Re/Ir/W and Os/Ir/W alloy coatings on impregnated tungsten cathodes

Abstract

An impregnated tungsten cathode was half sputter-coated with a 40%Re-40%Ir-20%W alloy at right angles to a previous half coating of an 80%Re-20%W alloy. Similarly, 80%Os-20%W and 40%Os-40%Ir-20%W alloys were sputter-coated onto another cathode. Iridium was shown to have a lower interdiffusion rate than rhenium and osmium in the ternary alloy forms. An increase in work function of 0.06 eV was obtained on the Re/Ir/W alloy-coated area compared to on the Re/W alloy-coated area. Adding Ir to the Os/W alloy results in a wider spread in the work function distribution and an increase in work function of 0.08 eV. Both of the ternary alloy-coated surfaces were shown to have a coverage of BaO that was similar to that of both of the binary alloy-coated surfaces. There was less barium in excess of the BaO stoichiometry found on the Os/Ir/W alloy-coated region than on the Os/W alloy-coated region.