Raman investigation of oxidation mechanism of silicon nanowires

Raman spectra are acquired from Si nanowires (NWs) with diameters of 2–15 nm oxidized for different time durations. The Si TO optical phonon peak downshifts asymmetrically finally becoming an amorphous Si peak after a long oxidation time. The spectral changes cannot be correlated using the phonon confinement model of cylindrical NWs. Microstructural observations disclose that the strain induced by oxidization breaks the NWs into small nanocrystals. By considering the morphological transformation, we adopt the phonon confinement models on wires and dots to explain very well the Raman spectra acquired from Si NWs with different diameters.