Microplasma synthesis of tunable photoluminescent silicon nanocrystals

Abstract

An atmospheric-pressure microplasma reactor was developed for the fabricationof tunable photoluminescent silicon nanocrystals. A mixture of argon,hydrogen, and silicon tetrachloride was activated by a capacitively couplednon-equilibrium plasma generated in a capillary glass tube with a volume less than1 µl. The microplasma efficiently decomposes silicon tetrachloride intoatomic silicon even though the residence time is approximately100 µs. Supersaturated silicon vapour then leads to gas phase crystal nucleation viathree-body collision, followed by rapid termination of crystal growth due to the shortreactor residence time. Silicon nanocrystals are continuously synthesized in gasphase at room temperature. The room-temperature photoluminescence (PL) ofas-synthesized material with hydrogen concentration around 0.7–0.8% exhibitedintense visible light emission with peak intensity centred around 670 nm. The PLspectrum was blue-shifted to 520 nm with increasing hydrogen content, implyingthat partially oxidized nanocrystals of diameter less than 3 nm were synthesized.