Innovative spongy TiO2layers for gas detection at low working temperature

The capillary distribution of reliable solutions for gas detections implies identifying high throughput and up-scalable approaches for the growth of porous active materials with high surface to volume ratio and high surface avaialability/reactivity. Thereby we implemented a competitive method to render thin (hundreds of nanometers) TiO2 layers highly sensitive to gas species. This method is easily implementable in gas sensor devices with an additional ending step at room temperature without any temperature needed for reaction. It is based on the local oxidation of sputtered Ti atoms that land grazing on the sensor architecture (called gig-lox process). The process gives rise to a contaminant-free TiO2 spongy structure consisting of rods separated by meso-pores arising from the grazing geometry; the rods, on their side, have an internal branched structure creating an interconnected network of nano-pores. The overall porosity amounts to ~50% of the volume. For sensing, we exploited the double-scale porosity of the layer such that the meso-pores behave as highways for the gas species to enter the whole thickness and deeply imbue the network of nanopores. This enhances the probability of surface interaction. The overall TiO2 structure accounts for more than one order of magnitude sensitivity exhibited by a 350nm- thick spongy layer to 44 ppm of ethanol at 250 o C. The sensitivity remains relatively high at 17 ppm of ethanol concentration. Moreover, the response of the material is independent of the ambient humidity with a response time as low as ~10s. Demonstrating high performances in low-power consumption sensing devices using this innovative layer with scaled thickness integrated by a simple procedure represents an important step forward both in terms of materials saving and in terms of industrial benefits.