Room Temperature Ferroelectricity in Continuous Croconic Acid Thin Films

TL;DR

This paper demonstrates room temperature ferroelectricity in nanometer-thin croconic acid films, achieved through a novel low-temperature vacuum deposition process, enabling potential flexible organic electronic devices.

Contribution

It introduces a new solvent-free growth method for continuous croconic acid thin films exhibiting ferroelectricity at room temperature.

Findings

Ferroelectricity confirmed by polarization hysteresis loops.

Nanometer-thin, polycrystalline films with controlled grain size.

Correlation between domain structures and grain patterns.

Abstract

Ferroelectricity at room temperature has been demonstrated in nanometer-thin quasi 2D croconic acid thin films, by the polarization hysteresis loop measurements in macroscopic capacitor geometry, along with observation and manipulation of the nanoscale domain structure by piezoresponse force microscopy. The fabrication of continuous thin films of the hydrogen-bonded croconic acid was achieved by the suppression of the thermal decomposition using low evaporation temperatures in high vacuum, combined with growth conditions far from thermal equilibrium. For nominal coverages >=20 nm, quasi 2D and polycrystalline films, with an average grain size of 50-100 nm and 3.5 nm roughness, can be obtained. Spontaneous ferroelectric domain structures of the thin films have been observed and appear to correlate with the grain patterns. The application of this solvent-free growth protocol may be a key to the development of flexible organic ferroelectric thin films for electronic applications.