ROOM-TEMPERATURE ADSORPTION OF BENZENE ON SI(111)7X7 BY THERMAL-DESORPTION SPECTROMETRY

The adsorption behaviour of benzene on Si(1 1 1)7 x 7 at room temperature was studied by thermal desorption spectrometry (TDS). Contrary to previous studies, benzene was found to adsorb molecularly on Si(1 1 1)7 x 7 at room temperature. A strong adsorption phase (at 350 K) was found to increase with exposure. Like the benzene adsorption geometry commonly observed on metal surfaces, this adsorption phase may correspond to a pi-bonded configuration with the ring parallel to the Si surface. A weaker desorption feature, which appeared as a broad shoulder at higher temperature, may be attributed to bonding involving defect sites on the Si surface. The adsorption on clean Si(1 1 1)7 x 7 surface was compared with that on sputtered and oxidized surfaces. Finally, the TDS profiles of a mixture of benzene and benzene-d6 showed that benzene adsorption does not involve C-H bond breaking and confirmed our proposed model of benzene adsorption on Si(1 1 1)7 x 7.