The absolute detection efficiency of vacuum electron multipliers, to keV protons and Ar+ ions

The single-ion detection efficiency of two types of electron multipliers is provided for incident energies reaching 10 keV. Absolute efficiencies above 90% were measured for a discrete dynode electron multiplier (DDEM), in response to Ar+ ions and protons, above an energy of 5 keV. The efficiency to detect protons is consistently higher than that of Ar+ ions, due to a higher secondary electron emission yield. For a channel electron multiplier we have measured a similar maximal detection efficiency for Ar+ ions; though strongly varying across the detector surface.