57Fe Implanted in Diamond

Abstract

Recent conversion electron Mossbauer Spectroscopy (CEMS) studies of 57Fe implanted in diamond are reviewed. Two techniques have been used in these studies. Firstly, in-beam Mossbauer (IBMS) measurements have been used to study the lattice sites of 57Fe in diamond under low dopant concentrations (≤ 1011 cm-2). Secondly, source-based CEMS measurements have been performed on synthetic single crystal diamonds produced by both high-temperature high-pressure (HTHP) processing and chemical vapour deposition (CVD). In the latter investigations 70 keV 57Fe ions were implanted in the samples to a dose of 5 x 1014 cm-2, and the spectra were studied up to annealing temperatures of 1470 K. The IBMS spectra were resolved into two symmetric doublets and a weak singlet, while the CEMS spectra for the HTHP and CVD samples were resolved into two doublets and two singlets (S1 and S2). All three measurements show that only about 10% of the probe atoms are at sites of high symmetry, the remainder are at highly perturbed configurations. The isomer shift of the singlet in the IBMS spectra is in good agreement with theoretical calculations for tetrahedral interstitial Fe. The singlets in the source based measurements at higher doses ≥ 1014 cm-2) have rather large isomer shifts attesting to the considerable lattice strain in the vicinity of the probes. The measurements also gave consistent isomer shifts for one of the doublets (δ = 0.00(4) mm/s), which was in agreement with the calculations for substitutional Fe. The large quadrupole splitting (≈ 2 mm/s), however, caution against any firm conclusions.