Structure observed in measured electron energy distribution functions in capacitively coupled radio frequency hydrogen plasmas

Electron energy probability functions measured with a passively compensated Langmuir probe in asymmetric capacitively coupled hydrogen and deuterium p lasmas exhibit structure. The otherwise relatively continuous distribution appears to have an abrupt peak in electron density near 5 eV. This structur e occurs at a higher energy in deuterium than hydrogen and there is a corre lation between floating potential and the voltage at which the structure is observed in the second derivative of the I(V) characteristic. While the ca use of the structure has yet to be clarified, spectroscopic observations an d computer-based hydrogen models indicate that the high energy tail of the distribution is strongly modulated during the radio frequency cycle. The ef fect of this modulation on plasma properties and probe measurements has yet to be explored. (C) 1999 American Institute of Physics. [S0003-6951(99)008 19-0].