Deformation pathway to high-pressure phases of silicon during nanoindentation

Abstract

The deformation pathway of silicon induced by nanoindentation is investigated in detail at the atomic level using molecular dynamics. Due to the complex stresses associated with the directional loading along a specific crystallographic orientation, the initial Si I lattice is transformed into two different high-pressure phases, namely, Si II and BCT5-Si. The Si II phase, where atoms have the six nearest neighbors, is generated through the tetragonal deformation caused by the compressive loading along the [001] direction. In contrast, the BCT5-Si phase, where each silicon atom has the five nearest neighbors, is formed by flattening the initially stepped sixfold rings of the diamond lattice onto the (110) plane of the BCT lattice. These reconstructive transformations are accomplished only by adding additional bonds and do not involve any bond breaking.

Origin of a Nanoindentation Pop-in Event in Silicon Crystal

“…2) Consequently, we obtained the complete scenario of structural changes induced in Si crystal directly under the diamond tip (Fig. 2), which agrees with previous achievements [22][23][24][26][27][28][30][31][32] and vindicates our MD-procedure with the Tersoff-type potential.…”

“…The interactions among Si atoms were defined by the three-body Tersoff-type interatomic potential [21] capable of capturing phase transformations between crystalline silicon structures [19,[22][23][24][26][27][28]. The interaction between the Si-crystal and a rigid, diamond, cono-spherical tip (the half apex angle of π/4, radius of R=5 nm) was defined by the repulsive Morse potential (cutoff radius 3 Å).…”

“…The identification of high-pressure Si phases formed during the MD-simulated indentation was based on the available structural data [23,24,[26][27][28] and the Si atoms' coordination number (nearest neighbors, NN). As a result -in addition to the Si-I and Si-II phases -we detected the following features of a highly stressed Si-crystal: (1) the BCT5-structure (body-centered tetragonal) with 5 nearest neighbors (NN=5; one at a distance of 2.31 Å and four at 2.44 Å); (2) the Si-III phase (bc8, body-centered-cubic)…”

Influence of Abrasive Shape on the Abrasion and Phase Transformation of Monocrystalline Silicon

“…The simulations on the mechanical properties and deformation mechanism of silicon indicated the appearance of the metastable phases, Si-II, Si-XII, and amorphous phase during nanoindentation process. Whilst, several simulated results showed that the Si-I transformed into two types of body-centered-tetragonal phase, i.e., β-Si and Bct5 with fivefold coordination [4,22,23]. The abrasive wear of monocrystalline silicon showed a new phase transformation route, i.e., an initial diamond cubic silicon turned into high density amorphous phase beneath the moving particle and, then transformed into low density metastable amorphous phase in both two-body and three-body abrasion [24,25].…”

“…Fang et al [18] assumed an ellipsoidal particle as the first approximation to model real particle contours in three-body abrasion. In addition, much effort has been paid for the abrasion properties of monocrystalline silicon at nanoscale by the molecular dynamics (MD) simulation [19][20][21][22][23]. For instance, Sun et al [24,25] simulated three-body and two-body abrasive wear of monocrystalline silicon with sphere particle in geometry in the nanoscale.…”