Inherent Enhancement of Electronic Emission from Hexaboride Heterostructure

Based on a nonequilibrium Green’s-function approach to the calculation of emission currents from first principles, we show that cathodes consisting of LaB6=BaB6 superlattices can yield an order-of-magnitude higher thermionic current densities than pure LaB6 cathodes. Because of a 0.46-eV lowering of the work function, such a heterostructure cathode could thus be operated at significantly lower temperatures. Neither the stability nor the magnitude of electronic tunneling coefficients is compromised in the superlattice system as compared to pure LaB6, which is in contrast to the generally reduced stability and large dipole barriers in the case of adsorbate-induced lowering of the work function. The heterostructure could thus be used as a cathode material that at the same time is stable and has emission properties superior to those of pure LaB6.