Figure 5
(a) Comparison of the frequency shift as a function of humidity for D5 and D12. The inset shows schematics of samples D5 and D12, respectively. (b) Stability of the performance of the SAW sensor (D10) under various relative humidity conditions, showing stable performance for over 60 days. (c) Responding and repeated characteristics of the sensor (D10) when the relative humidity is changed rapidly between 10%RH and 80%RH, showing the fast rise time < 1 sec and fall time of ~19 sec from 80%RH to 10%RH in (d). (e) The tested samples D9, D10 and D11 (with fr~225 MHz) show that the sensitivity of the sensors as well as the rise and fall times increases when the thickness of GO layer increases. (f) Frequency shift of the sensors with drop-casting GO layer at low humidity range from 0.5%RH to 20%RH (Y = a + bX, for D6: Y = 0.449 + 0.731X, R2 = 0.9959; for D7: Y = 1.427-2.634X, R2 = 0.9770, R2 exhibit the linearity).
