We report on a very significant enhancement of the thermal, chemical, and mechanical stability of self-organized TiO₂ nanotubes layers, provided by thin Al₂O₃ coatings of different thicknesses prepared by atomic layer deposition (ALD). TiO₂ nanotube layers coated with Al₂O₃ coatings exhibit significantly improved thermal stability as illustrated by the preservation of the nanotubular structure upon annealing treatment at high temperatures (870 °C). In addition, a high anatase content is preserved in the nanotube layers against expectation of the total rutile conversion at such a high temperature. Hardness of the resulting nanotube layers is investigated by nanoindentation measurements and shows strongly improved values compared to uncoated counterparts. Finally, it is demonstrated that Al₂O₃ coatings guarantee unprecedented chemical stability of TiO₂ nanotube layers in harsh environments of concentrated H₃PO₄ solutions.

Monoclinic Ta₃N₅ thin films were synthesized by thermal nitridation of directly sputtered Ta₂O₅ films. The dielectric constant of Ta₃N₅ film was found to be in between 7–9 and its band structure has shown a strong dependence on the pH of the electrolyte.

Although a proposal of resonance bonds in crystalline phase-change materials based on the GeSbTe system has been provided, we do not find any clear evidence in favor of the proposal. The ellipsometric study demonstrates that a change in the high frequency dielectric constant ε_∞ between the amorphous and crystalline phases is only scaled by the average bandgap (the Penn gap rule). Even for a pure antimony film, regarded as a prototype resonance bonding material, ε_∞ was found to follow the Penn gap rule. Experimentally, we did not find any evidence of a significant change in the optical transition matrix element during the phase change, which is necessary to support the idea of resonance bonds.