Effect of LaB6 films on field emission by knife edge cathodes

We present experimental and modeling results of electron field emission from metallic knife edge cathodes coated with LaB6 films. The cathodes are machined from copper, coated with Ti, and then sputter-coated with LaB6. The LaB6 work function (2.3 eV) is significantly lower than that of copper (4.7 eV) or Ti (4.3 eV). However, thick LaB6 films (100-300 nm) significantly reduce the field emission currents compared with the bare copper or Ti-coated cathodes. In contrast, field emission with thin (5-10 nm) LaB6 films significantly increase the emission currents. Modeling studies are investigating a hypothesis that explains these observations as resulting from a quantum transport barrier at the metal-LaB6 interface. It is hypothesized that penetration of the applied field reduces the interfacial barrier for the thinnest films.