Bidimensional Engineered Amorphous a -SnO 2 Interfaces: Synthesis and Gas Sensing Response to H 2 S and Humidity.

Two-dimensional (2D) transition metal dichalcogenides (TMDs) and metal chalcogenides (MCs), despite their excellent gas sensing properties, are subjected to spontaneous oxidation in ambient air, negatively affecting the sensor's signal reproducibility in the long run. Taking advantage of spontaneous oxidation, we synthesized fully amorphous a -SnO 2 2D flakes (≈30 nm thick) by annealing in air 2D SnSe 2 for two weeks at temperatures below the crystallization temperature of SnO 2 ( T < 280 °C). These engineered a -SnO 2 interfaces, preserving all the precursor's 2D surface-to-volume features, are stable in dry/wet air up to 250 °C, with excellent baseline and sensor's signal reproducibility to H 2 S (400 ppb to 1.5 ppm) and humidity (10-80% relative humidity (RH)) at 100 °C for one year. Specifically, by combined density functional theory and ab initio molecular dynamics, we demonstrated that H 2 S and H 2 O compete by dissociative chemisorption over the same a -SnO 2 adsorption sites, disclosing the humidity cross-response to H 2 S sensing. Tests confirmed that humidity decreases the baseline resistance, hampers the H 2 S sensor's signal (i.e., relative response (RR) = R a / R g ), and increases the limit of detection (LOD). At 1 ppm, the H 2 S sensor's signal decreases from an RR of 2.4 ± 0.1 at 0% RH to 1.9 ± 0.1 at 80% RH, while the LOD increases from 210 to 380 ppb. Utilizing a suitable thermal treatment, here, we report an amorphization procedure that can be easily extended to a large variety of TMDs and MCs, opening extraordinary applications for 2D layered amorphous metal oxide gas sensors.