Angular-resolved XANES measurements of the polar and azimuthal orientation of alkanethiols on InP(110)

This Letter describes investigations of the X-ray absorption near-edge structure of adsorbed hexadecanethiol monolayers on InP(110). The angular (azimuthal and polar)-resolved measurements reveal the substrate-dependent tilt-angle of the alkyl C–C backbone (about 34° from normal). A unique feature observed on these monolayers is the nearly complete alignment of the alkyl chains with respect to the azimuthal orientation. We suggest that this adsorbate system represents the case of a single-domain organic monolayer. We interpret this behaviour, which deviates strongly from the well-known thiol films on gold, silver or copper, in terms of structural constraints and dangling-bond-induced pre-orientation of the alkanethiol chains.