| Résumé | Diaryl and dialkyl chalcogenide molecules serve as convenient precursors to silicon–chalcogenide bonds, ≡Si–E–R groups, on silicon surfaces, where E = S, Se, and Te. The 254 nm light, coupled with gentle heating to melt and liquefy the chalcogenide precursors for 15 min, enables formation of the resulting silicon–chalcogenide bonds. R groups analyzed comprise a long alkyl chain, octadecyl, and a phenyl group. Quantification of substitution levels of the silicon-hydride on the starting ≡Si(111)–H surface by an organochalcogen was determined by XPS, using the chalcogenide linker atom as the atomic label, where average substitution levels of ∼15% were found for all ≡Si–E–Ph groups. These measured substitution levels were found to agree with 2-dimensional stochastic simulations assuming kinetically irreversible silicon–chalcogen bond formation. Due to the small bond angle about the chalcogen atom, the phenyl rings in the case of ≡Si–E–Ph effectively block otherwise reactive Si–H bonds, leading to the observed lower substitution levels. The linear aliphatic dialkyl disulfide version, ≡Si–S–n-octadecyl, is less limited by steric blocking of surface Si–H groups as is the case with a phenyl group and has a much higher substitution level of ∼29%. The series, ≡Si–S–Ph, ≡Si–Se–Ph, and ≡Si–Te–Ph, was prepared to determine the effect of chalcogenide substitution on the electronics of the silicon, including surface dipoles and work function. The electronics did not change significantly from the starting ≡Si–H surface, which may be due to the low level of substitution that is believed to be caused by steric blocking by the phenyl groups, as well as the relatively similar electronegativities of these elements relative to silicon. |
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