Manipulation of Niobium Dopant concentrations on TiO2 nanotube arrays film via dual-steps electrochemical method for humidity sensor

Abstract

Titanium dioxide (TiO₂) material is suitable for sensing applications due to higher electron mobility, stability, high sensitivity to water vapor and more easily desorb physisorbed water molecules. However, the non-homogeneous formation of TiO₂ nanotube arrays due to cracking structure is a common issue. Cracking during the preparation of TiO₂ nanotube arrays (TiO₂ NTAs) films can lead to the deterioration and malfunction of the nanotubes. The work presented here describes the niobium-doped TiO₂ NTAs (Nb-doped TiO₂ NTAs) films prepared by the dual-step electrochemical methods at different doping concentrations (1 to 7 at%). It was found that the film doped at 3 at% and annealed at 500 °C showed excellent conductivity with a value of 0.52 S. cm⁻¹. Results showed that the TiO₂ NTAs exhibited a humidity sensitivity of 239.85. The humidity sensing performance of the fabricated TiO₂ NTAs has been enhanced to 602.15 by doping with 3 at% of Nb. The enlargement of the area facilitated a slight increment of humidity sensitivity of Nb-doped TiO₂ NTAs films. This phenomenon was induced by reducing the average diameter of NTAs in TiO₂ film when the Nb dopant occupied the TiO₂ structure (59 to 48 nm). Nb is commonly combined with TiO₂ material as its regarded as a promising dopant for modifying crystalline structure. The Nb-doped TiO₂ NTAs shows high sensor stability since the Nb ions widen the host TiO₂ lattice thus improving the conductivity of TiO₂. The optimized Nb-doped TiO₂ NTAs films using the electrochemical cathodization method shows it is applicable for humidity sensor.