First-Principles Study on the Surface Chemistry of 1.4 nm Silicon Nanocrystals: Case of Hydrosilylation

As a leading surface-modification approach, hydrosilylation is critical to the practical use of silicon nanocrystals (Si NCs). However, the effect of hydrosilylation-induced surface chemistry on the electronic and optical properties of Si NCs is rather limitedly understood. By means of first-principles calculation at 0 K we show thermodynamically favored surface bonding for hydrosilylation of 1.4 nm Si NCs and the relative reactivity of alkenes and alkynes. The optical properties of hydrosilylated Si NCs are elucidated on the basis of their energy-level schemes and radiative recombination rates. The chain length (up to C12) of ligands hardly affects the absorption and emission of Si NCs. The increase of the surface coverage (up to 29%) of ligands causes the absorption onset to slightly redshift, hardly rendering changes to the light emission from Si NCs. As an added advantage, hydrosilylation may lead to enhanced light emission from Si NCs. Radiative recombination is very sensitive to surface chemistry for Si NCs. Only the coexistence of C=C and functional groups at the NC surface significantly modifies the electronic structures and optical behavior of Si NCs.