Single Source Electron Beam Evaporation of Bi-Sr-Ca-Cu-O Thin Films

Abstract

A modified electron beam evaporation technique for the deposition of BiSrCaCuO thin films has been developed. In contrast to the conventional hearthed electron beam crucible the design in the present study uses a copper crucible with a single groove around its circumference. The crucible is rotated continuously during deposition to reduce decomposition of starting material. Design details of the crucible are discussed. The variation in properties with speed of rotation and emission current have also been investigated. The variation in properties with starting material composition is also reported. It has been observed that a composition close to that of the n=2 member of the Bi system i.e. Bi₂Sr₂Ca₁Cu₂O_(8+x) is obtained under optimised conditions. The as deposited films had to be annealed after deposition to achieve conductivity and crystallinity in the films. It was observed that a two stage annealing process wherein the films are annealed at 500 deg C initially and then at 870 deg C in air is essential to get low resistance films. The films however have been found to be metallic upto 40 K and no superconducting transition has been observed. Oxygen annealing seems to degrade the conductivity of the films. Some reasons for this behavior have been discussed.