Steric Gating Directs Room-Temperature Hydrosilylation on Silicon Hydride Surfaces

Stable formation of Si–C bonded monolayers on hydrogen-terminated silicon at room temperature is often hindered by surface oxidation. We reported a mechanistic study of propargylamine and 1,5-hexadiene grafting on atomically flat, planar, and porous silicon surfaces. Using XPS, FTIR, AFM, and contact angle analysis, we showed that both surface roughness and molecular structure can govern reactivity and oxidation. While 1,5-hexadiene showed minimal oxidation, propargylamine induced oxidation that scales with roughness. Interestingly, on atomically flat silicon, dense Si–H groups sterically gate the surface, favoring alkyne–Si coupling. Notably, the distal amine group in grafted propargylamine promoted localized oxidation of nearby Si–H bonds through dipolar or hydrogen bonding effects—a rarely reported pathway. This revealed a new oxidation mechanism initiated by surface-bound nucleophiles. Our results highlight steric gating and distal-group effects as critical for tailoring silicon surface chemistry, with implications for molecular electronics and interface design.