Structural Investigation of a Self-Assembled Monolayer of a p-Nitroanilino-Terminated Thiol

Abstract

Monolayers of an end-group-modified thiol, 4-(12-mercaptododecyl)aminonitrobenzene (p-NO2−C6H4−NH(CH2)12SH) formed by self-assembly on Au substrates, were investigated by grazing-incidence reflection absorption infrared spectroscopy (IRRAS), X-ray photoelectron spectroscopy (XPS), near-edge X-ray absorption fine structure spectroscopy (NEXAFS), and contact angle measurements. The monolayer exhibits a packing of the alkyl chains which is 10−20% less dense compared to a monolayer of docosanethiol. The orientation of the aromatic end group was determined completely by a combination of IRRAS and NEXAFS. The 1,4-axis of the benzene ring is inclined to 52° with respect to the surface normal, and the plane of the benzene ring is rotated by 58° away from the plane defined by the 1,4-axis and the surface normal. No hydrogen bonding between the p-nitroaniline moieties is detected. The hydrocarbon chains do not show a preferred orientation. The film is described by a layered structure consisting of a layer of alkane...