Recombination coefficient of Cl atoms on Al2O3 walls determined by

Two-photon laser-induced fluorescence (TALIF) was used to monitor the decay of Cl atom density in the afterglow of an inductively-coupled plasma in pure Cl2 gas. The surface recombination coefficient, γ, at the reactor surfaces (anodized aluminium and alumina window) was deduced from the decay rate several ms into the afterglow when the gas temperature has cooled to the wall temperature, when a simple diffusion model becomes valid. The values obtained vary from 0.05 to 0.15 depending on gas pressure and RF power. The value of γ also increased significantly as the Cl2 flow rate was reduced, which we attribute to the effect of inevitable small air leaks. This is validated by adding a small flow of O2, and found that the addition of 0.5 % O2 to Cl2 can more than double the Cl surface recombination coefficient 1