfers in the substrate. In a last step, in situ temperature measurements have been made on wafers during a process using a LUXTRON® probe. This study shows the influence of the backside helium gap variation and the clamping ring temperature on the uniformity of substrate cooling.
Surface science models for CoMo hydrodesulfurization catalysts: Influence of the support on hydrodesulfurization activity
Authors: Coulier L. , Kishan G. , van Veen J. A. R. , Niemantsverdriet J. W.
Published: July 2002

Flat model systems of supported oxidic CoMo hydrodesulfurization (HDS) catalysts, consisting of a conducting substrate with a thin SiO2 or Al2O3 layer on top of which the active catalytic phase is deposited by spin coating, were used to study the influence of the support and the use of chelating agents on the formation of the active CoMoS phase. On Co/Al2O3 catalysts Co can only be partially sulfided due to the strong interaction with Al2O3. In the mixed phase CoMo/Al2O3 system, the presence of Mo facilitates the sulfidation of Co. Due to the interaction of Mo with the support the Co–Al2O3 interaction is blocked. In these catalysts the sulfidation of Co and Mo proceed at the same rate. In the case of CoMo/SiO2 catalysts the weak interaction with the SiO2 support results in the complete sulfidation of Co at low temperatures, while Mo sulfides at a slower rate. Thiophene HDS activity measurements showed that due to the stronger interaction, Al2O3 is a better support for CoMoS formation. By complexing CoMo on Al2O3 to chelating agents, like ethylenediaminetetraacetic acid (EDTA), the sulfidation of Co is retarded while that of Mo is facilitated. Although Mo also forms complexes with EDTA, these complexes are less stable than those of Co. Hence, the sulfidation of Mo precedes that of Co. Due to the absence of interaction with the support of the same sulfidation behavior was observed for both supports. The activity tests showed that these catalysts have the highest activity, irrespective of support.
Emission characteristics of Spindt-type platinum field emitters improved by operation in carbon monoxide ambient
Authors: Gotoh Y. , Nozaki D. , Tsuji H. , Ishikawa J. , Nakatani T. , Sakashita T. , Betsui K.
Published: July 2002

The electron emission characteristics of Spindt-type platinum field emitters that were improved by operation in a carbon monoxide gas ambient were investigated in detail. We present differences in the emission characteristics, such as the change of Fowler–Nordheim characteristics in the S–K chart, change in current fluctuation and emission pattern, and resistance against oxygen exposure due to the improvement. We found that the work function increased slightly during the introduction of carbon monoxide gas up to 10−4 Pa; but when the gas was evacuated, the work function recovered. The work function finally decreased at a pressure of 10−3 Pa. The emission characteristics were degraded during the oxygen exposure both for the nontreated and treated emitters. However, degradation was less significant for the carbon-monoxide-treated emitter than for the nontreated emitter. All these results suggest that the improvement can be attributed to the presence of carbon atoms or a carbon layer at the surface of the emitter.
Conical etching and electrochemical metal replication of heavy-ion tracks in polymer foils
Authors: Dobrev D. , Vetter J. , Neumann R. , Angert N.
Published: July 2002

Cone-shaped pores as well as cylindrical pores with tapered ends of various geometrical forms were produced via one-side etching of latent ion tracks in thin polymer foils by applying a hydrostatically controlled, neutralizing counter solution on the membrane side opposite to the etchant. The sizes and shapes of the pores depend on the specific composition and the hydrostatic pressure of the counter solution, and the time of etching. Metal replication of such pores provides two-dimensional arrays of sharp whiskers that may serve as electron emitters, being of interest for applications in electronics.
Characterization of the arc ion-plated CrN coatings oxidized at elevated temperatures
Authors: Hsieh W. P. , Wang W. C. , Wang C. C. , Shieu F. S.
Published: July 2002

Microstructure and chemistry of the arc ion-plated CrN coatings oxidized in air at temperatures ranging from 300 to 800 °C for 60 min were analyzed by x-ray diffraction (XRD), transmission electron microscopy (TEM), electron energy loss spectroscopy (EELS), and Auger electron spectroscopy (AES). The CrN coatings were prepared by cathodic arc ion plating deposition on a type 304 stainless steel with a Cr interlayer. The XRD result shows that oxidation of the CrN-coated steel above 500 °C produces two new phases, Cr2O3 and β-Cr2N, and the amount of both phases increases with the oxidation temperature. Cross-section TEM shows three distinct regions including the steel substrate, the Cr interlayer, and the CrN coating in the as-deposited specimen, in which the CrN layer exhibits a columnar structure and preferred orientation. Oxidation of the CrN-coated steel at high temperatures produces an oxide layer, Cr2O3, on the coating surface, and the underlayer is a mixture of CrN and β-Cr2N phases. Unlike the as-deposited specimen, the dual phase layer in the oxidized specimens has an equiaxed grain structure and the average grain size of the layer increases with the oxidation temperature. In addition, pronounced grain growth in the dual phase layer near the coating surface is observed in the specimen heat-treated at 800 °C. Elemental analyses of the CrN coating near the free surface by EELS and AES reveal that the O/N ratio of the coating and the thickness of the oxide layer increase with the oxidation temperature.
Micromachined piezoresistive cantilever array with integrated resistive microheater for calorimetry and mass detection
Authors: Abedinov N. , Grabiec P. , Gotszalk T. , Ivanov Tz. , Voigt J. , Rangelow I. W.
Published: July 2002

We describe a microcantilever calorimeter consisting of an array of ten cantilevers. Each single cantilever is capable of detecting heat energy with the resolution of 50 nW Hz(−0.5). The device is based on a Si microcantilever coated with a 1 μm thick layer of SiO2 deposited with a 700 nm thick layer of aluminum which forms a resistive microheater. Heat fluxes are monitored by detecting the cantilever deflection (bending) due to the bimaterial structure of the cantilever (dissimilar thermal expansion properties of SiO2 and Al). The resistive microheater serves for calibration of the heat flux and for temperature sensing. In our design a piezoresistive Wheatstone bridge detector is applied for measurements of the cantilever beam deflection. The cantilever displacement detection system enables investigations in ultrahigh vacuum and low temperature conditions. The microcantilevers are manufactured in a one-dimensional array having ten individual microcantilevers which is the first step in the fabrication of an infrared detector array with spatial resolution. The displacement sensitivity versus temperature change of the described sensor array as a function of temperature change is of about 2 nm/K and an estimated resolution limit of temperature detection is ≈10−3 K at 300 K. In order to demonstrate the cantilever bending sensitivity we employ the piezoresistive cantilever array as a picogram microbalance.
Investigation of the bonding strength and interface current of p-Si/n-GaAs wafers bonded by surface activated bonding at room temperature
Authors: Howlader M. M. R. , Watanabe T. , Suga T.
Published: July 2002

Equivalent bulk strength of the interface between p-Si/n-GaAs bonded through the surface activated bonding (SAB) method is found. The interface current was extensively investigated. Nonideal behavior of the pn junction current is found to be due to the tunneling current between the conduction band and valence band across the transition region associated with band gap states. Interface current decreases with increasing sputtering time and energy and vice versa. Irradiation time and energy dependent behavior indicates that the accumulation of radiation induced defects associated with the doping controls the interface current of p-Si/n-GaAs. Moreover, strong impact of the exposure to an ultrahigh vacuum atmosphere of the activated surfaces on the interface current of p-Si/p-Si is found. Finally it can be suggested that a laser diode can be fabricated by the bonding between p-Si and n-GaAs through the SAB method, because of the achievement of equivalent bulk strength of the interface.
Characterization of reactive ion etch lag scaling
Authors: Keil D. , Anderson E.
Published: July 2002

Recent advances in ultralarge-scale integration have typically depended on reductions in etched feature size. This has motivated efforts to find etch processes that will precisely etch increasingly smaller features while retaining the ability to etch larger features. As feature sizes push below 0.25 μm, reactive ion etch (RIE) lag control becomes increasingly important. Knowing how RIE lag scales with feature size for a given process aids in determining if that process must be discarded and a new one developed. In those situations where a process cannot be discarded, an understanding of RIE lag scaling aids in predicting fabrication difficulties for a given device design. Using a minimal set of initial assumptions, it is shown that a relationship can be derived which relates etch rate to the time development of the feature aspect ratio. It is then shown that this relationship can be used to derive an expression for the etch depth as a function of time and feature size. The assumptions made are justified by phenomenological observation rather than by an assumed mechanism. This approach enhances the generality of the results obtained, thus making them useful for a variety of practical etch engineering applications.
Infrared spectroscopic study of dimethylaluminum-hydride adsorption on oxidized, hydrogen-terminated, and reconstructed Si surfaces
Authors: Wadayama T. , Takeuchi K. , Mukai K. , Tanabe T. , Hatta A.
Published: July 2002

Adsorption and decomposition of dimethylaluminum-hydride (DMAH) on various Si(111) and Si(100) surfaces [chemically oxidized, hydrogen-terminated, reconstructed (7×7) and (2×1)] have been investigated at 90 K with a multiple reflection infrared (IR) attenuated total reflection (ATR) method. On the chemically oxidized Si(111) surface, IR absorption due to DMAH increased linearly with DMAH exposure, indicating that DMAH was merely condensed on the surface. Upon DMAH exposure to the hydrogen-terminated Si(111) surface, the stretch band of the surface monohydride (Si–H) diminished immediately, revealing that DMAH reacts with the terminated hydrogens. In contrast, DMAH exposure to the hydrogen terminated Si(100) surface leads to a slight intensity decrease in the bands due to surface hydrides (Si–Hx:x=1–3). On the reconstructed Si surfaces [Si(100)(2×1) and Si(111)(7×7)], IR bands due to DMAH could not be observed during the early stage of DMAH exposure, suggesting that the reactivity of DMAH with the reconstructed surfaces is extremely high. The surface reactivity at 90 K, as judged by IR absorption intensities of the methyl and Al–H groups in DMAH, decreases in the sequence, Si(100)(2×1), Si(111)(7×7), hydrogen-terminated Si(111), and hydrogen-terminated Si(100).
Polishing effect of the plasma on the growth of YBa2Cu3O7−δ films by radio frequency sputtering
Authors: Chou Hsiung , Lin P. I. , Hsu C. C. , Chow T. C. , Hong M. T. , Chen Y. C. , Liu J. R. , Tsai T. P.
Published: July 2002

The surface morphology of YBa2Cu3O7−δ (YBCO) films is crucial for applications such as multilayering and optical detection. In this article, we showed that the resputtering effect due to the rf plasma can planarize the surface morphology of YBCO films under specific conditions. By setting the relative position and angle of the heater to the gun, the plasma density over the substrate can be altered from an asymmetric to a symmetric distribution. When the substrate was near the plasma, the negative oxygen ions resputtered part of the mobile atoms from the surface of the film back into the plasma, which caused compositional distortion, delaying the merge of grains and leaving uncovered holes. With a longer distance, the resputtering effect was suppressed, and precipitates appeared on the surface of films, resulting in a rougher surface. At an optimum heater-to-gun configuration, the function of the resputtering effect produced a polishing effect on the surface of films, which made a smooth and precipitate-free YBCO film possible. We also found that this film with smooth and precipitate-free morphology exhibited suppressed superconductivity, Tc0 and Ton.