Abstract
Thermionic coatings of lanthanum boride were deposited onto molybdenum and tungsten substrates employing d.c. magnetron sputtering from LaB 6 targets. The influence of the deposition parameters on the structure and the morphology was investigated by means of scanning electron microscopy and X-ray diffraction. The work function and electron emission characteristics of the coatings have been studied by the thermionic emission method 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 measured to be approximately 2.8 eV. LaB 6-coated hairpin cathodes worked with comparable electron emission current at temperatures approximately 1000 °C below the operating temperature of uncoated tungsten filaments.
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