Symmetry lowering of LiNbO₃/LiTaO₃superlattice thin films studied by SHG

Identification of LiNbO3, LiNb3O8and Li3NbO4phases in thin films synthesized with different deposition techniques by means of XRD and Raman spectroscopy

“…LN films on C-sapphire substrates were deposited also by PLD, using a KrF excimer laser with 248 nm-wavelength and using LiNbO 3 congruent crystal as a target [33][34][35]. The films were deposited at 550 • C. The oxygen pressure and laser power were 50 mTorr and 2 J cm −2 , respectively.…”

Structural investigation of LN/LT¹ superlattice thin films by field effect scanning transmission electron microscopy equipped with electron disspersive x-ray spectroscopy

“…results by XRD and TEM-EDS, suggest the existence of Li-deficient phases. This is also supported by the observation by SHG microscopy [12] and micro-Raman spectroscopy [13]. The possible origin of the appearance is relatively high deposition temperature of superlattice thin films compared to that of LN single layer film because LN single layer films deposited at 550 C has the lattice constant closer to bulk LiNbO 3 .…”

“…It should be noted finally that the centrosymmetry of LiNb 3 O 8 are broken in thin films because our previous investigation by SHG microscopy observed the polarization dependent SHG signal, which is not allowed for centrosymmetric crystals [12].…”