Surface Science 402–404 (1998) 604–608 Competing interaction of different thiol species on gold surfaces D. Zerulla *, I. Uhlig, R. Szargan, T. Chasse ´ Institut fu ¨ r Physikalische und Theoretische Chemie, Universita ¨t Leipzig, Linne ´str. 2, D-04103 Leipzig, Germany Received 18 August 1997; accepted for publication 2 October 1997 Abstract Self-assembled monolayers (SAMs) of thiol molecules show very interesting properties. We have investigated the possibilities of creating mixed thiol films, consisting of two structurally and chemically very different thiol species. We used the aliphatic hexadecanethiol and the aromatic 2-mercapto-benzothiazol (MBT ). The interaction of both species after successive adsorption on gold was investigated using XPS. We found, that hexadecanethiol displaces the MBT from gold surfaces, similar to the removal of carbon contamination by the alkanethiol. In contrast, MBT cannot replace the adsorbed alkanethiol layer. Therefore, the creation of mixed films has to start with a partial coverage of hexadecanethiol, followed by the MBT, which now can assemble to the uncovered surface without disturbing the alkanethiol. © 1998 Elsevier Science B.V. All rights reserved. Keywords: Alkanethiols; Chemisorption; Gold; Mercaptobenzothiazole; Self-assembly; X-ray photoelectron spectroscopy 1. Introduction in nanometer scale, however, may lead to addi- tional possibilities of application. Monolayers of thiol molecules adsorbed on sub- Therefore, it is of interest to investigate the strates like gold and silver are well known for their behaviour of layers of aromatic thiols in compari- self-assembling properties. They are stable against son to layers formed by alkanethiols. 2- etching, act as lithographic resists and can be mercaptobenzothiazole (MBT ), known to form combined with functional groups, to mention only hydrophobic complexes with many metals and a few examples. Because of the potential technical therefore used as corrosion inhibitor or collector applications of such organized assemblies in a for mineral flotation [1,2], was chosen for the variety of fields e.g. chemical/optical sensors, these studies presented here. Beside its aromatic charac- systems have been studied with increased attention ter, MBT contains a nitrogen atom, which acts as for a number of years. Most of the studies are an additional ligator atom in a chelate type bond- concerned with layers of aliphatic thiols. The abil- ing at the surface and can be used as tracer atom ity to produce mixed thiol films on surfaces, con- for identification of the adsorbed species. sisting of molecules with different electronic and In connection to the experiments described chemical properties and combined with structuring above, the interaction between alkanethiols and hydrocarbon contamination, produced by sample transfer in air, was investigated. Because of the similarity of the behaviour, it seems to be meaning- * Corresponding author. Fax: ( +49 ) 341 36 399; e-mail: zerulla@server1.rz.uni-leipzig.de ful to discuss them in this context. 0039-6028/98/$19.00 © 1998 Elsevier Science B.V. All rights reserved. PII: S0039-6028(98)00015-6