2D Amorphous/Crystalline a-In2O3/In2Se3 Nanosheet Heterostructures with Improved Capability for H2 and NO2 Sensing

Spontaneous degradation of 2D transition-metal dichalcogenides/chalcogenides (TMDs/MCs) gas sensors in dry/ wet air represents one of the most significant drawback of these interfaces, hampering the reproducibility of the baseline resistance and sensor's signal stability (i.e., sensor's creep). Herein, we report a simple protection strategy stimulating the formation of a self -assembled oxide (a-MOx) over TMDs/MCs, which promotes effective passivation of the underlying surface and excellent gas sensing response. Liquid-phase-exfoliated few-layers 2D-In2Se3 have been annealed in air at 180 degrees C for 24 h to yield an a-In2O3/In2Se3 heterostructure comprising a self-assembled a-In2O3 amorphous skin (5-10 nm) over 2D-crystalline In2Se3 (5-30 nm). The isomorphic conversion of In2Se3 into a-In2O3 specifically enables the layered shape of the precursor 2D-In2Se3 to be preserved after annealing, therefore providing all the surface-to-volume advantages of 2D interfaces. The excellent baseline and sensor's signal reproducibility to H2 (5-100 ppm) and NO2 (400 ppb-1 ppm) after 1 year of delivery at 100 degrees C operating temperature demonstrated that the oxide skin effectively passivates the underlying 2D-In2Se3 from further oxidation. Significantly, the a-In2O3/In2Se3 heterostructure shows better H2 sensing response with respect to 2D TMDs/MCs sensors, with experimental detection limits as low as 5 ppm H2 and 400 ppb NO2, with associated RR (Ra/Rg) = 2.1 to 100 ppm H2 and RR (Rg/Ra) = 2.3 to 1 ppm NO2 in dry air. A charge carrier mechanism between the a-In2O3/In2Se3 heterostructure and H2, NO2, and H2O molecules is presented to discuss the humidity cross response to H2 and NO2. The passivation strategy here proposed can be extended to a large variety of TMDs/MCs, opening new perspectives for the effective exploitation of layered amorphous gas-sensing interfaces.