Showing papers on "Single crystal published in 1991"
738 citations
TL;DR: The resulting spectrum in the high-{ital T}{sub {ital c}} regime is suggestive of a strongly itinerant character of the state in the moderately doped CuO{sub 2} plane while appreciable weight remains in the charge-transfer energy region.
Abstract: Optical reflectivity spectra are studied for single crystals of the prototypical high-${\mathit{T}}_{\mathit{c}}$ system ${\mathrm{La}}_{2\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{CuO}}_{4}$ over a wide compositional range 0\ensuremath{\le}x\ensuremath{\le}0.34, which covers insulating, superconducting, and normal metallic phases. The measurements are made at room temperature over an energy range from 0.004 to 35 eV for the polarization parallel to the ${\mathrm{CuO}}_{2}$ planes. They are also extended to the perpendicular polarization to study anisotropy and to discriminate the contribution from the ${\mathrm{CuO}}_{2}$ plane. The present study focuses on the x dependence of the optical spectrum, which makes it possible to sort out the features of the excitations in the ${\mathrm{CuO}}_{2}$ plane and thus to characterize the electronic structure of the ${\mathrm{CuO}}_{2}$ plane in the respective phase. Upon doping into the parent insulator ${\mathrm{La}}_{2}$${\mathrm{CuO}}_{4}$ with a charge-transfer energy gap of about 2 eV the spectral weight is rapidly transferred from the charge-transfer excitation to low-energy excitations below 1.5 eV. The low-energy spectrum is apparently composed of two contributions; a Drude-type one peaked at \ensuremath{\omega}=0 and a broad continuum centered in the midinfrared range. The high-${\mathit{T}}_{\mathit{c}}$ superconductivity is realized as doping proceeds and when the transfer of the spectrum weight is saturated. The resulting spectrum in the high-${\mathit{T}}_{\mathit{c}}$ regime is suggestive of a strongly itinerant character of the state in the moderately doped ${\mathrm{CuO}}_{2}$ plane while appreciable weight remains in the charge-transfer energy region. The spectrum exhibits a second drastic change for heavy doping (x\ensuremath{\sim}0.25) corresponding to the superconductor-to-normal-metal transition and becomes close to that of a Fermi liquid. The results are universal for all the known cuprate superconductors including the electron-doped compounds, and they reconcile the dc transport properties with the high-energy spectroscopic results.
672 citations
TL;DR: In this paper, the structural chemistry of organotin carboxylates is described, covering data acquired for mono-, di-and tri-organotin compounds and complexes and a brief discussion is given for organotin amino-acid derivatives.
Abstract: This review describes the structural chemistry of organotin carboxylates, covering data acquired for mono-, di- and tri-organotin compounds and complexes. A brief discussion is given for organotin amino-acid derivatives.
443 citations
TL;DR: The surface microstructures of c-axis-oriented films of YBa2Cu3O7, deposited by off-axis magnetron sputtering on MgO and SrTiO3 single crystal (100) substrates, have been investigated and there is strong evidence that the films nucleate as islands and grow by adding material to the edge of a spirally rising step.
Abstract: The surface microstructures of c-axis-oriented films of YBa(2)Cu(3)O(7), deposited by off-axis magnetron sputtering on MgO and SrTiO(3) single crystal (100) substrates, have been investigated with scanning tunneling microscopy and atomic force microscopy. There is strong evidence that the films nucleate as islands and grow by adding material to the edge of a spirally rising step. This results in columnar grains, each of which contains a screw dislocation at its center. This microstructure may be of significance in determining superconducting properties such as critical current, and represents a significant difference between thin films (especially those grown in situ) and bulk materials.
387 citations
Patent•
31 Dec 1991TL;DR: In this paper, a display panel is formed using essentially single crystal thin-film material that is transferred to substrates for display fabrication and pixel arrays form light valves or switches that can be fabricated with control electronics in the thinfilm material prior to transfer.
Abstract: A display panel is formed using essentially single crystal thin-film material that is transferred to substrates for display fabrication. Pixel arrays form light valves or switches that can be fabricated with control electronics in the thin-film material prior to transfer. The resulting circuit panel is than incorporated into a display panel with a light emitting or liquid crystal material to provide the desired display.
310 citations
TL;DR: A bilayer CoSi2/TiN has been grown on (100)Si, starting from a (100 p) type Si wafer deposited with thin layers of Ti followed by Co metal, through a two-stage annealing in a nitrogen environment and an intervening etch.
Abstract: A bilayer CoSi2/TiN has been grown on (100)Si, starting from a (100) p‐type Si wafer deposited with thin layers of Ti followed by Co metal, through a two‐stage annealing in a nitrogen environment and an intervening etch. In this process, Co and Ti switch places to form CoSi2 covered with TiN on Si. Cross‐section transmission electron microscopy, and Rutherford backscattering/channeling spectrometry were used to characterize the bilayer sample. The CoSi2 was found to be single crystal, fully coherent, and epitaxial with (100)Si, whereas the TiN at the top of CoSi2 was polycrystalline. The stress in the CoSi2/TiN layer was found to be 1.9×1010 dynes/cm2. The planar (100) CoSi2/Si interface was interrupted with {111} ledges which are believed to be structural ledges present to maintain the coherency at the interface.
268 citations
TL;DR: It is shown that the electronic structure of the oxygen sublattice can be described in a band-structure picture while for the Ni sublATTice electron localization effects lead to a breakdown of the band-Structure picture.
Abstract: We have investigated the adsorption of NO on a thin NiO(100) film of several layers thickness grown on top of a Ni(100) surface in comparison with data of an in vacuo cleaved NiO(100) single crystal. The layer exhibits a high defect density. We demonstrate via application of several surface-sensitive electron-spectroscopic techniques [i.e., x-ray photoelectron spectroscopy (XPS), angle-resolved ultraviolet photoelectron spectroscopy (ARUPS), near-edge x-ray-absorption fine structure (NEXAFS), and high-resolution electron-energy-loss spectroscopy (HREELS)] that this layer has similar occupied (ARUPS) and unoccupied (NEXAFS) states as a bulk NiO(100) sample. In spite of its limited thickness, the band structure of the film exhibits dispersions perpendicular to the surface compatible with bulk NiO(100). It is shown that the electronic structure of the oxygen sublattice can be described in a band-structure picture while for the Ni sublattice electron localization effects lead to a breakdown of the band-structure picture. NO on NiO desorbs at 220 K. This indicates weak chemisorption. The NO coverage is close to 0.2 relative to the number of Ni surface atoms as determined by XPS.HREELS reveals that there is only one species on the surface documented by the observation of only one bond-stretching frequency. NEXAFS data on the system and a comparison with previous data on the system NO/Ni(100) indicate that the molecular axis of adsorbed NO is tilted by an angle of approximately 45\ifmmode^\circ\else\textdegree\fi{} relative to the surface normal. The N 1s XP spectra of the weakly chemisorbed species show giant satellites similar to the previously observed cases for weak chemisorption on metal surfaces. This is the first observation of an intense satellite structure for an adsorbate on an insulator surface, which shows that there must be sufficient screening channels even on an insulating surface. A theoretical assignment of the peaks is discussed. We compare the spectroscopic properties of the NO species on the thin-film oxide surface, which is likely to contain a certain number of defects, with NO adsorbed on a basically defect-free bulk oxide surface by thermal-desorption (TDS) and XP spectra. TDS and XP spectra of the bulk system are basically identical as compared with the oxide film, indicating that the majority of species adsorbed on the film is not adsorbed on defects but rather on regular NiO sites. Results of ab initio oxide cluster calculations are used to explain the bonding geometry of NO on regular NiO sites.
216 citations
TL;DR: In this article, X-ray line profile measurements were performed on monocrystalline specimens of the γ-hardened nickel-base superalloy SSR 99 with axes close to the [001] direction.
Abstract: X-ray line profile measurements were performed on monocrystalline specimens of the γ′-hardened nickel-base superalloy SSR 99 with axes close to the [001] direction. The aim was to measure the local lattice parameters in the γ-matrix and in the γ′-particles and to obtain information on the lattice mismatch and internal stresses. For this purpose, a special high-resolution double crystal diffractomoter with negligible instrumental line broadening was used. Measurements were performed on specimens in the initial state with cuboidal γ′-particles and on creep-deformed specimens containing the so-called γ/γ′-raft structure. In several cases the line profiles were measured as a function of the rocking angle, and the intensity distributions were mapped in reciprocal space around the (002) and (020) Bragg reflections. In the undeformed state these intensity distributionsindicate that the local lattice parameter varies spatially in the γ-phase. The line profiles of specimens in the initial state were asymmetric. A remarkable result obtained on creep-deformed specimes was that, whereas the asymmetry of the (020) line profiles was enhanced to the extent that a hump or a second peak appeared, the asymmetry of the (002) line profiles was reversed in sign. A quantitative evaluation yielded mean values of the constrained lattice mismatch which, in the case of creep-deformed specimens, differ significantly for the (001) and (010) lattice plane spacings. It is concluded that the orientation-dependent lattice spacings represent a triaxial state of residual stress which has its origin in the superposition of the originally present coherency stresses and the deformation-induced internal stresses. All observed features could be explained in detail in terms of a composite model of plastic deformation, which takes into account the dislocation networks deposited at the γ/γ′-interfaces during deformation.
195 citations
TL;DR: In this article, the packing and thermal motion of the terminal CH3 groups of monolayers of nalkane thiols self-assembled on Au(111)/mica films and a single crystal surface was studied.
Abstract: Low energy helium diffraction has been used to study the packing and thermal motion of the terminal CH3 groups of monolayers of n‐alkane thiols self‐assembled on Au(111)/mica films and a Au(111) single crystal surface. At low temperatures (<100 K), the terminal CH3 groups are arranged in domains containing a hexagonal lattice with a lattice constant of 5.01 A. As the length of the carbon chain is shortened, an abrupt decrease in the diffraction peak intensities is observed for CH3(CH2)9SH/Au(111)/mica, and no diffraction is observed for CH3(CH2)5SH/Au(111)/mica. This is indicative of a sudden decrease in surface order at around ten carbon atoms per chain. A semi‐quantitative estimation of the average domain size of each monolayer surface shows a maximum of 46 A at intermediate chain length [CH3(CH2)13SH/Au(111)/mica], decreasing to 26 A at longer [CH3(CH2)21SH/Au(111)/mica] and 41 A at shorter [CH3(CH2)9SH/Au(111)/mica] chain lengths. No phase transitions could be detected at the surfaces of these monolay...
191 citations
TL;DR: The second harmonic generation of 29 kinds of thienyl chalcone derivatives with a thiophene ring were examined in this article, and a large high quality single crystal of 60x15x10mm of this compound could be obtained from acetone solution.
180 citations
TL;DR: In this paper, the authors used Monte Carlo simulations on a square lattice for the case of nearest-neighbor attractive interactions to determine chemical, jump, and tracer diffusion coefficients D, Dj, and D*, respectively.
Abstract: Chemical, jump, and tracer diffusion coefficients D, Dj, and D*, respectively, have been determined by Monte Carlo simulations on a square lattice for the case of nearest‐neighbor attractive interactions. D was determined by the fluctuation autocorrelation method and by the Kubo–Green equation, using values of 〈(δN)2〉/〈N〉 determined from isotherms. 〈(δN)2〉/〈N〉 can only be determined above Tc and, for this situation, the two methods yield identical D values within the error of the simulations. Distinct high‐ and low‐T regimes for D are observed, because of the changes in 〈(δN)2〉/〈N〉 with T, with much higher activation energies and prefactors for T/Tc 1.4. For D* and Dj much smaller effects are seen. The numerical values of activation energies suggest that diffusing atoms are either isolated atoms in the dilute lattice gas or those which become detached from corners of close‐packed (1×1) islands below Tc, but have a higher nearest‐neighbor complement in the dense lattice gas above Tc.
TL;DR: In this article, the structural relationship between α and γ phases makes it possible to determine the left or right-handed chirality of all helices in the single crystals.
TL;DR: In this article, the structural and electronic properties of the recently discovered k-phase salts are examined from the viewpoint of lattice softness by calculating strain indices for short intermolecular contacts and the random potential arising from ethylene group conformational disorder prevents superconductivity in the iodide salt.
Abstract: The recently discovered k -phase salts k -(BEDT-TTF) 2 ]Cu[N(CN) 2 ]X (X=Cl,Br, I) are isostructural but differ in their superconducting properties: the Br-salt is an ambient-pressure superconductor with T c =116K, the Cl-salt becomes superconducting ( T c =128K) under a slight applied pressure of 03 kbar, and the I-salt does not exhibit superconductivity under an applied-pressure of up to 5 kbar We examine the structural and electronic properties of these three salts on the basis of their crystal structures determined at 127 K by single crystal X-ray diffraction measurements The band electronic structure of the three salts are virtually the same and do not account for the differences in the conduction properties The differences in the three salts with regard to superconductivity are examined from the viewpoint of lattice softness by calculating strain indices for short intermolecular contacts The random potential arising from ethylene group conformational disorder prevents superconductivity in the iodide salt
TL;DR: In this paper, the design of an ultrahigh vacuum microcalorimeter enabling calorimetric heats of adsorption to be obtained on single crystal surfaces as a detailed function of coverage is discussed.
Abstract: The design of an ultrahigh vacuum microcalorimeter enabling calorimetric heats of adsorption to be obtained on single crystal surfaces as a detailed function of coverage is discussed. The system comprises a pulsed supersonic molecular beam source, an ultrathin metal single crystal, and remote infrared temperature sensing. Sticking probabilities and coverages are determined pulsewise by the King and Wells method, and heat capacity calibrations are conducted in situ by laser beam pulsing. Results for CO and O2 on Ni{110} demonstrate excellent sensitivity to adsorption of ∼10−13 moles of gas (∼0.01 monolayer). The heat capacity of the calorimeter is 4.2 μJ K−1.
TL;DR: In this article, N2.5N alloy films, typically 1.5 μm thick, were grown on MgO(001) at temperatures between 400 and 850 °C by ultra-high-vacuum reactive magnetron sputtering in pure N 2.5Al0.
Abstract: Ti0.5Al0.5N alloy films, typically 1.5 μm thick, were grown on MgO(001) at temperatures Ts between 400 and 850 °C by ultra‐high‐vacuum reactive magnetron sputtering in pure N2. Films grown at Ts between ≂480 and 560 °C were single crystals in which the lattice misfit strain was partially relieved by glide of 〈001〉 misfit dislocations, with Burgers vector =a0/2〈011〉, on {011} planes. Cross‐sectional transmission electron microscopy investigation showed no evidence of residual extended defects in the films until thicknesses of ≂150 nm at which point threading dislocations, oriented along the [001] growth direction, were observed. Surface‐initiated spinodal decomposition, resulting in the formation of compositionally modulated NaCl‐structure platelets along [001] with width ≂1 nm, occurred over a narrow growth temperature range between 540 and 560 °C as a precursor to bulk phase separation of wurtzite‐structure AlN at Ts≥560 °C. The alloy was continuously depleted of AlN at higher growth temperatures until ...
TL;DR: In this article, the thermoelectric properties and Hall effects of a number of undoped Bi 2 Te 3 -Sb 2 Te3 pseudo-binary and Sb 2 Se 3 pseudo-ternary single crystal alloys grown by the Bridgman method were measured over the temperature range from 77 to 580 K. All of the alloys showed p -type extrinsic conduction and the analysis of the Seebeck coefficient and electrical conductivity indicated partial degeneracy at lower temperatures.
TL;DR: In this paper, the infrared reflection and Raman spectra of spinel type oxides M Cr 2 O 4 (Mg, Mn, Fe, Co, Ni, Cu, Zn) including Kramers-Kronig analyses and oscillator-fit calculations are presented.
TL;DR: The grossly nonstoichiometric perovskites SrTiO3−x with x = 0.28, 0.17, and 0.08 were obtained from a reaction of Sr2TiO4, TiO, and TiO2 at 1500°C as mentioned in this paper.
TL;DR: The dispersion of phonons on the (0001) surface of MoS2 was measured by high-resolution electron energy loss spectroscopy along both the and azimuths, which indicates that the bonding interactions of the surface atoms are different from those of the bulk, even in a layer lattice compound.
Abstract: : The dispersion of phonons on the (0001) surface of MoS2 was measured by high-resolution electron energy loss spectroscopy along both the and azimuths (i.e., r to K and r to M respectively). The surface phonons have lower energies than the corresponding bulk phonons, which indicates that the bonding interactions of the surface atoms are different from those of the bulk, even in a layer lattice compound. Since sputtered MOS2 lubricant films are composed of many small crystallites, the relative number of surface atoms in a film is much higher than in a single crystal. The stronger bonding of the surface layer may affect the amount of inter- vs intra-crystalline slip in the lubrication mechanism- This work also demonstrates the use and usefulness of a new technique (high-resolution electron energy loss spectroscopy) in this laboratory. Molybdenumdisulfide, Electron energy loss spectroscopy, Surface vibrational spectroscopy, Layer-lattice compounds.
TL;DR: The structures of the antifluorite-type copper chalcogenides Cu 2 Se and Cu 1.8 S were studied using single crystal X-ray diffraction data both below and above the transition point.
TL;DR: An X-ray single-crystal determination of the CuO structure has been made at 196 K, i.e. below the Neel temperature 230 K, and, as a check, the crystal structure at room temperature was also determined as discussed by the authors.
Abstract: An X-ray single-crystal determination of the CuO structure has been made at 196 K, i.e. below the Neel temperature 230 K, and, as a check, the crystal structure at room temperature was also determined. The correct space group for the structure at both temperature was found to be Cc. Earlier results of magnetic and neutron diffraction measurements can be explained as antiferromagnetic coupling between copper atoms via oxygen (superexchange) in chains running in the (1 0-1) direction. The structural results show changes with temperature in Cu-O distance in these chains: in each -Cu-O-Cu-group the longer is increased and the shorter decreased when passing from 196 K to room temperature. This implies a weaker antiferromagnetic coupling at room temperature. The refinement of CuO-structure at room temperature reported earlier by Asbrink and Norrby (1970) showed the symmetry to be C2/c. An attempt to refine CuO in the space group Cc with the old data was not successful. The different results obtained with different crystals are tentatively explained from published observations regarding valence fluctuations in CuO and non-stoichiometry caused by cation vacancies.
TL;DR: A low-frequency torsional oscillator has been used to search for flux-lattice melting in an untwinned single crystal and a remarkably sharp damping peak has been located.
Abstract: A low-frequency torsional oscillator has been used to search for flux-lattice melting in an untwinned single crystal of YBa2Cu3O(7-delta). The damping of the oscillator was measured as a function of temperature, for applied magnetic fields in the range H = 0.1-2.3 T. A remarkably sharp damping peak has been located. It is suggested that the temperature of the peak corresponds to the melting point of the Abrikosov flux lattice.
Patent•
10 May 1991
TL;DR: In this article, a single crystal Al film is formed on a GaAs (100) substrate and a plasma SiN film was formed as a passivation film, and the reliability of electrode wirings, which are formed of the single crystal wiring, on a compound semiconductor substrate, was improved.
Abstract: PURPOSE:To obtain a semiconductor device, which has a fine wiring, is highly integrated and is superior in high-frequency characteristics and high-speed operation, by a method wherein electrode wirings on a compound semiconductor substrate are formed of a single crystal wiring. CONSTITUTION:An single crystal Al film is formed on a GaAs (100) substrate and moreover, a plasma SiN film is formed as a passivation film. As a single crystal wiring does not contain a crystal grain boundary, which is the main cause for deteriorating the stress migration resistance and the electro-migration resistance, the reliability of electrode wirings, which are formed of the single crystal wiring, on a compound semiconductor substrate, in which fine formation is increasingly required is improved and at the same time, the uniformity of wiring work improved. Thereby, the disconnection of the electrode wirings due to stress migration can be prevented and a semiconductor device, which is high in integration and is provided with a highly reliable wiring, is obtained.
TL;DR: LiGe2(PO4)3 belongs to the Nasicon-type family and was determined on a single crystal from 3D X-ray data in this article, where the thermal expansion is positive along the c-axis, whereas shrinking is observed along the a-axis below 900 K, followed by dilatation.
TL;DR: In situ electrochemical scanning tunneling microscopy (STM) was applied to singlecrystal platinum(111), rhodium(111, and palladium(111) surfaces in an aqueous sulfuric acid solution as discussed by the authors.
Abstract: In situ electrochemical scanning tunneling microscopy (STM) was applied to single‐crystal platinum(111), rhodium(111), and palladium(111) surfaces in an aqueous sulfuric acid solution. Atomically flat surfaces of Pt(111) are roughened in solutions by the electrochemical oxidation–reduction cycle. It is shown that a single potential cycle causes the formation of many adatoms and very small clusters on the Pt(111) terrace. A steady‐state surface structure can be clearly observed after applying a few potential cycles. The STM image is composed of regularly arrayed islands whose diameter and height are in the ranges of 2–3 and 0.5–0.75 nm, respectively. Atomically flat terrace‐step structures can be also observed on Rh(111) and Pd(111) surfaces. The effect of oxidation–reduction cycle on these surfaces is also discussed.
TL;DR: In this article, the adsorption and reaction of HCOOH on the (0001)-Zn surface of ZnO was studied using high resolution electron energy loss spectroscopy (HREELS).
TL;DR: In this paper, the elastic constants on a single crystal of the shape-memory alloy NiTi in a wide temperature range are measured and step-like anomalies and hysteresis are detected at the austenitic-martensitic phase transition.
Abstract: The authors present measurements of the elastic constants on a single crystal of the shape-memory alloy NiTi in a wide temperature range. Step-like anomalies and hysteresis are detected at the austenitic-martensitic phase transition which provide evidence for the strain-order parameter coupling in the pre-martensitic phases. The results are discussed in the framework of existing Landau theory models.
TL;DR: In this paper, a tetrahedral anvil was used to grow monoclinic molybdenum trioxide (MoO3-II) with unit cell parameters.
TL;DR: The theory for the conductance with the STM tip near a single step and in the center of a pit is shown to agree well with experiment and theoretical results are presented for a periodic array of steps for which one-dimensional Kronig-Penney bands should be observable.
Abstract: A simple theory of the effect of monatomic steps on the local density of surface states and on the conductance of a scanning tunneling microscope (STM) has been developed. This theory is based upon reflection and transmission amplitudes for surface electron waves. It is assumed that a step acts as a repulsive barrier, which is entirely consistent with experimental observations on the (111) surface of a Au single crystal. Comparison to experiment has been made for a flat surface to establish that the model for the tip and barrier is adequate. The theory for the conductance with the STM tip near a single step and in the center of a pit is shown to agree well with experiment. Theoretical results are also presented for a periodic array of steps for which one-dimensional Kronig-Penney bands should be observable, especially at reduced temperature.