Ab initio calculation of electron affinities of diamond surfaces

Abstract

Diamond surfaces combine chemical inertness with, in some cases, a negative electron affinity. Such surfaces have great potential for use on cold cathodes in flat displays. We present ab initio plane wave electronic structure calculations which enable us to predict the electron affinities of many different diamond surfaces with various terminations and reconstructions. Such calculations give good accuracy and enable the study of perfect surfaces with a range of terminating species so that the effect of the passifying layer can be readily seen. Results for the (1 0 0) and (1 1 1) surfaces will be presented, giving a range of surfaces more comprehensive than previously published. We find that the electron affinity varies by over 5.5 V between oxygen and hydrogen coverings, and that this magnitude of variation can be understood as simply a rising from surface dipoles as polarised covalent bonds would be expected to produce. A brief discussion of some of the technical points of performing such a calculation is given, which combines ab initio LDA work with experimental results for the band gap for diamond in order to estimate accurately the position of the unoccupied levels.