Spatially and Temporally Resolved Atomic Oxygen Densities in a Micro Cavity Plasma Array

Micro cavity plasma arrays have numerous applications, such as the treatment of volatile organic compounds (VOCs) or the generation of ozone. In recent years, the focus has also shifted to plasma catalysis [1] , in which catalytic surfaces are combined with plasmas. The key to all of these applications is the generation of reactive species such as atomic oxygen within the plasma. Typically, atomic oxygen densities can be measured by laser spectroscopic methods. In the case of the micro plasma array [2] , which consists of thousands of cavities with a diameter between 50-200 µm, optical access is limited. For this reason, an optical emission spectroscopy (OES) approach, energy resolved actinometry (ERA) [3] , is used. 2D resolved measurements can be performed by using an ICCD camera in combination with a tuneable bandpass filter (550-1000nm). The discharge is operated in helium with an oxygen admixture of 0.1%. An argon admixture of 0.05% is used as actinometer gas. The triangular excitation voltage between amplitudes of 400-800V is varied at a frequency of 15 kHz. The atomic oxygen density per cavity increases with power. Very high dissociation degrees up to nearly complete dissociation are observed. Time resolved measurements show significant differences in oxygen density between the increasing potential phase and the decreasing potential phase.