Spatiotemporal evolution behaviors of micro Dielectric barrier discharge at different gas pressures are observed, and the formation mechanism is discussed. At p ≤ 1 kPa, the microplasma presents evident propagation perpendicular to the applied field. However, at p ≥ 50 kPa, some punctiform patterns are distributed on the glass dielectric surface randomly, indicating the existence of filamentary channels across the gas gap. At 1 kPa p 50 kPa, microplasma is almost uniformly dispersed in the microcavity. Furthermore, the simulated spatiotemporal distribution of electron density at p = 0.5 kPa and 90 kPa also demonstrates the different evolution behaviors of microplasma at different pressures. At low pressures, secondary electrons released from the dielectric surface induced by ion bombardment (γi) play a dominant role in the development of microplasma. The movement of ions is restricted by the local electric field, which leads to the propagation perpendicular to the applied field. However, at high pressures, the effects of secondary electrons stimulated by metastable atoms (γm) and photons (γp) become significant. The development of metastable atoms and photons would not be confined by the electric field, which means the discharge positions are distributed randomly in the gas space. In addition, with increasing pressure, the Auger neutralization and Auger de-excitation will also be important to induce secondary electron emission. At intermediate pressures, the sustainment and evolution of microplasma would be governed by a mix of the above-mentioned factors; therefore, the propagation and filaments both are weakened, and the microplasma is uniformly distributed in the microcavity. This work allows future application designers to possibly select a pressure regime to tailor the plasma for uniformity, localization, or directed transport, and enhances the understanding of Townsend-type microdischarges by showing that “pattern formation” is not a monolithic phenomenon but can arise from different primary mechanisms depending on the pressure.
Ma et al. (Thu,) studied this question.