title: Truly quantitative XPS characterization of organic monolayers on silicon: study of alkyl and alkoxy monolayers on H-Si(111).
abstract: The quantitative characterization of the chemical composition (bonding at grafted and ungrafted sites, surface coverage) is a key issue for the application of silicon-organic monolayer hybrid interfaces. The primary purpose of this article is to demonstrate that X-ray photoelectron spectroscopy (XPS) requires to be truly quantitative to deal with two main questions. The first one is accounting for X-ray photodiffraction (XPD), a well-known phenomenon that is responsible for azimuthal variations of the XPS signal intensity. A simple procedure is proposed to account for XPD in angle-resolved measurements. The second critical point concerns the choice of photoelectron attenuation lengths (AL). This article demonstrates that n-alkanethiol self-assembled monolayers on Au(111) can be used as a reference system to derive the effective monolayer thickness on silicon substrates and that one may use the empirical relationship established by Laibinis and co-workers to calculate the relevant ALs (Laibinis, P. E.; Bain, C. D.; Whitesides, G. M. J. Phys. Chem. 1991, 95, 7017). A self-consistent approach is presented to justify the above assertions and to give a complete compositional description of alkyl and alkoxy monolayers directly grafted on atomically flat H-Si(111) surfaces. Direct evidences are provided that a Si-C and a Si-O-C linkage is formed, respectively, after reaction with decene and decanol and that the ungrafted sites remain saturated with H atoms. Moreover, the quantitative spectra analysis of satellite peaks at fixed polar angle and three independent angle-resolved Si2p and C1s spectra all give the same surface coverage very close to its theoretical limit.
authors.affiliation: Institut d'Electronique, de Microélectronique et de Nanotechnologie, CNRS-UMR 8520, Avenue Poincaré, B.P. 69, 59652 Villeneuve d'Ascq Cedex, France. Xavier.Wallart@iemn.univ-lille1.fr
authors.forename: Xavier
authors.initials: X
authors.lastname: Wallart
authors.forename: Catherine
authors.initials: C
authors.lastname: Henry de Villeneuve
authors.forename: Philippe
authors.initials: P
authors.lastname: Allongue