Interlocked grain growth of YBCO film on magnesium oxide as observed by scanning tunneling microscopy

Thin films of YBa 2Cu 3O 7 on MgO deposited by RF magnetron sputtering to study their superconducting behavior, were examined by a Scanning Tunneling Microscope. The films were deposited at room temperature, sintered exsitu at 850°C, 900°C, 930°C,950°C and 980°C for 30 minutes each and cooled at rate of 100°C per hour in oxygen ambient. Topographic images taken in air show that the films which were initially amorphous in nature, gradually transform to a layered grain structure with the increase of sintering temperature. Films sintered at temperatures above 900°C are c-axis oriented and have a coarse grain structure. These grains are connected mutually by a well defined interlock, formed between the layers of neighboring grains. The mechanism of interlocking of layers from adjacent grains and its possible influence on the superconducting properties has been discussed.