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Electron-trapping polycrystalline materials with negative electron affinity

Nature Materials volume 7, pages 859–862 (2008)Cite this article

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 technologies4,5 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.

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Figure 1: The periodic supercell (13.35 Å×8.33 Å×28.96 Å) used to model the (310)[001](36.8∘) tilt grain boundary in MgO.
Figure 2: Comparison of the density of states of the grain-boundary supercell with bulk MgO.
Figure 3: Qualitative differences in electron trapping at grain boundaries in positive- and negative-electron-affinity materials.

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Acknowledgements

Computer time on HPCx was provided through EPSRC grant EP/D504872/1. We acknowledge useful discussions with P. Sushko, M. Stoneham and G. Besurker. K.P.M. is supported by EPSRC grant GR/S80080/01.

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  1. Department of Physics and Astronomy and The London Centre for Nanotechnology, University College London, Gower Street, London, WC1E 6BT, UK

    Keith P. McKenna & Alexander L. Shluger

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  1. Keith P. McKenna
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  2. Alexander L. Shluger
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Correspondence to Keith P. McKenna.

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McKenna, K., Shluger, A. Electron-trapping polycrystalline materials with negative electron affinity. Nature Mater 7, 859–862 (2008). https://doi.org/10.1038/nmat2289

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