bluuebunny/crossref_metadata_2025 huggingface dataset:
Integration of macromolecular diffraction data
Authors: Leslie A. G. W.
Published: July 2002

Diffraction intensities can be evaluated by two distinct procedures: summation integration and profile fitting. Equations are derived for evaluating the intensities and their standard errors for both cases, based on Poisson statistics. These equations highlight the importance of the contribution of the X-ray background to the standard error and give an estimate of the improvement which can be achieved by profile fitting. Profile fitting offers additional advantages in allowing estimation of saturated reflections and in dealing with incompletely resolved diffraction spots.
Preparation and preliminary X-ray diffraction studies of a new crystal form of L-asparaginase from Escherichia coli
Authors: Polikarpov I. , de Oliveira R. T. , Abrahão-Neto J.
Published: July 2002

L-Asparaginase is an enzyme which hydrolyzes asparagine to produce aspartic acid and ammonia. It is an effective chemotherapeutic drug, especially in the treatment of acute lymphoblastic leukaemia in children. The enzyme from Escherichia coli was crystallized in a new crystal form with space group C2, unit-cell parameters a = 76.3 (0), b = 134.6 (2), c = 64.8 (7) Å, β = 110.5 (1)° and a dimer in the asymmetric unit. Synchrotron-radiation diffraction data have been collected to 1.95 Å resolution.
Three-dimensional structure of the Gly121Tyr dimeric form of ornithine decarboxylase from Lactobacillus 30a
Authors: Vitali Jacqueline , Carroll Donald , Chaudhry Rochika G. , Hackert Marvin L.
Published: July 2002

Ornithine decarboxylases catalyze the conversion of ornithine to putrescine at the beginning of the polyamine pathway. Ornithine decarboxylase (ODC) from Lactobacillus 30a is a 990612 Da dodecamer composed of six homodimers. A single point mutation (Gly121Tyr) was found to prevent association of dimers into dodecamers. The dimeric protein has been crystallized at pH 7.0 in the presence of guanosine triphosphate (GTP). Crystals belong to space group P3221, with unit-cell parameters a = 111.8, c = 135.9 Å and one monomer in the asymmetric unit. The structure was determined by molecular replacement and refined using simulated annealing to R = 0.211 at 2.7 Å resolution. The GTP-binding site was analyzed in detail. The protein exhibits a novel binding mode for GTP which is different from that seen in most G-proteins or GTPases. Central to this binding scheme appear to be three lysines, Lys190, Lys374 and Lys382, which form salt bridges with the three phosphates, and Thr191, which hydrogen bonds with the guanine base. Furthermore, the structure suggests that there is some flexibility in the wing domain, which can change its orientation as the protein adapts to its environment. The active site is similar to that of the native enzyme, consistent with the observation that the enzyme activity does not depend on its dodecameric state.
Structure of a new neurotoxin from the scorpion Buthus martensii Karsch at 1.76 Å
Authors: He Xiao-Lin , Deng Jun-Peng , Wang Miao , Zhang Ying , Wang Da-Cheng
Published: July 2002

A new neurotoxin BmK M2, toxic to both mammals and insects, with the strongest toxicity in the BmK toxin series, has been purified from the Chinese scorpion Buthus martensii Karsch and crystallized with MPD at pH 7.5. The crystals are orthorhombic, belonging to space group P212121, with unit-cell parameters a = 36.64, b = 36.95, c = 37.23 Å. The structure was solved by molecular replacement and refined to R = 0.186 for all reflections to a resolution of 1.76 Å. The whole sequence (64 residues) of BmK M2 was determined by crystallographic analysis based on high-resolution data and the homologous model of BmK M8. The refined BmK M2 structure shows a non-proline cis peptide bond between Pro9 and His10 which enables the C-terminal segment to adopt a conformation different to that of the weak toxin BmK M8. Recently, a mutation analysis had suggested that both the tenth residue and the C-terminus play key roles in receptor binding. Therefore, these features may be related to the binding selectivity of the group III α-like toxins. The charge changes of residues 8, 10, 18, 28, 55 and 59 from neutral or negative to positive or neutral, which leads to a positive electrostatic potential surface, may be responsible for the high toxicity of BmK M2.
Structure and low-temperature thermal relaxation of ion-implanted germanium
Authors: Glover C. J. , Ridgway M. C. , Yu K. M. , Foran G. J. , Clerc C. , Hansen J. L. , Nylandsted-Larsen A.
Published: July 2002

The structure of implantation-induced damage in Ge has been investigated using high resolution extended X-ray absorption fine structure spectroscopy(EXAFS). EXAFS data analysis was performed with the Cumulant Method. For the crystalline-to-amorphous transformation, a progressive increase in bond-length was observed without the presence of an asymmetry in interatomic distance distribution (RDF). Beyond the amorphization threshold the RDF was dose dependent and asymmetric, where the bond-length and asymmetry increased as functions of ion dose. Such an effect was attributed to the formation of three- and five-fold coordinated atoms within the a morphous phase. Low-temperature thermal annealing resulted in structural relaxation of the amorphous phase as evidenced by a reduction in the centroid ,asymmetry and width of the RDF, as consistent with a reduction in the fraction of non four-fold coordinated atoms.The results have been compared to other EXAFS studies of amorphous Ge, and it issuggested thatthe range of bond-lengths reported therein is related to the sample preparation method and state of relaxation.
Local structure of silver clusters in the channels of zeolite 4A
Authors: Miyanaga T. , Hoshino H. , Endo H.
Published: July 2002

The Ag K-edge EXAFS measurements have been carried out at 50 K for fully Ag+-exchanged zeolite 4 A (Ag-4A) dehydrated at different temperatures under vacuum. In the Fourier transforms of the EXAFS oscillation the two distinct peaks appear around 2.2 Å and 3.0 Å, and a shoulder around 2.8 Å. The structural parameters (distance, coordination number and root mean square displacement) were derived by a three-shell (two Ag-O contacts and Ag-Ag contact) curve-fitting analysis. It is found that a silver cluster is formed with Ag-Ag distance 2.82 ± 0.02 Å and coordination number 4.9 ± 0.2. When the silver cluster is formed 6 Ag0 atoms and 8 Ag+ ions are arranged in a cubic closed-packed manner in the cage of the Ag-4A zeolite. The 8 Ag+ ions and 6 Ag0 atoms are confined in the framework of O atoms at distances of 2.28 ± 0.02 and 2.88 ± 0.02 Å, respectively.
In situ XAFS analysis system for high-pressure catalytic reactions and its application to CO2 hydrogenation over a Rh/Y-zeolite catalyst
Authors: Bando Kyoko K. , Saito Takeru , Sato Koichi , Tanaka Tomoaki , Dumeignil Franck , Imamura Motoyasu , Matsubayashi Nobuyuki , Shimada Hiromichi
Published: July 2002

An in situ XAFS cell was developed and used for the structural analysis of a Rh ion-exchanged zeolite catalyst during high-pressure hydrogenation of carbon dioxide. The in situ cell enabled analyses of the catalyst structures that changed with the reaction atmosphere and elapsed time; the peak assigned to Rh-O scattering changed to that assigned to Rh-Rh scattering at 404 K during the pretreatment by hydrogen. After 30 min of the carbon dioxide hydrogenation reaction, the peak intensity assigned to Rh-Rh scattering increased corresponding to the increase in the catalytic activity.
EXAFS measurements for liquid Ge–Si alloys
Authors: Inui Masanori , Matsusaka Tetsuya , Ishikawa Daisuke , Sakaguchi Yoshifumi , Hong Xinguo , Kazi Moynul Huq , Tamura Kozaburo
Published: July 2002

EXAFS measurements around the Ge-K edge have been carried out for liquid Ge-Si alloys for the first time to investigate the local strucure around a Ge atom. To perform the EXAFS measurements for the liquid alloys with high melting temperatures, a new sapphire cell have been developed. The measurements were carried out for the liquid alloys from 10% to 60% of Si and the crystalline ones from 10% to 70% of Si as a reference. EXAFS oscillations, x(k), are observed even at 1480°C for liquid Ge0.4Si0.6. The position of the first peak in the radial distribution function obtained from Fourier transform of x(k) is shifted towards smaller distance for liquid and crystalline alloys with increasing Si concentration. The results of a curve-fit analysis in a harmonic approximation show that Ge-Ge and Ge-Si bonds in the liquid alloys become long with increasing Si concentration while those become slightly short in the crystaline ones.
Temperature dependence of thermal expansion coefficient of silver nanoparticles and of bulk material determined by EXAFS
Authors: Dubiel Manfred , Brunsch Sven , Tröger Larc
Published: July 2002

The thermal expansion behaviour of silver fcc has been described by an anharmonic Einstein model using EXAFS data in the temperature range between 10 and 300 K. The linear expansion coefficient of a bulk silver foil agrees well with X-ray diffraction data. In the case of silver particles embedded in a silicate glass matrix, this parameter shows an increase for particles of 3.2 nm in size by 70% whereas samples with an average size of particles of 5.1 nm show no changes compared with bulk fcc. The increase for small particles reflects the size effect as well as the influence of the surrounding matrix of glass. The results reveal a substantial influence of the distribution of particle sizes on the expansion coefficient.
An EXAFS study of zinc coordination in microbial cells
Authors: Webb Samuel M. , Gaillard Jean-Francois , Jackson Bradley E. , Stahl David A.
Published: July 2002

Five microbes were isolated from metal amended enrichment cultures derived from the sediments of a lake contaminated by a zinc smelter. Each of these organisms was grown in pure culture in the presence of zinc. Quick Extended X-ray Absorption Fine Structure (QEXAFS) spectroscopy was used to investigate the average coordination environment of the zinc associated with the microbial biomass. Fitting of the first coordination shell of zinc shows that significant differences exist for each microbial species examined. The coordination environment of zinc varies between sulfurs to six-fold nitrogen/oxygen, with two microbial strains showing mixed coordination shells. Further study is required in order to characterize these sites and their locations within the cell.
XAS investigations of Fe(VI)
Authors: Kemner K. M. , Kelly S. D. , Orlandini K. A. , Tsapin A. I. , Goldfeld M. G. , Perfiliev Y. D. , Nealson K. H.
Published: July 2002

Recent attention has been given to a reexamination of results from the early Viking missions to Mars that suggested the presence of one or more strong oxidants in Martian soil. Since Fe is one of the main constituents of the Martian surface and Fe(VI) is known to be a highly reactive, strong oxidant, we have made XANES and EXAFS measurements of Fe(II), Fe(III), Fe(IV), and Fe(VI) in solid and solution forms. Results from these studies indicate a preedge XANES feature from Fe(VI) samples similar to that commonly seen from Cr(VI) samples. Results of first shell analysis indicate a linear relationship between the Fe-O bondlength and Fe valence state.
Quarter-Wave Plates and X-ray Magnetic Circular Dichroism on ID24 at the ESRF
Authors: Pizzini S. , Bonfim M. , Baudelet F. , Tolentino H. , San Miguel A. , Mackay K. , Malgrange C. , Hagelstein M. , Fontaine A.
Published: July 2002

The first XMCD measurements carried out on the ID24 energy-dispersive XAS beamline at the ESRF are reported. Circular-polarized X-rays are obtained using perfect diamond crystals as quarter-wave plates. The very small source divergence allows circular polarizations close to unity to be obtained.
Rotated-inclined focusing monochromator with simultaneous tuning of asymmetry factor and radius of curvature over a wide wavelength range
Authors: Watanabe Nobuhisa , Suzuki Mamoru , Higashi Yasuo , Sakabe Noriyoshi
Published: July 2002

A new single-crystal focusing monochromator for protein crystallography has been developed. In order to achieve simultaneous tuning of the beam demagnification rate and the radius of curvature for focusing over a wide wavelength range, the surface of an inclined monochromator was cylindrically bent. The monochromator is able to tune these two parameters simultaneously with a single rotation of the crystal about the azimuthal axis. A new monochromator incorporating this idea has been developed for beamline BL6B at the Photon Factory. The monochromator was designed for use in the wavelength range 0.87–1.90 Å, and beam focusing was tested at wavelengths of 1.04, 1.38 and 1.74 Å.
[4-(Diphenylphosphino)-9,9-dimethylxanthen-5-yl]diphenylphosphine oxide toluene hemisolvate
Authors: Ellis Dianne D. , Spek Anthony L.
Published: July 2002

In the title compound, C39H32O2P2·0.5C7H8, there are two distinct phosphorus centers. The P—C bond lengths around the diphenylphosphino group are around 0.04 Å larger than those in the phosphine oxide moiety. This corresponds to smaller C—P—C bond angles of 101.2 (15)° compared to 108.4 (9)° for the latter. The rigid dibenzopyran backbone is folded at an angle of 158.9 (1)°.
1-{[4-(4-Chlorophenyl)-1H-pyrrol-3-yl](2,4-dichlorophenyl)methyl}-1H-imidazole (RDS 416)
Authors: Camalli Mercedes , Pifferi Augusto , Costi Roberta , Santo Roberto Di , Massa Silvio , Artico Marino
Published: July 2002

The crystal structure of the title compound, C20H14Cl3N3, a potent antifungal agent discovered recently, is here reported. The elucidation of the structure may be useful to provide a better understanding of the interaction of imidazole agents with P-450-dependent enzymes involved either in ergosterol biosynthesis (in fungi) or in hormones biosynthesis (in humans).
Sandblasting: the only way to eliminate rust?
Authors: Batis G. , Kouloumbi N. , Soulis E.
Published: July 2002

The aim of the present work was to compare the performance of two coating systems applied on steel specimens. The first of them demands sandblasting pretreatment of the metal surface while the second one, which does not need it, leads to rust transformation. These systems were examined in three corrosive environments i.e. a geothermal fluid of low enthalpy, a 3.5 wt per cent NaCl solution and a 5wt per cent NaCl in a salt spray cabinet. The anticorrosive capability of the two coating systems was evaluated at predetermined exposure times by mass loss measurements of the steel substrate, by potentiodynamic polarization curves and by the half‐cell potential time evolution. Visual examination of the degree of rusting and blistering was also carried out. The results indicate that both coating systems exhibit almost similar protective behavior under the same conditions of pretreatment. In all cases, the corrosion rate increases with the increase of the surface roughness.
Individualizing employee relations
Authors: Welch Roger , Leighton Patricia
Published: July 2002

Focuses on the introduction of personal contracts to replace terms and conditions of employment derived from collective agreements in light of the findings from three surveys of employer organizations conducted in 1991/92, 1994/95 and 1995/96 by the Employment Relations R&D Centre at Anglia Polytechnic University. Argues that personal contracts reflect employer power and preferences rather than providing a mechanism for the empowerment of the individual employee through creating or increasing the ability of the individual to determine their terms and conditions of employment. Discusses the political and legal background to the decline in trade union power at the workplace. Contends that a real empowerment of employees is best achieved within a collectivist framework and is thus dependent on the re‐establishment and strengthening of individual and collective rights at work.
Managing key resources and capabilities: pinpointing the added value of corporate real estate management
Authors: Krumm Peter J.M.M. , Dewulf Geert , de Jonge Hans
Published: July 2002

Up to the 1980s the corporate competitive advantage was primarily focused on adapting the corporation to the (changing) environment. In the last decades corporations have become more aware of their resources and capabilities, and of the benefits of managerial attention towards managing the corporate assets. The transition from a passive, reactive attitude towards a proactive service oriented organisation proves to be a difficult task. This paper analyses the transition and describes an effort to identify products and services contributing to the added value of corporate real estate management to the bottom line of the corporation.
Danish Technological Institute SME sector networking model
Authors: Chaston Ian
Published: July 2002

In the late 1980s, the Danish Technological Institute received
funding to examine whether networking might provide a mechanism through
which to promote survival and growth among SME (small to medium‐sized
enterprises) sector firms. To overcome the absence of a large‐firm hub
in the SME sector, the institute evolved a five‐phase model in which an
independent individual external to the potential network became
responsible for brokering the interfirm co‐operation process. Plymouth
Business School, in collaboration with the institute′s UK subsidiary, UK
Business Net, undertook a study to gain further understanding of this
problem. Describes the nature of identified provision gaps and provides
the basis for evolving a detailed specification of the competences
required of a network broker. This knowledge permitted the redesign of
the broker competency development programme. Early results from
implementation of the new system indicate a significant improvement in
the capability of brokers to fulfil their assigned role in utilizing
networking as a potential mechanism for enhancing SME‐sector growth.
Automatic programming of cellular automata: identification approach
Authors: Adamatzky Andrew
Published: July 2002

To program cellular automata is to define cell neighbourhood and cell‐state transition rules in order to design an automation which exhibits determined patterns in its evolution or which transforms a given image into another image. In general, a tool for the automatic programming of cellular automata should translate the tuple (source‐configuration) → (target‐configuration) into a set of cell‐state transition rules. This is a problem which has not been completely solved yet. Attempts to show examples of automatic programming of cellular automata using identification algorithms. Results obtained can be used in the design of massively parallel processors with cellular‐automata architecture and a conventional, as well as non‐traditional (e.g. molecular and chemical), elementary base.
Assuring quality in management education: the Indian context
Authors: Jagadeesh R.
Published: July 2002

The increasing demand for postgraduate education in management in India has resulted in a steep rise in the number of institutes offering such education. However, the quality of education offered in many institutes is seriously being debated by students and prospective employers. The efforts to improve quality appear minimal, resulting in little or no improvement in quality. Provides a summary of status of quality in management education and critically analyses the issue of quality with the backdrop of problems, constraints, and conflicts. Further, the paper describes the structure and pattern of post‐graduate management education as offered in India, along with a description of regulatory agencies existing in the country to monitor the standards of management education. Towards the end, suggests appropriate solutions with several alternatives, to improve quality, discussing also their feasibility. The general objective is to provide help to develop strategies for improving quality of postgraduate education in management.
The evolution of software pricing: from box licenses to application service provider models
Authors: Bontis Nick , Chung Honsan
Published: July 2002

Software is the intellectual capital output of the codified knowledge of a programming team. The development cost is high, but the variable cost of sale is substantially lower (negligible) than for hard goods. Unfortunately, there does not exist a valid or reliable measure to value software. The trend has been to align pricing to the activities that buyers realize value from. However, new architectures change the nature of where value is realized and how service becomes part of the equation. There does not exist a perfect generic pricing model. Vendors must understand the value they provide to their customers and create a price structure that aligns pricing with value realization, but more importantly facilitates their business objectives of the product (and service).
An Experimental Investigation of the Transient Characteristics on a Flat-Plate Heat Pipe During Startup and Shutdown Operations
Authors: Wang Y. , Vafai K.
Published: July 2002

This work presents an experimental investigation of the thermal performance of a flat-plate heat pipe during startup and shutdown operations. Using the analytical model developed in a previously study, analytical and experimental results on the effect of input power and cooling heat transfer coefficient on the thermal performance of the heat pipe are presented and discussed. The results indicate that the wick in the evaporator section provides the largest resistance to the heat transfer process followed by the wick in the condenser section. It is found that the heat transfer coefficient has an insignificant effect on the maximum temperature difference across the heat pipe where this difference refers to the maximum difference on the outside surfaces of the flat-plate heat pipe. However, as expected, the input heat flux has a substantial effect on the temperature rise where the temperature rise refers to the temperature increase on the outside surface of the heat pipe. It is found that the temperature difference across the heat pipe depends mainly on the input power. The heat transfer coefficient strongly affects the time it takes to reach steady state while input power has a substantially smaller effect. Empirical correlations for the maximum temperature rise, the maximum temperature difference and the time constants are obtained. The experimental results are compared with the analytical results and are found to be in very good agreement. [S0022-1481(00)01803-X]
Estimated Flow Resistance Increase in a Spiral Human Coronary Artery Segment
Authors: Back L. H. , Banerjee R. K.
Published: July 2002

Coronary flow estimates were made for a spiral coronary artery segment (identified from a post-mortem replica casting) by using a modified Dean number based on the approximate coil radius of curvature, as suggested earlier. The estimates were found to correlate experimental pressure drop data for helical coiled tubes. Over a physiological range of mean Reynolds numbers from 100 to 400 for blood flow through main coronary arteries, estimates of the flow resistance increase relative to a straight lumen segment ranged from about 20 to 80 percent, and were of similar magnitude to those found in a flow study in a sinuous coronary vessel segment with no spiral. [S0148-0731(00)01706-4]
Coupled Helmholtz Resonators for Acoustic Attenuation
Authors: Griffin Steve , Lane Steven A. , Huybrechts Steve
Published: July 2002

Helmholtz resonators are used in a variety of applications to reduce the transmission of unwanted sound. This work demonstrates that mechanically coupled resonators can be used to design a particular transmission loss response, provide a wider bandwidth of attenuation, and adapt the transmission loss characteristics of a structure to attenuate disturbances of varying frequency. An analytical model is developed for a single, coupled resonator system mounted on a one-dimensional duct. Experiments are conducted on a similar system that uses a thin membrane to couple the resonator volumes. A simplistic model of the membrane is presented to estimate equivalent “piston” properties from measured physical properties. Experiments confirm that the coupled resonator system behaves as predicted by the model simulations, and that the transmission loss can be shaped by adjusting the mass or stiffness of the coupling member. The experimental results also illustrate the structural-acoustic coupling effects between the resonators and the membrane, and indicate that a more inclusive model of the membrane and acoustic dynamics is required in order to accurately predict the resonator transmission loss.
Design and Test of a Semi-Passive Flow Control Device for Inlet Distortion Suppression
Authors: Jaw Link C. , Cousins William T. , Wu Dong N. , Bryg David J.
Published: July 2002

Advanced turbine engines often operate with reduced stability margin to increase performance. Aircraft engine temperature and pressure inlet distortion have a major effect upon the stability of the compression system. Suppression of inlet distortion can provide a greater stability margin for the engine, thereby reducing operability restrictions on the engine by allowing closer operation to the stability limit. SMI has designed and tested a semi-passive distortion suppression system. The system uses flow injection to modify temperature and pressure inlet distortion. The prototype system was tested on a Honeywell T55 compressor rig. This paper presents both the design of the system and the test results. The test results show that this semi-passive distortion suppression system was able to reduce the surge margin degradation caused by the presence of pressure or temperature distortion. Special design considerations for this type of system are discussed, based upon the results of the prototype test. It is shown that distortion control can be a viable addition to the design of an aircraft engine.
Interoperability Standards in the Semantic Web
Authors: Ray Steven R.
Published: July 2002

The growth in the use of the Internet brings with it an increase in the number of interconnections among information systems supporting the manufacturing supply chain as well as other businesses. Each of these interconnections must be carefully prescribed to ensure interoperability. However, the sheer number of interconnections and the resulting complexity threaten to overwhelm the ability of the standards community or industry to provide the necessary specifications—a way out of this impasse must be found. This paper outlines the elements of an approach and the technology to move toward self-integrating systems, wherein the systems negotiate meaningful interfaces as needed in a dynamic environment.
Study of Surface Residual Stress by Three-Dimensional Displacement Data at a Single Point in Hole Drilling Method
Authors: Wu Z. , Lu J.
Published: July 2002

A method combining moire´ interferometry, Twyman–Green interferometry, and blind hole drilling method is proposed for simple and accurate determination of residual stress. The relationship between the three-dimensional surface displacements produced by introducing a blind hole and the corresponding residual stress is established by employing the Fourier expansion solution containing a set of undetermined coefficients. The coefficients are calibrated by 3D finite element method. The surface in-plane displacements Ux,Uy, and the out-of-plane displacement Uz produced by the relaxation of residual stress are measured by moire´ interferometry and Twyman–Green interferometry, respectively, after the hole-drilling procedure. The complete three-dimensional displacement data at any single point around the hole can be used for residual stress determination. The accuracy of the method is analyzed and the experimental procedure is described to determine the sign of residual stresses. As an implementation of the method, a shot peening residual stress problem is studied. [S0094-4289(00)00802-1]
A Study of Near-Field Entrainment in Gas Jets and Sprays Under Diesel Conditions
Authors: Post Scott , Iyer Venkatraman , Abraham John
Published: July 2002

This paper presents a computational study of entrainment characteristics in the near-field of gas jets under atmospheric and Diesel conditions and sprays under Diesel conditions. Computed flowfield information is used to estimate the rate of mass entrainment in the jet and derive the entrainment rate constant. The value of the entrainment rate constant is compared to experimental results in the literature. It is found that the computed values of the constant in the near-field are less than the values in the self-similar region of the jet with the values increasing monotonically from the orifice to the self-similar region. These results are consistent with experimental results. In the case of sprays, it is found that it is difficult to arrive at firm conclusions because the results are sensitive to several parameters that are not well known and to the numerics. The computed results for sprays are also discussed relative to measurements in sprays quoted in the literature. [S0098-2202(00)00802-6]
Method for atomic-layer-resolved measurement of polarization fields by nuclear magnetic resonance
Authors: Kempf James G. , Weitekamp Daniel P.
Published: July 2002

A nuclear magnetic resonance (NMR) method of probing the dielectric response to an alternating electric field is described, which is applicable to noncentrosymmetric sites with nuclear spin I>1/2. A radio-frequency electric field induces a linear quadrupole Stark effect at a multiple of the nuclear Larmor frequency. This perturbation is applied in the windows of an NMR multiple-pulse line-narrowing sequence in such a way that the resulting nonsecular spin interactions are observed as first-order quadrupole satellites, free of line broadening by the usual dominant static interactions. A simulation of the Ga69 spectrum for the nuclei within the two-dimensional electron gas of a 10 nm quantum well predicts resolution of individual atomic layers in single devices due to the spatial dependence of the polarization response of the quantum-confined carriers to the applied field. This method is part of a more general strategy, perturbations observed with enhanced resolution NMR. Experimentally realized examples in GaAs include spectrally resolving electron probability densities surrounding optically relevant point defects and probing the changes in radial electric field associated with the light-on and light-off states of these shallow traps. Adequate sensitivity for such experiments in individual epitaxial structures is achieved by optical nuclear polarization followed by time-domain NMR observed via nuclear Larmor-beat detection of luminescence.
Theory and Practice of Electroslag Melting
Authors: Mitchell A.
Published: July 2002

The mechanisms of heat transfer and heat generation in an electroslag process are considered and related to operating characteristics of the process. It is concluded that the form of heat transfer in the slag/mold wall region has a profound effect on the ingot surface. Also, it is noted that the presence of the slag layer has an over-all effect on the heat balance which accounts for the shallow ingot pool-profiles found in ESR ingots. The nature of chemical reactions in the electroslag process is briefly discussed in relation to the oxygen content of ESR ingots. Finally, the synergistic character of ESR process parameters is illustrated by considering the effect of power variations on the ingot solidification pattern.
New Developments in Plasma Arc Melting
Authors: Bhat G. K.
Published: July 2002

Designs of plasma arc melting and plasma arc remelting systems available for metal refining, scrap recycling, cast structure improvement, and, in general, for the manufacture of very high quality ferrous and nonferrous metal alloys are reviewed. The advantages of plasma melting and remelting techniques in comparison to the various primary and secondary melting techniques are discussed. Data relative to the materials produced by this special melting technique are provided.
Detachable (111) Cu Films Formed in Ultrahigh Vacuum
Authors: Horng C. T. , Vook R. W.
Published: July 2002

Epitaxial Cu films 1200 Å thick were formed on evaporated (111) NaCl films in an ultrahigh vacuum RHEED camera. Information on the surface structure, microstructure, and surface smoothness was obtained by in situ RHEED techniques. The microstructure of the Cu films was also studied by transmission electron microscopy. (111) Cu films were doubly positioned. The smoothness of the films increased with increasing Cu deposition rate. The microstructure of the as-deposited Cu films also depended upon the deposition rate. Annealing the Cu films improved their perfection. However, the final microstructure of the annealed films was independent of the initial deposition rate. These annealed Cu layers were used as substrates for the epitaxial growth of Ag films several monolayers thick.
Purification of rare gases and the measurement of low residual impurity levels
Authors: Rosai L. , Borghi M.
Published: July 2002

A system has been constructed for the quantitative measurement of low-impurity levels in rare gases at both above and below atmospheric pressure. This system, based on a gas chromatograph with metastable helium detectors, allows measurements to be made down to some tens of ppb impurity levels of all active gases, with good reproducibility. The technique has been used to determine the properties of a new type of single-stage rare gas purifier whose working principle is the chemical sorption of the active gases by means of a gettering material held at a suitable temperature. The purification efficiency is usually greater than 98% and the output impurity levels can be maintained at less than 1–3 ppm for long times.
Correlation between the chemical compositions and optical properties of AlSixNy embedded layer for attenuated phase-shifting mask in 193 nm and the modification of the R–T method for measuring n and k
Authors: Lin Cheng-ming , Loong Wen-an
Published: July 2002

The formation and variation of AlN, Si3N4, and nitride compositions in AlSixNy (x∼0.31, y∼0.51) embedded material have been shown to correlate with its optical properties. The increasing content of AlN, Si3N4, and nitrides will increase n and decrease k of AlSixNy. A simple and effective correction of measured reflectance R% and transmittance T% based on scalar scattering theory has been applied to the R–T method for determining n and k of embedded layers for 193 nm lithography masks. A 0.2 μm etched pattern of an AlSixNy embedded layer on an oxide/Si wafer substrate was successfully fabricated.
Influence of Ar+ ion bombardment on the chemical states of SrBi2Ta2O9 thin films fabricated by metalorganic decomposition
Authors: Park Yoon-Baek , Min Kyung-youl , Cho Kwang-Jun , Heo Sung , Lim Choul-Ho , Lee Moon-Keun , Lee Tae-Kwon , Kim Ho-Joung , Lee Soun-Young , Kim Yil-Wook
Published: July 2002

The SrBi2Ta2O9 (SBT) films studied for this report were prepared by metalorganic decomposition. The SBT thin film, which belongs to a Bi-layered perovskite structure where double Ta–O octahedron layers are sandwiched between (Bi2O2)2+ layers, was analyzed to characterize chemical states using x-ray photoelectron spectroscopy during depth-profiling analysis. When sputter etching was performed on the SBT film by Ar+ ion bombardment, the chemical states of constituents in the SBT film were changed as a function of the applied Ar+ ion-beam energy. Among the constituents of the SBT film, the Sr 3d peak was changed slightly by the change of Ar+ ion-beam energies. On the other hand, the changes of Ta 4f and Bi 4f peaks obviously depended on the applied Ar+ ion-beam energies. In particular, the Bi 4f peak changed dramatically from Bi–O states to Bi metallic states by the lower Ar+ ion-beam energies than in the cases of Sr and Ta. This change of chemical states of the SBT film resulted from the preferential sputtering of oxygen atoms. Following our present study, preferential sputtering of oxygen atoms was found to depend on the thermal stability and mass difference between oxygen and each constituent within the SBT films.
Simple vacuum heater and its application for annealing TiO2 films
Authors: Liu Chian , Macrander A.
Published: July 2002

A simple lamp heater design and use of permanent magnets to mount the heater to a commercial sputter deposition system are reported. The heater was applied to anneal a TiO2 thin film sample up to 350 °C. The annealing effect was evaluated using spectroscopic ellipsometry. The results were compared with that of another TiO2 sample grown under identical conditions but without aftergrowth annealing. The TiO2 samples were made by using reactive sputtering on a pure Ti target.
Secondary electron emission of MgO thin layers prepared by the spin coating method
Authors: Lee Jeonghee , Jeong Taewon , Yu SeGi , Jin Sunghwan , Heo Jungna , Yi Whikun , Kim J. M.
Published: July 2002

Three series of MgO thin films were prepared by the spin coating of MgO precursor solutions (aqueous and organic based solutions) and by electron-beam evaporation. The quality of the films coated on the Si (100) substrate was characterized by observing crystallinity and surface roughness of the films. The measurement of the secondary electron emission (SEE) yield of the MgO films does not reveal any significant dependence on the MgO film fabrication process. However, it was found that the magnitude of the SEE yield is strongly dependent on the sample bias voltage. The maximum SEE yield of over 6 was obtained for the films prepared by both aqueous and organic based solutions. MgO layer formation by precursor solutions is a promising method considering the fact of its easiness and convenience, which also gives a relatively large SEE yield comparable to the MgO layer prepared by electron-beam evaporation.
Estimates of differential sputtering yields for deposition applications
Authors: Stepanova M. , Dew S. K.
Published: July 2002

Angular and angle-resolved energy distributions of neutral atoms sputtered from elemental targets under ion bombardment are investigated by numerical and analytic modeling. Special emphasis is made on sub-keV ion bombardment, which is typical for sputter deposition sources. Scaling laws that define the distribution anisotropies are formulated. An approximate semiempirical description is suggested for anisotropic energy distributions.
Energy deposition and transfer in electron-beam lithography
Authors: Wu Bo , Neureuther Andrew R.
Published: July 2002

An analytical electron-resist interaction (ERI) model is developed based on detailed investigation of secondary electron production and binding energy related exposure events. Analysis shows that 80% of the exposure events are directly caused by secondary electrons for 100 keV primary electron energy. The number of secondary electrons and further cascade electrons is 1/20 and 1/300, respectively, of the incoming electrons. An algebraic expression is derived to describe the spatial distribution of the exposure events. The ERI model can be extended to chemically amplified resists.
Antireflection coatings for solar cells
Authors: Iles P. A.
Published: July 2002

The design factors, materials, and methods used to provide antireflection coatings on solar cells are described. The dependence of coating properties on the cell requirements is discussed. The methods used are well understood, and a firm basis exists for evaluation of impoved methods or materials for reducing cell reflectance.
Heat exchanges and columnar growth in electron-beam evaporation of silicon films for solar cell applications
Authors: Dey S. K. , Delahoy A. E. , Anderson W. A.
Published: July 2002

Heat exchanges in electron-beam evaporation of polycrystalline Si films are studied for the first time using an electrical model. The analysis is useful for evaluating the growth kinetics of the film which influence the diameter of the columnar structure. It is shown that Si deposition causes an unsteady thermal state resulting from the radiative interaction of the substrate with the source and adjoining system parts. The calculated values of the heat exchange rates between source, substrate and enclosure, and the temperature gradient along the substrate, are in reasonable agreement with the measured parameters. Columnar films up to 27 μm in thickness, 6μm in column diameter, and with 〈110〉 preferred orientation, have been produced by e-beam deposition of Si on Al-coated substrates at temperatures ranging from 400° to 600°C. SEM micrographs are included showing columnar structure, effects of etching, and previously unreported growth features and the dependence of the column axis on the direction of the vapor stream. The influence of deposition parameters on the column diameter is discussed. The absence of Al near the film surface, as determined by Auger analysis, precludes the possibiliy of liquid-phase crystallization in the present study.
Polycrystalline silicon on tungsten substrates
Authors: Bevolo A. J. , Schmidt F. A. , Shanks H. R. , Campisi G. J.
Published: July 2002

Thin films of electron-beam-vaporized silicon were deposited on fine-grained tungsten substrates under a pressure of ∠1×10−10 Torr. Mass spectra from a quadrapole residual gas analyzer were used to determine the partial pressure of 13 residual gases during each processing step. During separate silicon depositions, the atomically clean substrates were maintained at various temperatures between 400° and 780° C and deposition rates were between 20 and 630 Å min−1. Surface contamination and interdiffusion wer monitored by in situ Auger electron spectrometry before and after cleaning, deposition, and annealing. Auger depth profiling, x-ray analysis, and SEM in the topographic and channeling modes, were utilized to characterize the samples with respect to silicon–metal interface, interdiffusion, silicide formation, and grain size of silicon. The onset of silicide formation was found to occur at approximately 625° C. Above this temperature tungsten silicides were formed at a rate faster than the silicon deposition. Fine-grain silicon films were obtained at lower temperatures.
Issues in fabricating electron devices with submicrometer dimensions
Authors: Henderson R. C. , Mayer D. C. , Nash J. G.
Published: July 2002

Electron beam lithographic machines are being used to make prototype devices with submicrometer critical dimensions. However, building these devices requires developing new techniques of etching, and pattern overlay. Experience with MOS devices illustrates these needs. Plasma etching and self-aligning ion implantation techniques are used for dimensional control. Electron beam alignment strategies, involving the use of high-atomic-number benchmarks, have been developed for accurate registration of patterns. These techniques have been successfully applied to various modifications of MOS technology such as n- or p-channel and CMOS/SOS. Testing prototype devices, such as ring oscillators and charge coupled devices, has confirmed the higher speed and lower power consumption expected from reducing the size of these structures.
Single-reflection layer-scattering theory of low energy electron diffraction spectra
Authors: Hjalmarson Harold P. , Dow John D. , Mrstik B. J.
Published: July 2002

A simple general method for computing medium and low energy electron diffraction (LEED) spectra of layered materials has been developed for application to transition metal dichalcogenides. Electron transmission and reflection coefficients for each individual sheet of atoms are computed; the separate sheets are grouped into sandwiches which are stacked upon one another to form the crystal; the intersheet scattering is treated with the single-reflection approximation. For an unrelaxed lattice whose sandwiches are separated by the distance b and whose intrasandwich layers are separated by a, the scattered electron intensity is ‖ f (a)  ‖ 2 S (b), where f (a) is the single-sandwich form factor for the outermost sandwich. Lattice relaxation of the surface sandwich slightly modifies this result. The static structure factor S (b), which is a spiked function of energy and contains mainly bulk structural information, produces the principal peaks in the intensity versus energy spectrum, but the surface sandwich reflectivity ‖ f (a)  ‖ 2 smoothly modulates the peak intensities and contains most of the surface structure information. This method of fitting ‖ f (a)  ‖ 2 should be contrasted with most LEED analyses that concentrate on fitting peaks [which are related to S (b) and actually contain little surface structure information]. This simple single-reflection analysis of the surface structure is confirmed by a complete multiple scattering calculation.
Monte-Carlo calculations of backscattered electrons at registration marks
Authors: Stephani D.
Published: July 2002

Using the Monte–Carlo model given by Kyser and Murata image formation by backscattered electrons of three types of registration marks has been simulated. The marks considered consist of surface transitions in a silicon substrate, i.e., a step of 1 μm, a groove with vertical walls of 1 μm depth and 2 μm width and the inversion a bar of the same size with vertical walls. The primary electron beam was assumed to have an energy of 20 keV and a Gaussian distribution with FWHM of 0.1 μm. It has been found from the calculations, that the image of the three marks is primarily formed by the changing number of backscattered electrons. The contribution of the changing exit energy is of negligible influence. The contrast obtained in the image of the three marks decreases with increasing take off angle of the backscattered electrons. Furthermore, it is shown that a summing signal is superior to any difference signal, both derived with respect to the azimuthal angle.
High resolution electron-beam lithography on thin films
Authors: Adesida I. , Everhart T. E. , Shimizu R.
Published: July 2002

The influence of electron scattering on the resolution of electron-beam lithography has been studied. Theoretically, we have used two different Monte-Carlo approaches to study the spatial extent of energy dissipation in a thin film of electron sensitive polymer film coated on various thicknesses of silicon substrates. The two Monte-Carlo approaches are the conventional continuous-slowing-down approximation approach and the direct simulation approach in which individual inelastic scattering is taken into account. Experimentally, we have exposed lithographic patterns on the structures mentioned above. Agreement between both Monte-Carlo approaches and experiment is satisfactory. Results show that higher resolution in electron beam lithography can be achieved by using thin electron sensitive resist layers and thin substrates. Improvement in proximity effect is also obtained for thin structures.
Reactive Schottky barrier formation: The Pd/Si interface
Authors: Freeouf J. L. , Rubloff G. W. , Ho P. S. , Kuan T. S.
Published: July 2002

The initial stages of Schottky barrier formation for Pd on Si have been studied on atomically clean Si (111) and (100) surfaces. Comparison with thick reactively formed Pd2Si films establishes that the work function and electronic state density at the interface are predominately associated with the formation of a Pd2Si-like compound. These surface properties (as well as the lattice constant) vary with film thickness and annealing history. The observed changes in surface work function, electronic density of states, and lattice constant can be simply understood on the basis of stoichiometry variations in the silicide film in which the Pd2Si crystal structure is maintained. These results illustrate how aspects of interface reactions (compound formation, stoichiometry variations, surface segregation, etc.) may complicate experimental studies of interface formation in other systems (such as Pd/GaAs). Preliminary studies of ’’real’’ interfaces (native-oxide-covered substrates) illustrate the additional complications present in studies of such systems.