Unusual plastic strain-induced phase transformation phenomena in silicon

Area of Science:

• Materials Science
• Solid State Physics
• Nanotechnology

Background:

• Silicon (Si) is a critical electronic material.
• Pressure-induced phase transformations (PTs) in Si are well-documented.
• Strain-induced PTs in Si have not been studied in situ.

Purpose of the Study:

• To investigate in situ plastic strain-induced phase transformations in silicon.
• To explore the correlation between particle size, yield strength, and pressure for strain-induced PTs.
• To understand the mechanisms and applications of strain-induced PTs in silicon.

Main Methods:

• In situ observation of plastic strain-induced phase transformations.
• Theoretical prediction and experimental confirmation of Hall-Petch effect on strain-induced PTs.
• Application of compression, shear, and torsion under varying pressures.

Main Results:

• Strain-induced Si-I→Si-II PT initiates at 0.3 GPa under compression/shear, significantly lower than 16.2 GPa under hydrostatic pressure.
• Si-I→Si-III PT initiates at 0.6 GPa under strain, not observed under hydrostatic pressure.
• Coexistence of multiple phases (Si-I, II, III, XI) observed under torsion, with retained Si-II and Si-III at ambient pressure.

Conclusions:

• Plastic strain is a more effective driver for Si phase transformations than hydrostatic pressure.
• A dislocation pileup-based mechanism explains the observed phenomena.
• Findings offer new pathways for synthesizing nanostructured materials and advanced surface treatments.