Effect of indentation speed on deformation behaviors of surface modified silicon: A molecular dynamics study

Temperature Activates Contact Aging in Silica Nanocontacts

“…Despite Figs. 1 and 2, to our knowledge constituting the first experimental evidence for thermally activated aging in dry silica contacts, there is a wealth of experiments [37][38][39] and simulation [12,13,36,37,[40][41][42] works focused on stress-induced bond formation in a-SiO 2 , indirectly supporting our findings. Namely, several MD simulations [12,13,36] predict that the indentation process results in siloxane bond (i.e., Si─O─Si) formation between tip and surface, which was also confirmed by our MD simulations; see Fig.…”

“…Furthermore, it has also been experimentally validated to describe atomic rearrangements in silica glass surfaces induced using aberration-corrected transmission electron microscopy [37], transformation mechanisms [65] and thermal conductivity [65,66] in porous silica, and also the Hugoniot curves [58,67] describing the dynamic shock-induced response of silica. Additionally, a good agreement with experimental results has also been found in other mechanical properties such as the deformation behavior of amorphous silica upon indentation [40,41].…”

“…Interestingly, aberration-corrected transmission electron microscopy [37], pair distribution function analysis of 2D x ray [38], and NMR spectroscopy [43] revealed the soft nature of this bond. In fact, these works conclusively [38,[40][41][42][43] demonstrate the importance of bond angle change (of Si─O─Si or O─Si─O) versus bond stretching for strain accommodation in amorphous silica. Therefore, in our experiments, once the siloxane bond between tip and surface has been formed, the deformation process resulting from the slide-hold-slide protocol will first cause and angle distortion of the SiO 4 tetrahedron, as schematically represented in Fig.…”

“…Building on the success of MD in describing the mechanical properties of a-SiO 2 [37,38,[40][41][42][43] while providing the enlightening atomic-scale picture of such processes, here we follow these works in order to obtain the atomic detail of the thermal activated contact aging process. We considered the indentation process of a realistically large a-SiO 2 tip or surface composed by 352137 atoms with an experimentally matched roughness [45] and let them evolve under a constant loading force F N for long periods of time (see Appendixes C, D, and E and Fig.…”

“…[68]. Then, in order to remove the superperiodicity of 5 nm, we improved SiO 2 amorphization by following the standard melting-quenching procedure [2, 12,13,40,41,57,58,63,[65][66][67]69]. This protocol consisted of melting SiO 2 by heating it up to 5000 K in 250 ps at zero pressure followed by a quenching to 300 K with a cooling rate of 11 K=ps.…”