This paper demonstrates the enhanced NO2 sensing performance of graphene with defects generated by rapid thermal annealing (RTA). A high temperature of RTA (300-700 °C) was applied to graphene under an argon atmosphere to form defects on sp2 carbon lattices. The density of defects proportionally increased with increasing the RTA temperature. Raman scattering results confirmed significant changes in sp2 bonding. After 700 °C RTA, ID/IG, I2D/IG, and FWHM (full width at half maximum)(G) values, which are used to indirectly investigate carbon-carbon bonds' chemical and physical properties, were markedly changed compared to the pristine graphene. Further evidence of the thermally-induced defects on graphene was found via electrical resistance measurements. The electrical resistance of the RTA-treated graphene linearly increased with increasing RTA temperature. Meanwhile, the NO2 response of graphene sensors increased from 0 to 500 °C and reached maximum (R = ~24%) at 500 °C. Then, the response rather decreased at 700 °C (R = ~14%). The results imply that rich defects formed at above a critical temperature (~500 °C) may damage electrical paths of sp2 chains and thus deteriorate NO2 response. Compared to the existing functionalization process, the RTA treatment is very facile and allows precise control of the NO2 sensing characteristics, contributing to manufacturing commercial low-cost, high-performance, integrated sensors.
Keywords: defects; gas sensor; graphene; nitrogen dioxide; rapid thermal annealing.