Size Effect on the Short Range Order and the Crystallization of Nanosized Amorphous Alumina

Drawing inspiration from nature, where some organisms can control the short-range order of amorphous minerals, we successfully manipulated the short-range order of amorphous alumina by surface and size effects. By utilizing the atomic layer deposition (ALD) method to grow amorphous nanometrically thin films, combined with state-of-the-art electron energy loss spectroscopy (EELS) and X-ray photoelectron spectroscopy (XPS), we showed experimentally that the short-range order in such films is strongly influenced by size. This phenomenon is equivalent to the well-known size effect on lattice parameters and on the relative stability of different polymorphs in crystalline materials. Additionally, direct measurements of crystallization temperature have shown a dramatic increase in amorphous to crystalline phase transition temperature for thinner amorphous Al2O3 films. Finally, we show that the short-range order changes differently, as dictated by size, while still in the amorphous phase, before the amorphous to crystalline transformation takes place.