AVS 50th International Symposium
    Surface Science Thursday Sessions
       Session SS3-ThM

Paper SS3-ThM5
Growth Modes in a System Requiring Bulk Mass Transport: Step Motion and Island Nucleation on TiO@sub 2@ (110) Exposed to Oxygen

Thursday, November 6, 2003, 9:40 am, Room 328

Session: Oxide Structure, Growth, and Defects
Presenter: K.F. McCarty, Sandia National Laboratories
Authors: K.F. McCarty, Sandia National Laboratories
J.A. Nobel, Sandia National Laboratories
N.C. Bartelt, Sandia National Laboratories
Correspondent: Click to Email
We use low-energy electron microscopy (LEEM) to systematically investigate how the (110) surfaces of oxygen-deficient rutile crystals grow when exposed to oxygen. This growth is interesting because it requires a combination of bulk and surface diffusion -- as established by Onishi and Iwasawa (1996) using scanning tunneling microscopy, growth occurs as titanium interstitials from the bulk react with ambient and adsorbed oxygen. If the reaction only occurred at step edges, then one might expect to observe only step-flow growth. Instead, we find that distinct growth processes occur, depending primarily on temperature and oxygen pressure. The temperature/pressure dependence of these growth regimes has been systematically determined for a slightly reduced crystal. At high temperature, TiO@sub 2@ growth occurs by pure step flow without the nucleation of new islands. At low temperatures, however, crystal growth proceeds by two-dimensional islands nucleating and spreading laterally. In this layer-by-layer growth regime, the surface periodically oscillates between structures with 1x1 and 1x2 periodicity. The threshold temperature above which island nucleation does not occur depends upon the local terrace width and pressure. For a range of temperatures around the threshold, nucleation occurs on wide terraces but not on narrow terraces. In the regime of pure step flow, we analyze the rate at which isolated islands and interacting island arrays grow. Comparison of the experimental data to numerical simulations of island growth allows us to discuss the relative importance of Ti transport through the bulk and oxygen-containing species on the surface.