Polarity-dependent nonlinear optics of nanowires under electric field

Abstract

Polar materials display a series of interesting and widely exploited properties owing to the inherent coupling between their fixed electric dipole and any action that involves a change in their charge distribution. Among these properties are piezoelectricity, ferroelectricity, pyroelectricity, and the bulk photovoltaic effect. Here we report the observation of a related property in this series, where an external electric field applied parallel or anti-parallel to the polar axis of a crystal leads to an increase or decrease in its second-order nonlinear optical response, respectively. This property of electric-field-modulated second-harmonic generation (EFM-SHG) is observed here in nanowires of the polar crystal ZnO, and is exploited as an analytical tool to directly determine by optical means the absolute direction of their polarity, which in turn provides important information about their epitaxy and growth mechanism. EFM-SHG may be observed in any type of polar nanostructures and used to map the absolute polarity of materials at the nanoscale.

Strong In‐Plane Anisotropy and Giant Second Harmonic Generation Response of Organic Single‐Crystalline Microwire Arrays

“…The angle‐dependent SHG intensity of OH1 is different from other nanowires previously reported, such as Te, ZnO, GaAs, and DPFO, which show appreciable SHG signals when the polarization of FW laser is parallel or perpendicular to the microwires. [ 37–40 ] As for DAT2, polarization‐resolved SHG exhibits a fourfold rotational symmetry, and the SHG intensity reaches its maximum when the polarization direction is ±45 degrees to the microwires (Figure 4f). Calculating the polarization ratio ρ = ( I max − I min ) / ( I max + I min ) helps to provide a value of virtual unity.…”

The Microscopic Origin of Second Harmonic Generation Response: The Spatial Structure of Instantaneous Dipole Moments in Electron Excitation

“…Although there has yet no systematic mathematical description for dipole moment structure as the description for electron structure, two key strategies still can be found from our study to arrive at a large macroscopic SHG response. First, it is necessary that large magnitude of instantaneous dipole moments could be generated by electron transition from anion unit to cation unit, [32] here from the BO/AlO anion group to Ba cation. This requires an appropriate anion unit and cation, and an appropriate interaction between the anion unit and the cation.…”

Piezoelectricity, Pyroelectricity, and Ferroelectricity in Biomaterials and Biomedical Applications

“…The buildup of these free charges on the crystal's relative surface causes surface redox reactions, which allow the transformation of mechanical energy into chemical energy. [1,[28][29][30][31] Significant advancements in this field of study have been accomplished recently, resulting in the exploitation of various piezoelectric material-based catalysts, such as ZnO, [32][33][34] BaTiO 3 , [32][33][34] NaNbO 3 , [35,36] and KNbO 3 , [37] C 3 N 4 , [38] CdS, [39] and MoS 2 . [40]…”