X-ray Diffraction and Computation Yield the Structure of Alkanethiols on Gold(111)
A. Cossaro,1
R. Mazzarello,2
R. Rousseau,2*
L. Casalis,3
A. Verdini,1
A. Kohlmeyer,4
L. Floreano,1
S. Scandolo,5
A. Morgante,1,6
M. L. Klein,4
G. Scoles2,3,7
The structure of self-assembled monolayers (SAMs) of long-chain alkyl sulfides on gold(111) has been resolved by density functional theory–based molecular dynamics simulations and grazing incidence x-ray diffraction for hexanethiol and methylthiol. The analysis of molecular dynamics trajectories and the relative energies of possible SAM structures suggest a competition between SAM ordering, driven by the lateral van der Waals interaction between alkyl chains, and disordering of interfacial Au atoms, driven by the sulfur-gold interaction. We found that the sulfur atoms of the molecules bind at two distinct surface sites, and that the first gold surface layer contains gold atom vacancies (which are partially redistributed over different sites) as well as gold adatoms that are laterally bound to two sulfur atoms.
1 Istituto Nazionale per la Fisica della Materia–Consiglio Nazionale delle Ricerche (INFM-CNR) Laboratorio TASC, I-34012 Trieste, Italy.
2 International School for Advanced Studies, I-34014 Trieste, Italy.
3 Sincrotrone Trieste S.C.p.A., I-34012 Trieste, Italy.
4 Center for Molecular Modeling and Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104, USA.
5 Abdus Salam International Centre for Theoretical Physics and INFM/Democritos National Simulation Center, I-34014 Trieste, Italy.
6 Department of Physics, University of Trieste, I-34127 Trieste, Italy.
7 Department of Chemistry, Princeton University, Princeton, NJ 08544, USA.
* Present address: Pacific Northwest National Laboratory, Richland, WA 99352, USA.
To whom correspondence should be addressed. E-mail: morgante{at}tasc.infm.it
