Low-Temperature Crystallization of Germanium in the Thin-Film Ge/Al System

Crystallography Reports - The crystallization of thin germanium films during vacuum thermal deposition on an aluminum surface has been investigated. Significant changes in the morphology and...     

Structure and features of the surface morphology of <Emphasis Type="Italic">A</Emphasis><Superscript>4</Superscript><Emphasis Type="Italic">B</Emphasis><Superscript>6</Superscript> chalcogenide epitaxial films

The structure and features of the surface morphology of Pb_{1 − x} Mn _x Se (x = 0.03) epitaxial films grown on freshly cleaved BaF₂(111) faces and PbSe_{1 − x} S _x (100) (x = 0.12) single-crystal wafers were investigated by molecular beam condensation and the hot-wall method. It is shown that the epitaxial films, in accordance with the data in the literature for other chalcogenides, grow in the (111) and (100) planes, repeating the substrate orientation. Black aggregates are observed on the film surface of the films grown. The results obtained are compared with the data in the literature and generalized for other chalcogenides: A ⁴ B ⁶:Pb (S, Se, Te); Pb_{1 − x} Sn _x (S, Se, Te); and Pb_{1 − x} Mn (Se, Te). It is established that the formation of black aggregates, which are second-phase inclusions on the surface of epitaxial films obtained by vacuum thermal deposition, is characteristic of narrow-gap A ⁴ B ⁶ chalcogenides.     

Stabilization of lattice period in quinary solid solutions of the <Emphasis Type="Italic">A</Emphasis><Superscript>3</Superscript><Emphasis Type="Italic">B</Emphasis><Superscript>5</Superscript> compounds

The stabilizing effect of elastic strains on the lattice period of a quinary solid solution is considered. The expression for the stabilization factor for quinary solid solutions of the A_xB_1?xC_yD_zE_1?y?z type is derived. It is shown that the stabilizing influence of the substrate sharply increases in the vicinity of the region of the chemical spinodal. The stabilization factors are calculated for the Ga_xIn_1?xP_yAs_zSb_1?y?z and A1_xGa_yIn_1?x?yP_zAs_1?z quinary solid solutions isoperiodic to InAs, GaSb, and GaAs. It is shown that in the region of thermodynamic instability the stabilization factor has negative values. The changes in the composition of the above elastically strained quinary solid solutions are analyzed with respect to the equilibrium composition. It is also shown that stabilization of the lattice period does not signify the stabilization of its composition.     

Growth of tungsten whiskers oriented in <111> direction

The electron micro diffraction technique and pseudopotential ab initio calculations were implemented to study in details the formation and mechanism of growth of the tungsten whiskers during the reduction of nickel tungstate by CO gas. It has been shown that the W whiskers prefer to grow as crystals oriented in the <111> direction, and this process may be considered as the epitaxial growth on the hexagonal planes of Ni₄W particles. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Interface reconstruction in the Ga<Subscript>2</Subscript>Se<Subscript>3</Subscript>/GaAs(100) and In<Subscript>2</Subscript>Se<Subscript>3</Subscript>/InAs(100) nanoheterostructures

The surface of GaAs(100) and InAs(100) substrates thermally treated in selenium vapor has been investigated by transmission electron microscopy (TEM) and reflection high-energy electron diffraction. Transmission electron microscopy and high-energy electron diffraction data on these heterostructures confirms the epitaxial pseudomorphic growth of the gallium selenide Ga₂Se₃(100) and indium selenide In₂Se₃(100) phases with ordered stoichiometric cation vacancies. A model of the atomic structure of the Ga₂Se₃(100) and In₂Se₃(100) surfaces is proposed, and the 2 × 2 reconstruction of the GaAs(100) and InAs(100) surfaces after treatment in selenium vapor is discussed within this model.     

Structure of Triammonium <Emphasis Type="Italic">fac</Emphasis>-Trichloridotrioxidorhenate(VII) Chloride with <Emphasis Type="Italic">C</Emphasis><Subscript>3<Emphasis Type="Italic">v</Emphasis></Subscript> Crystallographic Symmetry of the Complex Anion

Abstract  

The unstable crystals of triammonium fac-trichloridotrioxidorhenate(VII) chloride have been obtained from ammonium rhenate(VII) solution in concentrated hydrochloric acid. The crystal structure consists of fac-trichloridotrioxidorhenate(VII) anions, chloride anions and ammonium cations. Each fac-trichloridotrioxidorhenate(VII) anion and each chloride anion lies in special position of 3m site symmetry (cell parameters: a = 9.026(3) Å; c = 7.690(4) Å; space group: P6₃ mc). The ammonium cation lies in special position of m site symmetry. The following anion geometrical parameters of the fac-trichloridotrioxidorhenate(VII) anion have been obtained: Re–O bond length of 1.720(2) Å, Re–Cl bond length of 2.5428(9) Å, the bond angles: O–Re–O of 103.5(1)° and Cl–Re–Cl of 79.8(1)°.     

Effect of flux composition on the morphology of KTiOPO<Subscript>4</Subscript> crystals

KTiOPO₄ crystals have been grown from flux of K₆P₄O₁₃ in the presence of K₂SO₄, Li₂SO₄, and Na₂SO₄ salts and V, Cr, Ni, Co, Cu, Mo, Ba, Ce, Er, and W impurities. The crystals grown are characterized by well-developed simple {100}, {011}, and {201} faces. In some cases, new ({111} and (031)) faces arise. Some distortion of crystals caused by their pulling in the [101] direction is observed.     

X-ray determination of solid solution composition in the melilite system åkermanite (Ak) — gehlenite (Ge) — soda melilite (Sm)

Expressions are given and discussed which allow a determination of the composition of solid solutions in the ternary system Ak Ge Sm. Resulting from X-ray measurements of the tetragonal melilite constants a₀ and c₀, the composition can be calculated within the limits of ±3% if the lattice constants are determined with an accuracy of ±0.001 Å.     

Synthesis and crystal chemical characteristics of the structure of <Emphasis Type="Italic">M</Emphasis><Subscript>0.5</Subscript>Zr<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> phosphates

Double phosphates of zirconium and metals with an oxidation degree of +2 of the composition M_0.5Zr₂(PO₄)₃ (M = Mg, Ca, Mn, Co, Ni, Cu, Zn, Sr, Cd, and Ba) are synthesized and characterized by X-ray diffraction methods and IR spectroscopy. The crystal structures of all the compounds are based on three-dimensional frameworks of corner-sharing PO₄-tetrahedra and ZrO₆-octahedra. Phosphates with large Cd²⁺, Ca²⁺, Sr²⁺, and Ba²⁺ cations octahedrally coordinated with oxygen atoms form rhombohedral structures (space group R3), whereas phosphates with small tetrahedrally coordinated Mg²⁺, Ni²⁺, Cu²⁺, Co²⁺, Zn ²⁺, and Mn²⁺-cations are monoclinic (space group P2₁/n). The effect of various structure-forming factors on the M_0.5Zr₂(PO₄)₃ compounds with a common structural motif but different symmetries are discussed.     

Synthesis and investigation of the new phosphates K<Subscript>2</Subscript><Emphasis Type="Italic">Ln</Emphasis>Zr(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> (<Emphasis Type="Italic">Ln</Emphasis> = Ce-Yb,Y) with langbeinite Structure

New orthophosphates of potassium, zirconium, and rare earth elements K₂LnZr(PO₄)₃ (Ln = Ce-Yb, Y) that crystallize in a langbeinite structure (cubic system, sp. gr. P2₁3, Z = 4) were prepared and investigated by X-ray diffraction and IR spectroscopy. The structure of the K₂PrZr(PO₄)₃ phosphate was refined by the Rietveld method using neutron powder diffraction data (DN-2 time-of-flight diffractometer, Joint Institute for Nuclear Research, Dubna). This structure is characterized by a mixed framework [PrZr(PO₄)₃] with large cavities in which potassium cations are located. Pr³⁺ and Zr⁴⁺ cations are distributed in order over two independent crystallographic positions. The limits of the incorporation of lanthanide cations into the anionic framework in phosphates with sodium-zirconium phosphate and langbeinite structures are considered.     

Nanoclusters based on pentagondodecahedra with shells in the form of <Emphasis Type="Italic">D</Emphasis>32, <Emphasis Type="Italic">D</Emphasis>42, and <Emphasis Type="Italic">D</Emphasis>50 deltahedra in crystal structures of intermetallic compounds

The TOPOS software package has been used to form a database of intermetallic compounds containing pentagondodecahedral d clusters (528 crystal structures of intermetallic compounds, 111 topological types, and 47 space symmetry groups). On the whole, 606 atomic d configurations have been selected which are described by 14 point symmetry groups. Examples of nanoclusters are presented which are precursors of the crystal structures of intermetallic compounds with the outer shell in the form of deltahedra D, which are formed above dodecahedra. These nanoclusters are identified in the automatic mode of structural data processing: D32 (K₈In₆Ge₄₀, Cs₃₀Na₃Sn₁₆₂), D ₄₂ (Ru₃Be₁₇, Y₃Cd₁₈, Ca₃(Cd₁₇Al)), and D ₅₀ (Yb₃Zn₁₈, Ce₃(Au₁₄Sn₃), Pr₃Cd₁₈, Eu₄Cd₂₅), where 32, 42, and 50 are the numbers of atoms in the shell. Similar deltahedra were found previously in icosahedral nanoclusters (precursors of intermetallic compounds). Structures with the dodecahedral nanocluster precursors containing D42 and D50 deltahedra are approximants of MCd_5.7 (M = Yb or Ca) quasicrystals and belong to the family of MCd₆ (M = Ce, Pr, Nd, Sm, Eu, Gd, Dy, Yb, Y, or Ca).     

Relationship between the lengths of covalent and intermolecular bonds in <Emphasis Type="Italic">X</Emphasis>-H...<Emphasis Type="Italic">Y</Emphasis> bridges

The formula exp(−ln2((r ^XH − r ₀ ^XH)/(r _sym ^XH − r ₀ ^XH))^5/3) + exp(−ln2((r ^YH − r ₀ ^YH)/(r _sym ^YH − r ₀ ^YH))^5/3) = 1 is proposed, which relates the lengths of both covalent and hydrogen bonds in homo- and heterobridges. This formula is justified by the experimental data from the CSD bank, which was obtained by neutron diffraction for 108 O-H...N hydrogen bridges with bond angles exceeding 170°.     

Correlation of the structural imperfection and morphology of Bi<Subscript>4</Subscript>Ge<Subscript>3</Subscript>O<Subscript>12</Subscript> crystals grown by the low-gradient Czochralski method

This paper reports on the results of investigations into the morphological structure of the facets of Bi₄Ge₃O₁₂ crystals grown by the Czochralski method under the conditions of low temperature gradient (0.1–1 K/cm). A correlation between the morphological features of the facets at the crystallization front and the formation of defects in the bulk of the crystal is revealed. It is demonstrated that the {112} facets remain regular while the growing surface deviates from the (112) crystallographic plane by an angle of up to 1°. At larger deviations, there occurs a crossover from the stable facet growth to the growth of macrosteps or normal growth depending on the growth conditions.     

Epitaxial low-temperature growth of In<Subscript>0.5</Subscript>Ga<Subscript>0.5</Subscript>As films on GaAs(100) and GaAs(111)<Emphasis Type="Italic">A</Emphasis> substrates using a metamorphic buffer

A complex investigation of epitaxial In_0.5Ga_0.5As films grown on GaAs substrates with crystallographic orientations of (100) and (111)A in the standard high- and low-temperature modes has been performed. The parameters of the GaAs substrate and In_0.5Ga_0.5As film were matched using the technology of step-graded metamorphic buffer. The electrical and structural characteristics of the grown samples have been studied by the van der Pauw method, atomic force microscopy, scanning electron microscopy, and transmission/ scanning electron microscopy. The surface morphology is found to correlate with the sample growth temperature and doping with silicon. It is revealed that doping of low-temperature In_0.5Ga_0.5As layers with silicon significantly reduces both the surface roughness and highly improves the structural quality. Pores 50–100 nm in size are found in the low-temperature samples.     

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.     

Effect of doping and heat treatment on the mechanical parameters of ZnSe<Subscript>(1 − <Emphasis Type="Italic">x</Emphasis>)</Subscript>Te<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> crystals grown from the melt

The mechanical properties of crystals of ZnSe_{(1 − x)}Te _x (0 < x < 1.3 wt %) solid solutions are investigated using the indentation method. The breaking points of doped and undoped crystals are measured by the uniaxial compression method. It is revealed that the microhardness anisotropy coefficient for crystals with a tellurium dopant content of ∼0.3 wt % is equal to unity. A change in the tellurium content in the solid solutions from 0.2 to 1.3 wt % leads to a linear increase in the microhardness by 23%. The brittle strength of the ZnSe and ZnSe_{(1 − x)}Te _x crystals varies in a similar manner. It is demonstrated that heat treatment and the presence of interblock boundaries affect the ultimate strength and the cracking resistance of the ZnSe_{(1 − x)}Te _x crystals. This is an important factor which should be taken into account in mechanical treatment of the materials under investigation.     

Low-Temperature epitaxial growth of InGaAs films on InP(100) and InP(411)<Emphasis Type="Italic">A</Emphasis> substrates

The structural and electrical characteristics of In_0.53Ga_0.47As epitaxial films, grown in the low-temperature mode on InP substrates with (100) and (411)A crystallographic orientations at flow ratios of As4 molecules and In and Ga atoms of γ = 29 and 90, have been comprehensively studied. The use of InP(411)A substrates is shown to increase the probability of forming two-dimensional defects (twins, stacking faults, dislocations, and grain boundaries), thus reducing the mobility of free electrons, and As_Ga point defects, which act as donors and increase the free-electron concentration. An increase in γ from 29 to 90 leads to transformation of single-crystal InGaAs films grown on (100) and (411)A substrates into polycrystalline ones.     

Defect structure of TiS<Subscript>3</Subscript> single crystals of the <Emphasis Type="Italic">A</Emphasis>-ZrSe<Subscript>3</Subscript> type

The defect structure of TiS₃ single crystals of the A-ZrSe₃ type has been determined based on X-ray diffraction data. Shear defects manifest themselves as displacements of ab layers (which can imitate a twin) by ～0.5a. Regular shears facilitate the formation of a superstructure along the c axis. A model of defect in the layer structure is proposed to explain the atomic displacements at an angle to the layer plane.