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 ult raviolet photoelectron spectra (UPS) were measured for 8-bromo-1-octanethio l (8BRT) SAMs prepared on Au (1 1 1) surfaces in ethanol (EtOH) and n-hexan e 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 fou nd that 8BRT SAM prepared in n-hexane solution mainly consists of physisorb ed molecules and they almost desorb at 100 degreesC, while 8BRT SAM prepare d in EtOH solution involves both physisorbed and chemisorbed molecules. For the SAM prepared in EtOH solution, we observed the valence electronic stat es which can be ascribed to S-Au bond of the chemisorbed ones after the des orption of the physisorbed molecules. (C) 2001 Elsevier Science B.V. All ri ghts reserved.