Synthesis of high-temperature superconducting thin films in microwave field

Abstract

The most widely used technique to obtain high-temperature superconducting (HTSC) thin films at present, i.e., the in situ method, has the disadvantage of heating the substrate up to 700–800 °C. This paper proposes a novel, low-temperature method for HTSC synthesis that is capable of producing new types of multilayer structures. The technique is based on the use of microwave (MW) field to treat a thin film deposited on a single-crystal substrate. The process of superconductor formation depends on the MW power, the sample volume, and the dielectric constant. The nature of the synthesis in MW field differs significantly from the ordinary high-temperature baking, since the solid-state reaction is initiated simultaneously in the entire volume and runs at a relatively high rate. Aerosol deposition proved to be the most suitable technique, especially when combined with ultrasonic aerosol homogenization. Scanning electron microscopy observations show that the film surface consists of comparatively densely ordered, almost round grains with sizes between 100 and 130 nm. X-ray diffraction analysis clearly demonstrates that no admixtures from the substrate have penetrated the layer. The resistance versus temperature characteristic is measured by four-probe technique and the critical current densities were 2×105 and 0.8×105 A/cm2 at 77 and 4.2 K, respectively.