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

Abstract

Indentation-induced plastic deformation of amorphous silicon (a-Si) thin films was studied by in situ Raman imaging of the deformed contact region of an indented sample, employing a Raman spectroscopy-enhanced instrumented indentation technique. Quantitative analyses of the generated in situ Raman maps provide unique, new insight into the phase behavior of as-implanted a-Si. In particular, the occurrence and evolving spatial distribution of changes in the a-Si structure caused by processes, such as polyamorphization and crystallization, induced by indentation loading were measured. The experimental results are linked with previously published work on the plastic deformation of a-Si under hydrostatic compression and shear deformation to establish a sequence for the development of deformation of a-Si under indentation loading. The sequence involves three distinct deformation mechanisms of a-Si: (1) reversible deformation, (2) increase in coordination defects (onset of plastic deformation), and (3) phase transformation. Estimated conditions for the occurrence of these mechanisms are given with respect to relevant intrinsic and extrinsic parameters, such as indentation stress, volumetric strain, and bond angle distribution (a measure for the structural order of the amorphous network). The induced volumetric strains are accommodated solely by reversible deformation of the tetrahedral network when exposed to small indentation stresses. At greater indentation stresses, the increased volumetric strains in the tetrahedral network lead to the formation of predominately five-fold coordination defects, which seems to mark the onset of irreversible or plastic deformation of the a-Si thin film. Further increase in the indentation stress appears to initiate the formation of six-fold coordinated atomic arrangements. These six-fold coordinated arrangements may maintain their amorphous tetrahedral structure with a high density of coordination defects or nucleate as a new crystalline β-tin phase within the a-Si network.

Mechanical Properties of Amorphous Silicon Nanoparticles

“…However, the difference is small, and there is a non negligible dispersion for S SiNP values. From nanoindentation experiments on a-Si films, Gerbig et al observed the formation of high-density a-Si or of the ordered β-tin phase, characterized by sixfold coordinated atoms, for contact stresses greater than 8.2 GPa [31]. In the present work, larger yield stress values are obtained in all cases.…”

Size Effects of Hardness and Strain Rate Sensitivity in Amorphous Silicon Measured by Nanoindentation

“…[1,2] In the literature, one can find evidence that processing conditions like deposition temperature, pressure, and flow rate of gases and processes like etching, chemical treatments, or ion implantation are known to affect the microstructural features as well as the distribution of volume and surface defects in this material. [3][4][5] To gain a deeper understanding between processing-structure-property-performance relationship for a-Si, much recent research interest has focused on characterizing hardness, Young's modulus, and pressure-induced phase transformations measured, i.e., by nanoindentation. [3,[5][6][7] This measurement method is particularly dedicated and successfully applied for studying of mechanical properties of thin films.…”

<i>In-Situ</i> Raman Measurements of Silicate Glasses during Vickers Indentation

“…Recently, some researchers developed in-situ Raman measurement system during indentation, and reported the spatial distribution of crystalline phases during pressureinduced transformations of crystalline silicon under a conospherical diamond indenter, 10) and the spatial distribution of five-fold coordinated silicon atoms in amorphous silicon under the indenter. 11) Although these are important pioneering works on in-situ structural changes in material under an indenter, there is no information on structural changes of oxide glass under a sharp diamond indenter.…”