Current fabrication of nanomaterials is facing the following two challenges: high selectivity toward specific chemical compositions or morphologies and their scalable production. This usually requires new extreme fabrication conditions beyond the conventional approaches. Thermal plasma jets are flows of partially ionized gases where gas and electron temperatures reach their equilibrium state around 10 000 K, and thus provide high fluxes of energy and chemically active species including electrons and ions with their strong spatial gradients. Such extreme environments can trigger reactions that are not thermodynamically favorable or require high activation barriers, leading to the production of materials with exotic chemical compositions or structures. Since their first operation in 1960, thermal plasma jets were soon recognized as a unique and effective medium for material transformation such as melting, vaporization, and pyrolysis and recently have also found their important applications in nanomaterial fabrication. In this Perspective, we briefly review the latest progress in the thermal plasma jet-assisted fabrication of nanomaterials from nanoparticles to low-dimensional nanostructures. A special focus is made on the advantages of the thermal plasma jet technology in nanostructure fabrication, discussing plasma properties responsible for the nanomaterial growth with high throughput, high purity, anisotropy, desired compositions, or narrow size distributions. This Perspective closes with an outlook of challenges and opportunities for further advancement in this emerging field.

Triple dc plasma torch system was used for the synthesis of nanoparticles. Three thermal plasma jets are ejected from each plasma torch and they are merged into a strong single plasma plume. Since the feedstock is injected into the jet merging area, this system is suitable for refractory nanoparticle synthesis and enable to high production yield caused by the complete evaporation is possible. In this paper, numerical simulation was carried out to analyze thermal plasma characteristic inside a reactor according to the plasma-forming gas and carrier gas compositions: Ar, Ar-H₂, and Ar-N₂ plasma; Ar, He, and N₂ carrier gas. Then, it was comparatively interpreted with the actually synthesized nanoparticle in order to understand the condensation process of nanoparticles. It was revealed that the thermal environment is able to control readily in the triple torch system by the operating condition depending on the target materials.

Aluminium nitride (AlN) nanoparticles were synthesized by using a non-transferred arc plasma. A pellet of micro-sized aluminium (Al) powders was evaporated by using an argon-nitrogen thermal plasma flame, and ammonia (NH₃) was introduced into the reactor as a reactive gas. The flow rate of NH₃ was controlled from 5 to 25 L/min at a fixed input power of 10.2 kW. In experiments, unreacted Al powder was found at low NH₃ flow rates at 5 and 10 L/min. The size and the crystallinity of the synthesized AlN particles increased with increasing flow rate of NH₃ until 20 L/min. The maximum particle size of AlN nanoparticle was about 100 nm at a 20 L/min NH₃ flow rate. At an excessive flow rate of NH₃ of 25 L/min, however, the size and the crystallinity of AlN were decreased. In order to analyze the experimental results for the thermal plasma synthesis of AlN nanoparticles, we carried out numerical simulations on the thermal plasma. The vortex flow of the thermal plasma near the Al pellet was gradually enhanced with increasing NH₃ flow rate from 10 to 20 L/min. The strength of the vortex flow, however, was decreased at the highest NH₃ flow rate of 25 L/min.