bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic circular dichroism of resonant X-ray emission spectra at L edges of rare-earth compounds
Authors: Fukui Keiji , Ogasawara Haruhiko , Harada Isao , Kotani Akio
Published: July 2002

We study the resonant X-ray emission spectroscopy (RXES) and the magnetic circular dichroism (MCD) at the L
2,3 absorption edges of rare-earth elements, especially gadolinium ion. To this end, an atomic model is adopted and the multiplet coupling effect is taken into account. Using the formula of the coherent second order optical process which consists of the excitation process from the 2p core state to the empty 5d state and of the radiative decay from the 3d core state to the 2p core hole, we calculate RXES-MCD spectra. By inspection, we have confirmed that the enhancement of the 2p-5d dipole matrix element proposed for MCD of X-ray absorption spectroscopy. In addition, characteristic features of the spectra observed in gadolinium metallic compounds are reproduced by our calculations.
Polarization dependence of resonant X-ray emission spectra in early transition metal compounds
Authors: Matsubara Masahiko , Uozumi Takayuki , Kotani Akio
Published: July 2002

We calculate the polarization dependent spectra of resonant X-ray emission in TiF3, VF3 and Cr2O3, which have one, two and three 3d electron(s) in the ground state, respectively. We study the detailed mechanism of the spectral structures, comparing with a previous result of TiO2. Then we discuss systematically the difference of spectra with the change of the 3d electron number from group theoretical consideration.
XAFS study on active Pr sites in zeolite as a photocatalyst for decomposition of nitrous oxide
Authors: Ebitani Kohki , Nishi Akio , Hirano Yoshiaki , Yoshida Hisao , Tanaka Tsunehiro , Mizugaki Tomoo , Kaneda Kiyotomi , Morikawa Akira
Published: July 2002

The praseodymium-exchanged mordenite degassed at 873 K acted as a highly active heterogeneous photocatalyst for the stoichiometric decomposition of N2O. Analysis of Pr L3-edge EXAFS revealed that the Pr species were isolated each other in the large channel of zeolite, and that the active Pr species were coordinated by ca. four oxygen atoms and one Al atom. On the other hands, the inactive Pr species are surrounded by ca. 10 oxygens of adsorbed waters. The former low-coordinated Pr species allowed a strong adsorption of N2O, which could be the first step of the decomposition reaction.
Extension of a tuned log spiral of revolution fluorescence XAFS detector, designed for optimal detection of a particular element Z, to XAFS of elements other than Z
Authors: Pease D. M. , Daniel M. , Budnick J. I. , Taylor B. , Frenkel A. , Pandya K. , Grigorieva I. K. , Antonov A. A.
Published: July 2002

Recently, it has been demonstrated that an x-ray detector in the form of a log spiral of revolution, covered with highly oriented pyrolytic graphite, is an excellent device for obtaining the fluorescence XAFS of an element of interest in the presence of competing fluorescence from other elements. In the present work we investigate the capabilities of a log spiral of revolution (LSR) detector, with a geometry optimized for one element (in this case Cr), if used for XAFS of other elements.
Polarized XAFS study of high-temperature phases of NaNbO3
Authors: Shuvaeva Victoria A. , Azuma Yusuke , Yagi Kenichiro , Sakaue Kiyoshi , Terauchi Hikaru
Published: July 2002

Temperature dependence of the Nb displacement relative to the center of oxygen octahedron in NaNbO3 has been studied by polarized Nb K XAFS. Spectra were measured at two orientations of a single crystalline sample. Room temperature EXAFS data are in a good agreement with earlier X-ray diffraction data: Nb antiferroelectric displacements were found to be orthogonal to the b axis. Analysis of the temperature dependent EXAFS data didn't reveal any abrupt changes of Nb-O distances in the phase transition points. In all high-temperature paraelectric phases Nb appeared to be displaced to the off-center positions. Displacements, orthogonal to b axis, remained almost constant, while displacement along b axis gradually increased with temperature, so that in the cubic phase the displacements along all axes became equal. This shows, that disorder plays an important role in the high temperature phases. The above results are supported also by the analysis of the pre-edge structure, - the integral intensity of the pre-edge peak was temperature-independent when the polarization vector of the X-rays was orthogonal to b axis and gradually increased with temperature when the polarization was parallel to b.
Magnetic circular dichroism of 3d
5/2 → 2p
3/2 resonant inelastic X-ray scattering at the Ho L
III-edge in Ho3Fe5O12
Authors: Nakamura Tetsuya , Kawamura Naomi , Iwazumi Toshiaki , Maruyama Hiroshi , Urata Akiri , Shoji Hironobu , Nanao Susumu , Kishimoto Shunji , Katano Rintaro , Isozumi Yasuhito
Published: July 2002

Magnetic circular dichroism (MCD) of resonant inelastic X-ray scattering (RIXS) of 3d
5/2 → 2p
3/2 decay (Ho Lα1) was measured at the Ho LIII-edge in Ho3Fe5O12. The MCD-RIXS, in which the intermediate state has the 2p
4f

n + 1 configuration due to the quadrupolar transition of 2p → 4f, was also observed at the pre-edge region of the Ho L
III-edge. The obvious superposition of two peaks, which comes from the high-energy off-resonant Raman scattering and the fluorescence, could be found in both the RIXS and the MCD-RIXS when the energy of the incoming X-ray was 7eV higher than the white line. The dependence of the integration of the MCD-RIXS spectra on the incident x-ray energy could roughly reproduce the MCD of X-ray absorption spectra (XAS).
The role of the electron inelastic scattering processes in EELFS spectra
Authors: Guy D. E. , Grebennikov V. I. , Surnin D. V. , Ruts Yu. V.
Published: July 2002

The pseudopotential model is used for the evaluation of the core level ionisation intensities (by the electron impact). The central atom effective phase shift is calculated for K EELFS spectra in this framework. The Si K EELFS spectra were calculated and compared with the experimental data. The comparison of experimental and calculated results is performed on the base of the electron dispersion law which takes into account electron-plasmon interaction.
Thermal effect in unoccupied molecular orbitals of C60 molecules adsorbed on a Si(001)-(2 × 1) surface studied by NEXAFS
Authors: Kondo Daiyu , Sakamoto Kazuyuki , Takeda Hideo , Matsui Fumihiko , Ohta Toshiaki , Amemiya Kenta , Uchida Wakio , Kasuya Atsuo
Published: July 2002

We report here the temperature-dependent unoccupied molecular orbitals (MO's) of C60 molecules adsorbed on a Si(001)-(2 × 1) surface measured using near edge x-ray absorption fine structure (NEXAFS). At 300 K, the NEXAFS spectrum reveals that the interaction between a 1.0 monolayer (ML) C60 film and a Si(001) surface is mainly the van der Waals force. After annealing the samples at 500 K, we observe an increment in the full-width at half-maximum of unoccupied MO's, which indicates the change of the interaction. Moreover, the lowest unoccupied molecular orbital (LUMO) shifts to the higher photon energy side and the intensity of the LUMO+1 relative to that of the LUMO+3 decreases in the NEXAFS spectrum. These results suggest that the strong interaction induced at 500 K has a covalent character, to which the LUMO+1 contributes.
endo-(1′R,2′R,5′S,7′R,9′S)-2-(9′-Benzyloxy-2′-phenyl-3′,6′-dioxabicyclo[3.2.2]nonan-7′-yl)-7-bromo-5,8-dimethoxynaphthalen-1-yl acetate
Authors: Brenstrum Timothy J. , Brimble Margaret A. , Turner Peter
Published: July 2002

The title compound, (1), is the product of a model synthesis of an analogue of the antibiotic medermycin, and is thought to be the result of an unusual 1,6-hydride shift.
[N-(2-Aminoethyl)-N,N-bis(3-aminopropyl)amine]dichlorocobalt(III) chloride, [Co(abap)Cl2]Cl
Authors: Fanshawe Rachel L. , Clark Charles R. , Blackman Allan G.
Published: July 2002

Structural analysis of the title compound, [Co(abap)Cl2]Cl, where abap isN-(2-aminoethyl)-N,N-bis(3-aminopropyl)amine (C8H22N4), confirms that the asymmetric amine ligand is oriented such that the N atoms of the five-membered chelate ring are in the same plane as the chloride ligands.
Geometric and static conditions of assembly
Authors: Valentovic Ernest
Published: July 2002

A table with three uneven legs standing on an uneven floor is a good example of static determination. We can determine the reactions of the legs for arbitrary loading for the table by using the laws of statics. The assembly of that statically determinate table/floor couple is without problems. The table with four legs is at once overdeterminated. Overdetermination is, for example, the four‐throw crankshaft lying not on two, but on four bearings. The correct assembly of such a crankshaft needs very high precision in manufacturing and supplementary assembly. This article deals with the influence of static overdetermination on the requirements of the precision of parts and on the supplementary fitting work of assembly. The article is linked to the author’s former article “Knowing your orientation” (Assembly Automation, Vol. 16 No. 2, 1996). The aim of both articles is to build up a theoretical base of DFA science.
Scenario building: a suitable method for strategic property planning?
Authors: Ratcliffe John
Published: July 2002

The scenario method has been widely used by decision makers in business, industry and government for over 30 years as an unrivalled technique to learn about the future before it happens. This paper examines the principles, practice and pitfalls of scenario building with the prime aim of presenting the technique as one singularly relevant to the study of future property investment, development and management decisions and land use policy formulation. The origins of the approach from its military‐based beginnings, through the popularised global environmental applications to the current widescale use by industry and commerce are traced. Some definitions are advanced to demonstrate the multi‐various nature of the method, and different types of scenario identified to show their adaptability and agility. The general purpose of the technique as a learning mechanism for organizations is explored, and the step‐by‐step process of scenario building specifically analysed. Conclusions are drawn which record the success of scenario building in many fields other than property and predict the adoption of the scenario approach as the principal behavioural technique for determining corporate real estate strategy in the future.
A metal‐forming approach to automatic generation of graded initial quadrilateral finite element meshes
Authors: Petersen S.B. , Gouveia B.P.P.A. , Rodrigues J.M.C. , Martins P.A.F.
Published: July 2002

This paper presents an algorithm for automatic generation of graded initial quadrilateral meshes targeted for the finite element analysis of metal‐forming processes. Meshing the domain geometry deals with a universe of shapes, and the procedure therefore takes into account the initial geometry of the billet. A grid‐based approach is utilised for generating an initial coarse mesh with well‐shaped (internal) elements, and in cases where non‐rectangular shapes are to be discretized, linking with the boundary is performed on the basis of constrained Delaunay triangulation. By analysing the contact situation between dies and mesh, an attempt is made to identify regions where plastic deformation is likely to be concentrated during the early stages of processing, and accordingly refinement of the mesh is performed locally by elemental subdivision. Simulation examples for closed‐die forging, forward rod and backward can extrusion substantiate the feasibility of this approach in terms of lowering the overall calculation error and limiting the interference between mesh and die.
A whistleblowing code for educational institutions
Authors: Vinten Gerald
Published: July 2002

This article discusses three important aspects of assessment within schools, namely, planning, testing and policy development. From the outset, emphasis is placed on the importance of planning for teaching and learning. It is argued that the development of assessment strategies at this stage is significant in terms of establishing clear learning outcomes for lessons taught. Some of the more widely used tests are also discussed in terms of how they might assist teachers to identify specific difficulties children may have with learning. The final section considers policy development in schools and suggests a possible framework for action. Throughout the article reference is made to recent research which supports the development of formative assessment strategies in the classroom context. It is concluded that planned assessment strategies have the potential for enhancing the quality of teaching and learning within the classroom.
Whistleblowing towards disaster prevention and management
Authors: Vinten Gerald
Published: July 2002

Disaster inquiries regularly contain a sad litany of what went wrong, procedures bypassed and ignored, and undue risks taken. It is clear in many of these cases that there were individuals in the know, who may have spoken up, but been over‐ruled or silenced. Some more persistent individuals decide to speak up external to the organisation, and hence become whistleblowers. Their efforts, although virtually by definition in the public interest, have not always been well received, certainly by their employers, and the agencies to whom they resorted, while pleased to have received their information, have invariably not reciprocated by offering employment protection, or even upholding confidentiality. Disaster case studies are presented involving a variety of industries from the nuclear power to the petroleum, aircraft, space and oil industries. The stresses on the whistleblower are indicated, one being the controversy remaining over their role, with opposition from some business leaders. The law offers first line protection, although experience in the USA suggests that this is insufficient in itself. In the more unified and compact jurisdiction of the UK, new legislation, coupled with political will, seems likely to produce a more effective regime. Organisations need to internalise whistleblowing as part of their natural systems and procedures, and codes of practice assist in this regard, as long as they are more than window‐dressing. Countries less advanced in their thinking and legislation are more at risk and, given the global consequences of the likes of an environmental disaster, need to be regarded as international pariahs.
On the Momentum Balance in Linear-Combination Models for the Transition Zone
Authors: Dey J.
Published: July 2002

The momentum balance of the linear-combination integral model for the transition zone is investigated for constant pressure flows. The imbalance is found to be small enough to be negligible for all practical purposes. [S0889-504X(00)00703-0]
On Heat Generation in Rolling Contacts Under Boundary and Mixed Lubrication
Authors: Chang L. , Zhao Yongwu , Hall P. B. , Thom R. , Moore C.
Published: July 2002

This paper reports on experiments and theoretical analyses of heat generation and scuffing failure in rolling contacts. The experiments were conducted with dry contacts, and the theoretical analyses were carried out using a deterministic thermal contact model. The research reveals that heat generated by asperity plastic deformation in the direction normal to the contact can be significant in high-load, high-speed contacts under boundary and mixed lubrication conditions. Under near rolling conditions, heat generated by the plastic deformation largely dominates that by the friction and is the main source leading to contact scuffing. This heat generation is shown to be significant compared to frictional heating even at relatively large slide-to-roll ratios. Parametric studies show that the ratio of asperity-plastic-deformation heating to frictional heating is sensitive to slide-to-roll ratio, hardness and surface finish but insensitive to contact load, rolling velocity and fluid/asperity load sharing.
Development of Hexaaluminate Catalysts for Combustion of Gasified
Biomass in Gas Turbines
Authors: Johansson E. M. , Danielsson K. M. J. , Ersson A. G. , Järås S. G.
Published: July 2002

There is an increasing interest in catalytic combustors fuelled by low-heating value (LHV) gases, with a LHV of 5–7 MJ/Nm3. This is because catalytic combustion could be advantageous compared to flame combustion with respect to stable combustion of LHV-gases and low conversions of fuel-N (mainly NH3) to NOX. In the present project, funded by the EU Joule Program, catalytic combustion of gasified wood for gas turbine applications is studied. A synthetic gas mixture of H2, CO, CO2,H2O,CH4,N2, and NH3, that resembles the output from a fluidized bed gasifier using biomass as raw material, is used. The gas mixture is mixed with air at atmospheric pressure and combusted over washcoated cordierite monoliths in a bench-scale laboratory quartz-reactor. The objectives of the work described here are twofold. To begin with, improvement of the thermal stability of hexaaluminate washcoats by substitutions of rare earth or transition metal compounds is being studied. Secondly, catalytic combustion of gasified biomass over these washcoats has been studied in a bench-scale unit. In this on-going project, obtained result show that it is possible to improve the surface area of hexaaluminate compounds up to 17 m2/g after careful synthesis and calcination up to 1400°C for four hours. The selectivity of NH3-conversion to N2 is at present at 60 percent, but varies strongly with temperature. Fuel components such as H2, CO, C2H4, and NH3 ignite at temperatures close to compressor outlet temperatures. This means that a pilot-flame may not be needed for ignition of the fuel. A comparison between a Pd-impregnated lanthanum hexaaluminate and a Mn-substituted lanthanum hexaaluminate showed that the ignition temperature and the NOX-formation varied strongly over the two different catalysts.
Valve Gear Refinement
Authors: Avsec Jurij , Marcic Milan , Oblak Maks
Published: July 2002

This paper describes a new type of valve gear cam—MULTICAM—which consists of seven curves and allows an optimum cam profile design. In order to calculate the cinematic and dynamic values and to assess the minimum oil film thickness in the valve gear, the mathematical model of an ideal valve gear was used. In addition, the comparison of the results between the polysine cam and the new MULTICAM cam design was made. By means of the new cam design the Hertz pressures were reduced at the point of contact between the cam and the cam follower and the lubrication properties at the top of the cam improved.
Features of Automotive Gas Tank Filler Pipe Two-Phase Flow:
Experiments and Computational Fluid Dynamics Simulations
Authors: Banerjee R. , Isaac K. M. , Oliver L. , Breig W.
Published: July 2002

Extensive flow visualization in an automotive fuel filler pipe made visible by introducing dyes and smoke in water and air, respectively, were conducted for nominal flow rates of 4–18 liters per minute. Video and still cameras were used for imaging. Features of the flow such as laminar-to-turbulent transition, progressive development of strong swirl along filler pipe axis, air entrainment, and mixing with the liquid were observed in the experiments. The experimental observations were supported by computational fluid dynamics (CFD) simulations of the flow which also showed features such as swirl and air entrainment.
Synthesis and Analysis of Stroke-Increasing and Force-Balancing
Mechanisms for Rod Pumping Units
Authors: Yi Lu , Leinonen Tatu
Published: July 2002

This paper introduces a creative synthesis and analysis of stroke-increasing and force-balancing mechanisms for rod oil pumping units by using the systematic linkage technique. The corresponding relations between the kinematic components in mechanisms and the link element in associated linkage are determined. Four acceptable associated linkages are used to create eight new types of mechanisms for rod oil pumping units. Formulas are derived for calculating stroke, counterweight mass, and driving force. For each synthesized mechanism, an analysis of properties, working loads, and strokes is conducted. Finally, a better mechanism for the rod oil pumping units is presented.
Local Furnace Data and Modeling Comparison for a 600-MWe Coal-Fired
Utility Boiler
Authors: Hwang Yuh-Long , Howell John R.
Published: July 2002

Reductions in furnace exit gas temperature (FEGT) by changing boiler operating variables and/or adding wall soot blowers and/or lowering burner elevations are investigated. Evaluation of these approaches requires experimental furnace testing and computational furnace modeling. The experimental facility is a Combustion Engineering corner-fired pulverized-coal boiler with a capacity of 606 MWe. Local gas temperature distributions, local radiative and total wall heat flux distributions, and stack NOx were measured during constant-load furnace tests under various combinations of burner configuration, burner tilt angles, excess-O2 setpoints and overfire airflow rate. These measurements are used for tuning and calibrating a furnace model based on the PCGC-3 code developed by Brigham Young University. The experimental data gathered in this work comprise a comprehensive set under controlled conditions on a very-large-scale coal-fired plant and provides information for use in comparing the predictions of furnace-design codes.
Numerical Simulation of Multiple Floating Structures With Nonlinear Constraints
Authors: Chakrabarti Subrata K.
Published: July 2002

A versatile and efficient numerical analysis is developed to compute the responses of a moored floating system composed of multiple floating structures. Structures such as tankers, semisubmersibles, FPSOs, SPARs, TLPs, and SPMs connected by mooring lines, connectors or fenders may be analyzed individually or collectively including multiple interaction. The analysis is carried out in the time domain assuming rigid body motion for the structures, and the solution is generated by a forward integration scheme. The analysis includes the nonlinearities in the excitation, damping, and restoring terms encountered in a typical mooring system configuration. It also allows for instabilities in the tower oscillation as well as slack mooring lines. Certain simplifications in the analysis have been made, which are discussed. The exciting forces in the analysis are wind, current, and waves (including a steady and an oscillating drift force), which are not necessarily collinear. The waves can be single frequency or composed of multiple frequency components. For regular waves either linear, stretched linear or fifth order theory may be used. The irregular wave may be included as a given spectral model (e.g., PM or JONSWAP). The vessels are free to respond to the exciting forces in six degrees of freedom—surge, sway, heave, roll, pitch, and yaw. The tower, when present, is free to respond in two degrees of freedom—oscillation and precession. The loads in the mooring lines are determined from prescribed tension-strain tables for the lines. Rigid mooring arms can be analyzed by allowing for compression in the load-strain table. Fenders may be input similarly through load compression tables. In order to establish the stability and accuracy of the solution, comparison of the results with linearized frequency domain analysis was made. The analysis is verified by several different model test results for different structure configurations in regular and random seas. Some of the interesting aspects of nonlinear system are shown with a few examples.
Approximate Two-Color Emission Pyrometry
Authors: Bhattacharjee S. , King M. , Cobb W. , Altenkirch R. A. , Wakai K.
Published: July 2002

Approximate methods for the determination of a temperature field using pure emission pyrometry applied to a two-dimensional nonoptically thin flame without variation along a line of sight are presented. In the absence of an absorption measurement, emission pyrometry depends on theoretical spectral information. Limitations of existing techniques stem from the fact that spectral information is a function of temperature only for the optically thin situation, by and large the situation to which current techniques apply, and temperatures above 1000 K. Through extensive narrow-band calculation using a simulated flame over polymethylmethacrylate, we show that the spectral information contained in the equivalent bandwidth ratio is approximately a constant for the 2.8 μm/1.8 μm band pair and appropriate bandwidths. The constant can be evaluated from emission measurements at a point where the temperature is known or can be estimated using, e.g., the maximum flame temperature of a simulated flame and the peak band intensities. The temperature field evaluated with this approximately constant value of the equivalent bandwidth ratio, Ar, is accurate to within five percent for temperatures down to 450 K. [S0022-1481(00)02601-3]
Simultaneous Measurement of the Orthogonal Components of Thermal
Diffusivity in PVC Sheet
Authors: Doss D. J. , Wright N. T.
Published: July 2002

An extension of the flash method is described that measures simultaneously the three orthogonal components of thermal diffusivity in specimens of moderate thermal diffusivity. Only part of the top face of the specimen is illuminated and the temperature histories are recorded at three points on the bottom face. A Marquardt parameter estimation algorithm coupled with a finite difference model of the diffusion equation analyzes these temperature histories to determine the components of thermal diffusivity. Illustrative measurements in stainless steel, glass, and PVC demonstrate that accurate three-dimensional thermal diffusivity measurements can be made in this way. The in-plane components of thermal diffusivity of as-supplied PVC sheet are shown to be about 20 percent greater than the out-of-plane component. This anisotropy appears to be due to the manufacturing process and exemplifies the need for such measurements. [S0022-1481(00)70101-0]
A Model of Dopant Transport During Bridgman Crystal Growth With
Magnetically Damped Buoyant Convection
Authors: Ma N. , Walker J. S.
Published: July 2002

This paper presents a model for the unsteady transport of a dopant during the vertical Bridgman crystal growth process with a planar crystal-melt interface and with an externally applied axial magnetic field. This dilute mass transport depends on the convective and diffusive mass transport of the dopant. The convective mass transport is driven by buoyant convection in the melt, which produces nonuniformities in the concentration in both the melt and the crystal. This convective transport is significant even for a strong magnetic field Bo=2 T. However, the electromagnetic damping of the melt motion produces a local region adjacent to the crystal-melt interface which is dominated by diffusion. Thus, this melt solidifies with a relatively radially uniform concentration, so that the radial distribution of dopants in the crystal is also relatively radially uniform. The transient model predicts the dopant distribution in the entire crystal. [S0022-1481(00)02301-X]
Calibration Issues in Development of ISO Standards for Fixed Steel
Offshore Structures
Authors: Moses Fred , Stahl Bernhard
Published: July 2002

A study supported by the American Petroleum Institute established that load and resistance factor design offers improvement in design and is supported by credible data, can yield improved designs of greater reliability and/or economy and is in reasonable accordance with current design practices. This paper discusses the criteria for calibrating the ISO-LRFD based on the API studies. Other topics include actual versus notional reliabilities, regional load factors, member versus system reliability, and selecting a design return period. The paper also describes safety indices for the combined loading interaction formulas. [S0892-7219(00)01301-7]
Offshore Safety Assessment and Safety-Based Decision-Making—The
Current Status and Future Aspects
Authors: Wang J. , Kieran O.
Published: July 2002

The offshore installations (safety case) regulations were developed in the UK in 1992 and came into force in 1993 in response to the accepted findings of the Piper Alpha enquiry. Recently, “the offshore installations and wells (design and construction, etc.) regulations” (DCR 1996) were introduced to offshore safety analysis. From the earliest stages of the installation's life cycle, operators must ensure that all safety-critical elements in both the software and system domains be assessed. Hazards can be identified and the risks associated with them can be assessed and evaluated using a number of techniques and decision-making strategies, all aimed at producing an installation with lifetime safety integrity. In this paper, following a brief review of the current status of offshore safety regulation in the UK, several offshore safety assessment frameworks are presented. These include top-down, bottom-up, probabilistic, and subjective approaches. The conditions under which each approach may be applied effectively and efficiently are discussed. Probabilistic safety-based decision-making and subjective safety-based decision-making are then studied. Two examples are used to demonstrate the decision-making approaches. Recommendations on further development in offshore safety analysis are suggested. [S0892-7219(00)00901-8]
A new mass-selective evaporation rate monitor
Authors: Genequand P.
Published: July 2002

The thermal energy of evaporated atoms has been directly used to produce a signal in an Omegatron-like structure. This signal is mass selective and proportional to the vapor flux and the ionization current. It is, in principle, independent of the velocity of the atoms in the vapor beam, and thus independent of the evaporation temperature. The first experimental results have shown that the ultimate sensitivity corresponds to a deposition rate lower than 0.1 Å/sec for a time constant of 0.2 sec. The mass resolution ΔM/M at half-peak height lies within 1.5%–3% in the mass range 20–200. The device has been operated at residual pressure above 10−4 Torr without significant alteration of the signal peak and without appearance of spurious peaks due to the residual gases.
Fabrication of open stencil masks with asymmetric void ratio for the ion projection lithography space charge experiment
Authors: Volland B. , Shi F. , Heerlein H. , Rangelow I. W. , Hudek P. , Kostic I. , Cekan E. , Vonach H. , Loeschner H. , Horner C. , Stengl G. , Buschbeck H. , Zeininger M. , Bleeker A. , Benschop J.
Published: July 2002

For the ion projection lithography space charge experiment [P.W.H. de Jager et al., J. Vac. Sci. Technol. B 17, 3098 (1999)] a suitable stencil test mask has been realized and used. This article addresses the stress engineering and fabrication process of this specific test mask with openings in the range of some few 100 nm up to some 100 μm. This large difference in stencil pattern dimensions causes reactive ion etching (RIE) lag (dependence of the etch rate on feature size and pattern density) during the fabrication process and considerable stress variations across the membrane field. The solution to these problems was by (i) implementing novel doping technologies to create variable thickness areas on the membrane serving as reinforcement and stress relief structures, and (ii) adjusting the design to feature sizes and pattern densities to the same order of magnitude for the e-beam lithography and RIE processing steps. The etching of the openings through the 3 μm thick Si membrane was done by inductively coupled plasma etching with gas chopping techniques. These methods as devoloped for this specific test mask can be used to improve the stencil mask technology in general.
X−ray photoemission and surface structure
Authors: Shirley D. A.
Published: July 2002

X−ray photoemission spectroscopy (XPS) is a ’’semisurface’’ technique that can be modified to study bulk properties, surfaces, or adsorbed species. As a bulk probe it is capable of yielding bandstructure information. It can distinguish amorphous from crystalline materials and is sensitive to magnetic and spatial order. Sensitivity to surface character is less pronounced. Relaxation effects are prominent in XPS spectra. Core−level binding energies of adsorbed species yield structural information if relaxation is considered. The same should be true for valence orbitals. Heterogeneous catalysis can be understood in a general sense as arising from the same origins as the relaxation energies in photoemission.
Stabilization of n-type semiconductors to photoanodic dissolution: II–VI and III–V compound semiconductors and recent results for n-type silicon
Authors: Wrighton Mark S. , Bolts Jeffrey M. , Bocarsly Andrew B. , Palazzotto Michael C. , Walton Erick G.
Published: July 2002

Semiconductor-based photoelectrochemical cells for the conversion of light to electricity are described. Such cells consist of a semiconductor photoelectrode, a counterelectrode, and an electrolyte solution containing electroactive species. Results for cells employing certain n-type II–VI (CdS, CdSe, CdTe) and III–V (GaP, GaAs, InP) photoelectrodes in solutions of electroactive X2−/Xn2−(X=S, Se, Te) species are reviewed. The key fact is that for a number of photoelectrode /X2−/Xn2− combinations we find that photoanodic decomposition of the semiconductor is virtually totally suppressed, allowing the sustained conversion of light to electricity. Preliminary results for n-type Si photoelectrodes derivatized with electroactive ferrocene reagents are also outlined, and the associated photoelectrochemical activity of the surface species is compared to results for naked Si exposed to solutions of ferrocene.
Simple dc method for the continuous measurement of work function changes
Authors: Barker R. A. , Felter T. E. , Semancik S. , Estrup P. J.
Published: July 2002

A simple dc procedure, based upon the retarding potential method, for making continuous measurements of work function changes is reported. It has the advantage of easy combination with leed and other surface techniques and has been useful in revealing structure in the Δφ vs exposure curve for hydrogen adsorption on tungsten(001). (AIP)
A simple technique for measuring electron beam angular divergence
Authors: Martin J. A. , Lagally M. G.
Published: July 2002

A technique for measuring electron beam angular divergence is described. Cross-sectional beam profiles are measured at several positions along the beam path using a modification of the knife edge technique.(AIP)
Surface-tunneling-induced 1/ f noise in Hg1−xCdxTe photodiodes
Authors: Anderson W. W. , Hoffman H. J.
Published: July 2002

The reverse bias dark curent of Hg1−xCdxTe (MCT) photodiodes is often dominated by tunneling across a pinched off surface depletion region. The width of this critical region may be modulated by charge exchange with slow surface states in a passivant insulator. Numerical calculations give the correct order of magnitude for observed 1/ f noise in ZnS passivated MCT photodiodes.
Inverse photoemission
Authors: Woodruff D. P. , Johnson P. D. , Smith N. V.
Published: July 2002

Inverse photoemission (or ultraviolet bremsstrahlung spectroscopy) is an emerging new technique for the study of the electronic structure of solid surfaces. It has the important characteristic of being able to probe states between the Fermi level and vacuum level. Here we survey current experimental practice and future prospects, including discussion of band-pass and low-pass photon filters, grating spectrographs, and electron sources. Examples of recent work are presented, drawing on studies of band mapping, energy-loss satellites, surface states, adsorbates, and spin polarization effects. Emphasis is on k-resolved inverse photoemission spectroscopy (KRIPES).
Interaction of hydrogen and oxygen on tungsten{100}
Authors: Smith A. Horlacher , Chung J. W. , Estrup P. J.
Published: July 2002

An experimental study of (H+O)/W{100} has shown that coadsorption of oxygen lowers the binding energy of the hydrogen adatoms by compressing islands of pure hydrogen. Temperature-programmed desorption of a hydrogen layer at low coverage θ(H) gives a single peak (β2) at 550 K; only at higher θ(H) does an additional peak (β1) appear at 450 K. The latter is caused by a reduction in the desorption energy due to the disappearance of the substrate reconstruction at high θ(H). The present work shows that, similarly, addition of oxygen to H/W{100} causes a β1 peak to grow in. This effect is not due to a direct ‘‘chemical’’ interaction between O and H which segregate under the experimental conditions. The decrease in the hydrogen binding energy arises as oxygen compresses the hydrogen, causing a local increase in θ(H) and hence, a disappearance of the reconstruction.
Discrimination between domain wall and uniformly incommensurate structures by surface extended x-ray absorption fine structure: Adsorption of chlorine on Ag{110}
Authors: Holmes D. J. , Panagiotides N. , Dus R. , Norman D. , Lamble G. M. , Barnes C. J. , Della Valle F. , King D. A.
Published: July 2002

A well-established problem in surface structure determination is the experimental difficulty in distinguishing a uniformly incommensurate structure from a domain wall structure. Surface extended x-ray absorption fine structure (SEXAFS), as a local structural probe, should provide an unambiguous means of making the distinction. We have studied chlorine adsorbed on Ag{110} by SEXAFS at several coverages. The Cl–Ag nearest-neighbor distance, 2.56±0.04 Å, is found to be substantially shorter than on the {111} and {100} faces, and is independent of coverage. At θ=0.75 an incommensurate phase is formed. A multishell analysis (up to 5.6 Å) allowed a complete structural determination and has, for the first time, confirmed our expectation. The Cl–Cl spacing unambiguously favors a domain wall structure. Structural models have been tested by laser simulation experiments, and by kinematic analysis of the low-energy electron diffraction data.
Investigations of adsorption on Pt and Rh by laser-induced desorption
Authors: Seebauer E. G. , Kong A. C. F. , Schmidt L. D.
Published: July 2002

The adsorption, desorption, equilibrium, and diffusion behavior of NO, CO, and H2 on Pt(111) and Rh(111) have been investigated using laser-induced thermal desorption. A pulsed infrared laser beam is focused onto a single-crystal surface, causing very rapid heating (∼1010 K/s) and nearly instantaneous desorption of surface species which are detected with a quadrupole mass spectrometer. Isosteric heats of adsorption of NO and CO are found to decrease as the coverage increases from 26±2 to 12 kcal/mol and from 32±2 to 16 kcal/mol, respectively. By combining the equilibrium and adsorption data, preexponential factors for desorption are found to decrease by a factor of 107 near saturation. Surface diffusion of deuterium and hydrogen on Pt(111) varies strongly with coverage. As the initial surface coverage θ of deuterium is varied from 0.001 to 0.33, the diffusion activation energy Ediff falls from 12 to 7 kcal/mol, and the preexponential factor D0 falls from 3×104 to 0.5 cm2/s. Concentration profiles measured directly by a variable aperture technique confirm that deuterium diffusion slows at low coverage. Hydrogen diffuses about twice as fast as deuterium. On Rh(111), Ediff for deuterium is nearly constant at 4 kcal/mol for 0.02<θ<0.33, while D0 remains near 7×10−4 cm2/s.
Ultraviolet-light-enhanced reaction of oxygen with gallium arsenide surfaces
Authors: Yu C. F. , Schmidt M. T. , Podlesnik D. V. , Yang E. S. , Osgood R. M.
Published: July 2002

Light-enhanced reaction of oxygen with gallium arsenide surfaces by irradiation with deep-UV, near-UV, and visible light was studied using Auger electron spectroscopy and x-ray photoelectron spectroscopy for submonolayer and above monolayer regimes, respectively. The onset of a strong wavelength dependence of the enhanced oxidation was observed after the oxygen coverage reached more than one-half a monolayer. An abrupt threshold for this wavelength dependence was also observed at ∼4.1-eV photon energy. A possible mechanism is presented to explain this strong wavelength dependence.
Model calculation for the tunnel current from a tungsten tip to a Ni(100) surface with a chemisorbed oxygen atom
Authors: Doyen G. , Drakova D. , Kopatzki E. , Behm R. J.
Published: July 2002

The tunnel current between a Ni(100) surface with a chemisorbed oxygen atom and a tip described by a single tungsten atom chemisorbed on a W(110) surface is calculated for different distances. The calculations are based on a model Hamiltonian and allow for tip–surface interaction. At small surface–tip separations (≤6 Å) a negative corrugation is found, i.e., Oad induces a dent in the constant current contours, in contrast to the contours of total charge density and that at EF. At larger distances they all exhibit a positive corrugation with maxima at the position of the Oad.
Infrared internal reflection studies of the surface photochemistry of dimethylcadmium on silicon
Authors: O’Neill James A. , Sanchez Esaul , Osgood Richard M.
Published: July 2002

An infrared spectroscopic technique employing the principle of total internal reflection has been used to examine the UV-induced surface photochemistry of dimethylcadmium on chemically altered silicon surfaces. Fourier transformed infrared spectra of both chemically and physically adsorbed molecules were recorded on oxidized and hydrogen ‘‘passivated’’ silicon surfaces (SiO2 and SiH) upon exposure to excimer laser radiation at 193 and 248 nm. By monitoring changes in the infrared spectrum of adsorbed dimethylcadmium during the irradiation process, insight into the role of the surface in the photodissociation of the adspecies is obtained.
Classically exact surface diffusion constants at arbitrary temperature
Authors: Voter Arthur F. , Cohen Jennifer M.
Published: July 2002

An expression is presented for computing the classical diffusion constant of a point defect (e.g., an adatom) in an infinite lattice of binding sites at arbitrary temperature. The transition state theory diffusion constant is simply multiplied by a dynamical correction factor that is computed from short-time classical trajectories initiated at the site boundaries. The time scale limitations of direct molecular dynamics are thus avoided in the low- and middle-temperature regimes. The expression results from taking the time derivative of the particle mean-square displacement in the lattice-discretized coordinate system. Applications are presented for surface diffusion on fcc(100) and fcc(111) Lennard-Jones crystal faces.
Properties of potassium adsorbed on Si(100)2×1
Authors: Pervan P. , Michel E. , Castro G. R. , Miranda R. , Wandelt K.
Published: July 2002

The properties of potassium adsorbed on a Si(100)2×1 surface were studied using work function change measurements, thermal desorption spectra of potassium, and coadsorbed xenon as well as ultraviolet photoemission spectroscopy measurements of clean and oxygen exposed K/Si surfaces at 300 and 55 K. The results strongly support the notion that potassium overlayers of ΘK≥0.5 exhibit metallic character.
Multipole confined diffusion plasma produced by 13.56 MHz electrodeless source
Authors: Boswell R. W. , Perry A. J. , Emami M.
Published: July 2002

An inductively coupled rf plasma source is shown to produce a large uniform diffusion plasma at low pressures in a reactor surrounded externally by small magnets arranged to produce cusp fields at the walls. Electron densities of >1011 cm−3 can be produced at pressures of <10−3 Torr argon with 800 W input power. With SF6 ion currents of 0.5 mA cm−2 uniform to ±1.5% over 15 cm diameter have been measured at 6×10−4 Torr and 400 W.
CO on NaCl(100): Model system for investigating vibrational energy flow
Authors: Chang Huan-Cheng , Noda Chifuru , Ewing George E.
Published: July 2002

Vibrational energy flow from CO physisorbed on NaCl(100) has been investigated. Infrared spectroscopy of monolayer CO reveals the narrowest linewidth reported for any surface-bound molecule. The vibrational band at 2154.98 cm−1 has a full-width at half-maximum (FWHM) of 0.09 cm−1 at 4 K. We believe that this residual linewidth is due to imperfections of the crystal face. Nevertheless it places a lower limit for all vibrational relaxation processes of 60 ps. The linewidth increases above 10 K, a behavior which can be accounted for by a vibrational phase relaxation mechanism. Attempts to photodesorb CO from its substrate by laser excitation into the vibrational absorption band reveal an exceedingly inefficient quantum yield of Φ≤10−7. Finally laser excitations of a multilayer of CO on NaCl(100) at 22 K demonstrate that vibrational energy can be stored in the adsorbed CO long enough to allow fluorescence however relaxation to the substrate reduces the fluorescence lifetime from that of the bulk crystal. These measurements (bandwidth, vibrational desorption quantum yield, and fluorescence lifetime) of monolayer and multilayer CO on NaCl(100) indicate that the vibrational motions are poorly coupled to this alkali halide substrate.
Precise measurement of flow rates of vaporized tetraethylgermanium carried by an inert gas
Authors: Gazicki Maciej , Schalko Hannes , Svasek Peter , Olcaytug Fethi , Kohl Franz
Published: July 2002

The ‘‘rate-of-rise’’ technique has been applied for the measurement of the flow rate of tetraethylgermanium carried in a stream of argon. A very precise time counter designed and constructed for this purpose is described. A simple model is presented where the flow rate of the vapor is proportional to its partial pressure and to the flow rate of the carrier gas and inversely proportional to the partial pressure of the carrier gas. The assumed applicability of the equation of state of the ideal gas to the discussed system is successfully tested by means of the flow rate dependence on temperature in the range from −19 to 20 °C and its comparison with data computed from the Clausius–Clapeyron equation. Finally thermodynamic properties of tetraethylgermanium namely vaporization enthalpy and saturated vapour pressure at standard temperature are calculated from the results of flow rate measurements.
Angular distribution of sputtered neutrals in a post magnetron geometry: Measurement and Monte Carlo simulation
Authors: Eisenmenger-Sittner C. , Beyerknecht R. , Bergauer A. , Bauer W. , Betz G.
Published: July 2002

The angular distributions of Cu particles sputtered from a cylindrical (post) magnetron were measured in a pinhole arrangement at various working gas pressures. The differentially pumped pinhole camera—described in a previous article—allows measurements in a pressure range up to 10 Pa and samples the three-dimensional distributions in planar sections. Two different planes, namely, parallel and perpendicular to the magnetron axis, were selected for the investigation. Cu was sputtered by Ar ions with an energy of about 0.5 keV from a post magnetron with a very uniform erosion zone. The orifice of the pinhole camera was located at a distance of 50 mm from the cathode surface and in the middle of the erosion zone. The working gas pressure was varied from 0.1 to 1 Pa. The angular distribution of particles was deduced from thickness measurements of films deposited on a semicircular substrate with a 21 mm radius centered around the pinhole. The pressure-dependent amount of scattering was studied by comparing the measured angular distributions with either analytic results neglecting scattering and with those calculated by Monte Carlo simulations of the gas phase transport. Experiment and simulation give good agreement, especially in the low-pressure range. For high working gas pressures good quantitative coincidence of calculation and experiment can only be achieved by introducing a pressure-dependent exponent n in the cosn θ particle emission characteristic from the target. Generally it can be concluded that, for all considered gas pressures, sputtered neutrals show angular distributions far from isotropy.