Surface Science Letters The deposition of Mo nanoparticles on Au(1 1 1) from a Mo(CO) 6 precursor: effects of CO on Mo–Au intermixing Ping Liu, Jos  e A. Rodriguez * , James T. Muckerman, Jan Hrbek Department of Chemistry, Brookhaven National Laboratory, Upton, NY 11973, USA Received 12 September 2002; accepted for publication 3 January 2003 Abstract Density functional theory and slab models are used to study the effects of CO on the configuration of Mo/Au(1 1 1) interfaces. In the absence of CO, the theoretical calculations show site exchange or intermixing after depositing Mo atoms on Au(1 1 1). The presence of CO prevents Mo–Au intermixing and, thus, enhances the mobility of Mo on the surface. This phenomenon can explain a novel growth mode found when using Mo(CO) 6 as a precursor for the preparation of metal nanoparticles on Au(1 1 1). Ó 2003 Elsevier Science B.V. All rights reserved. Keywords: Density functional calculations; Surface chemical reaction; Molybdenum; Gold; Carbon monoxide; Metal–metal interfaces 1. Introduction In the emerging field of nanotechnology, one of the goals is to make metal nanostructures in well defined and controlled arrays. Once an appropri- ate template is chosen, one can grow the metal nanoparticles by direct vapor deposition of metal atoms [1–3] or by using molecular precursors that adsorb and decompose on the surface of the tem- plate while depositing metal atoms [4,5]. The sec- ond approach is more convenient for industrial applications. In the area of catalysis, the use of transition-metal carbonyls as precursors of hetero- geneous catalysts (both mono- and bimetallic) has been suggested [6] and latter explored experi- mentally [7,8]. This class of compounds are also useful for thin-metal film deposition in the fabri- cation of sensors and electromagnetic devices [9]. Thus, transition-metal carbonyls appear as logical ‘‘reactants’’ for the synthesis of nanoparticles through chemical vapor deposition (CVD) [4,5]. To optimize the growth conditions, it is important to understand what factors control the chemistry of the process. Recently, our group have used Mo(CO) 6 for the preparation of Mo nanoparticles on Au(1 1 1) and for the subsequent synthesis of MoS x (via reaction with S 2 [5]) and MoO x (via reaction with NO 2 [10]) aggregates. Results of scanning tunneling micro- scopy (STM) show a growth mechanism for the metal nanoparticles that is very different from that seen after the physical vapor deposition (PVD) of Mo atoms [11]. This new growth mode could be a * Corresponding author. Tel.: +1-631-344-2246; fax: +1-631- 344-5815. E-mail address: rodrigez@bnl.gov (J.A. Rodriguez). 0039-6028/03/$ - see front matter Ó 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0039-6028(03)00023-2 Surface Science 530 (2003) L313–L321 www.elsevier.com/locate/susc