Strain-gradient facilitated formation of confined Ge/GeO2 nanoparticles with a cracked shell and enhanced two-photon absorption

The formation of the cracked shell is confirmed by HRTEM for the Ge/GeO₂ core/shell nanoparticles fabricated by the pulsed laser deposition method and a rapid thermal annealing technique. The determined two-photon absorption in Ge/GeO₂ core/shell nanoparticles with a cracked shell is an instantaneous nonlinear process and is enhanced almost 2 times compared with that in pure Ge nanoparticles. Our simulation results illustrate that the oxidation of confined Ge/GeO₂ core/shell nanoparticles results in the formation of cracks in GeO₂ shells. It indicates that strain gradients induced in the confined GeO₂ shell during the oxidation process can facilitate the formation of the cracked GeO₂ shell and the shape evolution of Ge/GeO₂ core/shell nanoparticles. These results demonstrate that the strain can manipulate the microstructure, morphology and optical properties of confined core/shell nanoparticles.