bluuebunny/crossref_metadata_2025 huggingface dataset:
Small hydrocarbons on metal surfaces: adsorption-induced changes in electronic and geometric structure as seen by X-ray absorption spectroscopy
Authors: Wöll Christof
Published: July 2002

Monolayers of several unsaturated and saturated hydrocarbons (ethylene, acetylene, benzene, n-hexane, cyclohexane, n-octane, n-hexatriacontane) adsorbed on a number of different metal surfaces [Cu(111), Au(111), Ru(0001) and Pt(111)] have been investigated by carbon K-edge X-ray absorption spectroscopy (XAS). Whereas the corresponding multilayer data qualitatively resemble the core-excitation spectra observed for the free molecules, generally significant modifications are observed in the monolayer data. For the saturated hydrocarbons, a strong quenching of the Rydberg R resonance at 287.7 eV and the appearance of a new broad feature at around 285.1 eV (M resonance) is observed for molecules in direct contact with the metal surfaces. In the case of the unsaturated hydrocarbons, for a number of metals, distinct new features are seen in the XAS data, revealing significant intramolecular distortions.
Magnetic X-ray circular dichroism on in situ grown 3d magnetic thin films on surfaces
Authors: Arvanitis Dimitri , Hunter Dunn Jonathan , Karis Olof , Hahlin Anders , Brena Barbara , Carr Roger , Mårtensson Nils
Published: July 2002

Epitaxic thin and ultrathin films on surfaces allow crystallographic phases that do not occur naturally in the bulk to be stabilized. They also offer new possibilities for an improved understanding of soft X-ray photoabsorption in magnetic systems. Data collected using the Elliptically Polarizing Undulator at BL 5.2 of the Stanford Synchrotron Radiation Laboratory are presented herein. Fe, Co and Ni films were prepared on Cu(100) surfaces. L
2,3-edge spectra were recorded with circular and linear light. Fresnel diffractometry was used to quantify the degree of transverse beam coherence. A quantitative analysis of the spectral features indicates a correlation of the spectral intensities and the transverse beam coherence. Resonant reflectivity spectra for Co ultrathin films that exhibit strong dichroism are presented. The reflectivity data indicate that interference effects of the reflected beams at the two interfaces are of importance, even for ultrathin films.
Linear combination of XANES for quantitative analysis of Ti–Si binary oxides
Authors: Lee Jae Sung , Kim Won Bae , Choi Sun Hee
Published: July 2002

A new method is demonstrated for the quantification of Ti—O—Si and Ti—O—Ti bonds in Ti–Si binary oxides. It is based on the linear combination of two reference X-ray absorption near-edge structure (XANES) spectra at the Ti K edge. The proper selection of a Ti—O—Si reference material is most important for the successful application of this method. Three Ti–Si binary oxide systems have been analysed by the new method: Ti–Si mixed oxides, titania supported on silica and Ti-substituted MCM-41 (crystalline mesoporous molecular sieve material invented by Mobil) with various Ti contents.
Unexpected Fe local order in iron oxide-coated nanocrystalline magnesium oxides with exceptional reactivities against environmental toxins
Authors: Moscovici Jacques , Benzakour Mouad , Decker Shawn , Carnes Corrie , Klabunde Kenneth , Michalowicz Alain
Published: July 2002

Mg oxide nanoparticles are very reactive materials used to mitigate atmospheric pollution and to sequester polluting molecules. Using Fe K-edge XAFS, we have studied the structure of iron oxide-coated MgO nanoparticles before and after reaction with CCl4. Before reaction, the local structure around Fe is totally different from that in iron oxide coatings on SrO and CaO nanoparticles, although these coated materials were prepared in the same way. In SrO and CaO, the iron oxide coating has been shown to be well separated from the bulk of the nanoparticle, whereas in MgO, Fe was found to mix with MgO. After reaction with CCl4, Fe-Cl bonds can be detected when the coated nanoparticle is saturated. Such Fe-Cl EXAFS signals have not been observed in previously studied nanoparticles.
Actinide coordination sphere in various U, Np and Pu nitrato coordination complexes
Authors: Den Auwer C. , Revel R. , Charbonnel M. C. , Presson M. T. , Conradson S. D. , Simoni E. , Le Du J. F. , Madic C.
Published: July 2002

Waste management of nuclear fuel represents one of the major environmental concerns of the decade. To recycle fissile valuable materials, intimate knowledge of complexation mechanisms involved in the solvent extraction processes is indispensable. Evolution of the actinide coordination sphere of AnO2(NO3)2TBP-type complexes (An = U, Np, Pu; TBP = tributylphosphate) with the actinide valence state have been probed by XAS at the metal L
III edge. Dramatic changes in the actinide coordination sphere appeared when the An(VI) metal is reduced to An(IV). However, no significant evolution in the actinide environment has been noticed across the series UO2
2+, NpO2
2+ and PuO2
2+.
A new reduced molybdenum oxide with a hollandite-type structure, PrMo6O12
Authors: Barrier N. , Tortelier J. , Gougeon P.
Published: July 2002

The title compound, praeseodymium hexamolybdenum dodecaoxide, PrMo6O12, crystallizes in the tetragonal space groupI4/mand is isostructural with NdMo6O12. Both compounds adopt a hollandite-related structure with a tripledcaxis compared to the mineral hollandite. Within the double chains of edge-sharing MoO6octahedra, the Mo atoms form infinite chains of Mo3triangular clusters. Another dominant feature of the structure is the ordering of the Pr3+cations within the square-shaped channels delimited by the Mo—O double strings.
2-Amino-4-chloro-6-(4-carbamoylpiperidin-1-yl)pyrimidine hemihydrate
Authors: Lynch Daniel E. , McClenaghan Ian
Published: July 2002

The structure of the title compound, C10H15ClN5O·0.5H2O, comprises non-planar molecules that associateviaN—H...N and N—H...O interactions to form a three-dimensional hydrogen-bonded array. The water molecule resides on a twofold axis and is also involved in the hydrogen-bonding network.
3-Carboxypyridinium chloride
Authors: Slouf Miroslav
Published: July 2002

The synthesis, crystallization and structure determination of the title compound, nicotinic acid hydrochloride, C6H6NO2+·Cl−, is part of a project on charge densities in crystals. The good quality crystals of the compound composed of light elements and in centrosymmetric space groupP21/mindicate their suitability for charge–density study.
2-[N-(tert-Butoxycarbonyl)tyrosyl]-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid nitromethane solvate
Authors: Deschamps Jeffrey R. , Flippen-Anderson Judith L. , George Clifford
Published: July 2002

The title compound, C24H28N2O6·0.825CH3NO2, is a member of the TIPP (i.e.Try–Tic–Phe–Phe) family of opioid ligands. The asymmetric unit contains one peptide molecule and one nitromethane molecule. Unlike other members of this familiy, this dipeptide has an extended conformation [i.e.ϕ1 = −103.6 (6)°, ω1 = 168.1 (4)°, ψ1 = 152.4 (5)°]. This conformation was further examined with the programCHEM3D. No significant energy difference was found between the energy-minimized conformation and a more tightly folded model conformation.
Moschamindole
Authors: Cox Philip J. , Fergusson Margot , Nahar Lutfun , Sarker Satyajit D.
Published: July 2002

The solid state structure of moschamindole {systematic name: 10-[2-(4-hydroxy-3-methoxyphenyl)]-1,2,3,4,10,10a-hexahydro-6H-furo[2,3,4-jk]pyrrolo[4,3,2-ef]-3-benzazocin-1-one}, C20H18N2O4is similar to its solution state structure, previously determined by NMR, and evidence of intermolecular hydrogen bonding is now presented.
Physical fitness and health‐related parameters in vegetarian and omnivorous students
Authors: Clarys P. , Deriemaeker P. , Hebbelinck M.
Published: July 2002

The completeness of a vegetarian diet is often questioned. Nevertheless, the literature indicates that a well balanced vegetarian diet is often healthier since the prevalence of prosperity diseases is significantly lower in vegetarians compared to omnivores. A total of 24 vegetarian students were examined regarding food intake, several critical blood parameters, physical performance and anthropometrical measures. The vegetarian population was compared with 24 omnivorous students for the same parameters. A lower energy intake for the vegetarians compared to the non‐vegetarians was found. The distribution of the three macronutrients differed significantly between the two populations. Vitamin intake was comparable and within the recommended daily intake. A similar profile was found for the mineral intake. The blood profile showed significantly lower vitamin B12 values for the vegetarians compared to the non‐vegetarians but values were within the recommended limits. Physical performance and anthropometric were completely comparable between the two populations.
Tyre pressure measurement using smart low power microsystems
Authors: Siddons J. , Derbyshire A.
Published: July 2002

Describes the progress made to date in testing and developing a system to monitor the environment within a commercial vehicle’s tyre ‐ its temperature and pressure ‐ by means of a radio link to a single central receiver inside the vehicle. Discusses the economic and safety implications of maintaining the correct pressure in vehicle tyres and reports that reactions from commercial vehicle suppliers have been positive.
School versus non‐school sports
Authors: Laios Athanasios
Published: July 2002

The development and promotion of sports is being carried out
through both school sports and non‐school sports or sports associations.
Seeks to investigate these two methods using the variables of
participation, expenditure, sports installations and human power.
Examines the advantages and disadvantages of the two systems. Using the
above mentioned variables, finds that European countries, including
Greece, indicate lower priority for school sport than the USA.
Recommends financial and legal considerations for improving the status
of school sports in Greece.
Computer‐aided designers? A study of garment designers’ attitudes towards computer‐aided design
Authors: Hardaker Carolyn H.M. , Fozzard Gary J.W.
Published: July 2002

Despite the benefits of computer‐aided design (CAD), its uptake by the garment industry in the UK has been somewhat slow. Many reasons have been suggested for this, one of which is the lack of appropriately skilled designers and pattern cutters. Comments on this situation and describes a garment CAD‐training programme set up at De Montfort University, Leicester. This training programme was used as the basis of an attitude assessment. A questionnaire‐based survey was developed to quantify the designers’ opinions of CAD and specifically whether these opinions were influenced by the designer’s age or prior computing experience.
Computer abuse: vandalizing the information society
Authors: Furnell Steven M. , Warren Matthew J.
Published: July 2002

Examines the damaging effects that malicious computer abuse, such as hacking and viruses, can have on the development of an information‐based society. Computing and telecommunications technologies are a key ingredient in the realization of this society, but are increasingly the targets of criminals and mischief makers. Highlights the apparent escalation in computer‐abuse incidents, as illustrated by a number of recent surveys, and examines the effects that these may have on the public perception of technology (and, hence, the smooth transition to the information society). Also presents some broad recommendations regarding what can be done to address the problem. This considers both technical measures to help safeguard systems and revised attitudes to computer abuse, to insure that incidents can be dealt with more effectively.
Does contingent reward reduce negotiation anchoring?
Authors: Diaz Julian , Zhao Rong , Black Roy
Published: July 2002

This article examines the role of contingent reward in reducing negotiation anchoring. A case study approach was adopted in the investigation undertaken. Five residencies were offered for sale and university students were assigned the task of negotiating the sales price of one of the houses. The results showed that where no asking price was given the settlement price was consistently lower than for those of incongruously high asking price. It is felt that these results are less biased than previous studies as a system of rewards was offered as the study was a step towards a real life setting.
Enzyme specificity under dynamic control II: Principal component analysis of α‐lytic protease using global and local solvent boundary conditions
Authors: Ota Nobuyuki , Agard David A.
Published: July 2002

The contributions of conformational dynamics to substrate specificity have been examined by the application of principal component analysis to molecular dynamics trajectories of α‐lytic protease. The wild‐type α‐lytic protease is highly specific for substrates with small hydrophobic side chains at the specificity pocket, while the Met190→Ala binding pocket mutant has a much broader specificity, actively hydrolyzing substrates ranging from Ala to Phe. Based on a combination of multiconformation analysis of cryo‐X‐ray crystallographic data, solution nuclear magnetic resonance (NMR), and normal mode calculations, we had hypothesized that the large alteration in specificity of the mutant enzyme is mainly attributable to changes in the dynamic movement of the two walls of the specificity pocket. To test this hypothesis, we performed a principal component analysis using 1‐nanosecond molecular dynamics simulations using either a global or local solvent boundary condition. The results of this analysis strongly support our hypothesis and verify the results previously obtained by in vacuo normal mode analysis. We found that the walls of the wild‐type substrate binding pocket move in tandem with one another, causing the pocket size to remain fixed so that only small substrates are recognized. In contrast, the M190A mutant shows uncoupled movement of the binding pocket walls, allowing the pocket to sample both smaller and larger sizes, which appears to be the cause of the observed broad specificity. The results suggest that the protein dynamics of α‐lytic protease may play a significant role in defining the patterns of substrate specificity. As shown here, concerted local movements within proteins can be efficiently analyzed through a combination of principal component analysis and molecular dynamics trajectories using a local solvent boundary condition to reduce computational time and matrix size.
A Multi-Sensor Approach for Rapid Digitization and Data Segmentation in Reverse Engineering
Authors: Chan V. H. , Bradley C. , Vickers G. W.
Published: July 2002

The development of a fully automated reverse engineering system currently faces two challenges; the time consuming digitization of the object due to the multi-view requirement of current industrial sensors and the conversion of copious amounts of 3-D cloud data into a compact form, compatible with CAD/CAM packages. An ideal reverse engineering system will automatically digitize the object from multiple viewpoints, segment the cloud data into constituent surface patches and generate an accurate solid model. The utilization of both a charged coupled device (CCD) camera and a 3-D laser digitizer, in the reverse engineering process, is a major step to attaining this goal. A neural network based segmentation algorithm is applied to stereo images for the location of the target object in the laser scanner work space and to generate the laser scanner path. The process automatically generates a description of an object’s surface which can be exported to a CAD/CAM package for design or manufacturing applications. [S1087-1357(00)00503-7]
On-line Quality Estimation in Resistance Spot Welding
Authors: Li Wei , Hu S. Jack , Ni Jun
Published: July 2002

A neural network model is developed for on-line nugget size estimation in resistance spot welding. The variables used consist of features extracted from both controllable process input variables and on-line signals. A systematic signal and feature selection procedure is developed. The three commonly observed on-line signals, dynamic resistance, force, and electrode displacement, have been proven to carry similar information. Thus, only dynamic resistance is used in the model. The obtained model has been demonstrated to be robust over various welding conditions including electrode wear. [S1087-1357(00)01204-1]
Heat Transfer and Pressure Drop of Laminar Flow in Horizontal Tubes With/Without Longitudinal Inserts
Authors: Hsieh S.-S. , Huang I.-W.
Published: July 2002

Heat transfer and pressure drop characteristics of water flow in horizontal tubes with/without longitudinal inserts used as a heat exchanger tubing was experimentally studied. Testing was performed on bare tubes and tubes with square and rectangular as well as crossed-strip inserts with aspect ratios AR=1 and 4 and varied ratios of inlet mixed mean temperature to wall temperature of 0.88 to 0.97. The Reynolds number ranged from approximately 250 to 1750 for flow visualization and from 1700 to 4000 for the pressure drop and heat transfer measurements. Flow visualization, using a dye injection method, revealed a highly complex flow pattern including a secondary flow formed in the cross section for crossed-strip inserts. The thermal entrance length was found and correlated in terms of Re for this type of inserted tubes. The enhancement of heat transfer as compared to a conventional bare tube at the same Reynolds number based on the hydraulic diameter was found to be about a factor of 16 at Re⩽4000, while the friction factor rise was only about a factor of 4.5 at Re⩽4000. [S0022-1481(00)01303-7]
A Parametric Model for a Class of Foam-Like Isotropic Hyperelastic Materials
Authors: Jemiolo S. , Turteltaub S.
Published: July 2002

A parametric model for foam-like materials is proposed and its correlation with experimental results is analyzed. The class of foam-like materials is assumed to be described by an isotropic elastic potential based on a general model proposed by Ogden. The class is parametrized using the relative mass density of the material. Functional relations between material parameters and the relative mass density are obtained from experimental data. A simple application problem, namely the optimization of a foam for maximum energy absorption under homogeneous compression, is formulated and solved numerically. [S0021-8936(00)02802-6]
Fabry-Perot Resonators Built With YBa2Cu3O7−δ Films on Si Substrates
Authors: Kumar A. R. , Boychev V. A. , Zhang Z. M. , Tanner D. B.
Published: July 2002

Fabry-Perot resonators were built from two superconductive YBa2Cu3O7−δ (YBCO) films separated by a spacer. Each film of 35-nm thickness was deposited on a Si substrate, about 204 μm thick. A slow-scan Michelson interferometer was employed to measure the transmittance of the resonator in the far-infrared frequency region from 10 to 90 cm−1 at temperatures between 10 and 300 K. Measurements showed that in the normal state the peak (or resonant) transmittance decreases as temperature is lowered, whereas in the superconducting state it can increase with decreasing temperature. The transmittance of the resonator was calculated using properties of individual reflectors obtained previously. When the effect of partial coherence is taken into consideration, the calculated transmittance is in good agreement with the experiments. Furthermore, the maximum possible resonant transmittance was predicted based on an optimization analysis in which the cavity length is varied. The effect of the YBCO film thickness on the transmittance peaks was also studied, showing that the resonant transmittance decreases but the finesse increases as the film thickness is increased. This study should help improve the future design of Fabry-Perot resonators based on HTSC thin films. [S0022-1481(00)00604-6]
Shock Wave Reflections in Dust-Gas Suspensions
Authors: Ben-Dor G. , Igra O. , Wang L.
Published: July 2002

The reflection of planar shock waves from straight wedges in dust-gas suspensions is investigated numerically. The GRP shock capturing scheme and the MacCormac scheme are applied to solve the governing equations of the gaseous and solid phases, respectively. These two schemes have a second-order accuracy both in time and space. It is shown that the presence of the dust significantly affects the shock-wave-reflection-induced flow field. The incident shock wave attenuates and hence unlike the shock wave reflection phenomenon in a pure gas, the flow field in the present case is not pseudo steady. The presence of the dust results in lower gas velocities and gas temperatures and higher gas densities and gas pressures than in dust-free shock wave reflections with identical initial conditions. It is also shown that the smaller is the diameter of the dust particle the larger are the above-mentioned differences. In addition, the smaller is the diameter of the dust particle the narrower is the width of the dust cloud behind the incident shock wave. Larger dust velocities, dust temperatures and dust spatial densities are obtained inside this dust cloud for smaller dust particles. The results provide a clear picture of whether and how the presence of dust particles affects the shock-wave-reflection-induced flow field.
Ontologies for Integrating Engineering Applications
Authors: Ciocoiu Mihai , Nau Dana S. , Gruninger Michael
Published: July 2002

In all types of communication, the ability to share information is often hindered because the meaning of information can be drastically affected by the context in which it is viewed and interpreted. This is especially true in manufacturing, because of the growing complexity of manufacturing information and the increasing need to exchange this information among various software applications. Different representations of the same information may be based on different assumptions about the world, and use differing concepts and terminology—and conversely, the same terms may be used in different contexts to mean different things. Often, the loosely defined natural-language definitions associated with the terms will be too ambiguous to make the differences evident, or will not provide enough information to resolve the differences. A solution to this problem is the use of taxonomies or ontologies of manufacturing concepts and terms, because ontologies provide a way to make explicit the semantics (i.e., the meaning) for the concepts used, rather than relying just on the syntax used to encode those concepts. Ontological techniques can be useful for giving unambiguous definitions of product and process capabilities and evolving designs and design requirements, unifying the differences in how knowledge is conceptualized across multiple product and process domains, and translating those definitions into the specialized representation languages of application systems. This paper gives an overview of current research and development on ontologies as it relates to mechanical engineering applications, along with examples of how ontologies can be used to facilitate the exchange of information among manufacturing applications.
Liquid Plug Flow in Straight and Bifurcating Tubes
Authors: Cassidy K. J. , Gavriely N. , Grotberg J. B.
Published: July 2002

A finite-length liquid plug may be present in an airway due to disease, airway closure, or by direct instillation for medical therapy. Air forced by ventilation propagates the plug through the airways, where it deposits fluid onto the airway walls. The plug may encounter single or bifurcating airways, an airway surface liquid, and other liquid plugs in nearby airways. In order to understand how these flow situations influence plug transport, benchtop experiments are performed for liquid plug flow in: Case (i) straight dry tubes, Case (ii) straight pre-wetted tubes, Case (iii) bifurcating dry tubes, and Case (iv) bifurcating tubes with a liquid blockage in one daughter. Data are obtained for the trailing film thickness and plug splitting ratio as a function of capillary number and plug volumes. For Case (i), the finite length plug in a dry tube has similar behavior to a semi-infinite plug. For Case (ii), the trailing film thickness is dependent upon the plug capillary number (Ca) and not the precursor film thickness, although the shortening or lengthening of the liquid plug is influenced by the precursor film. For Case (iii), the plug splits evenly between the two daughters and the deposited film thickness depends on the local plug Ca, except for a small discrepancy that may be due to an entrance effect or from curvature of the tubes. For Case (iv), a plug passing from the parent to daughters will deliver more liquid to the unblocked daughter (nearly double, consistently) and then the plug will then travel at greater Ca in the unblocked daughter as the blocked. The flow asymmetry is enhanced for a larger blockage volume and diminished for a larger parent plug volume and parent-Ca.
A Demonstration of Artificial Neural-Networks-Based Data Mining for
Gas-Turbine-Driven Compressor Stations
Authors: Botros K. K. , Kibrya G. , Glover A.
Published: July 2002

This paper presents a successful demonstration of application of neural networks to perform various data mining functions on an RB211 gas-turbine-driven compressor station. Radial basis function networks were optimized and were capable of performing the following functions: (a) backup of critical parameters, (b) detection of sensor faults, (c) prediction of complete engine operating health with few variables, and (d) estimation of parameters that cannot be measured. A Kohonen SOM technique has also been applied to recognize the correctness and validity of any data once the network is trained on a good set of data. This was achieved by examining the activation levels of the winning unit on the output layer of the network. Additionally, it would also be possible to determine the suspicious, faulty or corrupted parameter(s) in the cases which are not recognized by the network by simply examining the activation levels of the input neurons.
Simulation and Experimental Measurement of the Transmission Error of Real Hypoid Gears Under Load
Authors: Gosselin Claude , Guertin Thierry , Remond Didier , Jean Yves
Published: July 2002

The Transmission Error and Bearing Pattern of a gear set are fundamental aspects of its meshing behavior. To assess the validity of gear simulation models, the Transmission Error and Bearing Pattern of a Formate Hypoid gear set are measured under a variety of operating positions and applied loads. Measurement data are compared to simulation results of Tooth Contact Analysis and Loaded Tooth Contact Analysis models, and show excellent agreement for the considered test gear set. [S1050-0472(00)00901-6]
Characterization with XPS of a Thin Film of B2O2 Deposited on a Ag Substrate
Authors: Wang Yajun , Trenary Michael
Published: July 2002

XPS spectra are presented for a thin film of a suboxide of boron formed by condensing B2O2(g) on a clean Ag foil substrate. Spectroscopic characterization of boron suboxides are important as these compounds may exist as surface intermediates in the oxidation of solid boron and of boron compounds. The B2O2(g) source consists of a Knudsen cell in which B(s) and B2O3(s) are heated to 1123 K. Mass spectroscopic analysis confirms that only B2O2(g) effuses from the source. The condensed B2O2 film has a B 1s binding energy of 192.55 eV which allows this boron suboxide to be distinguished from the principal boron oxide B2O3, which has a binding energy of 193.5-194.0 eV [W. C. Foo, J. S. Ozcomert, and M. Trenary, Surf. Sci. 255, 245 (1991)].
Crystallization of amorphous-silicon films with seed layers of microcrystalline silicon by plasma heating
Authors: Kim Hae-Yeol , Park Chan-Do , Kang Youn-Seon , Jang Kuk-Jin , Lee Jai-Young
Published: July 2002

A novel solid-phase crystallization method is suggested for synthesizing large-grained polycrystalline silicon (poly-Si) films at low temperature (∼500 °C) and in a short time (1 h). Hydrogenated microcrystalline-silicon (μc-Si:H) and hydrogenated amorphous-silicon (a-Si:H) layers are sequentially deposited on a glass substrate in order to form a-Si:H/μc-Si:H bilayers before annealing through conventional furnace heating and a new annealing method, plasma heating, respectively. It is found that the crystallization rate of the bilayers during the plasma heating is much higher than that of the bilayers during the furnace heating. Moreover, the crystallization reaction is enhanced more effectively during the annealing in the case of the bilayers which are hydrogen-plasma treated between the depositions of μc-Si:H and a-Si:H layers than in the case of those which are not. Finally, poly-Si films with grains of ∼0.4 μm are obtained through the plasma heating method combined with the hydrogen-plasma treatment.
Gas-sensing device implemented on a micromachined membrane: A combination of thick-film and very large scale integrated technologies
Authors: Vincenzi D. , Butturi M. A. , Guidi V. , Carotta M. C. , Martinelli G. , Guarnieri V. , Brida S. , Margesin B. , Giacomozzi F. , Zen M. , Giusti D. , Soncini G. , Vasiliev A. A. , Pisliakov A. V.
Published: July 2002

We report developing a SnO2 thick-film gas sensor deposited by screen printing onto a micromachined dielectric stacked membrane equipped with an embedded polysilicon microheater and two resistors for temperature measurement. The microheaters were designed to enable an operating temperature of 400 °C at about 30 mW power consumption. A newly developed scheme for temperature measurement was adopted for on-line adjustment of the film temperature through a conventional low-power feedback circuit. The electrical response of the prototypes to CO and CH4 is discussed, and their performance is compared to traditional devices fabricated via thick-film methods.
Spin-dependent resonant tunneling in double-barrier magnetic heterostructures
Authors: Petukhov A. G. , Demchenko D. O. , Chantis A. N.
Published: July 2002

Recent advances in molecular beam epitaxial growth made it possible to fabricate exotic heterostructures comprised of magnetic films or buried layers (ErAs,GaxMn1−xAs) integrated with conventional semiconductors (GaAs) and to explore quantum transport in these heterostructures. It is particularly interesting to study spin-dependent resonant tunneling in double-barrier resonant tunneling diodes (RTDs) with magnetic elements such as GaAs/AlAs/ErAs/AlAs/GaAs and GaAs/AlAs/GaxMn1−x As/AlAs/GaAs. We present the results of our theoretical studies and computer simulations of transmission coefficients and current-voltage characteristics of RTDs based on these double-barrier structures. In particular, resonant tunneling of holes in the GaxMn1−xAs-based RTDs is considered. Our approach is based on k⋅p perturbation theory with exchange splitting effects taken into account.
Ion fluxes and energies in inductively coupled radio-frequency discharges containing C2F6 andc-C4F8
Authors: Goyette A. N. , Wang Yicheng , Misakian M. , Olthoff J. K.
Published: July 2002

We report ion energy distributions (IEDs), relative ion intensities, and absolute total ion current densities at the grounded electrode of an inductively coupled Gaseous Electronics Conference (GEC) radio-frequency (rf) reference cell for discharges generated in pure C2F6, c-C4F8, and in mixtures of each gas with Ar. These discharges contain several ions of significant intensity, with the dominant ion seldom that expected from direct ionization of the feed gas. Neither the C2F6 nor the c-C4F8 fraction in the Ar mixtures significantly influences the reactive ion composition. IEDs vary from single peaked to bimodal, the latter indicating rf modulation of the ions’ energy as they traverse the plasma sheath. Elevated gas pressures and higher fractions of either C2F6 or c-C4F8 all result in comparatively broader and more bimodal IEDs. IEDs in pure c-C4F8 discharges, compared to C2F6 discharges, generally exhibit more pronounced broadening and bimodality.
Development of edge field emission cold cathodes based on low work function Cu–Li alloy coatings
Authors: Tucek J. C. , Krauss A. R. , Gruen D. M. , Auciello O. , Moldovan N. , Mancini D. C. , Zurn S. , Polla D.
Published: July 2002

Vertical edge emitter arrays of thin walled (500–8000 Å) hollow cylinders have been fabricated by the deposition of Cu–20 at. % Li alloy (Cu4Li) thin films on arrays of Si posts, followed by selective etching of the Si core. What remains is a hollow cylinder of Cu4Li, where the thickness of the emitting edge is determined by the deposited film thickness. Additionally, lateral edge emitters were fabricated from arrays of holes in SiO2 or Si3N4 films on flat Si surfaces. In this case, the emitting edge is formed by selectively overetching the Si beneath the hole, creating an edge from the overhang of the SiO2 (Si3N4) thin film upon which the Cu4Li alloy is deposited. The Cu4Li alloy provides a surface covered with a monolayer of Li atoms formed via Gibbsian segregation. The formation of Li–Cu atom dipoles on the surface of the alloy yields a work function lower than that of either a pure Li or Cu surface, resulting in enhanced electron emission and very low threshold fields. The alloy coating maintains a segregated monolayer of Li atoms on the surface even under adverse operational conditions, including ion bombardment of the surface. Edge emitters offer many potential advantages over the standard microtip arrays including ease of fabrication, higher emission currents per emitter due to the larger emission area of the edge, and greater physical robustness. The Cu4Li edge emitters exhibit threshold fields as low as E0=5 V/μm, high current densities, and long-lived, stable emission.
Sulfur passivation of Ga2O3 (Gd2O3)/GaAs metal–oxide–semiconductor structures
Authors: Eftekhari G.
Published: July 2002

The properties of Ga2O3 films evaporated on unpassivated and passivated GaAs surfaces using a Gd3Ga5O12 source were studied. The properties of unpassivated (passivated) films were a strong (weak) function of substrate temperature with best results obtained at a substrate temperature of about 100 °C. The thermal stability of films evaporated at a substrate temperature of 100 °C was studied as well. The passivated films showed a better thermal stability. The bonds formed at the surface layer of passivated GaAs were used to explain the results.
Fabrication of diffractive optical elements for an integrated compact optical microelectromechanical system laser scanner
Authors: Wendt J. R. , Krygowski T. W. , Vawter G. A. , Blum O. , Sweatt W. C. , Warren M. E. , Reyes D.
Published: July 2002

We describe the microfabrication of a multilevel diffractive optical element (DOE) onto a microelectromechanical system (MEMS) module as a key element in an integrated compact optical-MEMS laser scanner. The DOE is a four-level off-axis microlens fabricated onto a movable polysilicon shuttle. The microlens is patterned by electron beam lithography and etched by reactive-ion-beam etching. The DOE was fabricated on two generations of MEMS components, each of which is briefly described. The compact design of the laser scanner is based on mounting a MEMS module and a vertical cavity surface-emitting laser onto a fused silica substrate that contains the rest of the optical system. The calculated scan range of the system is ±4° with a spot size of 0.5 mm.
Structural Investigation of Thin Films
Authors: Walker G. A.
Published: July 2002

In the investigation of the structural properties of thin films by x-ray diffraction the lack of material, interference from the substrate, and generally, high orientations of the grains makes analysis of the films very difficult. In order to fully characterize a thin film for stresses (macro- and micro-), grain size, orientation, faulting probability, and solid solution effects, it is necessary to employ a range of x-ray techniques with some special experimental conditions. It is shown that a full strnctural analysis of thin films (alloy films included) can be routinely carried out making comparison of different types of thin film possible. Two 12-kÅ-thick Al films are characterized and it is shown that large errors can occur in residual stress and solid solution effect if the data is not handled properly.
Solid Solution Effects in Thin Aluminum Films
Authors: Walker G. A. , Goldsmith C. C.
Published: July 2002

The effect of a solid solution of hydrogen, oxygen, nitrogen, or water vapor in the lattice of thin films of Al was studied by x-ray diffraction. The lattice parameter shift due to solid solution effect independent of residual strain or faulting was observed. This method is applied to thin films to determine nondestructively whether there are low concentrations of impurities affecting the lattice of the films. It is also shown that large errors occur in the value of the residual stress measured by certain x-ray techniques or in that of the solid solution concentration if both of these effects are not taken into consideration during the subsequent calculations.
Critical Phenomena in Films and Surfaces
Authors: Fisher Michael E.
Published: July 2002

The theory of critical phenomena in films (and general systems of restricted geometry) is reviewed, introducing the critical point shift exponent λ and the rounding or crossover exponent θ=1/ν, which describes the changeover from bulk behavior. The exponents α×, β×, and γ× for the surface corrections to bulk behavior are defined and discussed. The deficiencies of the “extrapolation” length concept, for representing the surface boundary conditions on the order parameter, are explained. Barber's recent scaling theory for surface properties is reformulated in terms of a gap exponent Δ1 for a surface field H1. In a range of exactly soluble models Δ1 equals 12; this is probably always a good approximation. The scaling relation β1=2−α−ν−Δ1 then predicts the critical behavior of the surface order. Comparisons of the theory are made with analytical and numerical work on Ising, Heisenberg, and spherical models and on ideal Bose fluid films. A table of exponents is presented.
Digital Computer Simulation of Charged Particle Beams and Electrostatic Lenses
Authors: Boers J. E.
Published: July 2002

A digital computer program for the simulation of charged particle beams in complex electrostatic lens systems is described. A large matrix is employed to simulate the potentials in rectangular or axisymmetric configurations, and relativistic trajectory computations are employed to simulate beams or charged particles of any energy. The beam may be injected with any energy or spatial distribution, including point sources. The program is intended to be an engineering tool which will produce results with an accuracy of one or two percent with modest effort in setting up the problem. Simulations of a CDC 6600 typically require 2 min or less, and complete solutions including plots of trajectories and equipotentials are frequently obtained in less than 30 sec. Results for some specific cases are shown to be within 2% of experimental or exact analytical results.
Nodular growth in thick-sputtered metallic coatings
Authors: Spalvins T. , Brainard W. A.
Published: July 2002

Thick-sputtered S-Monel, silver, and 304 stainless steel coatings were deposited on mica and metal substrates with various surface finishes to investigate the nodular growth in the coating by scanning electron microscopy. The geometry and the surface structure of the nodules are characterized. Compositional changes within the coating were analyzed by energy dispersive x-ray analysis. Defects in the surface finish (i.e., scratches, inclusions, etc.), act as preferential nucleation sites and form isolated and complex nodules and various surface overgrowths in the coating. The nodule boundaries are very vulnerable to chemical etching and these nodules do not disappear after full annealing. Further, they have undesirable effects on mechanical properties; cracks are initiated at the nodules when the coating is stressed by mechanical forces. These effects are illustrated by micrographs. Nodular growth within a coating can be minimized or eliminated by increasing the surface smoothness.
Surface etching mechanism of silicon nitride in fluorine and nitric oxide containing plasmas
Authors: Kastenmeier B. E. E. , Matsuo P. J. , Oehrlein G. S. , Ellefson R. E. , Frees L. C.
Published: July 2002

The etch rate of silicon nitride (Si3N4) in the afterglow of fluorine-containing plasmas is strongly enhanced when both nitrogen and oxygen are added to the remote discharge. This effect is attributed to the formation of nitric oxide (NO), which we identify as a highly reactive precursor for the etching of Si3N4. The Si3N4 etch rate, surface oxidation, and the depletion of the surface of N atoms show a linear dependence on the NO density. In order to determine the products of the NO reaction at the Si3N4 surface, mass spectrometry was performed in immediate proximity to the surface with a specially designed movable sampling orifice. Both SiF4 and N2 are identified as primary etch products, but a smaller amount of N2O was also detected. Based on our results, we suggest that NO enhances the removal of N from the Si3N4 surface by the formation of gaseous N2, and leaving behind an O atom, while the overall surface oxidation remains very low, and the reactive layers are very thin. This modified surface reacts more readily with F atoms than the Si3N4 surface.
Influence of electron cyclotron resonance nitrogen plasma exposure on the electrical characteristics of SiNx:H/InP structures
Authors: Redondo E. , Mártil I. , González-Dı́az G. , Castán H. , Dueñas S.
Published: July 2002

We have studied the influence of nitrogen plasma exposure of the InP surface on the electrical characteristics of electron cyclotron resonance deposited Al/SiNx:H/InP devices. Nitrogen plasma exposure was performed just before the SiNx:H deposition without vacuum breaking. A 30 s plasma treatment at low microwave power (60 W) sharply reduces the minimum of the interface trap density, from 4×1012 to 1.6×1012 eV−1 cm−2 (obtained by the high–low frequency capacitance method). We explain this reduction due to the formation of P–N and/or In–P–N complexes at the InP surface during the plasma-exposure step. These bonds are broken thermally after a rapid thermal annealing of the device. The minimum of the interface trap density, obtained at the optimum plasma exposure conditions, is among the lowest ones reported in the literature and similar to those obtained with more complicated processing technologies of the SiNx:H/InP structure. This is a clear indication that plasma exposure in N2 atmosphere seems to be a valuable and simple surface conditioning method.
Growth of GaInTlAs layers on InP by molecular beam epitaxy
Authors: Sánchez-Almazán F. , Gendry M. , Regreny P. , Bergignat E. , Grenet G. , Hollinger G. , Olivares J. , Bremond G. , Marty O. , Pitaval M. , Canut B.
Published: July 2002

Growth of GaInTlAs alloys on InP(001) has been attempted by solid source molecular beam epitaxy. Thallium incorporation into Ga1−xInxAs matrices was studied as a function of substrate temperature, arsenic overpressure, matrix composition, and growth rate. At high temperatures (>350 °C) thallium evaporates, whereas at intermediary temperatures (270–350 °C) thallium segregates into droplets on the surface. Only in the low temperature range (180–260 °C) can thallium be incorporated in some conditions, leading to mirror-like surfaces. Up to 18% Tl content was incorporated into a Ga0.70In0.30As matrix and up to 40% Tl into a GaAs matrix. For these high Tl concentrations, Tl droplets are avoided and Tl incorporation is achieved only when using high arsenic pressures. However, this limits surface adatom diffusion and leads to amorphous, polycrystalline, or twinned materials. Finally, a narrow window for single-crystal growth has been found for low Tl contents (4%) using optimized growth conditions with low V/III pressure ratios and high growth rates.
Applications of micropinch x-ray source
Authors: Semyonov O. G. , Gurey A. E. , Kanavin A. P. , Tikhomirov A. A.
Published: July 2002

An experimental model of a micropinch (vacuum spark) x-ray source was tested in x-ray lithography and x-ray microscopy applications. The image resolution for the proximity lithography and microscopy methods with the micropinch source was estimated. The proximity lithography with positive and negative resists was tested in vacuum; a protection system, shielding a mask from the discharge plasma blowoff, metallic debris, and extreme ultraviolet (EUV) radiation, was installed in front of the mask. Images of the biological specimens were also obtained with x-ray resists for one-pulse exposure and a series of pulses. The effect of microrelief leveling (polishing) of the solid surfaces irradiated by the high-power pulsed soft x-ray/EUV flux was observed experimentally, and an analytical model of the effect was suggested. The effect of structural modification of the thin layers irradiated by the high power EUV flux was predicted, and the transformation of the dielectric buffer layers from the amorphous to the crystalline state was realized experimentally.
Codoping of magnetron-sputter deposited ZnS:TbOF with Ag, Cu, and Ce for electroluminescent phosphors
Authors: Kim J. P. , Davidson M. , Moorehead D. , Puga-Lambers M. , Zhai Q. , Holloway P.
Published: July 2002

rf magnetron-sputter-deposited ZnS:TbOF thin-film electroluminescent (EL) phosphors 1 μm±10% thick were codoped with Ag, Cu, Ag+Cu, and Ce and tested with 60 Hz trapezoidal voltage pulses. After annealing at 500 °C for 60 min, the EL brightness at 20 V above threshold, B20, for Cu+Ag codoped ZnS:TbOF film was 67 cd/m2 compared to 55 cd/m2 for undoped ZnS:TbOF films. The B40 of Ce codoped ZnS:TbOF films annealed at the same conditions was 144 cd/m2 compared to 86 cd/m2 for undoped ZnS:TbOF films. While the brightness increase of Cu+Ag codoped ZnS:TbOF film is attributed to improve crystallinity and increased surface roughness, the increase due to Ce codoping of ZnS:TbOF film is more likely due to modified space charge in the ZnS:TbOF film.
Modeling of the slip flow in the spiral grooves of a molecular pump
Authors: Tsui Yeng-Yung , Kung Chia-Ping , Cheng Hong-Ping
Published: July 2002

A numerical methodology is applied to investigate the flow in the channels of a molecular pump in the slip flow regime. Both the slip and the no-slip boundary conditions are used to examine their effects on the flow field and the pumping performance. Also compared is the use of a rectangular channel model and a spiral channel model. In the latter model the flow channels are placed on the rotor of the pump while the former is sited on a stationary frame. It is shown that, by comparing with the no-slip condition, the slip condition leads to a weaker reverse flow in the channel and lower compression ratio. The results of the rectangular model are close to those of the spiral model, although there exists a minor degree of difference. This demonstrates that the rotational effects can be neglected. It is shown from the analysis that a pressure gradient in the circumferential direction is caused by the diffusion of the circumferential shear stress in the radial direction. However, by the present models the resulted pressure difference between the two side walls of the flow channel remains almost as a constant, irrespective of the flow rates. This is not true in the real flow.
Growth and characterization of rare-earth monosulfides for cold cathode applications
Authors: Modukuru Y. , Thachery J. , Tang H. , Malhotra A. , Cahay M. , Boolchand P.
Published: July 2002

We report the successful growth of bulk cubic lanthanum sulfide (LaS) and neodymium sulfide (NdS). Powder x-ray diffraction scans of the samples show the rocksalt phase with a lattice constant a0=5.857(2) Å and 5.694(2) Å for LaS and NdS, respectively. In Raman scattering, one observes the vibrational density of states (cubic symmetry) and identifies the longitudinal optical and transverse acoustic phonons at 261(284) and 100(92) cm−1 with LaS(NdS), respectively. These rare-earth monosulfides offer attractive alternatives to the commonly used cesiated surfaces to reach negative electron affinity at various III–V semiconductor surfaces.