Study of crystallization of LiNbO₃ films from metal alkoxides

Abstract

The crystallization process of epitaxial LiNbO₃ films on sapphire (0 0 0 1) substrates was investigated by Raman microprobe spectroscopy. LiNbO₃ gel films were prepared by the sol-gel method using metal alkoxide precursors on sapphire (0 0 0 1) substrates and heat treated at various temperatures below 500 °C to produce epitaxial LiNbO₃ films. Analyses by electron spectroscopy for chemical analysis and SEM revealed LiNbO₃ films were stoichiometric and homogeneous. Raman spectra of the film prepared at 250 °C indicated that the NbO₆ octahedral coordination structure in LiNbO₃ began to form as the initial state of crystallization. As the heat-treatment temperature was raised, the Raman bands became sharper and increased in spectral intensity and were seen to be the characteristic Raman bands of crystalline LiNbO₃. Refractive indices of the obtained films indicated appropriate values. As a method to crystallize the more highly preferred orientation to (0 0 6) LiNbO₃ film at relatively low temperature, the formation of an underlayer film from diluted solution prior to multiple dip-coating, was found to be very promising.