Schematic sketch of the experimental setup with vacuum equipment for low pressure plasma processing, rf power supply and matching network, as well as the implementation of the 160.28 GHz Gaussian beam microwave interferometer and Nd:YAG laser for photodetachment.
(a) Mean line integrated electron density ( ) and negative ion density ( ) as a function of rf power in oxygen rf plasma (40 Pa, 5 sccm), measured by microwave interferometry and simultaneous laser photodetachment. 19 (b) Proportion of the negative ion density to the electron density (electronegativity).
Temporally resolved line integrated electron density in a 10 Hz (50% duty cycle) pulsed oxygen rf plasma (40 Pa, 5 sccm) at rf power of (a) 91 W (low electronegative mode) and (b) 48 W (high electronegative mode), respectively. The rf power is enabled at −50 ms and disabled at 0 ms.
Total and early afterglow behavior of the line integrated electron density of a 10 Hz (50% duty cycle) pulsed (a) oxygen and (b) argon rf plasma (91 W, 40 Pa, 5 sccm).
Total and early afterglow behavior of the line integrated electron density of a 10 Hz (50% duty cycle) pulsed oxygen plasma (24 W, 40 Pa, 5 sccm). Additionally, the exponential fit function (6) for the early afterglow phase is shown. The corresponding fit parameters are m−2, m−2, and . (acronyms in Table I )
(a) Line integrated electron density in the plasma on-phase compared with the afterglow electron peak density , (b) the difference of peak ( ) and on-phase electron density ( ) divided by the on-phase electron density, and (c) the time constant ( ) of the electron density increase in the early afterglow versus rf power variation at 40 Pa and 5 sccm in an oxygen discharge.
Fit of the re-arranged analytical functions for electrons (6) ( ) and negative ions (5) ( ) to the experimental data. Whereby, the acronyms are explained in Table I . As expected, both exponential functions have about the same time constant of 53 μs, which reveals the electron production by negative ion detachment in the early afterglow.
Comparison between the experimental (gray) and model based ( ) electron density afterglow behavior for (a) 48 W and (b) 91 W, both at gas pressure of 40 Pa. Moreover, the calculated negative ion density of ( ) and of ( ) is shown.
This table presents and explains the acronyms of this paper.
Rate coefficients for attachment, recombination, detachment, and charge transfer processes in an oxygen discharge.
Initial conditions for the electron and negative atomic oxygen ion density from measurements, and the optimized initial conditions of other densities ( , , ) as well as the ambipolar diffusion coefficient by least square fit routine of the numerical 0d model calculations.
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