Azimuthal orientational correlations due to excluded volume epitaxy in growing anisotropic grains

Abstract

The microstructure of anisotropically shaped grains can strongly influence a range of material properties, including transport, mechanical and electro-optical. A grain-structure-related phenomenon, known as excluded volume epitaxy (EVE), is reported in this study. EVE is a local, inter-grain orientational correlations effect, which results from a combination of continuous nucleation of anisotropic grains and impingement of growing grains. Due to EVE, anisotropically shaped grains have a tendency to be similarly aligned in a local neighbourhood, despite the absence of any forced global orientation in the sample. The effect has been repeatedly observed by the authors in block copolymers, as illustrated by a representative TEM image. Optical microscopy of anisotropically shaped non-polymeric crystals revealed the generality of this effect. The simulation study revealed a tendency for azimuthal, inter-grain orientational correlation and re-confirmed the experimental observation of EVE.

Keywords:

• azimuthal orientational correlations
• anisotropic grains
• block copolymer microstructure
• transmission electron microscopy (TEM)
• grain growth

Acknowledgements

Funding from the US Army Research Laboratory through the Polymer Materials Center of Excellence at the University of Massachusetts-Amherst is acknowledged. The discussion with Professor D. Venkataraman, Department of Chemistry, University of Massachusetts Amherst about anisotropic crystals is kindly acknowledged. The authors also acknowledge the use of central facilities and the W.M. Keck electron microscope in the Material Research Science and Engineering Center (MRSEC) at the University of Massachusetts-Amherst.

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