Direct observation of S–Au bonding state of self-assembled monolayers by outermost-surface spectroscopy using metastable atom beam

Temperature dependencies of metastable atom electron spectra (MAES) and ultraviolet photoelectron spectra (UPS) were measured for 8-bromo-1-octanethiol (8BRT) SAMs prepared on Au (111) surfaces in ethanol (EtOH) and n-hexane solutions. For both 8BRT SAMs, it was found that molecules stand upright to the substrate and the film surfaces consist of Br atoms. However, we found that 8BRT SAM prepared in n-hexane solution mainly consists of physisorbed molecules and they almost desorb at 100°C, while 8BRT SAM prepared in EtOH solution involves both physisorbed and chemisorbed molecules. For the SAM prepared in EtOH solution, we observed the valence electronic states which can be ascribed to S–Au bond of the chemisorbed ones after the desorption of the physisorbed molecules.