Autor(es):
Marques, L. 
; Alves, L. L. ; Pintassilgo, C. D. ; Carrasco, N. ; Boufendi, L. ; Cernogora, G.
Data: 2013
Identificador Persistente: http://hdl.handle.net/1822/26866
Origem: RepositóriUM - Universidade do Minho
Descrição
Capacitively coupled radio-frequency discharges (ccrf) in nitrogen mixtures are frequently used for
the processing, modification and functionalization of different kinds of materials. Although nitrogen
plasmas have been studied for many years, and despite their growing interest in applications, there is
only partial knowledge about ccrf nitrogen plasmas.
This paper uses experiments and modelling to study ccrf discharges in pure nitrogen, at 13.56 MHz
frequency, 0.1–1 mbar pressures and 2–30 W coupled powers [1]. 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).
In the particular case of non-equilibrium ccrf discharges in nitrogen, a self-consistent modeling
strategy must account for the interplay between the transport of particles, in the presence of density
gradients and the rf field, and their production/destruction due to kinetic mechanisms involving both
electrons and heavy species. Simulations use a hybrid code that couples a two-dimensional timedependent
fluid module [2], describing the dynamics of the charged particles (electrons and positive
ions N2
+ and N4
+), and a zero-dimensional kinetic module, describing the production and destruction
of nitrogen (atomic and molecular) neutral species [3]. The coupling between these modules adopts
the local mean energy approximation to define space–time-dependent electron parameters for the fluid
module and to work out space–time-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 3–4.
