Growth and MBMS studies of reaction mechanisms for InxGa1−xAs CBE

The reaction mechanism involved in the growth of In_xGa_1−xAs lattice matched to InP by chemical beam epitaxy (CBE) was investigated using growth and modulated beam mass spectrometry studies. Emphasis was placed on elucidating how variations in substrate temperature, indium composition and arsenic overpressure influence growth kinetics and how sensitive changes in experimental conditions bring about deviations in the ideal stoichiometry (In_0.53Ga_0.47As) required for lattice matching to InP. Our observations indicate that the compositional variations in the InGaAs stoichiometry at high temperatures (> 485°C) arise because of the changes in the DEG decomposition: desorption branching ratio which is controlled by a temperature- and arsenic pressure-dependent surface population of indium atoms. The low temperature behaviour is governed by the availability of metal surface sites for triethylgallium decomposition which is increased by the presence of surface indium atoms.     

Quenching by Copper Atoms of the EL2-induced Luminescence in GaAs

It is shown that the introduction of copper atoms into GaAs crystals containing antistructure defects EL2 (isolated arsenic atoms on gallium sites As_Ga) leads to a practically complete disappearance of the EL2-induced luminescence bands peaked at 0.63 and 0.68eV. This effect is connected with the passivation of the EL2 defects (i.e. with the substantial decrease in their concentration) because of their interaction with copper atoms (they become bound by copper atoms) resulting in an appearance of electrically inactive AS_GaCU_Ga complexes.     

Quality and thermal stability of thin InGaN films

Laser diodes with InGaN quantum wells emitting at long wavelengths are required for the application in compact laser projection. However, quantum wells with indium contents higher than 20% show weak photoluminescence performance as a result of high defect densities. We analyzed the root causes of the low performance of such quantum wells in detail. The influence of the indium content, the annealing temperature and the barrier structure on the quantum-well stability was investigated. We found that quantum wells with indium contents higher than 20% degrade due to the diffusion of indium atoms. Vertical diffusion coefficients for different barrier materials are extracted.     

Electrical Resistivity and Thermally Stimulated Current in CuIn5Se8

From electrical resistivity measurements in the range from 240 to 450 K and from optical absorption measurements the energy gap value of CuIn₅Se₈ has been found to be 1.13 eV. Thermally stimulated current and electrical measurements at high temperature performed in indium annealed samples show deep levels at 0.55 and 0.79 eV, respectively. These defects are expected to be associated with interstitial indium or indium in copper site because of the In‐rich condition.     

Experimental Determination of f″ for Ga and In From Bijvoet Ratio

The imaginary components of the anomalous dispersion correction terms for the heavy atoms gallium and indium, evcaluated from a systematic and precise experimetal measurement of the Bijvoet ratios for the spherically ground single crystals of GaP and InP, are reported. The procedure used is based on the work of Engel and Sturm who refined the crystal structures involving light atoms using anomalous scattering and employed the measured structure factors to evaluate the f″ values of the heavy atoms. In the present work, instead of refining the crystal structure, the structure factors are obtained using a refinement program. The experimentally evaluated f″ values are in very close agreement with the reported theoretical values.     

Crystal structures of copper(II) nitrate complexes containing 4,4’-bipyridyl and halogen-substituted 2-[(2-hydroxyethylimino)methyl]phenols

The crystal structures of (μ-4,4’-bipyridyl)-di{nitrato-2,4-dibromo-6-[(2-hydroxyethylimino)methyl]phenolo (1-)copper} (I), (μ-4,4’-bipyridyl)-di{nitrato-2,4-dichloro-6-[(2-hydroxyethylimino)methyl]phenolo(1-)copper} (II), and (μ-4,4’-bipyridyl)-{4-chloro-2-[(2-hydroxyethylimino)methyl]phenolo(2-)copper-nitrato-4-chloro-2-[(2-hydroxyethylimino)methyl]phenolo(1-)copper} tetrahydrate (III) are determined. The crystal structures of compounds I and II contain binuclear complexes, in which each copper atom is coordinated by the singly deprotonated tridentate molecule of the corresponding azomethine, the monodentate nitrate ion, and bipyridyl that plays the role of a bridge between the central atoms. In the structures of compounds I and II, the coordination polyhedra of the copper atoms are slightly distorted tetragonal pyramids. The pyramid base is formed by the imine and bipyridyl nitrogen atoms and the phenol and alcohol oxygen atoms. The axial vertices of the pyramids are occupied by the oxygen atoms of the monodentate nitrato groups. The crystal structure of compound III involves tetranuclear complexes in which the coordination polyhedra of the central copper atoms are (4 + 1 + 1) bipyramids. The base of these bipyramids is formed by the imine and bipyridyl nitrogen atoms and the phenol and alcohol oxygen atoms. One apical vertex is occupied by the bridging phenol oxygen atom of the nearest complex. The sixth coordination site of the first copper atom is occupied by the chlorine atom of the salicylidene fragment of the neighboring complex related to the initial complex through the center of symmetry. In turn, the sixth coordination site of the second copper atom is occupied by the oxygen atom of the monodentate nitrato group.     

Triaquocalcium(18-crown-6) heptaiodopentacuprate(I), triaquostrontium(18-crown-6) heptaiodopentacuprate(I), and triaquozinc(18-crown-6) heptaiodopentacuprate(I)

Ca(H₂O)₃(18-crown-6)Cu₅I₇ (I), Sr(H₂O)₃(18-crown-6)Cu₅I₇ (II), and Zn(H₂O)₃(18-crown-6)Cu₅I₇ (III) are isostructural solids with a polymeric array of Cu₅I₇ stoichiometry. The repeat unit may be understood as a distorted tetrahedron of four copper(I) atoms, bridged on two faces and three edges by iodide atoms, bridged on an additional edge by an I–Cu–I sequence and linked in polymeric series by this copper atom and one of the face-bridging iodide atoms. The three solid materials display no emission in the visible when excited in the ultraviolet. Comparison with other polymeric cuprous iodide materials that do emit suggests that the quenching of the expected emission may stem from short Cu–Cu interactions (2.4–2.5 Å) that represent a bonding interaction.     

Structures of nitrato-(2-hydroxybenzaldehydo) (2,2′-bipyridyl)copper and nitrato-(2-hydroxy-5-nitrobenzaldehydo)(2,2′-bipyridyl)copper

Nitrato-(2-hydroxy-5-nitrobenzaldehydo)(2,2′-bipyridyl)copper (I) and nitrato-(2-hydroxybenzaldehydo)(2,2′-bipyridyl)copper (II) were synthesized and characterized by X-ray diffraction. The coordination polyhedron of the central copper atom in complex I can be described as a distorted tetragonal pyramid whose base is formed by the phenol and carbonyl oxygen atoms of the monodeprotonated 2-hydroxy-5nitrobenzaldehyde molecule and the nitrogen atoms of the 2,2′-bipyridyl ligand and whose apex is occupied by the oxygen atom of the nitrato group. In the crystal structure, complexes I are linked by the acido ligands and the NO₂ groups of the aldehyde molecule into infinite chains. In complex II, the central copper atom is coordinated by 2-hydroxybenzaldehyde, 2,2′-bipyridyl, and the nitrato group, resulting in the formation of centrosymmetric dimers. The coordination polyhedron of the central copper atom can be described as a bipyramid (4 + 1 + 1) with the same base as in complex I. The axial vertices of the bipyramid are occupied by the oxygen atom of the nitrato group and the bridging phenol oxygen atom of the adjacent complex related to the initial complex by a center of symmetry. In the crystal structure, complexes II are hydrogen bonded into infinite chains.     

Preparation, Characterisation and Crystal and Molecular Structure of [N2H5Cu(HEDTA)]H2O

Abstract  

New hydrazinium copper(II) hydrogen ethylenediaminetetraacetate monohydrate, [N₂H₅Cu(HEDTA)]H₂O has been prepared and characterized by analytical, spectral and thermal techniques. The conductivity value indicates the non-electrolyte nature of the complex. Analytical and bond length measurements indicate the distorted octahedral geometry around the copper ion with EDTA acting as pentadentate ligand. The crystal structure of the complex has been determined from single crystal X-ray analysis. The complex crystallizes in orthorhombic system; space group Pccn. The unit cell parameters are a = 25.1858(14) ?, B = 7.3305(4) ?, C = 15.8291(9) ?, α = 90°, β = 90°, γ = 90°, V = 2,922.4(3) ?³ and Z = 8. The copper ion is six coordinated, three carboxylate oxygen atoms and two nitrogen atoms from EDTA occupy five coordination sites, while the sixth site is occupied by hydrazinium cation and a water molecule present outside coordination sphere as lattice water. The complex undergo multi-step degradation to give copper oxide as the final residue.     

Copper(I) halide complexation to norbornene: (CuCl)5(norbornene)4: A complex of novel structure

Cu(I) bromide and chloride form complexes with norbornene which differ in stoichiometry and copper-halide motif. (CuCl)₅(norbornene)₄: [triclinic space group P¯1,a=12.138(6),b=22.849(6),c=5.953(1)Å,=90.012(3),=75.792(3), =87.776(4)°,Z=2,R=10.8%, 1365 obs. refl.] displays a structure of new motif in which an eight-membered ring of alternating copper and chloride atoms is bridged by a fifth copper atom which binds to ring chloride atoms in the 1,5 positions and is further bound to a terminal chlorine atom. The four copper atoms of the ring are each bound to a norbornene molecule. [CuBr(norbornene)]₄ crystallizes with an eight membered tub shaped ring of alternating copper and bromine atoms having each copper atom bound to a norbornene molecule via donation of the electrons of the double bond.     

EXAFS spectroscopy of quasicrystals

The results of the investigation of the features of the local structure of quasicrystalline materials by extended X-ray absorption fine structure (EXAFS) spectroscopy with the use of synchrotron radiation are analyzed. The advantages of this method from the point of view of deriving information about the local shifts of the atoms forming an icosahedral structure are demonstrated. The rearrangement of the local environment of copper and iron in Al-Fe-Cu ternary alloys at a transition from the crystalline to the quasicrystalline phase has been investigated. It is established that the nearest copper coordination retains the symmetry characteristic of the crystal; however, rotation and small displacements of copper matrix atoms lead to significant rearrangement of aluminum atoms around iron atoms. As a result, icosahedral clusters with pentagonal symmetry are formed around iron atoms and violation of the translational symmetry is accompanied by the transition of Al-Fe-Cu to the quasicrystalline state.     

Crystal and molecular structure of bis (μ-chloro)bis[chloro(1,1′-dimethyl-2,2′-diimidazolylsulfide)copper(II)]

The title compound is prepared from 1-methylimidazoline-2(3H)-thione (mimtH) and copper(II) chloride, in a 11 mole ratio in methanol. The crystals are monoclinic, space groupP2₁/n, witha=8.530(2),b=14.258(2),c=9.693(2) Å,=93.15(2)°,Z=2. The molecular structure shows a dimeric copper(II) complex, in which each copper is chelated by a 1,1-dimethyl-2,2-diimidazolylsulfide ligand, and bonded to three chlorine atoms, two bridging and one terminal. The coordination geometry of each copper is approximately square pyramidal, with two nitrogen atoms, a terminal chlorine, and one of the bridging chlorines forming the square plane. The second bridging chlorine forms the apex of the pyramid.     

Synthesis and structure of a hexaazamacrocyclic copper(II) complex with maleato ligand

A hexaazamacrocyclic copper(II) complex Cu(L)(H₂O) (O₂CCH = CHCO₂)⋅H₂O (1) (L = 3,10-bis(2-hydroxyethyl)-1,3,5,8,10,12-hexaazacyclotetradecane) was prepared and structurally characterized by a combination of analytical, spectroscopic, and crystallographic methods. In complex 1, the coordination geometry about the copper(II) ion is six-coordinate with four equatorial nitrogen atoms from the macrocycle and two oxygen atoms from the axial maleato and aqua ligands. In 1, the one end of the maleato ligand coordinates to the central copper atom, while the other end is not bonded. The macrocycle and the axial ligands are highly involved in multiple types of hydrogen bonding interactions, resulting in the stabilization of the maleato ligand as a “coordinated ligand counter anion.”     

In原子在GaAs(001)表面的成核与扩散研究

近年来,半导体量子点特别是InAs量子点的基本物理性质和潜在应用得到了广泛研究。许多研究者利用InAs量子点结构的改变以调制其光电特性。本文采用液滴外延法在GaAs(001)表面沉积了不同沉积量的In(3 ML、4 ML、5 ML),以研究In的成核机制和表面扩散。实验发现,随着In沉积量的增加,液滴尺寸(包括直径、高度)明显增大。不仅如此,在相同的衬底温度下,沉积量越大,液滴密度越大。利用经典成核理论,计算了GaAs(001)表面In液滴形成的临界厚度为0.57 ML,计算的结果与已报道的实验一致。从In原子在表面的迁移和扩散,以及衬底中Ga和液滴中的In之间的原子互混原理解释了In液滴形成和形貌演化的机理。实验中得到的In液滴临界厚度以及In液滴在GaAs(001)上成核机理,可以为制备InAs量子点提供实验指导。     

Structure of amorphous LaNi5D3.3 studied by neutron and X-ray diffraction

In situ neutron and X-ray diffraction measurements in a D₂ gas atmosphere at a constant pressure of 1 MPa were performed on amorphous LaNi₅D_3.3, which was prepared by mechanical alloying in a D₂ gas atmosphere. Reverse Monte Carlo (RMC) simulation based on the neutron and X-ray diffraction data was applied to construct a three-dimensional atomic arrangement of this amorphous alloy. The RMC model shows that more than 90% of the deuterium atoms occupy tetrahedral sites consisting of La and/or Ni atoms. Furthermore, the local environments around the Ni and La atoms were investigated by Voronoi polyhedral analysis of the RMC configuration of the metal atoms. The results show the presence of a number of prismatic-like polyhedra around a Ni atom.     

Synthesis and Crystal Structure of A Mononuclear Copper(II) Complex with 2-[3-(diethylamino)propyliminiomethyl]-5-methoxyphenolate

Abstract  

A Schiff base complex, Bis{2-[3-(diethylamino)propyliminiomethyl]-5-methoxyphenolate}copper(II) nitrate, has been synthesized and structurally characterized by elemental analyses and X-ray diffraction. In the complex, the Cu(II) atom is four-coordinated by two O and two N atoms from the two Schiff base ligands, 2-[3-(diethylamino)propyliminiomethyl]-5-methoxyphenolate, forming a distorted square-planar coordination.     

硒化铟材料的发展及其光电器件应用

自2004年发现石墨烯以来,二维材料以其丰富的带隙结构、独特的光电特性和无悬挂键的范德瓦耳斯表面等,极大地拓宽了半导体电子、光电子器件的设计维度。其中二维硒化铟材料成为最具竞争力的未来高迁移率光电子器件用候选材料,被诺贝尔奖获得者Andre Geim认为是“硅和石墨烯的‘黄金分割点’”。但人们对二维硒化铟材料的研究仅有不到十年的时间,对其制备及应用的认识仍然不足。本文综述了二维硒化铟材料及其光电器件的研究现状。另外,考虑到目前绝大多数二维硒化铟材料的研究是基于块状单晶体材料的机械剥离开始的,因此本文首先回顾了硒化铟晶体结构的认识及其制备方法的发展历程,在此基础上综述了二维硒化铟材料制备及其性能表征的前沿研究结果,探讨了器件结构、材料制备方法等因素对二维硒化铟场效应晶体管和光探测器电学输运特性的影响,最后分析了未来硒化铟材料及器件应用面临的机遇与挑战。     

Copper(II)-pyrazine-2,3-dicarboxylate Coordination Polymer with Monoethanolamine, [Cu(μ<Subscript>3</Subscript>-pzdc)(mea)]<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>

Abstract  

A novel Cu(II)-pyrazine-2,3-dicarboxylate complex with monoethanolamine ligand (mea), [Cu(μ₃-pzdc)(mea)]_n (1), has been synthesized and characterized by elemental, spectral (IR and UV–Vis.) and thermal analyses. The molecular structure of polynuclear complex has been determined by the single crystal X-ray diffraction technique. The pyrazine-2,3-dicarboxylate dianion exhibits tetradentate-μ₃ bridging ligand through three carboxylate oxygens and one nitrogen atom. The complex contains two copper(II) ions that exhibit two different coordination environments with two mea, two pzdc ligands, respectively. The Cu1(II) ion is coordinated by two carboxylate oxygen atoms, two N atoms and two O atoms of symmetry related carboxylate group, forming a distorted octahedral geometry, while Cu2(II) ion is coordinated by two bidentate mea ligands and remaining two coordination sites of distorted octahedral geometry are occupied by two carboxylate oxygen atoms of neighboring Cu1 molecule. Thermal analysis property and thermal decomposition mechanism of complex have been investigated by using thermal analyses techniques (TG, DTG and DTA).     

Effect of UV irradiation on Cu+-containing glasses

Optical absorption spectra of copper-containing silicate glasses were determined and the effects of UV irradiation on the spectra were studied. Oxalic acid was used as a reducing agent in order to obtain monovalent copper ions. Several absorption bands were observed as a result of UV irradiation at wavelengths of 430–480, 565–570, 620–690, 720–790, 800–900 and 307–310 nm. These bands were interpreted in terms of photochemical reaction and attributed to color centers, cupric ions (Cu¹⁺⁺), metastable copper atoms (Cu^o), and aggregates of copper atoms which were induced by UV irradiation.     

Structure of the metastable cubic B<Subscript>1</Subscript> phase of the La<Subscript>2</Subscript>Mo<Subscript>2</Subscript>O<Subscript>9</Subscript> single crystal

The structure of the metastable B₁ phase of the La₂Mo₂O₉ single crystal is investigated using X-ray diffraction. It is established that the crystal structure of the compound under investigation is described by the cubic unit cell with the parameter a = 7.158(5) Å, which makes it possible to index approximately 84% of the reflections measured for this single crystal. The structure of the metastable cubic B₁ phase is characterized by a local lowering of the symmetry for the La and Mo atoms, which are displaced from their positions on the threefold axis, thus forming three sites around it with an occupancy of 0.333(2). The O(1) atom in the structure of the metastable cubic B₁ phase remains in the 4a position on the threefold axis but occupies it by only 86%. The O(2) and O(3) atoms located in a general position occupy their own sites with occupancies of 0.77(2) and 0.35(2), respectively. The final R factor of the refinement of this structural model is 2.52%.