Infrared spectroscopy and surface chemistry of beta-Ga(2)O(3) nanoribbons

The structure and surface chemistry of crystalline beta-Ga2O3 nanoribbons (NRs), deposited in a thin layer on various metallic and dielectric substrates (mainly on Au), have been characterized using vibrational spectroscopy. The results have been analyzed with the aid of a previous ab initio theoretical model for the beta-Ga2O3 surface structure. Raman spectra and normal-incidence infrared (IR) transmission data show little if any difference from corresponding results for bulk single crystals. For a layer formed on a metallic substrate, IR reflection-absorption spectroscopy (IRRAS) shows longitudinal-optic (LO) modes that are red-shifted by approximately 37 cm-1 relative to those of a bulk crystal. Evidence is also seen for a bonding interaction at the Ga2O3/Au interface following heating in room air. Polarization-modulated IRRAS has been used to study the adsorption of pyridine under steady-state conditions in ambient pressures as high as approximately 5 Torr. The characteristic nu19b and nu8a modes of adsorbed pyridine exhibit little or no shift from the corresponding gas-phase values. This indicates that the surface is only weakly acidic, consistent with the theoretical prediction that singly unsaturated octahedral Ga sites are the only reactive cation sites on the NR surface. However, evidence for adsorption at defect sites is seen in the form of more strongly shifted modes that saturate in intensity at low pyridine coverage. The effect of H atoms, formed by thermal cracking of H2, has also been studied. No Ga-H or O-H bonds are observed on the pristine NR surface. This suggests that the previously reported presence of such species on Ga2O3 powders heated in H2 is a result of a partial reduction of the oxide surface. The heat of adsorption of atomic H on the pristine beta-Ga2O3(100) surface at 0 K is computed to be -1.79 eV per H at saturation (average of Ga-H and O-H sites), whereas a value of +0.45 eV per H is found for the dissociative adsorption of H2. This suggests that rapid recombinative desorption of H2 may limit the coverage of chemisorbed H on this surface.     

Self-assembly and hierarchical organization of Ga2O3/In2O3 nanostructures

We report on the realization of novel 3-D hierarchical heterostructures with 6-and 4-fold symmetries by a transport and condensation technique. It was found that the major core nanowires or nanobelts are single-crystalline In2O3, and the secondary nanorods are single-crystalline monoclinic beta-Ga2O3 and grow either perpendicular on or slanted to all the facets of the core In2O3 nanobelts. Depending on the diameter of the core In2O3 nanostructures, the secondary Ga2O3 nanorods grow either as a single row or multiple rows. The one-step growth of the unique Ga2O3/In2O3 heteronanostructures is a spontaneous and self-organized process. The simultaneous control of nanocrystal size and shape together with the possibility of growing heterostructures on certain nanocrystal facets opens up novel routes to the synthesis of more sophisticated heterostructures as building blocks for opto- and nanoelectronics.     

Preparation and electrical properties of ultrafine Ga2O3 nanowires

Uniform and well-crystallized beta-Ga2O3 nanowires are prepared by reacting metal Ga with water vapor based on the vapor-liquid-solid (VLS) mechanism. Electron microscopy studies show that the nanowires have diameters ranging from 10 to 40 nm and lengths up to tens of micrometers. The contact properties of individual Ga2O3 nanowires with Pt or Au/Ti electrodes are studied, respectively, finding that Pt can form Schottky-barrier junctions and Au/Ti is advantageous to fabricate ohmic contacts with individual Ga2O3 nanowires. In ambient air, the conductivity of the Ga2O3 nanowires is about 1 (Omega.m)-1, while with adsorption of NH3 (or NO2) molecules, the conductivity can increase (or decrease) dramatically at room temperature. The as-grown Ga2O3 nanowires have the properties of an n-type semiconductor.     

Crystallization kinetics study on N-(p-n-alkyloxybenzylidene)-p-n-alkylanilines (nO.m compounds)

A comparative systematic kinetic study of crystallization among various smectogens of higher homologues of the benzylidene aniline nO.m series (9O.2, 13O.2, 14O.2, 15O.2, 16O.2, 2O.16, 11O.16, 16O.16 and 18O.16) has been carried out by thermal microscopy and differential scanning calorimetry (DSC). The DSC thermograms were run from crystallization temperature to the isotropic melt for different time interval. The liquid crystalline behaviour together with rate of crystallization of smectic ordering in newly synthesized nO.m compounds (16O.2, 2O.16, 11O.16, 16O.16, 18O.16) with respect to their lower homologues are discussed in relation to the kinetophase (which occurs prior to the crystallization), end chain lengths, the odd-even effect and chain length ratio. The molecular mechanism and dimensionality in the crystal growth were computed from the Avrami equation. The characteristic crystallization time (t*) at each crystallization temperature was deduced from the individual plots of log t vs. DeltaH. Further, a qualitative approach was made to the crystallization process in smectic layers.     

Crystallization kinetics study on N-(p-n-alkyloxybenzylidene)-p-n-alkylanilines (nO.m compounds)

A comparative systematic kinetic study of crystallization among various smectogens of higher homologues of the benzylidene aniline nO.m series (9O.2, 13O.2, 14O.2, 15O.2, 16O.2, 2O.16, 11O.16, 16O.16 and 18O.16) has been carried out by thermal microscopy and differential scanning calorimetry (DSC). The DSC thermograms were run from crystallization temperature to the isotropic melt for different time interval. The liquid crystalline behaviour together with rate of crystallization of smectic ordering in newly synthesized nO.m compounds (16O.2, 2O.16, 11O.16, 16O.16, 18O.16) with respect to their lower homologues are discussed in relation to the kinetophase (which occurs prior to the crystallization), end chain lengths, the odd-even effect and chain length ratio. The molecular mechanism and dimensionality in the crystal growth were computed from the Avrami equation. The characteristic crystallization time (t*) at each crystallization temperature was deduced from the individual plots of log t vs. DeltaH. Further, a qualitative approach was made to the crystallization process in smectic layers.     

Epitaxial electrodeposition of Fe(3)O(4) thin films on the low-index planes of gold

Half-metallic ferrimagnetic materials such as Fe(3)O(4) are of interest for use in spintronic devices. These devices exploit both the spin and charge of an electron in spin-dependent charge transport. Epitaxial thin films of Fe(3)O(4) have been grown on the three low-index planes of gold by electrodeposition. On Au(110), a [110] Fe(3)O(4) orientation that is aligned with the underlying Au(110) substrate is observed. Thin films on Au(100) grow with three different orientations: [100], [111], and [511]. On Au(111), both [111] and [511] orientations of Fe(3)O(4) are observed. The [511] orientations are the result of twinning on [111] planes. A polarization value of approximately -40% at the Fermi level was measured by spin-polarized photoemission at room temperature for a thin film on Au(111).     

Octanuclear oxothiomolybdate(v) rings: structure and ionic-conducting properties

A family of alkali salts of octanuclear oxothiomolybdate rings has been synthesized by crystallization of the [Mo(8)S(8)O(8)(OH)(8)[HMO(5)(H(2)O)]](3-) (noted HMo(8)M(3-); M=Mo, W) and [Mo(8)S(8)O(8)(OH)(8)(C(2)O(4))](2-) (noted Mo(8)ox(2-)) anions in an aqueous solution of ACl (A=Li, Na, K, Rb). Single-crystal X-ray diffraction experiments have been performed showing that the alkali salts exhibit a similar three-dimensional structure. Disordered alkali ions form columns to which the anionic rings are anchored. Ionic-conductivity measurements on pressed pellets have revealed two different behaviors. The lithium salts of HMo(8)M(3-) (M=Mo, W) are moderately good proton conductors at room temperature (sigma=10(-5) S cm(-1)) and the profile of conductivity as a function of relative humidity shows that the conductivity is due to surface-proton motion (particle-hydrate-type mechanism). On the other hand, the lithium salt of Mo(8)ox(2-) competes with the best crystalline lithium conductors at room temperature (sigma=10(-3) S cm(-1)), and (7)Li NMR experiments confirm the mobility of the lithium ions along the one-dimensional channels of this material.     

Unusual 180 degrees P-O-P Bond Angles in ZrP(2)O(7)

The structure of cubic ZrP(2)O(7) at room temperature has been solved and refined using a combination of modeling and high-resolution neutron powder diffraction data. The cell edge is 24.74 ?, the space group is Pa&thremacr;, and Z is 108. For those P(2)O(7) units not on a 3-fold axis, the P-O-P angles range from 134 degrees to 162 degrees. Two crystallographically distinct P(2)O(7) groups are on three fold axes with P-O-P angles thus constrained to be 180 degrees on average. The structure of cubic ZrP(2)O(7) was also refined from data taken at 227, 290, 371, 435, and 610 degrees C. The 3 x 3 x 3 superstructure present at room temperature disappears at about 290 degrees C, and all P-O-P angles of P(2)O(7) are then constrained by symmetry to be 180 degrees on average. The exceptionally low thermal expansion shown by ZrP(2)O(7) above 290 degrees C is likely related to the unusual P-O-P angle.     

Characterization of the Potent Insulin Mimetic Agent Bis(maltolato)oxovanadium(IV) (BMOV) in Solution by EPR Spectroscopy

Bis(maltolato)oxovanadium(IV) (abbreviated BMOV or VO(ma)(2)) has been characterized by electron paramagnetic resonance (EPR) spectroscopy in CH(2)Cl(2), H(2)O, MeOH, and pyridine at both room and low temperatures. Spin Hamiltonian parameters for mono- and bis(maltolato)oxovanadium(IV) complexes [VO(ma)](+) (=[VO(ma)(H(2)O)(n)()](+), n = 2 or 3) and VO(ma)(2) (Hma = 3-hydroxy-2-methyl-4-pyrone, maltol) have been obtained by computer simulation (SOPHE). Configurations of solvated vanadyl/maltol complexes, VO(ma)(2)S, in solution (S = solvent) are proposed on the basis of a comparison of their hyperfine coupling constants with those obtained for related vanadium(IV) compounds in the literature. Whereas at room temperature pyridine coordinates to VO(ma)(2) in a position cis to the oxo ligand (cis isomer), in H(2)O or in MeOH solvated and unsolvated cis and trans adducts of VO(ma)(2) are all formed, with the cis isomer dominant. As expected, the coordinating ability was found to be in the order py > H(2)O approximately MeOH > CH(2)Cl(2). In aqueous solutions at room temperature and neutral pH, cis- and trans-VO(ma)(2)(H(2)O) complexes are present as major and minor components, respectively.     

Epitaxial growth of single-crystalline Al(2)O(3) films on Cr(2)O(3)(0001)

Thin, crystallographically oriented single-crystalline Al2O3 films can be grown epitaxially on Cr2O3(0001) by codeposition of Al vapor and O2 at a substrate temperature of 825 K. The properties and growth of these films were monitored by Auger electron spectroscopy (AES), low-energy electron diffraction (LEED), low-energy ion scattering (LEIS), and X-ray photoelectron spectroscopy (XPS). Two routes of preparation were investigated: (i) stepwise growth by alternating deposition of Al at room temperature and subsequent exposure to O2 at elevated temperatures; (ii) codeposition of Al and O2 at T > 800 K. The first route was consistently found to result in the growth of a complex interfacial oxide followed by the growth of polycrystalline Al2O3. The second mode of preparation provided homogeneous and ordered, probably (0001)-oriented, films of Al2O3 that maintained a LEED pattern up to a thickness around 10 A. The surface sensitive Cr MVV Auger transition at 34 eV was completely attenuated once the Al2O3 layer had reached a thickness of 6 A, pointing to film homogeneity at an early stage. This was confirmed by the absence of a significant Cr signal in LEIS spectra.     

Unique guest-inclusion properties of a breathing ionic crystal of K3[Cr3O(OOCH)6(H2O)3][alpha-SiW12O40].16 H2O

A microstructured ionic crystal, K(3)[Cr(3)O(OOCH)(6)(H(2)O)(3)][alpha-SiW(12)O(40)].16 H(2)O (1) was synthesized by the complexation of the Keggin-type polyoxometalate of [alpha-SiW(12)O(40)](4-) with a macrocation of [Cr(3)O(OOCH)(6)(H(2)O)(3)](+). Compound 1 possessed a straight channel, with an opening of approximately 0.5x0.8 nm, which contained the water of crystallization. The use of the macrocation with large size (0.7 nm) and small charge (+1) reduced the anion-cation interaction and was essential for the channel formation. The molecular structures of the polyoxometalate and the macrocation in 1 were retained under vacuum at 473 K. Analogues of 1 were synthesized with [alpha-PVW(11)O(40)](4-) or [Fe(3)O(OOCH)(6)(H(2)O)(3)](+). The water of crystallization in 1 was removed under vacuum at room temperature to form the closely packed guest-free phase 2. Compound 2 reversibly and repeatedly included water and polar organic molecules with two carbon atoms or less. Guest inclusion was highly selective and a difference of even one methylene group in the organic guest molecule was discriminated by the host. Polar organic molecules with longer methylene chains and nonpolar molecules such as dinitrogen and methane were completely excluded. The guest-inclusion properties could be explained by the ion-dipole interaction between the host and the guest, which is proportional to the dipole moment of the guest molecule and inversely proportional to the ion-dipole (host-guest) distance. Thus, small polar molecules were selectively absorbed. These distinctive guest-inclusion properties were successfully applied to the oxidation of methanol from a mixture of C(1) and C(2) alcohols. These results show unique guest inclusion and catalysis by rationally designed ionic crystals.     

Formation of well-aligned ZnGa(2)O(4) nanowires from Ga(2)O(3)/ZnO core-shell nanowires via a Ga(2)O(3)/ZnGa(2)O(4) epitaxial relationship

Formation of well-aligned and single-crystalline ZnGa(2)O(4) nanowires on sapphire (0001) substrates has been achieved via annealing of the Ga(2)O(3)/ZnO core-shell nanowires. Ga(2)O(3)/ZnO core-shell nanowires were prepared using a two-step method. The thickness of the original ZnO shell and the thermal budget of the annealing process play crucial roles for preparing single-crystalline ZnGa(2)O(4) nanowires. Structural analyses of the annealed nanowires reveal the existence of an epitaxial relationship between ZnGa(2)O(4) and Ga(2)O(3) phases during the solid-state reaction. A strong CL emission band centered at 360 nm and a small tail at 680 nm are obtained at room temperature from the single-crystalline ZnGa(2)O(4) nanowires.     

Synthesis and Crystal Structure of Bis［Bis（Cyclopentylcyclopentadienyl）Methyl－Erbium］［（C_5H_9C_5H）_4）_2ErCH_3］_2

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The self-assembly mechanism of the Lindqvist anion [W(6)O(19)](2-) in aqueous solution: a density functional theory study

The formation mechanism is always a fundamental and confused issue for polyoxometalate chemistry. Two formation mechanisms (M1 and M2) of the Lindqvist anion [W(6)O(19)](2-) have been adopted to investigate it's self-assembly reaction pathways at a density functional theory (DFT) level. The potential energy surfaces reveal that both the mechanisms are thermodynamically favorable and overall barrierless at room temperature, but M2 is slightly dominant to M1. The formation of the pentanuclear species [W(5)O(16)](2-) and [W(5)O(15)(OH)](-) are recognized as the rate-determining steps in the whole assembly polymerization processes. These two steps involve the highest energy barriers with 30.48 kcal mol(-1) and 28.90 kcal mol(-1), respectively, for M1 and M2. [W(4)O(13)](2-) and [W(4)O(12)(OH)](-) are proved to be the most stable building blocks. In addition, DFT results reveal that the formation of [W(3)O(10)](2-) experiences a lower barrier along the chain channel.     

纳米(NH4)3PMo6W6O40的室温固相合成及形成机理

以H3PMo6W6O40•23H2O和(NH4)2C2O4•H2O为原料，采用室温固相反应合成出(NH4)3PMo6W6O40•6H2O产物，用元素分析、IR、UV-Vis、XRD、TEM、TG-DTA、BET等手段确定其组成、结构和性能.结果表明，产物为纳米粒子，平均粒径为10 nm.纳米粒子保持着杂多阴离子的Keggin特征结构，比表面积为167.6 m2•g－1，且在465 ℃以下具有良好的热稳定性.反应中反应热能、结晶水和生成物H2C2O4•2H2O对形成小粒径的(NH4)3PMo6W6O40纳米粒子起关键作用.     

Co3O4 纳米棒的溶剂热合成及形成机理分析

Co3O4 nanorods have been synthesized at 160℃ for 10 h in the solution of oleic and n-cetane by an emulsion-solvothermal method using Co（NO3）2·6H2O as starting materials. The as-prepared product was characterized by X-ray powder diffraction（XRD）,transmission electron microscope（TEM）,and vibrating sample magnetometer（VSM）. The formation mechanism of the prepared product was analyzed based on formation of rod-like micelles of oleic acid. Cobalt ions can migrate into the micelle core for the nucleation and growth of Co3O4 . The results show that the as-prepared Co3O4 nanorods are with the average size 25×100 nm and in the cubic phase. The magnetic susceptibility meets about linearly with the applied magnetic field at room temperature,and the coercivity （Hc）and remanent magnetization（Ms）values of the product at room temperature are 353 Oe and 0.4 emu/g,respectively. This simple route is also expanded to synthesize other materials with the rod-like morphology.     

Theoretical and experimental determination of the electronic structure of V(2)O(5), reduced V(2)O(5-x) and sodium intercalated NaV(2)O(5)

In this work the electronic structure of V(2)O(5), reduced V(2)O(5-x) (V(16)O(39)) and sodium intercalated NaV(2)O(5) has been studied by both theoretical and experimental methods. Theoretical band structure calculations have been performed using density functional methods (DFT). We have investigated the electron density distribution of the valence states, the total density of states (total DOS) and the partial valence band density of states (PVBDOS). Experimentally, amorphous V(2)O(5) thin films have been prepared by physical vapour deposition (PVD) on freshly cleaved highly oriented pyrolytic graphite (HOPG) substrates at room temperature with an initial oxygen understoichiometry of about 4%, resulting in a net stoichiometry of V(2)O(4.8). These films have been intercalated by sodium using vacuum deposition with subsequent spontaneous intercalation (NaV(2)O(5)) at room temperature. Resonant V3p-V3d photoelectron spectroscopy (ResPES) experiments have been performed to determine the PVBDOS focusing on the calculation of occupation numbers and the determination of effective oxidation state, reflecting ionicity and covalency of the V-O bonds. Using X-ray absorption near edge spectra (XANES) an attempt is made to visualize the changes in the unoccupied DOS due to sodium intercalation. For comparison measurements on nearly stoichiometric V(2)O(5) single crystals have been performed. The experimental data for the freshly cleaved and only marginally reduced V(2)O(5) single crystals and the NaV(2)O(5) results are in good agreement with the calculated values. The ResPES results for V(2)O(4.8) agree in principle with the calculations, but the trends in the change of the ionicity differ between experiment and theory. Experimentally we find partly occupied V 3d states above the oxygen 2p-like states and a band gap between these and the unoccupied states. In theory one finds this occupation scheme assuming oxygen vacancies in V(2)O(5) and by performing a spin-polarized calculation of an antiferromagnetic ordered NaV(2)O(5.).     

盐卤硼酸盐化学XVII.MgO-B~2O~3-28%MgCl~2-H~2O体系20℃热力学非平衡态液固相关系研究

用动力学方法对MgO.nB~2O~3在28%MgCl~2-H~2O浓盐溶液中形成的过饱和溶液的结晶过程进行研究, 首次得到MgO-B~2O~3-MgCl~2-H~2O体系过饱和区内的液固相关系图, 即热力学非平衡态液固相关系图。该相图有六个相区: H~3BO~3,MgO.3B~2O~3.7.5H~2O, MgO.3B~2O~3.7H~2O, 2MgO.2B~2O~3.MgCl~2.14H~2O,3Mg(OH)~2.MgCl~2.8H~2O和5Mg(OH)~2.MgCl~2.8H~2O。拟合得到各结晶过程的动力学方程, 同时对结晶机制进行了探讨。     

Molecular construction of oriented crystalline NaMnF(3) and KMnF(3) with perovskite structures at room temperature

In this work, we report the fabrication of high-quality (101)-oriented orthorhombic NaMnF(3) and (100)-oriented cubic KMnF(3) perovskites via an organic monolayer template at room temperature. The controlled crystallization under the organic monolayer template is explained in terms of the electrostatic interactions and beneficial lattice matching between the organic template and the ions undergoing nucleation. The present study is of great importance in the preparation of oriented perovskite materials as well as in the understanding of the mechanism for organic-template-directed crystallization.