S. V. Gaponov

Microstructure and electrical properties of YBCO films

YBCO thin films were fabricated in situ on R-plane sapphire with YSZ buffer layers by inverted cylindrical magnetron sputtering. The films with , transition width , surface microwave resistance at 10 GHz and critical current density at 77 K were routinely fabricated at optimum deposition temperature and gas mixture pressure. The relations between the growth conditions, microstructure and electrical properties of YBCO thin films were investigated for a wide range of deposition temperatures. The variation of the film properties with deposition temperature is substantiated by a thorough analysis of changes in the microstructure and state of Cu-rich particles on the surface YBCO thin films. The particle formation observed in our experiment can be described using the classical thin film nucleation and growth model based on the concept of capture zones.

Tunable source of terahertz radiation based on the difference-frequency generation in a GaP crystal

A tunable source of terahertz (1–4 THz) radiation with a line width of 12 GHz is created on the basis of difference- frequency generation in a GaP crystal. Radiation of a pulsed Nd:YAG laser with a wavelength of 1064 nm and a tunable optical parametric oscillator is used as the pump. The radiation is generated in 10-ns-duration pulses with a pulse repetition rate of 10 Hz. The pulsed radiation power is about 15 mW.

The use of a scanning tunneling microscope (STM) for investigation of local photoconductivity of quantum-dimensional semiconductor structures

The possibility is demonstrated of using the STM for recording spectra of photoconductivity of quantum-dimensional semiconductor structures with a high spatial resolution. Studies are made into the local photoconductivity of GaAs/InxGa1−x As based quantum wells and quantum points as a function of the depth of location of the quantum-dimensional structure relative to the surface space charge region. For quantum points in the vicinity of the sample surface, spectra are obtained which are characterized by features associated with the individual energy spectrum of those points.

Study of correlation between the microstructure and phase inhomogeneities of Y-Ba-Cu-O epitaxial films and their DC and microwave properties

The influence of various kinds of structure and phase inhomogeneity on electrical properties of YBCO thin films prepared by inverted cylindrical magnetron sputtering has been investigated. A simultaneous analysis of the changes in the microstructure and electrical parameters has allowed us to define the contribution of each kind of inhomogeneity in the restriction of the films electrical parameters. It has been found that the transition temperature depends mainly on deviations of the c-axis lattice parameter from its optimum value, the critical current density depends mainly on the out of plane misorientation of the film domains and the microwave surface resistance depends mainly on the volume of the high-angle misoriented domains. By using atomic force and scanning tunnelling microscopy regions of YBCO films with modified properties around Cu-rich second phase particles were observed. It is suggested that superconducting properties of these regions are worse than the matrix due to Cu depletion. Usually the relative area of these inhomogeneities in our films is about 30% and can occupy up to 50% and, therefore, mostly determines the electrical properties of films. It is suggested that the processes of cation disorder deforming the film lattice play an important role in formation of structure and phase inhomogeneities in YBCO thin films.

Preparation and investigation of laser ablated PZT, PLZT and PbMg1/3Nb2/3O3 (PMN) ferroelectric films

Abstract Epitaxial thin films of Pb(ZrxTi1-x)O3, Pb1-xLax(ZryTiz)1–(x/4)O3, and PbMg1/3Nb2/3O3 were created by pulsed laser deposition on YBa2Cu3O7-x coated (100)SrTiO3 and (110)SrTiO3 substrates. Film properties were characterized by XRD, RBS and SEM. The remanent polarization and coercive field of the PZT(0.52, 0.48) film were 42 μCcm−2 and 55 kVcm−1. The change of film properties with deposition temperature were studied.

Growth and Formation of the Microstructure of YBCO Films Deposited by Magnetron Sputtering on Fianite Substrates

The dependence of the electrophysical and structural properties of the high-Tc YBa2Cu3O7 − δ superconductor films deposited by magnetron sputtering on fianite on the growth temperature is studied. Scanning electron microscopy and X-ray diffraction demonstrate that the layer-by-layer island growth of an YBa2Cu3O7 − δ film occurs on fianite substrates without an additional buffer layer. An increase in the deposition temperature leads to the division of the growing film into regions with strongly different microstructures. The regions of the first type are represented by a high-quality YBa2Cu3O7 − δ layer, and the regions of the second type consists of an YBa2Cu3O7 − δ layer with well-pronounced granule boundaries, which hinder the passage of an electric current.

Investigation of the compositional changes of a Y-Ba-Cu-O HTSC target under ion sputtering

An Auger electron spectroscopy study is reported of the elemental depth profile of Y-Ba-Cu-O HTSC targets subjected to ion-plasma sputtering in a magnetron deposition system and ion-beam sputtering in the Auger spectrometer chamber. It has been established that the process consists in all cases of predominant copper sputtering accompanied by the formation of a modified surface layer and of a copper-depleted region. This region is assumed to originate from intense copper diffusion from the bulk to the modified surface layer driven by a concentration gradient.

Effect of cation composition on the superconducting properties and on the microstructure of YBaCuO thin films

The surface morphology and superconducting properties of YBaCuO epitaxial films prepared through magnetron sputtering from targets of different cation composition were systematically studied. It was shown that small changes in the growth conditions and relatively small variations in the cation composition of the condensate noticeably affect the surface morphology of the films and their structural and superconducting properties, thus offering an efficient way of controlling the YBCO film parameters. It was found that the 90° off-axis configuration of the magnetron sputtering system permits realization of growth conditions in which the grown films do not contain CuO precipitates and exhibit good superconducting properties (Tc≥88 K, jc(77 K)≥4×106 A/cm2).

Special features in the synthesis and properties of thin Y-Ba-Cu-O high-temperature superconductor films free of secondary phases

Data on the structure and transport properties of thin Y-Ba-Cu-O (YBCO) high-temperature superconductor films obtained by magnetron sputtering of a stoichiometric target in a system with a 90° off-axis geometry are reported. It is shown that the films prepared under these conditions are free of copper-rich secondary phases and are characterized by the surface roughness height below 10 nm. The films possess a perfect structure and exhibit high superconducting properties: c-axis misorientation in microblocks FWHM(005)YBCO=0.4–0.5°; zero-resistance temperature Tco=89 K; critical (pinning) current density jp=1.5–2 MA/cm2 (77 K).

Investigation of inhomogeneities in thin films of high-temperature superconductors by scanning probe microscopy

Scanning tunneling microscopy and atomic force microscopy were used to study inhomogeneities in thin films of Y-Ba-Cu-O high-temperature superconductors caused by secondary-phase precipitates. It was established that Y-Ba-Cu-O films with high global critical parameters may constitute a complex heterogeneous system containing regions of different thickness and electrical properties. It is shown that these inhomogeneities may strongly influence the parameters of devices formed using these films.