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

摘要

2H MoSsub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"2/sub nanoflakes were exfoliated and surface-modified by amine (-NHsub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"2/sub) groups in a simple three-step water-based approach. The NHsub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"2/sub-modified MoSsub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"2/sub 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 inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink" tex-math notation="LaTeX"${t}_{{text {response}}} =1.2$ /tex-math/inline-formula s and inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink" tex-math notation="LaTeX"${t}_{{text {recovery}}} =3.1$ /tex-math/inline-formula 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 “italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"pseudo electron injection model/i” has been put forward. It established that the enhanced response was due to the increased electron transfer from the MoSsub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"2/sub–NHsub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"2/sub system (with lone pairs) to the humidity layer resulting in an electron accumulation at the MoSsub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"2/sub layer, and thus lowering the conduction band minima (CBM) of the MoSsub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"2/sub 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 MoSsub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"2/sub–NHsub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"2/sub layers, thereby finally expressing the enhanced response. From the models, extinction coefficients affecting CBM-lowering were calculated as inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink" tex-math notation="LaTeX"$alpha = -0.042$ /tex-math/inline-formula eV and inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink" tex-math notation="LaTeX"$beta = -0.49$ /tex-math/inline-formula eV nmsup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"?1/sup which supported the obtained results.