Visualization of Ferroelectric Domains in Thin Films of Molecular Materials Using Confocal Micro-Raman Spectroscopy

Ferroelectrics are an important class of functional materials. Among all their unique properties, the study of their ferroelectric domains and domain walls is of great interest due to their importance in ferroelectric applications. There are many methods to characterize ferroelectric domains, namely, scanning probe microscopy, optical microscopy, electron microscopy, etc. Currently, newly emerged molecular ferroelectrics are attracting much attention from chemists, physicists and researchers in material sciences due to their structural flexibility, light mass, simple fabrication, etc. However, for the characterization of molecular ferroelectric domains, most conventional methods require either a complicated preparation process or direct contact between physical probes and material surfaces, limiting the development of molecular ferroelectric materials. In this report, we have demonstrated that confocal micro-Raman spectroscopy, as a nondestructive and noncontact in-situ method, is very suitable for studying the ferroelectric polarization and structures of domains in molecular ferroelectrics. Taking recently reported molecular ferroelectric trimethylchloromethyl ammonium trichlorocadmium(II) (TMCM-CdCl₃) as an example, the non-180° domains have been characterized and visualized at different temperatures. Such a simple and extendable method requires minimum sample preparation, which would further benefit the research of molecular ferroelectric domain engineering and promote the miniaturization and integration of molecular ferroelectric films.