Recoil-Implanted Fe-57 In Diamond

The lattice sites of Fe-57 recoil implanted into diamond at low concentrations have been investigated in in-beam Mossbauer spectroscopy. Ar-40 ions incident at 110 MeV on an enriched Fe-57 foil were used to Coulomb excite and recoil implant Fe-57 nuclei into a pair of diamond targets. Conversion electron Mossbauer spectra were measured at sample temperatures of 300, 600, 700, and 800 K. The spectra were consistently resolved into three components: isomer shift of delta = + 0.16 mm/s: the doublets (D-1 and D-2) had quadrupole splittings of 2.33 mm/s and 2.10 mm/s, and isomer shifts of -0.51 mm/s and +0.04 mm/s, respectively. The line intensities and linewidths of the three components showed little change with temperature. Time-differential measurements showed no evidence of any dynamic rearrangement of the implanted Fe atoms within the time window of the measurements (100 ns). Comparison of the observed isomer shifts with theoretical calculations and similar measurements in Si allow us to attribute the singlet (f approximate to 10%) to interstitial Fe. The isomer shift of doublet D-2 is in agreement with the calculations for substitutional Fe. However, the large electric-field gradients of D-1 and D-2 caution against any firm conclusions on these components, but indicate that two differently disturbed implantation sites are populated with considerable lattice damage in the neighborhood of the implanted ions. [S0163-1829(98)02237-1].