Polarization control with plasmonic antenna-tips: A universal approach for optical nano-crystallography and vector-field imaging

TL;DR

This paper introduces a universal tilted antenna-tip method in tip-enhanced microscopy to control optical vector-fields, enabling detailed nano-crystallography and vector-field imaging of anisotropic materials with enhanced sensitivity.

Contribution

A novel tilted antenna-tip approach is developed to manipulate optical vector-fields in tip-enhanced microscopy, allowing for symmetry-selective imaging of nano-crystallographic structures.

Findings

Enhanced control of in-plane and out-of-plane optical field components.

High-resolution imaging of domain boundaries in 2D materials.

Applicable to various anisotropic linear and nonlinear optical responses.

Abstract

Controlling the propagation and polarization vectors in linear and nonlinear optical spectroscopy enables to probe the anisotropy of optical responses providing structural symmetry selective contrast in optical imaging. Here we present a novel tilted antenna-tip approach to control the optical vector-field by breaking the axial symmetry of the nano-probe in tip-enhanced near-field microscopy. This gives rise to a localized plasmonic antenna effect with significantly enhanced optical field vectors with control of both \textit{in-plane} and \textit{out-of-plane} components. We use the resulting vector-field specificity in the symmetry selective nonlinear optical response of second-harmonic generation (SHG) for a generalized approach to optical nano-crystallography and -imaging. In tip-enhanced SHG imaging of monolayer MoS$_2$ films and single-crystalline ferroelectric YMnO$_3$, we reveal nano-crystallographic details of domain boundaries and domain topology with enhanced sensitivity and nanoscale spatial resolution. The approach is applicable to any anisotropic linear and nonlinear optical response, and provides for optical nano-crystallographic imaging of molecular or quantum materials.