ELSEVIER Surface Science 370 (1997)245-251 surface science Study of scanning tunneling microscopy images and probable relaxations of the SrTiO3(100) surface by electronic structure calculations D.-K. Seo, K. Perdue, J. Ren, M.-H. Whangbo * Department of Chemistry, North Carolina State University, Raleigh, NC 27695-8204, USA Received 24 April 1996; accepted for publication 19 June 1996 Abstract Partial electron density plots were calculated for a model SrTiO3(100) surface with V~ x V~ ordered oxygen vacancy to examine why the bright spots of the scanning tunneling microscopy (STM) images of SrTiO3(100) observed in ultrahigh vacuum (UHV) correspond to the oxygen vacancy sites. Possible dependence of the image on the polarity and magnitude of the bias voltage was also discussed on the basis of partial electron density plot calculations. Our study strongly suggests that the UHV STM imaging involves the lowest-lying d-block level of every two Ti3+ centers adjacent to an oxygen vacancy, the tip-sample distance involved in the UHV STM experiments is substantially larger than that involved in typical ambient-condition STM imaging, and the Ti4÷ and Ti 3+ sites of SrTiO3(100 ) are reconstructed. Keywords: Scanning tunneling microscopy; Semi-empirical models and model calculations; Single crystal surfaces; Surface electronic phenomena; Surface relaxation and reconstruction; Titanium oxide 1. Introduction In the photoelectrolysis of water [1,2] and as a substrate for thin film deposition [3], the surface of perovskite oxides AMO 3 (A = alkali or alkaline earth, M=transition metal) play an important role. The surface defects of these compounds are critical as centers of chemical reactions [41, and the (100) surface of SrTiO3 has been the subject of a number of experimental [5-9] and theoretical [10-12] studies. The structure of SrTiO3 has * Corresponding author. Fax: + 1 919 5157832; e-mail: whangbo@chvzmw.chem.ncsu.edu alternating layers of TiO 2 and SrO, so that the top layer of a SrTiO3(100) surface can be either TiO2 or SrO. Auger electron spectroscopy analyses [ 5,6] indicate that the TiO2 plane constitutes most of the top layer of vacuum fractured SrTiO3 samples. Ultraviolet photemission spectroscopy studies show that the electronic properties of SrTiO3 (100) are strongly influenced by oxygen vac- ancies in the surface TiO2 layer [5], that a shallow occupied level appearing below the con- duction band is associated with the oxygen vacancy [5,1, and that the oxidation state of Ti changes from Ti 4+ to Ti 3+ by a nearby oxygen vacancy on the surface [6,1. Scanning tunneling microscopy (STM) studies of SrTiO3(100) (annealed at high 0039-6028/97/$17.00 Copyright © 1997 Elsevier Science B.V. All rights reserved PH S0039-6028 (96) 00953-3