Field-induced electron emission from electrically nanostructured heterogeneous (ENH) materials

This paper discusses the origins of field-induced electron emission from thin films of electrically nanostructured heterogeneous (ENH) materials. Such materials exhibit low macroscopic field (LMF) electron emission: as thin films on a conducting substrate, they emit electrons into vacuum when LMFs, typically about 1-10 V/microm, are applied. An ENH material comprises: a dielectric matrix, which may contain nanoscale inclusions of higher electrical conductivity; conducting channels that open in the dielectric between the inclusions (if present) and between them and the substrate; and an electron emitting channel that opens into vacuum. Electrically nanostructured heterogeneous materials can have a variety of different detailed structures and theories, but all can exhibit LMF emission under suitable circumstances. This paper provides an updated summary of an integrating overview recently presented to explain LMF emission. A central feature is that electrical nanostructure within the film can create internal field enhancement, thereby producing a high local field at the vacuum interface: this enables thermalised electrons to escape rapidly into vacuum by tunnelling. The question of what aspect of the system controls the emission current is a separate issue. Various features and implications of the theory are set out.