Showing papers on "Single crystal published in 2003"
TL;DR: CRYSTALS as mentioned in this paper contains a modern crystallographic human-interface design, and novel strategies incorporating chemical knowledge and sensible crystallographic guidance into crystal structure analysis software, which can still only be achieved under very favourable conditions.
Abstract: The determination of small-molecule structures from single-crystal X-ray data is being carried out by researchers with little or no crys- tallographic training. At the same time, completely automatic crystal structure analysis can still only be achieved under very favourable conditions. Many of the problems that cause automatic systems to fail could be resolved with suitable chemical insight, and until this is built- in, programs continue to need human guidance. CRYSTALS version 12 contains a modern crystallographic human-interface design, and novel strategies incorporating chemical knowledge and sensible crystallographic guidance into crystal structure analysis software.
2,573 citations
TL;DR: The removal of clathrated oxygen ions from the crystallographic cages in a single crystal of 12CaO·7Al2O3, leading to the formation of high-density electrons highly localized in the cages, may be regarded as a thermally and chemically stable single crystalline “electride.”
Abstract: We removed approximately 100% of clathrated oxygen ions from the crystallographic cages in a single crystal of 12CaO.7Al2O3, leading to the formation of high-density (approximately 2 x 10(21) cm-3) electrons highly localized in the cages. The resulting electron forms a structure that we interpret as an F+ center and migrates throughout the crystal by hopping to a neighboring cage with conductivity approximately 100 siemens per centimeter, demonstrating that the encaged electron behaves as an anion. The electron anions couple antiferromagnetically with each other, forming a diamagnetic pair or singlet bipolaron. The resulting [Ca24Al28O64]4+(4e-) may be regarded as a thermally and chemically stable single crystalline "electride."
719 citations
TL;DR: In this article, the correlation between the power of the excitation laser, the temperature of the sampled spot and the degree of oxidation of magnetite was accurately established, and three independent methods based on the quasi-harmonic approximation and on the ratio of the Stokes to anti-Stokes intensities were used to calculate the local temperature.
Abstract: Natural magnetite (Fe3O4) in the form of single crystal and powder was studied by laser Raman spectroscopy at various laser powers. The correlations between the power of the excitation laser, the temperature of the sampled spot and the degree of oxidation of magnetite were accurately established. In the course of the oxidation of the single crystal of magnetite, the first characteristic features of hematite appear at about 300 and 410 cm−1, at a temperature close to 240°C. This may explain the erroneous assignment of these modes to the intrinsic Raman modes of magnetite in some studies. For the finely powdered magnetite, which is much more easily prone to oxidation, the reaction mechanism proceeds via a metastable maghemite (γ-Fe2O3) before the final product hematite is formed. Three independent methods based on the quasi-harmonic approximation and on the ratio of the Stokes to anti-Stokes intensities were used to calculate the local temperature of the laser-heated spot. Temperature-induced shifts of phonon bands were also evaluated. The phonons shift at the following rates: A1g − 0.023(1) cm−1 K−1, T2g(2) − 0.030(2) cm−1 K−1, Eg − 0.019(5) cm−1 K−1 and T2g(1) − 0.00(1) cm−1 K−1. Copyright © 2003 John Wiley & Sons, Ltd.
515 citations
TL;DR: It is found that all polymorphs of carbamazepine possess identical strong hydrogen bonding patterns, similar molecular conformations, and stabilities that are within 0.7 kcal/mol of each other.
453 citations
TL;DR: In this article, the photoluminescence (PL) spectra of ZnO single crystal nanorods grown by catalyst-free metalorganic vapor phase epitaxy were analyzed.
Abstract: We report on the photoluminescent characteristics of ZnO single crystal nanorods grown by catalyst-free metalorganic vapor phase epitaxy. From photoluminescence (PL) spectra of the nanorods at 10 K, several PL peaks were observed at 3.376, 3.364, 3.360, and 3.359 eV. The PL peak at 3.376 eV is attributed to a free exciton peak while the other peaks are ascribed to neutral donor bound exciton peaks. The observation of the free exciton peak at 10 K indicates that ZnO nanorods prepared by the catalyst-free method are of high optical quality.
424 citations
TL;DR: Structural characterizations by transmission electron microscopy (TEM) and electron diffraction showed that nanowires of Au, Ag, and Cu are single-crystalline with a preferred [111] orientation, whereas Ni, Co, and Rh wires are poly Crystalline.
Abstract: Metallic nanowires (Au, Ag, Cu, Ni, Co, and Rh) with an average diameter of 40 nm and a length of 3−5 μm have been fabricated by electrodeposition in the pores of track-etched polycarbonate membranes. Structural characterizations by transmission electron microscopy (TEM) and electron diffraction showed that nanowires of Au, Ag, and Cu are single-crystalline with a preferred [111] orientation, whereas Ni, Co, and Rh wires are polycrystalline. Possible mechanisms responsible for nucleation and growth for single-crystal noble metals versus polycrystalline group VIII-B metals are discussed.
349 citations
TL;DR: In this paper, a wide and long ribbons of single-crystalline SnO2 have been achieved via laser ablation of a single crystal target using X-ray diffraction and transmission electron microscopy (TEM).
Abstract: Wide and long ribbons of single-crystalline SnO2 have been achieved via laser ablation of a SnO2 target. Transmission electron microscopy (TEM) shows the as-grown SnO2 ribbons are structurally perfect and uniform, with widths of 300-500 nm, thicknesses of 30-50 nm (width-to-thickness ratio of ∼ 10), and lengths ranging from several hundreds of micrometers to the order of millimeters. X-ray diffraction (XRD) pattern and energy-dispersive X-ray spectroscopy (EDS) spectral analysis indicate that the ribbons have the phase structure and chemical composition of the rutile form of SnO2. Selected-area electron diffraction (SAED) patterns and high-resolution TEM images reveal that the ribbons are single crystals and grow along the [100] crystal direction. Photoluminescence measurements show that the synthesized SnO2 ribbons have one strong emission band at ∼ 605 nm and a red-shift of ∼ 30 nm, as compared to standard SnO2 powder, which may be attributed to crystal defects and residual strains accommodated during the growth of the ribbons.
303 citations
TL;DR: Direct evidence for the sole existence of dimeric structure in the powder and the thin film of Zn(BTZ)(2) is provided and strong intermolecular interaction may be expected to enable good electron transport properties as compared with tris(8-hydroxyquinolinato)aluminum.
Abstract: Bis(2-(2-hydroxyphenyl)benzothiazolate)zinc (Zn(BTZ)(2)) is one of the best white electroluminescent materials used in organic light-emitting diodes (LEDs). Despite a large number of studies devoted to this complex, very little is known about its basic molecular and electronic structures and electron transport properties in LEDs. Therefore, we investigate the structures and electroluminescent properties. The unsolvated single crystal of Zn(BTZ)(2) was grown and its crystalline structure was determined from X-ray diffraction data. The crystal is triclinic, space group P-1, a = 9.4890(19) A, b = 9.5687(19) A, c = 11.685(2) A, alpha = 84.38(3) degrees, beta = 78.94(3) degrees, gamma = 83.32(3) degrees. The structure of the chelate is dimeric [Zn(BTZ)(2)](2) with two isotropic Zn(2+) ion centers having five-coordinate geometry. The present study provides direct evidence for the sole existence of dimeric structure in the powder and the thin film. The dimer is energetically more stable than the monomer. Analysis of the electronic structure of [Zn(BTZ)(2)](2) calculated by density functional theory reveals a localization of orbital and the distribution of four orbital "tetrads". The structural stabilities of both anion and cation and the distribution of the hole in the cation and that of the excess electron in the anion are discussed in terms of theoretical calculations. Strong intermolecular interaction may be expected to enable good electron transport properties as compared with tris(8-hydroxyquinolinato)aluminum.
287 citations
TL;DR: In this paper, the growth of single-crystal tubular ZnO whiskers was achieved via a process of first reduction and following oxidation of ZnS powders, and the products were characterized using x-ray powder diffraction, scanning electron microscopy, transmission electron microscope, and photoluminescence spectroscopy.
Abstract: The growth of single-crystal tubular ZnO whiskers was achieved via a process of first reduction and following oxidation of ZnS powders. The products were characterized using x-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, and photoluminescence spectroscopy. The whiskers are tubular single crystals with the [001] growth crystallographic direction, and most have outer diameters of ∼400 nm, lengths of up to 15 μm, and wall thickness range of 100–150 nm. Room-temperature photoluminescence spectrum of the whiskers reveals a strong and sharp UV emission band at 381 nm and a weak and broad green emission band at 583 nm. Possible growth mechanism of the ZnO whiskers was briefly discussed.
283 citations
TL;DR: The synthesis, properties, and electroluminescent device applications of a series of five new diphenylanthrazoline molecules 1a-1e are reported, demonstrating that they are promising n-type semiconductors for organic electronics.
Abstract: The synthesis, properties, and electroluminescent device applications of a series of five new diphenylanthrazoline molecules 1a−1e are reported. Compounds 1b, 1c, and 1d crystallized in the monoclinic system with the space groups P21/c, C2/c, and P21/c, respectively, revealing highly planar molecules. Diphenylanthrazolines 1a−1e have a formal reduction potential in the range −1.39 to −1.58 V (versus SCE) and estimated electron affinities (LUMO levels) of 2.90−3.10 eV. Compounds 1a−1e emit blue light with fluorescence quantum yields of 58−76% in dilute solution, whereas they emit yellow-green light as thin films. The diphenylanthrazoline molecules as the emissive layers in light-emitting diodes gave yellow light with a maximum brightness of 133 cd/m2 and an external quantum efficiency of up to 0.07% in ambient air. Bilayer light-emitting diodes using compounds 1a−1e as the electron-transport layer and poly(2-methoxy-5-(2‘-ethyl-hexyloxy)-1,4-phenylene vinylene) as the emissive layer had a maximum external ...
273 citations
TL;DR: A single crystal of 1-butyl-3methylimidazolium chloride [bmim]Cl, a prototype ionic liquid, has successfully been prepared and an X-ray crystallographic analysis has been performed as mentioned in this paper.
Abstract: A single crystal of 1-butyl-3-methylimidazolium chloride [bmim]Cl, a prototype ionic liquid, has successfully been prepared and an X-ray crystallographic analysis has been performed It reveals the presence of a hydrogen bonding network involving the chloride anion and the ring as well as the n-butyl hydrogen atoms, a strong hydrophobic interaction between the two n-butyl groups of the [bmim] cations, and a unique corrugated sheets structure of the imidazolium rings Considering the similarity of the Raman spectra of crystalline and liquid states, we suspect that the three dimensional structure determined in the present study also exist, at least partially, in the ionic liquid state
TL;DR: In this article, the growth of single crystal ZnO nanowires on a non-single-crystal substrate using a conventional sputter deposition technique was reported, where the substrate used was silicon wafers with copper metallization.
TL;DR: The reaction of Cu(NO3)2, glutaric acid and 4,4'-bipyridine in water affords a novel 3D coordination polymer which exhibits reversible desorption and adsorption of water molecules with retention of single crystallinity.
TL;DR: A fourth type of texture is identified from complex but symmetrical patterns of lines on diffraction pole figures for thin films formed by solid-state reactions, characterized by the alignment of planes in the film and substrate that share the same d-spacing.
Abstract: In the context of materials science, texture describes the statistical distribution of grain orientations. It is an important characteristic of the microstructure of polycrystalline films1,2,3,4,5, determining various electrical, magnetic and mechanical properties. Three types of texture component are usually distinguished in thin films: random texture, when grains have no preferred orientation; fibre texture6,7,8,9,10, for which one crystallographic axis of the film is parallel to the substrate normal, while there is a rotational degree of freedom around the fibre axis; and epitaxial alignment (or in-plane texture) on single-crystal substrates11,12,13,14,15, where an in-plane alignment fixes all three axes of the grain with respect to the substrate. Here we report a fourth type of texture—which we call axiotaxy—identified from complex but symmetrical patterns of lines on diffraction pole figures for thin films formed by solid-state reactions. The texture is characterized by the alignment of planes in the film and substrate that share the same d-spacing. This preferred alignment of planes across the interface manifests itself as a fibre texture lying off-normal to the sample surface, with the fibre axis perpendicular to certain planes in the substrate. This texture forms because it results in an interface, which is periodic in one dimension, preserved independently of interfacial curvature. This new type of preferred orientation may be the dominant type of texture for a wide class of materials and crystal structures.
TL;DR: By fixing charged colloidal crystals in a poly(acrylamide) hydrogel matrix, this paper fabricated photonic crystals whose diffraction peak wavelengths were tunable by applying mechanical stress.
Abstract: By fixing charged colloidal crystals in a poly(acrylamide) hydrogel matrix, we fabricated photonic crystals whose diffraction peak wavelengths were tunable by applying mechanical stress. The reflection spectrum for a single crystal grain was measured by applying microspectroscopy under compression. The photonic band gap wavelength shifted linearly and reversibly over almost the entire visible light wavelength region (460−810 nm).
TL;DR: In this paper, a 2D single crystalline layer of spherical diblock copolymer domains templated by lateral substrate topology melts via a continuous defect generation process, similar to that predicted by Kosterlitz, Thouless, Halperin, Nelson, and Young.
Abstract: We observe that a 2-D single crystalline layer of spherical diblock copolymer domains templated by lateral substrate topology melts via a continuous defect generation process, similar to that predicted by Kosterlitz, Thouless, Halperin, Nelson, and Young. The layer of spheres is allowed to order (or disorder) by annealing for 72 h at a given temperature, T, that corresponds to a given χNmin, where χ is the temperature-dependent Flory−Huggins parameter and Nmin is the number of mers in the minority block. The structure of the layer is revealed by imaging the ion beam etched film using scanning force microscopy. If χNmin > 9, the film is polycrystalline and the system appears to be kinetically trapped. For 9 > χNmin > 7.4, we observe that the film is a single crystal with quasi-long-range order and few defects, as expected for the 2-D crystal. As T is increased further (χNmin is decreased), we observe that defects are generated, predominantly dislocation pairs and other dislocation clusters with no long-ran...
TL;DR: It is argued that variability of mixing in batch crystallization may be a source of the variation in the number of crystals ultimately appearing in the sample.
TL;DR: In this article, the effect of N vacancies on the mechanical properties of epitaxial TiNx(001) layers with x=0.67-1.0 was investigated. And they attributed the observed vacancy hardening to a reduced dislocation mobility arising from an increase in the rate-limiting activation energy for cation migration.
Abstract: We investigate the effect of N vacancies on the mechanical properties of epitaxial δ-TiNx(001) layers with x=0.67–1.0. The relaxed lattice parameter increases linearly with x in good agreement with ab initio density functional calculations, indicating that deviations from stoichiometry are entirely due to anion vacancies. Hardness values increase continuously, while the elastic modulus decreases with increasing N-vacancy concentration. We attribute the observed vacancy hardening to a reduced dislocation mobility arising from an increase in the rate-limiting activation energy for cation migration.
Patent•
04 Mar 2003
TL;DR: In this paper, a polycrystalline Si layer is grown by thermally crystallizing an amorphous Si thin film so as to form the poly-crystaline Si thin layer, which is then divided at the hydrogen ion implantation portion in an exfoliating manner.
Abstract: A polycrystalline Si thin film and a single crystal Si thin film are formed on an SiO2 film deposited on an insulating substrate. A polycrystalline Si layer is grown by thermally crystallizing an amorphous Si thin film so as to form the polycrystalline Si thin film. A single crystal Si substrate, having (a) an SiO2 film thereon and (b) a hydrogen ion implantation portion therein, is bonded to an area of the polycrystalline Si thin film that has been subjected to etching removal, and is subjected to a heating process. Then, the single crystal Si substrate is divided at the hydrogen ion implantation portion in an exfoliating manner, so as to form the single crystal Si thin film. As a result, it is possible to provide a large-size semiconductor device, having the single crystal Si thin film, whose property is stable, at a low cost.
TL;DR: In this article, a single crystal of MnSi2−x was obtained by a modified Czochralski pulling technique in a cold copper crucible, which revealed the sample to be Mn4Si7.
TL;DR: In this article, single-crystal ZnSe nanowires have been synthesized via a thermochemical method in a N 2 atmosphere with CO and H 2 gases, and two emission bands at ca. 447 and 617 nm.
TL;DR: In this article, a hexagonal, single crystal GaN along the c-axis was grown on Si (111) surface through self-assembly by molecular-beam epitaxy.
Abstract: Dislocation-free vertical GaN pillars in nanoscale were grown on Si (111) surface through self-assembly by molecular-beam epitaxy. No extra catalytic or nanostructural assistance has been employed. These nanorods have a lateral dimension from ≲10 nm to ∼800 nm and a height of ≲50 nm to ≳3 μm protruding above the film, depending on the growth parameters. The top view of the nanorods has a hexagonal shape from scanning electron microscopy. Transmission electron microscopy shows that the nanorods are hexagonal, single crystal GaN along the c-axis. An extra peak at 363 nm originated from nanorods was observed in photoluminescence spectra at 66 K, which is ascribed to the surface states according to the results of surface passivation. Micro-Raman spectroscopy on a single nanorod reveals E1 and E2 modes at 559.0 and 567.4 cm−1, respectively. Large strain was observed in both the transmission electron micrograph and the Raman shift. A possible growth mechanism is discussed.
TL;DR: A successful method for fabricating conducting nanowire bundles inside an insulating ceramic single crystal by using unidirectional dislocations, which exhibit excellent electrical conductivity and may give special properties to commonly used materials.
Abstract: Low-dimensional structures, such as microclusters, quantum dots and one- or two-dimensional (1D or 2D) quantum wires, are of scientific and technological interest due to their unusual physical properties, which are quite different from those in the bulk. Here we present a successful method for fabricating conducting nanowire bundles inside an insulating ceramic single crystal by using unidirectional dislocations. A high density of dislocations (10(9) cm(-2)) was introduced by activating a primary slip system in sapphire (alpha-Al2O3 single crystal) using a two-stage deformation technique. Plate specimens cut out from the deformed sapphire were then annealed to straighten the dislocations. Finally, the plates on which metallic Ti was evaporated were heat-treated to diffuse Ti atoms inside sapphire. As a result of this process, Ti atoms segregated along the unidirectional dislocations within about 5 nm diameter, forming unidirectional Ti-enriched nanowires, which exhibit excellent electrical conductivity. This simple technique could potentially to be applied to any crystal, and may give special properties to commonly used materials.
TL;DR: In this article, single-crystal superconducting tin nanowires with diameters of 40-160 nm have been prepared by electrochemical deposition in porous polycarbonate membranes.
Abstract: Single-crystal superconducting tin nanowires with diameters of 40–160 nm have been prepared by electrochemical deposition in porous polycarbonate membranes. Structural characterization through transmission electron microscopy and x-ray diffraction showed that the nanowires are highly oriented along the [100] direction. Although the superconducting transition temperature is close to the bulk value of 3.7 K, the effect of reduced dimensionality is clearly evident in the electrical transport properties of the thinnest wires (40 nm diameter). Magnetization measurements show that the critical field of the nanowires increases significantly with decreasing diameter to ∼0.3 T for the thinnest wires, nearly an order of magnitude larger than the bulk value.
TL;DR: An isotropic 207Pb NMR spectrum corresponding to the glassy matrix with spherical shell type Pb shifts from the cubic sites, as well as an anisotropic spectral component corresponding to polar nanoclusters with a Pb shift parallel to the [111] direction, have been observed in a PMN single crystal, demonstrating a microscopic confirmation of the model of relaxors first proposed by Burns and Dacol.
Abstract: An isotropic 2 0 7 Pb NMR spectrum corresponding to the glassy matrix with spherical shell type Pb shifts from the cubic sites, as well as an anisotropic spectral component corresponding to polar nanoclusters with a Pb shift parallel to the [111] direction, have been observed in a PbMg 1 / 3 Nb 2 / 3 O 3 (PMN) single crystal. This represents a microscopic confirmation of the model of relaxors first proposed by Burns and Dacol. A sudden increase in the intensity of the anisotropic cluster line is seen for electric fields larger than the critical field around 210 K. This demonstrates the occurrence of an orientational percolation type transition to the field-induced ferroelectric phase with about 50% of the Pb nuclei still remaining in the spherical glass matrix. A similar though smaller increase of the intensity of this line is also seen in the zero field cooled data, demonstrating that relaxor PMN is an incipient ferroelectric.
25 Nov 2003-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, a nickel-base single crystal superalloy with minor carbon addition and non-carbon was carried out at different temperatures and stresses to investigate the relationship between microstructural change and testing temperature and stress, detailing the rafting microstucture and carbides precipitation.
Abstract: Creep tests of a nickel–base single crystal superalloy with minor C addition and non-carbon were carried out at different temperatures and stresses. Correlations between microstructural change and testing temperature and stress were enabled through scanning electron microscopy (SEM) and transmission electron microscopy (TEM), detailing the rafting microstucture and carbides precipitation. The results showed that minor carbon addition prolonged the second stage of creep strain curves and improved creep properties. Some carbide was precipitated during creep tests in modified alloy. M23C6 carbide precipitated at lower temperature (871–982 °C), while (M6C)2 carbide precipitated at higher temperature (>1000 °C), all of which was considered to be beneficial to creep properties. A small amount of MC carbide formed during solidification and its decomposition product (M6C)1 were detrimental to mechanical properties, which together with micropores provided the site of initiation of cracks and led to the final fracture.
TL;DR: In this article, the authors demonstrated that the crystal lines written by YAG laser irradiations are β-BaB2O4 (β-BBO) single crystals with the c-axis orientation along the laser scanning direction.
Abstract: The technique for the writing of crystal lines in glass by Nd:YAG laser irradiation, selective atom heat processing, is applied to rare-earth (Sm3+, Dy3+) barium borate glasses, and nonlinear optical β-BaB2O4 (β-BBO) crystal lines with a width of ∼5 μm are fabricated. The crystal lines show uniform colors in polarized optical microscope and second-harmonic generation (SHG) measurements. The azimuthal dependence of SHG signals in the crystal lines is the same as that in commercially available β-BBO bulk single crystals. It is demonstrated that the crystal lines written by YAG laser irradiations are β-BBO single crystals with the c-axis orientation along the laser scanning direction.
TL;DR: In this article, the authors used model-based information on the peak resistance to fracture of high angle grain boundaries, with a given tilt and twist misorientation across them, and detailed measurements of orientations of individual grains in the samples, to develop percolation maps of cleavage through the field of grains that predicted the actual path with about 70% accuracy when compared with experimental observations.
TL;DR: The microstructure of zinc oxide particles precipitated in the presence of a poly(ethylene oxide-block-methacrylic acid) (P(EO-b-MAA)) and a poly (methylene oxide block-styrene sulfonic acid) diblock copolymer was investigated in this article.
Abstract: The microstructure of zinc oxide particles precipitated in the presence of a poly(ethylene oxide-block-methacrylic acid) (P(EO-b-MAA)) and a poly(ethylene oxide-block-styrene sulfonic acid) (P(EO-b-SSH)) diblock copolymer was investigated. The crystals precipitated with the P(EO-b-MAA) copolymer consist of a region with a lower but still relatively high order close to a central grain boundary and regions of very high order further away from the central grain boundary. Selected area diffraction (SAD) found single crystalline particles in the control sample, confirmed the formation of single crystalline domains with slightly different orientations with the P(EO-b-MAA) copolymer, and confirmed the formation of a mosaic texture with the P(EO-b-SSH) copolymer. High-resolution transmission electron microscopy images exhibit little defects in the control sample. More defects are found close to the central grain boundary in the sample precipitated with P(EO-b-MAA). With the P(EO-b-SSH) copolymer, a single crystal...
TL;DR: In this article, a 12×5×0.8 mm GaN single crystal was grown on a 3 µm-thick GaN thin film synthesized on sapphire using the metal organic chemical vapor deposition (MOCVD) method.
Abstract: We grew a 12×5×0.8 mm GaN single crystal using the liquid phase epitaxy (LPE) method with Na flux. This GaN single crystal was grown on a 3 µm-thick GaN thin film synthesized on sapphire using the metal organic chemical vapor deposition (MOCVD) method. It grew in a polyhedral form larger than the MOCVD-GaN substrate. Results indicate that a MOCVD-GaN thin film on a sapphire substrate functions as a seed crystal in Na flux. The use of mixed nitrogen gas containing 40% ammonia instead of pure N2 gas also enabled the growth of a 10 µm-thick GaN homo-epitaxial film on an MOCVD-GaN film under 5 atm, the lowest reported pressure for growing GaN in Na flux. In this paper, we describe the liquid phase epitaxy (LPE) technique for growing bulk GaN single crystals, as well as the results of photoluminescence (PL) measurements. We also compare the PL intensity of the bulk GaN obtained in this study and the MOCVD-GaN. PL measurements revealed that the peak intensity of GaN single crystal grown by LPE indicates 40 times larger than MOCVD-GaN film. Also, dislocation density of bulk GaN crystals could be drastically reduced by the LPE growth technique.