Effects of nanomaterials on Cs3Sb photocathode emission performance

Abstract

A new approach to preparing the cesium antimonide photocathode has been developed. A tungsten sponge diffusion barrier layer, instead of the conventional nickel pipe, was used as the evaporation source so that a slow and uniform evaporation of the photoemissive materials, whose direction and amount could be well controlled, was realized. Then, the cathode substrate surface was modified with a nanoparticle layer, resulting in better photoemissive material adsorption and higher light absorbance. A new technique of treating the tungsten sponge, which worked as the barrier layer to the diffusion of the photoemissive materials, was studied. The tungsten–copper alloy was subjected to direct high-frequency heating in a vacuum chamber so that the copper in the alloy evaporated rapidly, resulting in smooth and shiny tungsten sponge. In comparison with the conventional method for fabricating the tungsten sponge, in which the copper in the tungsten–copper alloy was removed chemically, the new method removed the copper more completely, took less time, and caused less pollution. By means of direct-current magnetic sputtering, a layer of osmium nanoparticles of 50 nm diameter was deposited on the photocathode substrate surface. Then, a diode tube for the photocathode emission test equipped with a small titanium ion pump, whose pressure was as low as 5 × 10−8 Pa, was developed. A comparative emission performance test was carried out on the photocathode with the substrate surface covered with an osmium film vs that covered with osmium nanoparticles. The highest quantum efficiencies of the stable photoemission from the two photocathodes were 1.80 × 10−3 and 5.13 × 10−3, respectively. Moreover, the light absorptivity of the osmium nanoparticle-coated photocathode was 2.16 times that of the osmium film-coated photocathode, and the quantum efficiency of the former was 2.85 times that of the latter. Therefore, the improvement in the quantum efficiency of the osmium nanoparticle-coated photocathode is mainly attributed to the increase in the light absorptivity.