Die Abhängigkeit der Röntgenemissionsspektren vom chemischen Bindungszustand und der kristallographischen Orientierung der Proben und die Bedeutung dieser Effekte für mikroanalytische Untersuchungen

It is shown that also more subtle X-ray spectroscopic effects such as the dependence of the spectra on chemical bond and crystallographic orientation (of monocrystalline samples) can be measured by means of modern electron microprobe analysers because of their high resolving power. When neglected these effects can falsify microanalytic measuring data, but they also can widely extend their information content which is demonstrated at hand of examples. Some possibilities of applications of the electron microprobe analysers for fundamental investigations in the field of X-ray spectroscopy (e. g. energy band structure of solids) are demonstrated and specific advantages of their use are referred to.     

Eine Methode zur genauen Messung des Massenschwächungskoeffizienten für Röntgenstrahlung

In the measuring technique the substance to be examined (e.g. an intermetallic compound) is digested with acid and subsequently diluted by water so far that the attenuation, with well measurable thickness of the irradiated solution, can be easily measured. By preparing a reference solution without substance to be measured but having the same densities of the acid and water the attenuation of the acid and water can be eliminated. The technique is analogous with water-soluble salts. From the (μ/ϱ) value thus obtained the absorption coefficient μ₀ of the solid material can be determined using the pycnometrically determined density of the solid material. The practical measuring equipment with a plane-parallel sample cell and the method of evaluation are described. (μ/ϱ) values of the intermetallic compound CaCu₅ and of H₂O were determined in this way with maximum errors of ±1 per cent or ±0.5 per cent, respectively.     

Cold Neutron Scattering Investigation of Molecular Orientational Motion in Smectic A Phase of 4-Cyano- 4′-N-Alkylbiphenyl Liquid Crystal

The measured cold neutron scattering spectra obtained in the S_A phase of 4-cyano-4-alkylbiphenyl sample are investigated with emphasis: a) on the molecular uniaxial, within two potential barriers angular confined, stochastic reorientational motion, b) on the long molecular axis orientational fluctuations between two potential barriers as well as uniaxial simple rotational diffusion, and c) on the correlations of orientation between adjacent molecules due to Faber, with no localized motion implied.

It is shown that, for low Q values, where Faber approach could be utilized, the spectra are well represented by his continuum theory of molecular disorder, although the first model above, in a modified form, can not be completely ruled out.     

Some Results of the Analytical Evaluation of Isothermal Resistivity Measurements with Al – Zn – Mg Specimens

Isothermal measuring curves of a series of Al-4.5 at.% Zn-X at.% Mg (X = 0.2, 0.5, 1.0, 1.5, 2.25, 3.0) were evaluated analytically by means of the Johnson-Mehl-Avrami equation. Itturned out to be possible to fit the curves completely only by assumption of two process stages. The course of the parameters obtained their dependence upon the Mg content is interpreted by means of suitable model assumptions.     

Experiences with Quartz Oscillator Angle‐Sorting

Blanks ‐ the thin quartz plates industrially used for oscillators, nowadays produced at rates of millions per week ‐ need thorough controls of their properties. The most important of them, the correct orientation of the plates' surface relative to certain lattice planes or crystal axes, can be determined in a few seconds measuring time with an accuracy of a few arcseconds using the so‐called “Omega Scan”. This method and its further development in the last time will be described in some detail.     

Zum Einsatz der quantitativen Lichtmikroskopie bei der Versetzungsdichtebestimmung von GaAs-〈100〉-Kristallen

The linear analysis with the microscope EPIQUANT is applicable to metallographical measurement of the etch pit density of GaAs 〈100〉 crystals. The values of the linear analysis are converting to numbers of particles in the measuring field by means of mathematical-statistical equations. For large etch pit densities the measurement of the percentage fraction of etch pits of the measuring line is more precise as the measurement of the number of particles intersected by the measuring line.     

Structural properties of bulk GaN substrates: Impact of structural anisotropy on non‐polar and semi‐polar crystals

In this paper we show the structural parameters and structural anisotropy of the bulk GaN substrates of various crystallographic orientations (00.1), (10.0), (11.0) and (20.1) obtained by ammonothermal method. The structural parameters were investigated using high resolution X‐Ray Diffraction. Perfect crystalline structure manifests in very narrow peaks in X‐ray rocking curves. The full width at half maximum (FWHM) values of 16 and 18 arcsec for the symmetrical and asymmetrical peaks, respectively, have been observed. In addition, we observed structural anisotropy in the non‐polar and semi‐polar crystals, depending on the orientation of the sample relative to the X‐ray beam. It is conducted that this anisotropy is a intrinsic property of non‐polar and semi‐polar GaN substrates.     

Investigations on the defect depth of electroerosive-cut Te single crystals by reflection electron diffraction (RHEED)

Results of the experimentally determined defect depth due to electroerosive working of Te single crystals as a function of crystal orientation and electric cutting energy by RHEED are given. The abrasion of the disturbed surface layer was made by chemical etch polishing as well as by bombardment with Ar⁺ ions. The defect depths determined from the RHEED patterns depend on the crystal orientation and the applied cutting energy. In case of the lowest cutting energy, it has a value of about 3 μm for the (0001)-orientation and 6 μm for the (101 0)-orientation, the corresponding values for the highest cutting energy are about 8 μm and 20 μm, respectively. It is discussed in how far defect depths determined from the interpretation of RHEED patterns correspond to the “real defect depths” which can be determined by other measuring techniques.     

X‐ray Reflectivity from Sinusoidal Surface Relief Gratings

The sinusoidal shape of light‐induced surface relief gratings of polymers can be probed by x‐ray scattering techniques. A particular approach of kinematic x‐ray scattering theory is developed to interpret experimental scattering curves. The simulations demonstrate the particular sensitivity of x‐ray reflectivity for very small grating amplitudes. At angles of incidence close to the critical angle of total external reflection a grating amplitude h < 2 nm already provides measurable grating peaks. In general the grating amplitude h can be measured from the envelope function over the grating peak maxima. The capability of the approach is demonstrated by simulation of the reflection curve recorded from a polymer sample with non uniform grating height.     

Untersuchung von AIIIB-Halbleitereinkristallen mittels Rutherford-Rückstreuung energiereicher Protonen

Axial blocking in various binary (GaAs, GaP, InSb, GaN) and ternary ((Ga, Al)P; (Ga, Al)As; (Ga, Al)Sb; (Ga, In)As) single crystals and epitaxial layers of the A^IIIB^V-type has been investigated by means of Rutherford backscattering with 0.5 MeV- and 1 MeV-protons. The angular distributions of the latter has been measured with solid-state detectors and with photographic plates. The observed “zero-depth” values of the blocking dips are in fair agreement with theoretical predictions by Barrett. Some applications of proton blocking and channeling to A^IIIB^V-compounds by backscattering are briefly described and some measuring examples are given.     

Silicon nanowire growth on poly‐silicon‐on‐quartz substrates formed by aluminum‐induced crystallization

The vertical growth of Si nanowires on non‐monocrystalline substrates is of significant interest for photovoltaics and other energy harvesting applications. In this paper, we present results on using poly‐Si layers formed by aluminum‐induced crystallization (AIC) on fused quartz wafers as an alternative substrate for the vapor‐liquid‐solid (VLS) growth of vertical Si nanowires. Oxidation of the Al surface to Al₂O₃ before the a‐Si deposition was shown to be a key requirement in the formation of the poly‐Si template since it promotes the crystallization of the a‐Si into Si(111) which is required for vertical silicon nanowire growth. The effect of Al deposition technique (DC sputtering versus thermal evaporation) on a‐Si crystallization and Si nanowire growth was investigated. The use of Al thermal evaporation yielded AIC poly‐Si layers with the highest fraction of 〈111〉 grains as measured by orientation imaging microscopy (OIM) which enabled the growth of vertical Si nanowires. Cross‐sectional transmission electron microscopy analysis confirmed that the 〈111〉 Si nanowires grew epitaxially off of {111}poly‐Si grains in the AIC layer. This study demonstrates the potential of using AIC poly‐Si as a template layer for the vertical growth of silicon nanowires on amorphous substrates.     

A Study of the Nucleation Kinetics,Linear Growth and the Overall Crystallization Kinetics of Meltspun Pd80Si20 Amorphous alloy

Nucleation kinetics, linear growth rate and overall isothermal crystallization kinetics of Pd Si amorphous alloy are studied by means of DSC and optical microscopy. It is found that both the histograms of the crystallite sizes and the DSC isotherms (resp. the time dependences of the degree of transformation α(t)) are best described by the model comprosing the simultaneous occurrence of two reactions of crystallization: heterogeneous as well as homogeneous non-stationary nucleation with subsequent three-dimensional growth in both cases. From the fit of the experimentally measured and the calculated according the model thus proposed distribution curves N_i(Φ) the stationary rates of heterogeneous and homogeneous nucleation, the number of quenched-in nucleation sites and the transient time lags of heterogeneous and homogeneous nucleation have been estimated. Using the values of these parameters kintic curves degree of transformation vs. time have been generated, which are closed to the exerimental x(t) curves obtained by means of DSC at isothermal conditions.     

Light Scattering Experiments during Freezing and Melting

Anomalous light scattering has been observed at the solid-liquid interfaces of high purity systems during freezing as well as during melting. The model substances used are water, salol, cyclohexane and xenon. From light scattering experiments the existence of a layer of pre-ordered material at the solid-liquid interface is deduced. Light is scattered by long range fluctuations in this layer. The thickness of this layer is a few μM. The correlation length of the fluctuations in this layer has been determined to be ξ ≈ 260 nm. Dynamic and static light scattering experiments lead to the same correlation length. Xenon, salol and cyclohexane cover a range of a factor of 15 in viscosity at the melting temperature. Growth velocities have been varied by a factor of about 200. Thermal gradients at the solid-liquid interface have been varied in a wide range. No dependence of the correlation length on these parameters or on substance has been found in the experiments. The observations do not depend on the crystallographic orientation of the crystal surface nor on the orientation of the crystal surface relative to gravity. The interface-layer may be compared to the quasiliquid layer which has been found at crystal vapour interfaces at conditions close to the melting point. The existence of a pre-ordered layer in-between a crystal and its melt means that the crystal does not grow into the melt but into the pre-ordered layer.     

Characterisation of structures grown by Movpe using x-ray diffraction

This paper describes the double and triple axis diffractometers available for characterising heteroepitaxial layer structures in the laboratory environment. The relative merits of the techniques are described.To demonstrate the materials information available from the diffractometer data (usually referred to as rocking curves) examples are given of the analysis of layer thickness and lattice parameter values for single heteroepitaxial layers, two layer structures and multiquantum well structures. For layers with a defect density of less than 10⁵ per cm² detailed analysis of rocking curve data is carried out by comparing experimental results with simulated data.X-ray diffraction also offers a non-destructive means of fully characterising the state of relaxation of strained layer systems.     

On the Determination of the Size Distribution Functions of Spherical Precipitations in Al–Zn Alloys by Neutron Small-angle Scattering

The size distribution of approximately spherical incoherent precipitations of Zn in AlZn-alloys is calculated and experimentally tested by means of neutron small angle scattering (NSAS) at a double-crystal diffractometer (DCD). The scattering curves can be approximated by a Gaussian function, so that the size distribution is directly calculated for the experimentical scattering curves under application of a particular LAPLACE-transformation. The size distributions of the α′_m-phase of AlZn(16)-samples of different averaged radii of precipitations are calculated by means of FWHM which are determined by the fitting procedure of a computer programme and compared with TEM micrographs.     

Zur Ätzstruktur von Silizium-Einkristallen,besonders in versetzungsfreien Bereichen

In silicon crystals a real etching structure can be visualized by means of a suitable method of etching also in the domains free from dislocations. The shapes of etch pits are chiefly dependent on the orientation of the grinding faces. It may be that the etching structure comes from growth domains, bordered by faces {111}, at which impurities are segregated or adsorbed.     

Dielectric Behaviour of the Nematic Phase of 4-n-Pentyloxyphenyl 4-(3-Bromo-4-n-nonyloxybenzoyloxy)-3-ethyl-benzoate (PBNEB)

Due to the high viscosity of 4-n-pentyloxyphenyl 4-(3-bromo-4-n-nonyloxybenzoyloxy)-3-ethyl-benzoate (PBNEB) the dielectric reorientation processes take place in the kHz and MHz range respectively. We observed two different relaxation ranges in the nematic phase from 10 Hz to 10 MHz if the measuring field is parallel to the director and one relaxation range for the perpendicular orientation. Dielectric measurements at 6.7 GHz demonstrate that at this frequency ϵ′∥ and ϵ′⊥ can be regarded as high-frequency limit. The experimental values are discussed from the point of view of the Meier-Maier theory.     

Work‐hardening characteristics of Zn‐Ti alloy single crystals

Shear stress – shear strain curves of 0.14 at.%Ti alloyed Zn single crystals were measured in compression at different temperatures and shear strain rates. The work‐hardening coefficient for basal slip increases with decreasing temperature and increasing shear strain rate. The work‐hardening characteristics are compared with those reported for Zn single crystals with different constituents and purities. It is discussed with respect to the interaction of dislocations with dislocations, vacancies, vacancy agglomerates and solute atoms. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Investigation of experimental pole-figure errors by simulation of individual spectra

The errors in measuring the crystallographic texture described by pole figures are studied. A set of diffraction spectra for a sample of the MA2-1 alloy (Mg + 4.5% Al + 1% Zn) are measured, simulation of individual spectra on the basis of which the pole figures were obtained is performed, and their errors are determined. The conclusion about the possibility of determining the effect of errors of the diffraction peak half-width on the pole figure errors that was drawn in our previous studies is confirmed.     

Preparation,physicochemical and third order nonlinear optical properties of bis(tetrabutylammonium)bis(2‐thioxo‐1,3‐dithiole‐4,5‐dithiolato)mercurate(II)

Bis(tetrabutylammonium)bis(2‐thioxo‐1,3‐dithiole‐4,5‐dithiolato)mercurate(II) was prepared and characterized by elemental analyses, electronic absorption, infrared and X‐ray powder diffraction spectroscopy. The specific heat of the crystal was measured to be 1878.2 J.mol^–1K^–1 at 300 K. The thermal decomposition process was investigated by means of thermogravimetric analysis and differential thermal analysis measurements in air together with infrared and X‐ray powder diffraction spectra. The third‐order nonlinear optical properties at 800 nm were measured by femtosecond optical Kerr gate technique by using CS₂ as reference. The third‐order optical susceptibility of its acetone solution at the concentration of 9.27 × 10^–4 M was obtained to be 2.53 × 10^–14 esu. The second‐order hyperpolarizability was estimated to be 1.7 × 10^–32 esu and the response time was about 226 fs. The third order nonlinear optical properties at 532 nm were investigated by using the Z‐scan technique with 20 ps. It exhibited self‐focusing effect and saturable absorption. The second molecular hyperpolarizability was estimated to be 8.4 × 10^–32 esu. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)