bluuebunny/crossref_metadata_2025 huggingface dataset:
Inducing Passive Nonlinear Energy Sinks in Vibrating Systems
Authors: Vakakis A. F.
Published: July 2002

We study the inducement of passive nonlinear sinks in linear vibrating systems. These are substructures that absorb vibrational energy in a one-way, irreversible fashion. The systems considered are composed of strongly coupled, grounded damped linear oscillators with a strongly nonlinear attachment at the end. Applying a complex averaging technique we derive a set of modulation equations that is directly amenable to physical interpretation, and provides insight into the energy pumping phenomenon. For the case of a two DOF system we show that nonlinear energy pumping occurs when a certain frequency of envelope modulation crosses through zero; then the dynamics of the envelope modulation of the motion resemble the dynamics of a forced rigid body. For the case of an impulsively loaded multi-DOF chain with a nonlinear attachment at the end, we show that after some initial transients the response of the nonlinear attachment sets to a motion dominated by a “fast” frequency identical to the lower bound of the propagation zone of the linear chain. This feature reduces the study of energy pumping in the chain to a two DOF equivalent problem. The applications of the energy pumping phenomenon to practical engineering problems are discussed.
Track Tension Estimation in Tracked Vehicles Under Various Maneuvering Tasks
Authors: Huh Kunsoo , Hong Daegun
Published: July 2002

In this paper, track tension monitoring methodology is developed so that the track tension can be estimated under various maneuvering tasks such as longitudinal driving on sloping and/or rough roads, turning on flat or sloping roads, etc. The real-time information of the track tension is very important for tracked vehicles because the track tension is closely related to the maneuverability and the durability of tracked vehicles. In the case of longitudinal driving, a modified 3 DOF dynamics model is derived for tracked vehicles and is utilized for estimating the tractive force and track tension. In the case of turning, kinetic models for six road-wheels are obtained and used for calculating the track tension around the sprocket. This method does not require tuning of the turning resistance, which makes it difficult to estimate the track tension in turning. The estimation performance of the proposed methods is verified through simulations of the Multi-Body Dynamics tool. The simulation results demonstrate the effectiveness of the proposed method under various maneuvering tasks of tracked vehicles.
Dynamic Analysis of Geared Rotor-Bearing Systems by the Transfer Matrix Method
Authors: Choi Siu-Tong , Mau Sheng-Yang
Published: July 2002

An analytical study of the dynamic characteristics of a geared rotor-bearing system by the transfer matrix method is presented. Rotating shafts of the system are modeled as Timoshenko beams with effects of shear deformation and gyroscopic moment taken into account. The gear mesh is modeled as a pair of rigid disks connected by a spring-damper set along the pressure line and the transmission error is simulated by a displacement excitation at the mesh. The transfer matrix of a gear mesh is developed. The coupled lateral-torsional vibration of a geared rotor-bearing system is studied. Natural frequencies and corresponding mode shapes, and whirl frequencies under different spin speeds are determined. In addition, steady-state responses due to the excitation of mass unbalance, geometric eccentricity and transmission error of gear mesh are obtained. Effect of the time-varying stiffness of the gear mesh is investigated.
Specimen Design for Mixed Mode Interfacial Fracture Properties Measurement in Electronic Packages
Authors: Yeung Dickson T. S. , Lam David C. C. , Yuen Matthew M. F.
Published: July 2002

A four-layer center cracked beam (CCB) under four point bending loading is developed for the interfacial fracture properties measurement of electronics packaging materials. Determination of the mixed mode interfacial fracture properties along the second and third layers of the CCB specimen is carried out analytically. For a given test specimen, a stable test window (material combination and thickness ratio) has been identified using the analytical expression. Data yield from interfacial mixed mode fracture properties experimental measurement can be enhanced by testing within the testing window. [S1043-7398(00)00101-8]
Flow Structure in the Wake of a Rotationally Oscillating Cylinder
Authors: Mahfouz F. M. , Badr H. M.
Published: July 2002

The characteristics of the flow in the wake of a circular cylinder performing rotational oscillation about its own axis and placed horizontally in a cross-stream is investigated. The governing equations based on stream function-vorticity formulation are solved numerically to determine the flow field structure. The parameters dominating flow structure are Reynolds number, Re, amplitude of oscillation, ΘA and frequency ratio FR=S/S0 where S is the forcing frequency and S0 is the natural frequency of vortex shedding. The ranges considered for these parameters are 40⩽Re⩽200, 0⩽ΘA⩽π and 0⩽FR⩽2. The lock-on phenomenon has been predicted and its effect on the flow hydrodynamics has been determined. The lock-on phenomenon is found to occur within a band of frequency encompassing the natural frequency. This band, however, becomes wider as the amplitude of oscillation increases. The obtained results show that the flow pattern in the near wake has a strong dependence on the oscillation parameters but not the far wake. [S0098-2202(00)01102-0]
Dimension Inspection of Spatial Cams by CNC Coordinate Measuring Machines
Authors: Lin Psang Dain , Hsieh Jung-Fa
Published: July 2002

The problem of spatial cam inspection is still predominantly approached from simple gauging by manufacturers in today’s industry, despite the fact that Coordinate Measuring Machines (CMM) is both available and one of the most reliable and accurate metrological tools. Therefore, a kinematic model is presented in this paper to aid in the determination of the required NC data equations in order to move the probe to the desired position to inspect spatial cams on CNC CMM. This study originated from the need for advanced algorithms for the profile inspection of high precision manufactured spatial cams. To achieve this, the 4×4 homogeneous transformation matrix is employed to determine spatial cam profiles. Then, the CMM’s ability function matrix and the measuring-probe location matrix are derived. The desired NC data equations are obtained by solving the CMM link variables by equating the ability function matrix with the probe location matrix. A technique to minimize the sum of squared errors is also addressed by searching a best fit coordinate frame. To verify the validity of the method, this approach was implemented in software which was then used in a CNC CMM to measure a known spatial cam, with excellent results. The methodology developed in this paper can make the cam inspection process more flexible, automatic, and controllable. [S1087-1357(00)71001-X]
An Improved Series Expansion of the Solution to the Moving Oscillator Problem
Authors: Pesterev A. V. , Bergman L. A.
Published: July 2002

The problem of calculating the dynamic response of a one-dimensional distributed parameter system excited by an oscillator traversing the system with an arbitrarily varying speed is investigated. An improved series representation for the solution is derived that takes into account the jump in the shear force at the point of the attachment of the oscillator, which makes it possible to efficiently calculate the distributed shear force and, where applicable, bending moment. The improvement is achieved through the introduction of the “quasi-static” solution, which is an approximation to the desired solution, and is also based on the explicit representation of the solution of the moving oscillator problem as the sum of the solution of the corresponding moving force problem and that of the problem of vibration of the distributed system subject to the elastic coupling force. Numerical results illustrating the efficiency of the method are presented. [S0739-3717(00)01001-1]
Pristine and Overoxidized Polypyrrole by XPS
Authors: Losito I. , Malitesta C. , Sabbatini L. , Zambonin P. G.
Published: July 2002

An x-ray photoelectron spectroscopy (XPS) analysis was performed of polypyrroles (PPy) electrosynthesized on Pt in aqueous solution. Spectra were recorded both for the as-synthesized (pristine) polymer (specimen 1) and for the so-called “overoxidized” PPy (specimen 2). Electrosynthesis was accomplished potentiostatically at +0.7 V vs SCE in KCl 10 mM containing pyrrole 0.4 M. Overoxidized PPy was obtained by keeping the pristine polymer at the electrosynthesis potential for 5 h, in phosphate buffer solution (pH 7). C, N, O (1s), and Cl 2p (pristine) spectra are included. Some minor elements, P (in the overoxidized polymer), Na (in some overoxidized samples), and Si (in other samples of both types of PPy, but not in those here reported), were also detected.
UHV-Cleaved V2O3 (101¯2) by He I and He II UPS and XPS
Authors: Kurtz Richard L. , Henrich V. E.
Published: July 2002

V2O3 is a transition-metal oxide that exhibits a large metal-insulator transition at about 150 K. At room temperature, where these spectra were taken, it is metallic. Its metallic nature is evident both in the finite occupied density-of-states at the Fermi level, and in the double-peaked structure of the V 2p1/2 and 2p3/2 core-level peaks. The sample contains only V3+ cations, so the double-peaked structure does not arise from the presence of multiple valence states on the V cations. Caution must thus be exercised in interpreting cation 2p core-level spectra from such oxides. [See K. E. Smith and V. E. Henrich, Phys. Rev. B 50, 1382 (1994), for a discussion of the role of final-state screening in x-ray photoelectron spectroscopy core-level line shapes. See also R. L. Kurtz and V. E. Henrich, Surf. Sci. Spectra 5, 182 (1998).] The vanadium oxides exhibit a wide stoichiometry range (including Magneli phases); V2O3 is one the more stable lower oxides.
Core Level and Valence Band Spectra of Lead by XPS
Authors: Rondon Sonia , Sherwood Peter M. A.
Published: July 2002

Core and valence band XPS spectra were obtained from a lead metal foil. The XPS data were collected with a VSW HA150 spectrometer equipped with a monochromatic Al Kα x-ray source and multichannel detector. The sample is a high purity lead foil (99.99%) that was cleaned prior to data collection by Ar-ion sputtering. The present work presents a high resolution valence band spectrum which shows a well resolved splitting in the near-edge region. This report also includes the survey spectrum, and Pb 4f, Pb 5d, Pb 4d, O 1s, and C 1s core regions.
Characterization of silver coatings deposited from a hollow cathode source
Authors: Mah G. , McLeod P. S. , Williams D. G.
Published: July 2002

Silver coatings of 15–50-μ thickness were deposited from a hollow cathode source with substrate bias voltage between 0 and −80 V, and deposition rates varied from 2 to 30 μ/min. A study of the relationship between the substrate bias voltage and the coating characteristics was made. The crystallographic orientation of the coating varied with bias voltage. The microstructure and microhardness of the coatings were also examined as a function of the bias voltage. The microstructure of the coatings resembled that of sputtered coatings; grain structure was changed from columnar to equiaxed by increasing the bias voltage. With the changes in the morphology of the microstructure, the microhardness of the coating also varied by a factor of 2. The coating fractured in a ductile mode and showed excellent adhesion to its substrate.
Incorpation of Helium in Deposited Gold Films
Authors: Mattox D. M. , Kominiak G. J.
Published: July 2002

It is shown that sputter deposited gold films containing atomic ratios of helium-to-gold of up to 0.4 may be formed in a helium gas dc diode discharge. Gas content is primarily a function of substrate temperature and bias, gas pressure, and target voltage. Data indicate that high-energy neutral helium atoms originating at the target are important in the gas incorporation at low gas pressures and positive substrate biases. Maximum helium incorporation occurs at about −80 V bias, where the sticking coefficient is expected to approach unity. Deposition conditions are influential in the subsequent thermal release of the incorporated gas. Gas analysis was performed by heating and flash evaporation of the gas-containing film and then determining the pressure rise in a known volume. It is proposed that this technique is applicable to the formation of many nonequilibrium gas–metal/ceramic systems.
Electron-Stimulated Desorption and Work Function Studies of Clean and Cesiated (110) GaAs
Authors: Madey Theodore E. , Yates John T.
Published: July 2002

The surface of a degenerate p-type GaAs crystal, cleaved in ultrahigh vacuum to expose the (110) plane, has been examined as a function of cesium coverage using several methods. Electron stimulated desorption (ESD) of ions upon bombardment of the surface by 100-eV electrons is found to be extremely sensitive to trace quantities of adsorbed impurities. The work function-coverage relation for Cs+ deposited from a Cs zeolite ion gun was determined using a retarding potential method; the energy dependence of electron reflection in the range 0–10 eV was found to differ markedly between the clean and cesiated surfaces.
Extended Hückle Calculations of Relative Chemisorption Energies
Authors: Robertson J. C. , Wilmsen C. W.
Published: July 2002

The relative energies of chemisorption of molecules on a clean lead surface have been computed with an extended Hückel molecular orbital method. The calculations were carried out with several organic molecules in order to investigate the formation of monomolecular layers and their possible use as thin (10–20 Å) insulating Josephson tunneling barriers. Calculating the adsorption energy at various locations on the Pb surface yields a measure of the surface coverage and the most suitable organics for forming the monolayer. Nonoxidative adsorbates are found not to chemisorb on Pb while those which are oxidative do bond. The bonding energy of the acetoxy radical is found to be 4 eV and the ethyl radical energy is 0.6 eV.
Averaged Low-Energy Electron Diffraction Intensities from Ni(111)
Authors: Lagally Max G. , Ngoc Tran C. , Webb Maurice B.
Published: July 2002

Conventionally, crystal structures are determined by comparing diffracted intensities with kinematic intensities calculated for proposed models. Intensities in low-energy electron diffraction are complicated by multiple scattering and are calculable only in dynamic theories. Here it is demonstrated for both specular and nonspecular beams from Ni(111) that the kinematic intensity can be recovered from LEED data by averaging at constant momentum transfer, thus making the much simpler conventional analysis applicable to surfaces.
Quantitative Analysis of Thermal Desorption Spectra: Chemisorption of Carbon Monoxide on Tungsten
Authors: Winterbottom W. L.
Published: July 2002

Numerical analysis of the line shapes of thermal desorption spectra for CO on polycrystalline tungsten has been carried out. The results show that within the β phase there are at least six chemisorption substates; desorption from five of these states is a simple, first-order process. We have demonstrated that the desorption technique is capable of resolving surface states whose heats of activation for desorption differ by as little as 4 kcal/mole. The experimental frequency factors for the five first order states increase with increasing activation energy. All the results can be interpreted as indicative of a highly directional bonding that is not closely related to the crystallographic anisotropy of the tungsten surface.
Oxidation of (011) Iron at Room Temperature: Mainly LEED Aspects
Authors: Melmed A. J. , Carroll J. J.
Published: July 2002

The interaction of oxygen with (011) Fe at room temperature has been investigated using simultaneous combinations of LEED, ellipsometry, and surface potential measurements. This paper is concerned mainly with the LEED aspects. The sequence of LEED patterns found was either similar to that previously found or slightly different, depending on experimental conditions. In most experiments a new LEED pattern, p(2×1), was observed instead of the c(3×1) pattern previously reported. Direct keying of the LEED patterns to the ellipsometry-derived growth kinetics leads to further understanding of the oxidation mechanism. The occurrence of heterogeneous oxide nucleation is supported, and it is shown that an oxide consistent with the expected diffraction properties of FeO grows to a “limiting” thickness of about 25–30 Å in oxygen. The terminal oxide in the air is concluded to have about the same thickness but a significantly different structure.
Effect of annealing on the surface composition of stainless steel 410
Authors: Krishnaswamy S. V. , McLane S. B. , Müller E. W.
Published: July 2002

Atom-probe analysis shows the depletion of chromium from the surface of stainless steel 410 tips subjected to heating in vacuum. Times necessary for depletion are lower by a factor of 104 than those found by Park et al. in which planar surfaces were analyzed by the x-ray appearance potential technique. This is explained on the basis of the great sensitivity of depletion rate upon the surface-to-volume ratio. The atom-probe specimens have a surface-to-volume ratio similar to catalytic powders, and thus the results of preferential evaporation, may be more realistic for the study of powder catalysts which are subject to annealing. The present work also cautions atom-probe experimenters in drawing conclusions from the abundance of atomic species after an alloy tip has been annealed in vacuum.
The Cathode Ray Tube Display: Why Use Anything Else?
Authors: Anderson L. K.
Published: July 2002

The cathode ray tube (CRT), especially if the definition is extended to cover all electron-beam addressed display devices, both self-luminous and light-modulating types, remains preeminent in today's display world in spite of competition from a variety of newer laser beam and matrix addressed display technologies. In this paper, we examine some of the reasons for the CRTs success, give a few examples of its continuing adaptability, and speculate on those weak points which may let other technologies get a foot in the door.
Model for Exposure of Electron-Sensitive Resists
Authors: Greeneich J. S. , Van Duzer T.
Published: July 2002

A mathematical model for the exposure of electron-sensitive resists on a structure coated with a thin layer of resist is presented. The calculations yield contours of equal absorbed energy density in the resist and these are interpreted as the contours which bound the resist after development. We calculate the exposure for an electron beam of vanishingly small cross-section, a beam of Gaussian current-density distribution, single lines, parallel lines, and areas.
Surface crystallography via elastic low-energy electron diffraction
Authors: Duke C. B. , Lipari N. O. , Laramore G. E.
Published: July 2002

The data-reduction and microscopic-model approaches to the determination of surface structure via analyses of elastic low-energy electron diffraction intensities are reviewed. Applications of both methodologies are discussed. Attention is focused on the evaluation of structural parameters for adsorbed layers of S and O on metals. In particular, the examples of Ni(100) − c(2 × 2) − S and Ni(100)−c(2×2)−O are examined in enough detail to reveal that the sulphur overlayer does not seem to lead to appreciable surface reconstruction whereas the oxygen overlayer can.
Low-voltage triode sputtering and backsputtering with a confined plasma: Part IV. Heat transfer characteristics
Authors: Nevis B. E. , Tisone T. C.
Published: July 2002

A theoretical and experimental investigation of the heat transfer processes encountered in sputtering and backsputtering systems have led to a method of cooling which does not involve clamping a wafer or substrate to a liquid cooled holder. The basic philosophy of the new method is to take full advantage of radiative cooling of the wafer by: (a) designing the holder so that the wafer has an unobstructed view of the water-cooled bell jar and is thermally isolated from the holder; (b) increasing the emittance of the side of the wafer facing the bell jar by the application of a black body coating. In addition to the above two modes, it is shown that tilting the wafer from a horizontal plane up to 45 °, although introduced primarily to reduce step problems, results in a decreased heating rate and subsequent lower wafer temperatures. Whether one would use one, two, or all three modes depends upon the heating rate (sputtering or backsputtering level), and the maximum temperature the wafer could stand without device damage. For example, if one does not wish to exceed 250 °C in a backsputtered silicon wafer, and at the same time it is desired to maximize the backsputtering rate, then, by employing a properly designed holder, tilted at 45 ° with the top side of the silicon of a black body, one could backsputter at a level corresponding to a heating rate of 0.6 W/ cm2. This corresponds, conservatively, to a removal rate of gold of 2500 Å/min. Design curves are presented which permit the prediction of steady state silicon wafer temperatures as a function of heat rate and silicon top side emittance. These theoretical predictions are corroborated by experiments. This study indicates that much of the present sputtering and backsputtering of silicon wafers can be accomplished without clamping the wafer to a liquid-cooled holder.
Thin film instabilities and implications for ultrathin resist processes
Authors: Okoroanyanwu Uzodinma
Published: July 2002

The origin and nature of instabilities in ultrathin resist (UTR) polymer films (⩽100 nm) spin coated onto silicon wafer substrates are presented, along with the influence of the substrate on the morphological, thermophysical, and viscoelastic properties of the polymers. The defects, morphology, and density of UTR films spin coated from well-characterized and commercially available phenolic ESCAP polymer based XP-98248 resist from Shipley which were annealed below the glass transition temperature are presented as a function of film thickness and spin coating parameters. For each film, three distinct layers with different densities and varying degrees of roughness are observed: a surface layer, a bulk layer, and a substrate/film interface layer. The thickness of the surface layer is comparable to length scales of cooperative dynamics in polystyrene chains. Dependence of the density and roughness on total film thickness is observed for each layer, with the film/substrate interface layer showing the most variation for film thickness <53 nm, suggesting the onset of instabilities due to interfacial effects, polymer chain packing constraints, and cooperative dynamics. Within the thickness range of 65–100 nm, no dependence of defectivity on total film thickness and spin speed is observed. F2 (157 nm) laser imaging results obtained on these films are discussed. Significant differences between UTR films (∼60 nm) and thick resist films (>400 nm) imaging performance are observed. An explanation is given in terms of polymer cooperative dynamics and interfacial effects.
Remote-plasma-enhanced reaction between a silicon surface and trifluoro-acetyl-fluoride gas
Authors: Saito Yoji , Yamazaki Hirofumi , Mouri Isamu
Published: July 2002

We propose reactive gases, which can be easily decomposed, as the etching gas to avoid “greenhouse effects.” In this article, the etching reaction between silicon and the trifluoro-acetyl-fluoride (CF3COF) gas is demonstrated, using a remote plasma at room temperature. The etching reaction is significantly enhanced by the addition of oxygen and remote-plasma excitation. The etch rate of silicon and oxide by CF3COF/O2 is larger than that by CF4/O2 and C2F6/O2 at the same O2 content. According to the optical emission study, however, the density of excited fluorine decreases in the plasma by the added oxygen into the CF3COF system. Photoelectron studies indicate that the major role of the additional oxygen is to remove the deposited fluorocarbon films from the surfaces.
Cluster beam synthesis of nanostructured thin films
Authors: Milani P. , Piseri P. , Barborini E. , Podesta A. , Lenardi C.
Published: July 2002

The use of clusters as elemental building blocks can open routes toward the fabrication of a new class of nanostructured solids and devices. We report the synthesis of nanostructured films using supersonic cluster beam deposition. A new type of cluster source based on microplasma ablation has been developed. This allows a substantial improvement in terms of deposition rate and control on cluster mass distribution. These achievements make supersonic cluster beams a useful tool in the arena of cluster assembling of materials. We have applied this technique to the growth of nanostructured carbon thin films. The structure and morphology of the films can be controlled by varying the cluster mass distribution prior to deposition. Deposition conditions affect the surface roughness and the onset of scale-invariant morphology on a dimension domain extending from the nanometer up to the micrometer. The cluster beam deposition method shows very promising features in view of the large scale growth of nanostructured films with novel functional and structural properties. The patterning of three-dimensional nanostructured objects is also demonstrated.
Si nanowires synthesized from silicon monoxide by laser ablation
Authors: Tang Y. H. , Zhang Y. F. , Wang N. , Shi W. S. , Lee C. S. , Bello I. , Lee S. T.
Published: July 2002

By ablating a silicon monoxide target with a pulsed KrF excimer laser at 1200 °C in an Ar atmosphere, we have achieved production of high-purity Si nanowires in bulk quantities. The yield and linear growth rate can reach 30 mg/h and 500 μm/h, respectively. Transmission electron micrographs show that the sample of silicon nanowires consists of few nanoparticles.
Effect of temperature on etch rate of iridium and platinum in CF4/O2
Authors: Maa Jer-shen , Ying Hong , Zhang Fengyan
Published: July 2002

Iridium and platinum films were etched in the CF4/O2 plasma in an electron cyclotron resonance etch reactor. Wafers were placed on a heated chuck during etching, with the temperature maintained in the range of 70–250 °C before etching. A rf power was applied to the wafer chuck to generate a self-bias potential. At temperature below 100 °C, the iridium etch rate was low value. The iridium etch rate increased with temperature, and reached about 1500 Å/min above 200 °C. Platinum also showed a low etch rate value below 150 °C, increasing to about 1500 Å/min at 250 °C. The increase of etch rate at higher temperature was attributed to the formation of volatile compounds, IrF6 or PtF6.
dc cathodic polymerization of trimethylsilane in a closed reactor system
Authors: Yu Qingsong , Moffitt C. E. , Wieliczka D. M. , Yasuda Hirotsugu
Published: July 2002

dc cathodic polymerization of trimethylsilane (TMS) in a closed reactor system was investigated. The composition of reactive species in the gas phase was monitored during the deposition process by a residual gas analyzer. It was found that, in such a closed plasma system, the deposition of TMS plasma polymers could be visualized as three consecutive, time-delayed, consecutive three fundamental processes. In the early stage of plasma deposition (<60 s after the initiation of plasma), the deposition of plasma polymers was dominated by the polymerization of silicon-based species because the silicon-based species polymerized much quicker than carbon-based species. In the second stage of plasma deposition (between 60 and 120 s), the deposition was then dominated by carbon-based species due to the consumption of silicon in the early stage. In the final stage (more than 120 s), because of the total consumption of all the polymerizable species in the system, the deposition stopped and the deposited plasma polymer surface was continuously treated by nonpolymer forming gas plasma. As a result, the TMS plasma coatings obtained under such operations have a unique chemical structure that gradually changes from a lower carbon (C/Si ratio of ∼1.7 at the film/substrate interface) to carbon rich (C/Si ratio of ∼4.7 on the surface), as identified by x-ray photoelectron spectroscopy analysis.
Synthesis and microstructure of gallium phosphide nanowires
Authors: Shi W. S. , Zheng Y. F. , Wang N. , Lee C. S. , Lee S. T.
Published: July 2002

Gallium phosphide (GaP) nanowires of 22 nm in diameter and hundreds micrometers in length were synthesized by laser ablation of a powder mixture of GaP and gallium oxide (Ga2O3). The morphology and microstructure of GaP nanowires were investigated by transmission electron microscopy. Twins and stacking faults were observed on {111} planes of the GaP nanowires with special morphologies, and the formation of these defects was discussed. The growth of the GaP nanowires can be described by an oxide-assisted mechanism involving several oxidation-reduction reactions. The successful synthesis of GaP nanowires without any metallic impurities is beneficial for further exploration of their fundamental properties and applications.
Microstructural pressure sensor based on an enhanced resonant mode hysteresis effect
Authors: Brown K. B. , Ma Y. , Allegretto W. , Lawson R. P. W. , Vermeulen F. E. , Robinson A. M.
Published: July 2002

Enhanced hysteresis effects are seen in the resonant behavior of a magnetically actuated oscillating microcantilever at large deflections. These effects, which are produced by resonant mode coupling, take the form of abrupt changes in the amplitude of oscillation. These changes in amplitude and the actuating frequencies at which they occur depend on whether the actuating frequency is being increased or decreased. We have fabricated a microcantilever in which this phenomenon is strongly affected by the damping produced by the pressure of ambient gas. We have investigated this device for use as a pressure sensor in air from 10−3 to 102 Torr.
Limitations of focused ion beam nanomachining
Authors: Lehrer C. , Frey L. , Petersen S. , Ryssel H.
Published: July 2002

In this article, some limitations of the processing of structures with dimensions in the nanometer range by focused ion beams will be discussed. In order to enable exact depth control of nanometer structures, the effective sputter yield of silicon was determined as function of the ion dose. At ion doses below 1016 cm−2, the effective sputter yield is not constant and the volume of the area processed increases due to the implantation of ions. Material removal can be measured for doses above 2×1016 cm−2 and it reaches equilibrium for doses of about 3×1017 cm−2. This dose dependence of the effective sputter yield becomes especially effective in beam tail regions with low ion intensity. The shape of nanostructures is further determined by combining the beam shape and the angle dependence of the sputter yield which was experimentally determined. Using this approach with a Gaussian beam shape, a comparison of simulated and measured sidewall angles has shown good agreement for trench structures. Only sidewall regions close to the surface and to the bottom of deep structures show slight deviations. At the surface, non-Gaussian beam tails lead to unintentional sputtering at the corners of the processed area. At the bottom, forward scattered ions lead to higher sputter erosion.
Etch mechanisms of low dielectric constant polymers in high density plasmas: Impact of charging effects on profile distortion during the etching process
Authors: Fuard D. , Joubert O. , Vallier L. , Assous M. , Berruyer P. , Blanc R.
Published: July 2002

We have studied the etching of very high aspect ratio contact holes in hydrocarbon materials SiLK™, potential dielectric candidates for the next generation of interconnections. During the etch process, slight deformation of the etch profiles such as bowing are observed. Experiments described in this article suggest that bowing originates from the deflection of ions on the sidewalls of the polymer, generating some etching. The mechanisms leading to the ion deflection on the sidewalls are presented and discussed. This study also shows how the process can be tuned to minimize the bow formation.
Oxygen plasma effects on optical properties of ZnSe films
Authors: Yan Li , Woollam John A. , Franke Eva
Published: July 2002

Zinc selenide is an infrared transparent semiconductor material being considered for use in space as an infrared optical coating. In this work, zinc selenide thin films of different thicknesses were exposed to an electron cyclotron resonance generated oxygen plasma, often used to “simulate” the low earth orbital environment. The maximum fluence used in our experiments was equivalent to ∼16 years in the low earth orbital environment. ZnSe thin film optical constants (both before and after oxygen plasma exposure) were determined using variable angle spectroscopic ellipsometry from the vacuum ultraviolet at 146 nm through the middle infrared to 40 μm. A parametric dispersion model (Herzinger–Johs) was successfully used to fit the optical data over the entire range from ultraviolet to infrared. Comparing the pre- and post-oxygen plasma exposure data, few changes were observed in the middle infrared region, while drastic changes were seen in the vacuum ultraviolet through visible to near infrared (0.73–8.5 eV). This suggests that chemical changes upon plasma exposure, including oxidation, are found mainly in a thin layer near the surface. As the proposed application is for infrared coatings, and few infrared changes were seen under conditions roughly equivalent to 16 years in low earth orbit, ZnSe may indeed be useful for space infrared applications. Performance simulations of ZnSe coated infrared-operating electrochromic thermal-control surfaces confirm this conclusion.
A Bakeable Thermistor Vacuum Gauge
Authors: Roberts R. W. , McElligott P. E. , Jernakoff G.
Published: July 2002

A thermistor detector for measuring pressures in the range 10−4 to 1 Torr is described. This gauge operates at constant temperature (∼ 100 °C), has a small volume, and presents an innocuous surface to the vacuum system. This gauge is very stable, maintains its calibrations after a 450 °C bakeout, and is suited for use in ultrahigh-vacuum systems. Operating characteristics are described.
Film Deposition by Exploding Wires
Authors: Mattox D. M. , Mullendore A. W. , Rebarchik F. N.
Published: July 2002

The exploding-wire phenomena provide a high flux of high-energy atoms incident on a surface. Electron-microscopy studies of the nucleation and growth of films formed by exploding wires in vacuum show no deviation from the typical island-channel stages of growth commonly observed in vacuum-deposited and sputter-deposited films. Observations of the deposited material give some insight into the physical processes occurring in the expanding vapor cloud from the exploding wire. Applications and limitations of this technique for depositing thin films are discussed.
Applications of an Approximation to Molecular Flow in Cylindrical Tubes
Authors: Helmer John C.
Published: July 2002

A simple approximation is developed for the molecular flow of gas through a cylindrical tube. The pressure distribution along the wall of the tube is derived and is shown to be a good approximation to the short-tube formula of Clausing. Using these results, the problem of measuring the speed of a pump at the end of a tube is examined. If the pressure gauge is located a distance of one tube radius from the pump, then the intrinsic speed is directly measured in the plane of the gauge.

To determine the capture coefficient of an open-ended tube whose inner surface has a uniform sticking coefficient, we employ a differential equation which reproduces the Monte Carlo results of Smith and Lewin with an error of less than 5%. For tubes of infinite length the capture coefficient is given by k = 2(σ1/2)/(1 + σ1/2), where σ is the sticking coefficient of the inner-tube surface. We repeat the calculation for tubes which have the exit end closed by a surface of the same sticking factor.
Film-thickness resistance monitor for dynamic control of vacuum-deposited films
Authors: Provo J. L.
Published: July 2002

A simple, inexpensive film-thickness monitor has been developed which accurately and independently determines the thickness of a film at any time during a deposition process. The principle of operation is the change in resistance of a vacuum-deposited film on a polished sapphire substrate maintained at a constant deposition temperature. The device, which is easily calibrated and automated, was found to have routine application to many types of metal film depositions in production and the development laboratory. The relationship between film deposition thickness and measured conductance was found to be linear for metal films over a wide range of thickness at constant substrate temperatures, from room temperature to 600 °C. Data is presented which compares film thickness, as measured by interferometric and differential weighing techniques, with that predicted from resistance measurements. The monitor has been used for following changes in resistance during in situ, reactive, and air-exposed hydriding and for resistivity determinations of occluder film hydrides of erbium, scandium, and titanium.
Digitizing Auger data—a threefold approach to enhance analytical capabilities
Authors: Solomon J. S. , Baun W. L.
Published: July 2002

Digital recording of Auger profile and N′ (E) vs E spectral data is shown to enhance in−depth profile analyses, chemical combination studies, and quantitative analyses. Two instrumental schemes are described which output data either on paper tape or magnetic tape. The digitized data were processed with both large real−time or time−share computers. Some of the software operations employed include integration, smoothing, normalization, and plotting. Four advantages realized are: (i) no limit to the number of elements profiled; (ii) unexpected elements present in a profiled layer are not missed; (iii) chemical effects on Auger spectra can be observed as a function of depth; and (iv) comparison of spectra is greatly facilitated.
Hydrogen and helium implantation in vitreous silica
Authors: Mattern P. L. , Thomas G. J. , Bauer W.
Published: July 2002

The effects of 150–300-keV He+ and H+ implantation in vitreous silica have been examined by optical absorption spectroscopy, optical and scanning electron microscopy, gas reemission measurements, and microtopography. No surface blistering or exfoliation was observed at any implant temperature (≲200° to ∠800 °C), at fluences in excess of 1019 ions cm−2. The amount of compaction of the implanted layer was determined for high-fluence ion implantation and compared with existing data. Optical absorption studies show evidence for beam-assisted chemisorption, defect formation, and, with hydrogen implantation, the formation of large (∠1022 cm−3) concentrations of hydroxyl. Experimental results are correlated with gas diffusivity and solubility. Implications for fusion reactor applications are discussed.
Method of continuously measuring work function changes
Authors: Taylor J. L. , Weinberg W. H.
Published: July 2002

A method has been developed for measuring work function changes continuously. It is an ac variation of the diode technique and can be implemented easily in a standard retarding potential LEED/Auger system with derivative detection. Measurements for oxygen adsorption on an Ir single crystal illustrate that this method resolves work function changes within 5 meV.
Corrosion inhibition in sputter-deposited thin-film systems using an intermediary layer of palladium
Authors: Sharp D. J.
Published: July 2002

Accelerated and long term corrosion data are presented for the Ti–Ag and Cr–Au thin film metallization systems deposited by sputter deposition. The Ti–Ag conductor system is used as an electrode for high intensity silicon solar cells, and it has been found that an intermediate layer of 1500 Å of palladium greatly improves the environmental stability of the metallization. The Cr–Au system has been used as an electrical circuit pattern, and thin films of palladium (100–300 Å) have been incorporated to improve storage, processing, and service stability. A 100 Å palladium intermediary did not affect the etch patterning of the Cr–Au metallization. It is observed that the introduction of palladium modifies the anodic potential of the active metal producing a passive oxide when exposed to an electrolytic environment. It is proposed that this modified oxide, at exposed pinhole sites, is responsible for the increased corrosion resistance when palladium is present as an intermediate layer for either the Ti–Ag or Cr–Au metallization systems.
Preparation of CuI films on NaCl single crystals by reactive sputtering and characterization by electron microscopy and Rutherford backscattering
Authors: Reichelt K. , Mair G.
Published: July 2002

The structure and composition of reactively sputtered CuIx films have been investigated by electron diffraction and Rutherford ion backscattering. It has been found that under favorable conditions single-crystal films of CuI in the γ-structure are deposited. These films have a composition ratio Cu/I of approximately one.
Si–MBE: Growth and Sb doping
Authors: König U. , Kibbel H. , Kasper E.
Published: July 2002

Silicon epitaxial films are deposited on 51-mmφ Si substrates by the molecular beam technique. Silicon and the dopant antimony are evaporated from separate sources. Typical process conditions before and during the growth are as follows: substrate heat cleaning at 1173 K for five minutes, substrate temperature 1023 K, growth rate 1 μm/h, film thickness between 0.1 and 3 μm. This procedure is found to be sufficient for obtaining dislocation-free films. The total Sb concentration in the MBE films is measured by neutron activation analysis, the electrically effective concentration with Hall or C–V measurement. Carrier concentrations between 3×1014 and 2×1019 cm−3, and Hall mobilities between 100 and 1400 cm2/V s are obtained. Profiles of the total Sb concentration and of the carrier concentraton with its extremely abrupt substrate-to-epilayer interface elucidate the advantage of the low-temperature MBE technique.
Hydrogen depth profiling using SIMS—Problems and their solutions
Authors: Magee C. W. , Botnick E.M.
Published: July 2002

Problems associated with trace hydrogen detection by SIMS are discussed. These include: (1) residual gas contamination, (2) primary ion beam contamination, (3) detection of stray H secondary ions, (4) instrumental background at low mass (for quadrupole instruments), and (5) matrix-related sensitivity artifacts. In depth-profiling a proton implanted silicon sample, H detection limits of <2 × 1018 at/cm3 could be obtained, but only when the partial pressure of H2O was reduced to <1 × 10−10 Torr (1.33 × 10−8 Pa). The importance of using cesium primary ion bombardment is also discussed, as well as the ability to detect both hydrogen and deuterium in the same analysis.
A radiotracer technique for adsorption and catalysis studies: Application to 14C-benzene chemisorption and rehydrogenation on Pt(111)
Authors: Davis S. M. , Gordon B. E. , Press M. , Somorjai G. A.
Published: July 2002

A radiotracer counting system was developed for adsorption and catalysis studies in ultrahigh vacuum using small area, single crystal surfaces. The counting system utilizes a rugged, compact, and rotatable surface barrier detector with a sensitivity sufficient to detect about 1×1013 molecules cm−2 containing carbon-14. The operating characteristics and performance of this counting system are discussed along with its application to studies of 14C-benzene chemisorption and rehydrogenation on the (111) crystal face of platinum.
Contactless electrical testing of large area specimens using electron beams
Authors: Pfeiffer H. C. , Langner G. O. , Stickel W. , Simpson R. A.
Published: July 2002

An e-beam test system has been developed to detect opens and shorts in three-dimensional networks of conductors embedded in a dielectric matrix. The specimens, which measure up to 100×100 mm, are tested electrically without making physical contact and without mechanical stepping. The system comprise two flood beams and a focused probe beam deflected over the full specimen area at a resolution of better than 3000 lines at 1–2 kV beam energy. One flood gun is located at the rear, the other at the front of the specimen. The change in secondary emission imposed by impinging electrons charging or discharging the surface is detected as voltage contrast which allows one to discriminate between uninterrupted and interrupted as well as shorted pairs of conductors. The physical concept, the contrast mechanism, and the electron optics of the system will be presented together with experimental results.
Fabrication of x-ray masks using anisotropic etching of (110) Si and shadowing techniques
Authors: Tsumita N. , Melngailis J. , Hawryluk A. M. , Smith Henry I.
Published: July 2002

We describe a process for producing x-ray masks of grating patterns with extremely smooth line edges. The technique developed by Flanders, in which a square-wave profile relief grating in polyimide is obliquely shadowed with an x-ray absorber, is followed, except that the original square-wave structure is produced in (110) silicon by anisotropic chemical etching rather than in SiO2 by reactive ion etching. In this way, significant improvements in edge acuity are achieved because relief grating sidewalls are defined by atomic (111) planes. Holographic lithography is used to expose grating patterns in AZ 1350 over a thin Si3N4 layer on the (110) Si. The Si3N4 is patterned by reactive ion etching and serves as the mask for anisotropically etching the square-wave-profile grooves. At the proper crystallographic orientation the groove sidewalls are defined by (111) planes, and groove bottoms are approximately flat. The structure in Si is then transferred to polyimide which is obliquely shadowed and forms the x-ray mask. Grating patterns replicated in PMMA using the CK x-ray (4.5 nm) show straight lines with uniform widths and edges smooth to ∠±4 nm.
Ion–surface interactions during vapor phase crystal growth by sputtering, MBE, and plasma-enhanced CVD: Applications to semiconductors
Authors: Greene J. E. , Barnett S. A.
Published: July 2002

The effects of low-energy particle bombardment of growing films during vapor phase epitaxy are considered in some detail. Ion bombardment plays an important and sometimes dominant role in controlling the growth kinetics and physical properties of films deposited by glow discharge and ion beam sputter deposition, molecular beam epitaxy using accelerated dopants, and plasma- assisted chemical vapor deposition. Ion–surface interaction effects, including trapping, sputtering, preferential sputtering, and collisional mixing, are used to interpret and model experimental results concerning the effects of low-energy particle bombardment on nucleation, film growth, enhanced diffusion at interfaces, and elemental incorporation probabilities. Finally, recent results on the growth of unique single-crystal metastable semiconducting alloys are discussed.
Nozzle beam evaporant source
Authors: Ney R. J.
Published: July 2002

This report describes the design and operation of a unique-nozzle-beam gold deposition source that operates for extended periods of time without reloading. The source puts out a narrow beam of gold typically in the order of 2-1/2° included ‘‘cone’’ angle. Maximum deposition rates are in the order of 1600 Å/min at 2.5 in. ‘‘throw’’ distances.