Implantation sites of In, Cd, and Hf ions in diamond

The implantation sites of In, Cd, and Hf ions in diamond have been investigated with complementary electron emission channeling (EC) and perturbed $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ angular correlations (PAC) spectrometry on radioactive ${}^{111}\mathrm{In},$ ${}^{111m}\mathrm{Cd},$ and ${}^{181}\mathrm{Hf}$ probes implanted into natural type-IIa diamonds. The fraction of probes occupying specific sites were determined from comparisons of the measured axial channeling yields with channeling patterns calculated using the many-beam formalism of electron motion through the crystal. For the In-implanted sample the EC measurements, after room-temperature implantation and annealing at 1473 K or after implantation at 1373 K, show a substitutional or near-substitutional fraction of 32(4)%, a tetrahedral interstitial fraction of 10(3)%, and the remainder in highly disturbed environments. The $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ PAC measurements confirm the near-substitutional population, but show that about $10%$ of the In probes are at sites with nearest-neighbor point defects and $20%$ at sites with more distant defects, but none in a defect-free environment. The ${}^{111m}\mathrm{Cd}$ measurements confirm these results and show that the loss of anisotropy in the PAC signal is not due to ``aftereffects'' of the electron capture decay of In to Cd, but due to extended lattice damage produced by the implantation process. The In PAC measurements confirmed the previously observed In-defect interaction in diamond, with a quadrupole coupling frequency of ${\ensuremath{\nu}}_{Q}=117 \mathrm{MHz},$ and in addition, showed evidence of a new defect interaction with ${\ensuremath{\nu}}_{Q}=315 \mathrm{MHz}$ at annealing temperatures above 1473 K. A diamond sample implanted with overlapping profiles of ${}^{111}\mathrm{In}$ and hydrogen and annealed up to 1673 K showed no evidence of the higher-frequency component or of any signal attributable to the formation of In-H pairs. This suggests that in diamond no significant fraction of the implanted In atoms act as electrically active acceptors. In the ${}^{181}\mathrm{Hf}$-implanted diamond, the present EC and PAC measurements yield consistent results of a near-substitutional fraction of only $10%--15%,$ in contrast to earlier observations.