High-contrast imaging of 180{\deg} ferroelectric domains by optical microscopy using ferroelectric liquid crystals

TL;DR

This paper demonstrates that ferroelectric liquid crystals can be used as an optical microscopy technique to achieve high-contrast imaging of 180-degree ferroelectric domains in lithium niobate, enabling non-destructive domain analysis.

Contribution

The study introduces a novel optical microscopy method using ferroelectric liquid crystals to image ferroelectric domains with high contrast, which was not previously possible with standard liquid crystals.

Findings

FLCs produce high-contrast images of ferroelectric domains.

The method allows non-destructive, optical read-out of ferroelectric domains.

Potential applications include photonic devices and ferroelectric memory read-out.

Abstract

Ferroelectric liquid crystals (FLCs) couple the direction of their spontaneous electric polarization to the direction of tilt of their optic axis. Consequently, reversal of the electric polarization by an electric field gives rise to an immediate and lasting optical response when an appropriately aligned FLC is observed between crossed polarizers, with one field direction yielding a dark image, and the opposite direction yielding a bright image. Here this peculiar electro-optic response is used to image, with high optical contrast, 180{\deg} ferroelectric domains in a crystalline substrate of magnesium-doped lithium niobate. The lithium niobate substrate contains a few domains with upwards electric polarization surrounded by regions with downward electric polarization. In contrast to a reference non-chiral liquid crystal that is unable to show ferroelectric behavior due to its high symmetry, the FLC, which is used as a thin film confined between the lithium niobate substrate and an inert aligning substrate, reveals ferroelectric domains as well as their boundaries, with strong black and white contrast. The results show that FLCs can be used for non-destructive read-out of domains in underlying ferroelectrics, with potential applications in e.g. photonic devices and non-volatile ferroelectric memories.