Effect of rapid thermal annealing on Zn1‐xCdxO layers grown by radio‐frequency magnetron co‐sputtering

Zn_1‐xCd_xO layers were deposited on the sapphire substrate using the radio‐frequency magnetron co‐sputtering system. The grown Zn_1‐xCd_xO layers were carried out in the post‐annealing treatment for 1 min at the 800 °C oxygen‐ambient by the rapid thermal annealing (RTA) method. X‐ray diffraction (XRD) experiment shows that the Zn_1‐xCd_xO layers are changed from the single phase of the hexagonal structure at 0≤x ≤0.08 to the double phase of hexagonal‐and‐cubic structure at x =0.13. Thus, the maximum Cd‐composition ratio with the hexagonal structure was found out to be x =0.08. Also, the crystallinity of Zn_1‐xCd_xO layers at x =0.13 was remarkably improved by the RTA annealing treatment. This crystal quality improvement was thought to be associated with the relaxation of the compressive strain remaining in the Zn_1‐xCd_xO layers. Therefore, the results of XRD and transmittance lead that the crystal quality of the Zn_1‐xCd_xO layers forming the hexagonal ZnO phase is better than that forming the cubic CdO phase. Consequently, the reliable formation and the crystallinity of the Zn_1‐xCd_xO layers were achieved by using the RTA method of short‐time thermal‐annealing at the high temperature. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Molecular beam epitaxy of Ca1−xRxF2+x (R=Nd, Er) layers: study of RHEED pattern and lattice mismatch

Ca_1−xNd_xF_2+x and Ca_1−xEr_xF_2+x layers were grown on CaF₂(1 1 1) substrates at 600 and 550°C, respectively, by molecular beam epitaxy. Reflection high-energy electron diffraction (RHEED) investigation revealed that Ca_1−xNd_xF_2+x layers have two types of surface structure, namely (1×1) and ( )R30⁰ with hexagonal symmetry, depending on Nd mole fraction, while Ca_1−xEr_xF_2+x layers have three types of surface structure, namely (1×1) and (2×2) with hexagonal symmetry, and a triple rotated domain structure based on a rectangular cell depending on Er mole fraction. The lattice mismatch of the epilayers and substrate, which is important for applications involving buffer layers, was measured by X-ray rocking curve (XRC) analysis.     

Molecular and supramolecular structure of 5,5′,6,6′-tetrahydroxy-3,3,3′,3′-tetramethyl-1,1′-spirobisindane, tetrahydrofuran solvate

The crystal and molecular structure of 5,5′,6,6′-tetrahydroxy-3,3,3′,3′-tetramethyl-1,1′-spirobisindane tetrahydrofuran solvate, C₂₁H₂₄O₄·2(C₄H₈O), has been determined by single crystal X-ray analysis: the space group is monoclinic,P2₁/a, witha=10.77(1),b=25.357(8),c=19.009(7) Å, β-90.84(4)°,V=5190(5) ų,Z=8,D _x =1.24 gm/cm³. The structure is abis-catechol molecule which forms layers of either (R) or (S) configurational pairs. Layers are stacked to form solvent tunnels where adjoining layers are linkedvia hydrogen bonding. One hydroxyl oxygen on each end of catechol moieties act as a hydrogen donor while the remaining hydroxyl oxygen serves as donor and acceptor. The extensive hydrogen bonding, in conjunction with the spiro linkage forcing perpendicularly arranged aromatic rings, create the conditions for supramolecular control of the crystal structure. Consequently, they are also the primary factors responsible for the unusually high melting point of this bulky, branched, spirobis-catechol compared to other alkyl derivatives of catechol molecules.     

Structural characterization of interfaces in the AlxGa1?xAs/GaAs/AlxGa1?xAs heterostructures by high-resolution X-ray reflectometry and diffractometry

The structural properties of multiplayer Al_xGa_1−x As/GaAs/Al_xGa_1−x As systems (x ≈ 0.2) grown on GaAs(001) substrates are studied by the methods of double-crystal X-ray diffractometry and reflectometry. The depth profiles of deformation, amorphization, and density of the layers are obtained. It is shown that despite small differences (5–7%) in the densities of the Al_xGa_1−x As layers and the substrate and the small thickness of the AlAs layer (1–2 nm) separating the GaAs quantum well, it is possible to reconstruct the heterostructure model by the method of X-ray reflectometry and to determine the thickness of the transitional layers at a resolution of 0.1–0.2 nm. It is also established that the reflectometry data obtained complement the X-ray diffraction data considerably and allow one to estimate the roughness and the character of the aluminum distribution at the interfaces. __________ Translated from Kristallografiya, Vol. 50, No. 5, 2005, pp. 801–812. Original Russian Text Copyright ? 2005 by Lomov, Sutyrin, Prokhorov, Galiev, Khabarov, Chuev, Imamov.     

Photoemission core level and satellite study of TixRu1−xoxide layers

Combined photoemission core level and satellite structure investigations of pyrolytic titanium-rich Ti_xRu_1−x-oxide layers (0.90 ≦ x ≦ 0.97) and RuO₂ layers on titanium are used to gain structural and compositional information about these electro-catalytically active surfaces. By means of this method deviations from stoichiometry, the formation of carbon interstitials and the growth of anatase by ruthenium loss could be pointed out.     

Preparation of New Fibrous Organic-Inorganic Layered Compounds Derived from Zinc Hydroxyde

Abstract

A new preparation method of the fibrous organic-inorganic nanohybrids was established by the reaction of Zn(OH)₂ with various organic carboxylic acids. Interlayer spacings of the reaction products of Zn(OH)₂ with benzoic acid and p-phenyl azobenzoic acid were 1.46 and 2.04 nm, and these reaction products have layered structure. In IR spectra, new peaks of RCOO-Zn band appeared at around 1400 cm^?1 and 1550 cm^?1 indicating that hydroxyl groups reacted with organic carboxylic acids. SEM images of these reaction products showed fibrous morphology. The TEM image showed that the layer structure was constructed along the fiber direction.     

Stacking pattern of multi-layer InAs quantum wires embedded in In0.53Ga0.47−xAlxAs matrix layers grown lattice-matched on InP substrate

Multi-layer InAs quantum wires were grown on, and embedded in In_0.53Ga_0.47−xAl_xAs (with x=0, 0.1, 0.3 and 0.48) barrier/spacer layers lattice matched to an InP substrate. Correlated stacking of the quantum wire arrays were observed with aluminum content of 0 and 0.1. The quantum wire stacks became anti-correlated as the aluminum content was increased to 0.3 and 0.48. The origin of such stacking pattern variation was investigated by finite element calculations of the chemical potential distribution for indium on the growth front surface of the capping spacer layer. It is shown that the stacking pattern transition is determined by the combined effect of strain and surface morphology on the growth front of the spacer layers.     

A complex method for structural investigation of GaAs1−xPx epitaxial layers grown on GaAs substrates

A universal X-ray diffractometer is used for the structural complex investigation of GaAs_1−xP_x epitaxial layers, grown on the (100) face of GaAs substrate. Information is obtained from the analyses of diffraction patterns for some qualities of the epitaxial layers: crystallographical orientation, composition, thickness, as well as structure of the transition region. The suggested complex method has important advantages against the standard Laue method. It is far easier express and convenient for serial investigations.     

Superlattices and composition of phases of CVD layers based on TiCx,VCx, (Ti,V)Cx,and (Cr,Fe)7C3

Protective layers of TiC_x, VC_x, (Ti, V)C_x, and (Cr, Fe)₇C₃ on C100W1 tool steel have been investigated by X-Ray and electron diffraction. Superlattices have been observed in the VC_x− and (Cr, Fe)₇C₃−layers. As manufacturing of (Ti, V)C_x−layers the growth of carbides with low content of V and Ti respectively has been prefered.     

Studies of Nd(CH3CO2)3 · xH2O Complex Crystals

Three neodymium acetate crystals Nd(Ac) ₃ · xH₂O (x = 1.0, 1.5, 4.0) were synthesized in different pH values. According to the IR, thermal properties, and X-ray diffraction data, we found that neodymium acetates may be a transition state in the lanthanide acetate system. The tetrahydrate neodymium acetate has two kinds of tendency of structure and properties.     

Syntheses and Crystal Structures of Three Electron Poor N-Vinyltheophylline Derivatives

Abstract  

Protonation of the highly reactive 1:1 intermediates, produced in the reaction between triphenylphosphine and alkyl acetylenecarboxylates (or dialkyl acetylenedicarboxylates) by theophylline leads to vinyltriphenylphosphonium salts, which undergo Michael addition reaction with conjugate base to produce phosphorus ylides. Silica gel was found to catalyze conversion of the phosphorus ylides to electron-poor N-vinyl imidazoles in solvent-free conditions under thermal (90 °C, 1 h) conditions. The structures of these compounds were confirmed by IR, ¹H, and ¹³C NMR spectroscopy, and single crystal X-ray structure determination. The structural analysis of the products indicated that the reaction is completely regio- and stereoselective.     

The dependence of surface morphology of GaSb- and AlxGa1–xSb epitaxial layers on the conditions of LPE growth

The present work shows the dependence of surface morphology of the GaSb and Al_xGa_1–xSb epitaxial layers on the conditions of LPE growth. It is found that for LPE growth at 500 °C a supersaturation of 5—10 °C and a cooling rate of 0.24—0.4°C/min for GaSb epitaxial layers and 0.8—1.2 °C/min for Al_xGa_1–xSb epitaxial layers is necessary to obtain a flat and smooth surface.     

Thermally stimulated relaxation of misfit strains in Si<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Ge<Subscript>x</Subscript>/Si(100) heterostructures with different buffer layers

The regularities of the defect formation in Si_1−x Ge_x/Si heterostructures (x = 0.15 and 0.30), consisting of a low-temperature Si buffer layer and a SiGe solid solution, during their growth and subsequent annealings at temperatures 550–650°C are investigated by the methods of optical and transmission electron microscopy and X-ray diffraction. It is shown that the misfit-strain relaxation by plastic deformation under the conditions studied occurs most intensively in heterostructures with low-temperature SiGe buffer layers. The maximum degree of misfit-strain relaxation (no higher than 45%) is observed in the heterostructures with x = 0.30 after annealing at 650°C. The results obtained are explained by the effect of the nature and concentration of dislocation-nucleation centers, existing in low-temperature buffer layers, on the characteristics of the formation of a dislocation structure in the heterostructures under consideration.     

Controllable thermal expansion properties of In2 − xCrxMo3O12

Solid solutions In_{2 − x}Cr_xMo₃O₁₂ have been prepared via the solid state reaction method. The structural and thermal expansion properties have been characterized using X‐ray diffraction. All compounds exhibit monoclinic structure with space group P2₁/a at room temperature, and transform to orthorhombic structure at higher temperature. Compounds In_{2 − x}Cr_xMo₃O₁₂ (x = 0.7, 1.0 and 1.3) possess strong positive thermal expansion in the monoclinic structure, while their thermal expansion coefficients of orthorhombic structure vary from negative to positive with increasing Cr content. It is worthwhile to note that In_1.3Cr_0.7Mo₃O₁₂ and InCrMo₃O₁₂ have near zero thermal expansion properties.     

Electrical and optical properties of Cd1−xZnxS (0x0.18) grown by chemical bath deposition

Cd_1−xZn_xS films with 0x0.18 were grown by chemical bath deposition technique on glass substrates from an aqueous solution containing cadmium and zinc sulfate, ammonia and thiourea. Microstructural features, obtained from X-ray diffraction and scanning electron microscopy (SEM) measurements, reveal a predominance of Wurtzite structure and an homogenous microstructure formed by densely microcrystallines for all the samples studied. Cd_1−xZn_xS semiconductor was found to be resistive and of n-type. Also, the electron density decreases with increased x and the mobility reaches a maximum around x=0.12. Which means that the Cd_1−xZn_xS films at this composition are of high crystalline quality, i.e. having reduced intrinsic defect concentrations.     

Electroactive complex in thermally treated Ge-Si 〈Cu,Al〉 crystals

It is shown by Hall measurements that quenching complexly doped Ge_{1 − x} Si _x 〈Cu, Al〉 (0 ≤ x ≤ 0.20) crystals from 1050–1080 K leads to the formation of additional electroactive acceptor centers in them. The activation energy of these centers increases linearly with an increase in the silicon content in the crystal and is described by the relation E _k ^x = (52 + 320x) meV. Annealing these crystals at 550–570 K removes the additional acceptor levels. It is established that the most likely model for the additional electroactive centers is a pair composed of substituent copper and aluminum atoms (Cu _s Al _s ) or interstitial copper and substituent aluminum atoms (Cu _i Al _s ). It is shown that the generation of additional deep acceptor levels must be taken into account when using the method of precise doping of Ge_{1 − x} Si _x 〈Al〉 crystals with copper.     

Infrared optical characterization of epitaxial layer – substrate systems (II). Experimental results for AlxGa1−xAs/GaAS

Infrared reflectance and transmittance spectra and Raman scattering spectra of the epitaxial layer-substrate system Al_xGa_1−xAs/GaAs with compositions in the range x = = 0.08–0.49 are measured in the wavenumber range from 40 to 4000 cm⁻¹. In analysing the spectra in terms of the respective theoretical relations for an optical two-layer system the thickness of the layers, the optical mode characteristics and the free carrier parameters are determined. From a comparison with existing literature data for Al_xGa_1−xAs it is concluded that infrared optical measurements on epitaxial layer-substrate systems can be successfully employed to evaluate the material parameters of epitaxial layers with thicknesses down to a few micrometers.     

A rietveld study of the cation substitution between uvarovite and yttrium-aluminum synthetic garnets,obtained by sol-gel method

A series of synthetic garnets solid solutions is compositions between Y₃Al₂Al₃O₁₂ (Y-Al garnet) (YAG) and Ca₃Cr₂Si₃O₁₂ (uvarovite) was synthesized using the sol-gel method. The expected general formula is (Ca_xY_1-x)₃ (Cr_xAl_1-x)₂ (Si_xAl_1-x)₃O₁₂ where x = 0 to x = 1. The cation distribution in dodecahedral, octahedral and tetrahedral sites and bond distances in these synthetic garnets were determined using the Rietveld method. It shows the incomplete substitution in small sites. The smaller site the smaller substitution there is.     

A study of the vacancy-defect distribution in a GaAs/AlxGa1−xAs multi-layer structure grown at low temperature

We have grown a multilayer structure of GaAs and Al_xGa_1−xAs (x=0.25) by molecular beam epitaxy at low substrate temperature (250°C) in order to investigate the effects of annealing on arsenic precipitation and vacancy-defect formation. The as-grown heterostructure contained ∼5×10¹⁷ cm⁻³ gallium vacancies, but information about the individual layers was lost because the layer width (∼45 nm) was smaller than the average positron diffusion length (∼70 nm). Annealing at 500 and 600°C showed increases in the S-parameter (above the bulk value) of ∼2.5% and ∼1.5%, respectively, smaller than for a single LT-GaAs layer (∼3–4%). We explain this phenomenon by suggesting that the excess arsenic which migrates from the material with the higher precipitate/matrix energy (LT-Al_xGa_1−xAs) reduces the gallium vacancy concentration in the LT-GaAs and hence the S-parameter. This hypothesis is supported by SIMS data which shows a build-up of As in the LT-GaAs layers, and TEM images which indicate that arsenic precipitation occurs to a greater extent in the LT-GaAs than in the LT-Al_xGa_1−xAs.     

Dynamics of structural defects of LPE-grown Gax-In1−xP Layers

The structural properties of epitaxial Ga_xIn_1−xP, LPE-grown on 〈111〉-oriented GaAs-substrate, have been investigated. Two groups of samples have been distinguished with respect to the lattice parameters of the layers (a₁) and the substrate (a_s): group A with a₁ < a_s and Δa/a_s = (0.85 ÷ 2.98)%, and group B with a₁ > a_s and Δa/a_s = (0.11 ÷ 1.98)%. Group A is characterized by a structure, including orthogonal, and slanted at 60° towards the surface, linear dislocations, originating from mismatch ones. Group B is characterized by a segmented-surface structure. The optimum conditions for the growth of GaInP layers on GaAs substrates (initial temperature, saturation and composition of the melt, as well as cooling rate) are discussed on the basis of the data obtained.