Thermionic field emission properties of nitrogen doped ultrananocrystalline diamond (UNCD) coated silicon tip arrays are examined using thermionic field emission electron microscopy (TFEEM). Nitrogen doping has been shown to enhance the emission properties of diamond by the introduction of a donor level $1.7\mathrm{eV}$ below the conduction band minimum. The field enhancing geometry of the films initiates accelerated electron emission at the tipped structures which may be beneficial to thermionic energy converter design where space charge effects can significantly limit attainable current densities. Two temperature regimes of electron emission are observed; $600–800°\mathrm{C}$, where the emission is enabled because of the H passivation and $900–1100°\mathrm{C}$, where the emission is attributed to tunneling from nitrogen related states through the barrier of a clean diamond surface.

• Received 23 April 2005

DOI:https://doi.org/10.1103/PhysRevB.72.165404