Strain-dependence of χ(2) in thin film barium strontium titanate

Abstract

Optical second-harmonic generation (SHG) in reflection characterized variations in the second-order nonlinear optical susceptibility χ(2) of Ba1−xSrxTiO3 (BSTO) alloy films grown epitaxially on SrTiO3(001) (STO) as Sr molar ratio x changed from 0 to 1 and thickness from 10 to 50 nm. X-ray diffraction showed that BSTO films with x ≳ 0.1 were highly crystalline and compressively strained with out-of-plane (in-plane) lattice constant 4.09 > c > 3.97 (3.903 < a < 3.907 Å, pinned to substrate) for 0 < x < 1. Spectroscopic ellipsometry showed that the BSTO dielectric function was nearly x-invariant in the range of fundamental (780 nm) and SH (390 nm) wavelengths. SHG intensity peaked at x ∼ 0.3 for a given film thickness, suggesting that composition control can optimize ferroelectric and electro-optic properties of BSTO films grown on STO buffer layers.

Epitaxial, electro‐optically active barium titanate thin films on silicon by chemical solution deposition

“…Although non‐ferroelectric BTO films or powders stabilize in cubic symmetry, particularly for small grain size, the film under current study retains non‐vanishing EO response, which would not be present in crystal structures with inversion symmetry. Frey and Payne demonstrated that ultra‐fine‐grained, sol‐gel‐derived BTO powder can exhibit room temperature orthorhombic structure and maintain non‐zero second harmonic generation, which is also a second‐order nonlinear optical effect . The small and disperse grain sizes observed in the film, in combination with the relatively high defect density (Figure ), which also provides sources for depolarizing effects, are likely the primary contributors to the absence of finite macroscopic polarization and overall diminished EO response.…”

“…Frey and Payne demonstrated that ultra-fine-grained, sol-gel-derived BTO powder can exhibit room temperature orthorhombic structure and maintain non-zero second harmonic generation, 22 which is also a second-order nonlinear optical effect. 44 The small and disperse grain sizes observed in the film, in combination with the relatively high defect density (Figure 4), which also provides sources for depolarizing effects, are likely the primary contributors to the absence of finite macroscopic polarization and overall diminished EO response. Indeed, high Pockels coefficients are correlated with larger grain sizes.…”

Ferroelectric composite artificially-structured functional material: multifield control for tunable functional devices

“…Electric field and strain are important factors in tuning ferroelectrics [54,55,122]. They always couple with each other, and deduce to many fantastic properties.…”

“…A typical ferroelectric material usually has two polarization states, which are stable and can be converted reversely to each other by applying electric fields [51]. Moreover, ferroelectric polarization can be tuned by temperature and strain [52][53][54][55]. It is reported that ferroelectrics possess various interactions between mechanical, thermal, and electrical characteristics [56].…”