Influence of nitrogen impurities on the formation of active species in Ar-O2 plasmas V. Guerra, K. Kutasi, P.A. Sá and M. Lino da Silva Eur. Phys. J. Appl. Phys., 56 2 (2011) 24004 Published online: 28 October 2011 DOI: 10.1051/epjap/2011110194