Anomalous Crystal Growth on TiO2 Thin Film Induced by the AFM Tip

Abstract

Tip-induced nucleation and crystallization have been observed in polymer thin films. This work shows for the first time that it is possible to induce a rapid crystal growth on amorphous inorganic thin film using the AFM tip. The force applied on the AFM tip exerts an enormous pressure on the surface of an amorphous titania thin film. The movement of the tip displaced the spin-coated titania sol and deformed the film. The V-shaped grooves left by the passage of the tip measured 65 nm in width and penetrated 5 nm into the 15 nm thick film. Heat treatment in air at 723 K crystallizes the TiO2. Large TiO2 crystallized on the grooves compared to the surrounding film indicating an anomalous rapid crystal growth. It is speculated that the enormous tip pressure caused a local densification and structural rearrangement of the titania that presage nucleation resulting in a faster crystallization.