THE GROWTH-MECHANISM AND TOPOGRAPHY OF SUPERCONDUCTING YBA2CU3O7-DELTA AND BISRCACUO-2201 FILMS STUDIED BY SCANNING-TUNNELING-MICROSCOPY

The growth mechanism and surface topography of YBa2Cu3O7-delta (YBCO) and BiSrCaCuO-2201 (BSCCO) epitaxially grown superconducting films hav e been studied by scanning tunneling microscopy. We report here two gr owth mechanisms: screw dislocation growth and layered growth, and also the surface characterization and surface modification of thin films u nder a controlled manner. High-quality epitaxial thin films were grown in situ by excimer laser ablation. YBCO thin films were epitaxially g rown with the c-axis perpendicular to the SrTiO3 (100) Substrate surfa ce. On the flat substrate, the YBCO films were nucleated and grown in the screw dislocation manner. On the tilted substrate (alpha < 1 deg.) , the films show layered growth. The etching caused by field-induced e vaporation has been utilized to observe the initial stage of growth. E pitaxially grown BSCCO-2201 films were firstly synthesized in our labo ratory with the c-axis perpendicular to the ZrO2 substrates. Layered g rowth has been observed by STM. No screw dislocations were identified in our samples. Larger atomic flat areas were present, which are more stable than YBCO films. As a parent phase for the BSCCO 2212, 2223 ser ies, the study of the growth mechanism of 2201 films is very important to the synthesis of superconducting 2212, 2223 or other artificial la yered thin films.