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In situ observation of shear-driven amorphization in silicon crystals


Amorphous materials are used for both structural and functional applications1,2,3,4,5. An amorphous solid usually forms under driven conditions such as melt quenching4, irradiation6, shock loading7,8,9 or severe mechanical deformation10. Such extreme conditions impose significant challenges on the direct observation of the amorphization process. Various experimental techniques have been used to detect how the amorphous phases form, including synchrotron X-ray diffraction11, transmission electron microscopy (TEM)12 and Raman spectroscopy13, but a dynamic, atomistic characterization has remained elusive. Here, by using in situ high-resolution TEM (HRTEM), we show the dynamic amorphization process in silicon nanocrystals during mechanical straining on the atomic scale. We find that shear-driven amorphization occurs in a dominant shear band starting with the diamond-cubic (dc) to diamond-hexagonal (dh) phase transition and then proceeds by dislocation nucleation and accumulation in the newly formed dh-Si phase. This process leads to the formation of an amorphous Si (a-Si) band, embedded with dh-Si nanodomains. The amorphization of dc-Si via an intermediate dh-Si phase is a previously unknown pathway of solid-state amorphization.

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Figure 1: In situ TEM observation of deformation-induced dislocations and phase transformation in a 〈111〉-oriented Si nanopillar under compression.
Figure 2: Shear-driven amorphization in a dh-Si strip.
Figure 3: Atomic structures in a fully developed a-Si shear band.
Figure 4: Deformation-induced partial dislocations in a 〈100〉-oriented Si nanopillar under compression.


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S.X.M. acknowledges support from the National Science Foundation (NSF, CMMI 1536811) through the University of Pittsburgh. T.Z. acknowledges support from the NSF (DMR 1410331). This work was performed, in part, at the William R. Wiley Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the US Department of Energy, Office of Biological and Environmental Research and located at PNNL. PNNL is operated by Battelle for the US Department of Energy (contract no. DE-AC05-76RLO1830). This work was performed in part at the Center for Integrated Nanotechnologies, an Office of Science User Facility operated for the US Department of Energy Office of Science. The authors thank J.Y. Huang for his support on TEM, Z. Zeng for assistance with atomistic simulations and B.M. Nguyen in Los Alamos National Laboratory, X. Dai in Nanyang Technology University, and S. Krylyuk and A.V. Davydov at the National Institute of Standards and Technology for supplying samples.

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S.X.M., T.Z. and C.M.W. conceived and designed the experiment. Y.H. and L.Z. conducted the TEM experiments. F.F. and T.Z. performed the computer simulations and theoretical analysis. Y.H., T.Z. and S.X.M. co-wrote the paper. All authors discussed the results and commented on the manuscript.

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Correspondence to Chongmin Wang or Ting Zhu or Scott X. Mao.

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The authors declare no competing financial interests.

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He, Y., Zhong, L., Fan, F. et al. In situ observation of shear-driven amorphization in silicon crystals. Nature Nanotech 11, 866–871 (2016).

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