Interfacial Analysis of n-Alkanethiol Self-assembled Monolayers on GaAs(001) by Angle-Resolved X-ray Photoelectron Spectroscopy

Abstract

The compositional schoichiometry and structural morphology of n-alkanethiol self-assembled monolayers (SAMs) formed on the GaAs(001) surface was investigated by Angle-Resolved X-ray Photoelectron Spectroscopy (ARXPS). In order to decompose high resolution ARXPS spectra, synthetic lineshape calibration was first referred to Ar-ion beam sputtered GaAs using low-asymmetry Doniach-Sunjic lineshape profiles. Following SAM formation, the As-S chemical state was located at +1.8 eV from GaAs in the As 3d region in agreement with data following GaAs passivation with inorganic sulphides, and was estimated to represent a bond fraction of 30-50% relative to the total number of S-GaAs bonds. The surface was observed to be Ga-rich, but no Ga-S interface component could be resolved. The surface density of elemental As was quantified using fractional overlayer modeling. A value of 2.9-4.2x1o(14) cm(-2) was obtained, which represents a monolayer fraction of 35-50%. Similarly, fractional overlayer modeling was used to estimate the SAM uniformity, and a value of 92% was achieved.NRC publication: Ye