Oxygen-de®cient SnO 2 1 1 0): a STM, LEED and XPS study M. Sinner-Hettenbach a, * , M. G othelid b , J. Weissenrieder b , H. von Schenck b , T. Weiû a , N. Barsan a,1 , U. Weimar a a Institute of Physical and Theoretical Chemistry IPTC), University of T ubingen, Auf der Morgenstelle 8, D-72076 T ubingen, Germany b Materials Physics, Royal Institute of Technology, Teknikringen 14, S-100 44 Stockholm, Sweden Received 11 October 2000; accepted for publication 2 January 2001 Abstract The reconstruction process of SnO 2 1 1 0) was investigated by scanning tunneling microscopy STM), low energy electron diraction LEED) and X-ray photoelectron spectroscopy XPS). The high-temperature 1  1 reconstruction could be identi®ed as an intermediate face, transferable either to the 1  2 surface by annealing to higher temperature or back to the 4  1 reconstruction by annealing again at lower temperature. In this way, a new method to prepare well- ordered 4  1 terminated surfaces is introduced and the O/Sn ratio as well as the core-level positions of Sn 3d and O 1s were traced by XPS over a temperature range of 700±1200 K on freshly sputtered and on low-temperature long-time annealed SnO 2 1 1 0). STM images of the 1  1 surface show a new structure of in-plane oxygen, ordered locally in zigzag rows that contribute to the LEED pattern as a very diuse 2  1 intensity. Ó 2001 Published by Elsevier Science B.V. Keywords: Scanning tunneling microscopy; Low energy electron diraction LEED); Photoelectron spectroscopy; Tin oxides; Single crystal surfaces 1. Introduction Tin dioxide is of interest in a number of appli- cations. As indium±tin oxide it is widely used as transparent electrode in solar cell production or in electrochemistry. But our main interest grows from its application as gas sensitive resistor in ambient air environment. For a detailed under- standing of the surface properties relevant for gas or metal interaction, a comprehensive character- ization of the materialÕs surface is a prerequisite. The 1 1 0) face of single crystalline SnO 2 gained, as it is the thermodynamically most stable surface, wide attention as a model system for SnO 2 . Fun- damental surface properties of SnO 2 [1,2] and gas [3±6] or metal [7±9] interaction have been studied in the last two decades on this model system. The ion bombarded and subsequently annealed surface is of particular interest. On the one hand, because of the relatively easy preparation proce- dure by sputtering and annealing and on the other hand, because of the high surface conductivity which results from unsaturated tin on reduced and defective surfaces enabling even scanning tunnel- ing microscopy STM) studies. The ®rst systematic Surface Science 477 2001) 50±58 www.elsevier.nl/locate/susc * Corresponding author. Tel.: +49-07071-29-72478. E-mail addresses: martin.sinner@ipc.uni-tuebingen.de M. Sinner-Hettenbach), nb@ipc.uni-tuebingen.de N. Barsan). 1 Also corresponding author. Tel.: +49-07071-29-78765; fax: +49-07071-29-5960. 0039-6028/01/$ - see front matter Ó 2001 Published by Elsevier Science B.V. PII:S0039-602801)00705-1