Deposition and functionalization of thin films of carbon nanotubes using corona based electrostatic charge technique and their applications for gas detection

A new technique based on an electrostatic-force-directed-self- assembly has been developed to deposit thin films of multi-walled carbon nanotubes (MWCNTs) on thin dielectric wires of 8-10 mm length and 500 mum diameter using corona-charging technique. The same technique has also been developed to self-functionalize the nanotubes via acid-free dry route. Functionalization of the film was achieved in a few seconds. Infrared and Raman spectroscopic measurements confirmed grafting of the films with oxygenated functional groups. The electrostatically self-assembled films were used as sensors to detect gases such as NO₂ and NH₃ with high sensitivity and repeatability up to 100 ppm (parts per million). It was observed that resistance of the deposited films increased up to 9% when sensors were successively exposed to NH₃ and decreased up to 6% with NO₂ at room temperature. Recovery for the sensors was within few hours when exposed to NH₃ and several hours for NO₂ gas. The recovery was enhanced with UV exposure. It was realized that the corona based electrostatic self-assembly (CESA) pattering technique for batch fabrication of the sensors is fast, simple, low-cost, and required no specialized equipment. The technique also offers many technical advantages such as deposition at room temperature and self-functionalized CNT films for specific molecule detection.