Identification of vacancy defects in a thin film perovskite oxide

Vacancies are the dominant point defects in perovskite oxides, however, detecting and identifying the nature of vacancy defects in thin films remains challenging. This can be achieved using electron-beam methods but concentrations of several percent are required. Here we use a high-flux positron beam, providing high statistics positron lifetime measurements, to identify vacancies in laser ablated ${\text{SrTiO}}_3$ on ${\text{SrTiO}}_3$. The method is capable of subparts per million sensitivity and when combined with density-functional theory provides local structure information. The positron lifetime spectrum depth profile detects the presence of large vacancy clusters in a surface layer, a uniform distribution of Sr vacancies through the bulk of the film and resolves the interface with the substrate.

Figure 1

(Color online) Mean positron lifetimes against positron implantation energy, measured by variable energy positron beam positron-annihilation lifetime spectroscopy, for (a) ${\text{SrTiO}}_3$ thin film on ${\text{SrTiO}}_3$ and (c) ${\text{SrTiO}}_3$ single-crystal substrate. The Doppler broadening spectroscopy detected low-momentum fraction $S$ parameter depth profiles for the two samples are shown in (b) and (d), respectively. The Makhovian positron implantation profiles calculated for ${\text{SrTiO}}_3$ are shown in (e).

Figure 2

(Color online) The results of multiexponential positron lifetime deconvolution for [(a)–(d)] ${\text{SrTiO}}_3$ thin film on ${\text{SrTiO}}_3$ and [(e)–(h)] ${\text{SrTiO}}_3$ single-crystal substrate.