AVS 53rd International Symposium
    Surface Science Friday Sessions
       Session SS-FrM

Paper SS-FrM9
Structure and Properties of MBE-grown Epitaxial Anatase Films with Rutile Nanocrystalline Inclusions

Friday, November 17, 2006, 10:40 am, Room 2002

Session: Oxide Surfaces and Interfaces
Presenter: R. Shao, Pacific Northwest National Laboratory
Authors: R. Shao, Pacific Northwest National Laboratory
D.E. McCready, Pacific Northwest National Laboratory
C.M. Wang, Pacific Northwest National Laboratory
S.A. Chambers, Pacific Northwest National Laboratory
Correspondent: Click to Email
TiO@sub 2@ is a wide band-gap oxide which is of interest for photocatalytic oxidation of organic pollutants. It is known that TiO@sub 2@ nanoparticles, which are suspected to consist of an anatase core and a rutile shell, enhance photocatalytic reactions compared to the pure phases. It has been suggested that this phenomenon is due to enhanced electron-hole pair lifetimes associated with the spatial separation of carriers across the anatase/rutile interface due to a staggered band alignment. Fundamental insight calls for the preparation and characterization of a model system with a well-defined anatase/rutile interface. To this end, we have used a region of the molecular beam epitaxy growth phase space for TiO2 on LaAlO@sub 3@ (001) and SrTiO@sub 3@ (001) in which rutile inclusions nucleate within a continuous epitaxial anatase layer. We start by growing a pure anatase (001) layer and then change the growth conditions to drive the nucleation of rutile particles. Control of the density and size of the rutile nanocrystals is highly sensitive to the growth conditions. X-ray diffraction shows that the rutile [100] axis is normal to the film plane. The anatase/rutile interface is atomically sharp and the preferential orientations of rutile nanocrystals in the film are determined from high-resolution transmission electron microscopy. X-ray photoemission measurements for anatase, rutile and anatase/rutile composite films indicate that the interface forms a nested rather than staggered heterojunction. In this talk, we will present details of the growth and properties of this system along with a study of electron transport across the interface as measured by scanning tunneling microscopy.