Thermally Induced Desulfurization: Structural Transformation of Thiophene on the Si(100) Surface

We investigated the bonding structures of thiophene molecules adsorbed on the Si(100)-2 x 1 surface at 300 K and its evolution upon annealing by employing core level photoemission spectroscopy, near-edge X-ray absorption fine structure (NEXAFS), and ab initio calculations. The C 1s and S 2p core-level spectra measured at three different temperatures, 300, 350, and 400 K, are consistently interpreted in terms of the following structures suggested by theoretical calculations: the 2,3- and 2,5-dihydrothiophene (DHT), twisted 2,3- and 2,5-DHT, tetrahydrothiophene (THT), twisted THT, and the desulfurization and twisted desulfurization where the sulfur atom is dissociated from the thiophene ring. We find significantly enhanced desulfurization of thiophene molecules by mild thermal annealing, which is explained by new pathways between desulfurization and other structures.