Near-Field Optical Microscopy of Defects in Cholesteric Oligomeric Liquid Crystal Films

Abstract

This paper describes formation of 2-D-hexagonal structures with a periodicity ∼0.5–0.8 μm in the defects of thin films of cholesteric oligomeric liquid crystals prepared by the evaporation of the solvent from the oligomer solution on the substrate. These regular arrays were observed by scanning near-field optical and concurrent atomic force microscopy. The mechanisms considered are both Bénard-Marangoni and buoyancy convections induced by solvent evaporation and air-bubble creation around the condensed water droplets from the air during evaporative cooling. Hexagonal structures prepared by this method can be used in photonic devices for emission enhancement, for instance, in liquid crystal lasers and single photon sources with oligomeric liquid crystal hosts.

Keywords:

• cholesteric oligomeric films
• hexagonal arrays
• near-field microscopy

Acknowledgments

The authors acknowledge the support by the U.S. Army Research Office under Award No. DAAD19-02-1-0285 and National Science Foundation Award ECS-0420888. The work was also supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC03-92SF19460, the University of Rochester, and the New York State Energy Research and Development Authority. The support of DOE does not constitute an endorsement by DOE of the views expressed in this article.

Receipt of CLC oligomer from F. Kreuzer of Wacker, Munich is gratefully acknowledged. The authors thank K. Marshall and J. Starowitz for advice and support in the optical material laboratory, O. Lavrentovich and S. Shiyanovskii for discussion and providing useful references.