Direct Structural Identification and Quantification of the Split-Vacancy Configuration for Implanted Sn in Diamond

We demonstrate formation of the ideal split-vacancy configuration of the Sn-vacancy center upon implantation into natural diamond. Using ${\beta }^{-}$ emission channeling following low fluence ${}^{121}\mathrm{Sn}$ implantation ($2\times {10}^{12}\mathrm{atoms}/{\mathrm{cm}}^2$, 60 keV) at the ISOLDE facility at CERN, we directly identified and quantified the atomic configurations of the Sn-related centers. Our data show that the split-vacancy configuration is formed immediately upon implantation with a surprisingly high efficiency of $\approx 40\%$. Upon thermal annealing at $920°\mathrm{C}$ $\approx 30\%$ of Sn is found in the ideal bond-center position. Photoluminescence revealed the characteristic $\mathrm{Sn}{V}^{-}$ line at 621 nm, with an extraordinarily narrow ensemble linewidth (2.3 nm) of near-perfect Lorentzian shape. These findings further establish the $\mathrm{Sn}{V}^{-}$ center as a promising candidate for single photon emission applications, since, in addition to exceptional optical properties, it also shows a remarkably simple structural formation mechanism.

Figure 1

The two major structures that are generally considered for impurity-vacancy complexes in diamond. It is assumed that with a vacancy $V$ next to it the N impurity remains in a substitutional site (left), while for Sn the so-called split-vacancy configuration (right) has been proposed [25, 28]: the Sn atom moves from its substitutional site to a position midway between the two adjacent vacancies, which geometrically coincides with the so-called bond-center position in an undisturbed lattice.

Figure 2

(a)–(d) Experimental ${\beta }^{-}$ emission channeling patterns from ${}^{121}\mathrm{Sn}$ in diamond around the $⟨110⟩$, $⟨211⟩$, $⟨100⟩$, and $⟨111⟩$ directions in the as-implanted state. The plots (e)–(h) are the corresponding best fits of theoretical patterns considering 63% on substitutional and 41% on bond-center sites with rms $u_1({}^{121}\mathrm{Sn})$ of 0.18 and 0.11 Å, respectively. Note that due to the unusual surface cut of the diamond, it could not be oriented in all cases in such a way that the calculated patterns [$\pm 3°$ with (110) plane horizontal] cover the whole range of measured angles. The area in the best-fit patterns (e)–(h) which is not covered is shown in white.

Figure 3

(a)–(d) Experimental ${\beta }^{-}$ emission channeling patterns from ${}^{121}\mathrm{Sn}$ following $920°\mathrm{C}$ annealing. The plots (e)–(h) are the corresponding best fits of theoretical patterns considering 79% on ideal substitutional and 32% on ideal bond-center sites.

Figure 4

Confocal photoluminescence spectra from the diamond sample implanted with ${}^{121}\mathrm{Sn}+{}^{121\mathrm{m}}\mathrm{Sn}$ ions after annealing at $920°\mathrm{C}$ and following the decay of ${}^{121}\mathrm{Sn}$ to ${}^{121}\mathrm{Sb}$, i.e., $\mathrm{Sn}V$ related lines result from long-lived ${}^{121\mathrm{m}}\mathrm{Sn}$. The spectra were recorded at room temperature under 532 nm laser excitation with the focus at various depths. Note that the depth resolution is $\approx 4\mu \mathrm{m}$ due to the Rayleigh range of the used objective with numerical aperture 0.95.