Ultra-Small Bismuth Nanoparticle Synthesis from a Wire Precursor Via Atmospheric Pressure Plasma

Metal nanoparticles have shown interesting optical and electronic properties. At the nanoscale, metal nanoparticles exhibit a transition into a semiconductor behaviour and bandgap widening due to quantum confinement.1,2 Bismuth is a metal of great interest due to good thermoelectric properties,2 high density of states and potential for carrier multiplication. These are highly important attributes for optoelectronic applications. Commonly employed methods to synthesise bismuth nanostructures such nanotubes, nanorods, flakes and nanodots involve use of hazard chemicals, use of expensive vacuum equipment and/or multiple processing steps.3–5 Therefore, there is a need for a safe and low-cost synthesis method. In this regard, atmospheric pressure plasma processes are promising as they operate at ambient pressure and temperature eliminating the need of expensive vacuum equipment.

Here we present work on the synthesis of bismuth nanoparticles (Bi-NPs) by a one-step atmospheric pressure plasma process from a bismuth wire, either for direct deposition in the form of films or directly dispersed in liquid. Various plasma reactor architectures are examined to study the possible deposition conditions. The synthesised Bi-NPs are studied for their morphological, chemical, optical and electronic properties. The mean diameter of these NPs is in the range of 2-3 nm and present a degree of surface oxidation after being exposed to the atmosphere. Particle size can be finely controlled by simply regulating input power and gas flow.