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

High Resolution Image Download MS PowerPoint Slide 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 -MO x ) over TMDs/MCs, which promotes effective passivation of the underlying surface and excellent gas sensing response. Liquid-phase-exfoliated few-layers 2D-In 2 Se 3 have been annealed in air at 180 °C for 24 h to yield an a -In 2 O 3 /In 2 Se 3 heterostructure comprising a self-assembled a -In 2 O 3 amorphous skin (5–10 nm) over 2D-crystalline In 2 Se 3 (5–30 nm). The isomorphic conversion of In 2 Se 3 into a -In 2 O 3 specifically enables the layered shape of the precursor 2D-In 2 Se 3 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 H 2 (5–100 ppm) and NO 2 (400 ppb–1 ppm) after 1 year of delivery at 100 °C operating temperature demonstrated that the oxide skin effectively passivates the underlying 2D-In 2 Se 3 from further oxidation. Significantly, the a -In 2 O 3 /In 2 Se 3 heterostructure shows better H 2 sensing response with respect to 2D TMDs/MCs sensors, with experimental detection limits as low as 5 ppm H 2 and 400 ppb NO 2, with associated RR ( R a / R g ) = 2.1 to 100 ppm H 2 and RR ( R g / R a ) = 2.3 to 1 ppm NO 2 in dry air. A charge carrier mechanism between the a -In 2 O 3 /In 2 Se 3 heterostructure and H 2, NO 2, and H 2 O molecules is presented to discuss the humidity cross response to H 2 and NO 2 . 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.