Photo-modification and synthesis of semiconductor nanocrystals

Both photo-oxidation and photosynthesis manifest a strong interaction between nanoparticles and photons due to the large surface area-to-volume ratio. The final sizes of the semiconductor nanocrystals are determined by the photon energy during these phenomena. The photosynthesis is demonstrated in a Si-rich oxide and is similar to thermal synthesis, which involves the decomposition of SiOx into Si and SiO2, that is well known and often employed to form Si or Ge nanocrystals embedded in SiO2 by annealing SiOx at high temperature. However, photosynthesis is much faster, and allows the low-temperature growth of Si nanocrystals and is found to be pronounced in the SiO nanopowder, which is made by thermal CVD using SiH4 and O2. The minimum laser power required for the photosynthesis in the SiO nanopowder is much lower than in the Si-rich oxide formed by the co-sputtering of Si and SiO2. This is attributed to the weak bond strength of Si–Si and Si–O in the SiO nanopowder. Photosynthesis, which can control the size and position of Si nanocrystals, is a novel nanofabrication technique making the best use of the strong interaction between photons and nanoparticles.