  Molecular ferroelectric materials have attracted widespread attention due to
their abundant chemical diversity, structural tunability, low synthesis
temperature, and high flexibility. Meanwhile, the integration of molecular
ferroelectric materials and Si is still challenging, while the fundamental
understanding of the ferroelectric switching process is still lacking. Herein,
we have successfully synthesized the imidazole perchlorate (ImClO4) single
crystals and a series of high-quality highly-oriented thin films on a Si
substrate. A high inverse piezoelectric coefficient (55.7 pm/V) is demonstrated
for the thin films. Two types of domain bands can be observed (in the size of a
few microns): type-I band tilts ~60{\deg} with respect to the horizontal axis,
while the type-II band is perpendicular to the horizontal axis. Most of the
domain walls (DWs) are 180{\deg} DWs for the two bands, while some 109{\deg}
DWs can also be observed. Interestingly, the DWs in type-I band are curved,
charged domain walls; while the 180{\deg} DWs in type-II band are straight,
noncharged domain walls. After applying +20 V for 5 s through a PFM tip, the
180{\deg} DWs in type-I band shrink first, then disconnect from the band
boundary, forming a needle-like domain with a size of ~100 nm. The needle-like
domain will extend toward the band boundary after an inverse bias is applied
(-20 V), and expand along the band boundary after touching the boundary.
Whereas for the type-II domain band, the 180{\deg} DWs are more mobile than the
109{\deg} domain walls, which displaces ~500 nm after applying +20 V. While
such displacement is much shorter after the application of a negative bias for
the same duration, starting from the positively poled sample. We hope to spur
further interest in the on-chip design of the molecular ferroelectrics based
electronic devices.
