Adsorption of aromatic molecules on silicon surface and deactivation of HFC catalysts

Abstract

Adsorbed State of Thiophene on Si(100)-(2×1) Surface Studied by Electron Spectroscopic Techniques and Semi-empirical Methods The adsorbed state of thiophene on Si(100)-(2×1) surface has been studied by using low-energy electron diffraction (LEED), Auger elecrton spectroscopy (AES), and ultraviolet photoelectron spectroscopy (UPS). (2×1) LEED pattern at 300 K is sustained after the saturated exposure of thiophene, and the saturation coverage is estimated to be ~0.6 by AES, suggesting that thiophene molecule is chemisorbed molecularly on the Si(100) surface most likely by bonds between C and Si atom. UPS spectrum for the chemisorbed thiophene shows not only the σ orbital shift but also σ orbital shift. Semi-empirical PM3 calculations based on the cluster model propose that the thiophene adsorbs on the Si(100)-(2×1) surface by forming di-σ bonds between C atoms of thiophene and Si atoms of the surface. TDS (thermal desorption spectroscopy) results indicate the another adsorbed states, which is due to the bonding of S atom to Si atom. A Semi-empirical Study of Chemisorbed State of Benzene on Si(100)-(2×1) The chemisorbed state of benzene on Si(100)-(2×1) has been studied using a cluster model and semi-empirical PM3 calculations. Starting from four different initial sites as the possible adsorption sites, the most stable structure is obtained as the adsorption at the pedestal site, where one benzene molecule interacts with two silicon dimers of the surface. This stable adsorption of benzene on pedestal site has not been proposed previously, but in good accord with the experimental results. The carbon atoms bonded to silicon dimers have some $sp^3$ characters, in accordance with the experimental results of high resolution electron energy loss spectroscopy, while the others preserve the hybridization state in a free molecule. In addition, the saturation coverage of benzene predicted from the adsorbed state is in agreement with the experimental results. Deactivation...