Study of Thin Film Coatings by IR Phonon-Polariton Spectroscopy Methods

Abstract

The methods of vibrational spectroscopy in far and near fields are used for studying thin (nanometer thick) AlN and MgO films on sapphire. It is shown that in the case of monolayer AlN films formed by the method of sapphire nitridation, the frequencies of longitudinal optical phonons of the film decrease in comparison with those of a single crystal, but the frequencies of transverse optical phonons increase. This means that the crystal structures of the film and the surface of the sapphire substrate modify. The solid solution (Al₂O₃)_{1 – x}(AlN)_x of variable composition appears in the transition layer (at the interface); the parameters of the AlN crystal cell change smoothly. In the case of the epitaxial growth of MgO films on sapphire, during the first stage, most likely, only the crystal structure of the sapphire surface is modified because the frequencies of the optical phonons of MgO films and the single crystal are the same. With an increase in the thickness of the MgO film, tensile stresses are accumulated in it, changing the frequencies of the optical phonons.