Azimuthal Reorientation of Pentacene upon 2D Condensation

Abstract

We report a novel two-dimensional gas-solid phase transition of pentacene molecules on the Cu(110)-(2×1)O surface where the 2D condensation is accompanied by a reversible azimuthal rotation of the pentacene molecules. The change of the optical anisotropy associated with this reorientation allows us to explore the 2D condensation as a function of coverage and temperature by reflectance difference spectroscopy. As a result, the 2D heat of condensation of pentacene on Cu(110)-(2×1)O is determined to be 84 meV, which is more than one order of magnitude smaller than the respective value for 3D crystallization. Published by American Physical Society. Published by the American Physical Society under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. © 2013 American Physical Society.