Mössbauer Studies of ImplantedI129Ions in Semiconductors and Alkali Halides

The Groningen isotope separator has been used to implant ${\mathrm{Te}}^{129m}$ into single crystals of Si, Ge, and diamond as well as several alkali halides. The spectra of all semiconducting sources display two well-separated Mössbauer lines of approximately equal intensity. The parameters of the spectra were found to be only slightly dependent on the annealing temperature type of dopant already present in the semiconductors, Mössbauer source temperature, implantation temperature, and ${\mathrm{Te}}^{129m}$ dose. The results obtained for ${\mathrm{I}}^{129}$ in these semiconductors are qualitatively similar to the ${\mathrm{Fe}}^{57}$ data obtained by the Stanford group using the Coulomb excitation implantation technique with a Van de Graaff accelerator. The separation between the lines for the ${\mathrm{I}}^{129}$ sources is seen to be proportional to the separation obtained with the ${\mathrm{Fe}}^{57}$ sources. On the basis of the Mössbauer spectra, as well as the previously published channeling data and the systematics of the ${\mathrm{I}}^{129}$ isomer shifts, the lines are tentatively assigned to be due to iodine atoms in substitutional and interstitial sites. The nature of the interaction causing the very large shifts is briefly discussed. In contrast to the semiconductor results, the Mössbauer spectra obtained with ${\mathrm{Te}}^{129m}$ implanted alkali halide sources are very sensitive to annealing and to the ${\mathrm{Te}}^{129m}$ dose. Both single-line spectra as well as spectra displaying an unresolved structure were obtained. The isomer shifts obtained from the single-line spectra are quite large; about five times larger than the spread of isomer shifts previously obtained from the alkali iodides. For the case of ${\mathrm{I}}^{129}$ in LiF the large shift is probably caused by the large degree of overlap that an iodine ion experiences because of the smaller interatomic spacing in the LiF lattice compared to the alkali iodide lattices.