  The discovery of stable room temperature ferroelectricity in Croconic Acid,
an organic ferroelectric material, with polarization values on par with those
found in inorganic ferroelectric materials and highest among organic
ferroelectric materials, has opened up possibilities to realize myriads of
nano-electronic and spintronic devices based on organic ferroelectrics. Such
possibilities require an adequate understanding of the ferroelectric properties
of Croconic Acid grown on surfaces that are commonly employed in device
fabrication. While several macroscopic studies on relatively larger crystals of
Croconic Acid have been performed, studies on thin films are only in their
early stages. We have grown thin films of Croconic Acid on gold and cobalt
surfaces, which are commonly used in spintronic devices as metallic electrodes,
and studied the ferroelectric response of the films using ex-situ Piezoresponse
Force Microscopy at room temperature. We show that the polarization reversal in
Croconic Acid domains is sensitive to the substrate surface. Using the same
experimental protocol, we observe the robust polarization reversal of a single,
mostly in-plane electrical domain for a cobalt substrate, whereas polarization
reversal is hardly observed for a gold substrate. We attribute this difference
to the influence of substrates on the Croconic Acid molecular networks. Our
study suggests that to realize devices one has to take care about the substrate
on which Croconic Acid will be deposited. The fact that polarization switching
is robust on cobalt surface can be used to fabricate multifunctional devices
that utilize the cobalt-Croconic Acid interface.
