RESEARCH ON THERMIONIC ELECTRON EMITTING SYSTEMS
Final rept. 16 Jun 1965-15 Sep 1966
VARIAN ASSOCIATES INC PALO ALTO CA
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The report deals with the synthesis and evaluation of a unique type of thorium, thin-film, thermionic electron emitter. The synthesis procedure involves chemical vapor deposition of a surface layer of a refractory metal onto a thorium dispensing substrate. The unique features of the process are a high degree of preferred uniaxial crystal orientation which can be obtained in the deposited layer, and a measure of control over the particular direction in the layer that is preferentially oriented. By virtue of this orientation, surfaces can be fabricated consisting predominantly of one of the better emitting crystal planes of the particular combination of substrate and adsorbate and enhanced emission thus realized. In the majority of this years work the grain-oriented surface layers investigated were tungsten. Three different types of dispensers were evaluated, each utilizing a different thermochemical reaction for production of the free thorium necessary to sustain the surface coverage at emitting temperatures. Both thermal stability of preferred orientation and thermionic emission capabilities were evaluated. Methods were evolved for fabricating the emitting structures so as to enhance thermal stability. The emitters tested exhibited a spread of over 15 in their measured values of vacuum work function 3.0 to 3.55 eV. With a single exception they exhibited high thermionic constants 70-120. Thermal stability was good for one type of dispenser evaluated, and relatively poor for the other two.
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- Electricity and Magnetism