One-dimensional anodic TiO2nanotubes coated by atomic layer deposition:Towards advanced applications

Abstract

Atomic layer deposition (ALD) represents a unique deposition technique that allows to coat uniformly var-ious high aspect ratio (HAR) porous nanostructures, in addition to its traditional role to coat flat substrates(e.g. Si wafers). Self-organized anodic TiO2nanotube (TNT) layers belong among the most investigatedinorganic nanostructures. They possess highly functional materials with promising application potentialacross many technological fields. Herein, we review the utilization of ALD for the functionalization ofanodic TNT layers by secondary materials to advance their physicochemical and photoelectrochemicalproperties. First, the application of ALD for functionalization of porous aluminium oxide, which representfundamental HAR nanostructure, is briefly introduced. Then the main experimental parameters govern-ing the uniformity and the conformality of ALD coating within HAR nanostructures are discussed. Finally,the review focuses on the use of ALD to deposit secondary materials into TNT layers for various purposes— the introduction of pioneering studies is followed by particular examples of ALD based functional-izations of coated TNT layers for optimized visible-light absorption, charge separation and passivation,(photo)catalysis, stability, gas sensing, and energy storage.Atomic layer deposition (ALD) represents a unique deposition technique that allows to coat uniformly var-ious high aspect ratio (HAR) porous nanostructures, in addition to its traditional role to coat flat substrates(e.g. Si wafers). Self-organized anodic TiO2nanotube (TNT) layers belong among the most investigatedinorganic nanostructures. They possess highly functional materials with promising application potentialacross many technological fields. Herein, we review the utilization of ALD for the functionalization ofanodic TNT layers by secondary materials to advance their physicochemical and photoelectrochemicalproperties. First, the application of ALD for functionalization of porous aluminium oxide, which representfundamental HAR nanostructure, is briefly introduced. Then the main experimental parameters govern-ing the uniformity and the conformality of ALD coating within HAR nanostructures are discussed. Finally,the review focuses on the use of ALD to deposit secondary materials into TNT layers for various purposes— the introduction of pioneering studies is followed by particular examples of ALD based functional-izations of coated TNT layers for optimized visible-light absorption, charge separation and passivation,(photo)catalysis, stability, gas sensing, and energy storage.