Growth Mechanism in Atomic Layer Epitaxy (I) Re-evaporation of Cd and Te from CdTe(111) Surfaces Monitored by Auger Electron Spectroscopy

The mechanism of atomic layer epitaxy (ALE) of cadmium telluride has been studied. Auger electron spectroscopy is used to measure the isothermal re-evaporation rates of elemental Cd and Te deposits on the (111)A and (111)B surfaces of CdTe substrates. The results include an observation that the sticking coefficients of Cd and Te are smaller than unity at the growth temperatures typical of CdTe ALE. After desorption the substrates are left partially covered: 35% by a Cd overlayer on the (111)B surface and 72% by Te on the (111)A surface. The re-evaporation rates of Cd and Te experience a drastic change near the substrate-deposit interface. These rates appear two orders of magnitude smaller than those of bulk-like amorphous Cd and Te solids. The activation energies for reevaporation of the near-interface layer region are estimated to be: 1.5 eV for Te on the (111)A face, 1.0 eV for Te on (111)B and 0.5 eV for Cd on (111)B. It has also been shown that AES can be used to identify the polarity of the CdTe(111) surfaces. The relative difference in peak-to-peak intensity ratios of Cd MNN to Te MNN for (111)A and (111)B is (11 ± 2)%.     

Growth Mechanism in Atomic Layer Epitaxy (II). A Model of the Growth Process of CdTe on CdTe (111) Substrates

A realistic model of CdTe growth by atomic layer epitaxy (ALE) has been proposed. This model is based on experimental studies concerning the isothermal re-evaporation rates of elemental Cd and Te deposits on the (lll)A and (lll)B surfaces of CdTe substrates, on a study of surface morphology and crystal structure of CdTe single crystal overlayers grown by ALE on CdTe(lll)B substrates under various crystallization conditions as well as on the existing theories related to the interaction of thermally activated atoms or molecules with hot solid surfaces. This model includes: (i) an existence of transition layers of both Cd and Te₂ species, intermediate between a chemisorbed and a bulk-like film, which create reaction zones 3–4 monolayers thick near the substrate surface, and (ii) partial re-evaporation of the first, chemisorbed monolayer of the deposited constituent elements.     

Synthesis and Crystal Structure Analysis of One Dimensional Supramolecular [Cd (Glu) (Tu)2]n

The complex of [Cd (C₅H₆O₄) (CH₄N₂S)₂]_n ( I ) has been synthesized and its X‐ray crystal structure determined at room temperature, M = 394.74, monoclinic, space group Pc (No. 7), with lattice parameters a = 7.683(3), b = 11.566, c = 16.00(1) Å, β = 100.32 (4)°, and Z = 4. There are two different Cd sites in this complex. Cd (1) coordinates to four oxygen atoms from Glutaric anion and two sulfide atoms from thiourea. Cd (2) coordinates to three oxygen and two sulfide atoms. The Cd atoms are linked by glutaric anion to form one‐dimensional chains. The adjacent chains are held together by hydrogen bonds to form a three dimensional network.     

CdTe(110)表面原子与电子结构的第一性原理研究

采用基于密度泛函理论的第一性原理计算了CdTe(110)表面的原子和电子性质.结果表明,CdTe(110)理想表面在禁带中出现两个明显的表面态,弛豫后表层Cd原子和Te原子p态电子发生转移,Cd原子趋向于sp2平面杂化构型,Te原子趋向p3杂化的锥形构型.经过表面弛豫大大降低了表面能,增大了表面功函数,表面占据态和表面空态分别被推进价带顶之下和导带底之上,导致弛豫表面没有明显的表面态.     

Properties of Hg1‐xCdxTe epitaxial films grown on (211)CdTe and (211)CdZnTe

Hg_1‐xCd_xTe (MCT) epitaxial films have been grown employing single crystalline substrates of CdTe and Cd_0.96Zn_0.04Te with (211)Cd and (211)Te crystalline orientations. The Isothermal Vapor Phase Epitaxy (ISOVPE) technique without Hg overpressure has been used for the epitaxial growth. Substrates and films were characterized by optical microscopy, chemical etching and x ray diffraction (Laue technique). The electrical properties were determined by Hall effect measurements. The characterization results allowed to evaluate the crystalline quality of MCT films. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis and crystal structure of cobalt(III) complex with a Schiff base and azide

The cobalt(III) complex, [Co(L)₂(N₃)₂]₂(ClO₄)₂, L being a Schiff base N-[phenyl(pyridin-2-yl)methylene]aniline has been synthesized and the crystal structure determined using X-ray crystallography. The complex crystallizes in triclinic system, space group P-1 with unit cell parameters a=10.9367(9) ?, b=18.0817(17) ?, c=20.1629(16) ?, α=111.341(2)°, β=91.622(2)°, γ=107.5030(10)°, V=3499.1(5) ?³ and Z=2. It crystallizes with two independent molecules in the asymmetric unit. The two cobalt atoms are hexa-coordinate and have a distorted octahedral geometry, satisfied by four nitrogen atoms from two molecules of the Schiff base and two nitrogen atoms from the monodentate azide group. The perchlorate ions are non-coordinating.     

Characterization of Vacuum Evaporated Polycrystalline Cd0.96Zn0.04Te Thin Films by XRD,Raman Scattering and Spectroscopic Ellipsometry

Cd_0.96Zn_0.04Te thin films are deposited onto well cleaned glass substrates (Corning 7059) kept at room temperature by vacuum evaporation and the films are annealed at 423 K. Rutherford Backscattering Spectrometry and X‐ray diffraction techniques are used to determine the thickness, composition and crystalline structure and grain size of the films respectively. The films exhibited zinc blende structure with predominant (111) orientation. The surface morphology of the films is studied by Atomic Force Microscopy. The rms roughness of the as‐deposited films is 3.7 nm and on annealing the films at 423K, the rms roughness value decreases to 3.4 nm. The Raman spectra of the Cd_0.96Zn_0.04Te films are recorded at room temperature to study lattice vibrations and their interactions with other excitations. The intensity of the peak increases and the FWHM decreases on annealing the films. The pseudodielectric‐function spectra, ε(E) = ε₁(E) + i ε₂(E), of polycrystalline Cd_0.96Zn_0.04Te thin films in the 1.3 ‐ 5.5eV photon energy range at room temperature are measured by spectroscopic ellipsometry. The measured dielectric function spectra reveal distinct structures at energies of the E₁, E₁+Δ₁ and E₂ critical points are due to interband transitions.     

The effect of organic linkers on the supramolecular structures of two new Ni(II) cyclen complexes (cyclen = 1,4,7,10-tetraazadodecane)

Two new nickel(II)(cyclen) coordination polymers, {[Ni(cyclen)·(bipy)]·(ClO₄)₂}_n (1) and [Ni(cyclen)]₂·(squa)·(ClO₄)₂ (2) have been synthesized and characterized structurally, where cyclen is 1,4,7,10-tetraazadodecane. Compound 1 crystallizes in the monoclinic system, space group C2/c, with a = 10.5339(17) ?, b = 14.565(2) ?, c = 16.133(3) ?, β = 102.799(2)°, V = 2413.4(7) ?³. Compound 2 crystallizes in the orthorhombic system, space group P _{nm a} with a = 25.722(3) ?, b = 11.1168(12) ?, c = 11.4580(13) ?, V = 3276.3(6) ?³. In both compounds, each Ni^II center is in a distorted octahedral coordinated environment with four N_cyclen atoms and two N_pyridine atoms from 4,4′-bipyridine linker for 1 and two O_aqueou atoms from the coordinated water for 2, respectively. The complex 1 exhibits infinite zigzag 1D chains by linking of 4,4′-bipyridine coordinated. In complex 2, 2D sheet supramolecule generated through self-assembling by hydrogen bond.     

Crystal structure investigation of [Mn(3-CH3C5H4N)2(N3)2(H2O)2]

The crystal structure of the title compound has been determined by single crystal X-ray diffraction methods. [Mn(3-CH₃C₅H₄N)₂(N₃)₂(H₂O)₂] crystallizes in the space group P 1 with a = 7.444(2) Å, b = 7.691(2) Å, c = 8.926(3) Å, α = 99.82(3)°, β = 108.80(2)°, γ = 114.99(2)° and Z = 1. Least squares refinement gave a R value of R_w = 0.046 for 1414 observed reflections. The manganese atom in the title complex is octahedrally coordinated by two oxygen atoms of the water molecules and four nitrogen atoms; two N-atoms are the end atoms of azide groups and the other two nitrogen atoms belong to the 3-methylpyridine molecules. The polyhedra are linked via hydrogen bonds between the water molecules and the azide groups.     

Nanolayer of the A2IIIB3VI (111) phase with ordered cation vacancies on GaAs(111) and InAs(111)

The surface of GaAs(111) and InAs(111) substrates has been investigated by transmission and scanning electron microscopy after thermal treatment in selenium vapor. A pseudomorphic growth of single-crystal phases of indium selenide In₂Se₃(111) and gallium selenide Ga₂Se₃(111) is found; these compounds are crystallized into a sphalerite lattice with ordered stoichiometric cation vacancies. A model of an atomic surface is proposed for the In₂Se₃(111) and Ga₂Se₃(111) structures. The reconstruction of the (√3 × √3)-R30° surface of GaAs(111) and InAs(111) after treatment in Se vapor is considered within this model.     

Optical and opto‐electronic properties of polycrystalline Cd0.96Zn0.04Te thin films

Cd_0.96Zn_0.04Te thin films are deposited onto thoroughly cleaned glass substrates (Corning 7059) kept at room temperature by vacuum evaporation. The films are found to have good stoichiometry as analyzed by Rutherford Backscattering Spectrometry. The films exhibited zinc blende structure with predominant (111) orientation. The surface morphology of the films is studied by Atomic Force Microscopy. The rms roughness of the films evaluated by AFM is 3.7 nm. The pseudodielectric‐function spectra, ε(E) = ε₁(E) + i ε₂(E) at room temperature are measured by spectroscopic ellipsometry. The measured dielectric function spectra reveal distinct structures at energies of the E₁, E₁+ Δ₁ and E₂ critical points. The band gap energy of the films measured by optical transmittance measurement is 1.523 eV. The PL spectrum of the films shows intense emission due to free and bound exciton recombination and no emission associated with crystal imperfection and deeper impurity levels. The PL line shapes give indications of the high quality of the layers.     

Ultrahigh Vacuum Atomic Layer Epitaxy of Ternary II-VI Semiconductor Compounds

A concise discussion concerning the UHV ALE growth of ternary II-VI compounds is presented in this paper. Simultaneous reflection mass spectrometry (REMS) and reflection high energy electron diffraction (RHEED) measurements of the surface kinetic and structural parameters, respectively, governing the UHV ALE growth of Cd_1-xZn_xTe and Cd_1-xMn_xTe heteroepitaxial films are reported. In addition, a Monte-Carlo-based method for simulation of the UHV ALE process of CdTe (the model-compound for this growth technique) has been used for investigation of the Cd cation's fluxes reflected from the growing epilayer surface in different phases of the ALE process. The Cd⁺ ion-related REMS signals measured during CdTe growth have been compared with the simulation results.     

Synthesis and Crystal Structure of a One-Dimensional Chain Cadmium Coordination Polymer Bridged Through 1,2-bis(imidazol-1-yl)ethane

Abstract The cadmium(II) complex [Cd(phba)₂(bim)(H₂O)₂]_n (1) (phba = 4-hydroxybenzoate, bim = 1,2-bis(imidazol-1-yl)ethane) has been synthesized and structurally characterized by X-ray diffraction analysis. It crystallizes in the monoclinic space group C2/c, a = 23.820(4) ?, b = 9.5331(14) ?, c = 11.1086(19) ?, β = 111.519(4)°, V = 2346.7(7) ?³, Z = 4. The coordination geometry of Cd(II) atom is distorted octahedral; it is coordinated by two nitrogen atoms from the imidazole rings of two symmetry-related bim molecules, and four oxygen atoms from two symmetry-related phba anions and two water molecules. The Cd(II) atoms are bridged by bim molecules to form a one-dimensional chain. Graphical abstract Synthesis and crystal structure of a one-dimensional chain cadmium coordination polymer bridged through 1,2-bis(imidazol-1-yl)ethane Yuping Zhang, Liyan Wang, Shouwu Wang, Baolong Li, Yong Zhang The cadmium(II) complex [Cd(phba)2(bim)(H2O)2]n (1) has been synthesized and structurally characterized by X-ray diffraction analysis. The coordination geometry of Cd(II) atom is distorted octahedral; it is coordinated by two nitrogen atoms from the imidazole rings of two symmetry-related bim ligands, and four oxygen atoms from two symmetry-related phba anions and two water molecules. The Cd(II) atoms are bridged by bim ligands to form a one-dimensional chain.     

Synthesis and X-ray crystallographic characterization of [Cd(NO3)2(15-Crown-5)] and [Cd(NO3)2(18-Crown-6)]

Reaction of 15-crown-5 or 18-crown-6 in 3:1 (v/v) CH₃CN:CH₃OH with Cd(NO₃)₂·4H₂O followed by slow evaporation produces [Cd(NO₃)₂(15-crown-5)] or [Cd(NO₃)₂(18-crown-6)]. Crystals of [Cd(NO₃)₂(15-crown-5)] are orthorhombic with space group Pbca and cell parameters a = 13.562(5), b = 15.941(9), and c = 15.011(7) Å at 295 K. [Cd(NO₃)₂(18-crown-6)] crystallizes in the monoclinic space group C2/c with a = 11.235(2), b = 11.196(5), c = 15.385(3) Å, and = 99.89(2)° at 295 K. The metal center in [Cd(NO₃)₂(15-crown-5)] rests atop the macrocyclic donor array with two cis-bound nitrate anions and adopts a distorted tricapped trigonal prismatic geometry. [Cd(NO₃)₂(18-crown-6)] resides on an equatorial two-fold rotation axis with Cd²⁺ coordinated in the 18-crown-6 cavity and the nitrate anions oriented in twisted trans positions.     

Structure of bis(dipropyldithiocarbamate) cadmium(II), [Cd2(n-Pr2dtc)4] (dtc = dithiocarbamate)

The cadmium complex of bis(dipropyldithiocarbamate), [Cd₂(n-Pr₂dtc)₄] (dtc = dithiocarbamate) was crystallized from ethylether. It crystallizes in the monoclinic system, space group P _2I/c, with lattice parameters, a = 8.2532(1), b = 19.4519(1), c = 13.4163(2) Å, = 99.243(1)°, and Z = 4. The X-ray single-crystal structure of [Cd₂(n-Pr₂dtc)₄] reveals that the complex is binuclear in the solid state and the Cd atom has a distorted square-pyramidal coordination environment and four equatorial donors are the two bidentate chelate sulfur atoms from two dtc ligands, of which the sulfur atom from the bridging dtc ligand occupies the apical position of the symmetry-related Cd atom in the dimer structure.     

Synthesis and Crystal Structure of a Novel Mixed Ligand Cadmium(II) Complex of Benz-1,3-Thiazoline-2-Thione and 1,10-Phenanthroline

Abstract  A novel cadmium complex [Cd(C₇H₄NS₂)₂(phen)] was synthesized by the reaction of a polymeric complex, [Cd(C₇H₄NS₂)₂] _n , with 1,10-phenanthroline (phen) as a ligand. The crystal structure was determined by single-crystal X-ray diffraction. The crystallographic data are: triclinic , a = 8.3670(6) ?, b = 10.9898(8) ?, c = 17.1404(13) ?, α = 95.567(2)o, β = 95.881(2)o, γ = 109.034(1)o, V = 1471.26(19) ?³ and Z = 2. The final R value is 0.0375 for 7154 reflections. The compound [Cd(C₇H₄NS₂)₂(phen)] is monomeric revealing a coordination sphere of N₄S₂ type. The Cd atom is surrounded by two thiazole N atoms, two exocyclic S atoms from two bidentate 1,3-benzothiazole-2-thiolate anions and two 1,10-phenanthroline N atoms. The Cd cation is six-coordinate with a distorted octahedral geometry. Graphical Abstract  The synthesis and crystal structure of a novel monomeric complex ‘[Cd(C₇H₄NS₂)₂(phen)]’ obtained by the reaction of polymeric complex, [Cd(C₇H₄NS₂)₂] _n , with 1,10-phenanthroline is reported.      

Synthesis,Crystal and Molecular Structure of Cd2(sacch)4(Im)4

The title compound has been synthesized and its crystal structure determined at room temperature. Cd₂(Sacch)₄(Im)₄ F.W. = 1225.83, monoclinic. Space group: C2/c, Z = 4, a = 20.065(3) Å, b = 11.164(4) Å, c = 20.697(6) Å, β = 94.69(5)°, The coordination polyhedron of Cd(II) correspond to a five-coordinate trigonal-bipyramid. In the title complex, two of the saccharin groups act as monodentate ligands. The other two act as bidentate ligands. The two Cd(II) ions are bridged by the two bidentate saccharin groups and the distance is 4.75 Å.     

Synthesis, crystal structure, and thermal properties of {[Cd2(L1)3(sac)4]⋅2CH2Cl2}∞: A coordination polymer with non-interpenetrating ladders containing cadmium in a rare, trigonal bipyramidal coordination environment (L1 = 1,4-bis(4-pyridyl)-2,3-diaza-1,3-butadiene, sac = saccharinate)

The new coordination polymer, {[Cd₂(L1)₃(sac)₄]?2CH₂Cl₂}_∞:, has been prepared from the reaction of 1,4-bis(4-pyridyl)-2,3-diaza-1,3-butadiene (L1) with [Cd(sac)₂(H₂O)₄].2H₂O(sac = saccharinate) in a methylene chloride/ethanol solvent mixture. The compound features a non-interpenetrating ladder motif constructed from Cd(L1)3 T-shaped units. The Cd atoms are coordinated to three nitrogen donor atoms from three L1 ligands and two nitrogen donor atoms from two saccharinate ligands in a rare, trigonal bipyramidal coordination environment. The compoundwas further characterized by IR spectroscopy and DTA/TGA. {[Cd₂(L1)₃(sac)₄]?2CH₂Cl₂}_∞: crystallizes in the triclinic space group P-1 with a = 10.8747(19)Å, b = 12.626(2)Å, c = 15.749(3)Å, α = 111.839(3)^°, β = 97.442(3)., and γ = 106.239(3)^°     

Synthesis and Structure of Trans‐bis(ethanolamine)bis(saccharinato)mercury(II)

Trans‐bis(ethanolamine)bis(saccharinato)mercury(II), [Hg(ea)₂(sac)₂], where ea and sac denote the ethanolamine molecule and the saccharinate anion, respectively, crystallizes in the triclinic space group P (No. 2) with a = 9.4651 (5), b = 10.4365 (5), c = 11.9314 (6) Å, α = 84.402 (1)° β = 78.313 (1)°, γ = 75.307 (1)°, Z = 2, V = 1115.11 (10) ų. The structure consists of isolated [Hg(ea)₂(sac)₂] units in which the Hg(II) ion is octahedrally coordinated by two nitrogen and two oxygen atoms of two neutral ea ligands, and two nitrogen atoms of two sac ligands. The ea acts as a bidentate N‐ and O‐donor ligand and occupies the trans positions of the equatorial plane of the coordination octahedron forming a fivemembered chelate ring, while sac behaves as a monodentate N‐donor ligand occupying the axial positions. The average Hg‐N_sac and Hg‐N_ea bond distances are 2.739 (3) and 2.114 (7) Å, respectively. The crystal exhibits extensive hydrogen bonds between the hydroxyl and amine hydrogen atoms of the ea ligands and the sulfonyl, carbonyl and amine groups of the sac ligands.     

Preparation and investigation of (CuInSe2)x(2ZnSe)1‐x and (CuInTe2)x(2ZnTe)1‐x solid solution crystals

The (CuInSe₂)_x(2ZnSe)_1‐x and (CuInTe₂)_x(2ZnTe)_1‐x solid solution crystals prepared by Bridgman method and chemical vapor transport have been studied. The nature of the crystalline phases, the local structure homogeneity and composition of these materials have been investigated by X‐ray diffraction (XRD) and Electron Probe Microanalysis (EPMA) methods. The analysis revealed the presence of chalcopyrite‐sphalerite phase transition between 0.6 ≤ X ≤ 0.7. Lattice constants, value of σ position parameter and bond length between atoms were also calculated. It was found that the lattice parameters exhibit a linear dependence versus composition. The transmission spectra of solid solution crystals in the region of the main absorption edge were studied. It was established that the optical band gap of these materials changes non‐linearly with the X composition. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)