Examination of field emission from Lanthanum Hexaboride coated knife edge cathodes

We report experiments and analysis of field emission from metallic knife-edge cathodes coated with thin film Lanthanum Hexaboride (LaB6), a low work function material (∼2.5 eV). The emission current density is found to depend sensitively on film properties, particularly the thickness of the LaB6 layer. Films thinner than approximately 10 nm greatly enhance the emitted current. However, cathodes coated with a thicker layer of LaB6 are observed to emit less current than the uncoated metallic cathode even though the bare metal cathode possesses a higher work function (> 4 eV). A hypothesis is proposed to explain this surprising experimental finding, and a computational model is developed. This simulation model incorporates field emission as well as solid state electron transport from the metal substrate through the LaB6 thin film, and is found to support the proposed hypothesis and agree with experimental observations.