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Atomic force microscopy was employed to follow the development of Al 2 O 3 films deposited by atomic layer epitaxy (ALE) from AlCl 3 and H 2 O. In contrast to the earlier observations that substantial agglomeration takes place in the beginning of the ALE growth of polycrystalline films, only very small agglomerates were formed during the growth of the amorphous Al 2 O 3 films. Consequently, no pronounced surface roughening took place with increasing film thickness and the resulting films remained much smoother than the polycrystalline films deposited by ALE. Even a 730 nm thick Al 2 O 3 film had a root-mean-square roughness of only 0.7 nm.

The structural development of HfO2 thin films grown from HfCl4 and water onto glass substrates by atomic layer epitaxy at 500 °C was studied with X-ray diffraction, atomic force microscopy and scanning electron microscopy. The films were found to contain two regions of different crystallinity: a thin amorphous starting layer and a subsequent preferentially oriented polycrystalline layer. The films were built up of densely packed grains. Substantial surface roughening occurred along with increasing film thickness. The films were chlorine free as analyzed by Rutherford backscattering spectrometry.

The surface smoothness of TiO2 films grown by atomic layer epitaxy was improved by incorporating thin intermediate Al2O3 layers into them. The elimination of light scattering from the film surface caused a marked increase in the specular transmittance. Optical measurements, atomic force microscopy, scanning electron microscopy and X-ray diffraction were used in examining the relationships between the amount of Al2O3 added and the optical, morphological and structural properties of the films. The mechanism of the surface roughness reduction is discussed.