M. V. Belousov

The formation of two-layered YBa2Cu3O7- delta superconducting films and their microwave surface resistance

The structure and crystallographic orientation of YBa2Cu3O7- delta films on BaxSr1-xTiO3/MgO heteroepitaxial layers were investigated by the conventional methods of electron diffraction, electron microscopy and by specific methods of Raman scattering of light and backscattering of middle-energy ions. A film of over 350 nm thick may consist of an inner highly-oriented layer and an outer disoriented one. Measurements of the microwave surface resistance Rs at 60 GHz and 4.2 K have confirmed a complicated character of the film structure. It has been shown that the microwave response of two-layer films in a static magnetic field is determined by the losses in the outer disoriented or granular layer and that the dependence Rs(H-) appeals in the field H- starting from approximately 10 Oe.

The influence of growth temperature on the structural characteristics of YBa2Cu3O7- delta films: a Raman scattering study

Orientation of YBa2Cu3O7- delta films at the surface and at the film-(100) MgO substrate interface for various growth temperatures Ts have been studied using Raman scattering. On the film-substrate interface the films were c-oriented for Ts>670 degrees C and a-oriented for lower growth temperatures. Films grown at Ts approximately=670 degrees C to a thickness >0.2 mu m contained a transition from the c- to the a-orientation near the surface. A possible mechanism for the influence of growth temperature on the YBa2Cu3O7- delta film orientation is discussed.

Formation and Raman spectroscopic study of YBCO/STO/YBCO heteroepitaxial structures

Superconductor-ferroelectric-superconductor (SFS) structures were produced by magnetron sputtering of ceramic YBa2Cu3O7- delta and BaxSr1-xTiO3 targets. Raman spectroscopy was effectively used for characterization of superconducting and ferroelectric films in layered structures. Electrical characteristics, such as the temperature dependence of resistance, current-voltage and capacitance-voltage characteristics were measured. The possibility of applying SFS structures as cryoelectronic capacitors with voltage control is demonstrated.

Raman scattering and resistivity measurements for ion-irradiated YBa2Cu3O7 epitaxial films

Abstract Polarized Raman spectra and resistivity-temperature curves for 60 keV N+ ion-implanted epitaxial thin films of YBa2Cu3O7, deposited on SrTiO3 (110) substrates, have been measured. Ion implantation leads to an intensity decrease and a widening of the crystalline Raman lines until they vanish, and to the appearance and growth of a broad nonpolarized band centered at 580 cm−1 which isinherent to amorphous YBa2Cu3Ox films. The Raman spectra indicate coexistence of amorphous and crystalline phases in a wide dose range until the film structure is completely amorphized at doses about 1015 cm−2. The superconducting properties are observed to deteriorate and disappear upon only a slight damage of the lattice. A simple model of the lattice destruction upon N+ ion irradiation is proposed, taking into account formation and accumulation of cylindrical damage tracks consisting of two coaxial regions.

Modification of structure and resistivity of epitaxial YBa2Cu3O7-x films under ion bombardment

Abstract Raman scattering spectra for YBa 2 Cu 3 O 7−x films at 60 keV N + ion bombardment are investigated. The co-existence of amorphous and crystal phases, negligible oxygen losses, disorder in anion and cation subsystems is supposed to follow ion bombardment. The superconductivity suppression is observed at low fluences 3−4×10 13 cm −2 when distances between disordered regions are becoming comparable with the correlation length in the superconductor.