Decoupling the Conflicting Roles of Photoactivation and Boosting Chemiresistor Response by Pulsed UV Light Modulation

Abstract

UV photoactivation has been widely employed to trigger the response of semiconductor chemiresistors at room temperature (RT). Generally, continuous UV (CU) irradiation is applied, and an apparent maximal response could be obtained via optimizing UV intensity. However, owing to the conflicting roles of (UV) photoactivation in the gas response process, we do not think the potential of photoactivation has been fully explored. Herein, a pulsed UV light modulation (PULM) photoactivation protocol has been proposed. Pulsed UV-on facilitates the generation of surface reactive oxygen species and refreshes the surface of chemiresistors, while pulsed UV-off avoids the side effects of UVinduced desorption of the target gas and the decline of base resistance. PULM enables decoupling those conflicting roles of CU photoactivation, resulting in a drastic boost of response to trace (20 ppb) NO 2 from 1.9 (CU) to 131.1 (PULM UV-off), and a decline of limit of detection from 2.6 ppb (CU) to 0.8 ppb (PULM) for a ZnO chemiresistor. This work highlights that PULM allows full exploitation of the potential of nanomaterials for sensitively detecting trace (ppb-level) toxic gas molecules and opens a new opportunity for designing highly sensitive, low-power consumed RT chemiresistors for ambient air quality monitoring.

H2O2-Treated ZnO Nanostructures for Humidity-Tolerant O3 Chemiresistors Operated under Pulsed UV Light Modulation

“…The response of H 2 O 2 –ZnO in PULM is 176 (Figure c), which is 3.8 times higher than the response (46) in the CU mode (Figure c). Note that there maybe additional room to boost the O 3 response by further optimizing t on and t off parameters, as been illustrated in our previous work . Under the varied RH, the O 3 responses of the pristine and H 2 O 2 –ZnO chemiresistors under PULM mode have been shown (Figure b).…”

“…Simply, instead of CU photoactivation, UV is periodically turned on ( t on = 50 s) and off ( t off = 96 s) during PULM measurement, and the waveform is shown in the upper part of Figure a. PULM could make the best use of UV to “clean” the MOS surface, avoid the side effect of UV-induced desorption of target gas and decline of base resistance, and thus substantially boost O 3 response (UV-off envelope), as shown in Figure a. The response of H 2 O 2 –ZnO in PULM is 176 (Figure c), which is 3.8 times higher than the response (46) in the CU mode (Figure c).…”

“…To boost the O 3 response under humid air, the PULM measurement protocol has been performed (Figure ), and the detailed principle and operation can be found in our recent work . Simply, instead of CU photoactivation, UV is periodically turned on ( t on = 50 s) and off ( t off = 96 s) during PULM measurement, and the waveform is shown in the upper part of Figure a.…”

“…The responses to 45 ppb of O 3 at 50% and 90% RH are 1.30 and 1.28, respectively. To alleviate the UV-induced hydrophilicity (the origin of humidity degradation and poison) and further boost the response under a humid air background, pulsed UV light modulation (PULM) photoactivation with periodically switching on and off UV has been applied. Apart from enhanced response (as revealed by our recent work), periodical UV-off significantly alleviates the hydrophilicity transformation of the ZnO chemiresistor triggered by UV photoactivation and offers additional benefit in enhancing the humidity resistance.…”

“…The responses to 45 ppb of O 3 at 50% and 90% RH are 1.30 and 1.28, respectively. To alleviate the UV-induced hydrophilicity (the origin of humidity degradation and poison) and further boost the response under a humid air background, pulsed UV light modulation (PULM) photoactivation 33 with periodically switching on and off UV has been applied. Apart from enhanced response (as revealed by our recent work 33 XRD measurements were performed on a Rigaku (TTR-III) using Cu K radiation (λ = 1.5418 Å).…”