Characterization of the Surface to Thiol Bonding in Self-Assembled Monolayer Films of C₁₂H₂₅SH on InP(100) by Angle-Resolved X-ray Photoelectron Spectroscopy

Angle-resolved X-ray photoelectron spectroscopy (ARXPS) was used to characterize the bonding of alkanethiols to n-InP surfaces and to measure the monolayer thickness. A careful comparison of the angle-dependent spectra for three different sample preparations (oxidized InP(100), HF-etched InP(100), and HF-etched InP(100) with a self-assembled monolayer of C₁₂H₂₅SH) shows that the sulfur binds to In atoms on the surface. Comparison of the angle-dependence of the intensity ratios for the In 3d_5/2 core level of InP with the self-assembled monolayer (SAM) to that of sputtered InP provides a thickness for the SAM of 14 ± 4 Å, corresponding to alkane chains at a tilt angle of 44 ± 16° from the surface normal.