Showing papers on "Single crystal published in 2004"
TL;DR: HBN is shown to be a promising material for compact ultraviolet laser devices because it has a direct bandgap in the ultraviolet region and evidence for room-temperature ultraviolet lasing at 215 nm by accelerated electron excitation is provided.
Abstract: The demand for compact ultraviolet laser devices is increasing, as they are essential in applications such as optical storage, photocatalysis, sterilization, ophthalmic surgery and nanosurgery. Many researchers are devoting considerable effort to finding materials with larger bandgaps than that of GaN. Here we show that hexagonal boron nitride (hBN) is a promising material for such laser devices because it has a direct bandgap in the ultraviolet region. We obtained a pure hBN single crystal under high-pressure and high-temperature conditions, which shows a dominant luminescence peak and a series of s-like exciton absorption bands around 215 nm, proving it to be a direct-bandgap material. Evidence for room-temperature ultraviolet lasing at 215 nm by accelerated electron excitation is provided by the enhancement and narrowing of the longitudinal mode, threshold behaviour of the excitation current dependence of the emission intensity, and a far-field pattern of the transverse mode.
2,550 citations
TL;DR: In this article, the hole mobility for the organic conductor pentacene was obtained at room temperature and at 225 K. The number of traps was reduced by two orders of magnitude compared with conventional methods.
Abstract: We have obtained a hole mobility for the organic conductor pentacene of μ=35 cm2/V s at room temperature increasing to μ=58 cm2/V s at 225 K. These high mobilities result from a purification process in which 6,13-pentacenequinone was removed by vacuum sublimation. The number of traps is reduced by two orders of magnitude compared with conventional methods. The temperature dependence of the mobility is consistent with the band model for electronic transport.
856 citations
TL;DR: In this study, single-crystal-like anatase TiO(2) nanowires were formed in a network structure by surfactant-assisted self-assembling processes at low temperature by applying the titania nanomaterials with network structure as the Titania thin film of dye-sensitized solar cells.
Abstract: In this study, single-crystal-like anatase TiO(2) nanowires were formed in a network structure by surfactant-assisted self-assembling processes at low temperature. The crystal lattice planes of the nanowires and networks of such wires composed of many nanoparticles were almost perfectly aligned with each other due to the "oriented attachment" mechanism, resulting in the high rate of electron transfer through the TiO(2) nanonetwork with single-crystal-like anatase nanowires. The direction of crystal growth of oriented attachment was controlled by changing the mole ratio of acetylacetone to Ti, that is, regulating both the adsorption of surfactant molecules via control of the reaction rate and the surface energy. A single-crystalline anatase exposing mainly the [101] plane has been prepared, which adsorbed ruthenium dye over 4 times higher as compared to P-25. A high light-to-electricity conversion yield of 9.3% was achieved by applying the titania nanomaterials with network structure as the titania thin film of dye-sensitized solar cells.
839 citations
TL;DR: In this paper, a hole mobility for the organic conductor pentacene of 35 cm2/Vs at room temperature increasing to 58 cm2 /Vs at 225k was obtained.
Abstract: We have obtained a hole mobility for the organic conductor pentacene of 35 cm2/Vs at room temperature increasing to 58 cm2/Vs at 225K. These high mobilities result from a purification process in which 6,13-pentacenequinone was removed by vacuum sublimation. The number of traps is reduced by two orders of magnitude compared with conventional methods. The temperature depandence of the mobility is consistent with the band model for electronic transport.
750 citations
TL;DR: In this paper, the optical densities of the index matched coated spheres in a toluene/ethanol mixture and an appropriate reference dye in methanol were closely matched at the wavelength of excitation.
Abstract: [17] The diameters of a large number of spheres (typically ~ 200 spheres) were obtained from scanned TEM images processed using ImageJ and tabulated. The size distribution, defined as the standard deviation divided by the mean sphere diameter, was subsequently evaluated as such for all samples reported. The shell thickness cannot be obtained by simply taking the difference in mean diameters between the coated and bare spheres because shrinking of the cores can occur as a result of condensation of unreacted Si-OH groups when the spheres are re-dispersed in a basic solution for coating. [21] The quantum yield was determined as follows: the optical densities of the index matched coated spheres in a toluene/ethanol mixture and an appropriate reference dye in methanol were closely matched at the wavelength of excitation. To ensure that no reabsorption of the dye emission occurs, the optical densities were always maintained at a value below 0.1 at the excitation wavelength. The photo-luminescence spectra of both the sample of coated spheres and the reference dye were acquired using a SPEX Fluorolog 1680 spectrometer. Comparison of their corresponding integrated emission allowed the quantum yield of the sample to be determined. [22] Although the quantum yields of as-synthesized core±shell CdSe/ZnS NCs used were as high as 38 %, subsequent loss of the original surface ligands due to cap-exchange with AP and APS can lead to diminished quantum yields. Furthermore, the decline in the quantum yield due to processing is very dependent on the quality and thickness of the ZnS shell on the NCs, which can vary from sample to sample. [23] The standard deviation is more significant than the absolute value of the ratio due to the curvature of the microsphere, which may introduce inherent systematic error into the WDS measurement. [24] R. Study of intrinsic transport properties in single-crystal organic semiconductors has the potential to yield fundamental insights into the behavior of plastic transistors for flexible electronics. [1±4] The organic field-effect transistors (OFETs) that facilitate these studies are, however, complex structures whose properties depend on interactions between the semiconductor , gate dielectric, and electrodes. [5±7] Carrier trapping , charge doping, molecular reorientation, dipole formation , and a range of possible chemical interactions are among the many phenomena that can occur at the semiconductor/di-electric interface and degrade device performance. [8±11] We introduce an unusual device design that entirely avoids these effects by replacing the standard solid dielectric layer …
472 citations
TL;DR: In this article, a reactive TGG (RTGGG) was used to obtain highly oriented Pb(Mg1/3Nb2/3)O3-PbTiO3, Sr0.53Ba0.47Nb 2O6, and (N...
Abstract: Crystallographic texturing of polycrystalline ferroelectric ceramics offers a means of achieving significant enhancements in the piezoelectric response. Templated grain growth (TGG) enables the fabrication of textured ceramics with single crystal-like properties, as well as single crystals. In TGG, nucleation and growth of the desired crystal on aligned single crystal template particles results in an increased fraction of oriented material with heating. To facilitate alignment during forming, template particles must be anisometric in shape. To serve as the preferred sites for epitaxy and subsequent oriented growth of the matrix, the template particles need to be single crystal and chemically stable up to the growth temperature. Besides templating the growth process, the template particles may also serve as seed sites for phase formation of a reactive matrix. This process, referred to as Reactive TGG (RTGG), has been used to obtain highly oriented Pb(Mg1/3Nb2/3)O3-PbTiO3, Sr0.53Ba0.47Nb2O6, and (N...
465 citations
TL;DR: In this article, a third generation Ni-base single-crystal superalloy TMS-75 and its γ/γ " tie line alloys were designed to contain various volume fractions of γ, while the compositions of two individual phases were kept the same.
444 citations
TL;DR: The results obtained allowed us to assess the importance of knowing the carrier and removal status of Na6(CO3)(SO4)2, as a raw material for high-performance liquid chromatography, and their applications in materials science and engineering.
Abstract: [*] Dr. F. Li Department of Chemistry University of New Orleans New Orleans, LA 70148 (USA) Fax: (+1)504-280-6860 E-mail: fli@uno.edu Dr. Y. Ding, P. Gao, Prof. Dr. Z. L. Wang School of Materials Science and Engineering Georgia Institute of Technology Atlanta, GA 30332-0245 (USA) Fax: (+1)404-894-9140 E-mail: zhong.wang@mse.gatech.edu Prof. X. Xin Department of Chemistry Nanjing University Nanjing 20093 (P. R. China) [**] The authors gratefully acknowledge the financial support of the National Science Foundation of China (No.90101028) and the National Science Foundation. Zuschriften
433 citations
TL;DR: In this article, the authors used the hydrothermal method combined with a platinum inner container to grow zinc oxide (ZnO) single crystals with a large size of 50×50×15mm 3.
378 citations
TL;DR: It is evident that sorption of methanol vapor induces a change in intermolecular contacts and Pt...Pt interactions in going from red to orange, and a shift to higher energy is observed in the emission maximum with an increase in excited-state lifetime and emission intensity.
Abstract: A novel Pt(II) terpyridine complex that has a nicotinamide moiety linked to the terpyridyl ligand has been synthesized in good yield and studied structurally and spectroscopically. The complex, [Pt(Nttpy)Cl](PF6)2 where Nttpy = 4‘-(p-nicotinamide-N-methylphenyl)-2,2‘:6‘,2‘ ‘-terpyridine, is observed to be brightly luminescent in the solid state at room temperature and at 77 K. The complex exhibits reversible vapochromic behavior and crystallographic change in the presence of several volatile organic solvents. Upon exposure to methanol vapors, the complex changes color from red to orange, and a shift to higher energy is observed in the emission maximum with an increase in excited-state lifetime and emission intensity. The crystal and molecular structures of the orange and red forms, determined by single-crystal X-ray diffraction on the same single crystal, were found to be equivalent in the molecular sense and only modestly different in terms of packing. In both forms, the cationic Pt(II) complexes possess...
371 citations
TL;DR: A robust metal–organic open framework, namely, [Ni(cyclam)(bpydc)]·5H2O (1), is reported, which is constructed of linear coordination polymer chains made of the nickel– macrocyclic complex, which retains their crystallinity during the reversible desorption/adsorption of guest molecules.
Abstract: Metal–organic open-framework solids have been the focus of research interest because of their potential applications in molecular adsorption and separation processes, ion exchange, 6] catalysis, sensor technology, and optoelectronics. They can be designed and assembled to generate cavities or channels of various sizes and shapes by appropriate choice of the building blocks. However, despite extensive studies, information on how to design and synthesize metal– organic frameworks (MOFs) with permanent porosity is still limited. 16,17] Moreover, applications of MOFs are scarce compared to zeolites. This is because 1) they often collapse when the guest molecules occupying the voids are removed, 2) they are in general thermally unstable compared with inorganic zeolites and are destroyed at high temperatures (> 200 8C) or even at low temperatures under vacuum, and 3) they are often soluble in solvents and dissociate into their building blocks. 4, 13–15] Porous materials that retain their crystallinity during the reversible desorption/adsorption of guest molecules could be relevant as sensing devices. Here we report a robust metal–organic open framework, namely, [Ni(cyclam)(bpydc)]·5H2O (1), which is constructed of linear coordination polymer chains made of the nickel– macrocyclic complex [Ni(cyclam)](ClO4)2 (cyclam= 1,4,8,11tetraazacyclotetradecane) and 2,2’-bipyridyl-5,5’-dicarboxylate (bpydc ). Open framework 1 shows a reversible type I
TL;DR: In this article, single crystal ZnO nanowires are synthesized and configured as field effect transistors, and photoluminescence and photoconductivity measurements show defect-related deep electronic states giving rise to green-red emission and absorption.
Abstract: Single crystal ZnO nanowires are synthesized and configured as field-effect transistors. Photoluminescence and photoconductivity measurements show defect-related deep electronic states giving rise to green-red emission and absorption. Photocurrent temporal response shows that current decay time is significantly prolonged in vacuum due to a slower oxygen chemisorption process. The photoconductivity of ZnO nanowires is strongly polarization dependent. Collectively, these results demonstrate that ZnO nanowire is a remarkable optoelectronic material for nanoscale device applications.
TL;DR: The X-ray structures reveal spongelike dynamic behavior of the bilayer framework that reduces the interlayer distance in response to the amount of guest molecules.
Abstract: A metal-organic pillared bilayer open framework having 3D channels, [Ni2(C26H52N10)]3[BTC]4·6C5H5N·36H2O (BOF-1, 1), has been assembled from bismacrocyclic nickel(II) complex [Ni2(C26H52N10)(Cl)4]·H2O and sodium 1,3,5-benzenetricarboxylate (Na3BTC). The channels are occupied by pyridine and water guest molecules. When the single crystal of 1 was dried in air and then heated at 75 °C for 1.5 h, respectively, [Ni2(C26H52N10)]3[BTC]4·30H2O (1‘) and [Ni2(C26H52N10)]3[BTC]4·4H2O (2) resulted with retention of the single crystallinity. The X-ray structures reveal spongelike dynamic behavior of the bilayer framework that reduces the interlayer distance in response to the amount of guest molecules. Solid 2 differentiates various alcohols. When 1 was immersed in pyridine and benzene, guest molecules were exchanged with retention of the single-crystal nature to give rise to [Ni2(C26H52N10)]3[BTC]4·20pyridine·6H2O (3) and [Ni2(C26H52N10)]3[BTC]4·14benzene·19H2O (4), respectively. Furthermore, crystal 1 reacted with ...
TL;DR: In this paper, high quality MgO/Fe3O4 core−shell nanowires have been successfully synthesized by depositing an epitaxial shell of Fe 3O4 onto single crystal MgOs.
Abstract: High quality MgO/Fe3O4 core−shell nanowires have been successfully synthesized by depositing an epitaxial shell of Fe3O4 onto single crystal MgO nanowires. The material composition and stoichoimetric ratio have been carefully examined and confirmed with a variety of characterization techniques. These novel structures have rendered unique opportunities to investigate the transport behavior and spintronic property of Fe3O4 in its one-dimensional form. Room-temperature magnetoresistance of ∼1.2% was observed in the as-synthesized nanowires under a magnetic field of B = 1.8 T, which has been attributed to the tunneling of spin-polarized electrons across the anti-phase boundaries.
TL;DR: Single-crystal field effect transistors of the organic semiconductor dithiophene-tetrathiafulvalene (DT-TTF) were prepared by drop casting and the highest hole mobility observed was 1.4 cm2/Vs, which is the highest reported for an Organic semiconductor not based on pentacene.
Abstract: Single-crystal field effect transistors of the organic semiconductor dithiophene-tetrathiafulvalene (DT-TTF) were prepared by drop casting. Long, thin crystals connected two microfabricated gold electrodes, and a silicon substrate was used as a back gate. The highest hole mobility observed was 1.4 cm2/Vs, which is the highest reported for an organic semiconductor not based on pentacene. A high ON/OFF ratio of at least 7 x 105 was obtained for this device.
TL;DR: In this article, the effect of temperature, pH value and mineralizer on the morphology of ZnO nanostructures has been investigated and it is considered that pH value is the main factor to influence the morphology because of its effect on the initial nuclei and growth environment.
Abstract: Flower-like ZnO nanostructures, which consisted of sword-like ZnO nanorods, have been prepared by an organic-free hydrothermal process. The XRD pattern indicated that the flower-like ZnO nanostructures were hexagonal. The SAED and HRTEM experiments implied that the sword-like ZnO nanorods were single crystal in nature and preferentially grew up along the [001] direction. The effects of temperature, pH value and mineralizer on the morphology have been also investigated. It is considered that pH value is the main factor to influence the morphology because of its effect on the initial nuclei and growth environment of ZnO. Finally, the mechanism for organic-free hydrothermal synthesis of the flower-like ZnO nanostructure is discussed.
TL;DR: In this paper, the anisotropy of anionic conductivity in a mixed conductor oxide (La2NiO4+δ) with the 2D K2NiF4-type structure was measured on a high-quality single crystal.
TL;DR: In this article, the dependence of nanoindentation pile-up patterns and microtextures on the crystallographic orientation using high purity copper single crystals was studied. But the authors focused on the dependence on the texture mappings around the indents.
TL;DR: Experimental data on the structural features of nanorings and nanobows formed by bending single-crystal, PSD ZnO nanobelts exclusively support the electrostatic polar charge model as the dominant mechanism for bending.
Abstract: Bending of polar-surface-dominated (PSD) nanobelts of ZnO can be explained by one of two processes: electrostatic neutralization of the dipole moment via deformation (called an electrostatic polar charge model) or imbalances between surface tensions via surface-termination induced stresses. This article presents experimental data on the structural features of nanorings and nanobows formed by bending single-crystal, PSD ZnO nanobelts. Our data exclusively support the electrostatic polar charge model as the dominant mechanism for bending.
TL;DR: Coordination-driven self-assembly is employed to direct a single-crystal-to-single-Crystal [2 + 2] photodimerization that exhibits tunable fluorescence.
Abstract: Coordination-driven self-assembly is employed to direct a single-crystal-to-single-crystal [2 + 2] photodimerization that exhibits tunable fluorescence.
TL;DR: The early stages of passivation in high temperature water of a nickel-chromium-iron alloy (Alloy 600) have been investigated by X-ray Photoelectron Spectroscopy (XPS) and Scanning Tunneling Microscopy (STM) as mentioned in this paper.
TL;DR: This work reports the first successful synthesis and characterization of single-crystal wurtzite CdSe nanoribbons through a simple thermal evaporation process, yielding a sawlike shape with sharp teeth on one side.
Abstract: We report the first successful synthesis and characterization of single-crystal wurtzite CdSe nanoribbons through a simple thermal evaporation process. Asymmetric growth of the nanoribbons occurs, yielding a sawlike shape with sharp teeth on one side. This asymmetric growth is suggested to be induced by the polarization of the c-plane in the wurtzite crystal structure.
TL;DR: In this paper, single crystal high mobility organic field-effect transistors were prepared on prefabricated substrates using a "flip-crystal" approach, which minimized crystal handling and avoided direct processing of the crystal that may degrade the field effect transistors' electrical characteristics.
Abstract: We report on single crystal high mobility organic field-effect transistors prepared on prefabricated substrates using a “flip-crystal” approach. This method minimizes crystal handling and avoids direct processing of the crystal that may degrade the field-effect transistors' electrical characteristics. A chemical treatment process for the substrate ensures a reproducible device quality. With limited purification of the starting materials, hole mobilities of 10.7, 1.3, and 1.4cm2∕Vs have been measured on rubrene, tetracene, and pentacene single crystals, respectively. Four-terminal measurements allow for the extraction of the “intrinsic” transistor channel resistance and the parasitic series contact resistances. The technique employed in this study shows potential as a general method for studying charge transport in field-accumulated carrier channels near the surface of organic single crystals.
TL;DR: In this paper, the authors describe 30 years of research on the surface properties of magnesium oxide, considered as the model prototype oxide of cubic structure, and compare the properties of single crystals, thin films and powdered samples (sintered at progressive higher temperatures) with the aim of demonstrating that the gap between “believed perfect” single crystal surfaces, typical of “pure” Surface Science, and high surface area samples, typically of Catalysis Science, can be progressively reduced.
TL;DR: In this paper, a growth mechanism was proposed on the basis of growth kinetics and thermodynamics, and the composite nanobelt grows along [21 h 1 h 0], its top/bottom being ((0001), and side surfaces ((011 h 0).
Abstract: Heterostructured metal-semiconductor Zn-ZnO core-shell nanobelts and nanotubes have been synthesized. The core is a belt-shaped Zn single crystal, and the shell is an epitaxially grown ZnO layer of 5n m in thickness. The composite nanobelt grows along [21 h1 h0], its top/bottom being ((0001), and side surfaces ((011 h0). The Zn core is a single crystal, and the ZnO shell has an epitaxial orientation relationship with the core. The metal-based nanobelts have a distinct morphology from the nanowires reported in the literature. A growth mechanism is proposed on the basis of growth kinetics and thermodynamics. Sublimation of the Zn core results in the formation ZnO nanotubes. Since the discovery of oxide semiconducting nanobelts, 1 onedimensional (1-D) facet controlled nanomaterials have attracted much attention due to their potential applications in electronic and optoelectronic devices in nanoscale. 2 The terminology of “nanowires” is fairly popular in the literature, but nanowires represent quasi-one-dimensional nanomaterials that grow along a specific axial direction, whereas their side surfaces may not be well-defined. For nanobelts, it should be emphasized that they represent the 1-D nanomaterials that have specific growth direction and well-defined side facets. Analogous to carbon nanotubes, whose properties depend strongly on the helical angle at which the graphitic layer is rolled up, the properties of the nanowires and nanobelts should also depend on the anisotropic structure of their facet surfaces. Therefore, it is a critical step in materials synthesis to control the anisotropic growth of the side surfaces, which may lead to unique properties and selectivity.
TL;DR: In this paper, the authors studied the effect of grain boundary misorientation on hot cracking tendency and showed that even in alloys of high cracking sensitivity, solidification cracks may be avoided when only sub-boundaries are present, i.e., when the grain boundary angle is below a critical value.
TL;DR: In this article, the results indicated that the protonated single crystals can be exfoliated to MnO2 nanosheets by the intercalation of TMA+ ions followed by water-washing.
Abstract: We report in this paper the studies on protonation, exfoliation, and self-assembly of birnessite-type manganese oxide single crystals. The protonation was carried out by extracting K+ ions from the potassium manganese oxide single crystals in a (NH4)2S2O8 aqueous solution heated at 60 °C, exfoliation to nanosheets by the intercalation of TMA+ ions followed by water-washing, and the self-assembly of MnO2 nanosheets in a dilute NaCl solution. The structures of the samples at these stages were systematically investigated using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared, thermogravimetric analysis-differential thermal analysis, and chemical compositional analysis. Electron density distribution in the protonated single crystal was visualized by whole-pattern fitting based on the maximum entropy method. The results indicated that the protonated single crystals can be exfoliated to MnO2 u...
TL;DR: In this article, optical and electrical measurements on pentacene single crystals were used to extract the density of states in the highest occupied molecular orbital-lowest unoccupied molecular orbital band gap, and it was found that these highly purified crystals possess band tails broader than those typically observed in inorganic amorphous solids.
Abstract: We show that optical and electrical measurements on pentacene single crystals can be used to extract the density of states in the highest occupied molecular orbital-lowest unoccupied molecular orbital band gap. It is found that these highly purified crystals possess band tails broader than those typically observed in inorganic amorphous solids. Results on field-effect transistors fabricated from similar crystals imply that the gap state density is much larger within 5-10 nm of the gate dielectric. Thus, organic thin-film transistors for such applications as flexible displays might be significantly improved by reducing these defects.
TL;DR: In this article, single crystal high mobility organic field effect transistors (OFETs) were prepared on prefabricated substrates using a "flip-crystal" approach.
Abstract: We report on single crystal high mobility organic field-effect transistors (OFETs) prepared on prefabricated substrates using a "flip-crystal" approach. This method minimizes crystal handling and avoids direct processing of the crystal that may degrade the FET electrical characteristics. A chemical treatment process for the substrate ensures a reproducible device quality. With limited purification of the starting materials, hole mobilities of 10.7, 1.3, and 1.4 cm^2/Vs have been measured on rubrene, tetracene, and pentacene single crystals, respectively. Four-terminal measurements allow for the extraction of the "intrinsic" transistor channel resistance and the parasitic series contact resistances. The technique employed in this study shows potential as a general method for studying charge transport in field-accumulated carrier channels near the surface of organic single crystals.