Crystal metamorphosis at stress extremes: how soft phonons turn into lattice defects

摘要

Simulations of nanoscale indentations reveal the critical link between unstable vibrational waves and nucleation of crystal defects. Researchers looking to maximize the strength of devices such as transistors, solar cells, and superconductors through strain engineering are often frustrated by spontaneous defect nucleation. Ju Li from the Massachusetts Institute of Technology and colleagues have now developed an algorithm that can search for specific crystal vibrations, known as soft phonons, that can trigger defects to form. The team created a constrained optimization program to search for phonon instability, and then employed finite element modeling and molecular dynamic calculations to simulate nano-indentations in a model aluminum crystal. These computations showed that at extreme deformation stress points, a two-step mechanism transforms soft phonons into discrete atomic defects within tens of picoseconds.