Three-dimensional xenon dendrites: characterization of sidebranch growth.
In our experiments, we investigate in situ the growth of three-dimensional xenon crystals into an undercooled pure melt. Experimental studies have been extended from undisturbed growth conditions to more realistic growth conditions. Methods to characterize the transient growth of sidebranches of dendrites have been developed. Two types of sidebranches have been identified: Sidebranches initiated by selective amplification of thermal noise (type N) and sidebranches induced by macroscopic perturbations (type P). Type N sidebranches start to grow 3-7 tip radii behind the tip and are not correlated at the four fins. It has been verified that the sidebranch amplitude grows exponentially to z(2/5) as predicted by Brener and Temkin [E. Brener and D. Temkin, Phys. Rev. E 51, 351 (1995)]. Type P sidebranches are initiated by macroscopic perturbations. They start to grow at the tip and their amplitudes are significantly higher than the ones of type N sidebranches. The growth of type P sidebranches is symmetric at the four fins. The tip positions of type P sidebranches separate from the tip shape of a dendrite at a distance of about 5R from the tip, while for type N sidebranches this distance is about 10R.
Wittwer
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Laboratorium für Festkörperphysik, ETH Zurich, CH-8093 Zurich, Switzerland. owittwer@solid.phys.ethz.ch
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