Truly Quantitative XPS Characterization of Organic Monolayers on Silicon: Study of Alkyl and Alkoxy Monolayers on H-Si(111)

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• 作者：Xavier Wallart ; Catherine Henry de Villeneuve ; and Philippe Allongue
• 刊名：Journal of the American Chemical Society
• 出版年：2005
• 出版时间：June 1, 2005
• 年：2005
• 卷：127
• 期：21
• 页码：7871 - 7878
• 全文大小：382K
• 年卷期：v.127,no.21(June 1, 2005)
• ISSN：1520-5126

文摘

The quantitative characterization of the chemical composition (bonding at grafted and ungraftedsites, 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) requiresto 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 criticalpoint concerns the choice of photoelectron attenuation lengths (AL). This article demonstrates thatn-alkanethiol self-assembled monolayers on Au(111) can be used as a reference system to derive theeffective monolayer thickness on silicon substrates and that one may use the empirical relationshipestablished 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 assertionsand to give a complete compositional description of alkyl and alkoxy monolayers directly grafted on atomicallyflat 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 Hatoms. Moreover, the quantitative spectra analysis of satellite peaks at fixed polar angle and threeindependent angle-resolved Si2p and C1s spectra all give the same surface coverage very close to itstheoretical limit.