Continuous-wave laser annealing of Si-rich oxide: A microscopic picture of macroscopic Si-SiO2 phase separation

We report on the first observation of the macroscopic (long-range) phase separation in Si-rich oxide SiOx(x<2) obtained by continuous-wave laser annealing of free-standing SiOx films. The effect is analyzed by a unique combination of microscopic methods (Raman, transmission, photoluminescence, and infrared spectroscopy, transmission electron microscopy, electron energy loss spectroscopy, and x-ray photoelectron spectroscopy). Three regions can be distinguished on a SiOx free-standing film after 488 nm laser annealing at intensities above similar to 10(4) W cm(-2): central spot, ring around the central spot, and pristine film outside the irradiated area. In the pristine SiOx material, small Si nanocrystals (Si-nc) (diameters of a few nanometer) are surrounded by SiO2 with an addition of residual suboxides, the Si-nc being produced by annealing at 1100 degrees C in a furnace. The central spot of the laser-annealed area (up to similar to 30 mu m wide in these experiments) is practically free of Si excess and mainly consists of amorphous SiO2. The ring around the central spot contains large spherical Si-nc (diameters up to similar to 100 nm) embedded in amorphous SiO2 without the presence of suboxides. Laser-induced temperatures in the structurally modified regions presumably exceed the Si melting temperature. The macroscopic Si-SiO2 phase separation is connected with extensive diffusion in temperature gradient leading to the Si concentration gradient. The present work demonstrates the advantages of high spatial resolution for analysis in materials research.