Abstract
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.
Original language | English (US) |
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Article number | 041402 |
Journal | Physical Review B - Condensed Matter and Materials Physics |
Volume | 87 |
Issue number | 4 |
DOIs | |
State | Published - Jan 2 2013 |