Thermionic coatings were deposited onto molybdenum and tungsten substrates using dc magnetron sputtering from LaB6 targets. The influence of the deposition parameters upon the structure and morphology was investigated by means of scanning electron microscopy and X-ray diffraction. The work function and electron emission characteristics of the coatings were studied using coated tungsten filaments. After optimization of the sputtering parameters, argon pressure, substrate bias voltage and sputtering power density, extremely fine columnar coatings consisting of predominantly (100)-oriented La-B crystals were obtained. The work function was found to be approximately 2.8eV. LaB6-coated hairpin cathodes worked with a comparable electron emission current at temperatures that were approximately 1000C below the operating temperature of uncoated tungsten filaments.

Structure and Electron Emission Characteristics of Sputtered Lanthanum Hexaboride Films. Waldhauser, W., Mitterer, C., Laimer, J., Störi, H.: Surface and Coatings Technology, 1995, 74-75[2], 890-6