Work Functions and Conductivity of Oxide-Coated Cathodes

Abstract

The thermionic and hotoelectric work functions and the temperature variation of coating conductivity have been measured for an oxide cathode. Thermionic and photoelectric currents were measured in both retarding and accelerating fields. The two work functions are found to be different, but not by the amount predicted by applying simple semi-conductor theory to the data. Photoelectric currents fit a Fowler plot rather well over a limited range of frequencies.The large decrease in work function with applied field, the poor "saturation" of thermionic currents typical of oxide cathodes, and the behavior of the photoelectric currents in accelerating fields all suggest that one is dealing with a "patchy" surface. Applying "checkerboard" patch theory to the experimental data, one finds that most of the data is accounted for by assuming patches about 3xlO -4 cm on a side differing in work function by about .2 volt.*

Electron Emission Energy Barriers and Stability of Sc2O3 with Adsorbed Ba and Ba–O

“…An approximation for the escape distance can be made by considering a basic imagecharge restoring force on the electron and balancing it with the field pulling the electron from the cathode to the anode. 17 The latter can be estimated by assuming a typical cathode-anode voltage difference of 1000 V and cathode-anode separation of 1 cm, which yields an electron escape distance on the order of 0.1 microns. This is an upper bound as often times cathodes are tested at potentials up to 10 kV, which would give an escape distance closer to 0.01 microns.…”

“…The escape distance defines when an electron has been released from the surface and will be available to provide current in the cathode, and it is therefore the work function at this distance that is relevant for cathode performance. An approximation for the escape distance can be made by considering a basic image-charge restoring force on the electron and balancing it with the field pulling the electron from the cathode to the anode . The latter can be estimated by assuming a typical cathode–anode voltage difference of 1000 V and cathode–anode separation of 1 cm, which yields an electron escape distance on the order of 0.1 μm.…”

Density functional theory analysis of hexagonal close-packed elemental metal photocathodes

“…The hardness criterion rules out thallium, which is an extremely soft metal, while the high vapor pressures of Cd and Zn ensure that they are not vacuum compatible if the effects of desorption contamination are to be avoided [71]. Chemical stability is also an important criterion, especially if surface oxidation causes a significant change in the photocathode work function [72]. However, since a Mg photocathode has been demonstrated [36], the analysis presented here will not enforce restrictions based on chemical reactivity as it assumes pure metal surfaces.…”