Properties of a weakly ionized NO gas sensor based on multi-walled carbon nanotubes

摘要

Nitric oxide NO is one of the major targets for environmental monitoring, but the existing NO sensors are limited by their low sensitivity and narrow test range. Here, a NO gas sensor employing multiwalled carbon nanotubes (MWCNTs) was fabricated, and its properties in NO-N_2 mixture were investigated from both emission and ionization. The current I_e passing through the nanotubes cathode was found to decrease with increasing NO concentration and increase linearly in different slopes with the extracting voltage U_e. It is shown that the Schottky barrier of the MWCNTs calculated by I_e increased with NO concentration due to the adsorption of NO gas, which restrained the electron emission and consequently weakened the ionization. The positive ion currents I_c passing through the collecting electrode at different voltages of U_e were found to monotonically decrease with increasing NO concentration, which was induced by both of the reduced electron emission and the consumption of the two excited metastable states N_2(A~3∑_u~+) and N_2(a'~1∑_u~-) by NO. The sensor exhibited high sensitivity at the low temperature of 30 ℃. The calculated conductivity was found to be able to take place of I_c for NO detection in a wide voltage range of 80-150 V U_e.