Molecule orientation in self-assembled monolayers determined by infrared-visible sum-frequency generation spectroscopy

Laboratoire de Spectroscopie Moléculaire de Surface, Facultés Universitaires Notre-Dame de la Paix, Rue de Bruxelles, 61 B-5000 Namur, Belgium; Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, 104 S. Goodwin Ave., Urbana, IL 61801, USA; Laboratoire de Chimie Théorique Appliquée, Facultés Universitaires Notre-Dame de la Paix, Rue de Bruxelles, 61 B-5000 Namur, Belgium
Applied Surface Science (Impact Factor: 2.54). 10/2004; DOI: 10.1016/j.apsusc.2004.07.025

ABSTRACT The molecular orientation in self-assembled monolayers of thiophenol (TP) on Ag(1 1 1) and of para-nitroanilino-dodecane-thiol (NAT) on Au was investigated by infrared-visible sum-frequency generation between 500 and 1500 cm−1. Ab initio calculations were performed to determine the interface nonlinear response. The combined experimental and theoretical results reveal that the S–C bond of TP is tilted 37∘ from the Ag(1 1 1) surface normal, with the aromatic ring plane perpendicular to the surface. On Au, the tilt angle of the NAT molecule stabilizes below 60∘ at the end of film growth.

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