Vapor-liquid-solid (VLS) Si nanotowers were coated with nanocrystalline SiC to form a Si-SiC core-shell composite. Due to a mismatch in the coefficients of thermal expansion (CTE), the Si core was under a compressive stress following the deposition. The composite tower was then cross-sectioned using focused ion beam milling, exposing the Si core. Indentation into the Si showed an increased toughness as a function of diameter compared to similar sized Si nanotowers and nanospheres. This result is explained through enhanced dislocation and phase transformation plasticity in the Si core from the CTE compressive stresses.
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Acknowledgments The authors would like to thank J.D. Nowak for TEM contributions and V. Sivakov and S. Christiansen for growing the Si nanotowers. This work was supported financially by the National Science Foundation (CTS-0506748) and the Air Force Office of Scientific Research (AOARD-08-4134). Parts of this work were carried out in the Characterization Facility, University of Minnesota, which receives partial support from NSF through the MRSEC program.
Copyright 2012 Elsevier B.V., All rights reserved.
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