Effect of the seed crystallographic orientation on AlN bulk crystal growth by PVT method

The growth of AlN crystals by PVT method was investigated using TaC crucible in the temperature range of 2250‐2350 °C. AlN boules with 30 mm in diameter were successfully grown on the crucible lid by self‐seeded growth. The AlN boules consist of the spontaneously nucleated AlN single crystal grains with the {1010} natural crystalline face. The fast growth rate of more than 1 mm/h was achieved. AlN crystals grown on (11 0)‐, (10 0)‐, and (0001)‐face AlN seeds were investigated. Different experimental phenomena have been observed under particular condition. The crystal grown on (11 0)‐face seed has different natural crystalline face from the seed. For the crystal grown on (10 0) or (0001) seed, the crystal natural crystalline face is same as the crystallographic orientation of the seed. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Transmission electron microscopy investigation of B27 martensitic phase in polycrystalline YCu intermetallic compound

Polycrystalline YCu specimens with a CsCl‐type B2 structure made by induction melting were investigated by transmission electron microscopy (TEM). TEM studies show that an orthorhombic YCu B27 martensite with FeB‐type structure having lattice parameters a = 0.71 nm, b = 0.45 nm and c = 0.54 nm forms during deformation at ambient temperature. (101) twins are observed in the YCu B27 phase. The orientation relationship of B27 with B2 matrix is (001)[1 0]_B27 ‖ (112)[1 0]_B2. Effects of B27 phase formation on the ductility of YCu alloy are discussed. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optical imaging of the growth kinetics and polar morphology of zinc tris(thiourea) sulphate single crystals

Growth kinetics of zinc tris(thiourea) sulphate (ZTS) single crystals was imaged in two different growth geometries using laser shadowgraphy technique. Growth rates of the {010} and {001} faces were computed as a function of supersaturation. The time evolution of polar morphology of ZTS crystal based on the growth rates is presented. Except (00 ) face, all the other three faces are found to have a dead zone resulting in large induction period of growth. The anisotropy in the growth rates of the (001) and (00 ) faces was very high, resulting in polar morphology. Different chemical environments on two sides of the (001) slice are suggested as the possible cause for the polar morphology of the crystals. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Distinct Growth Phenomena Observed on Zinc Cadmium Thiocyanate Crystals by Atomic Force Microscopy

Atomic force microscopy is used to investigate the surface morphology of the prismatic (100) face of ZCTC crystal grown at 30°C at a supersaturation of 0.16. This surface is distinctly formed by periodic “macrosteps” that advance along different directions and join with each other leading to the interlaced growth layers with an inclination of about 137°. These two “macrostep” trains well correspond to the pyramidal faces of (0 ) and (01 ) in orientation, therefore they probably propagate from the edges of these faces. The “macrosteps” are practically formed by highly dense steps at the front with regular elementary steps in between. The alternation of “macrosteps” and elementary steps vividly reflects Chernov's “kinematic waves of steps” theory (Chernov , (1984)) on a nanometer scale. Wide indentations and long clefts are generated at the “macrosteps”. The former is generated by twodimensional nucleation growth at a relatively faster growth rate than that of the underlying layer. The latter is probably caused by step trains generated by individual growth sources that have not merged.     

Die Orientierung von Silberaufdampfschichten auf Wolfram

The Epitaxy of single silver crystals on tungsten single crystal surfaces in UHV is studied. The substrate was a W-ribbon recrystalized at high temperature. After the high temperatur treatment many differently oriented single crystal regions appeared on substrate surface. The orientation of the single crystal regions crystal regions was determined by means of etch pits. The experimentally found change of the silver crystal orientation with changing the substrate orientation gives the following epitaxial relationship It is shown that the observed epitaxial growth of silver on tungsten is due to the structural similarity of the parallel growing Ag/W-planes.     

Polarization‐angle dependence of photoluminescence intensity of ordered GaInP2 layers: observation of polarization memory

We compare measured and calculated polarization‐angle dependencies of the intensity of the photoluminescence emission from MOVPE‐grown GaInP₂ layers with different ordering parameters. We measured the polarization‐angle dependencies of the emission propagating along the [001], [110] and [1 0] directions at room temperature. Symmetry considerations were used to calculate the dependence of the relative intensity of the PL emission which was linearly polarized along different directions and to estimate the value of the valence‐band splitting by fitting the measured dependencies with calculated curves. An intriguing influence of the polarization of the exciting beam on the relative amount of the polarized PL emission was observed in the emission from the (110) plane. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The precipitation of sparingly-soluble metal ‘oxinates’ induction periods and nucleation rates

The precipitation of barium, strontium, calcium, magnesium, zinc, cadmium, lead, cobalt, nickel and copper 8-quinolinolates (‘oxinates’) was studied in buffer solutions (pHs from 10 to 4.5) at 22 °C: the metal cation and overall ‘oxinate’ with ‘oxine’ concentrations were varied from 0.0005 to 0.010 M (and saturation rations varied from 3 to 3.000). The induction periods, before the main growth surge, were measured at different metal oxinate concentrations (C) and saturation ratios S = (C)/S · P_r^1/3. Nucleation rates were determined from combined measurements of induction periods and final crystal numbers. Nucleation rates varied with saturation ratios according to the relation \documentclass{article}\pagestyle{empty}\begin{document}$ R_n = k_1 \cdot S^8 {\rm\ nuclei cm}^{ - {\rm 3}} {\rm sec}^{ - {\rm 1}} $\end{document} Induction periods decreased with increasing concentration and supersaturation; over the range t > 3.000 to < 1 sec, . Where t and t were factors that depended on nucleation rates and metal salt solubility. t values decreased and t values increased with decreasing solubility. Precipitation occurred through homogeneous nucleation. Low nucleation rates and prolonged induction periods in solutions of medium to high supersaturation were related to slow rate-determining stages in nucleus formation and to complex formation between metal cation and oxinate anion.     

Hydrothermal conversion of ZnO2 to ZnO flowers: A mechanistic investigation and characterization

In this article, we report a novel but simple method for the phase transformation of ZnO₂ to flower‐like ZnO microstructures hydrothermally at 90 °C with and without the assistance of hexadecylamine as surfactant. The generation of zincate ion ZnO$^{2-}_{2}$ as a growth unit from the reaction between ZnO₂ and peroxide ion O$^{2-}_{2}$ in situ plays a key role in the phase transformation of ZnO₂ to ZnO. The morphology, structure, and composition of the products have been investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Powder X‐ray diffraction (PXRD) and energy dispersive X‐ray analysis (EDX). It has been demonstrated that the as‐fabricated ZnO flowers are composed of self‐assembled brooms and rods in the presence and absence of hexadecylamine respectively. On the basis of experimental results, a possible reaction mechanism and the growth processes involved in the formation of flower‐like ZnO microstructures are discussed.     

Cover Picture: Cryst. Res. Technol. 5/2011

The cover picture shows spontaneously nucleated AlN boules grown on the crucible lids (above) and an AlN single crystal grown on the (10 0)‐face of a seed. (see pages 455–458) (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Hyperfine structure of Cr5+ EPR spectra in X-irradiated potassium halide crystals doped with CrO and Ca2+

The hyperfine structure has been investigated in the EPR spectra of X-irradiated KCl: CrO, Ca²⁺ and KBr: CrO, Ca²⁺ crystals. Preliminarily spectra were simplified by means of heating the crystals up to 400 K for KCl and 440 K for KBr, that destroys the less stable CrO · V centers. It is ascertained, that principal directions of g- and A-tensors do not coincide, and principal A-values are determined. Calculations, making use of the experimental meanings of g- and A-tensor components, showed, that the degree of distortion of oxygen tetrahedra in CrO · Ca²⁺ · V centers is almost the same in both KCl and KBr crystals; besides, these calculations suggest the existence of a strong covalent bonding between the central Cr⁵⁺ ion and four oxygen ligands in CrO ions.     

Kinetics of Etching of Dislocations in Ferroelectric Ammonium Hydrogen Tartrate Single Crystals

Ferroelectric crystals of Ammonium Hydrogen Tartrate (AHT) have been synthesised using the controlled reaction between NH₄Cl and (CHOHCOOH)₂ by diffusion process in silica gel medium. (010) cleavages of AHT crystals have been etched in 1.0 M and 1.5 M solutions of SrCl₂ solution. The lateral and normal velocities of the growth of pits were measured at different temperatures. The time dependence of the growth of the pit dimensions is found to be linear, whereas the temperature dependence of the growth of pits is found to be exponential, viz. \documentclass{article}\pagestyle{empty}\begin{document}$ \[V = A\,\exp \left({\frac{E}{{kT}}} \right)\] $\end{document}. The dissolution parameters, e.g. the activation energies and the pre-exponential factors for dissolution along the surface and along the dislocation lines have been computed. It is observed that the activation energy (E₁) of dissolution along [001] direction is found to be greater than the activation energy (E_b) along [100] direction and the implications are discussed.     

On the reproducibility of the orientation distribution function of texture samples from pole figures (V). Discussion of the reprojection relationship

The exact solution of the problem \documentclass{article}\pagestyle{empty}\begin{document}$ \tilde P_{hi} (y) \to \tilde f(g) $\end{document} is discussed from the view of the structure of the reprojection relationship and its numerical realization.     

Stage B work‐hardening of magnesium single crystals

The change in microstructure during tensile deformation of magnesium single crystals by basal slip was studied with electron backscatter diffraction in the scanning electron microscope. Two samples were plastically deformed up to shear strains of 0.37 and 1.28 belonging to work‐hardening stages A and B, respectively. The results show that the local misorientations resulting from rotations around the <10 0> axis strongly increase the work‐hardening coefficient in stage B. The mechanism of work‐hardening in stage B is discussed with respect to subgrain formation. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Wetting of InP by indium- and indium-tin melts

Orientation dependent wetting of InP substrates by In- and In_xSn_1−x melts saturated with InP was studied using the sessile drop method. The contact angle was found to depend on the substrate orientation as follows: It is shown that a tin admixture to the indium melt improves the wetting behaviour. Additional to the dependence on substrate orientation it was found an anisotropic wetting on all investigated faces.     

Absorption and ionic conductivity of oxygen-containing SrF2 crystals

An absorption band at 3644 cm⁻¹ is caused by isolated OH⁻ ions. O⁻ ions cause an absorption band at 213 nm the oscillator strength of which is 0.020. Charge-compensation of O⁻ ions is effected by F⁻ ion vacancies (F). As for CaF₂ crystals there occur monomers and dimers of [O⁻ – F] complexes. The mass action constants of association of F with oxygen centres are K_AD = ⅓ exp (4.28 – 0.82 eV/kT) for [O⁻ – F], K_AT = 4 exp (17.4 – 1.25 eV/kT) for [2 O⁻ – F] and K_AQ = exp (4.2 – 0.89 eV/kT) for [2 O⁻ – 2 F].     

The influence of the direct quench and indirect quench to Ta > Th on the decomposition behaviour of an Al-2 at.% Zn-1 at.% Mg alloy

The decomposition behaviour of an Al-2.0 at.% Zn-1.0 at.% Mg alloy after direct quench (DQ) and indirect quench (IQ:T = 23 °C, t) to the ageing temperature T = 160 °C (above the temperature of the rapid homogeneous nucleation, T_h) was investigated by means of TEM and isothermal resistivity measurements. The precipitation density of the η-particles yields a maximum value at pre-ageing times about 10 min at T = 23 °C. To clear up the reason for that phenomenon a loop-formation and clustering model was introduced.     

Surface preparation of AB semiconductors (Cd3As2, Zn3As2, Cd3P2, Zn3P2) under ultra-high vacuum conditions

The UHV surface preparation of AB materials (crystals and thin films) has been monitored with XPS and AES. Clean and stoichiometric surfaces of AB crystals were prepared by means of low energy ion bombardment and subsequent low temperature annealing. Stoichiometric Cd₃As₂ and Zn₃P₂ thin films with very low amounts of C and O were deposited by the evaporation of bulk material in the UHV. The quality of prepared AB crystal and thin film surfaces was sufficient to carry out density of states investigations (UPS, RELS) with success.     

Investigation of the homogeneity of Cu-Ni sintered materials using microprobe

The application of various parameters for the estimation of the degree of homogenization of Cu Ni sinters is investigated. For this purpose specimens were prepared with different Ni contents, different degrees of initial porosity and different sintering periods. Analysis is done by means of point and line technique. The following parameters were used: standard deviation from the mean Ni content, \documentclass{article}\pagestyle{empty}\begin{document}$ S_c = \sqrt {\frac{1}{n}\sum\limits_{i = 1}^n {\left({c_i - \bar c} \right)^2 } } $\end{document}, variation coefficient \documentclass{article}\pagestyle{empty}\begin{document}$ v = \frac{{S_c }}{{\bar c}} $\end{document}, maximum concentration grapient of nickel, \documentclass{article}\pagestyle{empty}\begin{document}$ g = \left({\frac{{dc}}{{dx}}} \right)_{\max } $\end{document} and the relation of the minimum to the maximum Ni concentration in different points of the sinter. – These parameters are enough precise for the representation of the degree of homogenization, but besides this the latter enables to express the homogeneity in the form of a fraction as measure for the homogeneity of a sinter.     

Dependence of doping element incorporation on temperature in the chemical vapour deposition of epitaxial silicon (III). Empirical incorporation characteristic of the Si-P-H system

The shape of the empirical incorporation characteristic of phosphorus in epitaxial silicon, deposited from silane-phosphine-hydrogen mixtures, shows two branches with different incorporation dependences on temperature (incorporation enthalpies). In the lower phosphorus-concentration range (N < 10¹⁸) the experimentally determined value of incorporation enthalpy can be explained as a complex quantity, including the enthalpies of the two phosphorus hydrides PH₃ and PH₂, the latter of which is formed by the partial decomposition of phosphine (PH₃) at deposition temperatures. — In the upper phosphorus-concentration range (N > 10¹⁸) the incorporation equilibrium of the dimeric phosphorus molecules, formed by the nearly complete decomposition of phosphine, is reflected in the incorporation enthalpy of the empirical incorporation characteristic.     

Magnetically induced rhombohedral distortion in the UxTh1−xSe and UxY1−xSe solid solutions

Solid solutions of U_xTh_1−xSe for x = 1.00 ÷ 0.80 and the solid solutions of U_xY_1−xSe for x = 1.00 ÷ 0.60 were studied by the X-ray diffraction over the temperature range 100 ÷ 200 K. In both systems rhombohedral distortions of the cubic rock-salt crystal structure was observed below the Curie temperatures. The temperature and composition dependences of the rhombohedral angle ω of the rhomboedral cell and the \documentclass{article}\pagestyle{empty}\begin{document}$ \frac{{c' - a'}}{{a'}} $\end{document} ratio were determined.