The BC8-Ge and ST12-Ge phases were transformed from the β-tin-Ge structure, which means that

these two metastable phases should exist in the previous area of β-tin-Ge phase. Since molecular dynamics simulation can present the crystal structure in detail at the atomic level during nanometric machining, the approach to estimate the formation of BC8-Ge and ST12-Ge in this study is by directly observing the atoms with coordination number 4 and their crystal structure in the previous area of the β-tin-Ge phase during and after unloading. Phase transformation during loading Figures 1 and 2 are the top cross-sectional views and side cross-sectional views of nanoindentation on the (010) germanium surface with penetration depth of 5 nm, which show the structural phase distributions at different depths from learn more the machined surface and

different sections from the side face, MAPK inhibitor respectively. Figures 3 and 4 show the distributions of the transformed structure when nanoindenting on the (101) surface, while Figures 5 and 6 show those of the transformed structure nanoindented on the (111) germanium plane. The extensive crystalline structure with fivefold coordinated atoms forms around the center of phase transformed region in all cases of nanoindentation in this work. The crystal structure at the atomic level is shown in Figure 7a, which is almost the same with the structure of bct5-Si. The bct5-Si structure has a body-centered tetragonal lattice with fivefold coordinated atoms. The first-principles total-energy 4EGI-1 clinical trial calculation and model potentials show that the structure is a low-energy phase of silicon and stable at ambient condition [26]. Since monocrystalline germanium is similar with silicon in many aspects such as crystal structure, physical property, and phase

transformation under pressure, they always adopt the same potential in MD simulations. This crystal structure of fivefold coordinated germanium atoms is believed to be the bct5-Ge. The bct5-Ge appears around the Celecoxib center of the indentation region instead of being located centrally in the nanoindentations on the (010), (101), and (111) germanium surfaces, which indicates that non-hydrostatic pressure can induce transformation from diamond cubic germanium into the bct5 phase, and the same holds true for silicon [7]. Figure 1 Top cross-sectional views of phase transformed region at different depths when nanoindenting on (010) germanium surface. At the depth of (a) approximately 9 nm, (b) approximately 7 nm, (c) approximately 6 nm, and (d) approximately 5 nm from the top of the substrate. Figure 2 Side cross-sectional views of phase transformed region induced by nanoindenting on the (010) germanium surface.