Portal de Periódicos da CAPES

Simulations of indentation-induced phase transformations in crystalline and amorphous silicon

2008; American Physical Society; Volume: 78; Issue: 3 Linguagem: Inglês

10.1103/physrevb.78.035205

1550-235X

В. И. Иващенко, P. E. A. Turchi, V. I. Shevchenko,

Force Microscopy Techniques and Applications

The pressure- and indentation-induced phase transformations in crystalline $(cd)$ and amorphous $(a)$ silicon are studied by using molecular dynamics simulations based on the modified Tersoff potential. The $s{p}^{3}{s}^{\ensuremath{\star}}$ tight-binding scheme is employed to gain insight into the origin of the change in conductivity during nanoindentation. The Gibbs free energy calculations predict the following pressure-induced phase transitions: $cd\text{-Si}\ensuremath{\rightarrow}\ensuremath{\beta}\text{-tin}$ $\text{Si}(\ensuremath{\beta}\text{-Si})$ (11.4 GPa); $cd\text{-Si}\ensuremath{\rightarrow}\text{high}$ density amorphous phase (HDA) (22.5 GPa); $a\text{-Si}\ensuremath{\rightarrow}\ensuremath{\beta}\text{-Si}$ (2.5 GPa); $a\text{-Si}\ensuremath{\rightarrow}\text{HDA}$ (8.4 GPa). Simulations of nanoindentation of crystalline silicon reveal discontinuities in the load-displacement curves. In the loading curves of the $cd\text{-Si}$ (100) substrate, the pop-in is assigned to the appearance of the $\ensuremath{\beta}\text{-tin}$ Si phase. During unloading, the pop-out is due to the formation of a low-density amorphous phase $a\text{-Si}$. The $a\text{-Si}\ensuremath{\rightarrow}\text{HDA}$ transformation takes place during nanoindentation of $a\text{-Si}$ in loading regime. Upon unloading the $a\text{-Si}$ phase is preserved. The structural transformations in $cd\text{-Si}$ and $a\text{-Si}$ during nanoindentation are treated in terms of triaxial and uniaxial compressions of the respective bulk samples. A change in conductivity from semiconducting to metallic during nanoindentation of the $cd\text{-Si}$ (100) and $a\text{-Si}$ slabs is explained in terms of a transformation of the localized electronic states in the band gap region. The results are compared to those of available theoretical models and experiments.