Pseudo Electron Injection in Amine-Modified MoS2-Based Sensor for Humidity Monitoring

2H MoS2 nanoflakes were exfoliated and surface-modified by amine (-NH2) groups in a simple three-step water-based approach. The NH2-modified MoS2 sheets were used as humidity sensitive layer for estimating various levels of relative humidity (RH) (10%-90%). The devices demonstrated a maximum response of 720% for 90% RH with t(response) = 1.2 s and t(recovery) = 3.1 s, respectively, when operated at 1 V. The device also displayed low hysteresis and good stability with a maximum error in response to +/- 5% when tested for 50 days. The device demonstrated a good response at lower RHs. To explain this enhancement of response, a novel pseudo electron injection model has been put forward. It established that the enhanced response was due to the increased electron transfer from the MoS2-NH2 system (with lone pairs) to the humidity layer resulting in an electron accumulation at the MoS2 layer, and thus lowering the conduction band minima (CBM) of the MoS2 system beneath. This accumulation amplified the device current significantly resulting in sensor performance enhancement. The CBM-lowering and electron population due to this pseudo electron injection were expressed as a function of the thickness of adsorbed humidity and the MoS2-NH2 layers, thereby finally expressing the enhanced response. From the models, extinction coefficients affecting CBM-lowering were calculated as alpha = - 0.042 eV and beta = -0.49 eV nm(-1) which supported the obtained results.

Automated summary

In this study, 2H MoS2 nanoflakes were exfoliated and modified with amine groups to create a humidity sensitive layer. The enhanced response to humidity levels was explained by a novel pseudo electron injection model, which resulted in improved sensor performance. The study demonstrated good stability and low hysteresis in the devices, with extinction coefficients supporting the obtained results.