Influence of processing parameters on electrical properties of carbon nanotube films

The quality of CNT films is important for many related applications. In this paper relevant processing parameters such as the sonication time, the CNT weight fraction and annealing process are investigated to characterize their influences on electrical properties of the produced CNT films. The results show that sonication time plays an important role for the quality of CNT films. At lower sonication time the film homogeneity is affected and very high resistance values are realized. A longer sonication time (approx. 10 minute) realizes better homogeneity and lower resistance values depending on the CNT concentration. Even the specimen spreading was significantly reduced thereby. More improvements of the electrical properties can be realized by annealing. The resistance value diminishes about a half by annealing during 30 minute at 200°C. This is due to the evaporation of moisture and gas of CNT films during annealing. A negative temperature dependence of the CNT film resistance (semiconducting behavior) was observed in both cooling and heating processes for a selected semiconducting SWNT specimen in the temperature range from 20°C to 90°C. Similar negative temperature dependence was also observed for unselected SWNT and MWNT specimens. For a specimen with semiconducting SWNTs the temperature coefficient is one order higher than those of unselected SWNT and MWNT specimens.