We measured energy distributions of negative ions at the grounded elec
trode of an oxygen parallel-plate rf discharge. Negative ions are gene
rated in the plasma sheath in front of the rf electrode, are accelerat
ed away from the driven electrode, and can be detected at the grounded
electrode. The maximum energy of the negative ions corresponds to the
negative self-bias voltage of the rf electrode. Structures in the ene
rgy distribution reflect sheath properties and characteristics of the
ion generation processes. (C) 1996 American Institute of Physics.