Silicon nanocrystal synthesis with the atmospheric plasma source HelixJet
The HelixJet, a plasma source operating under atmospheric pressure with RF power, was used for the synthesis of silicon nanoparticles (Si-NPs) in the context of relevance in nanomedicine, sensor technology, and nanotechnology. The HelixJet was operated with a variety of He/Ar/H2/SiH4 gas mixtures to characterize the Si-NPs in regard to their size, crystallinity, structure, and photoluminescence. Distinct varieties of nanomaterials in the size range from 3 nm to over 100 nm were synthesized depending on the operation parameters of the HelixJet. Admixture of H2 alongside high RF powers led to the formation of crystalline nanoparticles with a strong photoluminescence intensity, where the photoluminescence properties as well as the nanocrystal synthesis yield were tunable by adjustment of the synthesis parameters. Post-synthesis in-flight annealing allowed the formation of large crystalline nanoparticles. In addition, the experiments conducted in this study resulted in a design improvement of the HelixJet plasma source that extends the stability of the operating range. Furthermore, the added spatial separation of the He/H2 and He/Ar/SiH4 streams (SiH4 injection on-axis) minimizes material deposition within the HelixJet and enables continuous long-term operation.