Amorphous silicon under mechanical shear deformations: Shear velocity and temperature effects

Abstract

Mechanical shear deformations lead, in some cases, to effects similar to those resulting from ion irradiation. Here we characterize the effects of shear velocity and temperature on amorphous silicon (a-Si) modelled using classical molecular dynamics simulations based on the empirical Environment Dependent Inter-atomic Potential (EDIP). With increasing shear velocity at low temperature, we find a systematic increase in the internal strain leading to the rapid appearance of structural defects (5-fold coordinated atoms). The impacts of externally applied strain can be almost fully compensated by increasing the temperature, allowing the system to respond more rapidly to the deformation. In particular, we find opposite power-law relations between the temperature and the shear velocity and the deformation energy. The spatial distribution of defects is also found to strongly depend on temperature and strain velocity. For low temperature or high shear velocity, defects are concentrated in a few atomic layers near the center of the cell while, with increasing temperature or decreasing shear velocity, they spread slowly throughout the full simulation cell. This complex behavior can be related to the structure of the energy landscape and the existence of a continuous energy-barrier distribution.

In situspectroscopic study of the plastic deformation of amorphous silicon under nonhydrostatic conditions induced by indentation

“…59 Significant growth in the population of five-fold coordinated atoms was observed in simulations when the a-Si network was exposed to strains above a certain threshold (which may be affected by temperature and shear velocity). 2 In theoretical studies, an increase in the number of five-fold coordinated atoms has been linked to losses in intensity 7,15,24,27,55 and widening of the TO band. 6,24,27,55 In the present work, a decrease in the relative intensity of the TO band (see FIG 5b) and a sizable change in the width (see FIG 6) was observed at load L3.…”

“…As a consequence, current knowledge of the mechanisms of plasticity in covalent materials is lacking. 1,2 In addition to wide use in electronic and semiconductor applications, amorphous silicon (a-Si) has become a model material for covalent amorphous network studies due to its simplicity. 1-3 Hence, a-Si has been intensively investigated with regard to dynamic and structural properties in theoretical and experimental studies.…”

“…For example, plastic deformation of a-Si has been investigated under pure shear stress conditions (volume-conserving plane strain) in molecular dynamics (MD) simulations. 1,2,33-35 Argon and Demkowicz proposed a model that included the existence of two distinct atomic environments, solid-like and liquid-like, in any given a-Si network 1,33,36 The solid-like environment resembles the four-fold coordinated, diamond cubic (dc) Si structure. The liquid-like environment resembles a denser and five-fold coordinated liquid Si phase.…”

“…Other studies confirmed a link between the systematic increase in the fraction of (five-fold) coordination defects and the occurrence of elementary plastic events in a-Si networks under shear deformation. 2,34 Shear stress creates liquid-like five-fold coordinated atoms that facilitate the constant reorganization of the amorphous network and thus increase structural disorder. Indeed, only thermal effects can establish a long range order (crystallization) in shear deformed a-Si according to some simulations.…”

Scaling law for crystal nucleation time in glasses

“…Although crystallization of glasses proceeds over time-scales 8,9 , which are commonly larger than experimentally acceptable, the structural ordering in a glass can be accelerated by out-of-equilibrium processes resulted from reheating or applied shear deformation [10][11][12][13][14] . On the other hand, there are indications (see Refs.…”