Formation of n‑Alkyl Monolayers by Organomercury Deposition on Gold Frank Scholz, † Eva Kaletova ́ , ‡ Elizabeth S. Stensrud, ‡ William E. Ford, † Anna Kohutova ́ , ‡ Malgorzata Mucha, ‡ Ivan Stibor, ‡ Josef Michl, ‡,§, * and Florian von Wrochem* ,† † Sony Deutschland GmbH, Materials Science Laboratory, Hedelfinger Str. 61, 70327 Stuttgart, Germany ‡ Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, 16610 Prague, Czech Republic § Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309-0215, United States *S Supporting Information ABSTRACT: n-Alkyl self-assembled monolayers can be directly attached to gold through C−Au bonds by the deposition of organomercury salts on gold substrates, as shown here using n- butylmercury and n-octadecylmercury tosylate derivatives. The Hg atoms, which are codeposited during this process, are removed by thermal annealing at 95 °C, resulting in alkyl monolayers having a significantly enhanced thermal stability compared with alkanethiol monolayers, however, a lower degree of conformational order. The monolayer properties are elucidated by X-ray photoemission and IR spectroscopy, STM, ellipsometry, and contact-angle goniometry. SECTION: Surfaces, Interfaces, Porous Materials, and Catalysis T he stable attachment of organic molecules to metal substrates has numerous applications in several fields such as optoelectronic devices, sensing, corrosion inhibition, and biomedical applications. To date, hydrocarbons have been commonly attached to noble metals by using thiol anchor groups, which are prototypical for the formation of self- assembled monolayers (SAMs). Thiols form covalent bonds between the sulfur atom and the metal substrate 1 and are known to yield highly uniform, often crystalline self-assembled monolayers. 2−5 However, despite their dense packing, high molecular order, and ease of preparation, thiol-based monolayers have certain disadvantages, such as fluctuations in the electrical coupling to the metal, low thermal stability, and facile oxidation of the sulfur moiety. 6 For this reason, the need for alternative contacts 7−9 has spurred research in recent years. Among others, the direct attachment of molecules to the metal substrate by carbon−metal bonds has been considered, for example, by reacting diazonium salts with a variety of metals. 10,11 However, diazonium salts do not allow a self- limiting growth of well-defined SAMs. Alternatively, thermally stable alkylidene layers on molybdenum carbide 12 have been realized, including the versatile modification via olefin meta- thesis reactions, 13 and terminal alkynes have been adopted for direct metal−carbon bonding. 14 Also, the attachment of alkynyls to Au has been recently demonstrated. 15 The serendipitous discovery of the attachment of organo- mercury salts to gold 16−18 and investigations of the adsorption of organoplatinum complexes on platinum 19 led to the disclosure of monolayers formed by soaking Au in a solution of trialkylstannyl salts of tosic, trifluoroacetic, and triflic acids. 20 Recently, the first evidence of alkyl−Au 21 and fullerene−Au 22 contacts in mechanically controlled break junction studies appeared. In this Letter, we provide evidence that organomercurial compounds, n-alkylHgOTs, form well-defined n-alkyl mono- layers on gold surfaces, and we present a simple procedure for the realization of dense n-butyl and n-octadecyl monolayers via the solution deposition of n- butylmercury tosylate (C 4 H 9 HgOTs) and n- octadecylmercury tosylate (C 18 H 37 HgOTs) 23 on Au, followed by a thermal annealing cycle for Hg removal. As a result, the n-alkyl chains are directly attached to Au, even though the precise alkyl-Au binding mode is still under investigation. The SAM is chemically and thermally highly stable, showing molecular densities close to those of alkanethiol monolayers. An alternative approach for removing Hg in n-octadecyl/Hg SAMs has been developed in parallel, involving anodic oxidation of the initially formed monolayers. 23 The n-alkyl SAMs are grown by soaking clean Au substrates in a 1 mM THF solution of either C 4 H 9 HgOTs or C 18 H 37 HgOTs for 3 h. For XPS and STM analysis, atomically flat Au(111) surfaces are used as a substrate, as obtained by Received: June 9, 2013 Accepted: July 22, 2013 Published: July 22, 2013 Letter pubs.acs.org/JPCL © 2013 American Chemical Society 2624 dx.doi.org/10.1021/jz4011898 | J. Phys. Chem. Lett. 2013, 4, 2624−2629