Room temperature dislocation plasticity in silicon

Abstract

We present direct observations of room temperature dislocation plasticity in single crystalline silicon. Previous studies have shown that phase transformation and fracture are the relevant mechanisms of deformation in silicon. In contrast, using in-situ nanoindentation in a transmission electron microscope we find dislocation nucleation and metal-like flow. The results of finite-element modelling suggest that the presence of free surfaces in our unique sample geometry leads to preferential surface nucleation of dislocations and the suppression of phase transformation.Over fifty years of research on dislocation behaviour in silicon supports the conclusion that dislocations do not move during conventional mechanical testing at temperatures below 450 C [1,2]. Under extreme conditions such as indentation loading, where localized stresses can approach the theoretical shear strength of the material, dislocation structures have been observed in silicon. Traditionally, these are thought to result from either block slip [3,4] or phase transformations [5][6][7][8], rather than the nucleation and propagation mechanisms associated with conventional dislocation plasticity. However, recent results have shown evidence of room temperature dislocation plasticity in silicon in the absence of phase transformations through post mortem transmission electron microscopy (TEM) of shallow indentations [9]. Here we present the first in-situ observations of dislocation formation and propagation in silicon at room temperature.While indentation-induced dislocation nucleation has been widely documented for metallic systems [10][11][12], the high Peierl's barrier associated with covalently bonded materials tends to suppress dislocation activity. Prior research suggests that the indentation of silicon causes plastic deformation through a series of phase transformations [13]. During conventional indentation loading, silicon transforms

Mechanisms for Fatigue of Micron‐Scale Silicon Structural Films

“…Upon removal of the load, the dislocations are 'frozen' into the structure, and are thus readily observable. Additionally, there has been no direct evidence to date (e.g., from TEM imaging) where dislocations have been seen at arrested crack tips in silicon; roomtemperature dislocation plasticity in silicon has only been observed to date during the high combined compressive and shear loads of an indentation test [38] . Their third possible mechanism involved grain-boundary plasticity, where an amorphous grain-boundary region hitting the surface under stress would experience a non-conventional plastic deformation in shear, which would then cause a residual compressive stress, possibly resulting in the observed strengthening effect.…”

Influence of microstructure on the cutting behaviour of silicon

“…In this regard, the existing research details several aspects of silicon, but this material is so versatile that many new phenomena are still being explored to bridge the missing gaps in our existing understanding. Across a number of those research studies, ductility in silicon by large has been attributed either to the occurrence of high pressure phase transformation (HPPT) [1], crystal twinning [2] or surface nucleation of dislocations [3,4]. It is understood that the nucleation of dislocations is more prevalent than HPPT in the presence of free surfaces, for examples in, nanoparticles of silicon [5] while no evidence of crystal twinning during contact loading of silicon has been reported in the literature other than the work of Mylvaganam et al [2].…”

In situ TEM study of deformation-induced crystalline-to-amorphous transition in silicon

“…10 As such, in the absence of direct evidence, the necessity of the Si-II phase during the CAT process is uncertain, and has in fact been challenged by several research groups. 13,14,21 In an effort to directly observe the response of c-Si to indentation, Minor et al 22 carried out indentation tests inside TEM. They found no phase transformation and only dislocationmediated metal-like plastic deformation.…”