High-efficiency plasma-near-passage unipolar aerosol charger for sub-10 nm particles

A plasma-near-passage unipolar aerosol charger (PNP charger) was developed for high-efficiency charging of sub-10 nm particles, and for the first time, an extrinsic charging efficiency η extr > 0.7 was demonstrated for 10 nm particles. The key feature of this device is that particles are passed for a very short time through the high ion concentration region near the plasma , enabling a large n t -product ( n is the ion concentration, t is the residence time in the charging region) while minimizing t as much as possible. Analysis based on diffusion charging theory suggested that, at 3.0 L/min, the aerosol particles were exposed to a very high effective, path-averaged ion concentration of 1.1 × 1 0 16 m −3 for only 4.2 ms. This approach reduced diffusion loss of sub-10 nm particles and enabled highly efficient charging. Furthermore, the charged particle generation rate was the highest among previous studies for all particles below 10 nm. These results have the potential to reduce material loss and improve production throughput in device fabrication processes utilizing aerosol particles.