Adsorption states and thermal desorption behaviors of thiophene derivative self-assembled monolayers on Au(1 1 1)

Adsorption states and thermal desorption behavior of self-assembled monolayers (SAMs) of 2-thiophenethiol (TT) and 2-thiophenemethanethiol (TM) on Au(1 1 1) were investigated by X-ray photoelectron spectroscopy (XPS), scanning tunneling microscopy (STM), and thermal desorption spectroscopy (TDS), and were compared with those of thiophene (TP) SAMs. The S 2p XP spectra of thiophenethiol SAMs showed a variety of the adsorption states of the S atoms on the Au surface. STM imaging revealed that the surface structures of these thiophene derivative SAMs are markedly different from each other, possibly as result of a difference in the adsorption behaviors of the molecules. We found that although thiophene derivatives contain two active sulfur atoms with different chemical activities, the 2D SAM structure can be tuned by the insertion of a methylene group between the TP ring and the SH group. Decomposed desorption was observed in the TD spectra of TT and TM SAMs, as is observed in the TP SAM. Thiophenethiol SAMs show the different adsorption and desorption behaviors compared to alkanethiol SAMs.