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.