Films of amorphous aluminum oxide were deposited from vaporized alkylaluminum alkoxide compounds and oxygen. For example, a gaseous mixture of triethyldialuminum tri-sec-butoxide vapor and dry air deposits amorphous aluminum oxide films on substrates heated to temperatures around 400 °C. Transparent, smooth, adherent films of aluminum oxide were formed on silicon, glass and metal substrates. The new precursors display a number of advantages over previously used sources for aluminum oxide. They are non-pyrophoric, low-viscosity, low-cost liquids. High deposition rates, over 0.2 μm/min, were observed. The coatings have high purity, high electrical resistivity and high transparency to light. They are excellent barriers to diffusion of water and of ions, such as sodium. These films are useful in optical coatings, as wear-resistant hard coatings, and as diffusion barriers that protect flat panel displays, computer microcircuits, solar cells and metals from corrosion and degradation by impurities.