Investigation on the phase transformation of monocrystalline silicon during nanoindentation at cryogenic temperature by molecular dynamics simulation

SS Jiao and QM Huang and WJ Tu and J Chen and ZM Sun, PHYSICA B-CONDENSED MATTER, 555, 139-144 (2019).

DOI: 10.1016/j.physb.2018.11.039

High-pressure phase transformation of silicon is an important phenomenon as it is of scientific and technological importance for semiconductor industry and micro/nano electromechanical system. However, there are limited studies on the phase transformation at cryogenic temperature. In this study, molecular dynamics simulation was conducted to investigate the nanoindentation of monocrystalline silicon at 1 K. The force- displacement curve and the corresponding phase transformation were studied in details. During the loading process, the contact zone was affected by the applied stress and the original diamond cubic structure of silicon was distorted. With the increase of the depth, the distorted diamond cubic structure (DDS) was transformed into body-centered- tetragonal structure (bct-5) and Si-II. With the release of the force, the reverse transformations of Si-II to Si-III and Si-XII in junction with the pop-out events in the unloading curves can be clearly seen. It was also found that the phase distribution during the reverse transformation was strongly influenced by the indenter radius and indentation depth due to the different stress fields. At the higher depth, the unloading curves showed the unusual absence of pop-out and the appearance of surface extrusion. This can be ascribed by that the retained DDS outside the indentation after unloading not only restricts the transformation of Si-II but also brings the material extrusion on the surface due to the residual internal stress.

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