Electronic structure and the field emission mechanism of MgO-coated carbon nanotubes

Abstract

In an attempt to improve the field emission (FE) characteristics of carbon nanotubes (CNTs), we have performed a first-principles study on MgO-coated CNTs. A MgO slab covering a CNT tip under a strong electric field shows dielectric screening behaviourswith applied electric fields up to 0.3 V Å-1 and the effective dielectric constant approaches the bulk value within a few MgO layers. It is also found that the surface conduction band state of the MgO slab shifts down to the Fermi level as the applied electric field increases, indicating a FE mechanism different to that for CNTs without insulator coating. Electron emission via the surface conduction band of the insulator at the Fermi level is expected to enhance the FE current significantly, in agreement with a recent experiment.