Effects of βC Substituents and Terminal Unsaturated Groups on H-Abstraction Reactions of Unsaturated Molecules on the H-Terminated Si(100)−(2×1): Density Functional Theory Investigations

Factors influencing the viability of radical chain reactions for a series of organic moieties including alkenes (R CH CH 2 ), alkynes (R−C⋮CH), aldehydes (R CH O), nitriles (R C⋮N), and imines (R CH NH) on H-terminated Si(100)−(2×1) are investigated by using density functional theory (DFT) calculations in the framework of the surface cluster model. The increase of conjugation of the β-carbon substituent (R) significantly improves the stability of radical intermediates. However, the increased conjugation of the βC substituent concomitantly decreases the exothermicity of the H-abstraction process, implying the increase of conjugation of the βC substituent does not always facilitate the radical chain reaction on the silicon surface. On the other hand, the strong Si−O and Si−N linkages formed by the aldehyde and imine molecules, respectively, stabilize radical intermediates. It is anticipated that the aldehyde and imine with the βC substituent of the alkyl group are good candidates for the preparation of thin films via Si−O and Si−N linkages on the H−terminate silicon surface via the radical chain reaction. The trend of variation of the barrier height and reaction exothermicity of H-abstraction reactions for molecules with different βC substituents is rationalized by the relative strength of the formed βC−H bond.