Investigation of the nanodomain structure formation by piezoelectric force microscopy and Raman confocal microscopy in LiNbO_3 and LiTaO_3 crystals

摘要

Piezoelectric force microscopy (PFM) and Raman confocal microscopy have been used for studying the nanodomain structures in congruent LiNbO_3 and LiTaO_3 crystals. The high-resolution nanodomain images at the surface were observed via PFM. Raman confocal microscopy has been used for the visualization of the nanodomain structures in the bulk via layer-by-layer scanning at various depths. It has been shown experimentally that the nanodomain images obtained at different depths correspond to domain images at the polar surface obtained at different moments: the deeper the nanodomain, the earlier the moment. Such a correlation was applied for the reconstruction of the evolution of the domain structures with charged domain walls. The studied domain structures were obtained in highly non-equilibrium switching conditions realized in LiNbO_3 and LiTaO_3 via pulse laser irradiation and the electric field poling of LiNbO_3, with the surface layer modified by ion implantation. The revealed main stages of the domain structure evolution allow the authors to demonstrate that all geometrically different nanodomain structures observed in LiNbO_3and LiTaO_3 appeared as a result of discrete switching.