Scanning tunneling microscopy image contrast of monolayer platinum on graphite F. Atamny a,b,1 , T. B urgi b , R. Schl  ogl a , A. Baiker b, * a Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, D-14195 Berlin, Germany b Laboratory of Technical Chemistry, Swiss Federal Institute of Technology, ETH-Zentrum, CH-8092 Zurich, Switzerland Received 17 May 2000; accepted for publication 5 December 2000 Abstract Platinum particles supported on graphite have been investigated by scanning tunneling microscopy STM). For one monolayer thick Pt particles the individual Pt atoms form a characteristic intensity pattern due to a mismatch between the Pt and graphite lattice. Based on density functional theory calculations and model structures of Pt on graphite it is argued that the observed STM imaging contrast has its origin in the tip induced elastic deformation of the graphite underneath the Pt particle. The Pt±graphite potential is much stier than the graphite±graphite potential. The calcu- lations furthermore indicate that Pt adsorption is favored over top rather than hole sites and that the barrier for diusion is very low. Ó 2001 Elsevier Science B.V. All rights reserved. Keywords: Scanning tunneling microscopy; Graphite; Platinum; Catalysis; Density functional calculations 1. Introduction Metal particles deposited on carbon supports are used as catalysts in many reactions [1,2]. The microstructure and morphology of supported metal particles play an important role in determining the catalytic activity and selectivity of structure sensitive reactions. Considerable eort has been expended in the past on the characterization of the microstructure of supported metal particles by various techniques, such as transmission elec- tron microscopy and scanning electron micro- scopy. With the invention of scanning tunneling microscopy STM) the interest in the interaction mode between metal particles and graphite sup- port has increased not only because STM is a local technique with a very high spatial resolution, but also due to the STM ability to give more insight concerning local electronic properties on the na- nometer scale. Since the modi®cation of the local electronic structure near deposited metal particles are believed to aect the activity and/or selectivity of a catalyst, several groups investigated various metal/graphite systems by STM [2±10]. These Surface Science 475 2001) 140±148 www.elsevier.nl/locate/susc * Corresponding author. Tel.: +41-1632-3153; fax: +41-1632- 1163. E-mail addresses: fachri.atamny@unaxis.com F. Atamny), baiker@tech.chem.ethz.ch A. Baiker). 1 Present address: Unaxis Balzers Ltd., Display division, P.O. Box 1000, FL-9496 Balzers, Liechtenstein. 0039-6028/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PII:S0039-602800)01098-0