Eur. Phys. J. Appl. Phys. 45, 11002 (2009) DOI: 10.1051/epjap:2008198 T HE EUROPEAN P HYSICAL JOURNAL APPLIED PHYSICS Diagnostic of 13.56 MHz RF sustained Ar–N 2 plasma by optical emission spectroscopy F.U. Khan 1 , N.U. Rehman 2 , S. Naseer 3 , M.A. Naveed 2 , A. Qayyum 4 , N.A.D. Khattak 1 , and M. Zakaullah 2, a 1 Department of Physics, Gomal University, D.I. Khan, Pakistan 2 Department of Physics, Quaid-i-Azam University, 45320 Islamabad, Pakistan 3 Department of Physics, Peshawar University, Peshawar, Pakistan 4 National Tokamak Fusion Program, 3329 Islamabad, Pakistan Received: 8 January 2008 / Received in final form: 10 July 2008 / Accepted: 1st November 2008 Published online: 15 January 2009 – c  EDP Sciences Abstract. Optical Emission Spectroscopy (OES) is used to investigate the effect of argon gas mixing on the electron temperature, the degree of nitrogen dissociation and the active species concentration in a 13.56 MHz radio frequency (RF) sustained nitrogen plasma. The electron temperature is determined from Ar-I emission line intensities by using the modified Boltzmann’s plot method and is found to be increased with argon mixing in nitrogen plasma. The concentration of active species N2(C 3 Πu ) and N + 2 (B 2 Σ + u ) is monitored in terms of the emission intensities of nitrogen (0–0) bands of the second positive and the first negative systems respectively. The concentration of N2(C 3 Πu ) active species along with the degree of N2-dissociation is appreciably enhanced by argon mixing signifying the role of argon metastables in the excitation and dissociation processes. PACS. 52.80.Pi High-frequency and RF discharges – 52.70.Kz Optical (ultraviolet, visible, infrared) mea- surements – 81.65.Lp Surface hardening: nitridation, carburization, carbonitridation – 51.50.+v Electrical properties 1 Introduction There is a growing interest in the characterization of ni- trogen plasmas owing to their potential applications in materials processing such as nitriding of various materials especially iron-based alloys to improve their surface prop- erties including hardness, wear and corrosion resistance and fatigue strength [1,2]. During the nitriding process, the active species of nitrogen generated by an electric dis- charge facilitate the plasma-material interaction by trans- porting momentum and energy. To achieve a better nitrid- ing of the material surface, it is essential to optimize the production of active species in the discharge [3]. Optical emission spectroscopy (OES) is one of the ef- fective tools to characterize the different parameters of the plasma like electron temperature, electron energy distribu- tions functions (EEDFs), active species concentration and dissociation of molecules in the discharge [4]. It also pro- vides information regarding the sub-processes contribut- ing to excitation, ionization and dissociation of plasma species. During the excitation process, electron impact promotes a small fraction of plasma species into upper electronic states that decay and emit characteristic light in the visible and near ultra violet region. Therefore, the a e-mail: mzakaullah@qau.edu.pk electron temperature is one of the important parameters of the plasma that influences the production of the active species through inelastic collisions of electrons [5]. The metastable states of atoms and molecules also play a significant role in the excitation and ionization of plasma species owing to their ability to accumulate a significant amount of energy, which can be effective in various chemi- cal and physical processes [6]. Therefore, addition of inert gases such as argon, neon and helium in nitrogen plasma enhances the electron temperature, electron number den- sity, concentration of active species through Penning ex- citation and ionization in the plasma [7–10]. The present work is aimed at the investigation of the changes induced in the electron temperature and the ac- tive species concentration with the argon mixing in the nitrogen plasma. The nitrogen molecular dissociation and its dependence on discharge conditions are also studied by monitoring the emission intensities of selected radia- tive levels of atomic and the molecular nitrogen. Based on the measurements, plasma processing conditions can be optimized in terms of active species concentrations which are regarded important for nitriding. This work is the ex- tension of previous work [11], in which a 50 Hz pulsating dc discharge was investigated for the electron tempera- ture and the active species concentration as a function of input power and filling pressure. In the present work a Article published by EDP Sciences