Scanning tunneling microscopy study of different growth stages of YBa2Cu3O7− δ thin films

Abstract

Growth and surface structure of c-axis oriented YBa 2 Cu 3 O 7− δ (YBCO) thin films, laser-deposited on LaAlO 3(100), have been investigated by scanning tunneling microscopy (STM). By application of a special half-shadow technique for film preparation. different growth stages have been obtained simultaneously on a single substrate crystal. Stages of the growth process that have been observed by STM include nucleation and spreading of two-dimensional islands, their coalescence and growth, formation of well-developed growth hills and a continuous film. The growth mechanism of the films is layer growth with respect to the height of the YBCO unit cell in the crystallographic c-direction. In addition to repeated two-dimensional nucleation, Frank's spiral mechanism also plays an important role. Spiral step patterns on growth hills imaged by STM have been compared to classical crystal growth theory. On the atomic scale, two different rectangular surface lattices have been observed with spacings of 0.38 and 0.27 nm, respectively. A tentative assignment of the atomic-scale features is suggested.