Microplasma synthesis of tunable photoluminescent silicon nanocrystals

An atmospheric-pressure microplasma reactor was developed for the fabrication of tunable photoluminescent silicon nanocrystals. A mixture of argon, hydrogen, and silicon tetrachloride was activated by a capacitively coupled non-equilibrium plasma generated in a capillary glass tube with a volume less than 1 mu l. The microplasma efficiently decomposes silicon tetrachloride into atomic silicon even though the residence time is approximately 100 mu s. Supersaturated silicon vapour then leads to gas phase crystal nucleation via three-body collision, followed by rapid termination of crystal growth due to the short reactor residence time. Silicon nanocrystals are continuously synthesized in gas phase at room temperature. The room-temperature photoluminescence ( PL) of as-synthesized material with hydrogen concentration around 0.7-0.8% exhibited intense visible light emission with peak intensity centred around 670 nm. The PL spectrum was blue-shifted to 520 nm with increasing hydrogen content, implying that partially oxidized nanocrystals of diameter less than 3 nm were synthesized.