Sensors for Sub-ppm Gas Detection Based on Carbon Nanotubes

摘要

Single-walled carbon nanotube (SWCNT) was investigated as resistive gas sensors for nitrogen dioxide (NO_2) detection. Sensor films were spinning-coated on sapphire substrates. The equilibrium position, charge transfer, adsorption energy, and electronic band structures were obtained for different kinds of SWCNTs. Most molecules were adsorbed weakly by SWCNTs and could be either charge donor or acceptor to the carbon nanotubes. An efficient method for NO_2 gas detection in SWCNT ordered using dielectrophoresis (DEP) technology after dispersion in sodium dodecyl sulfate (SDS) surfactant solution. Atom force microscopy (AFM) and scanning electron microscopy (SEM) images revealed that SWCNTs were assembled between the microelectrodes. SWCNTs were affected by the electrophoretic force which was carried out by the related theoretical analysis in a nonuniform electric field. SWCNT field effect transistors (SWCNT-FETs) geometry was obtained. The electrical performance of NO_2 gas sensor with SWCNT-FETs structure was tested before and after NO_2 was introduced at room temperature. Experimental results showed that the efficient assembly of SWCNTs were obtained when the applied alternating current voltage was a frequency of 2 MHz and an amplitude of 10 V. SWCNT-based gas sensor had high sensitivity to NO_2, and the electrical conductance of NO_2 gas sensor reduced two times. SWCNTs surface gas molecules were washed out by means of ultraviolet ray irradiation for 10 min. NO_2 gas sensor can be reproduced. The gas detection mechanisms along with the optimal gas sensing parameters were also discussed.