Surface acoustic wave sensors for NO2 detection based on sulfur-doped graphene

Surface acoustic wave (SAW) sensors for NO2 gas detection have received increased attention mainly due to their high sensitivity and wireless operation. In this paper, sulfur-doped graphene (S-Gr) was integrated into a delay line configuration shear horizontal (SH) lithium tantalate (LiTaO3) SAW device for enhancing the performance of NO2 detection at room temperature. The center frequency of the sensor was 121.5 MHz and the insertion loss close to 10 dB. After device functionalization, the insertion loss of the sensor increased to 11.8 dB, with a phase shift close to +24° at the same frequency, due to the mass loading effect. Upon exposure to NO2, the sensor response over 1 ppm to 75 ppm gas concentration range increased from 0° to 1.13°. The sensitivity of the S-Gr-based SH-SAW sensor was 0.4°/ppm in the linear response range. An NH3 selectivity study was also performed to determine the S-Gr response to this interfering gaseous analyte. A sensitivity of 0.01°/ppm for NH3 was observed, a value about 40 times lower than the sensitivity for NO2.