Effects of chirality and impurities on the performance of carbon nanotube-based piezoresistive sensors

This paper presents a method to fabricate high purity, single chirality carbon nanotube (CNT) based sensor systems. Ultracentrifugation is initially used to create an 85% pure (6,5) CNT sample. This 85% pure sample has a gauge factor of −22.7 ± 0.5 which is significantly lower than the predicted gauge factor of 57 for a pure (6,5) CNT. However, this measured gauge factor closely matches the predicted gauge factor for the measured distribution of chiralities in the 85% pure sample. This indicates at a small number of impurities in the sensor can have a large effect on the strain sensitivity of the sensor. In order to increase the gauge factor of the 85% pure (6,5) CNT sample, an electrical breakdown technique is used to remove the low resistance and low gauge factor CNTs from the sensor. Using this technique it is possible to increase the gauge factor of the CNT-based piezoresistive sensor from −22.7 ± 0.5 to 34 ± 1. This result indicates that the majority of the impurities in the sensor can be removed during the fabrication process using the electrical breakdown technique.