Microstructures of phases in indented silicon: A high resolution characterization

This letter investigates the structural changes in monocrystalline silicon caused by microindentation with the aid of the high-resolution transmission electron microscopy. It shows that the transformation zone is amorphous when the maximum indentation load, P-max, is low, but a crystalline phase of high-pressure R8/BC8 can appear when P-max increases. The nanodeformation of the pristine silicon outside the transformation zone proceeds with the mechanical bending and distortion of the crystalline planes. Certain extent of plastic deformation took place due to dislocation slipping. The results seem to indicate that the shear stress component played an important role in the deformation of the transformation zone. (C) 2003 American Institute of Physics

Amorphous structures induced in monocrystalline silicon by mechanical loading

Different amorphous structures have been induced in monocrystalline silicon by high pressure in indentation and polishing. Through the use of high-resolution transmission electron microscopy and nanodiffraction, it was found that the structures of amorphous silicon formed at slow and fast loading/unloading rates are dissimilar and inherit the nearest-neighbor distance of the crystal in which they are formed. The results are in good agreement with recent theoretical predictions. (C) 2004 American Institute of Physics

Molecular Dynamics Simulation of Nanoindentation-induced Mechanical Deformation and Phase Transformation in Monocrystalline Silicon

This work presents the molecular dynamics approach toward mechanical deformation and phase transformation mechanisms of monocrystalline Si(100) subjected to nanoindentation. We demonstrate phase distributions during loading and unloading stages of both spherical and Berkovich nanoindentations. By searching the presence of the fifth neighboring atom within a non-bonding length, Si-III and Si-XII have been successfully distinguished from Si-I. Crystallinity of this mixed-phase was further identified by radial distribution functions

Mechanical Deformation Induced in Si and GaN Under Berkovich Nanoindentation

Details of Berkovich nanoindentation-induced mechanical deformation mechanisms of single-crystal Si(100) and the metal-organic chemical-vapor deposition (MOCVD) derived GaN thin films have been systematic investigated by means of micro-Raman spectroscopy and cross-sectional transmission electron microscopy (XTEM) techniques. The XTEM samples were prepared by using focused ion beam (FIB) milling to accurately position the cross-section of the nanoindented area. The behaviors of the discontinuities displayed in the loading and unloading segments of the load-displacement curves of Si and GaN thin films performed with a Berkovich diamond indenter tip were explained by the observed microstructure features obtained from XTEM analyses. According to the observations of micro-Raman and XTEM, the nanoindentation-induced mechanical deformation is due primarily to the generation and propagation of dislocations gliding along the pyramidal and basal planes specific to the hexagonal structure of GaN thin films rather than by indentation-induced phase transformations displayed in Si

314 HRTEM Studies of Plastic Deformation in Silicon Wafers due to Micro Indentation

The plastic deformation of silicon wafers caused by micro-indentation was studied by means of HRTEM. It was shown that under a low maximum indentation load (P_ ) the transformation zone is amorphous but its boundary is rough and nano-crystals of diamond silicon appear near an amorphous / crystalline border. Increasing P_ gives rise to crystalline high-pressure R8/BC8 phases in the transformation zone. The size of high-pressure phase grains varies between 3 nm and 15 nm, suggesting a coherent nucleation and growth mechanism. The micro-deformation outside the transformation zone proceeds by initial distortion of crystalline planes concentrated in nano-zones accompanied by initiation of dislocations that are advanced to slip systems. Details of the microstructure and its effect on the nano-deformation in micro -indentation are also discussed

Atomistic structure changes in monocrystalline silicon during nano-sliding and nano-indentation

The characterization of silicon structure at nanometre-scale is an important issue as nano-tribology and nano-machining becomes more and more imperative in the development of MEMS and NEMS. The paper investigates the nano-deformation and atomic structure changes of mono-crystalline silicon induced by asperities of different radii from 5 micron to 50 nm. The structural changes in silicon were studied by means of high resolution transmission electron microscope on cross-section-view samples. The study found that the amorphous phase transformation occurred under all the asperities though the scale of the transformation zones was different. The greater asperity of radius 5 micron initiated nearly spherical amorphous segment with radius of 250 nm and depth of 100 nm. However, the asperity of radius 50 nm created a much smaller amorphous zone with radius of 50 nm and depth of 30 nm. Different atomic structures were observed at the boundary between the transformation zone and pristine silicon. When the asperities were 50 nm in radius the boundary was smooth without a deformed region in its vicinity. Nevertheless, with the increase of the asperities size the boundary pattern became rougher and nano-crystals of pristine silicon grew inside the transformation zone. Nano-deformation outside the transformation zone also developed in different ways. With the small asperities, localized advance of stacking faults and limited number of single dislocations emanated from the bottom of the transformed zone. With the corse asperities, however, nano-deformation was associated with a pronounced mechanical deformation with the heavy bending and severe distortion of crystalline planes in the pristine silicon. Fragmented segments were often observed and the density of the stacking faults was also found to increase. Dislocation cores of 60 degree and 90 degree were developed. These classical dislocations were advanced to slip plane on the further increase of the asperity loading. However, nano-cracks were not observed with both the fine and corse asperities

The difference of phase distributions in silicon after indentation with Berkovich and spherical indenters

This study analyses the microstructure of monocrystalline silicon after indentation with a Berkovich and spherical indenter. Transmission electron microscopy on cross section view samples was used to explore the detailed distributions of various phases in the subsurfaces of indented silicon. It was found that an increase of the P-max would promote the growth of the crystalline R8/BC8 phase at the bottom of the deformation zone. Microcracks were always generated in the range of the P-max studied. It was also found that the deformation zones formed by the Berkovich and spherical indenters have very different phase distribution characteristics. A molecular dynamics simulation and finite element analysis supported the experimental observations and suggested that the distribution of the crystalline phases in the transformation zone after indentation was highly stress-dependent. (c) 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved

Atomistic structure of monocrystalline silicon in surface nano-modification

This paper presents both experimental and theoretical studies on the atomic structure changes of monocrystalline silicon brought about by surface nano-modification. The experiment revealed amorphous transformations with boundaries featuring faceting along {111} planes near the sample surface, which were altered to a random nature at the bottom of the transformation zone. The deformation outside the zone was minor near the surface, but advanced to heavy bending, extensive dislocations and plane shifting in the depth of the samples. Theoretical analysis closely reproduced this deformation, highlighting some scaling effects