The electron energy distribution function measured with improved energy resolution revealed a large number (≊90%) of low-energy electrons having an abnormally low electron temperature (T≊0.3 V) resulting in a considerably lower mean electron energy than found in all published probe measurements in argon rf discharges at 13.56 MHz. With increasing gas pressure an abrupt transition to a high-temperature mode was found. The low-temperature mode and the observed transition are attributed to a change from stochastic to collisional electron heating enhanced by the Ramsauer effect.

• Received 21 May 1990

DOI:https://doi.org/10.1103/PhysRevLett.65.996