Role of chain-chain interactions in the structure of monolayers of alkanethiolates on Au(111) and Ag(111): Do they really matter ?

J.G. SOLANO CANCHAYA; P. N. ABUFAGER; Y. WANG; M. ALCAMÍ; F. MARTÍN; M.L. MARTIARENA; K. REUTER; H.F. BUSNENGO

Edimburgo

Conferencia; 29 ECOSS European Conference on Surface Science; 2012

Though Au(111) and Ag(111) are very popular substrates for the grow of self-assembled monolayers (SAM) of alkylthiolates (SCn), and many theoretical investigations do exist, various fundamental issues remain unclear. For instance, the full coverage SAMs on Au(111) and Ag(111) differ in coverage (1/3 vs. 3/7) and tilt angle (~30° vs. ~0-10°), due to reasons that are not fully understood. It is very often claimed that these differences (between SAMs grown on a priori similar substrates) reflect that the structures of SAMs are dictated by a very subtle competition between the S-surface and the chain-chain interactions.In this work we compare the stability of many possible structures of SAMs of SCn on Au(111) and Ag(111) characterized by coverages 1/3 and 3/7 (for chains with n=1 to n=18 C atoms) through DFT-D calculations.  As expected, for long enough alkyl chains, the chain-chain contribution to the cohesive energy of the SAMs is larger than the one of the S-surface bond. However, in such cases chain-chain interactions also stabilize other higher coverage competing structures involving multilayers. Therefore, the different structural properties of the up-right monolayers of SCn on Au(111) and Ag(111) are largely determined by the different (coverage dependent) S-surface binding energies, which in turn, are due to the dissimilar reconstructions induced by the SAMs on both substrates. Thus, our results surprisingly show that the structures of the saturation coverage monolayers of SCn on Au(111) and Ag(111) are barely dictated by the chain-chain interactions in contrast with the usual belief.  <!-- @page { margin: 2cm } PRE { direction: ltr; color: #000000; widows: 0; orphans: 0 } PRE.western { so-language: es-AR } PRE.cjk { font-family: "DejaVu Sans", monospace; so-language: zh-CN } PRE.ctl { so-language: hi-IN } P { margin-bottom: 0.21cm; direction: ltr; color: #000000; widows: 0; orphans: 0 } P.western { font-family: "Liberation Serif", "Times New Roman", serif; font-size: 12pt; so-language: es-AR } P.cjk { font-family: "DejaVu Sans"; font-size: 12pt; so-language: zh-CN } P.ctl { font-family: "DejaVu Sans"; font-size: 12pt; so-language: hi-IN } -->