| AVS 59th Annual International Symposium and Exhibition | |
| In Situ Microscopy and Spectroscopy Focus Topic | Wednesday Sessions |
| Session IS+AS+OX+ET-WeM |
| Session: | In Situ Characterization of Solids: Film Growth, Defects, and Interfaces |
| Presenter: | Y.G. Du, Pacific Northwest National Laboratory |
| Authors: | Y.G. Du, Pacific Northwest National Laboratory D.J. Kim, Pacific Northwest National Laboratory T.C. Kaspar, Pacific Northwest National Laboratory S.E. Chamberlin, University of Wisconsin Milwaukee I. Lyubinetsky, Pacific Northwest National Laboratory S.A. Chambers, Pacific Northwest National Laboratory |
| Correspondent: | Click to Email |
TiO2 has attracted much attention because of its potential utility in hydrogen production via water splitting, environmental remediation, and dye-sensitized solar cell fabrication. Heteroepitaxial growth of anatase is a powerful and unique way to fabricate model surfaces of the less stable anatase polymorph for fundamental surface science studies. In this work, the growth of TiO2 anatase films on Nb doped SrTiO3(001) by molecular beam epitaxy has been studied in-situ by scanning tunneling microscopy. We show that the initial growth follows the Stranski-Krastanov mode, where islands form on top of a wetting layer consisting of two monolayers (ML) of TiO2. Well-defined (4x1) and (1x4) terraces are observed for film thicknesses in excess of 3 nm. At larger film thicknesses, large oriented crystallites form as a result of the coalescence of smaller islands. Within a given crystallite, either (4x1) or (1x4) reconstructed terraces account for majority of the surface. The anatase grows in units of bilayers, resulting in a step height of 2 ML. This result explains the fact that the measured period of the RHEED specular-beam intensity oscillations corresponds to the time required for deposition of 2 ML. Ar ion sputtering and UHV annealing results in a transformation to coexisting (4x1) and (1x4) reconstructed terraces on individual crystallites, as commonly observed by ex-situ STM studies. In addition, we show that the nucleation and growth of anatase films are influenced by Nb doping in the SrTiO3 substrates by comparing with similar growth occurring on pure SrTiO3 substrates.