Nordic Hysitron Laboratory, School of Chemical Technology, Aalto University, Vuorimiehentie 2A, Espoo, 00076 Aalto, Finland.
Nat Nanotechnol. 2011 Jul 24;6(8):480-4. doi: 10.1038/nnano.2011.118.
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.
硅晶体在电子工业中扮演着重要的角色，而硅纳米粒子在纳米机电系统、光子学和生物技术等领域有着应用。然而，硅中观察到的弹塑性转变尚未被完全理解；特别是，硅的塑性是由位错还是由相之间的转变决定的，这一点还不清楚。在这里，我们基于压缩实验和分子动力学模拟表明，体硅和硅纳米粒子的力学性能有显著差异。我们发现，体硅处于相对约束的状态，其塑性由相转变主导，而硅纳米粒子约束较小，表现出位错驱动的塑性。我们称这种转变为去约束，可以解释变形硅纳米楔中的相转变缺失现象。此外，这种现象与在形状记忆合金纳米柱中观察到的效应一致，为初始塑性的起源提供了深入的见解。
