Regensburg 2002 – scientific programme

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DY: Dynamik und Statistische Physik

DY 46: Poster

DY 46.18: Poster

Thursday, March 14, 2002, 15:30–18:00, D

Phase behavior of colloidal monolayers on hexagonally patterned substrates — •Matthias Brunner and Clemens Bechinger — University of Konstanz, Physics Department

Colloidal suspensions are well known as model systems for investigations of the melting and freezing in two-dimensional (2D) systems. While most of the previous work has been done on homogeneous substrates, much less is known about the phase behavior of 2D systems on patterned substrates although the latter is important when modeling the substrate potential of a crystalline, i.e. atomically corrugated surface. In contrast to earlier experiments, where periodic, one-dimensional substrate potentials were investigated [1], here we produce 2D patterned substrates for colloidal particles by the interference pattern of three laser beams which lead to a hexagonal substrate potential.

We present experiments where the density of particles is chosen in a way that each laser potential well is occupied by three electrically charged colloidal particles (trimer). Since the particle density is chosen to be below the limit of spontaneous crystallization, at small laser intensities a liquid structure is observed. At higher laser intensities a laser-induced crystal is found where the trimers are ordered with respect to their translational and orientational position. When the laser intensity is increased further, orientational order is lost, although the fluctuation strength of the particles becomes reduced. To explain this counterintuitive phenomenon, we discuss the role of particle fluctuations.

1. C. Bechinger, M. Brunner, and P. Leiderer, Phys. Rev. Lett. 86, 930 (2001).