FIELD ELECTRON-EMISSION STUDIES ON ZINC-OXIDE COATED TUNGSTEN MICROEMITTERS

Details of the preparation of zinc oxide coated tungsten microemitters, their emission characteristics as well as stability and the influence of thermal processing are presented in this paper. Although it was easy to coat the sharp tungsten microemitters with zinc oxide it was difficult to determine the thickness of the coating due to its opacity. A very high switch-on emission current I(e) greater-than-or-equal-to 10-mu-A was typically obtained by applying an anode voltage V(A) less-than-or-equal-to 7 kV. The same value of I(e) was maintained when reducing the applied voltage down to approximately 3 kV and sometimes even much less (approximately 1 kV). Spatial distributions thus obtained showed very bright emission spots scattered irregularly on the screen. Thermal processing and other conditioning treatments of these emitters considerably reduced the exhibited random fluctuations, thereby producing a high degree of stability of the emission process, especially at temperatures approximately 200-degrees-C. The effect of cooling the specimen to liquid nitrogen temperature is also studied. The insulating zinc oxide coating, in spite of being a good luminescent material, did not produce any luminescence effect during emission.