Density Functional Theory Study on the Oxidation of Hydrosilylated Silicon Nanocrystals

As a leading surface modification approach, hydrosilylation enables freestanding silicon nanocrystals (Si NCs) to be well dispersed in a desired medium. Although hydrosilylation-induced organic layers at the NC surface may somehow retard the oxidation of Si NCs, oxidation eventually occurs to Si NCs after relatively long time exposure to air. We now investigated the oxidation of hydrosilylated Si NCs in the frame work of density functional theory (DFT). Three oxygen configurations that may be introduced by the oxidation of a Si NC are considered. It is found that a hydrosilylated Si NC is less prone to oxidation than a fully H-passivated Si NC in the point of view of thermodynamics. At the ground state, backbond oxygen (BBO) and hydroxyl (OH) hardly change the gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of a hydrosilylated Si NC. At the excited state, the decrease in the HOMO–LUMO gap induced by the introduction of doubly bonded oxygen (DBO) is more significant than that induced by the introduction of BBO or OH. We have correlated the changes in the optical absorption (emission) of a hydrosilylated Si NC after oxidation to those of the HOMO–LUMO gap at the ground state (excited state).