Unexpected change in the electron affinity of diamond caused by the ultra-thin transition metal oxide films

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The energetics and electronic properties of oxides of selected transition metals (Cu, Ni, Ti and Zn) adsorbed onto a diamond (001) surface are examined using density functional simulations. We find that the stoichiometric oxides of Ti and Zn exhibit large negative electronic affinities of around 3 eV, whereas the oxides Cu and Ni have a relatively small impact on the affinity. Although reactions of most metal oxides with the diamond surface are exothermic in nature, we propose that titanium, which exhibit large binding energies per metal atom in addition to a large negative electron affinity, is of particular interest for the surface coating of diamond-based electron emitters.