Local density of states calculation for a discrete model of a diamond single atom tip

Recent studies of field emission from wide-band-gap semiconductors have concentrated on thin-film and needle geometries. It has been proposed that the emission originates from localized asperities (or crystallites) on the film (which can be of nanometer or even atomic size) or from very sharp tips approaching atomic size in the case of needle geometry. A quantity important in determining the origin of the tunneling electron states is the density of states function. In the present work we have calculated the local density of states at an atomically sharp diamond asperity (or tip) using a tight-binding model. A pyramidal-shaped cluster of 159 atoms is constructed to model the tip. The forces are calculated and used to optimize the atomic geometry of the top six layers of atoms. The bottom layers are fixed to simulate the bulk diamond. Results indicate that the local density of states of the topmost single atom on the tip is significantly different from that of the bulk and suggest that the discrete geometry of the structure plays a role in determining the field-emission characteristics.