Surface sensitivity of ultrasonically treated carbon nanotube network towards ammonia

Detection of ammonia by carbon nanotubes is an extensively studied area where tremendous progress was achieved so far in their sensing performance. In this paper, we focused on carbon nanotube network sensors of NH3 aiming to develop better understanding of their gas detection behavior and improved sensing response. Our experiments showed improved sensing performance for single-walled carbon nanotubes of (6,5) chirality ultrasonically treated at high power and then forming bundled nanotube network upon thermal annealing. Two chemiresistive sensing pathways were observed for such networks resulting in increased and decreased resistance in presence of different ammonia concentrations from 10(2) to 10(4) ppm. This multidirectional chemiresistive response was comprehensively explained via various phenomena, such as partial and full neutralization of p-type conductivity of the nanotubes, change of the Schottky barrier, and dipoles at the interface between nanotubes and gold electrodes. The proposed sensing mechanisms are believed to provide strong support for further development of ammonia sensors with optimized performance.