Pressure-driven phase transitions and reduction of dimensionality in 2D silicon nanosheets

GC Hwang and DA Blom and T Vogt and J Lee and HJ Choi and S Shao and YM Ma and Y Lee, NATURE COMMUNICATIONS, 9, 5412 (2018).

DOI: 10.1038/s41467-018-07832-4

In-situ high-pressure synchrotron X-ray powder diffraction studies up to 21 GPa of CVD-grown silicon 2D-nanosheets establish that the structural phase transitions depend on size and shape. For sizes between 9.3(7) nm and 15.2(8) nm we observe an irreversible phase transition sequence from I (cubic). II (tetragonal). V (hexagonal) during pressure increase and during decompression below 8 GPa the emergence of an X-ray amorphous phase. High-angle annular dark field scanning transmission electron microscopy (HAADFSTEM) and atomic force microscopy (AFM) images of this X-ray amorphous phase reveal the formation of significant numbers of 1D nanowires with aspect ratios >10, which are twinned and grow along the <111> direction. We discovered a reduction of dimensionality under pressure from a 2D morphology to a 1D wire in a material with a diamond structure. MD simulations indicate the reduction of thermal conductivity in such nanowires.

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