Sharper insights into stress-induced, crystalline-to-amorphous transitions in silicon can be realized with crack-resistant micropillars. Mechanical processes such as polishing during the manufacture of photovoltaic cell alter silicon's crystal structure and degrade device performance. Wei Zhang and Zhi-Wei Shan from Xi'an Jiaotong University in China and co-workers have now used high-resolution transmission electron microscopy to capture in situ images of these transitions in progress. The team designed a system of submicrometre pillars consisting of a crystalline silicon core encased in a nanoscale shell of amorphous silicon. The flexible shell helped prevent brittle fracture from occurring while the pillars were gradually compressed into mushroom shapes by an indentation tool. Real-time imaging revealed that mechanical force deformed the silicon framework through plastic motions only – a finding that upsets previous concepts of intermediate crystalline phases taking part in the amorphization process.
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