Modification and chemical transformation of Si(1 1 1) surface

Modification of hydrogen-terminated Si(1 1 1) surfaces by hydrosilylation of activated alkenes and further chemical transformation of the modified surfaces is reported. A Si(1 1 1)–H surface was reacted with activated alkenes such as acrylate esters, acrylonitrile, and maleic anhydride under mild conditions to give modified surfaces with terminal functional groups. A modified surface with a terminal ester group was reduced by LiAlH4 to give a hydroxy-terminated surface, and the hydroxy-terminated surface was transformed to a bromo-terminated surface. XPS analysis revealed that the brominated surface (triple bond; length of mdashSi(1 1 1)–CH2CH2CH2Br) had 32% coverage with the 3-bromopropyl group. Ester and amide formation reactions were carried out on hydroxy- and carboxy-terminated Si surfaces by reaction with tert-butoxycarbonyl glycine, glycine tert-butyl ester, 2,2,2-trifluoroethanol and 4-trifluoromethylbenzyl alcohol in the presence of carbodiimide. XPS characterization indicated that the esters and amide were successfully formed with coverage ranging from 16% to 58%. Coverage ratios of octadecyl ester modified surfaces were also estimated by combination of surface reduction and gas chromatography analysis to be 25–35%.