  Inspired by nature, we investigate the short-range order effect on the
physical properties of amorphous materials. Amorphous Al2O3 thin films exhibit
a higher proportion of their 4-coordinated Al sites close to the surface,
causing variations in the average short-range order of the film. Below some
thickness, the density of these films changes with size. In this work, we
address the short-range order effect, through the thickness, on the electronic
and optical properties of atomic layer deposited (ALD) Al2O3 thin films. Both
the refractive index and the permittivity were found to vary with size. The
refractive index increased with thickness, and for thick films (~50 nm) it was
comparable to that of bulk amorphous Al2O3. The permittivity increased with
thickness as well, but did not attain those of the bulk material. We discuss
how these effects correlate with the density and short-range order. These
results shed light on the size effects in thin amorphous oxides, and may guide
the design of electronic and optical components and devices.
