Anab initio investigation of Cu2Se and Cu4Se2

Summary Experimentally known copper selenium clusters show extraordinary geometrical features, especially short Cu-Cu distances. We report the first theoretical investigation of Cu₂Se and Cu₄Se₂. Various quantum chemical methods (SCF, MP2, CPF, CCSD, CCSD(T), LDF) are applied to determine the importance of dynamic electron correlation. We find that inclusion of correlation does not essentially change the electronic structure of the clusters but has a strong influence on geometries. To reduce the computational effort we apply effective core potentials (ECPs) in combination with small, but carefully optimized basis sets. The applicability of simple modellings of correlation energies for approximate inclusion of correlation effects in SCF geometry optimizations is tested.     

Monoclinic Cu2Se3Sn

A previously unknown modification of dicopper(I) triselenostannate(IV), Cu₂Se₃Sn, has been obtained from the Cu₂Se–SnSe₂ quasi‐binary system and investigated using X‐ray single‐crystal diffraction. The Se atoms are stacked in a closest‐packed arrangement with the layers in the sequence ABC. The Cu atoms occupy one‐third of the tetrahedral interstices, whereas the Sn atoms are located in one‐sixth of the tetrahedral interstices. All the atoms occupy general positions. The structure possesses pseudo‐inversion symmetry. The Cu₂Se₃Sn structure investigated in this paper (96 atoms per unit cell, ordered distribution of Cu and Sn over 12 cation positions) is a superstructure of the reported cubic (eight atoms per unit cell, random distribution of Cu and Sn over one cation position) and monoclinic (24 atoms per unit cell, ordered distribution of Cu and Sn over three cation positions) modifications.     

Solvothermal crystal growth of CuSbQ2 (Q=S, Se) and the correlation between macroscopic morphology and microscopic structure

A low temperature solvothermal method has been successfully used for preparation of two semiconductor compounds CuSbQ₂ (Q=S(1), Se(2)) by the reactions of Cu, Sb and S(or Se) powders in 1,2-diaminopropane at 160 °C for 10 days. The crystal structure of 2 was determined first time using single crystal X-ray diffraction analyses. The structures of 1 and 2 are discussed in the view of covalent bonds and weak interactions. Double CuSbQ₂ layers are assembled to a 3-D network structure by Cu?Sb and Q?Sb secondary bonds. In contrast with the isostructure of the two materials, the crystal morphology of them is quite different, brick-like crystals for CuSbS₂ and plank-like crystals for CuSbSe₂. The phenomenon is related to their different inter-planar interactions. Semiconductor properties of the microcrystal samples are measured and the band gaps of 1 and 2 are 1.38 and 1.05 eV, respectively.     

Interaction between Cr2Se3 and Cu2GeSe3

The interaction along the Cu₂GeSe₃-Cr₂Se₃ join has been investigated using differential thermal and X-ray powder diffraction analyses. It has been found that the join is quasi-binary with a degenerate eutectic based on the Cu₂GeSe₃ compound. Two new quaternary compounds have been found along the join, namely, Cu₂GeCr₆Se₁₂ and the γ phase. The phase is formed at 915°C by the peritectic reaction L + β-Cr₂Se₃ = γ and has the primary crystallization region up to 9 mol % Cr₂Se₃ in the temperature range 758–915°C. The room-temperature homogeneity range of the γ phase is 65–70 mol % Cr₂Se₃. The Cu₂GeCr₆Se₁₂ compound is formed by the peritectoid reaction γ + β-Cr₂Se₃=Cu₂GeCr₆Se₁₂ at 880°C, and its homogeneity range is 73–79 mol %. The X-ray reflections of the γ phase are indexed for the tetragonal crystal system with the unit cell parameters a = 12.043 Å and c = 9.180 Å. Samples with ferromagnetic properties are found in the homogeneity regions of both compounds.     

Epitaxial growth of pentacene films on Cu110

The molecular structure of thin pentacene (C(22)H(14)) films grown on a Cu(110) surface has been studied by means of He atom scattering, low energy electron diffraction, thermal desorption spectroscopy, x-ray photoelectron spectroscopy, and x-ray absorption spectroscopy. Depending on the actual film thickness three different crystalline phases have been identified which reveal a characteristic reorientation of the molecular plane relative to the substrate surface. In the monolayer regime the molecules form a highly ordered commensurate (6.5x2) structure with a planar adsorption geometry. For thin multilayers (thickness <2 nm) a second phase is observed which is characterized by a lateral ((-0.65 5.69) ( 1.90 1.37)) structure and a tilting of the molecular plane of about 28 degrees around their long axis which remains parallel to the surface. Finally, when exceeding a thickness of about 2 nm subsequent growth proceeds with an upright molecular orientation and leads to the formation of crystalline films which are epitaxially oriented with respect to the substrate. The present study thus demonstrates that also on metal substrates highly ordered pentacene films with an upright orientation of the molecular planes can be grown. Photoelectron spectroscopy data indicate further that thick films do not grow in a layer-by-layer mode but reveal a significant degree of roughness.     

溶剂热法制备球状Cu2ZnSnS4纳米晶及其表征

通过简单的溶剂热法合成了锌黄锡矿结构的Cu2ZnSnS4(CZTS)纳米晶,使用L-半胱氨酸作硫源和络合剂,以金属氯化物作前驱体,在180°C下反应16h成功获得了CZTS微球.使用X射线衍射(XRD)仪,场发射扫描电子显微镜(FESEM)、能量色散谱(EDS)、高分辨透射电子显微镜(HRTEM)、多功能X射线光电子能谱仪(XPS)、紫外-可见(UV-Vis)分光光度计对产物的物相、结构、形貌及光学性能进行表征.结果表明:所得的产物为纯相锌黄锡矿结构的CZTS纳米颗粒,CZTS微球直径为400-800nm,并可观察到微球是由大量厚度约20nm的纳米片构成;将CZTS颗粒均匀分散在异丙醇中,测试后估算其禁带宽度约1.58eV,与薄膜太阳能电池所需的最佳禁带宽度相近.并对其形成机理进行了初步探讨.     

Mixed Cu2Se Hexagonal Nanosheets@Co3Se4 Nanospheres for High-Performance Asymmetric Supercapacitors

Rational designing and constructing multiphase hybrid electrode materials is an effective method to compensate for the performance defects of the single component. Based on this strategy, Cu₂Se hexagonal nanosheets@Co₃Se₄ nanospheres mixed structures have been fabricated by a facile two-step hydrothermal method. Under the synergistic effect of the high ionic conductivity of Cu₂Se and the remarkable cycling stability of Co₃Se₄, Cu₂Se@Co₃Se₄ can exhibit outstanding electrochemical performance as a novel electrode material. The as-prepared Cu₂Se@Co₃Se₄ electrode displays high specific capacitance of 1005 F g⁻¹ at 1 A g⁻¹ with enhanced rate capability (56 % capacitance retention at 10 A g⁻¹), and ultralong lifespan (94.2 % after 10 000 cycles at 20 A g⁻¹). An asymmetric supercapacitor is assembled applying the Cu₂Se@Co₃Se₄ as anode and graphene as cathode, which delivers a wide work potential window of 1.6 V, high energy density (30.9 Wh kg⁻¹ at 0.74 kW kg⁻¹), high power density (21.0 Wh kg⁻¹ at 7.50 kW kg⁻¹), and excellent cycling stability (85.8 % after 10 000 cycles at 10 A g⁻¹).     

A Solvothermal Route to Cu2O Nanocubes and Cu Nanoparticles

IntroductionSynthesis of Cu2O and Cu nanostructures has beenactively researched for many decades because bothCu2O and Cu are important industrial materials on ac-count of their novel physical and chemical properties.In particular,Cu2O is a p-type metal ox…     

Synthesis and characterisation of the new oxyselenide Bi2YO4Cu2Se2

In this communication we report the synthesis, structure and preliminary characterisation of Bi2LnO4Cu2Se2 (Ln = Y, Gd, Sm, Nd, La) phases; these materials are members of a new family of layered oxychalcogenides.     

Physicochemical study of the Sb2Se3-Ho2Se3 system

The chemical interaction in the Sb₂Se₃-Ho₂Se₃ system was studied by physicochemical analysis methods (by differential thermal, X-ray powder diffraction, and microstructural analyses and also by density and microhardness measurements). The state diagram of the system was constructed. It was found that the Sb₂Se₃-Ho₂Se₃ section is a quasi-binary section of the Ho-Sb-Se ternary system. In the system, the compound HoSbSe₃ forms, which melts incongruently at 1050 K and crystallizes in the rhombic system at the unit cell parameters a = 11.855 Å, b = 11.316 Å, c = 4.139 Å, and Z = 4 in the space group Pbnm-D _2h ¹⁶ . The solubility of solid solutions based on Sb₂Se₃ at room temperature reaches 8 mol % Ho₂Se₃, whereas solid solutions based on Ho₂Se₃ were not detected.     

Synthesis and Single Crystal Structure of RbEr_2Cu_3Se_5

1 INTRODUCTION Halide fluxes are excellent media for growing single crystals of chalcogenides[1~3]. It is well known that during the single crystal growth via flux methods, occasional inclusion of the flux elements in the structure leads to the formation of new phases[4~9]. Several rare earth chalcogenides have been prepared through such reactive halid flux methods[4~9]. Thus we used RbCl as reactive flux to explore a new quaternary selenide by the reaction of ErCuSe precursor with Rb…     

A low-temperature X-ray diffraction study of the Cu2ZnSnSe4 thin films

Low-temperature XRD measurements were performed to confirm the phase composition and structural parameters of the electrochemically deposited Cu₂ZnSnSe₄ thin films on flexible metal substrates.     

纳米晶CuLa3Se5微波溶剂热合成及结构研究

采用微波溶剂热法合成纳米晶CuLa3Se5,具有快速,节能、纯度高、粒度小(平均粒径为20～30 nm)等优点.通过X射线粉末衍射(XRD)、透射电子显微镜(TEM)、扫描电镜能谱分析(EDS)和X射线光电子能谱(XPS)等手段表征其组成.讨论了微波溶剂热合成纳米晶的机制.漫反射紫外-可见吸收光谱(UV-Vis)表明标题化合物禁带宽度为2.27 eV,具有优良的半导体性能.     

A voltammetric study of the electrodeposition chemistry of the Cu + Se system

The simultaneous electrochemical codeposition of copper and selenium is investigated by cyclic voltammetry at vitreous carbon disk and rotating platinum electrodes. The stoichiometry of the copper selenides obtained can be controlled with adequate choice of the working potential and of the electroactive species concentrations. Electrochemical redissolution of the copper selenides is discussed.     

Solvothermal syntheses of nano- and micro-sized ZnO powders with a controllable morphology

Zinc oxide powders with different morphologies and grain sizes were synthesized using solvothermal methods from ethanolic zinc acetate solutions in the presence of lithium hydroxide. The influence of the temperature and the time of the reaction, as well as the pH value of the starting solution, on the ZnO particle size and morphology were examined. It was found that an increase in the pH value from 8 to 12 results in a significant decrease in the mean particle size. Also, the particles?? morphology can be changed from hexagonal plates and prisms to rods by controlling the reaction time and the temperature. The crystallization mechanism is discussed, based on established correlations such as the particle size/shape versus the reaction parameters. Dissolution/recrystallisation is the most probable growth mechanism responsible for the ZnO particles?? morphology obtained in the solvothermal (hydrothermal) reactions with a basic solution. The planar structure of the zinc-hydroxy-acetate molecule plays the main role in growing the structures during the sovothermal reactions with a slightly acid solution.     

Influence of substrate nature and growth conditions on the morphology of thin DMOAP films

We report some preliminary results on the morphology of thin N,N -dimethyl-n-octadecyl-3-aminopropyltrimethoxysilyl chloride (DMOAP) films. When deposited on a glass substrate, DMOAP forms a mono- or multi-layer structure parallel to the substrate. The surface topography of the film is probed by atomic force microscopy. In general, the free surface of such a film is not flat and smooth. Islands and holes are formed on the free surface of the films when a sufficiently flat substrate is used. The thin film surface topography depends strongly on the nature of the bare substrate, the curing conditions, and the immersion time of the substrate in the DMOAP solution. The film is always rougher than the bare substrate used. Annealing roughens the surface of the alkoxysilane thin films deposited on a glass substrate. For films on glass plates covered with an indium tin oxide layer, annealing has minor effects. The surface topography affects the microstructure of homeotropic smectic samples.     

Influence of substrate nature and growth conditions on the morphology of thin DMOAP films

We report some preliminary results on the morphology of thin N,N -dimethyl- n -octadecyl-3-aminopropyltrimethoxysilyl chloride (DMOAP) films. When deposited on a glass substrate, DMOAP forms a mono- or multi-layer structure parallel to the substrate. The surface topography of the film is probed by atomic force microscopy. In general, the free surface of such a film is not flat and smooth. Islands and holes are formed on the free surface of the films when a sufficiently flat substrate is used. The thin film surface topography depends strongly on the nature of the bare substrate, the curing conditions, and the immersion time of the substrate in the DMOAP solution. The film is always rougher than the bare substrate used. Annealing roughens the surface of the alkoxysilane thin films deposited on a glass substrate. For films on glass plates covered with an indium tin oxide layer, annealing has minor effects. The surface topography affects the microstructure of homeotropic smectic samples.