Nonlinear optical probing of nanocrystalline orientation in epitaxial ferroelectric thin films

Abstract

Epitaxially grown ferroelectric BaBi 4 Ti 4 O 15 thin films were studied by optical second-harmonic ͑SH͒ generation using a femtosecond titanium:sapphire laser at 800 nm wavelength. By varying both the incidence and the azimuthal angle and registering the second-harmonic intensity, a significant correlation was found between the azimuthal dependence of the measured SH signal and the nanoscopic texture of the samples, which was determined by electron microscopy and x-ray diffraction. In particular, two different types of grains with different crystallographic orientations generate different SH intensity maxima with fourfold azimuthal symmetry, distinguishable from an isotropic background due to a c-axis oriented main layer. This correlation suggests the use of the SH technique for a purely optical characterization of the film orientation and thickness.

Characterization of domain distributions by second harmonic generation in ferroelectrics

“…[50][51][52][53] However, in a ferroelectric with many possible domain variants, the quantitative analysis becomes very complex, which makes it difficult to achieve a completed picture for domain structures through the polarizationdependent SHG response only along the fixed domain directions of a ferroelectric sample. 37,42,54,55 To solve this problem, an azimuth-dependent SHG is introduced to distinguish the predominant domain orientation from many random variants, because a rotation of a sample around z-axis can change the ferroelectric polarization directions of individual domains relative to the incident beam without external electric field, where different oriented domains lead to different SHG responses. Therefore, in this work, we have developed an improved ferroelectric domain characterization technique by collecting azimuth-polarization-dependent SHG signals with varying both the polarization angle of the incident beam and the azimuth angle of sample relative to the beam.…”