MODELING AND SIMULATION OF CNT BASED GAS SENSOR

Abstract

The gas-adsorption, bandstructure, density of states and current-voltage characteristics of various gas-adsorbed carbon nanotube structures are studied. It is found that NO2 molecule is adsorbed to zigzag CNT with a distance of 2 A and binding energy of 794 meV showing that NO2 binds stronger with zigzag CNT than N2 or Ar does. From the bandstructure and density of states analysis, it is shown that while bare zigzag CNT is intrinsic and has no bands around Fermi energy, .NO2 adsorption makes it p-doped and also introduces extra bands around Fermi energy. It is seen that the armchair CNT has a constant conductance of 0.154 mS and is suitable for interconnects. The zigzag CNT has negligible current, mostly in pA range. The NO2 adsorbed zigzag CNT has higher current than bare zigzag CNT due to p-doping and a negative differential region is seen in its current-voltage characteristics. Both the Platinum contacted bare zigzag CNT and the Platinum contacted NO2 adsorbed CNT show Schottky-diode like current-voltage characteristics, which is actually explained by ballistic tunneling. The important difference between Platinum contacted CNTs with and without NO2 gas is that while the former has a cut-in voltage of 0.4 V, the latter has 0.2 V. The results show that NO2 detection by zigzag CNT is feasible and Platinum makes good contact with zigzag CNT. '