Secondary Material Modified Anodic TiO2 Nanotube Layers As Efficient Gas Sensors

Abstract

Gas sensors are extensively used in medical, automotive, agriculture, biogas, and mining industry for safety and environmental monitoring, including the detection of toxic compounds to prevent hazardous emission and explosion as well as air quality monitoring. 1D nanomaterials have shown great potential for sensor preparation due to their high surface-to-volume ratios resulting in countless absorption sites, and fast diffusion of gas molecules. The 1D geometry also facilitates the charge transport process [1,2].Among 1D nanomaterials, self-organized TiO2 nanotube layers have attracted considerable scientific and technological interest due to their wide possible range of applications including (photo-) catalysis, solar cells, hydrogen generation, biomedical uses or sensors [3,4]. The synthesis of the 1D TiO2 nanotube layers is usually carried out by electrochemical anodization of valve Ti metal sheets in various electrolytes. Compared to TiO2 nanotubes prepared by other methods (e.g. hydrothermal), anodic TiO2 nanotube layers have the advantage of being self-ordered with the nanotube openings on the top of the nanotube layer and being well-adhered to the Ti metal substrate, which can further be used as back contact for applications. Furthermore, anodic TiO2 nanotube layers can be produced with tunable tube dimensions [4]. Atomic Layer Deposition (ALD) can be used to produce conformal and homogenous coatings of thin layers of secondary materials an TiO2 nanotube layers, with precise control of the coating thickness, according to the deposition cycles [5]. Therefore, very thin films matching the thickness of the Debye length of a material can be deposited by ALD on the high surface area TiO2 nanotube layers giving the possibility for high sensitivity semiconductor gas sensors.The presentation will focus on the coating of anodic TiO2 nanotube layers with secondary materials using ALD and the possible use for low concentration gas sensing. Such secondary materials are, for instance, SnO2 [6] and ZnO [7]. The produced heterostructures show excellent sensing behavior for NO2 [6], in case of SnO2 coated TiO2 nanotube layers, and for ethanol [7], in case of ZnO coated TiO2 nanotube layers.