Croconic Acid: Surface and Electric Field Influence on Deposition

RM 216

Crystaline croconic Acid (CA) has been the focus of study due to its ferroelectric properties. In this study, croconic acid was modelled in combination with efforts to extend this function to thin films. Originally, CA properties were studied on an ideal silica surface, and models were developed to explain the fundamental differences in deposition properties on silica, with and without an applied electric field. The calulations provided theory to support the experimental observation of needle-like structures that CA forms in the absence of an electric field, while an ordered thin film forms with a strong electric field. Plane wave density functional theory within the VASP program was used to calculate surface structures. Recently, the models were extended to CA on other surfaces of interest to experimentalists. In the study of CA on gold with an initial canted motif and a strong electric field, croconic acid tries to keep itself in a canted motif during its movement across the gold surface. This is consistent with the polarization behavior observed by experimentalists. The opposite is true in the absence of a field, where the molecule moves more neutral to the surface, with no specific orientation. This agrees with previous experimental work, in which no polarization was observed, because of the cancellation of molecular dipoles due to flat dimerization of CA in respect to the gold surface. To further our study of CA on a silica surface, a hydrogenated silicon dioxide surface, more similar to the experimental sample, was used as the insulating surface. This was done to observe the hydrogen bonding behavior of CA under the presence or absence of an electric field. Relative energies were calculated among the reactive sites of CA to observe the favored motif and how it affects the dimerization of the molecule to form an ordered thin film.