Structure of Self-Assembled Monolayers of Alkylsiloxanes on Silicon: A Comparison of Results from Ellipsometry and Low-Angle X-ray Reflectivity

摘要

The thicknesses of alkylsiloxane monolayers on silicon silicon dioxide substrates have been measured using ellipsometry and low angle X ray reflection. Thicknesses measured by the two methods differ by 2.2 A (rms) for alkyl chains of 10 - 18 carbon atoms have a maximum difference of 4.2 A. Ellipsometry systematically yields a larger thickness. This discrepancy may result from differences between the two techniques in their sensitivity to the structure of the interface between silicon dioxide and the alkylsiloxane monolayer. The X-ray reflectivity measurements provide evidence that these organic monolayers do not build up as island structures and demonstrate that the approximate area projected by each alkyl group in the plane of the monolayer is approx. 20 + or - 4 A2. Keywords: Self assembly, Monolayer, Alkysiloxane, Ellipsometry, X ray reflectivity, Thickness, Alkyl compounds, Siloxanes, Silanes. (mjm)