Highly enhanced field emission current density of copper oxide coated vertically aligned carbon nanotubes: Role of interface and electronic structure.

We report the field emission (FE) properties of Cu coated vertically aligned carbon nanotubes (VACNTs) before and after oxidation. The current density was found to be the maximum (20 mA/cm$^2$) for 3 nm thick Cu coated VACNTs after oxidation. The variation in conventionally monitored parameters like work function and field enhancement factor does not explain the experimentally determined FE current density. A critical analysis of the electronic structure reveals the importance of presence of Cu$_2$O at the interface of CuO and VACNTs, which in turn controls the current density of these films. The highly enhanced FE current density of 3 nm Cu coated VACNTs after oxidation suggests its potential as a next generation electron source in vacuum microelectronic devices.