Properties of Resistive Hydrogen Sensors as a Function of Additives of 3D-Metals Introduced in the Volume of Thin Nanocrystalline SnO2 Films

Abstract

Analysis of the results of studying electrical and gas sensitive characteristics of the molecular hydrogen sensors based on thin nanocrystalline SnO₂ films coated with dispersed Au layers and containing Au+Ni and Au+Co impurities in the bulk showed that the characteristics of these sensors are more stable under the prolonged exposure to hydrogen in comparison with Au/SnO₂:Sb, Au films modified only with gold. It has been found that introduction of the nickel and cobalt additives increases the band bending at the grain boundaries of tin dioxide already in freshly prepared samples, which indicates an increase in the density N_i of the chemisorbed oxygen. It is important that during testing, the band bending eφ_s at the grain boundaries of tin dioxide additionally slightly increases. It can be assumed that during crystallization of films under thermal annealing, the 3d-metal atoms in the SnO₂ volume partially segregate on the surface of microcrystals and form bonds with lattice oxygen, the superstoichiometric tin atoms are formed, and the density N_i increases. If the bonds of oxygen with nickel and cobalt are stronger than those with tin, then, under the prolonged tests, atomic hydrogen will be oxidized not by lattice oxygen, but mainly by the chemisorbed one. In this case, stability of the sensors’ characteristics increases.