Spherulite-enhanced Macroscopic Polarization in Molecular Ferroelectric Films from Vacuum Deposition

TL;DR

This study demonstrates that microstructure density, particularly spherulite formation, is crucial for achieving macroscopic ferroelectric polarization in molecular ferroelectric films, advancing their fabrication and application potential.

Contribution

It reveals the role of microstructure, especially spherulites, in enabling macroscopic ferroelectricity in molecular films, which was previously not well understood.

Findings

Post-growth annealing promotes spherulite formation.

Microstructure density correlates with ferroelectric switching.

Dense microstructures enable macroscopic ferroelectric behavior.

Abstract

Proton-transfer type molecular ferroelectrics hold great application potential due to their large spontaneous polarizations, high Curie temperatures, and small switching fields. However, it is puzzling that preparation of quasi-2D films with macroscopic ferroelectric behaviors has only been reported in few molecular ferroelectrics. To resolve this puzzle, we studied the effect of microstructures on macroscopic ferroelectric properties of 5,6-Dichloro-2-methylbenzimidazole (DC-MBI) films grown using low-temperature deposition followed by restrained crystallization (LDRC) method. We revealed a competition between dense spherulites and porous microstructures containing randomly oriented nanograins in as-grown films. Post-growth annealing at moderate temperature promotes the formation of spherulites which leads to macroscopic ferroelectric polarization switching. These results highlight microstructure density as a critical factor for macroscopic ferroelectric properties, potentially resolving the puzzle for absence of macroscopic ferroelectric behavior in molecules ferroelectric films. We expect the approach for enhancing microstructure density offered in this work to greatly advance fabrication of quasi-2D molecular ferroelectrics films and to unlock their potential in device applications.