A Facile Way to Improve the Sensing Performance of CVD Graphene

The self-closed
$\pi $
bonds limit the molecular adsorption on graphene, which in turn leads to low sensitivity of the gas sensors. In this article, a gas sensor based on surface-oxidized chemical vapor deposited (CVD) graphene is presented for ammonia (NH3) gas sensing. Oxygen functional groups are introduced in graphene through the in situ UV-ozone (UVO) treatment, which is considered to be convenient, low cost, and compatible with large-scale preparation. The NH3 with concentration ranging from 50 to 500 ppm has been tested to evaluate the sensing performance of the proposed gas sensors. The results show that sensor treated for 4 min exhibits the best response to NH3 which is over four times than that of pristine graphene. More importantly, the sensing response increases linearly from 8.93% to 43.11% under 500-ppm NH3 as UVO treatment time increase in the range from 0 to 4 min, whereas the gas response decreased to 28.15% after exposure time is up to 8 min. This may be because surface oxidation dominates during short-term UVO exposure, but destructive etching dominates during a long-term exposure. In addition, the response speed of UVO-treated gas sensor is much faster than that of pristine graphene, whereas no significant change is observed in the recovery process. The proposed gas sensor also exhibits good selectivity, while there is a slight degradation of 5% in long-term stability after 18 days. The proposed facile method may provide reference value for the improvement of surface modification and gas sensing properties of other two-dimensional (2-D) materials.