Dresden 2006 – wissenschaftliches Programm

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O: Oberflächenphysik

O 14: Poster session I (Adsorption, Epitaxy and growth, Phase transitions, Surface reactions, Organic films, Electronic structure, Methods) (sponsored by Omicron Nanotechnology GmbH)

O 14.34: Poster

Montag, 27. März 2006, 18:00–21:00, P2

AFM Study of Defect-Induced Depressions of the Smectic-A/Air Interface — •Christian Bahr, Vincent Designolle, Stephan Herminghaus, and Thomas Pfohl — Max Planck Institute for Dynamics and Self-Organization, Bunsenstr. 10, 37073 Göttingen

The smectic-A/air interface of liquid-crystal droplets with antagonistic boundary conditions is studied by atomic force microscopy (AFM). The droplets are prepared on coated silicon wafers on which a planar alignment is preferred in contrast to the homeotropic alignment at the air interface. As a result, focal conic defects appear in the smectic-A phase causing a characteristic pattern of depressions in the droplet surface. The dimensions of the defect-induced depressions are measured by AFM as a function of temperature for two different compounds possessing a smectic-A – isotropic and a smectic-A – nematic transition. Whereas the results are independent of temperature in the smectic-A – isotropic case, reflecting the first-order nature of the transition, a pronounced temperature dependence is observed for the second compound, where the depth of the defect-induced depressions decreases continuously with increasing temperature and vanishes at the second-order transition to the nematic phase. These observations can be qualitatively explained through the behavior of the layer compressional elastic constant at the smectic-A – nematic transition.