Papers by Keyword: Structural Defects

Abstract: Radioluminescence technologies are at the front line of the optic and electronic studies. Effective, self-contained and safe radioluminescent light sources can find their application in space industry, in medicine and in military technologies. The question of the performance improvement of the solid-state radioluminescent light sources (SRLS) without raising the included activity of working radionuclide can be solved by upgrading the phosphor crystalline structure. The electron-beam treatment for zinc-sulphide phosphors initial batch has been studied in a wide range of concentrations of the activating agent (Cu) for improving the radioluminescent performances of the phosphors, for creating the structural defects that form centers of luminescence. The changes of the phase composition were investigated under different synthesis conditions. It is revealed that electron-beam treatment of the initial batch leads to the growth of the wurtzite phase content in zinc-sulphide phosphors synthesized below the phase transition temperature. The changes of the phase content promote the spectral redistribution under the tritium beta-excitation. It is obviously the reflection of the fact of «green» luminescence centers rearrangement between the volume of the crystal and its surface. The correlations between structural configuration and performances of ionizing luminescence were found. Electron beam treatment gave the 20% increase of brightness of the radioluminescence. The achieved enhancement of luminescence performances allows the development of advanced tight-packed SRLS with minimal radioactivity and high energy-light conversion.

Abstract: Methyl, methoxy and alcoxy groups with different number of carbon atoms were chemically grafted onto the surface of fumed silica nanoparticles. After chemical modification the nanopowders were annealed in vacuum at 700 °C. The effect of the amount of carbon atoms in grafted hydrocarbon groups and type of bonding to silica surface (Si-C v.s. Si-O-C) were studied. It was demonstrated that carbon incorporation results in the development of broad band photoluminescence that covers the wholevisible spectral range. Increasing of carbon incorporation resulted in increasing of photoluminescence intensity and red shift of the photoluminescence band maximum.

Abstract: Mass transfer has been studied at atomic scale by molecular dynamics simulation of friction stir welding and vibration-assisted friction stir welding using the modified embedded atom potential. It was shown that increasing the velocity movement and decreasing the angle velocity of the tool reduce the penetration depth of atoms into the opposite crystallite in the connected pair of metals. It was shown also that increasing the amplitude of vibrations applied to the friction stir welding tool results in increasing the interpenetration of atoms belonging to the crystallites joined

Abstract: The system approach to study the causes of operational characteristics disturbance for ceramic tool materials based on complex research and its systematization. In the present study the defects by volume and by surface are researched. The main directions of operational characteristics improvement for tool materials are showed.

Abstract: A brief review of experimental data on the effect exerted by both constant and pulse magnetic field upon the heterodiffusion in powders, polycrystalline and monocrystalline ferromagnetic metals and alloys is presented in the paper in order to analyze regularities and mechanisms of the initiation of numerous phenomena covered by the single term “magneto-diffusion effect”. The most probable mechanisms of the magnetic field influence on the diffusion processes are analyzed.

Abstract: Solar cells of common sizes contains many of these defects and it is not easy to determine the influence of particular defects on the characteristics of the whole solar cell. Therefore, in our research we use samples of size of square centimeter at which we can disentangle the influence of the defect. We localize the defect by using a CCD camera, we measure the electrical, thermal and optical properties of the sample and then study it by means an electron microscope, we find the damaged structure and put it to focused ion beam. We expect the change in electrical, thermal and optical properties of the sample.

Abstract: Temperature dependent photoluminescence (PL) properties of ZnO thin film prepared by sol-gel route were investigated. The excitonic-related emission peak at 3.336 eV dominates the spectra, and is attributed to the recombination of excitons bound to structural defects (DBX). Moreover, its thermal activation energy is 5.7 meV obtained by using least-squares fitting method. Compared to its larger localization energy, we propose that there exists a nonradiative relaxation path with energy released during the formation of DBX. The observed peak position of blue emission is in line with theoretical energy interval between the interstitial zinc level and valence band.

Abstract: AISI 304L austenite stainless steel was irradiated by a high-current pulsed electron beam (HCPEB) source in different process. The microstructures were investigated in detail by electron microscopy. The changes of hardness and corrosion resistance induced by irradiation were also tested. The relationship between corrosion resistance and the microstructures has been explored. The experimental results demonstrate the potential of proper HCPEB processing for improving the hardness and corrosion resistance of metallic materials.

Abstract: 4H-SiC homoepitaxial layers with different thicknesses from 12.5 µm up to 50 µm were investigated by microwave-detected photoconductivity decay (µ-PCD), deep level transient spectroscopy (DLTS) and defect selective etching (DSE) to shed light on the influence of the epilayer thickness and structural defects on the effective minority carrier lifetime. It is shown that the effective lifetime, resulting directly from the µ-PCD measurement, is significantly influenced by the surface recombination lifetime. Therefore, an adequate correction of the measured data is necessary to determine the bulk lifetime. The bulk lifetime of these epilayers is in the order of several microseconds. Furthermore, areas with high dislocation density are correlated to areas with locally reduced effective lifetime.

Abstract: In this study, structural defects of existing 709 reinforced concrete (RC) buildings in Eskisehir Province were represented. Structural defects such as gaps between adjacent buildings, strong beam-weak column, mezzanine floor, short column, corner column, discontinuous frame, anchorage beams, long span, segregation, corrosion, inconvenient column/beam lateral reinforcement, low concrete strength and inconvenient steel reinforcement were determined in the study. It was determined that %35 of existing buildings have discontinuous frame, %16 of them have long span problem. It was also observed that nearly %40 of the buildings have no column/beam lateral reinforcement and %70 of them have inadequate gaps.