Direct observation of substitutional Au atoms inSrTiO3

Abstract

Ion implantation and subsequent high-temperature annealing is an effective way to prepare metal nanoclusters dispersed in a dielectric for useful optical and electrical properties. However, there is very little understanding of the nucleation and growth process of these nanoclusters, their correlations with the sites of the implanted ions, and the behavior of defects (such as vacancies) generated during the ion-implantation process. Using high-angle annular dark-field imaging in aberration-corrected scanning transmission electron microscopy, we have directly observed that, at a dilute concentration, Au atoms implanted in $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_3$ are in a substitutional lattice position for both Sr and Ti. The congregation of Au atoms by diffusion to a critical concentration leads to the nucleation of an Au lattice within the $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_3$. The Au nanocluster and $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_3$ were found to maintain an orientation relationship of $\mathrm{Au}\left[001\right]∕∕\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_3\left[001\right]$ and $\mathrm{Au}\left(100\right)∕∕\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_3\left(100\right)$, which corroborated the results of a first-principles total-energy calculation. The interface between the Au cluster and $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_3$ was bridged by an $\mathrm{O}∕\mathrm{Ti}$ plane. The Au-O bond length was found to be $2.2\mathrm{\AA }$, which is the same as the Au-O bond length in AuO. Furthermore, the atomic planes adjacent to the interface in both Au and $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_3$ were found to be slightly stretched. The high concentration of vacancies generated during the Au implantation aggregated to form cavities in the $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_3$ lattice, and were faceted mostly along the $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_3$ {100} and (110) planes. The Au and vacancy clusters were spatially associated, indicating a strong interaction. Thus, the formation of cavities in Au-implanted materials indicates that the vacancy-clustering process prevails over the Frenkel-pair recombination.