Physical Review B
The structure and cooperative proton ordering of two-dimensional sheets of croconic acid were studied with scanning tunneling microscopy and first-principles calculations. Unlike in the crystalline form, which exhibits a pleated, densely packed polar sheet structure, the confinement of the molecules to the surface results in hydrogen-bonded chiral clusters and networks. First-principles calculations suggest that the surface stabilizes networks of configurational isomers, which arise from direct hydrogen transfer between their constituent croconic acid monomers. Some of these configurations have a net polarization. It is demonstrated through constrained molecular dynamics simulations that simultaneous proton transfer between any two molecules can occur spontaneously. This finding is a prerequisite for the occurrence of in-plane ferroelectricity based on proton transfer in 2D sheets.
This article may be downloaded for personal use only. Any other use requires prior permission of the author and APS Publishing. This article appeared at Phys. Rev. B 87, 041402 and may be found at http://dx.doi.org/10.1103/PhysRevB.87.041402
Kunkel, Donna A.; Hooper, James; Simpson, Scott; Rojas, Geoffrey A.; Ducharme, Stephen; Usher, Timothy; Zurek, Eva; and Enders, Axel, "Proton transfer in surface-stabilized chiral motifs of croconic acid" (2013). Physics Faculty Publications. 4.