The growth mechanism and topography of superconducting YBa 2Cu 3O 7−δ and BiSrCaCuO-2201 films studied by scanning tunneling microscopy

Abstract

The growth mechanism and surface topography of YBa 2Cu 3O 7 − δ (YBCO) and BiSrCaCuO-2201 (BSCCO) epitaxially grown superconducting films have been studdied by scanning tunneling microscopy. We report here two growth mechanisms: screw dislocation growth and layered growth, and also the surface characterization and surface modification of thin films under a controlled manner. High-quality epitaxial thin films were grown in situ by excimer laser ablation. YBCO thin films were epitaxially grown with the c-axis perpendicular to the SrTiO 3 (100) substrate surface. On the flat substrate, the YBCO films were nucleated and grown in the screw dislocation manner. On the titled substrate (α<1 deg.), the films show layered growth. The etching caused by field-induced evaporation has been utilized to observe the initial stage of growth. Epitaxially grown BSCCO-2201 films were firstly synthesized in our laboratory with the c-axis perpendicular to the ZrO 2 substrates. Layered growth 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 series, the study of the growth mechanism of 2201 films is very important to the synthesis of superconducting 2212, 2223 or other artificial layered thin films.