Reactions of substituted aromatic hydrocarbons with the Si(001) surface

The interactions of toluene, para-xylene, meta-xylene and ortho-xylene with the (001) surface of silicon have been investigated using Fourier-transfor m infrared spectroscopy. Infrared spectra show that these methyl-substitute d aromatic hydrocarbons are chemisorbed and oriented on the Si(001) surface at both 110 and 300 K. Peaks in the Si-H stretching region indicate that s ome dissociation occurs upon adsorption. Comparisons of infrared spectra of these molecules with deuterated and nondeuterated methyl groups reveal tha t the major source of decomposition is likely from C-H cleavage of the subs tituent groups, leaving the ring intact. Additionally, the striking similar ity of the infrared spectra of benzene, toluene and the xylene isomers sugg ests that the methyl-substituted aromatic rings interact with the Si(001) s urface in much the same way as benzene. Differences in relative peak intens ity point to the possibility that the methyl substituent groups may steer t he ring into different ratios of specific bonding geometries. (C) 2000 Amer ican Vacuum Society. [S0734-2101(00)10404-X].