S. F. Karmanenko

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.

Component composition and strain of barium-strontium titanate ferroelectric films

The effect of the ratios of the cationic components and internal strains on the critical temperature Tc and the dielectric characteristics of BSTO ferroelectric films grown on α-Al2O3 [1012] and LaAlO3 substrates were investigated. Ion backscattering diagnostics revealed a barium deficiency in the surface layer of the films and showed that the films differ in structural quality.

On the macroscopic and microscopic origin of the photovoltaic effect in YBCO thin films

Abstract The study of a photovoltaic component of the net voltage arising in illuminated YBCO thin films with different morphology was carried out. The anisotropy of the photovoltages in the film plane correlates with the anisotropy of such physical characteristics of the samples as resistivity and microwave absorption and implies the existence of a macroscopic preferential direction even in the film deposited on an isotropic MgO substrate. Disappearance of the photovoltaic signal below Tc in the films exhibiting an appreciable residual resistivity is an unambiguous indication of its relation with extended defects inside the superconducting YBCO phase. A model for the microscopic asymmetry of the flow of the photocurrent generated at the boundaries of an isolated defect was proposed, and the contributions coming from some types of extended structural defects into the effect were estimated.

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.

Structural defects in YBa2Cu3O7−δ superconducting films induced by gamma irradiation

Abstract The influence of 60 Co γ irradiation on the crystal structure and electrical properties of YBa 2 Cu 3 O 7−δ films has been studied. Estimations were made for the cross-section of defect production at low doses of γ irradiation. The grain boundaries are claimed to be effective sinks for radiation defects as is determined by Raman scattering spectroscopy. Analysis of the experimental data reveals a key role of ionization in the formation of defects on the oxygen sublattice.

The effect of electron irradiation on the electrical properties of ferroelectric BSTO films

We have experimentally studied the effect of a 200-eV electron beam on the capacitance, loss factor, and tunability factor of planar capacitor structures based on ferroelectric (Ba,Sr)TiO3 films. A significant drop in the level of dielectric losses with a slight decrease in the capacity upon irradiation to a dose of 1014 and 1015 cm−2 was observed in film structures for the first time. The mechanisms of the observed effects and the role of structural defects are discussed.

Dependence of the microwave surface resistance on the structure and thickness of superconducting cuprate films

An investigation is made of the microwave surface resistance Rs measured at 10 GHz and 77 K, as a function of the thickness of superconducting epitaxial films of yttrium barium cuprate grown on lanthanum aluminate substrates by magnetron sputtering. Films between 200 and 1800 nm thick have low values Rs (0.3–0.5) mΩ and do not show any deterioration. The level of Rs achieved in films of comparatively large thickness is mainly attributable to the low rate of film growth (0.8 nm/min).