Research On Preparation Of Silicon Nanocrystallites By Pulsed-Laser Ablation In Liquid And Their Photoluminescent Properties

In this thesis, Si nanocrystals (Si-ncs) with different morphologies and structures were obtained by pulsed laser ablation using different target materials and laser parameters. This work investigates the theory and process of the formation of Si-ncs, and clarifies the influence of the size, composition, structure and surface states of Si-ncs on the photoluminescence (PL) properties. The main conclusions are as below:(1) Nonagglomerated Si-ncs were synthesized by the ablation of microsecond-pulse laser on Si wafer in water. The mean size of Si-ncs was calculated under 5nm, and the size increases with the laser width. In this case, Si-ncs have the fcc structure rather than the diamond structure. It was found that the luminescence is attributed to the quantum confinement effect and surface states.(2) Si-ncs were perpared by using Si powder as target. The mean size of the Si-ncs increases along with the laser width. Unlike the fcc-Si obtained from Si wafer, here the Si-ncs shows diamond structure. Visible light emissions were detected from the suspension of Si-ncs. The luminescence is attributed to the quantum confinement effect and surface state, and the peaks show redshift with the increase of the laser width.(3) Disk-like Si-ncs were synthesized by the phase separation of SiO under laser ablation. The formations of disk-like Si-ncs are attributed to the oxide assisted growth of Si nanocrystals from the SiO decomposition. The diameter of these specific Si nanoparticles is range from 10 nm to 200 nm, and the thickness is in nano range. The Si-ncs shows a diamond structure. Visible light emissions were detected from the suspension of Si-ncs.