Field emission from metal tips covered by ultra-thin films of Zirkonia energy spectra features and current-voltage curves

Thermofield emission cathodes based on ZrO2/W heterostructures are widely used as a point electron source nowadays. At present issue results of simultaneous study of Volt-Ampere characteristics (VACH) and energy spectra of such cathodes are discussed just under field emission terms. Firstly, needle shaped tungsten cathodes were coated by thin (~ 10 nm) film of ZrO₂ by means of thermo-field diffusion methods under ultra high vacuum conditions. In this case the tungsten emitters were used as reference patterns and their characteristics were measured before the coating process. It is shown that VACH of coated emitters plotted in Fowler-Nordheim coordinates has non-linear character contrarily to “metallic” VACH. Such behavior of VACH may be attributed to complicated energy spectra obtained during VACH measurement and complex electronic structure of thin film. There are two peaks on the spectra plot with 3-5 eV distance between them depending on emission voltage. It is shown that energy spectra of coated cathodes may have fine structure. Finally, the work function of the coated cathodes is lower by 2 eV in comparison to pure W cathodes.