Nanoindentation Induced Deformation and Pop-in Events in a Silicon Crystal: Molecular Dynamics Simulation and Experiment

Abstract

Silicon has such versatile characteristics that the mechanical behavior and deformation mechanism under contact load are still unclear and hence are interesting and challenging issues. Based on combined study using molecular dynamics simulations and experiments of nanoindentation on Si(100), the versatile deformation modes, including high pressure phase transformation (HPPT), dislocation, median crack and surface crack, were found, and occurrence of multiple pop-in events in the load-indentation strain curves was reported. HPPTs are regard as the dominant deformation mode and even becomes the single deformation mode at a small indentation strain (0.107 in simulations), suggesting the presence of a defect-free region. Moreover, the one-to-one relationship between the pop-in events and the deformation modes is established. Three distinct mechanisms are identified to be responsible for the occurrence of multiple pop-in events in sequence. In the first mechanism, HPPTs from Si-I to Si-II and Si-I to bct5 induce the first pop-in event. The formation and extrusion of α-Si outside the indentation cavity are responsible for the subsequent pop-in event. And the major cracks on the surface induces the pop-in event at extreme high load. The observed dislocation burst and median crack beneath the transformation region produce no detectable pop-in events.

Reveal the Deformation Mechanism of (110) Silicon from Cryogenic Temperature to Elevated Temperature by Molecular Dynamics Simulation

“…Nanoindentations on the (110) Si were simulated by large-scale MD simulation at a temperature range of 0.5 K to 573 K. A new screened empirical bond-order potential (a screened version of potential developed by Erhart et al [17] and Moseler et al [18]) was used to model the interaction between Si atoms, which is suitable to describe the deformation mechanisms during nanoindentation, cutting of monocrystalline, and polycrystalline silicon under uniaxial tension [11,19,20]. The virtual spherical indenter with a diameter of 20 nm was used, which is modeled using a repulsive force: F=AH(r)(R−r)2 where A is force constant with a value of 10 eV/A 2 , H ( r ) is a step function, R is the indenter radius, and r is the distance from the silicon atoms to the indenter sphere center.…”

Failure mechanism and protective role of ultrathin ta-C films on Si (100) during cyclic nano-impact

“…The deformation mechanism is more complex when the substrate is silicon. At room temperature there is little dislocation-based plasticity in single crystal Si and its deformation is dominated by phase transformation (leading to 'pop-in' and 'pop-out' features in nanoindentation curves), accompanied by brittle fracture processes above a threshold load [46][47][48][49]. The effective forces corresponding to the set static impact loads were estimated from equating depths in nanoindentation and after the initial impact, as shown in Figure 11 (a).…”

Bending Nanoindentation and Plasticity Noise in FCC Single and Polycrystals

“…While numerous experimental nanoindentation studies have been conducted to understand size effects [1][2][3][4][5][6][7][8] and residual stresses [9][10][11][12] in nano-and microscale plasticity, it has been elusive to use surface nanoindentation to distinguish surface from bulk crystal plasticity features [13][14][15][16][17][18][19][20][21]. In a dislocation-free region, nanoindentation turns from elastic to plastic through a sudden burst, labeled as primary "pop-ins" [22][23][24][25][26][27][28][29][30]. However, in a dislocation-rich region, nanoindentation is characterized by a noisy response, with multiple secondary pop-in bursts at multiple depths [31].…”