Production of atomic oxygen by a microwave plasma

The ultimate goal of our work is to study the influence of atomic oxygen on the growth mechanism of metal oxide thin films deposited by reactive magnetron sputtering as the later is still not fully understood [1-3].
In order to achieve this goal, the first step is to develop a source of atomic oxygen. We choose to use a surfaguide microwave discharge operating at 2.45 GHz and with a pressure of 1.4 Torr in order to dissociate molecular oxygen [4]. This kind of discharge already gave high dissociation rates for N2 [5-6] and CO2 [7].
In the present case, we explore the working parameters space and the dissociation efficiency is monitored by Two-photon Absorption Laser-Induced Fluorescence (TALIF). The measurements are carried out in the post-discharge. The main advantage of this technique is to give access to the ground-state population of the O atoms by using 225.6 nm photons. The fluorescence signal is detected at 845 nm [8].
In this study, the following parameters were varied systematically: (i) mean power: from 100 to 700W, (ii) Ar/O2 ratio: from 0 to 98% and (iii) duty cycle: pulse period from 1500 to 2000 µs and duty ratio from 20 to 100%.
The dissociation rate of molecular oxygen is different depending which parameters is changed, e.g., the O atom density increase as the mean power is increase. The maximum of atomic oxygen production is observed for a mean power of 400 W, a pulse period of 1500 µs, a duty ratio of 30% and Ar/O2 ratio of 90%