Self-assembling of nanocavities inTiO2dispersed with Au nanoclusters

Abstract

There has been considerable research effort on tailoring the nonlinear optical properties of dielectric materials by dispersing nanometer-sized metallic clusters in them. It has been proposed that the optical response of this type of material is related to the quantum antidots (vacancy clusters), which is spatially located at the interface between the metal cluster and the dielectric matrix. In order to clarify the vacancy clustering behavior as well as its correlation with Au clustering, single crystal ${\mathrm{TiO}}_{2}$ has been implanted with Au ions at $975\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and subsequently annealed at $1275\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ for $10\phantom{\rule{0.3em}{0ex}}\mathrm{h}$. A characteristic self-assembling of nanocavities along the boundary between the region of Au clusters and the free surface has been observed in the present system. These cavities are faceted along ${\mathrm{TiO}}_{2}(110)$ and have a size of $\ensuremath{\sim}10\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$. High angle annular dark-field (HAADF) imaging in an aberration corrected scanning transmission electron microscope (STEM) revealed that vacancy clusters of $\ensuremath{\sim}2\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ in size also exist in the Au populated regions. Formation of cavities in Au-irradiated ${\mathrm{TiO}}_{2}$ strongly indicates that vacancy clustering processes prevail over Frenkel-pair recombination. Furthermore, the Au atoms substitution for Ti in ${\mathrm{TiO}}_{2}$ is also directly observed by STEM-HAADF imaging and by channeling Rutherford backscattering spectrometry.