Separation of Micron-Sized Dust Particles Using a Dusty Plasma Ratchet

The Feynman ratchet possesses the capability to convert random perturbations into directional transport of particles. The transport velocities of particles strongly depend on their sizes. Therefore, under appropriate parameter conditions, bi-dispersed particles can transport in opposite directions, resulting in particle separation. Here, exploiting the distinct responses of particles with different sizes to the system, we achieve the separation of micron-sized bi-dispersed dust particles in a designed dusty plasma ratchet both experimentally and numerically. To reveal the underlying mechanism of particle separation, we construct a three-dimensional model and perform Langevin simulations for the particle separation. Numerical simulations demonstrate that the charged dust particles undergo an asymmetric ratchet potential which governs the directional transport of dust particles along the saw channel. Importantly, the bi-dispersed dust particles are suspended at different heights within the saw channel and experience distinctive ratchet potentials with totally opposite orientations in asymmetry. Therefore, the two sizes of dust particles can flow along the saw channel in opposite directions, leading to the effective separation of dust particles. Significantly, this height-dependent transport mechanisms of dust particles uncovered here could account for the frequently observed transport phenomena of dust particles, such as the formation of dust cloud above wafer during plasma etching and the occurrence of dust vortices near the corners of chambers.