Showing papers on "Single crystal published in 1995"

Fabrication and Optical Properties of High-Performance Polycrystalline Nd:YAG Ceramics for Solid-State Lasers

Abstract: Transparent polycrystalline YAG with nearly the same optical characteristics as those of a single crystal were fabricated by a solid-state reaction method using high-purity powders (>99.99 wt% purity). The average grain size and relative density of the 1.1 at.% ND:YAG ceramics obtained were about 50 {micro}m and 99.98%, respectively. An oscillation experiment was performed on a cw laser by the diode laser excitation system using the fabricated ceramics. The experimental results indicated an oscillation threshold and a slope efficiency of 309 mW and 28%, respectively. These values were equivalent or superior to those of the 0.9 at.% ND:YAG single crystal fabricated by the Czochralski method.

Oxygen reduction on platinum low-index single-crystal surfaces in sulfuric acid solution. Rotating ring - Pt(hkl) disk studies

Abstract: The first results of a study of the oxygen reduction reaction on a rotating ring-disk electrode using single-crystal Pt disk electrodes are presented. The order of activity of Pt(hkl) in H{sub 2}SO{sub 4} increased in the sequence (111) (110), with 100% H{sub 2}O{sub 2} formation on Pt(111). 30 refs., 4 figs.

New nonlinear optical crystal: Cesium lithium borate

Abstract: A new nonlinear optical crystal CsLiB6O10 (CLBO), is described that can be grown from either stoichiometric melt or from solution. A large, high quality single crystal with dimensions of 14×11×11 cm3 was obtained by the top‐seeded Kyropoulos method. Fourth harmonic and fifth harmonic generations of the 1.064 μm Nd:YAG laser radiation with type‐I phase matching were realized in the CLBO crystal. Output pulse energies obtained were 110 mJ at 266 nm and 35 mJ at 213 nm.

Growth and Characterization of Sexithiophene Single Crystals

Abstract: Single crystals of unsubstituted sexithiophene (6T) were produced by a sublimation technique. X-ray structure shows that the molecule has a quasi-planar all-trans configuration, the torsional angles between adjacent rings being lower than their respective standard deviation. The unit cell belongs to space group P21h and presents the herringbone packing common to a great deal of planar molecules. Owing to the well-defined orientation of the molecules in single crystals, the polarization of vibration modes and coupling due to crystalfield effects could be unambiguously determined from polarized light IR spectroscopy. Raman spectra of the single crystals are also presented and compared to that of polycrystalline evaporated films.

Structure and Morphology of Poly(tetramethylene succinate) Crystals

Abstract: Crystals of an aliphatic polyester, poly(tetramethylene succinate) (PBS) are investigated using transmission electron microscopy. Single crystals grown from a 0.01 wt % dichlorobenzene solution show a terrace-like morphology above 65 °C and a leaflike one at lower temperatures. The molecules are packed perpendicular to the basal plane of the single crystals, and twin crystals with a (110) twin plane are frequently observed. The thickness of the single crystal lamellae increases smoothly with increasing crystallization temperature. Lattice parameters of the PBS crystal in the monoclinic unit cell are determined from the electron diffraction patterns of the single crystals and stretched films as a = 0.523 nm, b = 0.908 nm, c = 1.079 nm, and β = 123.87°. The dimension of the c-axis is shorter than the value calculated from a fully extended chain conformation, as has already been found for other aliphatic polyesters. Two types of negative spherulites are observed according to growth temperature.

Rapid formation of intermetallic compounds interdiffusion in the CuSn and NiSn systems

Abstract: Fundamental investigations were carried out to examine a new interconnection technology which is based on the rapid formation of intermetallic compounds composed of a high melting component (e.g. Cu or Ni) and a low melting component (e.g. Sn) between two layers of the high melting component at temperature just above the melting point of Sn. This reaction is known as isothermal solidification. The growth of the intermetallic compounds of the CuSn and NiSn systems were studied in thin films at temperatures from 513 to 673 K. At the beginning of interdiffusion, the Sn-rich intermetallic compounds ν (Cu6Sn5) and Ni3Sn4 grow fastest with a non-parabolic time dependence. The Cu3Sn phase grows parabolically, however, not the Ni3Sn2 phase. The Ni3Sn phase does not nucleate below 623 K in specimens with clean Ni/Sn interfaces. For the first time, the influence of the small grain size of the Cu or Ni thin films were studied by performing similar experiments with Cu or Ni single crystals. In the CuSn system the interdiffusion coefficients for Cu3Sn obtained from the thin film experiments are twice those obtained from the single crystal experiments. In the NiSn system there are no differences between thin film and single crystal results.

Long-time relaxation of the dielectric response in lead magnoniobate

Abstract: We measured the time dependencies of the dielectric permittivity of a single crystal lead magnoniobate in the zero-field\char21{}cooled regime. The logarithmic decay of the dielectric response was observed in the glassy phase. We measured the time $\ensuremath{\tau}$ from the moment of the field application for the phase transition from the glasslike to the field-induced ferroelectric state to take place, at temperatures below 220 K. The transition is accompanied by the emerging of the even harmonics of the permittivity. It is shown that $\mathrm{ln}\ensuremath{\tau}$ depends linearly on both the inverse temperature and the inverse applied field strength.

Elastic constants of single crystal γ – TiAl

Abstract: The six independent second-order elastic stiffness coefficients of a Ti{sub 44}Al{sub 56} single crystal ({ital L}1{sub 0} structure) have been measured at room temperature for the first time using a resonant ultrasonic spectroscopy (RUS) technique. These data were used to calculate the orientation dependence of Young`s modulus and the shear modulus. The Young`s modulus is found to reach a maximum near a [111] direction, close to the normal to the most densely packed planes. The elastic moduli and the Poisson`s ratio for polycrystalline materials, calculated by the averaging scheme proposed by Hill, are in good agreement with experimental data and theoretical calculations.

H in rutile-type compounds: I. Single-crystal neutron and X-ray diffraction study of H in rutile

Abstract: The crystal structure of natural hydrous rutile from a mantle eclogite nodule has been refined from single-crystal neutron diffraction data collected at 24 K. The chemical composition was 95.52 wt% Ti02, 0.74 wt% Fe203, 0.68 wt% A1203, 1.16 wt% Cr203, 1.86 wt% Nb205, and 0.04 wt% MnO, with approximately 13000 ppm OH-, as estimated by IR spectroscopy. The position of the H atom was located by examining the negative residuals in the difference Fourier maps. The refined position is near the shared edge of the cation octahedron at xl a = 0.42(1), ylb = 0.50(1), and zlc = 0 with a site occupancy of 2.7%, which is consistent with the H concentration estimated by IR spectroscopy. The O-H bond distance is 1.05 A and the OH vector is in the (001) plane, which is consistent with the strong w-polarization of the OH absorption observed in the IR spectra. Single-crystal X-ray data were collected from a synthetic anhydrous rutile crystal and a hydrous rutile crystal from the same mantle nodule as the sample used in the neutron study. The detailed X-ray structures of both rutiles were compared and no significant differences were found; the ale ratios and the 0 position were identical within error. Therefore, we conclude that the addition of H into rutile for the purpose of charge-balancing excess 3 + cations does not significantly change the structure.

Fabrication and Optical Properties of High‐Performance Polycrystalline Nd:YAG Ceramics for Solid‐State Lasers.

Abstract: Transparent polycrystalline YAG with nearly the same optical characteristics as those of a single crystal were fabricated by a solid-state reaction method using high-purity powders (>99.99 wt% purity). The average grain size and relative density of the 1.1 at.% ND:YAG ceramics obtained were about 50 {micro}m and 99.98%, respectively. An oscillation experiment was performed on a cw laser by the diode laser excitation system using the fabricated ceramics. The experimental results indicated an oscillation threshold and a slope efficiency of 309 mW and 28%, respectively. These values were equivalent or superior to those of the 0.9 at.% ND:YAG single crystal fabricated by the Czochralski method.

Crystal structure of KBe2BO3F2

Abstract: Potassium beryllium borate fluoride, KBe 2 BO 3 F 2 , is rhombohedral (hexagonal axes) R32 (No. 155), a = b = 4.427(4) A, c = 18.744(9) A, V = 318.3(4) A 3 , M = 153.93, D m = 2.40 g . cm −3 , D x = 2.41 g . cm −3 for Z = 3, F (000) = 222, μ = 11.84 cm −1 , T = 296 K. The crystal structure has been determined by single crystal X-ray diffraction and final R value for 260 unique reflections with I > 3(I) is 3.1%. The results reveal a new type of complex polyanions. All B atoms are planar triangularly coordinated while all Be atoms are tetrahedrally coordinated. The feature of the borate framework is infinite sheets [Be 2 BO 3 F 2 ] which may be described in terms of six-membered rings of [Be 2 BO 6 F 2 ] having Be-O and B-O edges in common. The nonlinear optical (NLO) properties of this compound are also discussed here and the [BO 3 ] 3− anionic groups are principally responsible for the second harmonic generation (SHG) effect

Activated dissociative chemisorption of methane on Ni(100): a direct mechanism under thermal conditions?

Abstract: The dissociative chemisorption of methane on a Ni(100) single crystal has been studied under thermal conditions as a function of pressure and temperature. The initial sticking coefficient was measured in the pressure range of 0.010–7.0 mbar at temperatures ranging from 375 to 500 K. A strong pressure dependence was observed, consistent with a direct dissociation mechanism under these thermal conditions. This was further confirmed by experiments where the gas at a low pressure was heated by a thermal finger facing the crystal surface. With the thermal finger at the same temperature as the surface, it was possible to ensure that the methane was fully equilibrated to the crystal and an activation energy of 59±1.5 kJ/mol was determined under isothermal conditions.

Single crystal silicon arrayed devices with optical shield between transistor and substrate

Abstract: A display panel is formed using a single crystal thin-film transistors that are 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 then incorporated into a projection display system with a light emitting or liquid crystal material to provide the desired light valve.

Magnetic excitation spectrum of mixed-valence SmB6 studied by neutron scattering on a single crystal

Abstract: The paramagnetic response of mixed-valence samarium hexaboride has been studied by inelastic neutron scattering using a low-absorption double-isotope single crystal of 154Sm11 B6. Measurements were performed for energy transfers 0

Phase transition(s) in titanite CaTiSiO 5 : An infrared spectroscopic, dielectric response and heat capacity study

Abstract: The structural phase transition in titanite near 500 K (averaged symmetries A2/a→P2 1/a) and a second anomaly around 900 K have been studied using infrared spectroscopy on single crystals aqnd powder samples, measurements of the dielectric properties and the specific heat. The same synthetic single crystal was used in all experiments. The phase transition near 500 K is associated with a break in the temperature evolution of phonon frequencies and absorption intensities. Some phonon signals decrease rapidly under further heating and their extrapolated intensities disappear at ca. 850 K. The most dominant temperature effect relates to Ti-O phonons with amplitudes along the crystallographic a axis. These phonons show large LO-To splitting and continue to soften under heating even at temperatures above the transitions point (ca. 500 K). The softening of these modes correlates directly with the increase of the real part of the dielectric constant with a well-pronounced anomaly at 500 K. The dielectric losses also increse with increasing temperature. Measurements under strong field do not show antiferroelectricity. The transition at 500 K generates a small but sharp λ-anomaly in the excess specific heat. A second, weaker anomaly was found near 850 K. The results are discussed in terms of thermodynamic models.

A helium atom scattering study of water adsorption on the NaCl(100) single crystal surface

Abstract: Structural and dynamic properties of H2O adsorbed on an in situ cleaved NaCl(100) crystal surface were studied by He atom scattering in the range of temperatures and partial pressures of 80–160 K and 5×10−7–5×10−10 mbar, respectively. A well‐ordered 2D H2O layer was formed during adsorption as well as by heating of 3D ice. The isosteric heat of adsorption in the monolayer regime was found to be in the range 58–63 kJ/mol. The structure of the 2D condensed phase was investigated for both modes of preparation and in both cases a (1×1) diffraction pattern was found. Time‐of‐flight spectra of the monolayer H2O/NaCl were measured in the 〈100〉 direction and phonon dispersion curves were determined. The observed dispersion‐free vibrational mode, with ℏω=5.5 meV, was identified as a frustrated translation of the water molecule parallel to the surface, via calculations for physisorption models of the H2O/NaCl interaction. Other salient features of the adsorption, the large heat of adsorption, and the magnitude of the frequency of molecular vibration perpendicular to the substrate, are reproduced in the calculations.

Anisotropy of the ZnO single crystal reflectivity in the region of residual rays

Abstract: The consistent parameters of hexagonal zinc oxide single crystals are obtained in the frame of the one-oscillator model by analyzing the dispersion spectra of IR light reflection. The anisotropy coefficients of the electron effective masses and the plasmon damping Coefficients are measured. The calculated values of electron mobility and conductivity for zinc oxide are in good agreement with the reference data available. [Russian Text Ignored]

Photoacoustic investigation of transport in semiconductors: Theoretical and experimental study of a Ge single crystal

Abstract: Photoacoustic (PA) heat-transmission measurements were used to study transport in a nearly intrinsic Ge single crystal. A theoretical model was developed which quantitatively describes excess carrier and thermal-wave space distributions, within the semiconductor under monochromatic cw modulated excitation. The PA heat-transmission, reflection, and photothermal-beam-deflection signals can be calculated using this model. It is shown that the frequency characteristic of the measurement system can be eliminated using measurements on different thicknesses of the same sample. It is also shown that both the normalized phase and amplitude spectra, as a function of the modulation frequency, can be used to determine the values of the thermal diffusivity, the excess-carrier lifetime, and the surface recombination velocity.

Adsorption of Water Vapor on the MgO(100) Single Crystal Surface

Abstract: The adsorption of H 2 O on the MgO(100) surface prepared by cleaving a single crystal in situ under ultrahigh vacuum has been studied. For the first time Low Energy Electron Diffraction (LEED) has revealed an ordering of the H 2 O monolayer with a c(4x2) translational symmetry at 150 K, highly sensitive Polarization Fourier Transform Infrared Spectroscopy (PIR) has shown a strong, very broad polarized absorption from ∼ 3050-3500 cm -1 in the spectral range of the symmetric and antisymmetric H 2 O stretching vibration ν 1 and ν 3 . The peak absorption is less than 0.1%, the integrated absorption 0.07 cm -1 and 0.11 cm -1 for p- and s-polarization, respectively, indicating that the molecular plane is nearly parallel to the surface. This broad polarized band is assigned to the ordered, nearly planar H 2 O monolayer with all OH groups participating in strong O-H...O bonds between nearest neighbor H 2 O molecules. In the ordered monolayer no dangling OH groups have been found. Additionally a sharp, p-polarized absorption at 3680 cm -1 has been observed, attributed to dangling OH bonds of the adsorbate on steps. At temperatures above 190K three sharp, polarized absorptions at 3672, 3626 and 3513 cm -1 with integrated absorptions in the range from 4.10 -4 to 5.10 -3 cm -1 and their disappearance above 240 K have been detected. They are ascribed to isolated H 2 O molecules on steps (3672 cm -1 ) and terraces, respectively. For D 2 O on MgO(100) all corresponding absorptions have been measured.

1 GHz tunable resonator on bulk single crystal SrTiO3 plated with YBa2Cu3O7-x films

Abstract: The performance of a small-size electrically tunable microwave resonator is reported. The parallel plate dielectric resonator is made of bulk single crystal SrTiO/sub 3/ coated with thin YBa/sub 2/Cu/sub 3/O/sub 7-/x films. High Q-factor and high tunability at relatively low bias voltage are observed. The dependence of Q-factor on bias voltage is discussed.