Silicon crystals have an important role in the electronics industry, and silicon nanoparticles have applications in areas such as nanoelectromechanical systems, photonics and biotechnology. However, the elastic-plastic transition observed in silicon is not fully understood; in particular, it is not known if the plasticity of silicon is determined by dislocations or by transformations between phases. Here, based on compression experiments and molecular dynamics simulations, we show that the mechanical properties of bulk silicon and silicon nanoparticles are significantly different. We find that bulk silicon exists in a state of relative constraint, with its plasticity dominated by phase transformations, whereas silicon nanoparticles are less constrained and display dislocation-driven plasticity. This transition, which we call deconfinement, can also explain the absence of phase transformations in deformed silicon nanowedges. Furthermore, the phenomenon is in agreement with effects observed in shape-memory alloy nanopillars, and provides insight into the origin of incipient plasticity.
Bibliographical noteFunding Information:
The authors gratefully acknowledge the CSC–IT Center for Science for computation resources and the Ceramic Society of Japan for invaluable assistance. R.N., D.C. and N.T. thank the Academy of Finland for partial support under the FINNANO programme and NANOSPIKE research project. A.B. and W.W.G. acknowledge the support of the National Science Foundation (NSF; CTS-0506748 and CMMI-00800896). R.N. acknowledges the involvement of the Research Foundation of Helsinki University of Technology, as well as the NANOINDENT EU-research grant. D.C. and R.N. thank R. Nieminen and K. Niihara for valuable discussions. The authors also thank A. Poludniak for careful reading of the manuscript and stimulating comments.