Showing papers on "Single crystal published in 1998"
TL;DR: In this paper, the optical properties of ZnO crystals using a variety of optical techniques were compared and it was concluded that the room temperature band gap is 3.3 eV and that the other values are attributable to a valence band-donor transition at ∼3.15
Abstract: Three different values (3.1, 3.2, and 3.3 eV) have been reported for the optical band gap of zinc oxide single crystals at room temperature. By comparing the optical properties of ZnO crystals using a variety of optical techniques it is concluded that the room temperature band gap is 3.3 eV and that the other values are attributable to a valence band-donor transition at ∼3.15 eV that can dominate the optical absorption when the bulk of a single crystal is probed.
1,388 citations
TL;DR: In this paper, a two dimensional nucleation during the initial growth was observed by in situ reflection high energy electron diffraction, followed by a morphology transition to 3D nucleation by using molecular beam epitaxy.
Abstract: ZnO single crystal thin films were grown on c-plane sapphire using oxygen microwave plasma assisted molecular beam epitaxy. Atomically flat oxygen-terminated substrate surfaces were obtained by pre-growth cleaning procedures involving an oxygen plasma treatment. A two dimensional nucleation during the initial growth which is followed by a morphology transition to three dimensional nucleation was observed by in situ reflection high energy electron diffraction. X-ray diffraction (XRD) and photoluminescence investigations suggest that the ZnO epilayer consists of a high quality layer on top of a transition layer containing a high density of defects in the interfacial region. A full width at half maximum (FWHM) of 0.005° is obtained for the ZnO(0002) diffraction peak in an XRD rocking curve, while a broad tail extending from the peak can also be observed. The photoluminescence spectra exhibit dominant bound exciton emission with a FWHM of 3 meV at low temperatures and free exciton emission combined with a ver...
1,261 citations
TL;DR: In this article, the topmost oxide layer was observed to hydroxylate after immersion in water, which was used to enhance the etch-selectivity of SrO relative to TiO2 in a buffered HF solution.
Abstract: In recent years, well-defined and nearly perfect single crystal surfaces of oxide perovskites have become increasingly important. A single terminated surface is a prerequisite for reproducible thin film growth and fundamental growth studies. In this work, atomic and lateral force microscopy have been used to display different terminations of SrTiO3. We observe hydroxylation of the topmost SrO layer after immersion of SrTiO3 in water, which is used to enhance the etch-selectivity of SrO relative to TiO2 in a buffered HF solution. We reproducibly obtain perfect and single terminated surfaces, irrespective of the initial state of polished surfaces and the pH value of the HF solution. This approach to the problem might be used for a variety of multi-component oxide single crystals. True two-dimensional reflection high-energy electron diffraction intensity oscillations are observed during homo epitaxial growth using pulsed laser deposition on these surfaces.
693 citations
Patent•
11 Feb 1998TL;DR: In this article, a single crystal structure is produced by melting the substrate surface with an energy beam, supplying the molten region with material which is to be introduced into the crystal structure, completely melting the supplied material, and regulating and/or controlling the energy supply such that the solidification velocity and temperature gradient lie in the dendritic crystalline region outside the globulitic region in the GV (gradient velocity) diagram.
Abstract: Producing single crystal structures, parts or workpieces of superalloys on substrates with one or more single crystal structures comprises: (a) melting the substrate surface with an energy beam; (b) supplying the molten region with material which is to be introduced into the single crystal structure; (c) completely melting the supplied material; and (d) regulating and/or controlling the energy supply such that the solidification velocity and temperature gradient lie in the dendritic crystalline region outside the globulitic region in the GV (gradient velocity) diagram. The supplied material may be the same as the substrate material or may be a different material having a similar crystal structure, preferably a Co, Fe or Ni base superalloy such as CMSX-4.
429 citations
TL;DR: In this paper, Doped alkaline-bismuth-titanate perovskite single crystals have been grown in ferroelectric phases with high piezoelectric actuation.
Abstract: Doped alkaline–bismuth–titanate perovskite single crystals have been grown in ferroelectric phases with high piezoelectric actuation. Rhombohedral-phase Na1/2Bi1/2TiO3–BaTiO3 crystals exhibit up to 0.25% free strain with low hysteresis along the cubic 〈001〉 direction (d33∼450 pC/N). Tetragonal phase crystals exhibit free strains as high as 0.85% with greater hysteresis characteristic of domain switching; low field d33 exceeds 500 pC/N. Strain energy densities exceed those of optimized polycrystalline lead perovskites, and actuation capability is retained at compressive stresses >100 MPa.
371 citations
TL;DR: In this article, the magnetoresistance behavior of Fe3O4 in polycrystalline thin film, powder compact, and single-crystal form is compared and it is shown that negative magnetoreduction with peaks at the coercive field, observed in thin films and powder compacts but not in the single crystal, is due to fieldinduced alignment of the magnetization of contiguous grains.
Abstract: The magnetoresistance behavior of Fe3O4 in polycrystalline thin film, powder compact, and single-crystal form are compared. Negative magnetoresistance with peaks at the coercive field, observed in thin films and powder compacts but not in the single crystal, is due to field-induced alignment of the magnetization of contiguous grains. The effect is associated with intergranular transport of spin-polarized electrons.
355 citations
TL;DR: In this article, the hardness of the multilayers for layer thicknesses (h) > 50 nm is explained by Hall-Petch model with grain boundaries and interfaces as barriers.
348 citations
TL;DR: In this article, crystal ion slicing was used to create a buried sacrificial layer in single-crystal c-cut poled wafers of LiNbO3, inducing a large etch selectivity between the sacrificial layers and the rest of the sample.
Abstract: We report on the implementation of crystal ion slicing in lithium niobate (LiNbO3). Deep-ion implantation is used to create a buried sacrificial layer in single-crystal c-cut poled wafers of LiNbO3, inducing a large etch selectivity between the sacrificial layer and the rest of the sample. 9-μm-thick films of excellent quality are separated from the bulk and bonded to silicon and gallium arsenide substrates. These single-crystal films have the same room-temperature dielectric and pyroelectric characteristics, and ferroelectric transition temperature as single-crystal bulk. A stronger high-temperature pyroelectric response is found in the films.
306 citations
TL;DR: In this paper, X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM) were combined to investigate the thickness, chemical composition, and structure of passive films formed in 0.5 M H 2 SO 4 on (100)Fe-18Cr-13Ni.
Abstract: X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM) were combined to investigate the thickness, chemical composition, and structure of passive films formed in 0.5 M H 2 SO 4 on (100)Fe-18Cr-13Ni. The XPS measurements show that aging under polarization at +500 mV/SHE causes a dehydration reaction of the outer chromium hydroxide layer of the passive film. This reaction results in a thickening of the mixed Cr(III) and Fe(III) inner oxide layer and increases the Cr 2 O 3 enrichment. This reaction consumes, in addition to chromium hydroxide of the outer layer, chromium from the metallic phase underneath the passive film. Only traces of nickel (hydroxide) are detected in the passive film, whereas Ni enrichment is observed in the alloy underneath the passive film. High-resolution STM images reveal that aging under polarization causes a crystallization of the inner Cr 2 O 3 oxide layer in epitaxy with the substrate. The epitaxial relationship is (0001) α-Cr 2 O 3 ||(100) Fe-18Cr-13Ni with [2130]α-Cr 2 O 3 ||[011] Fe-18Cr-13Ni. The crystallization proceeds with a faster kinetics than on (110) Fe-22Cr in the same conditions. The crystallization rate is modified by the presence of Ni in the alloy, which is enriched in the metallic phase underneath the film and slows down the formation of Cr 2 O 3 in the inner part of the film. This favors a more complete process of crystallization. Aging under polarization is beneficial to the further stability of the passive film in air.
260 citations
Patent•
27 May 1998
TL;DR: In this paper, an amorphous semiconductor thin film is crystallized by utilizing a catalyst element, the catalyst element is removed by performing a heat treatment in an atmosphere containing a halogen element.
Abstract: After an amorphous semiconductor thin film is crystallized by utilizing a catalyst element, the catalyst element is removed by performing a heat treatment in an atmosphere containing a halogen element. A resulting crystalline semiconductor thin film exhibits {110} orientation. Since individual crystal grains have approximately equal orientation, the crystalline semiconductor thin film has substantially no grain boundaries and has such crystallinity as to be considered a single crystal or considered so substantially.
229 citations
TL;DR: In this article, an X-ray diffraction investigation has been made of the crystal structure to determine the distribution of hydrogen bonds, to understand the crystalline thermal expansion and to determine influence of water on the polymer crystals and crystallisation process.
TL;DR: In this paper, the authors report on the material, electrical, and optical properties of metal-semiconductor-metal ultraviolet photodetectors fabricated on single-crystal GaN, with active layers of 1.5 and 4.0 μm thickness.
Abstract: We report on the material, electrical, and optical properties of metal–semiconductor–metal ultraviolet photodetectors fabricated on single-crystal GaN, with active layers of 1.5 and 4.0 μm thickness. We have modeled current transport in the 1.5 μm devices using thermionic field emission theory, and in the 4.0 μm devices using thermionic emission theory. We have obtained a good fit to the experimental data. Upon repeated field stressing of the 1.5 μm devices, there is a degradation in the current–voltage (I–V) characteristics that is trap related. We hypothesize that traps in the GaN are related to a combination of surface defects (possibly threading dislocations), and deep-level bulk states that are within a tunneling distance of the interface. A simple qualitative model is presented based on experimental results. For devices fabricated on wafers with very low background free electron concentrations, there is a characteristic “punch-through” voltage, which we attribute to the interaction of the depletion ...
01 May 1998-Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms
TL;DR: In this paper, the microstructure and physical properties of 6H-SiC amorphized by both ion and neutron irradiation were analyzed using high-resolution transmission electron microscopy (HRTEM).
Abstract: This paper presents results on the microstructure and physical properties of SiC amorphized by both ion and neutron irradiation. Specifically, 0.56 MeV Si ions have been implanted in single crystal 6H–SiC from ambient through >200°C and the critical threshold for amorphization was measured as a function of the irradiation temperature. From a high resolution transmission electron microscopy (HRTEM) study of the crystalline to amorphous transition region in these materials, elongated pockets of amorphous material oriented parallel to the free surface are observed. Single crystal 6H–SiC and hot pressed and sintered 6H and 3C SiC were neutron irradiated at approximately 70°C to a dose of ∼2.56 dpa causing complete amorphization. Property changes resulting from the crystal to amorphous transition in SiC include a density decrease of 10.8%, a hardness decrease from 38.7 to 21.0 GPa, and a decrease in elastic modulus from 528 to 292 GPa. Recrystallization of the amorphized, single crystal 6H–SiC appears to occur in two stages. In the temperature range of ∼800–1000°C, crystallites nucleate and slowly grow. In the temperature range of 1125–1150°C spontaneous nucleation and rapid growth of crystallites occur. It is further noted that amorphized 6H (alpha) SiC recrystallizes to highly faulted fcc (beta) SiC.
30 Sep 1998-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the ion-beam-induced crystalline-to-amorphous phase transition in single crystal (6 H) α-SiC has been studied as a function of irradiation temperature.
Abstract: The ion-beam-induced crystalline-to-amorphous phase transition in single crystal ( 6 H) α -SiC has been studied as a function of irradiation temperature. The evolution of the amorphous state has been followed in situ by transmission electron microscopy in specimens irradiated with 0.8 MeV Ne + , 1.0 MeV Ar + , and 1.5 MeV Xe + ions over the temperature range from 20 to 475 K. The threshold displacement dose for complete amorphization in α -SiC at 20 K is 0.30 dpa (damage energy=15 eV atom −1 ). The dose for complete amorphization increases with temperature due to simultaneous recovery processes that can be adequately modeled in terms of a single-activated process. The critical temperature, above which amorphization does not occur, increases with particle mass and saturates at about 500 K. Single crystals of α -SiC with [0001] orientation have also been irradiated at 300 K with 360 keV Ar 2+ ions at an incident angle of 25° over fluences ranging from 1 to 8 Ar 2+ ions nm −2 . The damage accumulation in these samples has been characterized ex situ by Rutherford backscattering spectrometry–channeling (RBS/C) along the [0001] direction, Raman spectroscopy, cross-sectional transmission electron microscopy (XTEM), and mechanical microprobe measurements.
TL;DR: In this paper, a complex perovskite type material BaMg13Ta23O3 (BMT) with remarkable microwave dielectric properties was studied by microprobe Raman scattering in a wide temperature interval from 30 up to 1200 K.
TL;DR: In this article, a given undoped GaN layer deposited on (0001) sapphire by metalorganic chemical vapor deposition and a given high-pressure-grown GaN single crystal have been studied by three different techniques: Hemispherically scanned x-ray photoelectron diffraction, convergent beam electron diffraction and chemical etching.
Abstract: In order to resolve any doubt in lattice polarity calibrations, a given undoped GaN layer deposited on (0001) sapphire by metalorganic chemical vapor deposition and a given high-pressure-grown GaN single crystal have been studied by three different techniques: Hemispherically scanned x-ray photoelectron diffraction, convergent beam electron diffraction, and chemical etching. We conclude that Ga-polar surfaces are resistant to a 200 °C molten NaOH+KOH etching whereas N-polar surfaces are chemically active. All the observed flat GaN films grown on (0001) sapphire have Ga polarity. On the contrary, the native flat faces of undoped GaN bulk crystals have N polarity.
TL;DR: In this paper, the process of sulfate adsorption on Cu(111) from a sulfuric acid electrolyte (5mM H2SO4) and the resulting surface structures have been investigated by in-situ scanning tunneling microscopy (STM) and cyclic voltammetry (CV).
TL;DR: In this article, a large single crystal (6mmO × 50 mm) of YbB12 was grown by floating zone method using a newly developed image-furnace with four xenon lamps.
TL;DR: In this article, a metal nanoparticle system has been prepared by 200 Kev Ag+ ion implantation into perfect single crystal SiO2 at room temperature to dose: 6.7×1016/cm2.
Abstract: A metal nanoparticle system has been prepared by 200 Kev Ag+ ion implantation into perfect single crystal SiO2 at room temperature to dose: 6.7×1016/cm2. The system presents quasidual-layer structure: the shallower implanted layer containing noninteracting small Ag nanoparticles and the deeper layer containing interacting large nanoparticles, in which great red shift, about 1 eV, comparing with the plasmon resonance frequency of the noninteracting nanoparticle, can be clearly observed. The red shift is attributed to the multipoles interaction among the high density nanoparticles at external electric field. Moreover, the magnitude of red shift increases with implanted dose.
TL;DR: In this paper, the transient oxidation stage of single crystal NiAl was investigated using scanning electron microscopy, transmission electron microscope, electron diffraction, and high-resolution electron microscope.
TL;DR: In this paper, the adsorption of H2O on a single-crystal α-Al2O3(0001) surface was examined using laser-induced thermal desorption (LITD) and temperature-programmed DESORption (TPD) techniques.
Abstract: The adsorption of H2O on a single-crystal α-Al2O3(0001) surface was examined using laser-induced thermal desorption (LITD) and temperature-programmed desorption (TPD) techniques. α-Al2O3(0001) mode...
TL;DR: In this article, the dielectric properties of a single crystal rutile (TiO2) resonator have been measured using whispering gallery modes and the loss tangent and dielectoric constant of monocrystalline Rutile was determined accurately.
Abstract: The dielectric properties of a single crystal rutile (TiO2) resonator have been measured using whispering gallery modes. Q factors and resonant frequencies were measured from 300 to 10 K. Q factors as high as 104, 105, and 107 were obtained at 300, 80, and 10 K, respectively. Using the whispering gallery mode technique we have determined accurately the loss tangent and dielectric constant of monocrystalline rutile and obtained much more sensitive measurements than previously reported. We show that rutile exhibits anisotropy in both the loss tangent and permittivity over the range from 10 to 300 K.
TL;DR: In this article, the preparation of ordered ultra-thin cerium oxide overlayers on nonreconstructed Pt(111) single crystal surfaces is reported, and thin electron-beam evaporated CeO2 layers (d = 21 A) decompose during heating in ultra-high vacuum (UHV) at T = 1000 K and form domains of ordered PtCe2 and Ptce3 surface alloys.
30 Nov 1998-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the deformations of a face-centered cubic polycrystal are simulated under idealized (plane strain compression) rolling conditions, and the influence of the local neighborhood on crystal deformation is examined by conducting a series of numerical experiments on the same set of crystals.
Abstract: The deformations of a face-centered cubic polycrystal are simulated under idealized (plane strain compression) rolling conditions. A polycrystal is constructed using 1099 rhombic dodecahedron shaped crystals, each discretized with 48 tetrahedra elements. The rhombic dodecahedron is a 12-sided, space-filling polyhedron and serves as an idealized crystal geometry. The material behavior is specified at the level of a single crystal with rate dependent slip. The numerical formulation maintains compatibility and equilibrium in a weak sense using hybrid finite element methodology. The influence of the local neighborhood on crystal deformation is examined by conducting a series of numerical experiments on the same set of crystals. Each simulation uses a different spatial mapping of orientations to effectively alter the neighborhood of each crystal, allowing the dependence of deformation on crystal orientation to be examined. Comparisons are made to earlier results obtained with brick shaped crystals and to the results obtained with a second polycrystal consisting of 172 crystals with 576 elements in each rhombic dodecahedron. Coarse crystal discretizations are adequate for modeling bulk anisotropic properties, but a detailed investigation of local neighborhood effects require a finely discretized mesh that is better able to capture gradients in the deformation field.
TL;DR: In this paper, the thin film structure and hole mobility of dihexyl quaterthiophene are reported, and the mobility ranges from 0.05 to 0.23 cm2/Vs, depending on the deposition temperature.
Abstract: The thin film structure and hole mobility of 5,5‘‘‘-dihexylquaterthiophene are reported. Films sublimed onto Si/SiO2 or carbon grids held at 30−100 °C are single-crystal-like over tens of micrometers as shown by electron diffraction. The orientation has the long axis of the quaterthiophene core nearly perpendicular to the substrate. The mobility ranges from 0.05 to 0.23 cm2/Vs, depending on the deposition temperature, much higher than would be expected based on earlier thiophene oligomer data.
TL;DR: The transport and magnetic properties of magnetite (Fe3O4) thin films grown epitaxially on single crystal MgO(100) and SrTiO3 (100) substrates, and with multiple grain orientations on polycrystalline Sr TiO3 substrates have been investigated in this paper.
Abstract: The transport and magnetic properties of magnetite (Fe3O4) thin films grown epitaxially on single crystal MgO(100) and SrTiO3(100) substrates, and with multiple grain orientations on polycrystalline SrTiO3 substrates, have been investigated. The films are grown using pulsed laser deposition and their epitaxial quality determined using ion channeling measurements. Transport and magnetic studies of Fe3O4 films as a function of thickness and morphology suggest that epitaxial strain and growth defects affect the width and temperature of the Verwey transition. In addition, these factors also significantly influence the magnetic coercivity of the films. The low-field magnetoresistance (MR) behaviors of epitaxial and polycrystalline films as a function of temperature have been compared and they were found to be quite similar, suggesting very small contribution to the MR from grain boundaries.
TL;DR: In this article, the title compound has been synthesized by slow diffusion of aqueous solutions containing K4[Mo(CN)7]·2H2O and [Mn(H 2O)6](NO3)2, respectively.
Abstract: The title compound has been synthesized by slow diffusion of aqueous solutions containing K4[Mo(CN)7]·2H2O and [Mn(H2O)6](NO3)2, respectively. The compound crystallizes in the monoclinic system, space group P21/c. The Mo site is surrounded by seven −C−N−Mn linkages in a distorted pentagonal bipyramid fashion. There are two distorted octahedral Mn sites, one with four and the other with three Mn−N−C−Mo linkages. The structure is three-dimensional and of low symmetry. It consists of ladders made of edge-sharing lozenge motifs (MoCNMnNC)2 running along the a direction. These ladders are linked further along the b and c directions. Both temperature dependences of the magnetic susceptibility and field dependences of the magnetization have been investigated along the three crystallographic directions, a, b, and c*. The angular dependence of the magnetization in the ab plane as a function of the external field has also been measured. These single crystal magnetic measurements have revealed that the compound orde...
TL;DR: In this article, the authors present low-frequency dielectric loss and nonlinearity measurements in SrTiO3 thin films grown by pulsed laser deposition on SrRuO3 electrode layers.
Abstract: We present low-frequency dielectric loss and nonlinearity measurements in SrTiO3 thin films grown by pulsed laser deposition on SrRuO3 electrode layers. A low loss tangent in the order of 10−4, close to the level found in SrTiO3 single crystals, was observed. Combined with a large tunability, this resulted in a figure of merit for frequency and phase agile materials that can rival that observed in single crystals. The result is potentially significant for tunable microwave device applications, and it points to stress and interface effects as the possible causes for higher dielectric losses in thin films.
TL;DR: A review of the current state of knowledge of the interaction of oxygen, nitrogen and mixed O+N layers with rh surfaces is presented in this article, highlighting structural aspects and their impact on the surface reactivity.