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.