Decoupling sensor morphology and material: Atomic layer deposition onto nanocolumn scaffolds

We have demonstrated direct surface modification of nanocolumn relative humidity sensors with conformal coatings deposited by atomic layer deposition (ALD). TiO2 and Si nanocolumn films were fabricated using glancing-angle deposition (GLAD). Both film types were subsequently coated with ≈0.3–4 nm thick ALD TiO2. The impact of the addition of subnanometer TiO2 layers on water contact angle, sensor responsivity, and the utility of an ultraviolet regeneration procedure has been tested. We have found that TiO2 coatings as thin as 0.5 nm provide much of the humidity sensing and regeneration functionality of a photocatalytic TiO2 film. In principle, any GLAD film architecture may be used as a scaffold for an active sensing layer, decoupling surface functionality and nanoscale morphology. Such capability offers an additional degree of freedom for designers of nanostructured gas sensors.