Effective distribution coefficient of Si in Fe—Si alloys at floating zone melting

Effective distribution coefficients of silicon in Fe—Si alloys with 1.0–12.1 at.% Si in floating zone melting at various solidification rates were determined. The dependence of k_ef on the solidification rate was compared with the Burton-Prim-Slichter equation. Effective distribution coefficients extrapolated to a zero solidification rate were compared with equilibrium distribution coefficients taken from the equilibrium phase diagram of Fe—Si.     

Iron environment in calcium-soda-phosphate glasses and vitroceramics

The structure of calcium-soda-phosphate glasses and vitroceramics with relatively high iron content was investigated by X-ray diffraction, electron paramagnetic resonance (EPR) and Mössbauer spectroscopy. The X-ray diffraction analysis proves the vitreous state of the as prepared samples and the development of crystalline phases in the annealed samples. The ferric ions disposed in sites that give rise to the absorption line with g_ef ≈ 4.3 in the EPR spectra of vitreous samples are not more evidenced in the spectra of the annealed samples, from which only of a symmetric and narrowed line with g_ef ≈ 2 is recorded. The room temperature ⁵⁷Fe Mössbauer spectra both of glass and vitroceramic samples consist of two quadrupole doublets characteristic for octahedral sites of Fe²⁺ and Fe³⁺ ions. The isomer shift for glass samples decreases and for vitroceramic samples increases with the iron oxide content.     

The Effective Temperature of Surfaces of Liquid Metals and Some Non-Metals

An estimation of decrease of atomic bond energy by raising temperature for surfaces of liquid metals and some non-metals had been made. The calculation values of the derivative du_sdu_b where u_s and u_b, are bond energy of atoms in surface and bulk of a liquid, are significantly above 1 and in limits from 2 to 10. It was supposed that this results from anomalously intensive thermal expansion of surface layers of liquids – the effect which is well known for crystal surfaces. This expansion was explained by the effective temperature of these surfaces which, thus, was found to be by several times above those for bulk of liquids.     

Contributions to the surface preparation of semiconductor materials of low hardness

Starting from the general demands made upon semiconductor surfaces (measuring samples, substrates) and the critical material properties, the boundary conditions for the surface preparation of substances of low hardness are stated and technological variants for Bi_1−xSb_x, Pb_1−xSn_xTe, and PbS_1−xSe_x are presented. The results show that almost defectfree surfaces of a high quality can be produced in a repeatable way. The depths of significant and detectable damages are determined depending on the technique in question.     

Untersuchung gestörter Oberflächenschichten an Siliziumeinkristallen

It has been proved that by densitometric measurements of reflections of Kikuchi photograms a numeric value can be found for the quality of polished surfaces of Si single crystals. This value is given by the proportion ΔS₁/ΔS₀, characterizing the relation of the initial state of surface and the state of deeper layers, not being affected by mechanical working. This method enables to estimate the quality of crystal surfaces.     

Kristallographische Polarität von AIIIBV - Mischkristallen

From the measurement of X-ray intensity differences of opposite {111}-surfaces in Ga₁ – _xAl_xAs- und Ga₁ – _xAl_xSb-mixed crystals with high Al concentration it was concluded which of the two surfaces is terminated by a layer of the group V atoms. The results are correlated with etching studies.     

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.     

Quench Hardness Anisotropy of Rhombohedral Crystals: Calcite

Variation of microhardness with orientation of indenter (A) and quenching temperature T_q is studied on freshly cleaved surfaces {100} of natural rhombohedral crystals of calcite by producing Knoop indentations for various applied loads. The relation between hardness H_A and quenching temperatures for the high loads (40–80 g) is graphically established. It also depends on the crystal orientation. The anisotropic indices are also determined.     

The thermal expansion of microcracks and grain boundaries in crystals (I). A new mechanism of crack formation

Apart from known reasons for crack formation it may be effected by the spontaneous microcrack wall heating. This heating takes place because of crack widening and formation of relatively free surfaces (crack walls). These surfaces must have the effective temperature that is well above the temperature in the bulk of crystals, as it has been shown earlier by the author. Simple equations for the thermal expansion of microcracks had been suggested. It has been shown that at the temperature above of 0.9T_m (T_m is the melting point) for the pure metals the spontaneous, without external stresses, crack formation takes place that may cause creep and superplasticity proceeding by the diffusion mechanism. At T_m the spontaneous cracking results in the crystal crushing to the microcrystallites, that is the spontaneous cracking may be considered to be the melting mechanism. From this point of view the intensive thermal expansion of liquids in temperature range from T_m to the critical temperature involves mainly the enlargement of microcrystallite gaps. By using this supposition simple equations for thermal expansion of liquids have been proposed.     

Understanding supersaturation‐dependent crystal growth of L‐alanine in aqueous solution

The dependence of crystal growth rate of L‐alanine on solution supersaturation was investigated by combining experiments and molecular dynamics (MD) simulations. The experimental results show that lower supersaturated solution yields more elongated L‐alanine crystals along the c‐axis, i.e., the aspect ratio (c/b) of the crystal decreases with the increase of solution supersaturation, which is due to the higher supersaturation inducing a rise in the relative growth rate between the main side surface (the (120) surface) and the main end surface (the (011) surface). MD simulations on the two surfaces in contact with different supersaturated solutions revealed that the solute molecules tend to be more efficiently attached to the (011) surface than to the (120) surface at both supersaturations studied, as the interaction between the solute molecules and the L‐alanine molecules in the first layer of the (011) surface is stronger than that of the (120) surface. However, higher supersaturation leads to larger relative interaction energy between the (120) and (011) surfaces, suggesting an increase in the relative growth rate of the two surfaces (R₍₁₂₀₎/R₍₀₁₁₎) with supersaturation, which is in agreement with the experimental results.     

Darstellung,Struktur und Eigenschaften von Nb-, Mo-, W- und Ru-dotiertem VO2

Monocrystals of doped VO₂ having the general composition V_1–xMe_xO₂ were prepared by chemical transport with TeCl₄. A summary of the morphological, structural, electric and magnetic properties is given. The habit of the doped crystals depends on the doping factor x. The boundary surfaces are {110}-prismatic and {111} pyramidal ones. At x = 0.04 the lattice constants change rapidly between the monoclinic M1-and the tetragonal R-phase. The typical change of resistance, which amounts four orders of magnitude for pure VO₂, and the transition temperature T_c decrease with increasing x.     

Selective etching and epitaxial refilling of silicon wells in the system SiH4/HCl/H2

Wells were etched in (100) silicon by different kinds of selective etching and were selectively refilled by using different gas systems. Masking materials were SiO₂ and Si₃N₄; for the refilling the systems SiCl₄/H₂ and SiH₄/HCl/H₂ were studied. By using a combination of weak anisotropic gas etching with HCl (Si₃N₄ films as mask) and of SiH₄/HCl/H₂ as refilling system, plane surfaces without ridges at the boundary of the mask and without nuclei on the mask were reached. The results were obtained by SEM, light microscopic and profile investigations and are compared with the other kinds of etching and refilling.     

Growth kinetics of RF-sputtered nickel films in the beginning stages

By the analysis of X-ray reflectivity angle dependence the existence of a characteristic nucleus height h in the island stage of nickel growth have been found. As the condensation time τ rises, the value of h increases according to a linear law, and the portion of substrate surface occupied by nuclei is described by a curve with saturation. The formation latent period of the fraction with preferential size h is extremely small, that, in principle, allows to produce smooth surfaces, even if the effective thickness is only about several atomic layers. The kinetic characteristics are identical both at growing on monocrystalline silicon and amorphous SiO_x substrates.     

Compositions of melts for growth of functional single crystals of complex oxides and other compounds

The melt compositions (M _c) are calculated for growing crystals with valuable physical properties. The calculation is based on the compositions of the invariant points of the liquidus curves for 33 congruently and 12 incongruently melting solid phases of 42 fusibility diagrams of binary systems. These systems include Na, Ca, Ba, Mg, and Y aluminates; Bi and Pb germanates; Li, K, Ba, and Bi borates; Ba, Fe, Sr, and Bi titanates; Li, K, Cs, Ba, Zn, Ca niobates; Li, Pb, and Gd molibdates; Pb and Nd tungstates; etc. More than 60 studies with data on the experimentally found melt compositions (M _e) for growing the noted crystals are analyzed. It is shown that the melt compositions M _c and M _e for growth of congruently and incongruently melting crystals are similar. Large-size stoichiometric crystals of high optical quality are grown using these melt compositions. Nonstoichiometric crystals of low structural quality are grown from melt compositions either corresponding to the stoichiometric ratio of the components (M _s) or similar to the compositions at invariant points (M _i). In these cases, a large difference is observed between the melt compositions M _c, M _s, and M _e.     

Optical absorption spectra of epitaxial layer - gradient layer - substrate systems

Theoretical relations are derived for the photon energy dependence of the absorption coefficient of epitaxial layer — gradient layer — substrate systems assuming a spatially linear variation of the gap energy in the gradient layer. It is shown that optical absorption measurements on such systems can be used to determine the gap energy of the epitaxial layer. Numerical calculations for the system GaAs_0.3P_0.7—GaAs_1—xP_x—GaP are presented.     

Compaction of adsorbed alkali metal submonolayers on the {111} and {0001} surfaces of metal crystals

The structural mechanism has been suggested of formation of the ordered surface hexagonal structures with an increase of the coverage during adsorption of alkali metal atoms on the {111} surfaces of face-centered cubic and {0001} surfaces of a hexagonal metal crystal. The coverage θ_s providing the formation of close-packed hexagonal adsorbed layers in adsorption systems is determined for alkali metals. The theoretically calculated and the experimentally obtained θ_s values are in good agreement.     

Improved Spatial Resolution in Electron Probe Microanalysis of Multilayer Structures

A method is described to measure composition profiles of layer systems on substrates by electron probe microanalysis with an improved effective spatial resolution down to 0.1 μm. The resolution problem in microanalysis of angle lapped layers and the related experimental problems are discussed and examples of composition profile measurements at GaAs-Al_xGa_1–xAs double-heterostructures are presented.     

Surface layers of crystalline and vitreous silicates in alkaline solution

Phenomena occurring at the surfaces of calcium silicates in alkaline solutions have been studied. This knowledge is very important in understanding the behavior of suspensions of glazes, felspars or clay minerals. This behavior has been found to depend partially on whether the surface of the materials in question has a high degree of order or not — in other words, whether the solid is crystalline or vitreous. It is also found that surfaces of crystalline materials which have been disturbed or destroyed, by grinding for instance, show a behavior between the extremes of the completely crystalline or completely vitreous systems.An analysis is given for the manner in which the net change of the surface layers of åkermanite (Ca₂MgSi₂O₇), pseudowollastonite (CaSiO₃) and anorthite (CaAl₂Si₂O₈) are built up in alkaline CaCl₂ solutions and which processes occur during their formation. Special attention is given to the mutual stimulation of adsorption of Ca²⁺ and OH^? ions by pseudowollastonite.     

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.