Effects of post-growth treatment and coating with ultrathin metal layers on the band bending and field electron emission of diamond films

Abstract

Band bending formation on thin nanocrystalline diamond films and field electron emission after post-growth treatments was investigated. It was found that treatment of the diamond surface with hydrogen plasma substantially decreases the density of point defects, forms the downward band bending and enhances the field electron emission from the films. In the case of an argon plasma treated diamond surface, new point defects were induced and their energy distribution was changed. Nevertheless, the downward band bending was formed and the field electron emission was enhanced similar to the H–plasma-treated diamond surface with minor density of defects. These effects were interpreted in terms of the electrical dipole formation on the plasma treated diamond surfaces. Coating the diamond films with ultrathin metal (Ni, Ti) layers revealed the dependence of the band bending and field emission behavior on the type and thickness of the metal used. The deposition of a few monolayers of Ni on the diamond surface was found to raise the position of the Fermi level relative to the valence band maximum and cause the downward band bending, reducing the field emission threshold. It was suggested that the charge of the surface dipoles on the metal coated diamond surfaces (as in the case of the H and Ar plasma treatments) plays a key role in the band bending formation.