Features of water vapor adsorption and desorption on the surface of non-stoichiometric tin dioxide films

Abstract

Herein, the influence of water vapor adsorption and desorption processes on the surface of SnO2−δ nanocrystalline films with different concentrations of oxygen vacancies on their electrical conductivity at room temperature was studied. SnO2−δ films were synthesized by means of reactive magnetron sputtering of tin in an argon-oxygen plasma followed by 2-stage oxidative annealing. The concentration of oxygen vacancies in the films was varied by changing the 2nd stage annealing temperature within the range 350–400 °C. It was found that in the films with the highest concentration of oxygen vacancies (~1020 cm−3) in the region of low relative humidity (less than ~30 %), an increase in electrical conductivity was observed due to the dissociative adsorption of water molecules with the formation of hydroxyl groups. The adsorption of water vapor on the surface of SnO2−δ films at room temperature at relative humidity values higher than ~30 % was found to induce a decrease in the electrical conductivity of the samples. The generation of positive and negative EMF pulses between the open surface of SnO2−δ nanocrystalline films and the one covered by waterproof materials under the adsorption and desorption of water vapor, respectively, was detected. The change of resistance and the generated EMF value under the adsorption-desorption processes was found to increase with the concentration of free charge carriers in the films.

Bismuth oxysulfide thin films for light and humidity sensing

“…The recovery of the film resistance after the start of pumping out also occurs quite quickly: during the first second, the current decreases down to 10% of the stationary value reached at the maximum humidity. There are many publications devoted to the creation of humidity sensors based on nanostructured metal chalcogenides and oxides [15][16][17][18][19][33][34][35]. Most of the above resistive sensors have a long response/recovery times and a large hysteresis observed on the kinetics of sensors' resistance change during water adsoprption/desorption processes.…”

“…Another interesting application of oxide and chalcogenide semiconductors and, in particular, bismuth compounds is associated with creation of devices for relative humidity sensing [15][16][17][18][19]. One of the simplest types of RH sensors is resistive, where resistance changes under variation of RH value [20][21].…”