Effect of the dc field on the near-surface plasma of a highly nonuniform microwave discharge
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MA–SURFACE INTERACTION
Effect of the dc Field on the NearSurface Plasma of a Highly Nonuniform Microwave Discharge Yu. A. Lebedev and E. V. Yusupova Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, Leninskii pr. 29, Moscow, 119991 Russia Received January 16, 2012; in final form, March 1, 2012
Abstract—The effect of the dc electric field on the nearsurface plasma of an electrode microwave discharge at pressures of 1–5 Torr was studied by the emission spectroscopy method. It is shown that the dc field weakly affects the vibrational distribution of nitrogen molecules in the C3Πu state, but changes the structure of the nearsurface plasma (shifting the intensity maxima of the emission bands) and the strength of the microwave field near the electrode surface. It is also found that the ratio between the intensities of bands of different sequences of the second positive system of nitrogen radiated from the same state depends on the position along the discharge axis. DOI: 10.1134/S1063780X1208017X
1. INTRODUCTION Interest in studies of nonequilibrium lowtempera ture plasmas created by microwave radiation near var ious surfaces is motivated by several reasons. Such plasmas occur, in particular, when processing surfaces by a nonequilibrium chemically active plasma (including the growth of diamonds and nanotubes; see, e.g., [1, 2]) and in the problems of plasma aerody namics, when the discharge is created near the surface of a body moving in the atmosphere in order to alter its aerodynamic characteristics (see, e.g., [3, 4]). It is obvious that the development of new methods to control plasma parameters is very important. These parameters can be controlled, e.g., by varying the gas pressure and/or applying different plasmaforming gases or different gas additives. An efficient method is also the application of external fields, in particular, a dc electric field. This method necessitates investiga tions of discharges under the combined action of microwave radiation and a dc electric field. In this work, the nearelectrode plasma of an electrode microwave discharge (EMD) [5–7] in nitrogen at pressures of 1–5 Torr in the presence of an external dc electric field of different polarity was studied by the emission spectroscopy method. Interest in studies of EMDs superimposed by a dc field is also stimulated by the possibility of using an EMD as a plasma cathode in a dc discharge [8]. 2. EXPERIMENTAL SETUP AND DIAGNOSTIC TECHNIQUES The experiments were carried out at the EMR3 setup (see [5–8] for details). A schematic of the setup is shown in Fig. 1. The discharge chamber was a
15cmdiameter stainlesssteel cylinder. The antenna electrode (a 5mmdiameter copper cylindrical tube) was inserted into the discharge chamber from above through a vacuum seal. In the standard EMD operat ing mode, the antenna electrode was galvanically con nected to the grounded chamber and had the same potential as the chamber. In these experiments, the electrode was insulated from the chamber by insulator 2. In order
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