Theoretical investigation of electronic structure and field emission properties of carbon nanotube-ZnO nanocontacts

A density functional theory study is performed to understand electronic structures and field emission properties of carbon nanotube-ZnO nanocontacts. The carbon nanotube-ZnO nanocontacts have high energetic stabilities and small energy gaps. The energy gaps of the nanocontacts exhibit an oscillatory behavior as a function of the length of carbon nanotubes. The ionization potentials of all carbon nanotube-ZnO nanocontacts are smaller than 7.155 eV of the ZnO nanocage. The ionization potentials of carbon nanotube-ZnO nanocontacts with more 2 carbon layers exhibit odd-even oscillation in the absence and presence of an electric field. The carbon nanotube-ZnO nanocontact with 4 carbon layers has a smallest ionization potential of 3.625 eV under 0.2 eV/ external electric field. These results indicate that the field-emission properties of simplex ZnO and carbon nanotube materials can be enhanced significantly by the formation of carbon nanotube-ZnO nanocontacts.