Preparation of ZnO nanowires by electrochemical deposition

AbstractThis work reports the results from the synthesis of nanostructured ZnO thin films via electrochemical deposition on glass substrates coated with F doped SnO2. The influence of the deposition parameters on the properties of the obtained ZnO films was studied. The Raman spectra of the ZnO films contain the typical for ZnO vibrational bands. The scanning electron microscope micrographs demonstrate that the films consist of ZnO nanowires. Growing of ZnO in the conditions with addition of H2O2 in lower concentration and without flowing air results in larger grain formation. The ZnO layers demonstrate high diffuse reflection

Origin of giant photocontraction in obliquely deposited amorphous Ge_xSe_{1-x} thin- films and the intermediate phase

Obliquely deposited amorphous Ge_xSe{1-x} thin-films at several compositions in the 0.15 < x < 0.333 range, and at several obliqueness angles in the 0 < alpha < 80 range at each x were evaporated on Si and glass substrates. Here alpha designates the angle between film normal and direction of vapor transport. Raman scattering, ir reflectance and optical absorption measurements were undertaken to characterize the vibrational density of states and optical band gaps. Edge views of films in SEM confirm the columnar structure of obliquely (alpha = 80) deposited films. Films, mounted in a cold stage flushed with N2 gas, were irradiated to UV radiation from a Hg-Xe arc lamp, an

Measurements of Step and Kink Energies and of the Step Edge Stiffness from Island Studies on Pt(111)

By using temperature-variable scanning tunneling microscopy, we studied two-dimensional vacancy islands on Pt(111) between 593 and 713 K. Due to the difference in the step free energies of A and B steps, the equilibrium shape of the vacancy islands has a threefold symmetry. From the analysis of the equilibrium shape of the vacancy islands, we calculate the angular dependence of the step free energy on Pt(111). The absolute values for the step free energies per atom of A and B steps are determined from the equilibrium shape fluctuations to be beta(A)=348 +/- 16 meV/atom and beta(B)=300 +/- 14 meV/atom, respectively. Furthermore, we derive the temperature dependence of the step-edge stiffness (beta) over tilde with (beta) over tilde (A) between 510 and 453 meV/atom and (beta) over tilde (B) between 1974 and 1104 meV/atom in the temperature range considered. From the stiffness, we obtain the kink formation energies for A and B steps, epsilon(A)=143 +/- 9 meV and epsilon(B)=206 +/- 9 meV, respectively

Island coalescence and diffusion along kinked steps on Cu(001): Evidence for a large kink Ehrlich-Schwoebel barrier

Using temperature-variable scanning tunneling microscopy, we studied the coalescence of vacancy islands on Cu(001) in ultra-high vacuum. From the temperature dependence of the relaxation of merged vacancy islands to the equilibrium shape we obtain an activation energy of the island coalescence process of 0.76 eV. From that value we deduce an activation energy for the atomic hopping coefficient of E-rh = 0.89 eV. Comparing our result with previous STM data on step fluctuations with dominant diffusion along straight step segments (E-rh = 0.68 eV; [M. Giesen, S. Dieluweit, J. Mol. Catal. A: Chem. 216 (2004) 263]) and step fluctuations with kink crossing (E-rh = 0.9 eV; [M. Giesen-Seibert, F. Schmitz, R. Jentjens, H. Ibach, Surf. Sci. 329 (1995) 47]), we conclude that there is a large extra barrier for diffusion of atoms across kinks on Cu(001) of the order of 0.23 eV. This is the first direct experimental evidence for the existence of a large kink Ehrlich-Schwoebel barrier on Cu(001). (c) 2007 Elsevier B.V. All rights reserved

An experimental approach for synthesis of Fe-Al-O multiferroic fibrous material

peer reviewedBasic principles of the electro-hydrodynamics are applied for synthesis of solid state Fe-Al-O multi-ferroic fibrous material. For that purpose stable blend spinning solutions comprised of a high molecular assisting organic polymer and salts of iron and aluminum are developed. These solutions are tested under electrospinning conditions and synthesis of homogeneous as spun non-woven mats characterized by fibre mean diameters in the microand nano-size range is successfully demonstrated. Multi-step thermal procedure is applied for the consecutive solvent evaporation, polymer pyrolisis and final fibre calcination. Electronoptical imaging technique and XRD are applied for revealing the sample morphology and the phase composition correspondingly. The results obtained outline the wide possibilities for fabrication of multi-ferroics fibrous nano-materials on the basis of Fe-Al-O

Steady-state surface stress induced in nobel gas sputtering

We have measured the surface stress on single crystal Cu(100) surfaces as induced by bombardment of the surface with the noble gas ions Ar, Ne and He at room temperature. Regardless of the ion type and energy, the induced stress is compressive and saturates as a function of sputter time at a value between 2 and 15 N/m. Saturation time and magnitude of the induced stress depend on the ion species and their energy. The time dependence can be accounted for by assuming a steady state thickness of a defective surface layer, which arises from a balance between sputtering and ion implantation. (C) 2002 Elsevier Science B.V. All rights reserved

Mixing kinetics and write-once optical recording characteristics of Sb/Se bilayer films

Bilayer Sb/Se films are irradiated with 12 ns pulses from an ArF laser (extended areas) and from a focused Ar+ laser (micron-sized areas). Real-time reflectivity measurements are used to determine if the process occurs within the solid or liquid phase and the transformation time, in addition to measure the optical contrast and the medium sensitivity. Transmission electron microscopy is used to analyze the structure of the transformed areas and the medium resolution. The results show that mixing is initiated by preferential melting at the gram boundaries and an amorphous phase is produced upon irradiation a high energy densities. Finally, the characteristics of the mixing process in Sb/Se films as a write-once optical recording mechanism are discussed in terms of the sensitivity and resolution of the recorded spots and the time required for recording.This work has been partially supported by CICYT (Spain) under TIC-93 program.Peer Reviewe

Laser assisted modification and chemical metallization of electron-beam deposited ceria thin films

Excimer laser processing is applied for tailoring the surface morphology and phase composition of CeO2 ceramic thin films. E-beam evaporation technique is used to deposit samples on stainless steel and silicate glass substrates. The films are then irradiated with ArF* excimer laser pulses under different exposure conditions. Scanning electron microscopy, optical spectrophotometry, X-ray diffractometry and EDS microanalysis are used to characterize the non-irradiated and laser-processed films. Upon UV laser exposure there is large increase of the surface roughness that is accompanied by photo-darkening and ceria reduction. It is shown that the laser induced changes in the CeO2 films facilitate the deposition of metal nano-aggregates in a commercial copper electroless plating bath. The significance of laser modification as a novel approach for the production of CeO2 based thin film catalysts is discussed. © 2009 Elsevier B.V. All rights reserved.This work has been performed in the frame of the Bulgarian-Spanish Scientific Cooperation Agreement, supported by the Bulgarian Academy of Sciences and the National Research Council of Spain (CSIC).Peer Reviewe