Size distribution of metallic colloids in alkali halide single crystals

The size distribution of Ag colloids in KCl single crystals reported by Jain and Arora is compared with the predictions of a theoretical model proposed by the authors.     

Energy distribution of plasma-assisted electron and ion emission from TGS single crystals

Electron and ion emission accompanying non-thermal plasma processes, produced at the surface of TGS single crystals under driving ac electric field exceeding 10³ V/cm, have been carried out. These plasma-assisted emission of electrons and ions were examined by means of time and energy distribution measurements. The intensity of registered charges (electrons and ions) displayed on the 2 ms time scale are represented by two distinct peaks. Time dependent energy spectrum of charges, detected under our experimental conditions, involves electrons and ions with maximum energy up to 30-40 eV for first peaks and up to 70-80 eV for second one. Additionally, the energy of electrons is focused at about 10-15 eV for first and second peaks and about 60-70 eV for second ones; the ion energy spectrum for both peaks exhibits only distinct low energy maximum focused at about 5-15 eV.     

Stable forms of two-dimensional crystals and graphene

We show that the “two-dimensional” graphene is stable due to transverse short-range displacements of carbon atoms, which may be described in a framework of Ising model with competing interactions. When temperature decreases, two transitions, high temperature disorder into order and order into low-temperature glass, arise. The graphene looks like a microscopic “washboard” with the wavelength of about 2–4 Å. Due to up–down asymmetry of the lattice distortions in graphene on substrate, a mini-bandgap arises. This leads to many new phenomena: a rectification of AC current induced by microwave or infrared radiation, the existence of self-trapping and a new type of fermionic mini-exciton-polaritons.     

Ranges and profiles of distribution of low-energy ions channeling in metal and semiconductor single crystals

In the present work peculiarities of trajectories and energy losses, ranges and profiles of distribution of low-energy different-mass ions channeling in thin single crystals of metals and semiconductors have been thoroughly studied by computer simulation in binary collision approximation. The character of oscillations of channeled-ion trajectories depending on their energies, aiming points from the axis of a channel, kind of interaction potential, crystal lattice type and temperature has been determined. It has been found that, in the case of light ions even at low energy, the main contribution to energy loss is made by inelastic energy losses, whereas for heavy ions, already at E < 10 keV, elastic energy losses exceed inelastic ones. Profiles of the distribution of channeled ions have been calculated depending on crystal lattice type, kind of ions and their energy.     

X-ray phase-contrast study of dissolution of NaCl crystals

The X-ray phase contrast method is used to study changes in a solution during the dissolution of NaCl crystals. The effect of the solution concentration on the refractive index for X rays is studied experimentally. The possibility of determining the refraction decrement in a local region of the solution is demonstrated.     

Transport characteristics and surface potential distribution of electrically stressed TiO2 single crystals

We investigated transport and local electrical properties of Pt/TiO₂ single crystal/Ti planar junctions with micron-sized gaps between the electrodes. Potential profiles, obtained by scanning Kelvin probe microscopy (SKPM), clearly showed that negative (positive) electrical stress to the Pt electrodes significantly reduced (hardly affected) the Pt/TiO₂ contact resistance. In addition, the SKPM results revealed that the electrical stress caused modification of resistance and local work function of the TiO₂ surface. All the results suggested that the electrical stress caused alteration of physical properties at the TiO₂ surface between the electrodes as well as the Pt/TiO₂ interface.     

The distribution of silicon in single crystals of Fe-Si alloys grown from the melt

A method of measuring the distribution of the silicon concentration in single crystals of Fe-Si alloys was elaborated on the basis of determining the relative Seebeck coefficient of these alloys with respect to the reference metal. The dependence of the relative Seebeck coefficient of Fe-Si alloys versus copper on the concentration of silicon was measured in the range of 2–12 weight % Si. The distribution of silicon in a series of single crystals of Fe-Si alloys grown from the melt was also determined.The author thanks the members of the department of the mechanical properties of solids of the Institute of Physics, Czechoslovak Academy of Sciences, and especially the head of the department, Ing. B. esták, CSc., for making it possible to prepare the single crystals and for discussion of the paper. He also thanks Dr. M. Matyá, CSc., for valuable remarks and Ing. Z. Kubita for passing on his experience in the use of the measuring method. He is indebted to members of the analytical laboratory of the State Research Institute for Materials Protection, the analytical laboratory of the Metals Research Institute and the chemical department of the. Institute of Physics, Czechoslovak Academy of Sciences, for careful analyses of the samples.     

Creep of cadmium single crystals

The creep of cadmium single crystals has been investigated in the temperature range of 78 to 297 K. It has been shown that the transient creep of Cd single crystals is described by a time dependence of the creep strain rateå t ^–m wherem is a function of the resolved shear stress and temperature. The activation areaA* depends on the resolved shear stress,, A ^{* –r} wherer=1 for room temperature andr 1·4 for 204 and 78 K. The activation enthalpy does not practically depend on the resolved shear stress in the whole region of the resolved shear stress measured and with increasing temperature it increases roughly withT ². For temperatures above 200 K the nonconservative jog motion is proposed to be the dominant thermally activated process.The authors are very grateful to Dr. P.Kratochvíl for valuable discussions.     

The applications of single crystals

The word ‘crystal’ comes from a Greek word meaning clear ice which was also applied to rock crystal (clear, transparent quartz). It was not until about the 17th century that the word was extended to other naturally occurring, transparent minerals which showed a regularity of outward form. It was appreciated at this time that this regularity resulted from an inner symmetry of atomic arrangement and it has since been realized that almost all solid materials are, to some extent at least, crystalline although this is often not apparent from their outward appearance. Indeed most materials of practical importance are polycrystalline-they consist of an aggregate of randomly-arranged small crystals-although single crystals have been used for special purposes for some considerable time, e.g. the crystals of calcite that are used to make Nicol prisms, and the crystals of galena (lead sulphide) that were used in early ‘crystal’ wireless receivers. But in recent years increasing use has been made of single crystals for a wide variety of purposes and the demand for single crystals of particular materials is such that large quantities of single crystals of materials such as ethylene diamine tartrate or terphenyl are now grown artificially by one of several techniques now available for the growing of single crystals.     

Purity of rubrene single crystals

Liquid chromatography connected with mass spectroscopy reveals that the oxidized form of rubrene is the major impurity in commercial powder of rubrene as well as in rubrene single crystals. One form of rubrene impurity can be transformed into the other. In solution, rubrene undergoes photo-oxidation completely until the red color of the rubrene solution disappears. Single crystals, due to compact packing of molecules and the required molecular shape change during oxidation, oxidize only on the surface.     

Photoluminescence of PbFCl and PbFBr single crystals

The luminescence properties of single crystals of PbFCl and PbFBr at 4.2 K under ultraviolet irradiation are presented for the first time. In PbFCl three and in PbFBr four emission bands have been observed. The red bands are ascribed to Pb⁺ centres. Direct exciton recombination is absent in both compounds.     

Classical trajectory calculations of the energy distribution of ejected atoms from ion bombarded single crystals

The energy distribution of particles ejected from single crystal surfaces has been calculated using classical dynamics. The model utilizes a microcrystallite of 4 layers with ~60 atoms/layer which is bombarded by 600 eV Ar⁺ at normal incidence. Calculations have been performed for the clean (100) face of copper as well as for copper with oxygen placed in various coverages and site geometries. The energy distributions for Cu, O, Cu₂, CuO and Cu₃ are reported for this system. The distribution for clean Cu exhibits structure which is shown to arise from preferred ejection mechanisms in the crystal. For oxygen adsorbates, the effect of the oxygen binding energy on the peak in the energy distribution of the ejected oxygen atoms is examined by arbitrarily varying the well-depth of the Cu-O pair potential. In general, higher values of the binding energy produce a maximum in the curve at higher energies and also produce a broader energy distribution. The O₂ and Cu₂ dimer distributions are found to peak at approximately the same energy as the O and Cu curves when compared on a kinetic energy/particle basis, although their widths are considerably smaller. Finally, we predict that the CuO energy distribution should be wider than either the Cu₂ or O₂ distributions since it results from the convolution of the Cu and O distributions which are quite different.     

Trapping centers and their distribution in Tl2In2Se3S layered single crystals

Thermally stimulated current (TSC) measurements have been carried out on Tl₂In₂Se₃S layered single crystals in the temperature range of 10–175 K. The TSC spectra reveal the presence of two peaks (A and B). The electronic traps’ distributions have been analyzed by different light illumination temperature techniques. It was revealed that the obtained traps’ distribution can be described as an exponential one. The variations of one order of magnitude in the traps’ density for every 30 meV (A peak) and 59 meV (B peak) were estimated. Moreover, the mean activation energy, attempt-to-escape frequency, capture cross section and concentration of the traps were determined.     

Colour centre-free perovskite single crystals

Yb³⁺:YAlO₃ (YAP) and Yb³⁺:GdAlO₃ (GAP) are interesting 1 μm high-power laser media thanks to their very good thermo-mechanical properties. However, as-grown perovskite single crystals exhibit colour centres. Parasitic thermal load generated by these centres is deleterious for high-power laser action and can lead to crystal damages. Moreover these defects decrease Yb³⁺ lifetime. They are related to trapped holes on the oxygen network. In the present work, several schemes to remove colour centres are presented. Attention is focused on cerium codoping, thermal annealing under reducing atmosphere and growth of non-stoechiometric compounds.