Chemoresistive properties of NiO surface-modified Nb-doped TiO2 mesoporous thin films

Abstract

Functionalized metal oxide thin films are widely applicable in heterogeneous catalysis and gas sensing due to their distinct electrochemical properties. Given their importance in practical applications, developing a comprehensive understanding of their chemoresistive behavior is essential, which requires the precise engineering of thin-film-based nanostructures. Here, we report the on-chip fabrication of mesoporous Nb-doped titania (Nb_xTi_1−xO₂) thin films with template-controlled mesoporosity via dip-coating and subsequent calcination on conductometric transducers. The pore wall surfaces of mesoporous Nb_xTi_1−xO₂ films were surface-modified with variable NiO loadings via atomic layer deposition (ALD) to produce NiO-loaded Nb_xTi_1−xO₂ thin films (XNiO–Nb_xTi_1−xO₂). The NiO loading was controlled by adjusting the number of ALD cycles (X = 5–200). The chemoresistive properties of the synthesized mesoporous Nb₋Ti_1−xO₂ and XNiO–Nb_xTi_1−xO₂ thin films were investigated under different environmental conditions, namely oxidizing and reducing gases. The XNiO–Nb_xTi_1−xO₂ thin films showed an enhanced response to reducing gases, particularly acetone and ethanol, compared to unloaded mesoporous Nb_xTi_1−xO₂. Among them, 5NiO–Nb_xTi_1−xO₂, featuring discontinuous NiO-decorated species, exhibits the strongest response to acetone. The superior sensing performance of the on-chip fabricated 5NiO–Nb_xTi_1−xO₂ sensor toward acetone is attributed to the high surface area of the mesoporous thin films and surface-modification with NiO species, which enhances the sensing properties through chemical sensitization.