Surface potential and local conductivity measurements of micropatterned aromatic monolayers covalently attached to n-Si(111) via Si-C and Si-O bonds

Abstract

The surface potentials and local conductivity of self-assembled monolayers (SAMs) formed using aromatic molecules covalently bonded to n-type silicon (111) via Si–C and Si–O bonds were measured using Kelvin probe force microscopy (KPFM) and conductive AFM (CAFM). Surface potential measurements were done using micropatterned SAMs with hexadecyl SAM as a reference to eliminate surface potential variations due to the cantilever tips. Micropatterning was conducted via vacuum ultraviolet photolithography at λ = 172 nm. Ellipsometry, X-ray photoelectron spectroscopy, static water contact angle and atomic force microscopy tests show that the aromatic SAMs were well-organized despite the short molecular lengths of the precursors. KPFM results show that Si–C bonded SAMs have higher surface potentials compared to Si–O SAMs, which is in agreement with dipole moments estimated by Molecular Orbital Package semi-empirical computations. CAFM scans showed conductive domains for the aromatic SAM regions, and Si–O SAMs exhibited a higher current than Si–C SAMs.