On the role of graphite in ultrananocrystalline diamond films used for electron field emitter applications

Abstract

This Feature Article gives an account of the different pieces of work conducted by various groups around the world aimed at constituting a single model explaining the enhancement of conductivity and electron field emission properties in diamond. The scope of the presence of graphite phase or the evolution of intermediate energy levels within the band gap or defects in the diamond phase being causes of such enhancement has been explored by various groups. Along with this we present the studies performed by our group, the enhancement of the field emission and conductivity employing different approaches like ion irradiation, ion implantation, ion doping in the plasma or formation of composite films. From our studies we reveal that such modifications of properties are related to microstructural alterations. The prominent change observed, and contributing to this enhancement, is the increase in the grain boundaries, with sp2 graphitic phases residing in them. The effect of n- or p-type doing into diamond is ruled out. The betterment of the field emission and conductivity is attributed to the interconnected sp2 phases within the grain boundaries, which form itineraries for electrons to traverse through the material.