Highly-sensitive detection of the lattice distortion in single bent ZnO nanowires by second-harmonic generation microscopy

TL;DR

This paper demonstrates a highly-sensitive, non-invasive optical method using second-harmonic generation microscopy to detect lattice distortions in single bent ZnO nanowires, surpassing traditional electron microscopy sensitivity.

Contribution

The study introduces SHG microscopy as a sensitive, all-optical technique for in situ detection of lattice distortions in ZnO nanowires, with high sensitivity and without vacuum requirements.

Findings

SHG intensity ratio decreases significantly with increased bending

Non-axisymmetrical SHG patterns indicate twisting distortion

Method detects lattice distortion with sensitivity better than 0.01 nm

Abstract

Nanogenerators based on ZnO nanowires (NWs) realize the energy conversion at nanoscale, which are ascribed to the piezoelectric property caused by the lattice distortion of the ZnO NWs. The lattice distortion can significantly tune the electronic and optical properties, and requires a sensitive and convenient measurement. However, high-resolution transmission electron microscopy (HRTEM) technique provides a limited sensitivity of 0.01 nm on the variation of the lattice spacing and requires vacuum conditions. Here we demonstrate a highly-sensitive detection of the lattice distortion in single bent ZnO NWs by second-harmonic generation (SHG) microscopy. As the curvature of the single bent ZnO NW increases to 21 mm-1 (<4% bending distortion), it shows a significant decrease (~70%) in the SHG intensity ratio between perpendicular and parallel excitation polarization with respect to c-axis of ZnO NWs. Importantly, the extraordinary non-axisymmetrical SHG polarimetric patterns are also observed, indicating the twisting distortion around c-axis of ZnO NWs. Thus, SHG microscopy provides a sensitive all-optical and non-invasive method for in situ detecting the lattice distortion under various circumstances.