THE MEASUREMENT OF ELECTRON-ENERGY DISTRIBUTION-FUNCTIONS IN METHANE-HYDROGEN PLASMAS

The electron energy distribution function (EEDF) is a key factor in the reaction kinetics of any plasma. The EEDF can, in principle, be obtained from the second derivative of the electron retarding region of a Langmuir probe characteristic. In the high frequency discharges used for the deposition of diamond-like carbon, the method is complicated by both the electric field sustaining the plasma and a tendency for the probe to exhaust the bulk of the electron distribution in the region of the plasma space potential. Experimental details of a novel, low current, asymmetric Langmuir probe, designed to circumvent these problems, are discussed, together with measurements of EEDFs made on a range of hydrogen-methane plasmas.