Aggregation of Silicon Nanocrystals Prepared by Laser Ablation in Deionized Water

Luminescent silicon nanocrystals (Si-ncs) prepared in colloidal suspensions are a potentially very important material for future optoelectronics, biology, photonics etc. We report on fabrication of luminescent Si-ncs in deionized water. The Si-ncs were formed at room temperature by two different techniques: (1) red luminescent Si-ncs by electrochemical etching and pulverizing of porous silicon films, and (2) blue luminescent Si-ncs by laser ablation with various laser fluence ranging from 0.07 to 6 mJ/pulse. Our attention is focused on aggregation and aging of Si-ncs in deionized water. It was observed that fine Si-ncs were agglomerated into well-defined spheres at low laser fluence while the shock waves inhibited their formation at higher fluence. Aging in deionized water promoted aggregation of irregular Si-ncs fragments into larger spheres with keeping their Si bulk crystallinity.