Surface characterization and electrochemical properties of alkyl, fluorinated alkyl, and alkoxy monolayers on silicon

Alkyl and fluorinated alkyl monolayers covalently bonded to the silicon (11 1) surface have been prepared by UV illumination of the H-Si(111) surface w hile immersed in a solution of olefin precursor under high vacuum. An alkox y monolayer covalently bonded to the silicon (111) surface is formed by the reaction of the H-Si(111) surface with a heated solution of primary alcoho l precursors under high vacuum. Ellipsometry, X-ray photoelectron spectrosc opy, and atomic force microscopy are used to characterize the three monolay ers. The alkyl monolayer is measured to have the largest number of organic adsorbates per surface silicon atom. Properties of the monolayers on the si licon surface are probed by cyclic voltammetry. The hydrophobic alkyl monol ayer slows the oxidation of the silicon surface by water. The three monolay ers also slow the rate of electron transfer across the silicon-electrolyte interface by acting as a tunneling barrier. The alkyl monolayer in tetrahyd rofuran exhibits a large and reproducible blocking of the electron transfer .