2.2.3. Spectroscopy

Various spectroscopic techniques are needed to map the complex interactions between SAMs and the metal support [16,17]. X-ray photoelectron spectroscopy (XPS) records the element composition and the chemical state of the SAMs. The high-resolution XPS spectra of S 2p usually show a doublet at the binding energy ranging from 160 to 165 eV, attributed to the formation of the Au-S bond between alkanethiol molecules and the metal support. The functional SAM groups can be identified by Fourier-transform infrared spectroscopy (FTIR), and Raman spectroscopy can be used to detect structural changes in SAMs [68]. Surface plasmon resonance (SPR) spectroscopy is a powerful technique to measure the SAM thickness, showing a change in the tilt angle when the SAM thickness varies. Notably, the adsorption kinetics can be monitored online by SPR coupled with ellipsometry [62].
