Ultrathin highly porous alumina films prepared by alucone ABC molecular layer deposition (MLD)

Abstract

Highly structured porous alumina thin films have many practical uses, including membrane applications and catalyst encapsulation. One route to synthesizing these films that offers exceptional control over film thickness to several angstroms starts with the molecular layer deposition (MLD) of an aluminum alkoxide (alucone) film. Oxidizing the alucone film removes the organic component and produces the desired nanoporous alumina. The pore size can be controlled by selection of the length of the carbon chain in the polymer film. In this study, 500nm silica nanoparticles were coated with 10–40cycles of alucone using a three-step ABC MLD process. Trimethylaluminum, ethanolamine, and maleic anhydride were used as precursors. The organic component of the alucone films was removed in air by calcination at elevated temperature or in water at room temperature. It is shown that the pore size of the porous films can be increased from 0.6 to 0.8nm by depositing an alucone film having longer carbon chains. Film surface area, composition, thickness, and pore size were measured, confirming that the ABC MLD process can produce high quality porous alumina films and provide a pathway to tune nanopore size in these films.