Measurements on electron energy distribution function (EEDF) by a Langmuir probe show that inert gas mixing can change EEDF from a Maxwellian to a 'two-temperature' structure in an inductively coupled low pressure nitrogen discharge. This result suggests the existence of two groups of electrons: low and high energy. Each group of electrons has distinct behaviour as gas mixing ratio changes. As a result, this causes discrepancies between the measured electron temperature by a Langmuir probe and that by optical line–ratio technique, since these two techniques are sensitive to the energy distribution of low and high energy electrons, respectively. A detailed experimental investigation of the evolution of EEDF with different inert gas mixtures (Ar/N2, He/N2, Ne/N2 and Xe/N2) at an operating pressure of 10 mTorr is performed, from which the distribution temperature of both low and high energy electrons is calculated and compared with the temperature obtained from the Global Model. It is found that with the measured energy range and under the experimental condition studied, inelastic collisions (both excitation and ionization) play a key role on the shape of EEDF when inert gas is mixed in the discharge.
Plasma sheath in the presences of non-Maxwellian energetic electrons and secondary emission electrons