Effect of the defect structure character in calcite single crystals on X-ray diffraction

The paper presents experimental results for the dependence of the integral intensity of anomalous transmission T_i and Laue reflection R_i of X-rays on the structural quality of calcite single crystals as obtained by a two-crystal spectrometer. The relation between X-ray dynamic and kinetic scattering as a function of the sample thickness, densities of perfect dislocations in perfect CaCO₃ crystals and of atom-vacancy complexes in calcite crystals with „background”︁ has been found. Distortions due to perfect grown-in dislocations in calcite are shown to exceed those produced in crystals with „background”︁. The latter appear to be more X-ray transparent. A comparison with results of twin layer thickening experiments on CaCO₃ crystals of different qualities again points to the different nature of these distortions. In CaCO₃ crystals with the dislocation density of up to 2 × × 10³ cm⁻², the X-ray scattering, in our experiments, was consistent with the dynamic diffraction theory, while at higher dislocation densities, the X-ray scattering markedly differs from it.     

Reflectivity measurements of thin SiO2 layers in the soft-X-ray region

Energy and angular dependent reflectivity measurements of differently prepared SiO₂ layers were made in the soft X-ray region in order to study differences in their optical and electronic behaviour caused by the technological process. The optical constants of the layers were determined by fitting the angular dependent reflectivity data with a multilayer model which takes into account the roughness of all interfaces. Detailed knowledge of the polarization level of the primary beam from the synchrotron radiation source is needed for reliable results. The energy dependent reflectivity measurements indicate that high-pressure dry-oxidized layers have a more perfect structure than normal dry-oxidized layers. Independent on the deposition process the Si SiO₂ interface roughness amounts to ± 1 nm. The Si_2p-XANES of Si and SiO₂ were detected.     

Investigation of GaN heteroepitaxial layers by means of the kossel effect technique

GaN heteroepitaxial layers grown on spinel substrates have been investigated by the Kossel effect technique. The excitation of GaK_α X-rays inside the crystal lattice was carried out either by means of 1.25 MeV protons or 40 KeV electrons. Both methods give similar results concerning the values of the lattice parameters and the sign of polarity. Following the proton irradiation a lattice expansion normal to the surface occurs. A comparison of our results with those of other authors shows that the growth direction is the same for {111} spinel and {0001} sapphire substrates.     

Periodic Multilayers MoSi2/Si with a Large Number of Periods

Different approaches to decreasing mechanical stresses developed in MoSi₂/Si multilayers with increase of number of periods due to structural reconstruction in layers of amorphous silicon and nanocrystalline MoSi₂ were studied by scattering CuKα X-ray radiation at small and large angles, cross-sectional electron microscopy and micrometry of substrate sag. It was shown that effective relaxation of mechanical stresses in MoSi₂/Si multilayers is achieved by annealing them at ∼320 °C during 1 hour, or by deposition of layers at substrate temperature ∼320 °C, or by increasing sputtering gas pressure up to 7 × 10^—3 Torr in case of argon. Optimal conditions for deposition of MoSi₂/Si multilayers with periods N > 10³ and high reflectivity of X-rays with wavelengths 12.4—20.0 nm are: substrate temperature T_s = 220 °C, argon pressure P_Ar = 3 × 10^—3 Torr, layer deposition rate 1 nm/s.     

Organometallic Vapour Phase Epitaxy of Galliumnitride Using Ga(CH3)3 · N(CH3)3-Adduct Pyrolysis

Epitaxial layers of GaN have been grown on {1102} sapphire in atmospheric OMCVD system using Ga(CH₃)₃ · N(CH₃)₃ adduct and NH₃ as reactants. Optimum growth conditions for crystallographically perfect layers have been found at temperatures between 850 and 1000 °C. With increasing temperature the growth rate decreases whereas the concentration of free carriers increases. In photoluminescence spectra only the donor-acceptor pair recombination could be found. It is concluded that the donor oxygen (O_N) and the acceptor carbon (C_N) are the dominant impurities.     

Crystal structure of the orthorhombic basic copper nitrate,Cu2(OH)3NO3

The crystal structure of the orthorhombic copper salt Cu₂(OH)₃NO₃ (natural gerhardtite) has been determined from X-ray diffractometer data by means of three-dimensional Patterson and Fourier syntheses, and refined by difference Fourier syntheses and least-squares methods to a finalR index of 0.097 for 532 reflections. Crystals of Cu₂(OH)₃NO₃ are orthorhombic:a=6.087(2),b=13.813(4),c=5.597(2) Å,Z=4, space groupP2₁2₁2₁. The Cu atoms form deformed hexagonal pseudocells (010). Each Cu(1) ion is surrounded by an approximately square planar arrangement of four OH ions at 1.929, 1.952, 1.993 and 1.998 Å and by two O (of NO₃ ions) at 2.359 and 2.480 Å, completing a deformed coordination octahedron; each Cu(2) ion is similarly coordinated by four OH at 1.989, 1.997, 2.009 and 2.018 Å, one OH at 2.309 Å, and one O at 2.384 Å. The structure involves layers of such deformed octahedra, of theC6-type, linked together by hydrogen bonds through the NO₃ ions. Similarities to and differences from the structure of the monoclinic polymorphous form are discussed.     

Dislocation arrangements in cyclically deformed polycrystalline molybdenum

The present paper deals with the cyclic stress-strain behaviour of polycrystalline molybdenum at room temperature and the dislocation structures built up within this material during the fatigue process. A cyclic stress-strain curve of molybdenum deformed in a strain-controlled and symmetrical push-pull test is shown. At strain amplitudes e_a < 3 × 10⁻³ arrangements of relatively homogeneously distributed dislocations are observed in the stage of the stabilization of mechanical properties. The characteristics of these dislocation arrangements are similar to those of dislocation structures of unidirectionally deformed molybdenum single crystals. At strain amplitudes e_a > 3 × 10⁻³ dislocation structures are developed with an inhomogeneous dislocation distribution (bundles structures). The dislocation density in the surface layers of fatigued specimens shows larger values than within the material. The cyclic deformation after a change from a small deformation amplitude to a larger one, or vice versa, is connected with characteristic changes of dislocation density.     

Electron diffraction study on the electrostriction of ruby

The pseudo-cubic lattice of ruby was so deformed, when immersed in a strong electric field, that it showed an induced superlattice structure along the [110] axis. The field strength was about 2 × 10⁴ kV/cm at the specimen. Electron diffraction pattern from the superlattice informed on the orientation of the Al₂O₃ dipoles in ruby. The ruby deformed by electron bombardment was accompanied by an emission of red light (wavelength: 6000 Å).     

Dislocation energy levels in deformed silicon

Abstract-Energy levels in deformed silicon have been directly measured by transient junction capacitance techniques. If complex slip band formation is not suppressed, a large variety of states are observed after deformation with a prominent state at E_v − 0.68 ev. After annealing at 900°C the complex defect spectra simplify to two dominant states at E_v + 0.35 ev and E_c − 0.38 ev. In more homogeneously deformed silicon where slip band formation is suppressed, the dominant state at E_c − 0.68 ev is not observed after deformation and the spectra resembles that obtained after annealing the complex spectra at 900°C.     

Aus flüssiger Phase abgeschiedene,dotierte VO2-Schichten und deren Widerstands-Temperatur-Verhalten

The preparation of VO₂ layers by a liquid-phase process is described. Undoped VO₂ layers and layers doped with Al and W are prepared, respectively. The resistance-temperature behaviour of the layers was investigated: The VO₂ layers reach nearly the quality of monocrystalline material. The recrystallization of the VO₂ layers is of great importance for the effectiveness of doping.     

Stoichiometry of Thin Layers of CuInSe2 Investigated by ESCA

The stoichiometry of thin epitaxial layers of CuInSe₂ on CaF₂ and GaAs substrates was determined by the ESCA method. Substrate temperature was varied. It was found, that layers of exact stoichiometry are got at substrate temperatures around 700 K.     

Epitaxial growth of silicon carbide layers by sublimation “Sandwich method” (II) structural defects and growth mechanism

Structural defects of α-SiC epitaxial layers grown by sublimation “sandwich-method” in vacuum at the temperatures ranging from 1600 to 2100 °C have been investigated by X-ray topography and optical microscopy methods. It was shown, that perfect SiC layers with the homogeneous polytype structure and small dislocation density (≦ 10² cm⁻²) may be obtained on the substrates with any crystallographic orientation at the conditions close to quasi-equilibrium one. The presence of impurities and silicon deficiency in the vapour phase, lead usually to the deterioration of morphological and structural perfection of SiC layers. There are the following structural defects: uncoherent polytype inclusions (mainly β-SiC), pores, dislocations, specific stacking faults. Morphological peculiarities of the SiC epitaxial layers and possible growth mechanisms are discussed.     

Orthorhombic Polymorph of ErP5O14, Crystal Structure and Characterization

Erbium pentaphosphate crystals have been characterized and the structure of the orthorhombic polymorph (type III) determined by X-rays. It has been found that the orthorhombic samples of ErP₅O₁₄, space group Pnma, crystallize mainly at higher temperatures and usually are much larger than monoclinic crystals, space group C2/c, obtained from lower-temperature crystallizations. Differences in fluorescence and upconversion properties between orthorhombic and monoclinic polymorphs have been detected.     

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)     

Structure defects investigation of GaAs and AlxGa1−xAs epitaxial layers

The paper is concerned with the results of investigation of structure defects in gallium arsenide and Al_0.3Ga_0.7As epitaxial layers. It was found that structure defects in layers under investigation are responsible for the excess component of the Schottky diode's reverse current.     

Thermoluminescence studies of Al2O3 crystals doped with Cobalt impurity

Thermoluminescence (TL) studies of cobalt-doped Al₂O₃ crystals irradiated with X-rays have shown that the TL glow curve consists of three peaks at 105, 195 and 260°C. Bleaching, annealing and quanching studies have been performed in order to understand the nature of colour centers responsible for the formation of the three peaks. The values of the fundamental parameters like trap depth and frequency factor are estimated from TL data and the results obtained are discussed.     

Emissionsmikroskopische Untersuchungen zur plastischen Verformung und Versetzungsmarkierung an NbFe2

By means of a homogenous compression device the Laves phase NbFe₂ was deformed plastically while being observed in an emission electron microscope. In connection with these experiments the possibility of marking dislocations was investigated emerging from the crystal by means of a thermal treatment under vacuum conditions in the emission electron microscope. Slip traces on the surfaces were observed only above a critical temperature (transition brittle-ductile). During a high temperature treatment under vacuum oxide nuclei grow on the surface. These nuclei seem to decorate dislocations emerging from the crystal. On surfaces of plastic deformed samples the oxide nuclei mark slip traces.     

Burgers Vectors of Dislocations in Creep-deformed Fe3Si Single Crystals

In creep-deformed Fe₃Si single crystals the Burgers vectors of the dislocations were examined by transmission electron microscopy. The Burgers vector in a sample deformed under conditions of 60 MPa and 575–600 °C was of the type 1/2 〈110〉, whereas 〈111〉 superlattice dislocations were not found. 1/2 〈110〉 is the shortest translation distance in the D0₃ superlattice structure of Fe₃Si.     

Kinetics of ion exchange in glasses

The kinetics of $\text{K}{}^{\mathrm{+}}\text{?}\text{Na}{}^{\mathrm{+}}$ exchange in two glass systems, 20Na₂O·(60?x)B₂O₃· (20 + x)Si₂ (where x = 0, 15, 30 and 45 mol%) and Na₂O·3SiO₂, were studied as a function of glass composition, salt bath composition, exchange temperature and time The distribution of K in the glass specimens after exchange in molten KNO₃ was determined with an electron probe. Stresses in these speciments were measured photoelastically. The interdiffusion coefficient $\text{D}$ for ion exchange was calculated as a function of local composition in the glass using the Boltzmann-Matano method. The strong variation of $\text{D}$ in any particular glass approximated that predicted by a mixed alkali model (as advanced by Lacharme), where the glass in the ion-exchanged region approximates a composite of stacked layers of mixed alkali glasses with a gradually varying alkali ratio. The small discrepancy between the experiment and the mixed alkali model was partly, but not fully, reconciled by considering the strains in the glasses. The observation which remained unexplained was that the calculated stress profiles did not show perfect agreement, both in magnitude and in shape, with the experimentally measured stress profiles. It appeared that the kinetics of ion exchange in the glasses were also influenced by a network relaxation process which may have occurred well below the glass transition temperature.     

Influence of Microdefects on the Generation of Dislocations in Homoepitaxial Gallium Phosphide Layers Grown on LEC Substrates

GaP LEC substrates doped with sulphur (N_D – N_A roughly (3–7) × 10¹⁷ cm⁻³) were characterized by transmission electron microscopy. This material was found to contain microdefects such as perfect perismatic dislocation loops, and spherical precipitates. Cross-sectional TEM investigations perfomed have shown that above all perfect dislocation loops lying directly at the substrate/layer interface are sources for the formation of extended dislocations propagating through the epitaxial layer. Using the methods of selective photoetching and AB-etching on (110) cleavage faces this phenomenon was observed, too.