Atmospheric pressure plasma synthesis of monophase bismuth nanocrystals

Nanostructured single-phase metal crystals with single and well-defined crystal structures exhibit unique, predictable, and stable properties that are distinct from those of multiphase crystals. However, synthesizing such pure nanocrystals is challenging, as bismuth exhibits multiple polymorphs and crystal phases that often prevent achieving monophase crystals, especially under atmospheric pressure. In this study, we present a gas-phase synthesis method using non-equilibrium plasma to produce high-purity, monophase bismuth nanocrystals (BiNCs) at atmospheric pressure. This approach employs a solid bismuth precursor, eliminating the need for hazardous solvents and offering a safer, more environmentally friendly alternative. By controlling plasma absorbed power and incorporating hydrogen to the process gas, localized melting and surface nucleation are promoted, resulting in the formation of BiNCs with a rhombohedral crystal phase. High-resolution transmission electron microscopy, X-ray diffraction and Raman spectroscopy confirmed the crystallinity of the BiNCs, exhibiting sharp faceting in some cases. X-ray photoelectron spectroscopy and energy-dispersive X-ray spectroscopy revealed that the nanocrystals were predominantly composed of elemental bismuth with minimal surface oxidation when exposed to the atmosphere.