Growth of ultrathin Al2O3 films on Polydopamine-modified polyethylene terephthalate by atomic layer deposition

Abstract

Atomic layer deposition (ALD) has drawn considerable attention recently for depositing functional films on polymers. However, most polymers are inert and thermally fragile, thus posing many challenges during deposition. This study presents a novel strategy for ALD of an ultrathin Al2O3 film on alkali-treated polyethylene terephthalate (PET) via polydopamine (PDA) modification. The tightly adherent PDA layer exhibited numerous robust active sites (phenolic hydroxyl groups), which are highly desirable for precursor chemisorption during ALD. The modification process was systematically characterized. The PET substrate showed many active sites and a smooth surface after 24 h of PDA deposition. The island growth mode was found during the ALD of an Al2O3 film on the samples. The PDA layer absorbed a large quantity of the precursor (trimethylaluminum [TMA]) during the initial deposition, contributing to the early nucleation and continuous growth of the Al2O3 film. In addition, the presence of the PDA layer narrowed the region of TMA infiltration into the PET, resulting in the formation of a conformal film on the surface. Transmission electron microscopy indicated that an Al2O3 film with a thickness of about 10 nm was formed on the PDA-modified PET substrate after 100 ALD cycles, and exhibited excellent water vapor blocking characteristics. These findings suggest that the added PDA layer has tremendous potential to act as a bonding layer between polymers and ALD functional films.