An experimental and theoretical approach to investigate the effect of chain length on aminothiol adsorption and assembly on gold.
Despite the numerous studies on the self-assembled monolayers (SAMs) of alkylthiols on gold, the mechanisms involved, especially the nature and influence of the thiol-gold interface are still under debate. In this work the adsorption of aminothiols on Au(111) surfaces has been studied by using surface IR and X-ray photoelectron spectroscopy (XPS) as well as by density functional theory (DFT) modeling. Two aminothiols were used, cysteamine (CEA) and mercaptoundecylamine (MUAM), which contain two and eleven carbon atoms, respectively. By combining experimental and theoretical methods, it was possible to draw a molecular picture of the thiol-gold interface. The long-chain aminothiol produced better ordered SAMs, but, interestingly, the XPS data showed different sulfur binding environments depending on the alkyl chain length; an additional peak at low binding energy was observed upon CEA adsorption, which indicates the presence of sulfur in a different environment. DFT modeling showed that the positions of the sulfur atoms in the SAMs on gold with similar unit cells [(2√3×2√3)R30°] depended on the length of the alkyl chain. Short-chain alkylthiol SAMs were adsorbed more strongly than long-chain thiol SAMs and were shown to induce surface reconstruction by extracting atoms from the surface, possibly forming adatom/vacancy combinations that lead to the additional XPS peak. In the case of short alkylthiols, the thiol-gold interface governs the layer, CEA adsorbs strongly, and the mechanism is closer to single-molecule adsorption than self-assembly, whereas for long chains, interactions between alkyl chains drive the system to self-assembly, leading to a higher level of SAM organization and restricting the influence of the sulfur-gold interface.
Sorbonne Universités, UPMC Univ. Paris 06, UMR CNRS 7197, Laboratoire de Réactivité de Surface, 75005 Paris (France).|UMR CNRS 7197, Laboratoire de Réactivité de Surface, 75005 Paris (France).|Department of Chemical Engineering and Waterloo Institute for Nanotechnology, University of Waterloo, 200 University Ave. W. Waterloo, ON, N2L 3G1 (Canada).
Erin
E
Bedford
Sorbonne Universités, UPMC Univ. Paris 06, UMR CNRS 7197, Laboratoire de Réactivité de Surface, 75005 Paris (France).|UMR CNRS 7197, Laboratoire de Réactivité de Surface, 75005 Paris (France).
Vincent
V
Humblot
Sorbonne Universités, UPMC Univ. Paris 06, UMR CNRS 7197, Laboratoire de Réactivité de Surface, 75005 Paris (France).|UMR CNRS 7197, Laboratoire de Réactivité de Surface, 75005 Paris (France).
Christophe
C
Méthivier
Sorbonne Universités, UPMC Univ. Paris 06, UMR CNRS 7197, Laboratoire de Réactivité de Surface, 75005 Paris (France).|UMR CNRS 7197, Laboratoire de Réactivité de Surface, 75005 Paris (France).
Claire-Marie
CM
Pradier
Department of Chemical Engineering and Waterloo Institute for Nanotechnology, University of Waterloo, 200 University Ave. W. Waterloo, ON, N2L 3G1 (Canada).
Frank
F
Gu
Sorbonne Université, UPMC Univ. Paris 06, UMR 7574, Laboratoire Chimie de la Matière Condensée, Collège de France, 75005 Paris (France). frederic.tielens@upmc.fr.
Frederik
F
Tielens
Sorbonne Universités, UPMC Univ. Paris 06, UMR CNRS 7197, Laboratoire de Réactivité de Surface, 75005 Paris (France). souhir.boujday@upmc.fr.|UMR CNRS 7197, Laboratoire de Réactivité de Surface, 75005 Paris (France). souhir.boujday@upmc.fr.
Souhir
S
Boujday
adsorption; density functional calculations; gold; self-assembled monolayers; thiols