Field Emission in Emerging Two-Dimensional and Topological Materials: A Perspective

Since the first field emission model or the well-known Fowler-Nordheim (FN) law was formulated about a century ago (in 1928), it remains an active topic to discover different aspects of field emission due to new materials and structures, geometrical effects, high current space charge effects, short pulse regime, and analytical models. Despite its simplicity, the original FN law, or its improvement, the Murphy-Good (MG) model remains as the important equations to characterize different field emitters. With the emergence of two-dimensional (2-D) materials such as graphene, transition-metal dichalcogenide (TMD) materials, and topological materials (such as topological insulators and semimetals) in the past two decades, new experiments and theoretical models are produced to study the validity of FN law and MG model on field emission from these quantum materials and to explore their applications as compact field emitters operating at low turn-on field. In this short perspective, after a very brief introduction of FN law and some recent (selected) improvements, we proceed to review the experimental works measuring field emission from the abovementioned quantum materials. The key performances, such as experimental growth methods, and emission characteristics, such as turn-on field, field enhancement factor, and field emission current density, are summarized and compared. During the discussion, we also highlight some recent models proposed to account for the effects of nonparabolic dispersion and topologically nontrivial bandstructures within these quantum materials. We suggest the importance of having consistent physics-based models to understand the field emission from these quantum materials and reinforce the presence of a non-FN scaling law due to their unique properties absent from the traditional bulk materials. Finally, we conclude by highlighting some possible new directions that may be further explored in future.