Study On The Gas-sensitivity And Related Properties Of Carbon Nanotube Film

Carbon nanotube (CNT) is a new type of one-dimensional nanostructured material that was discovered in 1991, which has a cylindrical geometry structure. In terms of their chiral properties and diameters, CNTs can be either metallic or semiconducting. CNTs unique structure exhibits fantastic physical and chemical characteristics, and shows potentials in wide. With the more research efforts, CNTs attract attentions from scientists worldwide. They can be used for nanomechanical-based devices, sensors, actuators and signal processor et.al. CNTs show potentials as a sensor material. In this study, gas-sensitivity, humidity-sensitivity and thermoelectric effect of CNT films have been investigated. In the CNT films, their total resistance consists of the resistance of CNT junctions and their own resistance. It is found that the former is positive exponentially proportional to temperature, while the latter is negative exponentially proportional to temperature. The resistanc of the treated CNT films is decided by that of CNT junctions that is proportional to the distance between CNTs. The gas-sensitivity of CNT films has been studied in air,ethanol,ammonia atomsphere. It is indicated that it is at room temperature that CNT films have stronger gas-sensitivity. In air atomsphere , the CNT films have the most sensitivity to water vapour, while they are not sensitive to CO2,CH4,O2. The biggest change of resistance of CNT films is about 18% between dry air and air of 48% humidity. The CNT films are rather sensitive to ethanol and ammonia gas, the sensitivities can reach 28% and 70% in room temperature, respectively. Meanwhile, the response time and the recovery time are very short. In addition, the study shows chemical treatments have enhanced gas-sensing characteristics greatly. The results have also been discussed and analysed. Humidity-sensitivity of CNT films has been studied. It is revealed that in water vapour, the biggest change of resistance of CNT films can reach 250% comparing to that in air. And the change of resistance in CNT films is proportional to relative humidity. The humidity-sensing mechanism has been discussed and analysed briefly. The thermoelectric effect of CNT films has also been studied in this research. The study shows that the thermoelectric force is proportional to temperature difference. The Seebeck coefficience is -15μv/K~-60μv/K, which exhibits that CNT films are n-type. In addition, the parameters such as Femi energy and electron concentration in the CNT films have been calculated.