Nitrogen-doped carbon oxide quantum dots for flexible humidity sensor: Experimental and SCC-DFTB study

Abstract

A flexible resistive-type humidity sensor based on N-type nitrogen-doped carbon oxide quantum dots (NCQDs) is presented. The NCQDs were synthesized by using simple hydrothermal method with reactions via citric acid and urea. The UV–vis, FE-TEM and XPS analysis confirm a successful doping of N atoms and existence of oxygen-containing functional groups into carbon quantum dots with the homogeneous spherical structure. The NCQDs humidity sensor exhibits high humidity response, good repeatability, and high stability as well as linear response to humidity in the range of 20–90% RH. The humidity sensing mechanism has been in-depth investigated by self-consistent charge density functional tight-binding (SCC-DFTB) including dispersion interaction. The SCC-DFTB reveals an important role of N doping with physisorption via direct charge transfer sensing mechanism.