bluuebunny/crossref_metadata_2025 huggingface dataset:
A New Optimization Method for Dynamic Design of Planar Linkage With Clearances at Joints—Optimizing the Mass Distribution of Links to Reduce the Change of Joint Forces
Authors: Feng B. , Morita N. , Torii T.
Published: July 2002

This paper presents a new optimization method for dynamic design of planar linkage with clearances at joints. The general consideration is to optimize the mass distribution of links to reduce the change of joint forces. The mass, the center position of mass and the moment of inertia the moving links are taken as the optimizing variables. The objective functions are taken as the changes of the amplitude and direction of the joint forces and they are minimized. The optimized result shows that the magnitude of joint force can be controlled hardly to change and the direction of joint force can be controlled to change smoothly with respect to the crank angle, although the clearances exist at the joints. The link shape can be formed with the optimized variables by using the small element superposing method (SESM) and a design example is given.
Fluid Shear Stress-Induced Alignment of Cultured Vascular Smooth Muscle Cells
Authors: Lee Ann A. , Graham Dionne A. , Dela Cruz Sheila , Ratcliffe Anthony , Karlon William J.
Published: July 2002

The study objectives were to quantify the time- and magnitude-dependence of flow-induced alignment in vascular smooth muscle cells (SMC) and to identify pathways related to the orientation process. Using an intensity gradient method, we demonstrated that SMC aligned in the direction perpendicular to applied shear stress, which contrasts with parallel alignment of endothelial cells under flow. SMC alignment varied with the magnitude of and exposure time to shear stress and is a continuous process that is dependent on calcium and cycloskeleton based mechanisms. A clear understanding and control of flow-induced SMC alignment will have implications for vascular tissue engineering.
Scaling of Sea Ice Fracture—Part I: Vertical Penetration
Authors: Bazˇant Z. P.
Published: July 2002

Based on the premise that large-scale failure of sea ice is governed by fracture mechanics, recently validated by Dempsey’s in situ tests of fracture specimens of a record-breaking size, this two-part study applies fracture mechanics and asymptotic approach to obtain approximate explicit formulas for the size effect in two fundamental problems. In the present Part I, the load capacity of a floating ice plate subjected to vertical load is determined, and in Part II, which follows, the horizontal force exerted by an ice plate moving against a fixed structure is analyzed in a similar manner. The resulting formulas for vertical loading agree with previous sophisticated numerical fracture simulations as well with the limited field tests of vertical penetration that exist. The results contrast with the classical predictions of material strength or plasticity theories, which in general exhibit no size effect on the nominal strength of the structure.
Error Analysis of the Cylindrical Capacitive Sensor for Active Magnetic Bearing Spindles
Authors: Ahn Hyeong-Joon , Jeon Soo , Han Dong-Chul
Published: July 2002

This paper discusses the effects of mechanical errors of the cylindrical capcitive sensor (CCS) for active magnetic bearing (AMB) spindles, including the roundness error of a rotor and the mounting error of a sensor. The CCS has earned much interest as an AMB sensor due to its advantages of high resolution and spatial-averaging effect. An analytical model of the CCS is given and its spatial-averaging effect is shown quantitatively. The analytical model of the measuring process with the variation of sensor geometry shows that the CCS is more robust to roundness errors than the generally used probe sensor. This is verified through simulations and experiments on measuring orbits of rotors with harmonic roundness errors. In addition, the effects of mounting errors of the sensor are modeled and investigated. [S0022-0434(00)02601-0]
Model of Grain Deformation Method for Evaluation of Creep Life in In-Service Components
Authors: Kim Hyo-Jin , Jung Jae-Jin
Published: July 2002

The creep life can be evaluated by the degree of grain deformation since the grains of Cr-Mo base material deform in the direction of stress. The grain deformation method using image-processing technique is developed for life assessment of in-service high temperature components. The new assessment model for the method is presented to apply to in-service components and is verified by interrupted creep test for ex-serviced material of 1Cr-0.5Mo steel. The proposed model, which is irrespective of stress direction, is to evaluate mean of the absolute deviation for the measured aspect ratios of the grains sections. [S0094-4289(00)00801-X]
On Void Growth in Elastic-Nonlinear Viscous Solids Under Creep and Cyclic Creep Conditions
Authors: Mohan R. , Brust F. W.
Published: July 2002

The growth of initially spherical periodic grain boundary voids in an elastic-nonlinear viscous material is investigated. Large geometry changes are taken into account to correctly capture the trend of void growth rate and evolution of void shape. To this end, an axisymmetric unit cell model of the damaged material is considered. The temporal characteristics of the void growth rate and shape changes and void interaction effects were determined for several triaxial stress states, under constant stress conditions. The results are compared with existing approximate analytical models for void growth rate in a purely nonlinear viscous solid. The finite element calculations indicate that while the effect of elasticity is minimal in determining the transient time for void growth, the growth rates after the initial transient may be more rapid in elastic-nonlinear viscous materials compared with the rates for purely nonlinear viscous materials, especially so under high triaxial stress states. In addition, the approximate analytical expression for void growth rates significantly under predicts the rates for high triaxial stress states and predicts a wrong trend for low triaxial stress states. Calculations of void growth under balanced strain cycling conditions are also performed. The results indicate that void growth can occur, consistent with experimental observations under balanced cycling loading conditions, provided nonlinear shape changes are taken into account. In addition, the analyses show that the cavity growth rate is constant under balanced cyclic loading conditions. This observation is in agreement with the experimental findings of Barker and Weertman (1990, Scr. Metal. Mater. 24, pp. 227–232). That material elasticity does not play any role in void growth or shrinkage under balanced cyclic creep conditions is also clearly demonstrated by the results. [S0094-4289(00)00803-3]
Emulsions Versus Neat Oils in the Cold Rolling of Carbon Steel Strips
Authors: Shirizly A. , Lenard J. G.
Published: July 2002

Low carbon steel strips were cold rolled using various lubricants. The objectives were twofold. The first concerned whether the use of an emulsion would lower the loads on the mill as much as a neat oil would. The second was to study the effect of the lubricant on the surface roughness of the rolled product. The strips were rolled dry first. This was followed by using water only as the lubricant. Four other lubricants were then employed: SAE 10 and SAE 60 automotive oils, the SAE 10 base oil with 5 percent oleic acid added and the SAE 10 base oil, emulsified, using water and polyoxyethylene lauryl alcohol as the emulsifier, 4 percent by volume. The roll loads were lowered when any of the lubricants, including water, neat oils and the emulsion, was introduced in the contact zone. However, effect of the viscosity on the loads was not found to be significant. The roughness of the rolled strip was found to be reduced as the lubricant viscosity was reduced. [S0742-4787(00)01203-0]
Effect of Internal Coolant Crossflow Orientation on the Discharge Coefficient of Shaped Film-Cooling Holes
Authors: Gritsch M. , Saumweber C. , Schulz A. , Wittig S. , Sharp E.
Published: July 2002

Discharge coefficients of three film-cooling hole geometries are presented over a wide range of engine like conditions. The hole geometries comprise a cylindrical hole and two holes with a diffuser-shaped exit portion (a fanshaped and a laidback fanshaped hole). For all three hole geometries the hole axis was inclined 30 deg with respect to the direction of the external (hot gas) flow. The flow conditions considered were the hot gas crossflow Mach number (up to 0.6), the coolant crossflow Mach number (up to 0.6) and the pressure ratio across the hole (up to 2). The effect of internal crossflow approach direction, perpendicular or parallel to the main flow direction, is particularly addressed in the present study. Comparison is made of the results for a parallel and perpendicular orientation, showing that the coolant crossflow orientation has a strong impact on the discharge behavior of the different hole geometries. The discharge coefficients were found to strongly depend on both hole geometry and crossflow conditions. Furthermore, the effects of internal and external crossflow on the discharge coefficients were described by means of correlations used to derive a predicting scheme for discharge coefficients. A comparison between predictions and measurements reveals the capability of the method proposed. [S0889-504X(00)01601-9]
Dynamical Modeling of Deepwater-Type Cylindrical Tuned Liquid Damper With a Submerged Net
Authors: Kaneko Shigehiko , Mizota Yasuo
Published: July 2002

An analytical model for describing the effectiveness of a deepwater-type cylindrical tuned liquid damper (TLD) with a submerged net for suppressing horizontal vibration of structures is first proposed. In this study, we performed calculations to estimate the effectiveness of a deepwater-type cylindrical TLD based on a proposed dynamical model and compared with experimental results obtained by shaking table experiments and free oscillation tests. In particular, the effect of hydraulic resistance produced by a submerged net and the liquid depth ratio (the ratio of the liquid depth to the diameter of the cylindrical tank) are examined intensively. In the analysis, employing finite amplitude wave theory and Galerkin method in the case of cylindrical tank, we obtained hydrodynamic forces and the free surface elevations. Then, combining the hydrodynamic forces with the equation of motion of the structure, damped transient responses were calculated. The calculated results thus obtained were compared with the experimental results, by which the validity of the modeling methodology was confirmed. [S0094-9930(00)00101-3]
Chromium Nitride by XPS
Authors: Milošev Ingrid , Strehblow Hans-Henning , Navinšek Boris , Panjan Peter
Published: July 2002

Chromium nitride (CrN) 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 Cr (0.08 μm) was deposited between the substrate and the 2.8 μm thick CrN 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 CrN 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-monochromatized 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 chromium and nitrogen (Cr 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 a least squares fitting procedure.
Atomic scale Pb chains on Si(100)
Authors: Dong Zhen-Chao , Fujita Daisuke , Yakabe Taro , Sheng Hanyi , Nejoh Hitoshi
Published: July 2002

The growth of Pb on Si(100) 2×1 is found by scanning tunneling microscopy to form one-dimensional ad-dimer chains at a coverage far below a monolayer, analogous to the behavior of group-III elements (Ga, Al, In) on the same surface but with a buckled dimer configuration. The asymmetric dimerized structure is retained for c(8×4) and c(4×4) reconstructions of higher coverage. Tunneling spectra for the Pb dimers exhibit a surface-state band gap of ∼1.2 eV and thus suggest a nonmetallic property for the Pb chains, in agreement with the dimerization and buckling feature of Pb atoms. The parallel ad-dimer adsorption structure also suggests an approach to obtaining long atomic lines via the selection of the single domain Si(100) as substrates.
Understanding reflectance anisotropy: Surface-state signatures and bulk-related features
Authors: Schmidt W. G. , Bechstedt F. , Bernholc J.
Published: July 2002

Using a real-space multigrid method and ab initio pseudopotentials we calculated the reflectance anisotropy spectra for (001) growth structures of GaP and InP as well as for stepped Si(111):H and hydrogenated Si(110) surfaces. Our results, obtained within DFT-LDA, show good qualitative agreement with recent experiments. Further improvement is achieved by using a numerically efficient GW approach with approximations for local-field effects and dynamical screening. We find the contributions to the anisotropy signal related either directly to surface states or to transitions between surface-perturbed bulk wave functions. Our results demonstrate the high sensitivity of RAS to the surface structure and chemistry and show that the optical transitions causing the anisotropy signal take place mainly in a few uppermost atomic layers of the substrate.
Surface loss coefficients of CFx and F radicals on stainless steel
Authors: Singh Harmeet , Coburn J. W. , Graves David B.
Published: July 2002

The surface loss coefficients of CFx (x=1–3) and F radicals have been measured on the stainless steel walls of the differential pumping systems of a plasma reactor. This measurement is made by comparing the beam to background signal ratio of the radicals measured by appearance potential mass spectrometry. The surface loss of the radicals in the differential pumping stages of the vacuum system, in addition to the pumping of the species due to the vacuum pump, increases the beam to background signal ratio of the radical species. The measured loss coefficients are found to be lower than those reported on surfaces that have been exposed to fluorocarbon plasmas. This suggests that the loss coefficients of the species are dependent on the surface coverage of the radicals (CFx and F), which are lower on the walls in the differential pumping system. The measured loss coefficients in the differential pumping system are an order of magnitude lower than the loss coefficients measured in the afterglow of plasma chambers reported in the literature. We suggest the difference in the loss coefficients of radicals in the plasma chamber and those measured in this work are due to the differences in surface coverage in the two cases.
Application of thick film and bulk coating technology to the Subterrene program
Authors: Stark W. A. , Wallace T. C. , Witteman W. , Krupka M. C. , David W. R. , Radosevich C.
Published: July 2002

The Subterrene is a rock-melting earth-penetration system representing a significant advancement in excavation technology. Temperatures of 1700–2000 K are involved, and heated refractory metal or alloy probes are used. Corrosion problems are severe on the exterior surfaces of the refractory metals used; bulk coatings having the required properties would be extremely desirable, provided they could be deposited upon a substrate as a tenacious coating. Within the Subterrene, pyrographite radiant heaters are operating at temperatures to 2450 K. Graphite receptors added to improve the radiant heat transfer react with the molybdenum and tungsten penetrator bodies to form the respective carbides. A 30-μ thick CVD film of TaC may be applied to inhibit this reaction. The techniques of applying these films, their nature, and the results of their application, are discussed. The environment of an operating penetrator is described, and the requirements and properties of exterior coating are outlined.
The Determination of Surface Structure by LEED—Problems and Prospects
Authors: Robertson W. D.
Published: July 2002

Given an imperfect crystal and an imperfect apparatus to measure the scattered intensity of low-energy electrons, the general problem is to determine the location of all atoms on, and in, diperiodic surface layers relative to a three-dimensional crystalline substrate. The immediate problem is to identify characteristic features in the experimental data (intensity profiles) that will indicate how the complete dynamic analysis may be reduced to yield a most probable structure in a given case; that is, how to identify the geometric signal in a background of multiple scattering “noise”? Recently proposed techniques for averaging out the primary effects of multiple scattering do, indeed, promise to provide the mechanism for unambiguous structure determination. With effective atomic scattering factors for low-energy electrons (also from averaging techniques) surface physics and chemistry can proceed on the same terms as solid state physics.
Physisorption of Ar, Kr, CH4, and N2 on 304 Stainless Steel at Very Low Pressures
Authors: Troy M. , Wightman J. P.
Published: July 2002

Physisorption isotherms have been measured for argon, krypton, methane, and nitrogen on 304 stainless steel in the temperature range 77–90 K and in the pressure range 10−9−10−4 Torr. A static technique was used to obtain the isotherms whereby the pressure change of the test gas in a constant-volume system was measured on immersion of the commercially available 304 stainless-steel nipple in different cryogenic baths. The ionization gauge was operated at reduced emission current (25–40 μA) to minimize gauge pumping. Adsorption measurements were made at two positions on the nipple and then subtracted to give an isotherm for adsorption on a geometric area of 47.5 cm2. This difference technique was used to minimize the effect of a measured thermal gradient along the nipple wall above the bath level. The effect of system outgassing on the adsorption measurements was shown to be negligible. The isotherm data at each temperature were described empirically using the Dubinin-Radushkevich (DR) equation. Complete correlation by the (DR) equation of the temperature dependence of adsorption was not achieved for any of the adsorbates. Mean energies of adsorption calculated from the slopes of the DR plots were 1290, 1545, 1490, and 1903 cal/mole for Ar, Kr, CH4, and N2, respectively. This is the same order as has been reported for these gases on Pyrex; however, the interaction is about 10% higher on stainless than on Pyrex for each gas. Isosteric heats of adsorption calculated from the DR equation were 4.9, 6.4, 5.9, and 6.2 kcal/mole for Ar, Kr, CH4, and N2, respectively at θ=0.002.
Semiconductor Memory—a 1972 Look
Authors: Finch Tudor R.
Published: July 2002

During the past 15 yr design of digital systems has been guided, and directed in large part, by the rapidly evolving solid state technologies. From transistor to silicon LSI and through several generations of magnetic core memories, the combined cost, speed, and reliability improvement has been several orders of magnitude for both logic and memory. It is now reasonably clear that such cost-performance capability will be considerably extended through more extensive use of LSI, in particular with 20–200 nsec semiconductor memories. Realization of such cost and performance improvement will have a major impact on digital systems.
Inelastic Diffraction of Low-Energy Electrons from Aluminum: Surface Plasmon Dispersion Relation
Authors: Duke C. B. , Bagchi A.
Published: July 2002

A two-step diffraction model is used to calculate the inelastic scattering of low-energy 50≲E≲150 eV electrons from Al (100) and Al (111). Analysis of experimental data for the specular beam of electrons scattered from Al (111) permits the approximate determination of the surface-plasmon dispersion relation; ℏω(P∥)=10.1−0.7P∥+10P∥2eV; and damping Γ(P∥)=1.4+0.7P∥eV for P∥ measured in reciprocal Angstroms. Analysis of data for both faces using several diffracted beams permits the identification of the dynamical origin of most of the prominent structures evident in the inelastic cross sections. The dispersion relation of the bulk plasmons is taken insofar as possible from high-energy-electron-transmission data. However, analysis of the low-energy (reflection) data leads to a lower threshold plasmon energy ℏωb≃14.2 eV, than that extracted from most high-energy (E∼20 keV) experiments (ℏωb≃15  eV). This discrepancy may result from the use in the reflection experiments of single-crystals rather than polycrystalline films.
Effects of Oxygen on Silver Surface Structure
Authors: Rovida G. , Pratesi F. , Maglietta M. , Ferroni E.
Published: July 2002

The chemisorption of oxygen on the (100), (110), and (111) faces of silver single crystals was studied with LEED, secondary electron spectroscopy, and other auxiliary techniques. The effect of exposures to oxygen at pressures up to 1 Torr and temperatures up to 500 °C was investigated using a crystal isolation valve. The chemisorbed oxygen causes mainly a strong faceting of the (100) and (110) faces, and a 4×4 superstructure on the (111) face. The effect of the internally diffused oxygen on the surface behavior was also investigated.
Quantum-Mechanical Theory of the One-Phonon Inelastic Scattering of Gas Atoms in Three Dimensions by a Simplified Continuum Model of a Solid
Authors: Goodman Frank O.
Published: July 2002

A quantum-mechanical treatment of the one-phonon inelastic scattering of gas atoms in three dimensions by a solid surface is presented. Three major approximations made in the calculations are (i) the first order distorted wave Born approximation is used to calculate the relevant transition probabilities, (ii) atoms near the surface of the solid are treated, from the point of view of their dynamics, as though they were in the bulk, and (iii) the gas-surface interaction is represented by an infinite-step potential with zero well-depth, thus eliminating the possibility of bound states of gas atoms at the surface. The theory is a generalization of the one-dimensional theory reviewed by F. O. Goodman to three dimensions. For the system He-Ag, comparisons are made with experimental scattering distributions and speed measurements of the type reported by R. B. Subbarao and D. R. Miller. Using independently-measured values of the various theoretical parameters, satisfying agreement between theory and experiment is obtained.
Photoemission Spectra from Adsorbed O on W(110) and CO on W(100)
Authors: Baker J. M. , Eastman D. E.
Published: July 2002

Photoemission energy distribution curves are presented for adsorbed layers of O on W(110) and CO on W(100) surfaces. The electronic energy levels of adsorbed oxygen initially form a 2.0 eV-wide peak at −6.4 eV below the Fermi level which shifts to −6.0 eV and broadens to 2.8 eV with increasing coverage. Provision for simultaneous LEED, Auger spectroscopy, and flash desorption enable the structure and coverage of the adsorbed layers to be determined. β phase CO adsorbed in either the (1×1) or C(2×2) structures on W(100) produces a photoemission peak at −6.0 eV with a weaker peak at −3.5 eV. Adsorption of CO in the a phase gives rise to a 2.2 eV-wide peak at −8.9 eV which is identified as originating from levels essentially the same as those of molecular CO.
The Bond-Energy Bond-Order (BEBO) Model of Chemisorption
Authors: Weinberg W. H.
Published: July 2002

The bond-energy bond-order (BEBO) model of chemisorption allows an estimate to be made of the interaction energy between a gaseous specie and a solid surface as a function of either bond length or bond order, i.e., the length or order of either the gas-surface bond being formed or the bond of the gaseous molecule being broken. The relationship between bond energy and either bond length or bond order is deduced from spectroscopic correlations for gaseous molecules, and a linear relationship between bond energy and bond order is assumed for the surface-adsorbate interaction. The geometry of the surface orbitals is taken to be that predicted by the crystal field model. The model allows a prediction of several relevant quantities in gas-surface interactions, namely: (1) binding energies for molecular adsorbed species, (2) binding energies for atomically adsorbed species, (3) activation energies to chemisorption, and (4) activation energies to dissociative chemisorption. The model is illustrated for the adsorption of H2, CO, NO and O2 on Pt, W and Ni surfaces.
Interlot Density Variation of A Siloxane Manometer Fluid
Authors: Orcutt Ronald H.
Published: July 2002

The mean value of density for six samples of a siloxane manometer fluid is 1.06311 g/cm3 with an estimated standard deviation of 11×10−5 g/cm3 for the lot-to-lot variation in density of this fluid. From this result it is concluded that for use of this material in manometry to the 0.01% level the density of the actual fluid used must be determined.
High Speed Beam Deflection and Blanking for Electron Lithography
Authors: Lin L. H. , Beauchamp H. L.
Published: July 2002

A fast magnetic deflection system and beam blanking unit have been incorporated into the electron optical column of a commercial SEM for application to electron lithography. The achieved response-time of the deflection system is about 1 μsec. Double deflection coils are located outside of a glass tube enclosing the electron beam. A thin silver film deposited on the inside surface of the tube serves to conduct charge to ground but does not significantly impede high-frequency deflection fields. A ferrite magnetic shield is placed between the deflection coils and the surrounding iron pole-piece of the objective lens. The function of the shield is to minimize the undesirable eddy currents induced in the iron by the deflection field. The response time of the beam blanking unit is about 10 nsec. The unit employs a pair of electrostatic plates which blank the beam by deflecting the latter against an aperture-stop. The center of deflection of the plates coincides with the crossover point produced by the first condenser lens. Under this condition the beam can be deflected and blanked without affecting the position of the writing spot. The spot position is also insensitive to unequal charging of the contaminated plates by stray electrons. The writing spot position drift, caused by electron charging of other surfaces in the column, has also been minimized by properly restricting the beam width in the column and centering the beam on the final aperture.
A comparison of pumping speed measurement methods
Authors: Denison D. R. , McKee E. S.
Published: July 2002

In order to reconcile differences in ion pump speeds reported by American and European users, a comparison of pumping speed measurements using the Fischer-Mommsen [E. Fischer and H. Mommsen, Vacuum 17, 309 (1967)] method and the 3-gauge conductance tube method [Apparatus of AVS tentative standard 4.1, Suppl. III (b)] was made using a pump with a speed of about 230 liter/sec. The results were checked against a third technique—the measurement of time required to exhaust a pipette of known volume and known initial pressure with the pump chamber pressure held constant. The pipette method and the Fisher-Mommsen method agree and the 3-gauge method results in speeds about 8% higher. Data are presented showing the advantages and disadvantages of measuring pumping speeds with pure gases and with gas mixtures such as air.
Surface polaritons—propagating electromagnetic modes at interfaces
Authors: Burstein E. , Chen W. P. , Chen Y. J. , Hartstein A.
Published: July 2002

Surface polaritons are interface electromagnetic modes whose propagation constants depend on the dielectric constants and magnetic permeabilities of the interfacing media. We discuss here (i) the nature of the modes which exist at single-interface and at slab (two-interface) configurations, (ii) the methods for coupling bulk polaritons and surface polaritons, and (iii) the use of surface polaritons as electromagnetic probes of surfaces and interfaces.
The influence of vacuum specific time constants on thermal desorption experiments
Authors: Edwards D.
Published: July 2002

A method is described in which the temperature shift in the maxima of thermal desorption transients due to vacuum-related effects can be evaluated. Is is applied to finite pumping speed and finite conductance corrections to the desorption peak temperatures. Particularly simple expressions are found for the temperature shift in lowest order and are seen to be applicable whenever the measured desorption transient (p or dp/dt) closely approximates the sample desorption rate (dns/dt).
Mechanisms for CF2 radical generation and loss on surfaces in fluorocarbon plasmas
Authors: Zhang Da , Kushner Mark J.
Published: July 2002

During fluorocarbon plasma etching, plasma-surface reactions result in the surface acting as either a source or sink for reactive species, thereby impacting the properties of the bulk plasma. For example, experiments have shown that surfaces in radio frequency (rf) capacitively coupled discharges can be either sources or sinks of CF2 depending on, among other properties, the sheath potential. The coupling of rf bulk and surface reactions, and their combined effects on the CF2 density, were investigated using an integrated plasma equipment and surface kinetics model. While CF2 sticking on surfaces led to its loss, CF2 can be generated from surfaces by energetic ion bombardment resulting in sputtering of polymeric films, or neutralization and dissociation of ions. The net effect of a surface for CF2 production depends on the relative rates of these loss and generation processes. A surface can transform from a net CF2 sink at low incident ion energies to a CF2 source at high ion energies because the CF2 yield by ion–surface interactions typically increases with increasing ion energy. The sensitivity of the model to probabilities of major surface reactions was also investigated.
Study of grass formation in GaAs backside via etching using inductively coupled plasma system
Authors: Nam P. S. , Ferreira L. M. , Lee T. Y. , Tu K. N.
Published: July 2002

Grass formation in GaAs backside via etching with Cl2 based chemistry was studied using the inductively coupled plasma (ICP) system. A parametric approach adjusting rf bias power, ICP source power, pressure, and gas ratio was performed to observe the effect of etching condition on grass formation. Scanning electron microscopy was used to investigate the surface morphology as well as the cross section of the via hole. Vertical grass was observed at the bottom of the via hole at certain unique processing and etching conditions. The grass growth is attributed to the surface defects on GaAs induced during a backside thinning combined with weak physical ion bombardment in the etch condition. We found that the grass formation can be prevented by pre-etching with Ar bombardment on the surface
Nanoheteroepitaxy: Nanofabrication route to improved epitaxial growth
Authors: Zubia D. , Zaidi S. H. , Hersee S. D. , Brueck S. R. J.
Published: July 2002

Nanoheteroepitaxy is a fundamentally new epitaxial approach that utilizes three-dimensional stress relief mechanisms available to nanoscale heterostructures to eliminate defects provided the island diameter is below a critical value 2lc. Analysis shows that 2lc∼(15–30)× the critical thickness hc. In the case of GaAs on Si (∼4% misfit), 2lc∼40 nm. In material systems such as GaN on Si (∼20% misfit), where the misfit is much larger and interfacial defects are unavoidable, the nanoheteroepitaxial structure is shown to reduce the formation and propagation of threading defects. Nanostructured substrate parameters that impact growth are discussed and interferometric lithography is introduced as a method for fabrication of large-area substrates for nanoheteroepitaxy. Si nanoisland diameters as small as 20 nm are demonstrated. Scanning and transmission electron microscopy data of GaN grown on Si (via organometallic vapor phase epitaxy) shows reduced threading defects in nanostructured samples compared to growth on planar substrates. Photoluminescence intensity data of nanostructured samples is enhanced by ∼100× as compared to planar-growth samples.
Characterization of showerhead performance at low pressure
Authors: Hash D. B. , Mihopoulos T. , Govindan T. R. , Meyyappan M.
Published: July 2002

The performance of showerheads used in semiconductor processing applications has been examined over a wide range of Knudsen number and Reynolds number. Both computational fluid dynamics and direct simulation Monte Carlo techniques have been used to characterize the showerhead flow with the intent of developing correlations between the upstream velocity and the pressure drop across the showerhead. Empirical correlations developed to account for entrance effects and rarefaction are also examined. Recommendations are made concerning boundary conditions and, when appropriate, correlations for given pressures and flow rates.
Cavity ring down detection of SiH3 in a remote SiH4 plasma and comparison with model calculations and mass spectrometry
Authors: Kessels W. M. M. , Leroux A. , Boogaarts M. G. H. , Hoefnagels J. P. M. , van de Sanden M. C. M. , Schram D. C.
Published: July 2002

Spatially resolved SiH3 measurements are performed by cavity ring down spectroscopy on the SiH3 Ã2 A1←X̃2 A1 transition at 217 nm in a remote Ar–H2–SiH4 plasma used for high rate deposition of hydrogenated amorphous silicon. The obtained densities of SiH3 and its axial and radial distribution in the cylindrical deposition reactor are compared with simulations by a two-dimensional axisymmetric fluid dynamics model. The model, in which only three basic chemical reactions are taken into account, shows fairly good agreement with the experimental results and the plasma and surface processes as well as transport phenomena in the plasma are discussed. Furthermore, the SiH3 density determined by cavity ring down spectroscopy is in good agreement with the SiH3 density as obtained by threshold ionization mass spectrometry.
Real-time growth rate metrology for a tungsten chemical vapor deposition process by acoustic sensing
Authors: Henn-Lecordier L. , Kidder J. N. , Rubloff G. W. , Gogol C. A. , Wajid A.
Published: July 2002

An acoustic sensor, the Leybold Inficon Composer™, was implemented downstream to a production-scale tungsten chemical vapor deposition cluster tool for in situ process sensing. Process gases were sampled at the outlet of the reactor chamber and compressed with a turbomolecular pump and mechanical pump from the sub-Torr process pressure regime to above 50 Torr as required for gas sound velocity measurements in the acoustic cavity. The high molecular weight gas WF6 mixed with H2 provides a substantial molecular weight contrast so that the acoustic sensing method appears especially sensitive to WF6 concentration. By monitoring the resonant frequency of exhaust process gases, the depletion of WF6 resulting from the reduction by H2 was readily observed in the 0.5 Torr process for wafer temperatures ranging from 300 to 350 °C. Despite WF6 depletion rates as low as 3%–5%, in situ wafer-state metrology was achieved with an error less than 6% over 17 processed wafers. This in situ metrology capability combined with accurate sensor response modeling suggests an effective approach for acoustic process sensing in order to achieve run-to-run process control of the deposited tungsten film thickness.
Oxygen loss and recovering induced by ultrahigh vacuum and oxygen annealing on WO3 thin film surfaces: Influences on the gas response properties
Authors: Santucci S. , Lozzi L. , Maccallini E. , Passacantando M. , Ottaviano L. , Cantalini C.
Published: July 2002

In this work the surface reversibility towards the incorporation and lack of oxygen of thin WO3 films has been studied by means of high resolution x-ray photoemission spectroscopy (XPS). The thin films (150 nm), have been thermally evaporated onto Si substrates, and either left as prepared, or pretreated in oxygen at atmospheric pressure by a 24 h long annealing at 300 °C. We used conventional monochromatized XPS measurements to follow the W4f, O1s peaks and the valence band of such samples, as introduced in ultrahigh vacuum (UHV), or after cycles of annealing in UHV and reannealing in oxygen at atmospheric pressure. We observed that annealing in UHV gives rise to a lack of oxygen in the as deposited and 300 °C annealed samples strongly modifying the W4f peak and producing the increase of metallic states at the Fermi edge. For these samples, the thermal annealing in oxygen produces recovering of the WO3 surface electronic structure and, again, a successive heating in UHV causes a lack of oxygen. This shows a substantial reversibility of the effects produced by the annealing cycles. The WO3 films submitted to the UHV thermal treatments have been also investigated as resistive gas sensors towards NO2. We observed an evident lowering of the base resistance and a decrease of their response if compared with that one of the samples not treated in vacuum. A gradual shift of the base line towards that of not UHV treated sensor has been also observed, after many working hours in air at 200 °C. This effect has been attributed to the oxygen reincorporation on the surface.
Measurements of neutral and ion composition, neutral temperature, and electron energy distribution function in a CF4 inductively coupled plasma
Authors: Singh Harmeet , Coburn J. W. , Graves David B.
Published: July 2002

In this article, we present comprehensive measurements of the neutral number densities, ion number densities, and the electron energy distribution function in a CF4 inductively coupled plasma at pressures between 1 and 30 mTorr, and deposited powers between 150 and 550 W. High degrees of dissociation are observed at the lower pressures. We believe this is a result of the large electron temperature at the lower pressures. The measurements of all the dominant radical and stable neutral species using appearance potential mass spectrometry allows the estimation of the neutral temperature at the neutral sampling aperture. The neutral temperature is also estimated from the change in the number density of a trace amount of argon added to CF4 when the plasma is turned on. Neutral temperatures up to 930 K are measured at the sampling aperture. The increase in neutral temperature with power at a constant pressure results in a decrease in the total neutral number density at a constant pressure. The electron temperature is sensitive to the neutral number density, especially at low densities. This leads to a significant increase in the electron temperature with power, resulting in the higher degrees of dissociation observed at low pressures. The number densities of radicals and their corresponding ions are generally strongly correlated in the plasma. We show indirect evidence for large surface loss coefficients for C and CF radicals.
Metamorphic heterojunction bipolar transistors and P–I–N photodiodes on GaAs substrates prepared by molecular beam epitaxy
Authors: Hoke W. E. , Lemonias P. J. , Kennedy T. D. , Torabi A. , Tong E. K. , Bourque R. J. , Jang J.-H. , Cueva G. , Dumka D. C. , Adesida I. , Chang K. L. , Hsieh K. C.
Published: July 2002

Metamorphic heterojunction bipolar transistor (M-HBT) structures and metamorphic P–I–N (M-PIN) photodiode structures were grown on GaAs substrates. A compositionally graded AlGaInAs buffer layer was used to expand the lattice constant to that of InP. Cross-sectional transmission electron micrographs of the M-HBT structure showed that the dislocations from compositional grading were predominantly localized in the buffer layer and that the device layers possessed planar interfaces. Secondary ion mass spectroscopy depth profiles of the 4×1019 cm−3 beryllium-doped In0.53Ga0.47As base layer exhibited sharp doping interfaces, indicating that metamorphic growth was not causing enhanced beryllium diffusion. The current gain of large emitter M-HBT devices approached the current gain for the same device structure grown on an InP substrate. A P–I–N photodiode structure was also grown metamorphically on a GaAs substrate and lattice matched on an InP substrate. Both types of photodiodes showed almost identical responsivities and bandwidths. A responsivity to 1.55 μm radiation of 0.55 A/W, which corresponds to an external quantum efficiency of 44%, was obtained with M-PIN photodiodes. The 3 dB bandwidths exceeded 20 GHz for M-PIN photodiodes with diameters of 25 μm or smaller. These results are very encouraging for the application of metamorphic technology to nonmajority carrier devices.
Effects of As2 versus As4 on InAs/GaSb heterostructures: As-for-Sb exchange and film stability
Authors: Nosho B. Z. , Bennett B. R. , Whitman L. J. , Goldenberg M.
Published: July 2002

We have used cross-sectional scanning tunneling microscopy and x-ray diffraction to characterize and compare the effects of As2 versus As4 on the growth of InAs/GaSb heterostructures by molecular beam epitaxy. When GaSb surfaces are exposed to an As2 flux, the As exchanges with the surface Sb in an anion exchange reaction that creates layers of GaAs. In contrast, when GaSb surfaces are exposed to As4 fluxes, there is no evidence of the As-for-Sb exchange reaction. When comparing the use of As2 and As4 in periodic InAs/GaSb superlattices, the differences in the As incorporation rate into GaSb is further evident in x-ray diffraction spectra as a shift in the average lattice constant of the epilayer due to GaAs bond formation. Although inhibiting the exchange reaction would be useful in the minimization of the cross incorporation of As in the GaSb layers, the growth of InAs/GaSb heterostructures using As4 can be complicated by the introduction of film instabilities that have not been observed in growths using As2.
Structural and electroacoustic studies of AlN thin films during low temperature radio frequency sputter deposition
Authors: Engelmark F. , Iriarte G. F. , Katardjiev I. V. , Ottosson M. , Muralt P. , Berg S.
Published: July 2002

AlN is a material used in a wide variety of applications such as electroacoustic devices, blue diodes, IR windows, thermal conductors, metal–insulator–semiconductor structures, integrated circuit packaging, etc. In this work thin piezoelectric AlN polycrystalline films have been grown on Si and SiO2 using rf magnetron sputter deposition in an Ar/N2 gas mixture. The structural properties of the films have been optimized by varying the deposition parameters, such as process pressure, gas mixture, substrate temperature, discharge power, etc. [K. Tominaga et al., Jpn. J. Appl. Phys., Part 1 35, 4972 (1996); H. Okana et al., ibid. 31, 3446 (1992); K. Kazuya, T. Hanabusa, and K. Tominaga, Thin Solid Films 281-282, 340 (1996)]. It was found that the best film texture was obtained for a particular set of parameters, namely process pressure of 4 mTorr, substrate temperature 350 °C, discharge power 350 W, and a gas mixture of 25% Ar and 75% N2. The films as examined by x-ray diffraction exhibited a columnar structure with a strong (001) texture, and a full width at half maximum (FWHM) rocking curve of 1.6°. Atomic force microscopy measurements indicated a surface roughness with a rms value of 8 Å. Classical nonapodized transversal surface acoustic wave filters operating at a frequency of 534 MHz were fabricated to characterize the electroacoustic properties of the films. The measurements indicated a coupling coefficient of 0.37% and a phase velocity of 4900 m/s. Further, thin epitaxial films were grown on (001)α-Al2O3 (sapphire) under the same deposition conditions except the substrate temperature. The films exhibited a (001)AlN//(001)α-Al2O3 plane orientation with a (002) rocking curve FWHM value of about 0.4°, showing a relatively good alignment of the c axis. The in-plane orientation was [110]AlN//[120]α-Al2O3 corresponding to a rotation of the AlN film of 30° with respect to the (001)α-Al2O3 surface. Cross-sectional transmission electron microscopy studies indicated a population of both thread and edge dislocations with decreasing concentrations with film thickness.
GaN focused ion beam micromachining with gas-assisted etching
Authors: Chyr I. , Steckl A. J.
Published: July 2002

Halide gases, such as Cl2, IBr, or ICl, are common etchant species for the etching of III nitrides and other compound semiconductor materials in plasma etching processes. We have investigated the Ga+ focused ion beam milling of GaN in conjunction with gas-assisted etching (GAE) by halide gases I2 and XeF2. We have observed that I2 and XeF2 GAE with a 30 keV Ga+ ion beam leads to significantly enhanced GaN etch rates. When these gases are utilized with appropriate ion beam scan strategies (such as ion beam current, beam dwell time, and beam overlap), we have measured GaN etch rate enhancements of 6× to 9× and 2× to 3× faster for I2 and XeF2, respectively.
Thermal conductivity measurements of thin-film resist
Authors: Chu Dachen , Touzelbaev Maxat , Goodson Kenneth E. , Babin Sergey , Pease R. Fabian
Published: July 2002

In electron-beam and photolithography, local heating can change the resist sensitivity and lead to variations in significant critical dimension. Existing models suffer from the lack of experimental data for the thermal properties of the polymer resist films. We present the measurements of both out-of-plane and in-plane thermal conductivity of thin resist films following different exposure conditions. An optical thermoreflectance technique was used to characterize out-of-plane thermal conductivity; the out-of-plane thermal conductivity of exposed SPR™-700 resist increases as a function of exposure dose. We also designed and fabricated a free-standing micro-electrode structure for measuring the in-plane thermal conductivity and results for poly(methylmethacrylate) films were obtained, indicating that, unlike polyimide films, there is no appreciable anisotropic behavior.
Plasma etching of cesium iodide
Authors: Yang X. , Hopwood J. , Tipnis S. , Nagarkar V. , Gaysinskiy V.
Published: July 2002

Thick films of cesium iodide (CsI) are often used to convert x-ray images into visible light. Spreading of the visible light within CsI, however, reduces the resolution of the resulting image. Anisotropic etching of the CsI film into an array of micropixels can improve the image resolution by confining light within each pixel. The etching process uses a high-density inductively coupled plasma to pattern CsI samples held by a heated, rf-biased chuck. Fluorine-containing gases such as CF4 are found to enhance the etch rate by an order of magnitude compared to Ar+ sputtering alone. Without inert-gas ion bombardment, however, the CF4 etch becomes self-limited within a few microns of depth due to the blanket deposition of a passivation layer. Using CF4+Ar continuously removes this layer from the lateral surfaces, but the formation of a thick passivation layer on the unbombarded sidewalls of etched features is observed by scanning electron microscopy. At a substrate temperature of 220 °C, the minimum ion-bombardment energy for etching is Ei∼50 eV, and the rate depends on Ei1/2 above 65 eV. In dilute mixtures of CF4 and Ar, the etch rate is proportional to the gas-phase density of atomic fluorine. Above 50% CF4, however, the rate decreases, indicating the onset of net surface polymer deposition. These observations suggest that anisotropy is obtained through the ion-enhanced inhibitor etching mechanism. Etching exhibits an Arrhenius-type behavior in which the etch rate increases from ∼40 nm/min at 40 °C to 380 nm/min at 330 °C. The temperature dependence corresponds to an activation energy of 0.13±0.01 eV. This activation energy is consistent with the electronic sputtering mechanism for alkali halides.