acta physica slovaca

Abstract: We present an overview of the quantification of the ions in the growth process of both amorphous (a-Si:H) and microcrystalline silicon ( c-Si:H). In the deposition of a-Si:H the ion energies are typically in the 20-30 eV range. The fluxes relative to the growth rate are typically 25%. However, the actual contribution to growth is 5-10%. The ion bombardment expressed in ion kinetic energy per deposited atom is an important parameter in the resulting material structure. The amount of energy that is needed to create a dense network decreases with increasing substrate temperature, thereby indicating the interexchangebility of these two parameters. The deposition of microcrystalline silicon by RF-PECVD is, due to the high ionization potential of hydrogen with respect to that of silane, dominated by ions instead of by radicals as in the deposition of a-Si:H. This implies the need of considering ions in the growth models of microcrystalline silicon. Ion mass spectra show the presence of polymerisation reactions of ions in the gas phase. It appears that ions with 3 or 4 silicon atoms are the most dominant species present. Detailed investigation of the amount of hydrogen on ions with 6 or more Si atoms indicate the possible presence of ring structured silicon ions.

Abstract: A novel technique of reactive-ion molecular beam epitaxy for the Si carbonisation is demonstrated. For a suggested temperature regime and technological recipe, stoichiometric -SiC was obtained. This was proved by an in-situ diffraction patterns observation and after process X-ray photoelectron spectroscopy and atomic-force microscopy investigation.

Abstract: Eutectics are a paradigm of micron scale composite materials with improved properties. Improved mechanical properties and thermal stability of eutectics as compared with ceramics or single crystals of component phases are a consequence of the presence of huge amounts of interfaces. Interface morphology and ordered structures also invites to explore other properties of regular eutectics such as light guiding effects, anisotropic ion conduction, use as structured substrates for patterned films, etc. In this work we report on the production of several eutectic crystals of wide band gap materials, grown from the melt by unidirectional solidification. The structure, mechanical properties and interface morphology were determined using different techniques including X-ray diffraction, SEM, TEM, Raman and optical spectroscopy techniques. Examples of lamellar microstructures are provided by the ZrO2-CaO, ZrO2-NiO and CaF2-LiF systems. Planar light guiding and anisotropic ion conduction are some of the unconventional properties of these regular composites. ZrO2-MgO, ZrO2-Al2O3 and CaF2-MgO are examples of fibrous eutectics. The alumina-zirconia composite presents excellent mechanical properties also related to the presence of residual thermostresses that have been measured using different piezospectroscopic effects. The fluorite-magnesia eutectic is an example of semifaceted non-regular composite showing light guiding effects.

Abstract: Hydrogenated amorphous silicon is nowadays extensively used for a range of devices, amongst others solar cells. Solar cell technology has matured over the last two decades and resulted in conversion efficiencies in excess of 15%. In this paper the operation of amorphous silicon solar cells is briefly described. For tandem solar cell, amorphous silicon germanium is often used as material for the intrinsic layer of the bottom cell. This improves the red response of the cell. In order to optimize the performance of amorphous silicon germanium solar cells, profiling of the germanium concentration near the interfaces is applied. We show in this paper that the performance is strongly dependent on the width of the grading near the interfaces. The best performance is achieved when using a grading width that is as small as possible near the p-i interface and as wide as possible near the i-n interface. High-rate deposition of amorphous silicon is nowadays one of the main issues. Using the Expanding Thermal Plasma deposition method very high deposition rates can be achieved. This method has been applied for the fabrication of an amorphous silicon solar cell with a conversion efficiency of 5.8%.

Abstract: The YBa2Cu3Ox(YBCO)/Au and Tl2Ba2CaCu2Oy(TBCCO)/Au sandwich-type heterostructures were studied with the aim to enhance the interface quality of high temperature superconductor (HTS) in contact with a normal metal which is frequently used in cryoelectronic devices. To characterize the superconducting properties of thin films and interfaces of superconductor/normal metal (SN) heterostructures, the resistance vs. temperature (R-T) dependences, current-voltage characteristics (I-V) and dI/dV-V characteristics were measured. The YBCO/Au heterostructures exhibit tunnel properties due to the existence of the so-called native barrier created from oxygen depleted YBCO surface layer. Our results show that the properties of YBCO based planar tunnel junctions are strongly influenced by the state of superconductivity at the SN interface. On the other hand, in TBCCO/Au heterostructures a direct metallic contact is realized in the most cases. Our investigations show that the degradation of TBCCO/Au interface is negligible and no native oxide barrier on the surface of TBCCO film was observed. These results confirm that the surface of TBCCO film in close contact with Au is much more stable in comparison with YBCO films and therefore the TBCCO films are more suitable for the preparation of HTS planar structures and tunnel junctions.

Abstract: Electron spectroscopic techniques such as Auger electron spectroscopy (AES), X-ray induced photoelectron spectroscopy (XPS) and Elastic peak electron spectroscopy (EPES) are powerful methods for the measurements of chemical composition and bonding among atoms found in the analyzed near surface region of a few nanometer range (AES, XPS) and for determination of a basic electron transport parameter – the inelastic mean free path of signal electrons (EPES). Analytical applications of AES and XPS require knowledge of the reliable theoretical model relating the measured signal intensity to the number of atoms emitting the monitored Auger electrons and photoelectrons. The present review will address briefly (i) typical procedures of quantitative analysis commonly used in AES and XPS, (ii) electron elastic scattering effects, (iii) surface sensitivity of the methods used and (iv) applications of the EPES for determination of the inelastic mean free path values and their energy dependencies.

Abstract: In Bi2212 thin-film based stacks, c-axis critical currents larger than the depairing critical current have been observed. It has been proposed recently that flux lines bound to screw dislocations with Burgers vectors parallel to the c axis of layered superconductors can lead to such an enhancement of the c-axis critical current, if the superconducting samples are small with respect to the c-axis penetration depth. We provide further arguments in favour of this interpretation.

Abstract: Using a differential calculus on N-dimensional vector space, we realize a GLX,qij(N) quantum group bosons. With the help of the generators and of a two-parameter GLp,q(2)-bosons, we construct the deformed centreless Virasoro algebra on the quantum plane . Also a realization of the deformed version of the area-preserving diffeomorphisms on the torus T2 has been done.

Abstract: We calculate the energy distribution of an anisotropic model of universe based on the Bianchi type I metric in the Tolman's prescription. The energy due to the matter plus gravitational field is equal to zero. This result agrees with the results of Banerjee and Sen and Xulu. Also, our result supports the viewpoint of Tryon and Rosen.