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

2H MoS ₂ nanoflakes were exfoliated and surface-modified by amine (-NH ₂ ) groups in a simple three-step water-based approach. The NH ₂ -modified MoS ₂ 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 ${t}_{{\text {response}}} =1.2$ s and ${t}_{{\text {recovery}}} =3.1$ 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 MoS ₂ –NH ₂ system (with lone pairs) to the humidity layer resulting in an electron accumulation at the MoS ₂ layer, and thus lowering the conduction band minima (CBM) of the MoS ₂ 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 MoS ₂ –NH ₂ 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.