Direct work function measurement of activated M-type dispenser cathodes

M-type dispenser cathodes were activated in a vacuum chamber and the absolute work function determined from the contact potential difference between the cathode and a precisely calibrated probe tip. The experimental test setup allowed for cathodes to be activated and the work function measured without breaking vacuum. In addition to the commercially available Os-Ru coating from Ceradyne, Inc., a 3M Company, the work functions of Os-Ru coatings with engineered microstructures were measured to quantify microstructural influences. The work functions of both pre- and post-activation cathodes are presented and discussed in light of the microstructure of their Os-Ru coatings.