Theoretical Study Of The Gas Sensor Based On Carbon Nanotubes

Since the discovery of carbon nanotubes, the excellent mechanical, electrical,magnetic, optical and corrosion resistance properties of carbon nanotubes have attracted great attention of the scientific community, and aroused the interest of researchers. Carbon nanotubes have very high specific surface area and the surface has a lot of dangling bonds,this makes it has very strong adsorption of gases.After the adsorption of gas on the carbon nanotubes, the charge transfer between the metropolis and carbon nanotubes, which leads to the change of carbon nanotubes’ Fermi level, and then affects the conductivity of carbon nanotubes. The change of carbon nanotubes’ conductivity can be used to detect gas before and after the gas adsorption, so the carbon nanotube has a good application prospect in the field of gas sensor.The carbon nanotubes have different response to different gases and also have different response to different concentrations of the same gas, which makes carbon nanotubes gas sensor can not only detect the gas concentration can also detect gas. The research shows that the carbon nanotube gas sensor has the advantages of fast response、short recovery time、high sensitivity and being reused,compared with the traditional gas sensor. However, pure carbon nanotubes only have very high sensitivity to very few gases such as hydrogen and oxygen, and don’t have a good response to CO, NO and other toxic gases, which limits the development of pure carbon nanotubes gas sensor.In order to increase the gas sensitivity of carbon nanotubes gas sensor to these toxic gases, We need to modify the pure carbon nanotubes by the means of doping and modification.On the basis of the research about the pure carbon nanotubes, this paper has studied the effects of boron and nitrogen atoms doping linely on the properties of carbon nanotubes.Taking one configuration as an example, we study the adsorption of Cl2, NO, CO, H2 and other gases on the carbon nanotubes doped with boron and nitrogen atoms,and calculate and analyze the effects of gas adsorption on the electronic structure of the doped system. Itprovides a theoretical basis for the application of the carbon nanotubes doped with boron and nitrogen atoms in the gas sensor. The specific research contents are as follows:(1) First of all, we calculate the system’s total energy when H2 adsorpts on the point,the bridge and the hollow position of six-member ring of(6,0)、(4,2)、(6,6) three kinds of chiral pure carbon nanotubes,the results showed that, regardless of what kind of chiral carbon nanotubes, the energy is the lowest on the point position. The lower the energy, the more stable the system,Therefore, H2 adsorpting at the point position of carbon nanotubes is the most stable for pure carbon nanotubes. Then we calculate the conductance and I-V curve of these three kinds of pure carbon nanotubes before and after the adsorption of H2,And analyse the influence of the change of the nanotube’s chiral on the gas adsorption.(2) Secondly, aiming at the limitation of the gas response of pure carbon nanotubes,this paper focuses on the study of boron and nitrogen atom line doping. We respectively have selected(5,5) armchair carbon nanotubes and(8,0) zigzag carbon nanotubes as the object of boron 、 nitrogen atoms line doping. The boron and nitrogen atoms in a six membered ring doping can be seen as special fore and aft closure of the doped lines, in consideration of the armchair doping and sawtooth doping, a total of three line doping methods. We study the formation energy, bond length and band of three kinds of lines, and analyze the relationship between the chiral and doping of the nanotube.(3) In the study of the gas sensing properties of boron and nitrogen atom line doped carbon nanotubes, we selected the highest stability ring doped configuration. The electronic structures of Cl2, NO,CO, H2 and other gases adsorbed on six element ring doped carbon nanotubes were calculated and analyzed respectively; The relationship between the adsorption gas oxidation, reduction and the chiral carbon nanotubes was discussed; The study provides a theoretical support for the gas sensing properties of boron and nitrogen doped carbon nanotubes.