Ferroelectric materials have many applications such as nonvolatile random access memories, sensors, capacitors, microactuators and optical components. We discovered that the ferroelectric assembly of molecules with a small dipole moment can be tracked and understood at the single-molecule level. Styrene molecules on gold surfaces form a variety of ordered structures from which the mechanism and energetics of assembly can be derived. This work will lead to a better understanding of both the finite domain size required for ferroelectric ordering to occur and the nanoscale mechanism of ferroelectric ordering and switching, which are both key questions in the field of ferroelectric devices.

Ferroelectric assembly of individual styrene molecules on Au{111}.[1]

     Ferroelectric materials have an interesting set of properties such as controllable polarization, piezoelectricity, and nonlinear optical and dielectric activity. As such, they have been utilized for many applications such as nonvolatile random access memories, sensors, capacitors, microactuators, and optical components. In recent years, device miniaturization has led to an interest in the development of smaller ferroelectric materials with even faster switching rates. This has raised questions about the relevant size effects that lead to deviations from bulk properties and the ultimate cessation of ferroelectric properties. By studying styrene, a simple hydrocarbon with a weak dipole moment, we have already begun investigating ferroelectric ordering and ferroelectric transitions at the single-molecule level.[1] This preliminary work demonstrated that important ferroelectric properties such as spontaneous polarization, long-range ordering and piezoelectricity could be achieved in nanoscale domains of a weakly polar molecule on a metal surface. We now aim to study ferroelectric assembly, switching, and the effect of an external electric field on a range of similar molecules with different dipole moments. This work will lead to a better understanding of both the finite domain size required for ferroelectric ordering to occur and the nanoscale mechanism of ferroelectric ordering and switching.
      As part of the ferroelectric assembly work we also discovered a novel effect of how the presence of organic molecules affects surface stability. Our experiments revealed that the presence of styrene, a weakly adsorbed molecule, dramatically restructures the gold surface at temperatures as low as 80 K.[2] This work has important consequences for many studies in which Au is used as a support for, or as an electrical contact to, molecules. One cannot assume that the atomic structure of the surface is static in the presence of weakly adsorbed molecules. By testing a series of similar molecules our work has subsequently revealed that the π-system of the molecule is responsible for the effect.

1. Baber, A. E.; Jensen, S. C.; Sykes, E. C. H. Dipole-Driven Ferroelectric Assembly of Styrene on Au{111}. Journal of the American Chemical Society 2007, 129, 6368-6369.
2. Baber, A. E.; Jensen, S. C.; Iski, E. V.; Sykes, E. C. H. Extraordinary atomic mobility of Au{111} at 80 Kelvin: Effect of styrene adsorption. Journal of the American Chemical Society 2006, 128, 15384-15385.