Kelvin probe force microscopy studies on the influence of hydrocarbon chain length on 1-alkene self-assembled monolayers on Si (111)

Abstract

Surface potential contrasts were measured for n-type silicon (111) modified with 1-alkene self-assembled monolayers (SAMs) of varying hydrocarbon chain lengths (n = 10–20) using Kelvin probe force microscopy (KPFM). Micropatterned SAMs were used in KPFM analysis, with hexadecyl SAM acting as a reference to avoid possible variations due to different KPFM cantilever tips used for analysis. Micropatterning was performed via vacuum ultraviolet photolithography at λ = 172 nm. Individual samples were also analyzed by ellipsometry, X-ray photoelectron spectroscopy, static water contact angle tests and atomic force microscopy to determine SAM quality. Surface potential changes observed between the different SAMs were attributed to differences in the dipole moment of the precursor molecules, changes in SAM dielectric properties due to differences in molecular packing, and varying oxygen content at the surface.