Structure and electron emission characteristics of sputtered rare-earth hexaboride films

Thermionic coatings based on the hexaborides of rare-earth elements were deposited onto molybdenum and tungsten substrates using dc magnetron sputtering from LaB6, CeB6, SmB6 and YB6 targets. Films were investigated by means of scanning electron microscopy and X-ray diffraction. The work function and electron emission characteristics of the coatings were studies by the thermionic emission method and by the contact potential method. After optimization of the sputtering parameters extremely fine-columnar coatings consisting of predominantly (100) oriented La-B, Ce-B and Sm-B crystals were obtained. The Y-b films showed nearly amorphous film growth. The work function was measured to be in the range of 2.6 to 3.3 eV. Coated cathodes worked with comparable electron emission current at temperatures approximately 1000 deg C below the operating temperature of uncoated tungsten filaments. (author). 9 refs., 2 figs., 1 tab., 4 photos