Electron densities and temperatures in a diamond-depositing direct-current arcjet plasma

Langmuir probe measurements of electron density and temperature are made in the plume of a de arcjet reactor. A de are is struck in an argon or argon/hydrogen mixture at 6 atm pressure and expands through a converging/diverging nozzle into the reactor with a pressure of 25 Ton. Methane and methane/nitric oxide are added in the diverging nozzle, and diamond film grows on a substrate in the gas plume. Electron temperatures of 1-2 eV are significantly hotter than the neutral gas temperature in the plume. Electron densities range from 10(10) to 10(13) cm(-3), well above the Saha equilibrium for the gas temperature and pressure and well below the equilibrium for the electron temperature. (C) 1997 American Institute of Physics.