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 stu dy the surface structure of self-assembled monolayers (SAMs) prepared by al kanethiols and azobenzenethiols on Au (111) and GaAs (100). The thickness o f these SAMs was determined as the vertical distance between sulfur atoms a t the interface of thiols and substrates and the surface of SAMs. Molecular tilt angles were calculated based upon molecular length at a fully extende d configuration. The thickness difference caused by the addition of CH2 uni ts was detected as 1 Angstrom per CH2 unit in a series of SAMs formed by az obenzenethiolates. In addition, the mo and amide nitrogen atoms in these mo lecules were distinguished from each other based upon their chemical states and locations on the substrate surface. (C) 1999 Elsevier Science B.V. All rights reserved.