Nanoparticle synthesis using the atmospheric pressure plasma source HelixJet
Nanoparticles hold unique properties such as high surface-to-volume ratios or quantum confinement effects, making them viable for countless applications in various scientific fields such as biomedicine, catalysis, detectors and sensing, opto-electronics or energy storage and harvesting.
This thesis focuses on the synthesis and surface modification of silicon and metal nanoparticles, as well as multi-elemental core-shell or Janus particles using atmospheric plasma jets as a tool. Both a bottom-up approach in the form of gas phase synthesis using the reactive gas silane as well as a top-down approach using solid state source materials are demonstrated.
As a first step, the HelixJet atmospheric plasma source is modified for a long term operation at high admixtures of reactive gases. Particles synthesized in the gas phase are analyzed using a Scanning Mobility Particle Sizer (SMPS) and their crystallographic structure is made visible using Transmission Electron Microscopy (TEM). For a suitable set of parameters, silicon nanocrystals with diameters in the range of 3 to 7 nanometeres are synthesized. Measurements reveal a strong photoluminescence (PL) intensity in the visible red spectral region for these silicon nanocrystals.
The combination of silicon particle synthesis and a fly-through annealing stage results in the formation of Janus particles with a special half-sphere structure containing a silicon-manganese alloy. When introducing a source metal wire into the middle axis of this jet, metal particles are produced even from high melting point metals such as tungsten.
The influence of plasma parameters, such as power and gas flow, on the particle morphology and crystal structure is investigated using transmission electron microscopy, revealing that the average size of the tungsten nanocrystals can be tuned.
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