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Tuesday, November 17, 2009

Highly birefringent vaterite microspheres: production, characterization and applications for optical micromanipulation

Simon J. Parkin, Robert Vogel, Martin Persson, Maren Funk, Vincent L. Loke, Timo A. Nieminen, Norman R. Heckenberg, and Halina Rubinsztein-Dunlop

This paper reports on a simple synthesis and characterization of highly birefringent vaterite microspheres, which are composed of 20–30 nm sized nanocrystalls. Scanning electron microscopy shows a quite disordered assembly of nanocrystals within the microspheres. However, using optical tweezers, the effective birefringence of the microspheres was measured to be Δn = 0.06, which compares to Δn = 0.1 of vaterite single crystals. This suggests a very high orientation of the nanocrystals within the microspheres. A hyperbolic model of the direction of the optical axis throughout the vaterite spherulite best fits the experimental data. Results from polarized light microscopy further confirm the hyperbolic model.

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