bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of Externally Fired and Internal Combustion Gas Turbines Using Biomass Fuel
Authors: Ferreira Sandro B. , Pilidis Pericles
Published: July 2002

There is a difference of opinion regarding the relative merits of gas turbines using biomass fuels. Some engineers believe that the internal combustion gas turbine coupled to a gasifier will give a higher efficiency than the externally fired gas turbine using pretreated biomass that is not gasified. Others believe the opposite. In this paper, a comparison between these schemes is made, within the framework of the Brazilian perspective. The exergetic analysis of four cycles is described. The first cycle is externally fired (EFGT), the second uses gasified biomass as fuel (BIG/GT), each of them with a combined cycle as a variant (EFGT/CC and BIG/GTCC). These four are then compared to the natural gas turbine cycles (NGT and NGT/CC) in order to evaluate the thermodynamic cost of using biomass. The comparison is carried out in terms of thermal efficiency and in terms of exergetic efficiency and exergy destruction in the main components. The present analysis shows that the EFGT is quite promising. When compared to the NGT cycle, the EFGT gas turbine shows poor efficiency, though this parameter practically equals that of the BIG/GT cycle. The use of a bottoming steam cycle changes the figures, and the EFGT/CC—due to its higher exhaust temperature—results in high efficiency compared to the BIG/GTCC. Its lower initial and maintenance cost may be an important attraction.
Bicrystal-Based Modeling of Plasticity in FCC Metals
Authors: Lee B. J. , Ahzi S. , Parks D. M.
Published: July 2002

In this paper, intermediate modeling of polycrystalline plasticity is proposed for rigid viscoplatic large deformations. This approach is based on the use of a bicrystal as the elementary local element representing the polycrystal. The local homogenization is obtained by considering the bicrystal volume-averaging and the jump conditions at the assumed planar interface between the two crystals. Two interaction laws based on Taylor and Sachs type assumptions are proposed. These bicrystal-based averaging schemes are different from the classical Taylor and Sachs models since they allow for stresses and strains to vary from one single crystal to the other. We simulate uniaxial tension and compression as well as plane strain compression tests. Results in terms of stress-strain curves are shown in comparison to those of the pure Taylor and Sachs models. We also show results for texture evolution and discuss their comparison with the experimental measurements.
A Multiscale Model of Plasticity Based on Discrete Dislocation Dynamics
Authors: Zbib Hussein M. , Diaz de la Rubia Tomas , Bulatov Vasily
Published: July 2002

We present a framework coupling continuum elasto-viscoplasticity with three-dimensional discrete dislocation dynamics. In this approach, the elastic response is governed by the classical Hooke’s law and the viscoplastic behavior is determined by the motion of curved dislocations in a three-dimensional space. The resulting hybrid continuum-discrete framework is formulated into a standard finite element model where the dislocation-induced stress is homogenized over each element with a similar treatment for the dislocation-induced plastic strain. The model can be used to investigate a wide range of small scale plasticity phenomena, including microshear bands, adiabatic shear bands, stability and formation of dislocation cells, thin films and multiplayer structures. Here we present results pertaining to the formation of deformation bands and surface distortions under dynamic loading conditions and show the capability of the model in analyzing complicated deformation-induced patterns.
A Left Ventricle Model to Predict Post-Revascularization Ejection Fraction Based on Cine Magnetic Resonance Images
Authors: Han Hai-Chao , Oshinski John N. , Ku David N. , Pettigrew Roderic I.
Published: July 2002

The left ventricular ejection fraction (LVEF) is an important clinical indicator of the cardiac function and long-term outcome for patients with coronary artery disease. A biomechanical model of the left ventricle was developed to quantitatively predict post-revascularization LVEF based on noninvasive magnetic resonance imaging. The myocardium was categorized into normal, hibernating, and infarcted regions from the ventricular short-axis images. Assuming that hibernating tissue would potentially regain contractility after revascularization, the expected maximum post-revascularization LVEF was calculated for four patients with chronic left ventricular dysfunction. The predictions were within three ejection fraction points of the follow-up LVEFs. This model may be useful to estimate the outcome and efficacy of revascularization plans.
Control-Oriented Model for Camless Intake Process—Part I1
Authors: Ashhab M.-S. S. , Stefanopoulou A. G. , Cook J. A. , Levin M. B.
Published: July 2002

The improvement of internal combustion engine is largely accomplished though the introduction of innovative actuators that allow optimization and control of the flow, mixing, and combustion processes. The realization of such a novel system depends on the existence of an operational controller that will stabilize the engine and allow experimental testing which, consequently, leads to further development of the actuator and the engine controller. This iterative process requires a starting point which is the development of a control-oriented model. Although not fully validated, the control-oriented model reveals issues associated with uncertainties, nonlinearities, and limitation of different subsystems. Moreover, it aides in defining the controller structure and the necessary parameters for the calibration of the closed loop system. In this paper (Part I) we describe the development process of a control-oriented model for a camless intake process. We first model the multicylinder crankangle-based breathing dynamics and validate it against experimental data of a conventional engine with cam-driven valve profile during unthrottled operation. We then employ the assumption of uniform air pulses during the intake duration and derive a simple input-output representation of the cylinder air charge, pumping losses and associated uncertainties that can be used for designing an electronic valvetrain controller (Part II). [S0022-0434(00)02901-4]
Simple Formulas for Direct Design of Discrete-Time Lead Compensators
Authors: Messner William
Published: July 2002

Traditionally, servo engineers have designed discrete-time lead compensators by first designing a lead compensator in the w-domain, and then converted to the z-domain by using a bilinear transformation with frequency prewarping. This technical note presents two new simple formulas for determining the zero and the pole of a discrete-time lead compensator directly in the z-domain from the desired maximum phase lead and the desired frequency at which that phase lead should occur. [S0022-0434(00)01502-1]
Free Vibration Analysis of Composite Plates
Authors: Afshari Payman , Widera G. E. O.
Published: July 2002

A series of plate elements, based on the modified complementary energy principal, are developed to study the free undamped vibration response of laminated composite plates. The Mindlin thin plate theory is selected to govern the general characteristics and behavior of these plate elements. A series of in-plane strain functions are assumed from which the corresponding in-plane strains and corresponding stresses for each lamina are determined. The transverse stresses are then computed by satisfying the equations of the equilibrium. Eight-noded isoparametric elements are utilized to describe the displacement field. These hybrid plate elements are used to form the stiffness and the consistent mass matrices. The fundamental natural frequencies are then computed by solving the generalized eigenvalue problem and their application demonstrated via a number of examples. [S0094-9930(00)02603-7]
Elemental Chromium by XPS
Authors: Kelly D. , Jung D. R.
Published: July 2002

X-ray photoelectron spectroscopy (XPS) spectra of elemental chromium (Cr) are presented. The specimen is a polycrystalline solid and was analyzed after argon ion-sputtering to remove surface contamination. The spectra were collected with a Fisons Instruments ESCALab 220i-XL instrument using monochromatized Al Kα x-rays. Spectra include a survey scan and the Cr 2p, 2s, 3p, 3s, and valence band regions. Also included is the Cr L3M3,2M4,5 Auger transition.
Optical spectroscopic analyses of OH incorporation into SiO2 films deposited from O2/tetraethoxysilane plasmas
Authors: Goullet A. , Vallée C. , Granier A. , Turban G.
Published: July 2002

Silicon dioxide thin films are deposited on (100) silicon substrates at low pressure (5 mTorr), from O2/tetraethoxysilane (TEOS) helicon plasmas. The reactor is operated at 300 W radio frequency power without any intentional heating or biasing of the substrate. The samples are characterized using infrared spectroscopy, ultraviolet-visible ellipsometry, and complementary density measurements. Changes in film properties are observed varying the TEOS fraction in the gas mixture. Good quality SiO2 films, insensitive to postdeposition exposure to atmospheric water, are deposited for low TEOS fractions (<5%) in the mixture. As the O2 flow rate decreases, porous SiO2 and polymeric SiOxCyHz samples are successively obtained. Aging over 5 months of intentionally produced porous films has been investigated using Fourier-transform infrared spectroscopy. The 2900–3800 cm−1 OH absorption stretching band is quantitatively analyzed with three deconvolution bands. These films are hygroscopic and they show changes in the infrared spectra indicating an incorporation of additional highly associated hydroxyl groups. In addition, the development of the 935 cm−1 Si–OH stretching band and the evolution of the Si–O–Si stretching peak are due to interactions between the airborne absorbed water and silica network. On the other hand, isolated silanol species are rather insensitive to the postdeposition exposure to the atmospheric water. The respective contribution of growth induced and after growth ex situ incorporated Si–OH groups is established. Using the Bruggeman effective medium approximation, we found that water molecules account well for the dielectric properties of these highly associated SiOH groups mainly originating from postdeposition silica hydrolysis.
Evaporation and ion assisted deposition of HfO2 coatings: Some key points for high power laser applications
Authors: Andre B. , Poupinet L. , Ravel G.
Published: July 2002

Optical interference filters made by layers of optical coatings are used to shape and transport laser beams. If a defect is present in the stack (cosmetic defect, stoichiometry defect, absorption band…), and high laser power density is reached, a strong energy into the material can be deposited involving the destruction of the coatings (either by melting or mechanical failure). One of the key methods to achieve high performance coatings is to reduce such defects as much as possible. Hafnia (HfO2) coatings are undoubtedly one of the most successful materials for high power laser applications. Associated with a low index material such as silica, high laser induced damage threshold (LIDT) interference filters can be achieved. Hafnia is often the LIDT limiting factor. During the evaporation HfO2 particles create buried defects in the deposited material. These defects are sources of the coating damage during laser irradiation. To avoid this phenomenon we have evaporated metallic hafnium that was oxidized by oxygen inlet into the vacuum chamber or use an oxygen ion beam bombardment during the film growth. Argon or, better, xenon ions in the beam produced densities as high as 99% of the bulk, with low water content, and an improved optical transmission in the mid infrared window. This article deals with the optimization of such a deposition process regarding coating density, mechanical stresses, and optical properties (optical absorption). Films deposited by HfO2 evaporation are compared especially using photothermal mapping. The stoichiometry of the defects determined thanks to localized Auger spectroscopy clearly indicates how injurious such defects could be for high laser flux applications. Finally, laser damage thresholds of the films at 1.06 μm are measured and possible damage mechanism discussed.
Growth of high-quality (Al,Ga)N and (Ga,In)N heterostructures on SiC(0001) by both plasma-assisted and reactive molecular beam epitaxy
Authors: Ploog K. H. , Brandt O. , Muralidharan R. , Thamm A. , Waltereit P.
Published: July 2002

We discuss the strategies essential for the growth of high-quality (Al,Ga)N/GaN and (Ga,In)N/GaN heterostructures on SiC(0001) substrates by molecular beam epitaxy (MBE) using either N2 plasma discharge or NH3 cracking as an active nitrogen source. Optimization of substrate preparation, nucleation, and growth conditions are the important issues to improve the surface morphology, interface abruptness, structural integrity, and electronic properties. A breakthrough in preparing the SiC(0001) surface was achieved by ex situ etching in H2 at 1600 °C and subsequent in situ cleaning via several cycles of Ga deposition and flash-off at 800 °C. By far the best results are then obtained, when growth is initiated directly, i.e., without any specific nucleation phase, for both plasma assisted (PA)MBE and reactive (R)MBE. Using growth rates of 0.5–1.2 μm/h the optimum growth temperature Ts was found to be 700 °C for GaN. Any deviation from the optimum Ts and the optimum III/V flux ratio can be easily detected by reflection high energy electron diffraction and adjusted appropriately. Using these careful optimization strategies, both PAMBE and RMBE produce (Al,Ga,In)N heterostructures on SiC(0001) of high morphological, structural, and electronic quality in a very reproducible manner. The only difference between the two nitrogen sources is the very limited incorporation of In in (Ga,In)N in the presence of hydrogen from the NH3 cracking on the growing surface. In PAMBE-grown (Ga,In)/GaN single and multiple quantum wells we achieved In mole fractions from 0.05 to 0.70 in 3 nm wells which very efficiently emit in the violet to yellow spectral range at 300 K.
Thermal Transpiration—A Continuum Gasdynamics View
Authors: Williams James C.
Published: July 2002

Thermal transpiration—the phenomenon in which, at low pressures, a pressure difference is maintained across a small bore tube (or orifice) by a temperature difference—has been studied experimentally and theoretically for almost a century. In spite of this, the phenomenon is subject to neither physical explanation nor mathematical analysis in the transition regime. In the present work, the model for thermal transpiration in the near continuum regime is reviewed and extended to include a current model for velocity slip at the wall including thermal creep. The mathematical model formulated has been tested against recent experimental data for the thermal transpiration effect. It is shown that this model predicts both the trends and magnitudes of the effects of overall pressure level, overall temperature ratio, and gas on the thermal transpiration pressure ratio, as long as the pressure level is reasonably high, i.e., as long as the flow is in the near continuum regime.
Surface Phonons and Gas Surface Interactions
Authors: Armand G. , Masri P. , Dobrzysnski L.
Published: July 2002

Modifications to the band frequencies of a crystal occur with gas adsorption on the surface. If the adsorbed species are small mass or if they are strongly bonded, theoretical calculations predict the appearance of new frequencies which lie above the band frequencies of the crystal (surface phonons) and of a modification of the Rayleigh waves. Results of calculations with different models of monoatomic crystals and one adsorbed layer are presented. Two main consequences are discussed: the entropy variation due to adsorption, which yields a modification of the pre-exponential factor of the desorption rate equation; the amount of energy exchange between a colliding particle and a crystal, which decreases as the surface phonon-frequencies increases. Experimentally the existence of surface phonons correlated to adsorption can be supported by data from energy loss of low energy electrons and by infrared absorption measurements. Indirect support is also provided by experimental results dealing with the pre-exponential factor of desorption rates, and with reflection of light atom beams at a crystal surface.
Low Energy Electron Spectroscopy—a Tool for Studies of Surface Vibrations
Authors: Ibach Harald
Published: July 2002

Surface vibrations are investigated with a high resolution electron spectrometer (ΔE≈10 meV). For sufficiently low electron energies the electrons are scattered mainly by the extended electric dipole field associated with certain types of surface vibrations. The excitation of Fuchs-Kliewer surface modes in infrared-active materials is illustrated in zinc oxide. On the cleaved (111) silicon surface a surface phonon of ℏω=56 meV is found. Furthermore, the localized modes of oxygen adsorbed on a (111) silicon surface are discussed. The sensitivity of electron spectroscopy is several orders of magnitude higher than light spectroscopy.
In Situ Sputter Cleaning of Thin Film Metal Substrates For UHV-TEM Corrosion Studies
Authors: Heinemann Klaus , Poppa Helmut
Published: July 2002

A prerequisite for conducting valid corrosion experiments by in situ electron microscopy techniques is not only the achievement of UHV background pressure conditions at the site of the specimen but also the ability to clean the surface of the thin metal substrate specimen before initiation of the corrosive interaction. A miniaturized simple ion gun has been constructed for this purpose. The gun is small enough to be incorporated into an UHV electron microscope specimen chamber with hot stage in such a way as to permit bombardment of the substrate specimen while observing it by transmission electron microscopy TEM. It is shown that the ion beam generated is confined well enough to cause a sputtering removal of substrate material at a rate of approximately 5–10 Å/min and to prevent the sputter deposition of contaminating material from the specimen holder. Thin single crystal Ni (100) film samples were used to demonstrate the applicability of the sputter cleaning technique, to show the removal of ion beam induced radiation damage by annealing, and to evaluate preliminary oxidation tests by selected zone dark-field microscopy.
The influence of sodium on the Si-SiO2 interface
Authors: DiStefano T. H. , Lewis J. E.
Published: July 2002

Internal photoemission and thermionic emission are used to determine the dipole polarization layer produced by sodium ions at a Si-SiO2 interface. The electronic energy barrier at the interface is reduced by the sodium ion dipole from 4.25 eV for a clean Si-SiO2 interface to a saturation limit of 2.6 eV for a sodium coverage of 1.3×1015 Na/cm2. The interface is quite sensitive to the presence of sodium, since only about 0.01 monolayer of sodium is sufficient to cause an appreciable reduction of the threshold for internal photoemission.
Wave propagation and power deposition in magnetically enhanced inductively coupled and helicon plasma sources
Authors: Kinder Ronald L. , Kushner Mark J.
Published: July 2002

Magnetically enhanced inductively coupled plasma (MEICP) and helicon sources for materials processing are of interest because of their ability to deposit power within the volume of the plasma beyond the classical skin depth. The location and manner of power deposition can vary substantially depending on the mode of operation and reactor conditions. The coupling of electromagnetic fields to the plasma typically occurs through two channels; a weakly damped heliconlike wave that penetrates into the bulk plasma and an electrostatic wave. The electrostatic wave can often be suppressed resulting in the helicon component being responsible for the majority of the power deposition. A computational investigation was conducted to quantify this heating and determine the conditions for which power can be deposited in the downstream region of MEICP devices. For typical process conditions (10 mTorr, 1 kW ICP) and magnetic fields above 40 G, radial and axial electric fields exhibit nodal structure consistent with helicon behavior. As the magnetic fields are increased, axial standing wave patterns occur with substantial power deposition downstream. The ability to deposit power downstream with increasing B field is ultimately limited by the increasing wavelength. For example, if the plasma is significantly electronegative in the low power–high magnetic field regime, power deposition resembles conventional ICP due to the helicon wavelength exceeding the reactor.
Investigating surface stress: Surface loss in ultrathin single-crystal silicon cantilevers
Authors: Yang Jinling , Ono Takahito , Esashi Masayoshi
Published: July 2002

We investigated the effect of surface treatment in an ultrahigh-vacuum chamber on the Q factor of ultrathin single-crystal silicon cantilevers with different thicknesses (60, 170, and 500 nm) and different surface orientations. When the length is L>30 μm, the Q factor is proportional to the thickness and surface loss dominates, whereas when L<30 μm, support loss surpasses the surface loss. Heating can remove the SiO2 layer and absorbates and results in an increase of the Q factor. Hydrogen termination leads to a larger relative increase of the Q factor in thinner structures than in thicker ones. Heating and H exposure improve the Q values of Si(100)-oriented cantilevers more than Si(110)-oriented ones, and they result in the opposing resonance frequency response for these two surfaces.
Investigation of the outgassing characteristics of the materials comprising a plasma display panel
Authors: Han H. R. , Lee Y. J. , Yeom G. Y.
Published: July 2002

Long gas evacuation time before the introduction of the discharge gases into the panel is one of the major problems in the production of a plasma display panel (PDP). In this study, the outgassing characteristics during the panel evacuation stage were investigated using a quadrupole mass spectrometer. The origin of the impurity gas was studied by measuring the outgassed species from each layer comprising the PDP. Dominant species observed during the evacuation of the panel were H2, H2O, N2, O2, and CO2 and water vapor was the most abundant species. When the outgassing characteristics of the panel were compared with the outgassing characteristics from each layer comprising the panel, the material most responsible for the water vapor turned out to be a MgO layer. The outgassing experiments of single panels have also shown that the long outgassing time of PDP is mostly related to the MgO layer and possibly also to red, green, and blue layers and white dielectric material coated on the each single panel. Therefore to reduce the gas evacuation time, controlled atmosphere appears to be required during the deposition of these materials and the storage of those deposited panels.
Optical filters for plasma display panels using organic dyes and sputtered multilayer coatings
Authors: Okamura T. , Fukuda S. , Koike K. , Saigou H. , Yoshikai M. , Koyama M. , Misawa T. , Matsuzaki Y.
Published: July 2002

Optical filters for plasma display panels (PDPs) have been studied. We obtained the sputtered seven-layer coatings (comprising alternate layers of silver and indium–tin–oxide) on substrates of polyethylene terephthalate by a roll-to-roll process. The coatings were designed in order to minimize interfacial reflectance between the coatings and the adjacent layer to it. The coatings have a surface resistance of 2.2 Ω/sq, a transmittance of 1%∼12% in the near-infrared region of 800–1200 nm, and visible-light transmittance of approximately 70%. In combination with these multilayer coatings working as shields of electromagnetic wave and near-infrared light, organic dyes were also applied to control transmission properties of the optical filters and to improve PDPs picture quality.
Characterization of inductively coupled plasma etched surface of GaN using Cl2/BCl3 chemistry
Authors: Tripathy S. , Ramam A. , Chua S. J. , Pan J. S. , Huan Alfred
Published: July 2002

We have investigated plasma-induced damage of the inductively coupled plasma (ICP) etched surface of n-type GaN using Cl2/BCl3 chemistry. The surface morphology of the etched GaN under different plasma conditions is analyzed by atomic force microscopy. X-ray photoelectron spectroscopy is used to correlate the chemical changes induced by plasma etching of the GaN surface. We have carried out photoluminescence measurements of etched GaN surfaces subjected to varying ICP conditions. The intensity of the band-edge and yellow luminescence transitions was used to evaluate the damage introduced into the semiconductor during dry etching.
Spectroscopic ellipsometry measurements of chromium nitride coatings
Authors: Aouadi S. M. , Mihut D. M. , Kuruppu M. L. , Kirkpatrick S. R. , Rohde S. L.
Published: July 2002

Coatings of chromium and chromium nitride with various compositions were deposited on silicon substrates using ion-assisted reactive magnetron sputtering. These coatings were characterized using x-ray diffraction (XRD), Rutherford backscattering (RBS), and spectroscopic ellipsometry (SE). The primary chromium nitride phases (Cr2N and CrN) in the chromium nitride films were identified using XRD. The chemical composition of selected samples was determined from RBS measurements. The refractive indices of Cr, Cr2N, and CrN were deduced from the analysis of the SE data. Based on these refractive indices, ellipsometry was used successfully to identify the microstructure and the roughness of a number of chromium nitride coatings grown under different deposition conditions.
Effect of ammonia plasma pretreatment on silicon–nitride barriers for Cu metallization systems
Authors: Qin W. , Mo Z. Q. , Tang L. J. , Yu B. , Wang S. R. , Xie J.
Published: July 2002

The barrier properties of plasma-enhanced chemical vapor deposited (PECVD) SiN thin films capped on post chemical mechanical polishing Cu film were investigated by various analytical techniques, such as secondary-ion mass spectrometry (SIMS), transmission electron microscopy, and atomic force microscopy, focusing on the effect of NH3 plasma pretreatment. SiN films were deposited at 400 °C in a sequential multistage deposition system. Much less Cu contamination was detected at the surface of SiN deposited with plasma pretreatment, compared to that without plasma pretreatment. Also, the amount of Si diffused into Cu during deposition was found to be significantly reduced after NH3 plasma pretreatment. Similar Cu diffusion behavior was observed in SiN films deposited with or without plasma pretreatment, after being annealed at 450 °C. However, SIMS analysis revealed that Cu diffused faster in SiN deposited with plasma pretreatment than in SiN deposited without plasma pretreatment, after being annealed at 550 °C.
Ultrathin zirconium oxide films as alternative gate dielectrics
Authors: Chang J. P. , Lin Y-S. , Berger S. , Kepten A. , Bloom R. , Levy S.
Published: July 2002

ZrO 2 films were deposited on Si(100) wafers by the rapid thermal chemical vapor deposition process using a zirconium (IV) t-butoxide Zr(OC4H9)4 precursor and oxygen. Interfacial zirconium silicate formation was observed by high resolution transmission electron microscopy and medium energy ion scattering. The intermixing of the interface can be suppressed by forming a thin silicon nitride layer on the silicon substrate prior to ZrO2 deposition. The dielectric constant of ZrO2 achieved in this work is 15–18 with very small capacitance–voltage hysteresis, ideal for metal–oxide–semiconductor field effect transistor (MOSFET) application. The NMOSFET device has good turn-on characteristics, however, the transconductance is lower than expected due to the incomplete removal of zirconium silicate at the source and drain contacts and poses integration challenges to use ZrO2 as the gate dielectric material.
Optical emission characteristics and mode transitions in low-frequency inductively coupled plasmas
Authors: Ostrikov K. N. , Xu S. , Shafiul Azam A. B. M.
Published: July 2002

Optical emission characteristics of the 500 kHz flat-coil inductively coupled discharges in pure argon, nitrogen, and gas mixtures of Ar+H2, N2+Ar, and N2+H2 are investigated. Variation of input power and operating gas pressure lead to hysteresis in the optical emission intensity (OEI), which is associated with the transitions between the electrostatic (E) and electromagnetic (H) discharge operating regimes. The characteristics of the hysteresis loops and character of mode transitions appear to be different in pure gases and gas mixtures. It has been observed that the E→H transition are always discontinuous, while the H→E transitions appear smooth in pure nitrogen and N2-dominated discharges. Dependence of the E→H transition threshold on gas composition in Ar+N2, Ar+H2, and N2+H2 mixtures is investigated and underlying mechanisms are discussed. It is also shown that the OEI of nitrogen species can efficiently be controlled by small Ar or H2 admixtures. Addition of argon enhances the optical emission of N2, N2+, N, and N+ species, whereas the effect of hydrogen admixture is the opposite.
Metallization of poly(vinylchloride) by Fe, Ni, Cu, Ag, and Au
Authors: Carlo S. R. , Perry C. , Torres Jessica , Fairbrother D. Howard
Published: July 2002

The evolution of the metal-polymer interface during the physical vapor deposition of Fe, Ni, Cu, Ag, and Au on poly(vinylchloride) (PVC) has been studied in situ using x-ray photoelectron spectroscopy. At low metal exposures, all of the metals studied reacted with PVC, forming a metal chloride. For those metals with more than one stable oxidation state, the salt produced corresponded to the metal’s lowest stable oxidation state, e.g., CuCl instead of CuCl2. Higher metal exposures resulted in deposition of a metallic overlayer. For Fe, Ni, Cu, and Au the variation in the metal’s reactivity (measured by the metal/metal-chloride ratio as a function of metal coverage), was observed to increase in the order Fe≈Ni>Cu>Au.
Simple Differential Pumping Stage for Connecting High to Ultrahigh-Vacuum Systems
Authors: Kornelsen E. V. , Domeij B.
Published: July 2002

Measurements have been made of the nitrogen pressure ratio across a connecting stage as a function of the nitrogen exposure on the high-pressure side. The stage consisted of a titanium evaporator in a spherical glass bulb (8-cm diameter) which was connected to two glass ultra-high vacuum systems via short axially aligned tubes. When an unobstructed straight line path was allowed between the two systems, at least 99% of the transmitted gas was the direct “streaming” component which did not encounter the titanium surface. For the particular design reported here, the resulting pressure ratio was 3.3×104. When the streaming path was obstructed, pressure ratios as high as 3×107 were measured. Saturation of the chemisorption on the evaporated titanium occurred at ∼8×1014 molecules per cm2 of macroscopic area. A single evaporator containing 0.12 g of titanium was able to deposit more than 300 films. Expressions are given from which the performance of other stages of similar design but of different dimensions can be estimated.
Modulation of Bayard-Alpert Gauges
Authors: Redhead P. A.
Published: July 2002

Modulation of the ion current in Bayard-Alpert gauges allows operation at pressures below the normal x-ray limit and the measurement of pressures of electronically desorbable gases (e.g., O2, CO, and Cl2). Modulation by the method originally proposed (mode I) has two undesirable features: (a) modulation may cause pressure bursts, and (b) some modulation of the x-ray photocurrent occurs. Various alternate modulation methods are examined to determine which method minimizes the undesirable effects. A modulator external to the grid is only effective with electron currents less than 5 mA and with an open end grid. Two methods using a modulator internal to the grid are shown to be satisfactory; in the first (mode II), proposed by Lange and Singleton, the ends of the grid are left open and the modulator is switched from grid potential (Vg) to about (Vg − 20) V. In the second (mode III) the ends of the grid are cloud and the modulator is switched from (Vg − 20) to (Vg − 60) V.
The Adsorption of Atmospheric Gases on Molecular Sieves at Low Pressures and Temperatures. The Effect of Preadsorbed Water
Authors: Stern S. A. , DiPaolo F. S.
Published: July 2002

The adsorption of nitrogen, helium, neon, and air on Molecular Sieves 5A, 10X, and 13X was studied at 77.3 °K and in the pressure range from 102 to 10−6 Torr. The capacities of freshly activated adsorbent samples for nitrogen were found to increase markedly below 10−3 Torr after consecutive adsorption-desorption cycles. This “conditioning effect” may explain the large discrepancies in the data of previous investigators. The nitrogen isotherms can be represented above 10−2 to 10−4 Torr by either the Freundlich or the Dubinin–Radushkevich equations, while the helium and neon isotherms obey Henry’s law. The effect of preadsorbed water is to decrease the adsorptive capacity of Molecular Sieve 5A for nitrogen; when the amount of water exceeds 7 wt%, the capacity for nitrogen is almost completely suppressed. It is suggested that this behavior is due to the migration of hydrated cations, which block the apertures to the cube octahedral cavities of the adsorbent.
Thermal desorption of implanted inert gas ions from nickel
Authors: Edwards D.
Published: July 2002

The thermal desorption spectra of low−energy inert gas ions implanted into a nickel crystal are reported. Particularly simple, surface sensitive, first−order desorption transients are obtained at low−implantation energies and at low−incident doses. Desorption rate constants are derived for one of the well−resolved desorption transients and allow a comparison of theoretical peak profiles with the experimental measurement. A diffusion process is observed for the desorption of high−energy (1−7 keV) neon in nickel and the activation energy for neon diffusion in nickel is obtained.
Chemisorption of O and H on the free-electron-like metals Al and Mg studied by photoelectron spectroscopy
Authors: Flodström S. A. , Petersson L.-G. , Hagström S. B. M.
Published: July 2002

Photoemission with He I (21.2 eV) and He II (40.8 eV) radiation has been used as a tool to study chemisorption on Al and Mg. Recent theories predict resonances in the metal valence bands for O2 and H2 exposure. These resonances have been experimentally verified in the case of oxygen. A comparison between positions and widths of the theoretical and experimental resonances is made.
Interface properties of Si on sapphire and spinel
Authors: Schlötterer Heinrich
Published: July 2002

It is shown for the special example of silicon films on sapphire and spinel that the ’’interface’’ between both single crystals is more complex than the simple superposition of two different lattice planes. The structural, mechanical, chemical, optical, and electrical aspects of the interface are discussed. It is shown that, depending on the kind of aspect, we can describe it as a two-dimensional interface, a three-dimensional transition layer, or a three-dimensional intermediate layer. All the quoted properties depend both on the kind of preparation of the surface, like polishing or heat treatment, and on the epitaxial deposition process itself, e.g., on temperature and growth rate. A model for this special example of heteroepitaxy will be presented.
Characterization of surfaces by low-energy helium scattering
Authors: Horne James , Miller David R.
Published: July 2002

An experimental apparatus is described which permits excellent sensitivity and energy resolution in atomic and molecular beam surface scattering experiments. It is suggested that the Boxcar Integrator, a low cost, commercial instrument, is ideally suited to these experiments and, for helium scattering, yields more information than the conventional lock-in amplifier technique. Preliminary data on low-energy helium scattering from unoriented W(100) facets, produced by annealing a tungsten ribbon, shows sharp diffraction effects due to a surface structure grating at least 70 Å in characteristic size. Applications to inelastic scattering studies are briefly discussed.
Tin dioxide films prepared by dc sputtering from a pressed powder target
Authors: Sabnis Anant G. , Feisel Lyle D.
Published: July 2002

Tin dioxide films were prepared by dc glow-discharge sputtering, using a target of compressed SnO2 powder. The films thus produced are conductive at room temperature (σ=3×10−5 Ω−1 cm−1). By mixing Sb2O3 powder with SnO2 powder in varying proportions, conductivity as high as 1 Ω−1 cm−1 was achieved. Conductivity and optical absorption increases with increasing Sb content. Transparency as high as 85% is obtained in doped 90-nm films on glass. An Sb2O3 content of 10% and more increases the lattice disorder of the films, thereby making them nonconducting. Such films can be made conductive by heat treatment. These films are n type and nondegenerate. The activation energy decreases with increasing antimony content.
Calibration of tungsten–rhenium alloy thermocouples below room temperature
Authors: Sandstrom D. R. , Withrow S. P.
Published: July 2002

Three tungsten-rhenium alloy thermocouple combinations are calibrated and numerically represented by a polynomical in temperature for the range 77–290 K. (AIP).
Oxide barriers on GaAs by neutralized ion-beam sputtering
Authors: Meiners L. G. , Pan Ru-Pin , Sites J. R.
Published: July 2002

Tantalum and silicon oxides have been sputter deposited onto gallium arsenide using a 500-eV beam of neutralized argon atoms. MIS devices show very low leakage and capacitances that can be varied from full accumulation to depletion with the application of modest voltages. Other measurements (breakdown field, dielectric constant, adherence, Auger profile, and photoluminescence) also suggest that these structures hold potential usefulness for insulated-gate GaAs circuitry.
Lateral interactions in adsorbed layers
Authors: Bradshaw A. M. , Scheffler M.
Published: July 2002

Various mechanisms giving rise to attractive and repulsive forces between adspecies are considered. Such interactions can be classified as through-space (direct) or through-substrate (indirect), although a clear distinction is not possible. We describe in particular the interactions between both permanent and oscillating dipoles as well as those due to short-range overlap. The effect of these interactions on work function change, adsorption energy, UPS, and ir spectra are discussed. The adsorption systems Xe and CO/Pd(100) are used for the purposes of illustration.
Carbon monoxide oxidation reaction over Rh
Authors: Campbell Charles T. , Shi Shei-Kung , White J. M.
Published: July 2002

The catalytic oxidation of carbon monoxide to form CO2 over polycrystalline Rh has been investigated experimentally and by numerical simulation. Transient CO2 production rates have been measured under a variety of conditions. The results are analyzed in terms of the Langmuir–Hinshelwwod combination of coadsorbed oxygen and carbon monoxide. A complex reaction model is presented which successfully simulates the present results. The model requires a transition in the activation energy for the Langmuir–Hinshelwood process from 14.3–25 kcal mol−1 accompanied by the appearance of inhibition to CO adsorption by adsorbed oxygen above 529 K.
Theoretical and experimental investigations of the electronic structure of oxygen on silicon
Authors: Chen M. , Batra Inder P. , Brundle C. R.
Published: July 2002

While the oxidation stages of silicon beyond one monolayer have been extensively documented by photoemission and Auger experiments, the question as to whether initial chemisorption of oxygen is molecular or dissociative is controversial. We have carried out theoretical calculations using the extended tight-binding method simulating both O2 and O overlayer adsorption on Si(111) surface. Comparison of published and our new uv photoemission spectra with our calculated density of states indicates a better agreement with the dissociated oxygen model than with the molecular one. We have also studied the x-ray photoemission of oxygen on Si(111) from submonolayer to several monolayers of oxide (∠ 8Å). Our data is consistent with initial dissociative adsorption but incompatible with molecular adsorption.
Surface structures of metallic monolayers on metal crystal surfaces
Authors: Biberian J. P. , Somorjai G. A.
Published: July 2002

The structures of adsorbed metals on single crystal surfaces of other metals have been reviewed and tabulated. Most of the adsorbates of over 100 systems studied form ordered surface structures that may undergo changes as the coverage in the monolayer is increased. At low coverages the adsorbate and substrate surface structures are closely related indicating the predominance of the adsorbate–substrate interaction in determining ordering. At higher coverages there are more complex ordering characteristics. Although the relative atom sizes and magnitudes of adsorbate–substrate and substrate–substrate interactions influence the ordering in the monolayer general conclusions that have predictive value must await the avialability of more experimental results on more metal adsorbate–substrate systems.
An o-ring-sealed rotary feedthrough for UHV applications
Authors: Pararas A. , Ceyer S. T. , Yates J. T.
Published: July 2002

A differentially pumped o-ring-sealed rotary feedthrough for ultrahigh vacuum applications is described. Its simplified design results in a significant reduction of machining requirements, compared to previous designs.
Measurement of stresses generated in cured polyimide films
Authors: Goldsmith Charles , Geldermans P. , Bedetti F. , Walker G. A.
Published: July 2002

We have measured ‘‘in situ’’ the stresses generated in polyimide films produced from the ethyl ester of benzophenone tetracarbolic acid and methylene dianiline during the curing cycle. The room temperature stress in a fully cured film (to 400 °C) is approximately 70 MPa. The stresses at room temperature vary with the cure temperature and are due to coefficient of thermal expansion mismatch between film and substrate. The in situ measurements show that the glass transition temperature is the same as the maximum cure temperature that the film experiences. The stress measurements were made using an x-ray double crystal lattice curvature technique.
Regularities and irregularities in SIMS/FAB spectra of alkali halides analyzed via the bond-breaking model
Authors: Dunlap Brett I. , Campana Joseph E. , Green Brian N. , Bateman Robert H.
Published: July 2002

Relative ion intensities for cluster ions of the type [M(MX)n]+ and [X(MX)n]− from the SIMS spectra of alkali halides for n<100 are presented. The envelopes of the positive and negative ion spectra are quite similar and can be fit using a random bond-breaking model on the Bethe lattice approximating the bulk crystal structure. Irregularities occur in the vicinity of certain n values with ion intensity enhanced relative to that of the envelope. The greater intensity at these ‘‘magic numbers’’ is consistent with the bond-breaking model if the overall probability of breaking any bond of the bulk crystal is small. However, the reduced ion intensity immediately following the enhancement is only consistent with the subsequent unimolecular cluster ion decomposition. Mass-resolved mass spectra are reported exceeding m/z 25 000 from neutral atom bombardment of alkali iodides.
Theoretical determination of ionization efficiency for an orbitron device and variation with the main working parameters
Authors: Petit B. , Feidt M. L.
Published: July 2002

A knowledge of the distribution function for electrons describing stable and unstable trajectories, respectively, and the evaluation of the stable electrons’ mean lifetime deduced from the properties of the ‘‘electrostatic mirror’’ corresponding to the endplates, allow us to perform a theoretical calculation of ionization efficiency for an orbitron device. The ionization efficiency of the device is calculated for various geometrical and electrical parameters using the preceding theoretical considerations. Comparison between experiments and calculations allow us to validate the theoretical model.
Pellet acceleration study with a railgun for magnetic fusion reactor refueling
Authors: Honig J. , Kim K.
Published: July 2002

Design, construction, and preliminary testing of a two-stage pellet injection system capable of achieving hydrogen pellet velocities of 5–10 km/s are described. The system, which is intended for the refueling of magnetic fusion devices, combines a gas gun with a small-bore, plasma-arc-driven electromagnetic railgun. The gas gun uses hydrogen gas as the propellant and injects a medium-velocity pellet into the railgun. Once inside the railgun, the propellant gas following the pellet is electrically broken down forming a plasma arc armature. The propulsive force of this plasma arc armature further accelerates the pellet to higher velocities.
Techniques for evaluating mechanical properties of hard coatings
Authors: Mehrotra P. K. , Quinto D. T.
Published: July 2002

This paper describes specialized methods for measuring coating adhesion, microhardness, and microfracture toughness of hard coatings. Coating adhesion is an interfacial property which may be characterized by scratch or indentation techniques which yield a decohesion critical load or an interfacial fracture toughness parameter. Microhardness measurements are shown to be satisfactory if light indenter loads are applied to polished coating surfaces; microhardness profiles may be measured at room and elevated temperatures on a taper section of the coating. The Palmqvist microfracture toughness of hard coatings may additionally be determined from the same microhardness indentations.
Structure and properties of coevaporated WSix films
Authors: Ahn K. Y. , Herd S. R. , Baglin J. E. E. , Han J. U.
Published: July 2002

The crystallization behavior and electrical resistivity of WSix films (coevaporated on poly-Si on SiO2) with x ranging from 1.0 to 2.4 were examined in a high-resolution TEM before and after annealing at 1000 °C. The amorphous as-deposited films with high resistivities (up to 650 μΩ cm) become crystalline WSi2 after annealing accompanied by a precipitous drop in resistivity to values below 30 μΩ cm. The as-deposited Si-rich films showed a reduction in thickness, up to −15% for x=2.4, while metal-rich films showed an increased thickness, up to 13% for x=1.0. The minimum resistivity of 28 μΩ cm was found in a sample with as-deposited composition of WSi1.4 which also had the largest thickness. The difficult problem of determining the thicknesses before and after the interaction of WSix with the CVD poly-Si was solved by first measuring the thin SiO2 thickness (220 Å) using the Si lattice fringes, and then comparing the thicknesses of poly-Si and WSix with that of SiO2. Annealed WSix films with thickness ranging from 1200 to 2500 Å showed one to two grains per film thickness for an as-deposited x=2.4 to 1.4. The grain size appeared smaller (three to four grains per thickness) for x<1.4. For a film with x=1.0, W5Si3 and WSi2 were identified by electron diffraction. The density of annealed films was determined by counting the number of atoms per cm2 by Rutherford backscattering spectrometry, and it ranged from 11 to 12.5 g/cm3.