acta physica slovaca

Abstract: The current-voltage and capacitance-voltage behaviour of amorphous SiGe layers sputtered onto p-type Si substrates, have been studied in the temperature range of 80-320 K by using Al Schottky contacts as test structures. Although a significant influence of the preparation conditions was obtained on the electrical behaviour of the structures, they exhibited similar specific features of the electrical characteristics. These features are mainly due to deep energy states which are present in the sputtered layers and at the amorphous/crystalline interface.

Abstract: The films under study were deposited by e-beam evaporation of yttria-stabilized zirconia (YSZ) crystalline samples on the n-doped Si (111) substrate at 750 C. The XRD patterns of the films revealed their polycrystalline structure with a mixture of different phases, mainly the face-centered cubic one. The electrical conductivity and the activation energy as the functions of the yttria content indicated the influence of isolated oxygen ion vacancies as well as the associated point defects. The relative permittivities ($\varepsilon _{r}=17-26$) measured at room temperature and 1MHz confirmed YSZ as a high-k gate dielectric also in the form of thin film. The measured microhardness data, evaluated according to Jonsson-Hogmark composite hardness model, (H = 5.9 -- 10.8 GPa), as well as a high refractive index (n = 1.96 -- 2.20) render from YSZ a promising material for protective coatings and optical applications, respectively.

Abstract: Directionally solidified binary eutectics are multiphase composites with lamellae or rods of one phase embedded in a matrix of the other phase. Coupled growth from binary liquid produces periodic patterns consisting of well-aligned microstructures. The existence of steep and well defined interfaces make these materials promising candidates for photonic devices such as planar and fibre waveguides or luminescent materials. Here we review some of these applications. We also describe the production of some binary eutectic fluorides with well aligned fibrous microstructures which have been used as precursor materials to obtain centimetre-long alkaline and alkaline-earth fluoride single crystal fibres (SCF), with diameters of the order of light wavelength to find application as optical fibres.

Abstract: In this paper the examples of combined analytical methods usable for the characterization of thin film systems are presented. As  the optical methods variable angle spectroscopic ellipsometry and spectroscopic reflectometry are used. It is shown that these methods can be employed for the complete determination of both the optical and material parameters of the materials forming the films. Moreover, it is shown that using the combined methods of AFM and the optical methods specified it is also possible to determine the values of the parameters characterizing some defects of the film systems under investigation. Discussion of the reliability of the methods enabling us to determine the values of the statistical quantities describing the boundary roughness of the thin films is also presented. A detailed attention is devoted to the results achieved for these quantities by atomic force microscopy for very finely rough film boundaries (i.e. nanometrically rough boundaries). The practical meaning of the combined methods presented is illustrated using the characterization of several samples of TiO2 films, hydrogenated polymorphous silicon films and oxide films originating by thermal oxidation of gallium arsenide substrates.

Abstract: In this article the possibilities of the wavelet transform use within atomic force microscopy data processing are presented. Both discrete and continuous wavelet transform is used for different processing and analytical purposes including denoising, AFM scan error detection, background removal and multifractal analysis. It is shown that the use of wavelet transform can be very effective within AFM data analysis, namely for highly irregular data.

Abstract: SiO2Si structure can be formed at low temperatures by use of nitric acid (HNO3) oxidation of Si  (NAOS) method.  When Si wafers are immersed in ~40 wt% HNO3 solutions at 108 C, ~1 nm SiO2  layers are formed. The subsequent immersion in 68 wt% HNO3 (i.e., azeotropic mixture of HNO3 with water) at 121 C increases the SiO2 thickness. The 3.5 nm-thick SiO2 layers produced by  this two-step NAOS method possess a considerably low leakage current density (e.g., 0.01 A/cm2 at the forward gate bias, V_G, of 1.5 V), in spite of the low temperature oxidation, and further  decreased (e.g.,  0.0008 A/cm2 at V_G=1.5$ V) by post-metallization annealing at 250 C in hydrogen atmosphere. In order to increase the SiO2 thickness, a bias voltage is applied during the NAOS  method.  When 10 V is applied to Si with respect to a Pt counter electrode both immersed in 1 M HNO3 solutions at 25 C, SiO2 layers with 8 nm thickness can be formed for 1 h.

Abstract: Ultrashort  period  (1.5 - 3.2 nm)  Cu/Si  and  Ni/C multilayers for X-ray interference mirrors are presented. The  multilayers  were prepared by ultra-high vacuum electron beam  deposition onto a heated substrate.  An optimum deposition temperature of 80 C was found in both cases.   The multilayer  quality  was probed  by  the  specular  X-ray reflectivity  and  interface diffuse scattering  at CuK_\alpha1 wavelength.  An  asymmetry  between  the metal-on-metalloid and metalloid-on-metal interfaces was  detected,  the  larger  interface  width amounting  to  0.5 nm and 0.65 nm  in  Cu/Si  and  Ni/C, respectively.  It is induced mainly by  the  metal  layer growth  and  diffusion of metalloid into  metal.  Thermal stability   tests  were  performed.  Cu/Si  mirrors   are applicable  only  at operation temperatures  below  100 C while  the Ni/C multilayer break-down occurred at 350 C. Ni/C mirrors are superior to Cu/Si ones also in terms  of shorter  vertical  and lateral correlation  lengths  with important implications for the specular imaging contrast.

Abstract: The application of nuclear analytical methods on surface and interface study is presented. Two topics are included in the presentation - polymer-metal interaction studies and study of single-crystalline structures using RBS-channeling method. Diffusion of Ag atoms in polyethyleneterephtalate (PET) was studied using Rutherford Backscattering Spectroscopy (RBS) and Elastic Recoil Detection Analysis (ERDA). The samples were prepared by deposition of Ag thin layers on polymer surface using CVD and diode sputtering techniques. Faster diffusion of Ag atoms was observed from non-compact Ag layers prepared by diode sputtering than from those prepared by CVD technique. The samples of erbium doped lithium niobate (Er:LiNbO3 ) were prepared by standard Czochralski method and treated by Annealed Proton Exchange (APE) procedure to create planar wave-guide for further optical application. The position of Er atoms in the crystal lattice of pristine and APE treated Er:LiNbO3 samples were studied by Rutherford Backscattering Spectrometry (RBS)-channeling method. The Er^{3+} ion position in the pristine and the APE treated Er:LiNbO3 samples are compared.

Abstract: In this paper we present the results of X-ray Photoemission Spectroscopy (XPS) study of the surface chemistry of Laser-assisted Chemical Vapour Deposition (L-CVD) deposited tin oxide SnOx thin films before and after subsequent exposure to molecular hydrogen (hydrogenation) at room and elevated temperature up to 800 K. As-deposited L-CVD tin oxide thin films exhibited a nonstoichiometric composition with a relative concentration [O]/[Sn] equal to 1.29 +- 0.05. After exposure to 10 000 L of hydrogen at room temperature the relative concentration [O]/[Sn] was almost the same. After the same exposure to hydrogen at elevated temperature the relative concentration [O/Sn] decreases what confirms the effect of drastic reduction to the almost stoichiometric tin oxide SnO thin films. This evident reduction of L-CVD tin oxide thin films was confirmed by the shape analysis of corresponding XPS Sn3d_{5/2} and O1s peaks using the deconvolution procedure in which the different contribution of O-Sn^{2+} and O-Sn^{4+} bondings were determined.

Abstract: The conductivity mechanism of zirconium oxide films grown 1554 days in water of 360 C on tubes of Zr1Nb, Zr Sn Nb(Fe), and IMPZry-4, respectively, was investigated by I-V measurements at various temperatures. The high current flowing at voltage application is due to electron injection and decreases slowly obeying a power law until steady state conditions by a built-up space charge are reached. Switching off the voltage, a short-circuit current of opposite polarity due to the outflowing space charge is observed, which decreases obeying a power law. By integration of the extraction current, the space charge as linear function of the injection voltage could be assessed, the extracted charge being equal to the injected charge.

Abstract: We report on the results of the investigation of surface morphology, structure and optical properties of plasma deposited thin films of hydrogenated amorphous silicon determined by atomic force microscopy, X-ray diffraction and UV-Vis and IR spectroscopy. The influence of the both hydrogen dilution of silane plasma in the plasma deposition and the film thickness on the film properties was investigated. The structure, the refractive index and the optical band gap of the dilution series and the thickness series were analyzed. The changes are discussed and correlated with the changes of the surface morphology and the hydrogen to silicon bonding. The results show that at dilution of ~30 the transition from amorphous to crystalline phase occurs and the sample becomes a mixture of amorphous phase, polycrystalline phase with nano-sized grains and voids. The optical band gap becomes larger than that of the undiluted sample.