bluuebunny/crossref_metadata_2025 huggingface dataset:
5-Chloro- and 5-bromobenzfurazan 1-oxide revisited
Authors: Pink Maren , Britton Doyle
Published: July 2002

At room temperature the two title compounds are isomorphous. Both have a disordered structure that includes a major component, one of the title compounds, and a minor component, the 6-halo isomer, occurring at the same site in the crystal. When the chloro compound is cooled to as low as 98 K, there is no change in the structure and no significant change in the degree of disorder. When the bromo compound is cooled, it undergoes a second-order phase transition at 282 K to a second polymorph, structurally very similar, but with two molecules in the asymmetric unit. In both isomorphs and both polymorphs the molecules occur in two-dimensional layers that are essentially the same. In the low-temperature form of the bromo compound the layers have shifted relative to each other by approximately 0.7 Å in y. In the low-temperature form the disorder, which is still present after the transition, decreases as the temperature is lowered.
Structurally ferroelectric SrMgF4
Authors: Abrahams S. C.
Published: July 2002

The crystal structure of 0.06% Ce-doped SrMgF4, strontium magnesium tetrafluoride, reported by Ishizawa et al. [(2001), Acta Cryst. C57, 784–786]  is shown to satisfy the structural criteria for ferroelectricity and to have a predicted Curie temperature T

c
≃ l450 K. The estimated spontaneous polarization P

s
≃ 11 × 10−2 C m−2 is consistent with classification as a two-dimensional ferroelectric in which minor Δx and major Δy, Δz atomic coordinate component displacements are required for ferroelectric switching.
[MPh4][BPh4], M = P, As and Sb
Authors: Lloyd M. A. , Brock C. P.
Published: July 2002

The structures of [MPh4][BPh4], M = P, As and Sb, crystallize in a superstructure (I\overline 4, Z′ = 1/2) of the P\overline 421
c, Z′ = 1/4, structure known for MPh4, M = C, Si, Ge, Sn and Pb. The arrangement of the ions is the same as for CaWO4 (scheelite; I41/a, Z′ = 1/4), which is typical of many other ionic XYO4 structures. Crystals of [MPh4][BPh4] turn a pinkish amber when exposed to UV light; ESR spectra confirm that free radicals are generated.
Cristobalite-Related Phases in the NaAlO2–NaAlSiO4 System. II. A Commensurately Modulated Cubic Structure
Authors: Withers R. L. , Thompson J. G. , Melnitchenko A. , Palethorpe S. R.
Published: July 2002

The crystal structure of a new cubic cristobalite-related sodium aluminosilicate Na1.45Al1.45Si0.55O4 [P213, a = 14.553 (1) Å] has been modelled using a modulation wave approach and the model tested against X-ray powder diffraction data using the Rietveld method. Owing to there being 64 independent positional parameters and eight independent Na sites, refinement of the tetrahedral framework atom positions and Na occupancies was not possible. The framework was modelled successfully in terms of q
1 = 1\over 4〈020〉_p^*-type (p = parent) modulation waves with the requirement that the MO4 (M = Al0.725Si0.275) tetrahedra be as close to regular as possible. Na/vacancy ordering was modelled successfully in terms of q
2 = 1\over 4〈220〉_p^* modulation waves. Only the Na-atom positions were refined. The significance of this unique modulated cubic cristobalite-related structure and the possible insight it provides to understanding β-cristobalite are discussed.
Concerning inorganic crystal structure types
Authors: Bergerhoff G. , Berndt M. , Brandenburg K. , Degen T.
Published: July 2002

All representatives of an inorganic crystal structure type can be found systematically in the new database SICS (Standardized Inorganic Crystal Structures). It is derived from the Inorganic Crystal Structure Database (ICSD) by selecting the best determination of each phase. In addition, each entry is given in a standardized description and complemented by searchable descriptors \Delta, which give the difference between all structures of an isopointal set. Because of the large number of structures the full information on relationships present can only be found by means of the new database itself. Some examples are given here in printed form. The limitations and the possibilities of expansion of SICS in terms of the concept of `structure types' are demonstrated.
Paracrystalline lattice distortions and microdomains in manganese ferrites near the cubic-to-tetragonal transition
Authors: Červinka L. , Hosemann R. , Vogel W.
Published: July 2002

The line profiles of X-ray reflexions from different Mn
x
Fe3 − x
O4 samples were investigated. Sample I (x = 1.66) is cubic with no anomalies; small paracrystalline distortions, g < 0.1%, cannot be excluded and are calculated to be of this magnitude from considerations of a simple volume effect of the larger Mn3+ ions. Samples II–IV (x = 1.88) show interesting effects which are closely connected with the development of the tetragonal structure, observed when x > 1.80. Sample II (quenched) shows paracrystalline distortions which can be quantitatively explained on the basis of the Jahn–Teller effect: the tragonally deformed single Mn3+O2−
6 octahedra are statistically oriented and statistically distributed over B sites and have a mean tetragonality {\bar \epsilon} = 0.014. In sample III (cooling rate 20°C.min−1) about 26% of the volume consists of microdomains which result from a correlation between the orientations and positions of Jahn–Teller octahedra; quantitive agreement with the theory can be obtained by introducing a correlation factor γ = 2. In sample IV (cooling rate 7°C.min−1) this correlation proceded in such a way that the crystal consisted of 74% tetragonal matrix which had already attained a value of c/a = 1.056, and about 22% of tetragonal microdomains oriented in two other directions with a value c/a < 1.056. In addition about 3 to 5% of a cubic phase is present. If the mean tetragonality of the microdomains is taken to be {\bar \epsilon} = 0.020 the experiments correspond quantitatively with the theory. The detailed study of sample III proves H
¼ ¼ ¼ are the paracrystalline coordination statistics with a fluctuation α = 27 XU in the direction [111] and β = 38 XU perpendicular to it. This is explained by a model of the spinel structure having two kinds of blocks: a tetrahedral A-structure and Jahn–Teller affected octahedral subcubes at B sites; the separation distance is ¼ √3a = 3.7 Å.
Anharmonic thermal vibrations in Mg2Si
Authors: Cooper M. J. , Panke D.
Published: July 2002

The recent X-ray diffraction data front Mg2Si, obtained by Panke & Wölfel (Z. Kristallogr. (1969), 129, 9) show systematic differences in the structure factors from those predicted by a model which assumes harmonic thermal vibration of the atoms. These differences indicate an anharmonic component in the thermal vibration of the magnesium atoms, consistent with their tetrahedral site symmetry. An analysis of these data has therefore been carried out in terms of a model which includes anharmonic thermal vibration and a least-squares refinement gave a value of the anharmonicity parameter (β
Mg = − 2.39 × 10−12 erg.Å−3) which is similar in magnitude to those found for other systems with the fluorite structure.
Comparisons of atomic thermal motions for graphite at 300 K based on X-ray, neutron, and phonon-spectrum data
Authors: Chen R. , Trucano P.
Published: July 2002

The mean-square amplitudes of vibration in graphite based on an X-ray charge-density analysis are 0.0032 (2) and 0.0140 (3) Å2 parallel to and perpendicular to the basal plane, respectively. Values for the parallel vibrations of 0.0031 (6) and 0.0032 Å2 were derived from temperature-dependent neutron measurements and a calculated phonon spectrum. The neutron measurements and the phonon spectrum both predict lower values [0.0090 (20) and 0.0098 Å2] for the out-of-plane vibrations. This small discrepancy may be caused by small changes in the core atomic scattering factors from the free-atom values or by a deficiency in the phonon-spectrum model.
Determination of electronic polarizabilities of ions in orthosilicates
Authors: Pohl D. , Eck J. C. , Klaska K.-H.
Published: July 2002

Electronic polarizabilities of cations have been obtained for the sodium D line (in Å 3): Mg2+ 0.1, Fe2+ 3.3, Zn2+ 5.4, Zr4+ 4.6. The polarizability of the O2- ion varies from one structure to another. It has been shown that calculation of electronic polarizability is possible only if an accurate structure refinement is available.
Polymorphous crystallization and diffraction of threonine deaminase from Escherichia coli
Authors: Gallagher D. Travis , Eisenstein Edward , Fisher Kathryn E. , Zondlo James , Chinchilla Diana , Yu Hoon Dae , Dill Jonathan , Winborne Evon , Ducote Karin , Xiao Gaoyi , Gilliland Gary L.
Published: July 2002

The biosynthetic threonine deaminase from Escherichia coli, an allosteric tetramer with key regulatory functions, has been crystallized in several crystal forms. Two distinct forms, both belonging to either space group P3121 or P3221, with different sized asymmetric units that both contain a tetramer, grow under identical conditions. Diffraction data sets to 2.8 Å resolution (native) and 2.9 Å resolution (isomorphous uranyl derivative) have been collected from a third crystal form in space group I222.
Estimating Lysozyme Crystallization Growth Rates and Solubility from Isothermal Microcalorimetry
Authors: Darcy Patricia A. , Wiencek John M.
Published: July 2002

A microcalorimetric technique has been developed to measure crystal-growth kinetics and enthalpies of crystallization. The enthalpy of crystallization of hen egg-white lysozyme in 0.1 M acetate buffer at pH 4.6 was determined at 287 K using this technique. The enthalpies were directly measured to be −14.3 ± 2.0 and −14.6 ± 1.3 kcal mol−1 (1 kcal mol−1 = 4.184 kJ mol−1) for 3 and 5% NaCl solutions, respectively, which is in good agreement with values estimated from previous solubility measurements. Non-linear regression of the transient heat flow allowed measurement of the crystal growth rate as a function of protein supersaturation as well as the solubility. The crystal growth rates determined by this method were found to agree with those in the literature under the same solution conditions.
The Role of Validation in Macromolecular Crystallography
Authors: Dodson Eleanor
Published: July 2002

The importance of validation techniques in X-ray structure determination and their relation to refinement procedures are discussed, with particular reference to atomic resolution structures. The requirements of deposition and publication, and the role of validation tools in this are analysed. The need for a rigorously defined file format is emphasized.
Protein Sequence Alignment Techniques
Authors: Barton Geoffrey J.
Published: July 2002

The basic algorithms for alignment of two or more protein sequences are explained. Alternative methods for scoring substitutions and gaps (insertions and deletions) are described, as are global and local alignment methods. Multiple alignment techniques are explained, including methods for profile comparison. A summary is given of programs for the alignment and analysis of protein sequences, either from sequence alone, or from three-dimensional structure.
Low-salt crystallization of T7 RNA polymerase: a first step towards the transcription bubble complex
Authors: Chen Chun Jung , Liu Zhi-Jie , Rose John P. , Wang Bi-Cheng
Published: July 2002

DNA-dependent RNA polymerase is the key enzyme responsible for the biosynthesis of RNA, a process known as transcription. This process, which decodes the genetic information from DNA, is one of the most significant events in a biological system. The crystallization of both native and a chimeric T7/T3 RNAP using high-salt conditions has been reported previously but these conditions proved unsuitable for DNA–RNAP complex formation since at high-salt concentrations the DNA binding affinity to RNAP is reduced. A search for low-salt crystallization conditions has yielded new low-salt crystals of native T7-RNAP, a chimeric T7-RNAP (T7/T3 RNAP) which contains the T3 promoter recognition sequence, and a T7-RNAP containing an N-terminal histidine tag. The crystals, which are better suited for DNA–RNAP complex formation, belong to space group P3121 with a = 136, c = 156 Å, contain a single molecule per asymmetric unit and diffract to 2.7 Å resolution. Packing analysis shows that the new low-salt crystals have packing contacts similar to those observed in the high-salt T7-RNAP crystals reported previously. The diffraction anisotropicity observed in crystals of T7 RNAP is explained in term of crystal packing.
Crystallization and preliminary X-ray diffraction analysis of the NAD-dependent non-phosphorylating GAPDH of the hyperthermophilic archaeon Thermoproteus tenax
Authors: Brunner Nina A. , Lang Dietmar A. , Wilmanns Matthias , Hensel Reinhard
Published: July 2002

Recombinant non-phosphorylating NAD+-dependent glyceraldehyde-3-phosphate dehydrogenase (GAPN) of the hyperthermophilic crenarchaeote Thermoproteus tenax has been overexpressed, purified and crystallized using the hanging-drop vapour-diffusion technique. Crystals of different habits were obtained from several precipitant solutions (salts and polyethylene glycols). Preliminary X-ray analysis was performed with crystals grown in ammonium formate, which belonged to the primitive hexagonal space group P622, and had unit-cell parameters a = b = 184.8, c = 133.0 Å, γ = 120°. Assuming a molecular weight of 55 kDa, a Matthews parameter of 3.3 Å3 Da−1 is calculated assuming two molecules per asymmetric unit. The diffraction limit of these crystals is 2.5 Å resolution.
Characterization of the ruthenium–dinitrogen tetraamine complexes by XAFS spectroscopy
Authors: Okamoto Kaoru , Takahashi Toshikazu , Kohdate Kenji , Kondoh Hiroshi , Yokoyama Toshihiko , Ohta Toshiaki
Published: July 2002

A reaction between N2 and trans-RuIICl2L (L = 2,5,9,12-tetramethyl-2,5,9,12-tetraazatridecane) in aqueous solutions has been investigated by XAFS spectroscopy. Ru K-edge EXAFS clearly revealed that there exists an N2-bridged binuclear complex and that the Ru-Ru distance is 4.96 Å with the coordination number of 0.5. The Ru K-edge energies of the N2 complexes are closer to that of RuIIICl2L+ rather than that of RuIICl2L, indicating back donation from the Ru dπ to the N2 π* orbitals.
XANES study on Ruddlesden-Popper phase, Lan+1NinO3n+1 (n = 1, 2, and ∞)
Authors: Park Jung-Chul , Kim Dong-Kuk , Byeon Song-Ho , Kim Don
Published: July 2002

Ruddlesden-Popper phase, Lan+1NinO3n+1 (n = 1, 2 and ∞) compounds were prepared by citrate sol-gel method. We revealed the origin of the variation of the electrical conductivities in Lan+1NinO3n+1 (n = 1, 2 and ∞) using resistivity measurements, Rietveld analysis, and X-ray absorption spectroscopy. According to the XANES spectra, it is found that the degree of 4pπ - 4pσ energy splitting between 8345 eV and 8350 eV is qualitatively proportional to the elongation of the out-of-plane Ni-O bond length. With the decrease of 4pπ - 4pσ splitting, the strong hybridization of the σ-bonding between Ni-3d and O-2p orbitals creates narrow antibonding σ* bands, which finally results in the lower electrical resistivity.
Mg and Al K-edge XAFS measurements with a KTP crystal monochromator
Authors: Takata Y. , Shigemasa E. , Kosugi N.
Published: July 2002

There has been a strong demand for monochromator crystals with a large lattice spacing in order to measure EXAFS spectra at the Mg and Al K-edges. We have introduced a pair of KTP crystal at BL1A of the UVSOR facility and examined its performance in the energy range between 1200 and 2000 eV. This crystal monochromator can supply stable photon beams enough to measure the EXAFS spectra for the Mg and Al K-edges. Advantages of the KTP crystal are discussed in comparison with a YB66 crystal monochromator.
Phase formation during the decomposition of ammonium heptamolybdate – an in situ XAFS and XRD investigation
Authors: Wienold Julia , Jentoft Rolf Erik , Ressler Thorsten
Published: July 2002

The decomposition of ammonium heptamolybdate was investigated by in situ XAFS and in situ XRD to elucidate the influence of different atmospheres on the products formed The formation of different decomposition products and various intermediates is described in detail.
EXAFS study of the Fe
x
/ZrO2 composite nanomaterials obtained by sol–gel synthesis
Authors: Kriventsov Vladimir , Kochubey Dmitrii , Navio Jose Antonio , Hidalgo Maria Carmen , Colón Gerardo , Tsodikov Mark , Maksimov Yuri , Suzdalev Igor
Published: July 2002

The local Zr and Fe arrangements in the nanocomposite system Fex/ZrO2 (x=0-0.2) obtained by sol-gel method were studied by EXAFS. The phase composition was found to vary significantly on iron loading. For the samples calcined at 500 or 600°C, at x≤0.01, the formed ZrO2 is a mixture of monoclinic and tetragonal structures. Only tetragonal structure is revealed at x≥0.05 with the exception of Fe0.2/ZrO2, calcined at 500°C, where new non-typically short Zr-Zr distances (3.29, 3.43Å) were observed. At low iron loading (less than one monolayer) Fe3+ ions were found to localize within the pre-surface layers of ZrO2 nanoparticles showing property of isolated ions. For greater Fe loading, iron exhibits either two-dimensional layer structure or two-phase system.
Present state and perspectives of synchrotron radiation diffraction imaging
Authors: Baruchel J. , Härtwig J. , Pernot-Rejmánková P.
Published: July 2002

The modern third-generation synchrotron radiation sources offer enhanced possibilities for all variants of imaging techniques. The quantitative and qualitative improvements with respect to previous synchrotron diffraction imaging work, which include the investigation in transmission of bulky samples, the use, as an additional parameter, of the sample-to-detector distance, and the use of the coherence of the beam, are illustrated by several examples. Emphasis is given to the possibilities associated with modern electronic detectors for this type of imaging. The new techniques implemented at the ESRF that take full advantage of new capabilities, and more particularly that of `topo-tomography', are presented.
Synchrotron X-ray topography of electronic materials
Authors: Tuomi T.
Published: July 2002

Large-area transmission, transmission section, large-area back-reflection, back-reflection section and grazing-incidence topography are the geometries used when recording high-resolution X-ray diffraction images with synchrotron radiation from a bending magnet, a wiggler or an undulator of an electron or a positron storage ring. Defect contrast can be kinematical, dynamical or orientational even in the topographs recorded on the same film at the same time. In this review article limited to static topography experiments, examples of defect studies on electronic materials cover the range from voids and precipitates in almost perfect float-zone and Czochralski silicon, dislocations in gallium arsenide grown by the liquid-encapsulated Czochralski technique, the vapour-pressure controlled Czochralski technique and the vertical-gradient freeze technique, stacking faults and micropipes in silicon carbide to misfit dislocations in epitaxic heterostructures. It is shown how synchrotron X-ray topographs of epitaxic laterally overgrown gallium arsenide layer structures are successfully explained by orientational contrast.
1,4-Butylenebis(diphenylphosphine selenide)
Authors: Hundal Rajbir , Lobana Tarlok S. , Turner Peter
Published: July 2002

The title compound, C28H28P2Se2, is located on an inversion centre. The Se—P bond length is 2.1055 (5) Å.
Bis(2-hydroxyethylammonium) oxalate
Authors: Jordanovska Vera , Naumov Pancě , Kim Moon-Jib , Lee Han-Jun , Ng Seik Weng
Published: July 2002

In bis(2-hydroxyethylammonium) oxalate, 2C2H8NO+·C2O42−, hydrogen bonds involving the hydroxy and ammonium groups connect the carboxyl O atoms of the oxalate anion into a three-dimensional network structure.
N∊-Benzyloxycarbonyl-Nα-(2-nitrobenzenesulfonyl)-L-lysine
Authors: Giraldés José , McLaughlin Mark L. , Fronczek Frank R.
Published: July 2002

The title compound, C20H23N3O8S, is in an extended conformation. The COOH group does not form hydrogen-bonded carboxyl dimers, but forms an intermolecular hydrogen bond with the NCOO carbonyl O atom [O...O 2.666 (2) Å]. The N atom bonded to S is pyramidal, and forms a bifurcated intramolecular hydrogen bond with carboxy and nitro O atoms.
The Mathematical Work of Norbert Wiener (1894‐1964)
Authors: Chatterji S.D.
Published: July 2002

Describes some parts of Wiener’s significant contribution to mathematics in as simple and non‐technical a language as possible. Looks at Wiener’s early research and how he applied integration theory to potential theory, but not without first explaining the background to integration theory. Then describes one of Wiener’s most important works – that on Brownian motion, and how other theories such as harmonic analysis flowed from his study of Brownian motion. Concludes with a brief chronology of Wiener’s life.
The Variation of Viscosity With Temperature and Pressure for Various Real Lubricants
Authors: Bair Scott
Published: July 2002

To date, nearly all analyses of lubricant traction behavior in the Hertzian zone of concentrated contact have been performed with viscosity correlations which understate the effect of pressure and temperature at high pressures. We present viscometer measurements of lubricant viscosity for pressures to 1.4 GPa and temperatures to 165°C for various lubricants including automotive transmission fluids, aerospace lubricants, a turbine oil, and a metal working oil. Parameters of a free-volume correlation are provided for use in numerical modeling of traction, film thickness, and roughness interactions in concentrated contact.
Infrared Low-Temperature Turbine Vane Rough Surface Heat Transfer Measurements
Authors: Boyle R. J. , Spuckler C. M. , Lucci B. L. , Camperchioli W. P.
Published: July 2002

Turbine vane heat transfer distributions obtained using an infrared camera technique are described. Infrared thermography was used because noncontact surface temperature measurements were desired. Surface temperatures were 80°C or less. Tests were conducted in a three-vane linear cascade, with inlet pressures between 0.14 and 1.02 atm, and exit Mach numbers of 0.3, 0.7, and 0.9, for turbulence intensities of approximately 1 and 10 percent. Measurements were taken on the vane suction side, and on the pressure side leading edge region. The designs for both the vane and test facility are discussed. The approach used to account for conduction within the vane is described. Midspan heat transfer distributions are given for the range of test conditions.
Educational Aspects of the Solar Splash Regatta
Authors: Morehouse Jeffrey H.
Published: July 2002

The rationale behind and the educational goals of the Solar Splash intercollegiate solar/electric boat competition are examined. An assessment is made as to how well these educational goals are being met, including a brief discussion of competition participant problems. An apparent “mismatch” is identified between the Solar Splash rules and resultant boat designs and the goals for most collegiate engineering design courses, and possible methods of correction are discussed.
Cyclic Deformation Behavior and Dislocation Substructures of Hexagonal Zircaloy-4 Under Out-of-Phase Loading
Authors: Lin Xiao
Published: July 2002

Macroscopic response and microscopic dislocation structures of Zr-4 subjected to biaxial fatigue under different phase angles of 30°, 60°, 90° and different equivalent strain ranges of 0.8%, 0.6%, 0.4% were studied. The testing results show that the delay angle between the stress deviators and strain increment tensors is strongly dependent on phase angle and the equivalent strain range. When phase angle equals 60°, the delay angle has the minimum variation range for all specimens. The mean value of the delay angle decreases with increasing phase angle or the equivalent strain range. The variation range and average value of the Mises equivalent stress have the maximum in S3 with the phase angle of 90°. They decrease as the equivalent strain range decreases. Zr-4 displays a pronounced initial hardening followed by a continuous softening for all specimens during out-of-phase cycling. The stabilized saturation stresses of Zr-4 under out-of-phase cycling are much higher than that under uniaxial cycling. It indicates that Zr-4 displays an obvious additional hardening. As the phase angle increases, the typical dislocation structure changes from dislocation cells to tangles. The dislocation-dislocation interactions increase resulting in an additional hardening. In essence, the degree of additional hardening depends, among other factors, on the maximum shear stress ratio of resolved shear stresses and critical resolved shear stresses (RSS/CRSS). [S0094-4289(00)00601-0]
In situ cleaning of microfabricated field emitter cathodes
Authors: Schwoebel P. R. , Olson R. T. , Panitz J. A. , Brodie A. D.
Published: July 2002

The use of microfabricated field emission cathodes in applications of technological importance has been hindered by difficulties in obtaining acceptable emission characteristics in the vacuum environment of the device. We have investigated in situ surface cleaning and annealing using high pulsed electron emission. Extraction of high current densities provides a reliable means to shape and clean microfabricated field emitter tips, thereby enhancing their temporal stability and emission spatial uniformity.
Effects of (Ba, Sr)TiO3 film thickness on electrical properties of (Ba, Sr)TiO3/(Ba, Sr)RuO3 capacitor
Authors: Oh Se Hoon , Park Kyung Woong , Park Jeong Hee , Kim Boum Seock , Choi Duck Kyun
Published: July 2002

The electrical properties of (Ba, Sr)TiO3/(Ba, Sr)RuO3 capacitors as a function of the (Ba, Sr)TiO3 film thickness were investigated. It was found that the electrical properties degraded, as the thickness of the dielectric film decreased. As the thickness of the (Ba, Sr)TiO3 films varied from 30 to 200 nm, the dielectric constants and Teq were 122, 0.96 and 515, 1.5 nm, respectively. The corresponding leakage current densities were 2.7×10−5 A/cm2 at 30 nm and 2.14×10−8 A/cm2 at a 200 nm (Ba, Sr)TiO3 thickness. However, after postannealing at 700 °C, the dielectric constants and Teq of (Ba, Sr)TiO3/(Ba, Sr)RuO3 capacitors with a 30 nm (Ba, Sr)TiO3 thickness were 230 and 0.51 in N2 and 200 and 0.59 nm in O2, respectively, and the leakage current levels were 1.67×10−6 A/cm2 in N2 and 1.64×10−7 in O2. Electrical properties of postannealed specimens improved when compared to those of as-deposited (Ba, Sr)TiO3/(Ba, Sr)RuO3 capacitors. The dielectric constant and leakage current density annealed in N2 is a little bit higher than those of the film annealed in an O2 atmosphere. These differences appear to be attributable to an increased surface roughness and grain boundary defects. Electrical properties such as the leakage current and the relative dielectric constant, are closely related to the surface morphology, in particular, the grain size and grain boundary of the films.
Interface control and band offset at the Ga0.52In0.48P on GaAs heterojunction
Authors: Cai C. , Nathan M. I.
Published: July 2002

A new switching procedure was applied in the growth of the lattice-matched heterojunction of Ga0.52In0.48P/GaAs by gas source molecular beam epitaxy. The new switching procedure exposed the GaAs surface to the Ga source instead of thermally cracked AsH3 or PH3 before starting the growth of the Ga0.52In0.48P layer. The interface charge density and the conduction band offset were determined by measuring the Schottky barrier height using current versus voltage and capacitance versus voltage characteristics. The interface charge density could be reduced to near zero using the new switching procedure with an exposure time of 64 s. The value of the conduction band offset was 0.2 eV at the interface of zero charge.
Partial pressure of TiCl4 in CVD of TiN
Authors: Peterson John R.
Published: July 2002

In developing a TiN coating for cobalt cemented WC–TiC–TaC tools, the effect of TiCl4 partial pressure in an H2+N2 atm was studied over the range of approximately 0.03–0.30 atm. The two temperatures of deposition studied were 1000 and 1080 °C. Low TiCl4 partial pressure combine to produce columnar grains > 10 μ in length and faster coating rates. Higher TiCl4 partial pressures in the range of 0.05–0.10 atm produce random oriented grains of approximately 1 μ or less and slower coating rates. TiCl4 pressures greater than 0.30 atm at 1000 °C nearly stop deposition of TiN. The TiN coating is especially useful in minimizing wear on carbide cutting tools.
High absorptivity solar absorbing coatings
Authors: Mattox D. M. , Sowell R. R.
Published: July 2002

A high absorptivity is essential in the efficient use of a solar collector. In this paper we review some of the fundamental considerations in solar absorbing coatings and present reflectance data on several chemically treated surfaces which appear to be black in the solar spectrum. Reflectivity data are also presented for a lead sulfide “selective paint” which uses a silicone binder.
Oh! Where Have the Mountains of Titanium Scrap Gone?
Authors: Gray Jerry J.
Published: July 2002

Results of a secondary titanium market survey indicated that an oversupply of titanium scrap does not exist. The mountains of scrap that existed during the late 1950’s and early 1960’s were consumed down to mole hills by the mid to late 1960’s. During the past two and one-half years, even the mole hills’ roots were consumed. The titanium scrap situation is illustrated by a 10-year statistical model (see Table I). The model in the form of a table contains sponge, ingot, and scrap production and consumption statistics. Three assumptions were used, two concerned with fabrication productivity and the third with nonrecoverable scrap losses. Over the total 10-year period, scrap consumption was larger than scrap supply by 7.6%. For the first six years, 18% more scrap was consumed than was generated. For the last four years, scrap supply and demand were in balance, almost within 100 tons. Currently (1969–1970), scrap is in short supply. For the future, table data trends indicate that the short supply will continue. A major effect of the tight supply will be upward pressure on the price of ingot. Scrap is migrating to the steel (including direct alloying and deoxidizing, ferrotitanium production, and exports) and aluminum industries, instead of returning for recycling, because of lower scrap processing costs and technological needs for titanium metal which cannot be met with sponge.
Formation of Superconducting Nb3Al and Nb3Al–Ge Films
Authors: Isao A. , Noguchi T. , Uchida Y. , Kono A.
Published: July 2002

The formation of Nb3Al or Nb3Al–Ge compounds on niobium substrates is described. The film formation was followed using optical microscopy and x-ray diffraction techniques. Electrical resistance measurements at cryogenic temperatures were obtained to determine critical transition temperature for superconductivity. The films wee prepared by three processes: (a) dipping the Nb substrate into an Al–Ge melt contained in a graphite crucible, holding for several seconds followed by a thermal diffusion treatment; (b) vacuum deposition of Al or Al–Ge on Nb followed by heat treatment similar to that in (a). The advantage of vacuum deposition is better control of the film thickness of Al or Al–Ge; (c) and simultaneous deposition of Nb and Al on Nb substrates in vacuum. The deposition rate of Nb and Al was controlled at a 3:1 atomic ratio. Germanium was simultaneously deposited with Al. The Nb3Al or Nb3(Al–Ge) films were formed at temperatures between 1350° and 1650°C for both the (a) and (b) processes with the critical superconductive transition temperature between 15 K and 17.5 K. The films prepared by simultaneous deposition of Al and Ge show that the superconducting behavior depends on the diffusion heat treatment. A heat treatment at 1000°C for 30 min resulted in a Nb3Al film having 3:1 atomic ratio. The critical superconducting temperature for the films produced by these processes was between 15 K and 16 K without an ordering heat treatment. A lowering of the heat treatment (diffusion) temperature for the simultaneously deposited films resulted in a critical superconducting temperature that is in agreement with values reported by Neugebauer for superconducting Nb3Sn. The lower heat treating temperatures of 1000° and 1200°C are expected to result in higher critical current densities.
Compositional Determination of rf Co-Sputtered Multicomponent Systems
Authors: Hanak J. J.
Published: July 2002

A technique of synthesis of nearly complete two- and three-component systems is described, which consists of one-cathode, multiple-target, rf co-sputtering of the constituent elements onto one large substrate. A new and simple approximate method of compositional determination of co-sputtered films is introduced which is based on the assumptions of superposition of the sputtered species and the constancy of geometry-dependent deposition profiles. Compositional analysis of any portion of the deposited film can be obtained from film thickness measurements and the knowledge of the deposition profiles, which need to be determined only once for a given sputtering geometry.
Sputtering of Chemisorbed Nitrogen with Ar+
Authors: Winters Harold F.
Published: July 2002

Flash filament techniques and mass spectrometry have been used to make sputtering measurements for nitrogen which is chemisorbed on a tungsten surface and bombarded with Ar+ ions. The sputtering rate for a given energy between 20 eV and 300 eV is described by the equation dN/dt=−S(N/)N0)ni, where N is the surface coverage, N0 the saturation surface coverage, ni the ion flux, and S the sputtering ratio measured at saturation. The sputtering ratio for nitrogen was found to be ∼0.02 at 17 eV, indicating a low threshold energy for sputtering of the strongly bound nitrogen atom. This result suggests that the well-known experimental relationship between sublimation energy (∼7 eV/nitrogen atom) and threshold energy may not hold for chemisorbed gases. For all energies between 100 and 300 eV the measured sputtering ratio for nitrogen was approximately twice that found for tungsten from atomically clean tungsten. This is particularly surprising when one considers that nitrogen covers less than 20% of the geometrical surface area. This result may, indicate a large sputtering ratio even for gases with large binding energies.
Sputtering Techniques for Controlling Composition of Thin Films of High-Tc Superconducting Compounds
Authors: Gavaler J. R. , Janocko M. A. , Hulm J. K. , Jones C. K.
Published: July 2002

Presently known, high transition temperature (≳15 K) superconducting materials have either the β-W (A-15) or rocksalt (B-l) crystal structure. Although these compounds retain the desired crystal structure over a wide composition range, optimum Tc’s are obtained only when the compounds are nearly stoichiometric. Films of some of these materials, including compounds in the Nb–Al, Nb–Sn, and Nb–Al–Ge systems, have been prepared by sputtering. To control composition, various targets have been employed, including ingots made by arc melting, hot-pressed powder mixtures, and multiple targets. Compound formation was achieved in most cases (as verified by x-ray diffraction analysis) regardless of target material used, however, the Tc’s of the films varied from < 10 K to over 16 K. The influence of target material on stoichiometry and on Tc is discussed, and some of the high-field superconducting properties of the deposited films are reported.
Properties of ZnO Films Prepared by dc and rf Diode Sputtering
Authors: Vuillod J.
Published: July 2002

A brief description of the dc and rf diode sputtering unit is first presented. The study of properties of the films is reviewed taking into consideration two main parameters, oxygen partial pressure and substrate temperature. Reflection electron diffraction and x-ray diffraction studies show that the films on amorphous fused quartz substrates are highly oriented. Neutron activation analysis is used to determine the impurities in films (Cu, Ag, Br, Na, Au, Fe, In). Two ranges of resistivity were observed depending on the sputtering atmosphere. The temperature dependence of resistivity for high and low resistivity ZnO films is presented as well as impedance behavior vs frequency and optical transmittance for films annealed or not. ESR investigation of films (resistivity ∼109 Ω⋅cm, thickness 0–5 μ) shows a signal at g = 2.00. Finally, a tentative explanation of defects is presented.
Thickness Dependence of Electron Mobility of InSb Films
Authors: Wieder H. H.
Published: July 2002

The thickness dependence of the room temperature electron mobility of InSb films is shown to be in good qualitative but poor quantitative agreement with theoretical mobility limiting models based on diffuse or specular surface scattering. An alternative model based on the presence of a surface accumulation layer on films with bulklike properties is shown to provide a fair quantitative agreement with experimental data.
Impurities on Thorium Metal: Auger Study of Bulk-to-Surface Equilibria
Authors: Ellis Walton P.
Published: July 2002

The segregation of impurities on surfaces of polycrystalline thorium metal has been studied by Auger electron spectroscopy. The interstitial contaminants S, C, and P, present in the bulk in the parts per million range, were found to equilibrate rapidly and reproducibly with the surface at elevated temperatures. With sulfur, initially present at 15±5 ppm, three equilibrium ranges were found: (1) at 900–1100 °C the surface is saturated, (2) at 1100–1170 °C sulfur returns to the bulk with ΔH=−48.4±2.1 kcal/mole for the reaction S(bulk) → S(surface), and (3) above 1170 °C ΔH=−18.8±1.3 kcal/mole. Corrections were made for changing sulfur Auger peak width. Carbon (285 ppm) returned to the bulk at ∼480 °C with ΔH≃−14±2 kcal/mole, and phosphorus (50 ppm) returned at ∼790 °C with ΔH≃−19±2 kcal/mole. The effect was also seen for oxygen and chlorine but no quantitative data were taken. Electron-impact desorption was also observed.
Surface Quantization and Surface Transport in Semiconductor Inversion and Accumulation Layers
Authors: Stern Frank
Published: July 2002

Recent experimental and theoretical work on the properties of inversion layers and accumulation layers near semiconductor-insulator interfaces is summarized, with emphasis on quantization effects associated with strong normal electric fields.
Ion Implanted N-Type Resistors on High-Resistivity Substrates
Authors: Hanson J. W. , Huber R. J. , Fordemwalt J. N.
Published: July 2002

The method of fabrication and measured characteristics of phosphorous ion-implanted resistors made on high-resistivity 15–20 Ω cm p-type silicon substrates are presented. The process included a shallow boron-implanted layer at the surface to prevent surface inversion due to Qss. It is demonstrated that enhancement N-channel MOSFET devices can be processed together with the implanted resistors. The range of phosphorous doses studied was 1×1012–5×1014/cm2 and the range of anneal temperatures considered was 500–950 °C. Results are given for measurements of sheet resistivity vs dose and anneal temperature, and for temperature coefficient of resistance. The advantages of using high-resistivity substrates for the implanted resistors are discussed.
The initial epitaxy of Cu on (111) Ag films
Authors: Horng C. T. , Vook R. W.
Published: July 2002

The initial growth of Cu on (111) Ag surfaces was examined in situ by RHEED and later by TEM and TED. The substrates were very smooth (111) Ag films, single positioning oriented, evaporated on NaCl/mica in UHV just prior to Cu growth. The Cu overgrowths were double positioning oriented and contained microtwins. The mode of Cu growth depended on the substrate temperature. Cu deposited at 210 °C formed island-type overgrowths. At 25 °C, Cu formed a very smooth overgrowth up to about two monolayers. Thereafter island growth occured. From the smooth Cu–Ag bilayers, anomalous RHEED patterns were obtained similar to those observed by Gradmann and Krause on Ag–Cu bilayers. These authors interpreted their diffraction patterns in terms of a postulated regular network of interfacial dislocations. However, high-resolution TEM of Cu–Ag bilayers in the present work revealed a very low density of dislocations and only an extremely rare irregular network.
Enhancement in field emission of silicon microtips by bias-assisted carburization
Authors: Kichambare P. D. , Tarntair F. G. , Chen L. C. , Chen K. H. , Cheng H. C.
Published: July 2002

Ultrathin carbon layers with thicknesses below 50 Å have been deposited on silicon microtip arrays by bias-assisted carburization (BAC) using microwave plasma chemical vapor deposition. The tip radius of these silicon tips is reduced below 55 nm under low deposition temperature. The field emission characterization has been performed in a high-vacuum environment. An enhancement in the field emission is observed of about 3 orders of magnitude in BAC silicon microtips over untreated silicon microtips. With an applied voltage of 1100 V, emission currents of 80 and 120 μA have been achieved for the films grown (at dc bias of −200 V for 40 min) with 15% and 25% CH4/H2 gas ratio, respectively. An emission current of 40 μA has been achieved for the film grown (at dc bias of −300 V for 40 min) with 3.5% CH4/H2 ratio. The BAC silicon emitter has good emission stability at a constant voltage of 1100 V. These investigations indicate that further improvement of this technology will lead to simple and inexpensive field emission display devices.
Two-channel spectroscopic reflectometry forin situmonitoring of blanket and patterned structures during reactive ion etching
Authors: Stutzman Brooke S. , Huang Hsu-Ting , Terry Fred L.
Published: July 2002

In this article we present a low-cost, high-speed, high-accuracy in situ thin film measurement system for real-time process monitoring and industrial process control. This sensor, the two-channel spectroscopic reflectometer (2CSR), is a hybrid of spectroscopic ellipsometry and spectroscopic reflectometry. In 2CSR a polarized beam of white light is directed at the sample. The reflected light is resolved into its two orthogonal components, s and p, using a Wollaston prism. These data, |Rs|2 and |Rp|2, are recorded simultaneously as a function of wavelength using a two-channel spectrometer with linear array detectors. The fact that 2CSR has no moving parts, coupled with the use of the two-channel linear array detectors, enables high-accuracy data acquisition across the sensor’s spectral range in 6 ms. This makes the 2CSR ideal for real-time high-speed process monitoring and control in an industrial setting. We have used the 2CSR to make accurate in situ, high speed film thickness measurements during the plasma etching of both silicon dioxide and polycrystalline silicon samples. We show that, in addition to our ability to measure blanket film thicknesses and etch rates, the accuracy of the 2CSR makes this a viable technique for patterned wafer analysis.
Continuous transfer of Ge by the tip of a scanning tunneling microscope for formation of lines
Authors: Shklyaev Alexander A. , Shibata Motoshi , Ichikawa Masakazu
Published: July 2002

Nanostructures such as continuous Ge lines about 5 nm in width and 2 nm in height were created on Ge wetting layers on Si(111) substrates with a scanning tunneling microscope (STM). Postfabrication annealing initiated growth of the lines in the lateral dimension thereby improving their uniformity. STM and electron diffraction data obtained for lines after annealing showed that the lines have a nonepitaxial structure consisting of tiny particles. Continuous intersections of lines can be achieved when sharp tip apexes are used. The results demonstrate the possibility of using the STM for direct massive transfer of individual atoms in the fabrication of nanostructures.
Comparison of three different methods for coupling of microwave and terahertz signals generated by resonant laser-assisted field emission
Authors: Alonso Kevin , Hagmann Mark J.
Published: July 2002

Photomixing in resonant laser-assisted field emission can cause the emitted current to oscillate at frequencies from dc to over 100 THz, and thus shows promise for new ultrawide band devices. The signal occurs at the apex of the emitter, and we consider three methods for coupling this signal to an external load while avoiding the effects of dispersion of the bunched electron beam and the large series beam impedance (≈1 GΩ). These methods are use of (1) a tapered Goubau transmission line, (2) a dielectric transmission line, and (3) traveling-wave log-periodic zigzag antennas. We conclude that each of these methods could give an output power of 100 pW with an oscillating tunneling current of 1 μA at 10 THz. The output power is proportional to the square of the current for 100 μW with 1 mA.
Synthesis of fluorinated diamond-like carbon films by the plasma immersion ion processing technique
Authors: Hakovirta M. , Lee D. H. , He X. M. , Nastasi M.
Published: July 2002

The synthesis of fluorinated diamond-like carbon (F-DLC) films was investigated for the first time using the plasma immersion ion processing technique. A pulsed glow discharge plasma was generated at a pressure of 1 Pa from acetylene and hexafluoroethane gas mixtures and the films were deposited on silicon 〈100〉 substrates by applying a pulsed bias to the substrate holder. The film hardness, wear resistance and nonwetting properties were found to be strongly dependent on the fluorine content incorporated into the coatings. With an optimum gas ratio, the deposited F-DLC films were found to have nonwetting properties similar to Teflon®, but were 10 times harder (8 GPa).
Recent development of diamond microtip field emitter cathodes and devices
Authors: Kang W. P. , Davidson J. L. , Wisitsora-at A. , Kerns D. V. , Kerns S.
Published: July 2002

Recent development of diamond field emitter cathodes and devices fabricated from molding process is presented. Practical modifications involving the sp2 content, surface treatment, boron doping, and tip sharpening to further enhance diamond field emission are discussed. A new fabrication process for achieving ultrasharp diamond tips with a radius of curvature less than 5 nm has been achieved and shows significant improvement in emission characteristics. Discussion of this enhanced emission in diamond microtips is presented in accordance with analysis of emission behavior. The development of high site density of uniform diamond microtip arrays is presented. We also report the development of a new technique to fabricate self-aligned gate diamond emitter diodes, which achieve very high emission characteristics at extremely low applied voltage. The latest development aims to integrate diamond field emitters with silicon-based MEMS processing technology and achieve totally monolithic diamond field emitter devices on silicon wafers. Preliminary results in the triode configuration demonstrate promising transistor characteristics suitable for vacuum microelectronic applications.