Determination of locations of sulfur, amide-nitrogen and azo-nitrogen in self-assembled monolayers of alkanethiols and azobenzenethiols on Au (111) and GaAs (100) by angle-resolved X-ray photoelectron spectroscopy

Angle-resolved X-ray photoelectron spectroscopy (ARXPS) was employed to study the surface structure of self-assembled monolayers (SAMs) prepared by alkanethiols and azobenzenethiols on Au (111) and GaAs (100). The thickness of these SAMs was determined as the vertical distance between sulfur atoms at the interface of thiols and substrates and the surface of SAMs. Molecular tilt angles were calculated based upon molecular length at a fully extended configuration. The thickness difference caused by the addition of CH₂ units was detected as 1 angstrom per CH₂ unit in a series of SAMs formed by azobenzenethiolates. In addition, the azo and amide nitrogen atoms in these molecules were distinguished from each other based upon their chemical states and locations on the substrate surface.