Effects of methyl substitution on room-temperature chemisorption of para-xylene on Si(1 0 0)2 × 1 and modified surfaces: a thermal desorption and DFT study

The room-temperature (RT) adsorption and surface reactions of para-xylene (1,4-dimethylbenzene) on Si(1 0 0)2 × 1 have been investigated by thermal desorption spectrometry (TDS), low-energy electron diffraction (LEED), and Auger electron spectroscopy (AES). p-Xylene is found to adsorb on Si(1 0 0)2 × 1 at a saturation coverage of 0.30 monolayer without inducing discernible change to the 2 × 1 reconstruction. The chemisorption of p-xylene on the 2 × 1 surface primarily involves bonding through the phenyl group in a [4 + 2] cycloaddition configuration. Upon annealing, approximately 10% of the adspecies is found to desorb molecularly (at 350–500 K) while the majority remains on the surface after H abstraction from the methyl group (near 810 K). Condensation oligomerization of p-xylene has also been observed on Si(1 0 0)2 × 1 and could likely be enhanced upon irradiation by low-energy electrons. On sputtered and oxidized Si(1 0 0) surfaces, additional thermally induced fragmentation of the adsorbed p-xylene is found. Furthermore, large post-exposure of atomic hydrogen to the adsorbed p-xylene could not only lead to Si–C bond cleavage and the formation of alkane adspecies, but also play an important role in controlling various thermal reactions.