Structure of Nanoclusters on Oxide Substrates--Bi_(2)O_(3) on SrTiO_(3)

摘要

The structure of small clusters of Bi_(2)O_(3) on the (001) surface of SrTiO_(3) are examined using ab initio density functional theory. In these clusters the local Bi environments are highly distorted, resembling locally those in the ordered alpha and beta phases of Bi_(2)O_(3), but on the surface arranged together in different ways as in the disordered delta phase. Thus we propose that the stabilization of the delta phase of Bi_(2)O_(3) on this surface arises not from the epitaxial matching of Bi...Bi with Sr..Sr, but from mismatch between cluster Bi-O and surface Sr-O bond lengths. This gives rise to critical areas (i.e., maximum domain sizes) for individual Bi-O islands on the surface, thus promoting different arrangements of the Bi and the formation of a disordered surface phase. The formation of the film is associated with a considerable decrease in the band gap.