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 µl. The microplasma efficiently decomposes silicon tetrachloride into atomic silicon even though the residence time is approximately 100 µs. 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.