Pulsed-laser annealed amorphous/crystalline a-V2O5/VO2 heterostructure for selective NO2 and H2 sensing

Amorphous/crystalline metal oxide heterostructures represent a new class of gas sensing platforms, as they offer relevant concentration of adsorption sites within the amorphous phase and the occurrence of amorphous/crystalline heterojunctions. Herein we propose a simple synthesis based on nanosecond pulsed laser annealing (ns-PLA) to produce at room temperature amorphous/crystalline a-V2O5/VO2 heterostructure interfaces. By coupling sol-gel derived amorphous V2O5 thin-film with finely tuned laser pulses, we induced a controlled crystallization and nanostructuring of VO2 crystalline phase (20 wt%) embedded in an amorphous a-V2O5 matrix (80 wt%). The amorphous/crystalline a-V2O5/VO2 behaves as a n-type sensor when exposed to NO2 (400 ppb–1 ppm), H2 (20–500 ppm) and humidity (20–80 % RH) at 100 °C temperature. We demonstrated that with increasing relative humidity, relative responses (RRs) to NO2/H2 gases increases/decreases, entailing a synergistic/anti-synergistic effect of humidity. Pt-nanoparticles (Pt-NPs) decoration of a-V2O5/VO2 improves both H2 detection limit down to 5 ppm, and RRs. Corresponding to 100 ppm H2, RR increases from 1.12 ± 0.04 (not decorated) to 1.30 ± 0.04 (decorated).. Remarkably, Pt-NPs decoration hampers both NO2 detection and humidity cross-influence on H2 sensing, representing a promising strategy to improve the sensor's selectivity. Finally, a gas sensing response mechanism of the a-V2O5/VO2 heterostructure to H2, NO2 and H2O is presented.