Electronic Structure Tuning and Band Gap Engineering of Carbon Nanotubes: Density Functional Theory

In this work, we have theoretically studied the changes in electrical properties of two different geometrical structures of carbon nanotubes upon oxygen doping. We used different doping mechanisms to study band structure variations of the doped structures. Doping carbon nanotubes with oxygen atoms created new band levels in the band structure and as a consequence an up shift of the Fermi level. The new band levels are located around the middle of the band gap of pristine carbon nanotubes, whereas filling up the lowest conduction bands cause the up shift of the Fermi level. The number of new band levels is directly correlated to different dopant concentrations. The new peaks appeared in the density of states are stemmed from the new bands in the band gap region. These new bands are solely attributed to doping carbon nanotubes with oxygen atoms. Compared to recently reported experimental studies our findings are in good agreement with the measured electrical characteristics of carbon nanotubes gas sensors based on transistors. Finally we simulated Raman spectroscopy for doped and un-doped nanotube samples and investigated the variations of frequency modes. We also studied the changes of the intensity spectra for both G(+) and D modes.