A sensitive humidity sensor at low pressure with SnO2 QDs

Abstract

The humidity sensor working at low pressure has importance in fruit processing industries, space applications, and vacuum coatings. So, it is imperative to develop a sensor to measure very low levels of humidity in a vacuum domain. In the present work, a resistive humidity sensor made of SnO 2 Quantum Dots(QDs) is demonstrated. The huge surface area (160 m 2 /g) of QDs provides plenty of oxygen vacancies at the surfaces which help to absorb moisture even at a low pressure of ~5 mbar starting from the atmospheric pressure. These QDs characterized by XRD, TEM, and optical spectroscopic techniques reveal structural details including the presence of vacancies. The performance of the QDs sensor due to the humidity effect is further proved by flow dry N 2 flow. The role of surface hydroxyl groups and their tie-in with RH sensing with high reproducibility performance under vacuum are exclusively highlighted for the first time with SnO 2 QDs at room temperature. • Surfactant free synthesis of SnO2 quantum dots. • Huge specific area and surface defects creation for adsorption of moisture. • Room temperature humidity sensor performing even at low pressure of ~ 5 mbar. • Spectroscopic evidences of surface hydroxyl and H+ mediated resistive mechanism for humidity sensor.