Application of microfabrication technology to thermionic energy conversion. Final report, 1 April 1979-31 March 1981

The first-year effort emphasized study of the kind of microstructures that could improve the performance of thermionic converters. Two ideas considered to have a fair chance of success emerged from this study: (1) use of a very closely spaced diode to eliminate the space-charge limitation of electron flow from emitter to collector, cesium vapor being used to control the work function of the emitter; and (2) use of field emission electrons, injected into a relatively large diode gap from microcathodes built into the collector, to produce ions to neutralize the space charge. The gas in the diode gap would be a mixture of cesium (to control the emitter work function) and xenon to optimize the ionization. A number of schemes were attempted to build closely spaced diodes with spacing in the 1 to 5 ..mu..m range, which overcame the problems of lateral differential expansion, surface irregularities on the electrodes, and heat loss down the pillars holding the gap spacing. Theoretical studies on using field emitter electrons to produce the space charge neutralizing ions showed that this approach was feasible. However, the program was terminated before any experimental work could be initiated in this area