Selective Passivation of 2D TMD Surface Defects by Atomic Layer Deposited Al2O3 for Enhancement of Recovery Properties of Gas Sensor

Abstract

Two-dimensional (2D) transition metal dichalcogenides (TMDs) which possess a large surface-to-volume ratio have been actively studied for room temperature gas sensing applications. [1] However, due to its intrinsic defects or vacancies on TMD surface, incomplete recovery of TMD gas sensors hinders the realization of reliable and repeatable use in industry. [2] Few efforts have been studied for enhancing the recovery characteristics of TMD gas sensors such as, introducing micro-heater or light source, and surface modification by chemical doping. [3] However, those methods need additional power source which is not favorable for low-power electronic device as well as those are not the fundamental solution for improving recovery characteristics. Here, we demonstrate an improvement of recovery rate of TMD gas sensors by selectively passivating TMD surfaces’ defects or vacancies with Al2O3 using atomic layer deposition. SEM analysis confirms that nucleation and growth procedure of atomic layer deposited Al2O3 occurs along the grain boundaries and defects of 2D MoS2 and WS2, not covering inert basal plane. Also, Raman, Photoluminescence and XPS spectra show no oxidation of TMD surface and the slight n-doping effect of Al2O3, which attributes to improvement of gas sensor response. Our unique and unreported defect passivated TMD gas sensors show 400 % response toward 10 ppm of NO2, and the recovery rate rises up from 74% to 96% as the number of ALD cycle increases even at room temperature. As well as NO2, NH3, which is the reducing gas, shows an increase of more than 30% implying that our proposed method is a promising strategy for improving the recovery rate of 2D TMD gas sensors.