Elucidating different $NO_{2}$ sensing mechanisms in oxidized PbS nanocrystals

TL;DR

This study investigates how surface composition and oxidation of PbS nanocrystals influence their $NO_{2}$ sensing mechanisms, providing a model to optimize room-temperature sensors with scalable fabrication.

Contribution

It introduces a detailed model linking surface chemistry, sensing response, and fabrication processes for PbS-based $NO_{2}$ sensors, supported by experimental and DFT simulation data.

Findings

Surface stoichiometry affects $NO_{2}$ binding strength.

Thermal treatment tunes sensor sensitivity and response.

Intermediate oxidation enhances $NO_{2}$ interaction.

Abstract

In this work we provide an in-depth analysis of the sensing mechanisms of $NO_{2}$ by lead-sulfide nanocrystals (PbS-NCs). A detailed model for the sorption mechanism is proposed, and the correlation is established between experimental sensing characteristics and the surface composition, based on both experimental characterization and ab initio (DFT) simulations. We demonstrated how the sensitivity and the sensing dynamic response can be tuned by a post-deposition multistep dry-thermal process at mild temperature, that alternates vacuum-assisted annealing and heating in open-air. Sensors with different surface compositions were fabricated, and their dynamic response was characterized at low concentration of $NO_{2}$ (0.5 ppm) in air, at ambient temperature. DFT simulations indicate that both surface stoichiometry and oxidation critically govern $NO_{2}$ interaction on PbS, with sulfur-rich terminations favoring weaker binding and faster desorption, while intermediate oxidation enhances interaction and overoxidation leads to surface passivation, in agreement with the measured experimental sensing dynamics. By linking surface composition, adsorption chemistry, and resistance transduction within a single framework, this work provides clear indications to design room-temperature, low-ppm $NO_{2}$ microsensors fabricated through a simple and scalable processes.