acta physica slovaca

Abstract: Resistance anomaly in high-temperature superconductors (HTS) YBa2Cu3Ox (YBCO) and Bi2Sr2CaCu2Oy (BSCCO) thin film microstrips, covered by gold thin film, was observed. The resistance of the microstrip bilayer increases up to about 30% above the bilayer normal state resistance RN at the beginning of the superconducting phase transition. Although in a number of recent publications, reporting an increase of the electrical resistance above the superconductor normal state resistance Rn, concerning of nonequilibrium quasiparticle and pair electrochemical potentials in mesoscopic systems, or as a result of structural nonhomogeneity of the samples, we argue that the resistance anomaly in our HTS/Au bilayers is associated with the proximity effect that accompanies superconducting-normal metal interface. The sharpness of resistance peak confirms a possibility to prepare HTS/Au interface with very high quality.

Abstract: We present a summary of some published results concerning the preparation and study of the properties of CeO2 buffer layers on R-plane Al2O3. Further, we discuss some of our results which concern to CeO2 films prepared by electron gun-evaporation, by on-axis rf magnetron sputtering in mixture of Ar and O2 and by off-axis rf diode sputtering in pure oxygen. As-deposited films show granular structure except for films prepared by electron gun-evaporation which already consist of rectangular blocks. Atomic Force Microscopy (AFM) reveals that the presence of even negligible (111) parasitic peak in X-ray diffraction spectrum of the as-deposited films strongly influences the rocking curve and surface morphology after post-deposition heat treatment in air. The post-annealings suppress (111) peak in X-ray spectrum, however, the rocking curves and AFM results differ depending on the method of preparation. Some rocking curves seem to be a superposition of a very narrow rocking curve (0.04o) with a broader one (0.5-1.4o). The origin of such behaviour is discussed.

Abstract: In this paper a brief review of the optical methods based on the simultaneous interpretation of the different optical experimental data obtained for thin film systems is presented. These methods are known as the multi-sample methods. It is shown that these optical multi-sample methods are very useful for analyzing many thin film systems. In particular it is illustrated that selected optical multi-sample methods are powerful for studying the following problems: investigations of growing the native oxide layers on the semiconductor surfaces; suppression of the influence of the transition interlayers between the substrates and thin films and determination of the optical constants of bulk materials. Concrete experimental examples demonstrating the foregoing statements are presented in this paper as well.

Abstract: A tribological investigation of nanostructured carbon films performed with atomic force microscope is presented. Surface morphology is self-affine, with different correlation lengths corresponding to an inhomogeneous distribution of deposited carbon clusters. After reducing topographical effects, the friction coefficient turns out to be 0.15 (in air), with a slight dependence on the cluster distribution.

Abstract: Multilayer gratings are thin film structures possessing periodicities both in the normal and lateral directions. They combine the properties of surface gratings and planar multilayers thus providing a high throughput and high spectral resolution on higher diffraction orders. The unique diffraction properties are utilized in the X-ray and ultraviolet optics where no lenses or mirrors comparable with those for visible light are available. Multilayer gratings act as constant resolution dispersion elements in a broad spectral range. A fan of grating diffractions in real space is represented by a set of points on equidistant truncation rods in the reciprocal space. The kinematical theory of X-ray scattering explains well the positions of the grating truncation rods while the dynamical theory is inevitable to calculate the intensities along the truncation rods (grating efficiency). The properties of multilayer gratings are exemplified on two differently prepared lamellar gratings with the nominal normal and lateral periods of 8 nm and 800 nm, respectively. The fabrication steps are described in detail. The specular and non-specular X-ray reflectivities at wavelength 0.15418 nm were measured on one of the samples. The dynamical theory of X-ray scattering with a matrix modal eigenvalue approach was applied to extract the real structural parameters such as the surface and interface roughnesses, individual layer thicknesses, and the lamella width to the grating period ratio. The X-ray reflectometry is completed by microscopy observations which provide complementary and direct information on the local surface profile.

Abstract: A summary is given of different elementary processes influencing the thermal balance and energetic conditions of substrate surfaces during plasma processing. The discussed mechanisms include heat radiation, kinetic and potential energy of charged particles and neutrals as well as enthalpy of involved chemical surface reactions. The energy and momentum of particles originating from the plasma or electrodes, respectively, influence via energy flux density (energetic aspect) and substrate temperature (thermal aspect) the surface properties of the treated substrates. For a few examples as magnetron sputtering of a-C:H films, sputter deposition of aluminum on micro-particles, and atomic nitrogen recombination in an ECR plasma the energetic balance of substrates during plasma processing are presented.

Abstract: We have developed a new method of observing energy distribution of interface states at ultrathin SiO2/Si interfaces based on XPS measurement under bias. The analysis of the energy shift of the substrate Si 2p peak for the MOS structure vs. the bias voltage between Si and Pt provides the interface state spectra. We have also developed a new method of eliminating the interface states based on cyanide treatment. When the cyanide treatment is applied to solar cells with the MOS structure, an energy conversion efficiency is increased to 16.2 % in spite of the simple cell structure.

Abstract: The wavelength - dependent refractive index, extinction coefficient as well as the thickness of the film can be found by various spectrophotometric techniques. When the film is deposited on transparent substrate, the so-called envelope method used for transparent films with interference effects in transmittance and reflectance spectra is available. However, when the film is deposited on thick absorbing substrate, only spectral reflectance measurements are possible. The optimised envelope method is suitable to solve for optical parameters of thin films on absorbing substrates simultaneously. The algorithm assuming a thin isotropic film with parallel interfaces is described here. Moreover, in this study the spectrophotometric iso reflectance contours method is shown to be a powerful tool for determining the film thickness. Both methods are presented using a hypothetical film. The error analysis of the simulated reflectance spectrum shows the advantages and limitations of the methods. It is reported that the main source of errors in determining the optical constants and the thickness is associated with reflectance measurements. The methods described here are applied for determining the optical parameters of ZnO and Y2O3 thin films deposited by rf diode sputtering on Si substrates.

Abstract: In this review paper a uniform matrix formalism enabling us to include the important defects of thin film systems into the formulae for their optical quantities is presented. The following defects are discussed: roughness of the boundaries; inhomogeneity represented by profiles of the refractive indices; transition interface layers and volume inhomogeneity. It is shown that this formalism is relatively very efficient. This fact is demonstrated using a theoretical example representing a complicated thin film system exhibiting defects.

Abstract: We have studied the domain branching in surface layers of the excimer laser treated Finemet ribbon. Small circular holes produced by laser radiation on the surface of ribbons reduce the power losses at higher frequencies. The domain structure was visualized by means of a SEM and by a set-up based on the Kerr effect. In the close proximity to the circular holes the demagnetizing field causes the domain refinement. On the basis of the minimum energy`s condition we have calculated the geometric parameters of the newly formed small domain. We have compared the calculated parameters with the experimentally determined values.

Abstract: An average Hamiltonian, which contains pair-atomic effects, is used to develop a theory of the micromaser. A modified master equation is derived and both a steady-state and a time-dependent solutions are found showing that the trapping conditions are disturbed by influence of two-atomic events. An approximate as well as an exact spectrum are calculated and narrowing of linewidth is demonstrated within the framework of presented theory.

Abstract: A scheme for generating maximally entangled states of bimodal high-Q cavity field is presented. Its implementation is based on a Jaynes-Cummings like one photon interaction mechanism between a single three level Rydberg atom in the lambda configuration and two modes of the radiation field. The practical feasibility of the project is discussed.

Abstract: The crystallization kinetics of the Fe53.5Ni20Cu1Nb3Si13.5B9 glassy ribbon was investigated by differential scanning calorimetry. The phase identification in the linearly heated samples was performed by X-ray diffraction. The linear heating thermograms indicate an anomalous heating rate dependence. It was found that both kinetics and mechanisms of glass crystallization suddenly change when the heating rate falls below its critical value, w = 20 K min-1. The crystallization proceeds as a two step (R1 and R2) transformation using small heating rates w < 20 K min-1. The activation energies E*1 = 302 kJ mol-1 and E*2 = 345 kJ mol-1 indicate atomic transport mechanisms. The ordered Fe3Si and Fe3NiSi1.5 nanocrystalline phases crystallize separately in the R1 and R2 steps. In the same material both phases crystallize simultaneously in one crystallization step (R3) by the viscous flow mechanism (E*3 = 718 kJ mol-1) at higher heating rates, 20 K min-1. The DSC experiments gave evidence of the diffusion of nickel, which starts before the crystallization and controls an alternative crystalline phase nucleation.