bluuebunny/crossref_metadata_2025 huggingface dataset:
Nanoscopic unequivocal analysis of twinned crystal structures with tetragonal or orthogonal unit cells by electron microdiffraction
Authors: Leicht M. , Remmele T. , Stenkamp D. , Strunk H. P.
Published: July 2002

In this study, a particular type of nanoscopic twinned crystal structure which can occur in any tetragonal or orthogonal crystal structure with a ratio of lattice parameters c/a=c/b=2 is presented. This type of twinning is characterized by twin components whosecaxes are oriented perpendicular to one another, by twin-habit planes parallel to {102} planes, and by a superstructure along the twin boundaries which is described by orthogonal unit cells with lattice parameters 2a, 2a,a. Furthermore, the suitability of electron microdiffraction, a diffraction technique of transmission electron microscopy (TEM) with a moderately convergent beam, for the analysis of such twinned crystal structures is demonstrated. For this demonstration, electron microdiffraction is applied to the chalcogenide compound Cu2In3Se5, which indeed exhibits the proposed twinned crystal structure.
Fourier modelling of the anisotropic line broadening of X-ray diffraction profiles due to line and plane lattice defects
Authors: Scardi Paolo , Leoni Matteo
Published: July 2002

A new model of line-profile broadening due to the effect of linear and planar lattice defects has been incorporated into the conventional Rietveld algorithm for the structural refinement and whole-pattern fitting of powder data. The proposed procedure, applied to face-centred cubic (f.c.c.) structure materials, permits better modelling, even in the case of anisotropic line broadening and otherhkl-dependent effects that can be related to the presence of dislocations and planar defects (stacking faults and twinning). Besides better quality of the profile fitting, detailed information on the defect structure can be produced: dislocation density and cut-off radius, stacking- and twin-fault probabilities can be refined together with the structural parameters. For each phase (in different samples or in multi-phase samples) the appropriatesize–strainmodel can be selected. The Fourier formalism, which is the basis of the line-profile modelling, also permits an easy adaptation to different lattice-defect models. New approaches can be easily introduced and tested against or together with the existing ones. Finally, the devised program can also be used for the simulation of powder patterns for materials with different types and amounts of line and plane lattice defects.
Magnetic subperiodic groups
Authors: Litvin Daniel B.
Published: July 2002

The magnetic subperiodic groups, the 31 magnetic frieze-group types, the 394 magnetic rod-group types and the 528 magnetic layer-group types, are derived and given symbols based on the symbols for the nonmagnetic subperiodic groups in Volume E of International Tables for Crystallography. The symbols are constructed in analogy to the Opechowski–Guccione symbols for magnetic space groups. Tables are given that list one group from each type. Each group is specified not only by its symbol but also by explicitly listing the coset representatives of the coset decomposition of the group with respect to its translational subgroup.
Dynamical scattering and electron diffraction from thin polymer lamellar crystals – poly(tert-butylethylene sulfide)
Authors: Dorset Douglas L. , Dumas Philippe , Cartier Laurent , Lotz Bernard
Published: July 2002

Strong violations of Friedel symmetry are observed in hk0 electron diffraction patterns from lamellar crystals of poly(tert-butylethylene sulfide) obtained at 120 kV. These deviations are largely explained by a multislice dynamical scattering calculation based on the crystal structure model. Further improvement is found when a secondary scattering component is added, in keeping with a perfect crystallite thickness less than that of the lamellar thickness. Despite the multiple-scattering perturbations, the frustrated chain packing can still be determined by direct methods followed by Fourier refinement. However, the Friedel-related intensities must be averaged before calculation of normalized structure factors.
Structural relationships in crystals accommodating different stereoisomers of 2-amino-3-methylpentanoic acid
Authors: Dalhus Bjørn , Görbitz Carl Henrik
Published: July 2002

A reinvestigation of the crystal structure of the 1:1 mixture of the two racemates DL-isoleucine and DL-allo-isoleucine, with a detailed analysis of interatomic distances between alternative side-chain positions, reveals a systematic distribution of the four stereoisomers in this crystal. Two different molecular chains exist in the crystal and each such chain accommodates a single diastereomeric pair only (L-isoleucine:D-allo-isoleucine or D-isoleucine:L-allo-isoleucine). The crystal is built up by a stacking of such chains in two dimensions and three different packing modes for the two types of chains are discussed. Crystallization experiments of the two individual racemates in the 1:1 mixture of DL-isoleucine:DL-allo-isoleucine have been undertaken. The structure of the racemate DL-isoleucine is presented. The molecular arrangements in this racemate and the 1:1 DL-isoleucine:DL-allo-isoleucine mixture are closely related. Furthermore, the spontaneous resolution of enantiomers upon crystallization of the other racemate, DL-allo-isoleucine, is rationalized on the basis of the aforementioned analysis of interatomic distances in the 1:1 DL-isoleucine:DL-allo-isoleucine complex. Structural data for a new L-isoleucine: D-allo-isoleucine complex are also given.
A novel intergrowth structure between ReO3-type and tetragonal tungsten bronze-type in the Zr/Nb/W/O system
Authors: Krumeich F. , Liedtke G. , Mader W.
Published: July 2002

The intergrowth structure of a zirconium niobium tungsten oxide has been determined by transmission electron microscopy methods. Electron diffraction patterns reveal the parameters of the monoclinic lattice: a = 19.0, b = 3.9 and c = 13.8 Å; β = 93.5°. Additional reflections in higher-order Laue zones indicate the presence of a diagonal glide plane, leading to a larger unit cell. A structure model of composition Zr
n
Nb8−2n
W12+n
O56 (0.5 < n < 1) has been derived from high-resolution lattice images. Alternating slabs of ReO3-type and of tetragonal tungsten bronze structure are intergrown coherently. Two five-membered rings of MO6 octahedra belonging to adjacent tetragonal tungsten bronze subcells are connected by having two octahedra in common. For the first time, this arrangement of double pentagons is observed in a regular structure.
Charge Density in Orthorhombic NiSO4.7H2O at Room Temperature and 25 K
Authors: Ptasiewicz-Bak H. , Olovsson I. , McIntyre G. J.
Published: July 2002

The charge-density distribution in the title compound nickel sulfate heptahydrate has been determined by multipole refinement against single-crystal X-ray intensity data. For the refinement at 25 K hydrogen positions and displacement parameters were fixed to values determined from neutron data. The charge density based on the deformation functions of all atoms in the structure is compared with the individual densities calculated from the deformation functions of only nickel or the separate water molecules. In this way the effects of simple superposition of the individual densities have been studied. The individual deformation density around nickel is in good qualitative agreement with that expected for an approximately octahedral Ni(H2O)6
2+ complex in a weak ligand field. However, the maximum densities are not found precisely in the planes defined by nickel and the six water ligands, which illustrates that it is necessary to consider the crystal field due to the whole crystalline environment. The individual densities of the water molecules show clear polarization of the lone-pair densities according to the coordination of the water molecules: tetrahedral coordination leads to two resolved lone-pair peaks, whereas planar trigonal coordination leads to just one single peak. Crystal data: NiSO4.7H2O, M

r
= 280.87, P212121, Z = 4. At T = 25 K: a = 6.706 (3), b = 11.796 (6), c = 11.949 (6) Å, V = 945 (1) Å3, D

x
= 1.977 Mg m−3. At 295 K: a = 6.751 (4), b = 11.746 (7), c = 12.003 (8) Å, V = 952 (1) Å3, D

x
= 1.959 Mg m−3. X-ray study: F(000) = 584, λ(Mo Kα) = 0.71069 Å, μ = 2.255 mm−1. At 25 K: R(F) = 0.014 for 10 185 reflections. At 295 K: R(F) = 0.015 for 5723 reflections. Neutron study at 25 K: λ = 1.215 Å, μ = 0.261 mm−1, R(F) = 0.034 for 1381 reflections.
Charge Density Study of 2-Pyridone
Authors: Yang H. W. , Craven B. M.
Published: July 2002

The crystal structure of 2-pyridone has been redetermined from high-resolution X-ray data collected at 123 K. The molecule is in the lactam form. Bond lengths (corrected for rigid-body libration) and angles have been determined with s.u.'s of 0.001 Å and 0.1°, respectively. The hydrogen-bonded cyclic dimers which occur in the vapor and in solution are absent in the crystal where molecules are linked by N—H...O hydrogen bonds to form puckered chains. There also appears to be a weaker C—H...O interaction (H...O, 2.57 Å) and weak C—H...π or van der Waals interactions occurring on both sides of the pyridone ring. Following a refinement of the structure assuming Stewart's rigid pseudo-atom model, the electronic charge density distribution in the crystal and its Laplacian have been calculated for atoms at rest. The total electrostatic potential has been mapped for an isolated molecule and the molecular dipole moment has been determined [8.8 (19)  D; 1D ≃ 3.33564 × 10−30 C m]. Critical points in the electron density have been located for the bonds within the molecule and for the molecular interactions cited above. For the C—H...π interactions, only the spherical components of the valence density for the pyridone ring atoms contribute effectively at the critical points. Hence, these may be better described as van der Waals interactions.
3,4:9,10-Perylenetetracarboxylic dianhydride (PTCDA) by electron crystallography
Authors: Ogawa Tetsuya , Kuwamoto Kiyoshi , Isoda Seiji , Kobayashi Takashi , Karl Norbert
Published: July 2002

The crystal structures of the α and β modifications of PTCDA were analyzed as projected structures along the a axes by electron crystallography using an imaging plate. The results for the α modification agree well with the sheet-and-stack structure obtained by X-ray diffraction by M. L. Kaplan et al. (private communication, full set of crystal structure data). Projected onto the (102) plane, which is parallel to the molecular sheets, the long molecular axis makes an angle of 42° with the b axis and the hexagonal benzene rings appear slightly elongated, indicating a slight inclination of the molecular plane from the (102) lattice plane. For the β modification, it was concluded that the molecules are aligned in a herringbone packing scheme on the (102) plane similar to that of the α modification, but with a slightly different angle of the long molecular axis with the b axis (38°).
Symmetry, pseudosymmetry and packing disorder in the alcohol solvates of L-leucyl-L-valine
Authors: Görbitz Carl Henrik , Torgersen Eirin
Published: July 2002

The dipeptide L-Leu-L-Val can crystallize as a hydrate in the hexagonal space group P65 [Görbitz & Gundersen (1996). Acta Chem. Scand.
50, 537–543], but forms 1:1 solvates when methanol, ethanol and 2-propanol are used as precipitating agents. The structures of these complexes can be divided into hydrophobic and hydrophilic layers. The alcohol molecules are embedded in the hydrophobic layers, but with the hydroxyl groups as crucial parts of the hydrogen-bonding network. L-Leucyl-L-valine–methanol (1/1) crystallizes in the space group P21 with Z = 2. L-Leucyl-L-valine–ethanol (1/1) has very special systematic absences, and the structure could not be solved with direct methods. Unraveling the actual build-up of the crystal was an unusual process involving modeling with molecular graphics programs. The solution shows a structure which formally belongs to the space group P21, with four dipeptide molecules and four solvent molecules in the asymmetric unit (Z = 8). Additional non-crystallographic symmetry in three dimensions fixes all cell angles, including β, to 90°. L-Leucyl-L-valine–2-propanol (1/1) is structurally closely related to the ethanol solvate, but owing to a rare type of packing disorder the length of the a axis is halved (Z = 4, P212121). The hydrogen-bonding pattern is still the same as in the ethanol solvate, which means that the hydrogen-bond periodicity along the a axis in the 2-propanol solvate is two unit-cell lengths.
Experimental evidence for the amino-group non-planarity in nitroanilines: neutron diffraction study of 2-methyl-5-nitroaniline at 100 K
Authors: Ellena Javier , Goeta Andrés E. , Howard Judith A. K. , Wilson Chick C. , Autino Juan C. , Punte Graciela
Published: July 2002

An appreciable degree of pyramidalization of the amine N atom is observed in the title compound. The existence of polar chains, induced by N—H...O synthons, is confirmed. C—H...O interactions, not noted in a previous X-ray study, were found to stabilize further the known head-to-tail assembling of the chains. The structure can be described as non-polar (101) layers, embodying chains interlinked by centrosymmetric dimers, connected by C(aryl)—H...π interactions. The latter are not present in m-nitroaniline, 2-methyl-4-nitroaniline and other related compounds with chains built from similar N—H...O synthons and assembled head-to-head. This finding implies that an obvious relationship between molecular recognition patterns and crystal structures should not be assumed.
Charge and momentum densities of cubic tetracyanoethylene and its insertion compounds
Authors: Bélemlilga Dominique , Gillet Jean-Michel , Becker Pierre J.
Published: July 2002

Charge and momentum electron densities provide complementary views of cohesive forces in solids. This is particularly true for molecular crystals. The examples of cubic tetracyanoethylene (1,1,2,2-ethenetetracarbonitrile) and its alkali-metal insertion compounds are analyzed from a theoretical point of view. Besides the usual deformation density maps and anisotropy of Compton profiles, it is shown that interaction charge density and interaction Compton profiles can be defined and reveal the subtleties of the intermolecular interactions. It is shown that owing to the large cavities in the crystal, alkali-metal atoms can be inserted, leading to a strong charge transfer to the molecules and to a metallic character; the mechanism of insertion is revealed well by the combination of charge and momentum density studies. The combination of the two techniques of X-ray diffraction and Compton scattering should be of great help in the study of rather weak interactions present in molecular solids.
Chiral recognition between host and guest: a binaphthyl-18-crown-6 host with D-phenylglycinium methyl ester perchlorate guest. A difficult structure solved with CRUNCH
Authors: Cram Donald J. , de Graaff R. A. G. , Knobler Carolyn B. , Lingenfelter David S. , Maverick Emily F. , Trueblood Kenneth N.
Published: July 2002

The complex between (R)-4,5,7,8,10,11,13,14,16,17-decahydro-2,19-diphenyldinaphtho[2,1-q:1′,2′-s][1,4,7,10,13,16]hexaoxa[2,5,8,11,14,17,19]cycloicosaheptene {Chemical Abstracts name: (R)-4,5,7,8,10,11,13,14,16,17-decahydro-2,19-diphenyldinaphtho[2,1-q:1′,2′-s][1,4,7,10,13,16]hexaoxacycloicosin} and D-2-phenylglycinium methyl ester perchlorate, C9H12NO_2^+.ClO_4^-.C42H40O6.H2O, crystallizes in the orthorhombic space group P212121 with two C9H12NO_2^+.C42H40O6 complexes, two ClO_4^- ions and two molecules of water in the asymmetric unit. Crystal data: M

r
= 924.44, a = 23.048 (7), b = 34.383 (6), c = 11.992 (6) Å, V = 9503 (6) Å3, Z = 8, D

x
= 1.292 Mg m−3, F(000) = 3904, μ(Cu Kα) = 1.261 mm−1, T = 175 K, R = 0.0896 for all 7784 reflections, 1208 parameters refined in three blocks with 29 restraints. Nearly twenty years elapsed between the first data collection and the solution of the structure with the direct-methods program CRUNCH. The structural details are of interest because enantiomers of this host show a high degree of discrimination between enantiomers of α-amino acids and their esters. The crystal structure demonstrates the influence of C—H...O and C—H...π interactions on the unexpected orientation of the guest in the host cavity. The same orientation is found in both of the unique complexes, and the geometric details are in agreement with solution studies.
Modulated structure of Ag2SnO3 studied by high-resolution electron microscopy
Authors: Oku Takeo , Carlsson Anna , Bovin Jan-Olov , Svensson Christer , Wallenberg L. Reine , Linke Christoph , Jansen Martin
Published: July 2002

The modulated structure of Ag2SnO3, disilver tin trioxide, was investigated by high-resolution electron microscopy and electron diffraction along four different directions. Electron diffraction showed an incommensurate one-dimensional modulated structure with a modulation wavevector of 1/6.4a*. High-resolution images showed a large number of superstructure domains with the size range 10–100 nm and orientations related by hexagonal rotation. The modulation was determined to be displacements along the c axis of the Ag atoms both in octahedral and linear coordination. An approximate structure model with a commensurate sixfold superstructure, with an orthorhombic cell (P212121, a = 2.922, b = 1.267, c = 0.562 nm), is proposed. Calculated images and electron diffraction patterns, based on this model, agree well with experimental observations.
The application of non-systematic many-beam dynamic effects to structure factor determination
Authors: Gjønnes J. , Høier R.
Published: July 2002

A method for utilizing non-systematic many-beam dynamic effects for determination of accurate relations between Fourier potentials is described. The effects which are used can be understood and described in terms of three-beam interactions; although quantitative evaluation is based on more interacting beams. The effects are most readily observed in Kikuchi patterns; experimental patterns from silicon are used as an example.
Melting Points of Lysozyme and Ribonuclease A Crystals Correlated with Protein Unfolding: a Raman Spectroscopic Study
Authors: Jacob J. , Krafft C. , Welfle K. , Welfle H. , Saenger W.
Published: July 2002

The effects of a temperature increase on monoclinic and tetragonal lysozyme single crystals were investigated by polarizing microscopy, X-ray diffraction and laser Raman spectroscopy. To prevent dissolution, the mother liquor was removed, and the crystals were covered by the oil poly-(chlorotrifluoroethylene). Upon heating, their macroscopic shape was stable beyond 453 K but a change (or loss) of birefringence was observed around 352 and 367 K for the tetragonal and monoclinic crystal forms, respectively, which is associated with tighter packing and higher crystal forces in monoclinic lysozyme. Raman spectral changes in the amide I and amide III regions indicated denaturation of the protein within the crystalline environment at temperature where birefringence changes, and differences in the S—S band suggest that in monoclinic lysozyme, denaturation is accompanied with disruption of some S—S bonds. Comparison with thermal denaturation and gel formation (\beta-aggregation) of lysozyme in solution indicates that intermolecular interactions are mainly involved in the stabilization of the denatured lysozyme crystals. The behavior of ribonuclease A is very different. This protein unfolds and refolds reversibly in solution and its crystals melt at the unfolding temperature at 333 K, i.e. loss of structure induces breakdown of crystal lattice and macroscopic shape. Although the crystal lattice of proteins is stabilized by only few intermolecular contacts, its breakdown with increasing temperature is primarily a result of thermal unfolding of the polypeptide chains.
Crystallization and preliminary X-ray diffraction studies of piratoxin III, a D-49 phospholipase A2 from the venom of Bothrops pirajai
Authors: Wen-Hwa Lee , Toyama Marcos H. , Soares Andreimar M. , Giglio José R. , Marangoni Sérgio , Polikarpov Igor
Published: July 2002

Piratoxin III (PrTX-III) is a phospholipase A2 (PLA2, E.C. 3.1.1.4, phosphatide sn-2 acylhydrolase) isolated from Bothrops pirajai. Crystals of PrTX-III were obtained using the vapour-diffusion technique and X-ray diffraction data have been collected to 2.7 Å resolution. The enzyme was crystallized in the space group C2 with unit-cell parameters a = 60.88, b = 100.75, c = 48.19 Å, β = 123.89°. A molecular-replacement solution of the structure has been found using bothropstoxin I from the venom of B. jararacussu as a search model.
S K- and Mo L-edge X-ray absorption spectroscopy to determine metal–ligand charge distribution in molybdenum–sulfur compounds
Authors: Rompel Annette , Cinco Roehl M. , Robblee John H. , Latimer Matthew J. , McFarlane Karen L. , Huang Jiong , Walters Marc A. , Yachandra Vittal K.
Published: July 2002

Mo L-edge and S K-edge X-ray absorption spectroscopy were applied to investigate the charge distribution between Mo and S in a series of Mo thiolate compounds, which serve as amide-sulfur H-bonding models and exhibit different redox potentials arising from polar group effects and ligand hydrogen bonds near the redox center. For all oxidized complexes, the S K-edge spectra exhibit a thiolate-based pre-edge feature centered at 2470.2 eV and the inflection point occurs at 2472.0 eV. No intense pre-edge feature is observed in the spectra for the reduced Mo model compounds and the energy shift of the S K-edge position depends on the S-ligand. Correlations between ligand charge density and the redox potential of the Mo-S cores are observed.
Verification of a distortion in the microstructure of GaN detected by EXAFS using ab initio density functional theory calculations
Authors: Dimakis Nicholas , Bunker Grant , Katsikini M. , Paloura E. C.
Published: July 2002

X-ray absorption fine structure (XAFS) measurements on a series of epitaxially grown GaN samples have shown a distortion in the microstructure of GaN. More specifically the central N atom is 4-fold coordinated but the four Ga atoms are not equidistant. It has been shown that 2.9 to 3.5 of them (depending on the growth conditions) are found in the expected from XRD distance of 1.94 Å and the remaining are at a distance longer by approximately 15%. Second derivative calculation of the conformation energy using the Density Functional Theory (DFT) is used to investigate if the symmetric GaN cluster as given by XRD is the most energetically favorable configuration and if not which distorted structure corresponds to the most energetically favorable one. A very good agreement between DFT results and experimental XAFS spectra has been found. Generalization this technique to other dislocated clusters is also discussed.
Chemical transferability of single- and multiple-scattering EXAFS Debye–Waller factors
Authors: Dimakis Nicholas , Bunker Grant
Published: July 2002

No abstract
Towards a limited XANES refinement in strongly correlated systems
Authors: Ignatov Alexander
Published: July 2002

Three components of O1 atom displacements have been derived from the direct fit of the polarized E||ab Cu K-edge XANES spectrum of Nd1.85Ce0.15CuO4-δ superconductor. The best fit is achieved for a 60 to 40% mixture of 2x2 undistorted antiferromagnetic and modified charge density wave (MCDW) domains. The local structure of the MSDW is characterized by correlated displacements of ΔO1||=0.12±0.04, ΔO1⊥=0.25±0.08, and ΔO1z=0.12±0.1 Å. An agreement factor over the range of 8980-9040 eV is 2-3 times smaller than it may be obtained from single-electron MS calculations. This improvement comes from accounting for many-body excitations and the relationship between electronic and local structure in the CuO2 planes.
2-Amino-4,6-bis(4-chlorophenylthio)pyrimidine
Authors: Lynch Daniel E. , McClenaghan Ian
Published: July 2002

The structure of the title compound, C32H22Cl4N6S4, (I), comprises two unique molecules that separately associateviaa three-centre N—H...N/S interaction to form two linear one-dimensional hydrogen-bonded chains. The dihedral angles between the two phenyl rings and the pyrimidine ring for each molecule are 84.6 (1) and 87.8 (1)°, and 83.9 (1) and 80.1 (1)°.
The changing face of the higher education student: proceedings of an Internet conference
Authors: Scoffield Susan
Published: July 2002

This paper is an account of the proceedings of an Internet conference which was sponsored by Education + Training. The conference identified a number of issues and questions arising from the increasingly complex environment of Higher Education. The changing characteristics of the relationship between the providers of Higher Education and its various customer markets and publics are discussed in the proceedings. Views, opinions and examples of responses to change were shared during the conference.
Smart sensor research at the French Laboratoire Central des Ponts et Chaussées
Authors: Ehrlich Jacques , Coche Georges , Zerrouki Amal
Published: July 2002

Highlights two works being carried out by the French Laboratoire Central des Ponts et Chaussées in the field of smart sensors. The first concerns the knowledge of loads applied to bridges in order to evaluate extreme load effects and fatigue load effects over their lifetime. To achieve these goals, a data acquisition system based on smart sensors extracting and classifying extrema in the traffic loads signal has been developed. The second concerns distributed systems software cost reduction by means of a generic model. The aim of the model is the design of a software generator for smart sensor‐based systems. The key of the system is in the description of an instrumentation plan under the form of a data dependence graph (DDG). The goal of the generator is to map and “execute” that DDG on the physical architecture according to the number of transducers, their affectation to the smart sensors and a PC‐based system controller.
Performance indicators as quality assurance: the Scottish Community Education PI scheme
Authors: McCulloch Kenneth , Tett Lyn
Published: July 2002

Examines the role of performance indicators (PIs) as a means of quality assurance. Uses, as a case study, the national scheme of performance indicators for Community Education Services in Scotland, and shows how the process of development led to a particular approach to evaluation. Considers the relationship of this scheme to other approaches to performance indicators in education contexts and develops an analytical framework. Explores the relationship between purpose, product and context, with particular reference to the ways in which practices and ideologies reflect, reproduce or subvert pre‐existing, unequal relations of power.
Tools for Stress Analysis of Microelectronic Structures
Authors: Mirman Boris
Published: July 2002

Tools and goals of microstructural stress analysis are reviewed. Common misconceptions regarding the analysis are explored. [S1043-7398(00)00703-9]
Edges of Regression and Limit Normal Point of Conjugate Surfaces1
Authors: Chen Ningxin
Published: July 2002

The presented paper utilizes the basic theory of the envelope surface in differential geometry to investigate the undercutting line, the contact boundary line and the limit normal point of conjugate surfaces in gearing. It is proved that (1) the edges of regression of the envelope surfaces are the undercutting line and the contact boundary line in theory of gearing respectively, and (2) the limit normal point is the common tangent point of the two edges of regression of the conjugate surfaces. New equations for the undercutting line, the contact boundary line and the limit normal point of the conjugate surfaces are developed based on the definition of the edges of regression. Numerical examples are taken for illustration of the above-mentioned concepts and equations. [S1050-0472(00)00104-5]
In-Plane Gravity Loading of a Circular Membrane
Authors: Tejeda R. O. , Lovell E. G. , Engelstad R. L.
Published: July 2002

This paper develops the displacement field for a circular membrane which is statically loaded by gravity acting in its plane. Coupled to the displacements are the stress and strain distributions. The solution is applicable to the modeling of next generation lithographic masks, ion-beam projection lithography masks in particular. [S0021-8936(00)00803-5]
Towards a Reynolds Equation for Gas Lubricated Bearings When Contact Occurs
Authors: Anaya-Dufresne M. , Sinclair G. B.
Published: July 2002

The various existing forms of Reynolds equation are known to yield pressure fields which are unbounded and nonphysical when contact occurs. With a view to developing a Reynolds equation that is suitable for contact, here we revisit Taylor’s plate scraping problem for incompressible flow. This problem has an infinite pressure where the scraper contacts the plate. By suitably modifying Maxwell’s slip condition, the scraping problem can be reformulated so as to lead to finite pressures. This is shown locally via asymptotics, and globally via convergence checks. The approach looks sufficiently promising to consider the further development needed for the compressible flow present in gas lubricated bearings.
Full-State Feedback Control of a Variable-Speed Wind Turbine: A Comparison of Periodic and Constant Gains
Authors: Stol Karl , Balas Mark
Published: July 2002

An investigation of the performance of a model-based periodic gain controller is presented for a two-bladed, variable-speed, horizontal-axis wind turbine. Performance is based on speed regulation using full-span collective blade pitch. The turbine is modeled with five degrees-of-freedom; tower fore-aft bending, nacelle yaw, rotor position, and flapwise bending of each blade. An attempt is made to quantify what model degrees-of-freedom make the system most periodic, using Floquet modal properties. This justifies the inclusion of yaw motion in the model. Optimal control ideas are adopted in the design of both periodic and constant gain full-state feedback controllers, based on a linearized periodic model. Upon comparison, no significant difference in performance is observed between the two types of control in speed regulation.
A Constraint Solving-Based Approach to Analyze 2D Geometric Problems With Interval Parameters
Authors: Joan-Arinyo R. , Mata N. , Soto-Riera A.
Published: July 2002

Many applications of geometric nature can be modeled by geometric problems defined by constraints in which the constraint parameters have interval uncertainty. In a previous work, we developed a method for solving geometric constraint problems where parameters are narrow intervals in the domain of the geometric problem. Based on this work, we present a new approach to solve more general problems with non-trivial-width interval parameters that may not necessarily be in the domain of the problem. We show how our approach is successfully applied to a number of problems like solving geometric problems with tolerances, checking constraint feasibility and analyzing link motion of planar mechanisms.
Estimation of Reference Misalignment of a Spur Gear and its Application to Profile and Lead Measurement
Authors: Su, Xiaogen , Menq, Chia-Hsiang , Houser Donald R.
Published: July 2002

In this paper, the effect of the reference misalignment on the tooth measurements of an involute spur gear is examined. Analytical relations between the profile/lead traces and the reference misalignment parameters are derived. These relations can be employed to estimate the misalignment parameters when three or more profile and lead traces are available. The estimated parameters may be subsequently used to remove the effect of the reference misalignment on the profile and lead traces. Experiments are conducted to verify the proposed method and to illustrate the applications of the developed approach.
Exact Analysis of Dynamic Sliding Indentation at any Constant Speed on an Orthotropic or Transversely Isotropic Half-Space
Authors: Brock L. M.
Published: July 2002

A plane-strain study of steady sliding by a smooth rigid indentor at any constant speed on a class of orthotropic or transversely isotropic half-spaces is performed. Exact solutions for the full displacement fields are constructed, and applied to the case of the generic parabolic indentor. The closed-form results obtained confirm previous observations that physically acceptable solutions arise for sliding speeds below the Rayleigh speed, for a single critical transonic speed, and for all supersonic speeds. Continuity of contact zone traction is lost for the latter two cases. Calculations for five representative materials indicate that contact zone width achieves minimum values at high, but not critical, subsonic sliding speeds. A key feature of the analysis is the factorization that gives, despite anisotropy, solution expressions that are rather simple in form. In particular, a compact function of the Rayleigh-type emerges that leads to a simple exact formula for the Rayleigh speed itself.
Forced Vibration Analysis for Damped Periodic Systems With One Nonlinear Disorder
Authors: Chan H. C. , Cai C. W. , Cheung Y. K.
Published: July 2002

The steady-state responses of damped periodic systems with finite or infinite degrees-of-freedom and one nonlinear disorder to harmonic excitation are investigated by using the Lindstedt-Poincare method and the U-transformation technique. The perturbation solutions with zero-order and first-order approximations, which involve a parameter n, i.e., the total number of subsystems, as well as the other structural parameters, are derived. When n approaches infinity, the limiting solutions are applicable to the system with infinite number of subsystems. For the zero-order approximation, there is an attenuation constant which denotes the ratio of amplitudes between any two adjacent subsystems. The attenuation constant is derived in an explicit form and calculated for several values of the damping coefficient and the ratio of the driving frequency to the lower limit of the pass band. [S0021-8936(00)01101-6]
The Clemson Limit Stress Diagram for Ductile Parts Subjected to Positive Mean Fatigue Loading
Authors: Wang Shyh-Jen , Dixon Marvin W. , Huey, Cecil O. , Chen Su-Chen
Published: July 2002

The Bagci, Gerber, Goodman, quadratic, and Soderberg diagrams are some of the diagrams proposed to serve as practical design tools for the design of ductile metals loaded in fatigue with positive mean and alternating stresses. However, all of these diagrams are either conservative, or have domains containing stress greater than yield strength of material. This paper presents the Clemson diagram, which has the same format as the aforementioned diagrams with the exception that the exponential power order varies with the material property. The Clemson diagram has a great potential to fit the experimental data and appears to better fit the limited data found in the open literature. A good initial approximation of an acceptable design for parts made of ductile ferrous materials can be obtained by using the proposed diagram. [S1050-0472(00)00301-9]
Statistical Analysis of Perfect Contact and Wear Durability Conditions of a Single-Degree-of-Freedom Contact Slider
Authors: Ono Kyosuke , Iida Kohei
Published: July 2002

In this paper, the design condition of a single-degree-of-freedom (1DOF) contact slider over a random wavy surface of a disk is analyzed statistically. It is numerically confirmed that when the slider is in contact with a disk, spacing variation histograms are close to Gaussian even if surface waviness histogram is not close to Gaussian. The design condition of the slider and the surface waviness necessary for perfect contact sliding is derived from 3σs<δ, where σs and δ are the standard deviation of spacing variation and the static penetrating depth, respectively, and it is verified both numerically and experimentally. The necessary condition for wear durability under uniform contact pad pressure is also derived. An example of the slider-to-disk interface design which satisfies both perfect contact sliding and wear durability is shown. In order to evaluate σs adequately, frequency response of slider must be integrated over the range from fr/2 to 2 fr where fr is the contact resonance frequency. It is found that a disk surface should be extremely smooth to satisfy both the perfect contact sliding and wear durability conditions. [S0742-4787(00)03001-0]
Vacuum Deposition of Thick Coatings and Free-Standing Parts Using Electron-Beam Evaporation
Authors: Chambers D. L. , Bower W. K.
Published: July 2002

Continued improvements in electron-beam evaporation technology have led to applications for vacuum deposition to apply thick coatings and to fabricate free-standing parts. The use of improved electron-beam guns, rod-type source feeders, high-capacity power supplies, and beam-sweep control components has permitted high-quality thick coatings and shapes to be continuously deposited in thicknesses from 0.010 in. to more than 0.100 in. The deposition of three materials using electron-beam heated sources is described. The materials are: magnesium, as a subliming material; gold, as an evaporating metallic element; and Type 304 stainless steel, as an alloy. Descriptions of the electron-beam equipment, the materials handling, the vacuum systems, the tooling, and rate monitors are presented, together with a discussion of the continuous-deposition process techniques. Evaporation–deposition parameters for the various materials and typical conditions for the film depositions are reported. Measurements were made to determine deposition rates at various electron-beam power levels for all of the deposited materials. The effects of the substrate temperature and the deposition rate on the deposited films were investigated and data are presented showing at several temperatures and rates. Metallographic analyses and mechanical property measurements are discussed showing the variation in coating characteristics as a function of the deposition conditions. A discussion of alloy deposition is included with a description of techniques used to deposit a specific alloy (Type 304 stainless steel) as an example of alloy deposition. A description is given of the equipment and process control used to deposit thick stainless-steel parts. Metallographic and chemical analyses of these deposits are reported, including the variations in alloy composition as a function of film thickness.
Preparation of AlN films by pulsed laser deposition using sintered aluminum nitride and elemental aluminum as raw materials
Authors: Wu J. D. , Sun J. , Ying Z. F. , Shi W. , Ling H. , Li F. M. , Zhou Z. Y. , Wang K. L. , Ding X. M.
Published: July 2002

Aluminum nitride films have been prepared on Si (100) substrates through two methods: basic pulsed laser deposition from sintered aluminum nitride ceramics and plasma-aided reactive pulsed laser deposition from elemental aluminum metal. The latter was performed in a nitrogen plasma environment generated from electron cyclotron resonance microwave discharge. The films deposited by both methods have been characterized by various techniques to examine the morphology and to determine the composition and structure. The formation of aluminum nitride compound was confirmed in the deposited films. The films prepared by basic pulsed laser deposition are found to contain oxygen impurities, while those obtained through the plasma aided method have exhibited a stoichiometric AlN composition. The films have shown better crystalline quality when prepared at higher temperatures, however, when aided by the nitrogen plasma the films contain pure AlN compound with much better crystalline quality even prepared at low temperatures. Mechanisms relevant to the deposition processes are also discussed with particular emphasis on the contributions of the nitrogen plasma to the film formation. A comparison of the different characteristic features associated with the films prepared by the two methods shows that the plasma aided method has reasonable advantages in preparing compound films.
Structure and mechanical properties of ion-plated thick films
Authors: Enomoto Yuji , Matsubara Kiyoshi
Published: July 2002

Copper and other metallic films deposited onto a vacuum-heat-treated tungsten substrate are prepared by ion plating for film thicknesses from 5 to 30 μ. The fracture cross section and surface morphology of films are examined by means of a scanning electron microscope. The structure of ion-plated films formed under usual plating conditions is, in general, a columnlike (or spongelike) structure containing a number of microporosities. In some cases, the layered structure of dense–porous is observed. When the ionization of metallic atoms is enhanced during the ion plating using three auxiliary cathodes with hot filaments, the film consists of dense and equiaxed structure. Further, the effect of film structure on mechanical properties of films (Knoop hardness, friction, and wear) is also examined.
Chemically induced enhancement of nucleation in noble metal deposition
Authors: Allara D. L. , Hebard A. F. , Padden F. J. , Nuzzo R. G. , Falcone D. R.
Published: July 2002

Organic disulfides, chemisorbed as monolayers on aluminum and silicon oxides, have been found to induce significant changes in the morphologies of thermally evaporated Au and Ag films for film thicknesses (mass average) up to 100–200 Å. Measurements of the electrical conductivities as a function of film thickness show a marked shift of the onset of conduction to lower thickness for films deposited on treated substrates compared to films on untreated substrates. Transmission electron microscopy shows that the conductivities correlate qualitatively with sample morphology. In particular, films on treated substrates show metal clusters of higher densities which connect at lower coverages than do films on untreated substrates.
Thermal desorption of strained monoatomic Ag and Au layers from Ru(001)
Authors: Niemantsverdriet J. W. , Dolle P. , Markert K. , Wandelt K.
Published: July 2002

Model-independent or complete analysis of thermal desorption spectra suggests, in agreement with low-energy electron diffraction, that attractive lateral interactions between Ag atoms on a Ru(001) substrate lead to island formation for Ag coverages above 0.15 ML, with zeroth-order desorption kinetics and coverage-independent activation energy of desorption E, and preexponential factor ν. For the system Au/Ru(001), on the other hand, E and ν decrease monotonically with coverage, indicating that Au–Au interactions on Ru(001) are repulsive. For ΘAg<0.15 and ΘAu<1 the systems exhibit a clear compensation effect between E and ν.
Effects of particle clouds in a plasma etch system on silicon dioxide wafer contamination
Authors: Collins S. M. , O’Hanlon J. F. , Carlile R. N.
Published: July 2002

Particle contamination of silicon dioxide wafers was studied in a Tegal MCR-1 etch system. The goal of the work was to understand the effect of ramping versus stepping the rf power and the effect of a magnetically induced local particle trap in close proximity to the wafer on wafer contamination. The effect of ramping the rf power versus not ramping the rf power on wafer contamination was studied to test a hypothesis that ramping the power would cause a reduction in wafer contamination [G. S. Selwyn, J. E. Heidenreich, and K. L. Haller, J. Vac. Sci. Technol. A 9, 2817 (1991)]. For this reactor the results were inconclusive, but suggested that gas flow patterns played a dominant role. Wafers were passed through an etch process with and without a magnetically induced particle trap. The results suggested particle deposition was increased in the presence of the trap, however, the number of particles added was of the same magnitude as the standard deviation.
Particle contamination characterization in a helicon plasma etching tool
Authors: Selwyn Gary S. , Bailey Andrew D.
Published: July 2002

There is much current interest regarding the formation, transport, charging, and behavior of particulate contamination in high density plasma tools, as these tools are generally regarded as the future of plasma processing for the semiconductor industry due to the need to obtain greater anisotropy and faster process rates concurrently with reduced surface damage. Because of the low pressures in which these tools typically operate (<5 mTorr), the likelihood of homogeneous nucleation processes leading to particle contamination problems is low. Similarly, the effect of ion drag is also expected to be greater, possibly leading to reduced particle trapping effects. Yet, few laser light scatter studies have been performed in high density plasma tools.

This study is the first in situ characterization of particle contamination in a plasma etching tool using a helicon source. It was performed during normal process conditions for poly-Si etching and also under intentionally altered process conditions designed to produce particles. The effect of a bipolar, electrostatic chuck on wafer particle deposition was also investigated. Results showed that under normal process conditions, few particles were deposited onto the wafer; those that were observed were attributed to thermal stress effects resulting in flaking of deposition films, probably on the quartz bell jar of the source. Results also suggest that the electrostatic chuck increased particle deposition when the clamping voltage was applied. No trapping was observed over the wafer or near the source. However, some trapped particles were observed below the wafer platform. These particles showed unusual motion, but probably have minimal effect on wafer contamination. The issues pertaining to particle contamination formation and transport in this high density plasma tool are discussed.
Quantitative uses of the x-ray photoelectron spectroscopy valence band region in the analysis of polymer blends
Authors: Thomas Elizabeth A. , Fulghum Julia E.
Published: July 2002

Valence band spectra from similar polymers frequently show significant differences in appearance. Recent improvements in x-ray photoelectron spectroscopy instrumentation allow for valence band (VB) spectra with good signal to noise to be rapidly acquired. This study utilizes the VB region for the quantitative determination of the surface composition of several binary polymer systems using multiple linear regression. The systems evaluated include: poly(vinyl chloride)/poly(methylmethacrylate) blends which phase separate, chemically derivatized poly(vinyl methyl ketone), miscible polybutylmethacrylate isomers used in a study of liquid crystal alignment, and acrylate copolymers whose surface composition has been quantified using time-of-flight secondary ion mass spectrometry. For systems in which comparisons to core level spectra are possible, good agreement is found between quantification of core level and valence band spectra.
Monte Carlo simulation of growth and decay processes in a cluster aggregation source
Authors: Briehl Boris , Urbassek Herbert M.
Published: July 2002

Using a spatially homogeneous Monte Carlo simulation, we model the agglomeration and fragmentation processes of Cu atoms and clusters in an Ar buffer gas. We model Cu dimer formation to occur via the stabilization of metastable Cu2* complexes by Cu or Ar atom collisions. In cluster growth and fragmentation, the heating and cooling effects caused by the binding and recoil energies are taken into account. In this scenario, we study the influence of the dwell time in the cluster source, the gas temperature, and the Cu and Ar densities on the cluster distribution. We find the cluster size distribution to follow a log-normal distribution. Both the average cluster size and the bound atom fraction increase monotonically with the dwell time in the source, until a saturation level is reached, in which cluster formation and decay balance each other. We find an optimum temperature window for the formation of large clusters: For smaller temperatures, collision processes are frozen in, while at larger temperatures, Ar collisions become inefficient for cluster cooling. It is furthermore shown that even a small initial dimer content in the clustering gas speeds up the clustering process considerably. Finally, we show by way of an example how to apply the present model to the description of cluster formation in a spatially inhomogeneous cylindrical aggregation source.