Electron-trapping polycrystalline materials with negative electron affinity

Abstract

The trapping of electrons by grain boundaries in semiconducting and insulating materials is important for a wide range of physical problems, for example, relating to: electroceramic materials¹ with applications as sensors, varistors² and fuel cells, reliability issues for solar cell³ and semiconductor technologies^4,5 and electromagnetic seismic phenomena in the Earth’s crust⁶. Surprisingly, considering their relevance for applications⁷ and abundance in the environment, there have been few experimental or theoretical studies of the electron trapping properties of grain boundaries in highly ionic materials such as the alkaline earth metal oxides and alkali halides. Here we demonstrate, by first-principles calculations on MgO, LiF and NaCl, a qualitatively new type of electron trapping at grain boundaries. This trapping is associated with the negative electron affinity of these materials⁸ and is unusual as the electron is confined in the empty space inside the dislocation cores.