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Oxidation-Induced Redshifts in the Energy Gap of Silicon Quantum Dots

To investigate the effects of Si/O bond at the surface of silicon quantum dots (Si QDs) on the electronic properties of Si QDs, first principle calculations have been performed for Si QDs consisting of 10-87 Si atoms (0.6-1.5 nm in diameter) by using the CASTEP software package. In these calculations the Si dangling bonds on the surface of Si QDs are passivated by hydrogen atoms and oxygen. Four different oxygen configurations have been studied, they are double-bonded, backbonded, bridge-bonded and inserted, respectively. We find that a significant reduction of energy gap is caused by the presence of double-bonded oxygen, whereas for other three oxygen configurations there is just a slight reduction on energy gap. As a result, the model which contains Si=O bond is considered the most appropriate to explain the photoluminescence redshifts in oxidized porous silicon.