Layered amorphous a-SnO2 gas sensors by controlled oxidation of 2D-SnSe2

• Published in: Sensors and actuators. B, Chemical Vol. 350; p. 130890
• Main Authors: Paolucci, V., De Santis, J., Lozzi, L., Giorgi, G., Cantalini, C.
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 01-01-2022; Elsevier Science Ltd
• Subjects: Adsorbed water; Adsorption; Ammonia; Amorphous a-SnO2; Amorphous metal oxides; Conduction model; Crystal structure; Crystallization; Flakes; Gas sensor; Gas sensors; Gases; Humidity; Liquid phases; Nitrogen dioxide; Operating temperature; Oxidation; Oxidation of TMDs/MCs; Relative humidity; Self-assembly; Sensors; Thin films; Tin dioxide; Oxidation of TMDs/MCs; Amorphous a-SnO2; Gas sensor; Amorphous metal oxides
• ISSN: 0925-4005; 1873-3077
• DOI: 10.1016/j.snb.2021.130890

2D-layered amorphous a-SnO2 is utilized for the first time to detect NO2, H2 and NH3 gases at 100 °C operating temperature opening new perspectives for the exploitation of amorphous metal-oxides interfaces for gas sensing applications. Liquid-phase exfoliated 2D-SnSe2 flakes have been subjected to controlled oxidation in air (from 1 h to 170 h) at temperatures below the crystallization temperature of SnO2 (200 °C) yielding template self-assembled, amorphous a-SnO2 thin-layers (10–40 nm thick) grown over 2D-SnSe2. A suitable oxidation process has been optimized by “in operando” monitoring the base line resistance (BLR) while changing the annealing conditions, demonstrating that at least 48 h at 200 °C are required to stabilize BLR, corresponding to the formation of a self-terminating a-SnO2 oxide with excellent BLR and sensor’s signal reproducibility over one year. Humidity cross-response on gas sensing demonstrated that increasing the relative humidity (RH@25 °C) from dry air to 80%, (Rg/Ra) to 1 ppm NO2 increases from 2.2 to 5.7 while (Ra/Rg) to 100 ppm H2 and NH3 decreases from 2.7 to 1.7 and from 1.8 to 1.6 (σ ± 0.2). A preliminary ab-initio DFT modeling of water adsorption over amorphous a-SnO2 highlighted that dissociative adsorption is thermodynamically favored. The thin film sensor’s conduction model, comprising stacked layers of a-SnO2/SnSe2 flakes, is explained by the formation of Schottky barriers between the flakes. The seamless texture of amorphous a-SnO2 skin with no grain-boundaries, no crystal-planes orientations, greatly simplify gas sensing mechanisms assumptions, paving the way for a new class of “layered amorphous metal-oxides gas-sensors” (LAMOS).
•A new class of layered amorphous tin dioxide (a-SnO2) for gas sensing applications.•A controlled oxidation to produce self-assembled a-SnO2 over crystalline 2D-SnSe2.•In operando monitoring the base line resistance to optimize the a-SnO2 skin growth.•A seamless passivating a-SnO2 skin with tunable thicknesses as to the Debye length.•A DFT case-study example of single water molecule adsorption over amorphous a-SnO2.