Capacitively coupled radio-frequency discharges in nitrogen at low pressures
AuthorsAlves, Luís Lemos
Marques, Luís S A
Pintassilgo, Carlos D.
KAUST DepartmentClean Combustion Research Center
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AbstractThis paper uses experiments and modelling to study capacitively coupled radio-frequency (rf) discharges in pure nitrogen, at 13.56MHz frequency, 0.11 mbar pressures and 230W coupled powers. Experiments performed on two similar (not twin) setups, existing in the LATMOS and the GREMI laboratories, include electrical and optical emission spectroscopy (OES) measurements. Electrical measurements give the rf-applied and the direct-current-self-bias voltages, the effective power coupled to the plasma and the average electron density. OES diagnostics measure the intensities of radiative transitions with the nitrogen second-positive and first-negative systems, and with the 811.5 nm atomic line of argon (present as an actinometer). Simulations use a hybrid code that couples a two-dimensional time-dependent fluid module, describing the dynamics of the charged particles (electrons and positive ions N 2 + and N 4 + ), and a zero-dimensional kinetic module, describing the production and destruction of nitrogen (atomic and molecular) neutral species. The coupling between these modules adopts the local mean energy approximation to define spacetime-dependent electron parameters for the fluid module and to work out spacetime-averaged rates for the kinetic module. The model gives general good predictions for the self-bias voltage and for the intensities of radiative transitions (both average and spatially resolved), underestimating the electron density by a factor of 34. © 2012 IOP Publishing Ltd.
SponsorsThis work is supported by a PICS Cooperation Program, financed by the Portuguese Foundation for Science and Technology (FCT) and by the Centre National de la Recherche Scientifique (CNRS). The calculations were performed on SeARCH (Services & Advanced Computing with HTC/HPC) funded by FEDER through the COMPETE program and by the Portuguese FCT under contract CONC-REEQ/443/EEI/2005. Et Es-sebbar thanks the ANR programme (ANR-09-JCJC-0038 contract) for his Post-Doctoral grant.