Field emission from low-work function cathode coatings

We report experiments and analysis of field emission from copper knife-edge (CKE) cathodes, both bare and coated with low work function (2.6 eV) Lanthanum hexaboride (LaB6) thin films. The bare CKE cathode exhibits evidence of space charge limited emission currents at high field strengths. The LaB6 coated cathodes exhibit a nonlinear Fowler-Nordhiem (FN) type emission. An intermediate saturation region is observed from field emission data, which is more prominent at elevated (185 C) temperature. Surprisingly, the LaB6 coated cathodes are observed to emit less current than the higher work function (> 4 eV) bare CKE cathode. A hypothesis and corresponding model including both field emission and solid state electron transport from the Cu substrate, through the LaB6 thin film, is proposed to explain the experimental observations.