Flexible and Transparent Single Wall Carbon Nanotube Network Gas Sensors Fabricated on PDMS Substrates

Abstract

Recent interest in mobile sensor networks has increased the need for a mechanically stable, low power consuming, high sensitivity gas sensors for environmental monitoring applications. Here, we present results on the gas-sensing operation of flexible and transparent single wall carbon nanotube (SWCNT) network sensors fabricated on poly-dimethyl siloxane (PDMS) substrates. The SWCNT network thin film was fabricated by vacuum filteration of SWCNTs dispersed in solution. The SWCNT network was transferred to the PDMS substrate and electrical measurements show that the thin film conductance scales with SWCNT density and showed stability to bending induced applied surface tension. Gas sensing operation showed that the sensitivity to NH3 gas exposure (measured by the change in conductance) depended on NH3 concentration and also SWCNT density. When NH3 gas adheres to the surface of the SWCNT, conductivity is reduced by electron donation induced hole concentration reduction. Also, the adhered molecules increases scattering, decreasing carrier mobility. Since for a sparse network, the conduction would be quasi-one dimensional the scattering effect of the adhered NH3 gas should be higher. This dependence was shown in Fig. 1, where the lower density SWCNT thin film (under percolation threshold) showed higher sensitivity to NH3 gas exposure. We will report on the gas exposure sensitivity of SWCNT thin film depending on SWCNT density and demonstrate low level (< 10 ppm) gas sensing capabilities.