Langmuir probe and spectroscopic studies of RF generated helium-nitrogen mixture plasma M. A. Naveed, N. U. Rehman, S. Zeb, S. Hussain and M. Zakaullah Eur. Phys. J. D, 47 3 (2008) 395-402 Published online: 21 March 2008 DOI: 10.1140/epjd/e2008-00055-9