Exploiting electron spectroscopies to probe the structure and organization of self-assembled monolayers: a review

In this paper, we review and discuss the use of electron spectroscopies to characterize self-assembled monolayers (SAMs). The review concentrates on thiol-derived monolayers on gold with emphasis on n-alkanethiols, considered as archetypal systems. Since they are relatively simple model systems (ease of preparation, high structural order, and flexibility in the structure of chemical groups exposed to the surface), they are particularly well-suited reference samples for molecular level understanding of surface phenomena and for disclosing the potential of surface sensitive techniques. Some examples concerning silane-derived monolayers are also discussed. Many different spectroscopic techniques have been applied to characterize SAMs. Among them, electron spectroscopies, such as XPS, UPS, photoemission with synchrotron radiation, and HREELS, have been used to investigate the structure of alkanethiols on gold, and in particular, to characterize the S-Au bond, the packing density, the crystalline order, and molecular orientation. We try here to provide an overview on the structural information that can be obtained from those techniques. Damage processes induced by X-ray and electron beam are discussed in detail. (C) 2003 Elsevier B.V. All rights reserved.