Morphology-controlled atmospheric pressure plasma synthesis of zinc oxide nanoparticles for piezoelectric sensors

Zinc oxide nanoparticles, especially those with a high aspect ratio (i. e., nanorods and nanowires), are of great interest for many applications as they are piezoelectric, photocatalytic and antimicrobial. In the present study, a plasma flight-thru synthesis method was developed that allows controlling the particle size and shape of the zinc oxide nanoparticles. In a direct current thermal plasma reactor operated at atmospheric pressure, zinc powder injected into the plasma jet was molten, vaporized and oxidized, which allowed growing zinc oxide nanoparticles. The particle spectrum ranged from small nanospheres to nanorods, nanowires and multipodic nanoparticles such as tetrapods. The influence of the oxygen rate and the plasma power (correlated to the discharge current) on the particle morphology was studied, and the feasibility of the nanowire-like particles as piezoelectric sensor material was investigated. Piezoelectric test sensors, equipped with the plasma-synthesized zinc oxide nanowires, successfully responded to mechanical stimulation after poling.