Plastic strain-induced phase transformations in silicon: drastic reduction of transformation pressures, change in transformation sequence, and particle size effect

TL;DR

This study reveals that plastic strain can induce phase transformations in silicon at significantly lower pressures than hydrostatic conditions, with effects influenced by particle size, enabling new manipulation of silicon's phases.

Contribution

It is the first in-situ study demonstrating plastic strain-induced phase transformations in silicon, showing drastic pressure reductions and size effects, and exploring synthetic path control.

Findings

Plastic strain induces phase transformations at much lower pressures.

Particle size significantly affects transformation pressures.

Reversible phase transformations are achievable at ambient conditions.

Abstract

Pressure-induced phase transformations (PTs) between numerous phases of Si, the most important electronic material, have been studied for decades. This is not the case for plastic strain-induced PTs. Here, we revealed in-situ various unexpected plastic strain-induced PT phenomena. Thus, for 100 nm Si, strain-induced PT Si-I to Si-II (and Si-I to Si-III) initiates at 0.4 GPa (0.6 GPa) versus 16.2 GPa ($\infty$, since it does not occur) under hydrostatic conditions; for 30 nm Si, it is 6.1 GPa versus $\infty$. The predicted theoretical correlation between the direct and inverse Hall-Petch effect of the grain size on the yield strength and the minimum pressure for strain-induced PT is confirmed for the appearance of Si-II. Retaining Si-II at ambient pressure and obtaining reverse Si-II to Si-I PT are achieved, demonstrating the possibilities of manipulating different synthetic paths.