Properties of 57Fe hot-implanted into diamond crystals studied by Mössbauer emission spectroscopy between 4 and 300 K

Abstract

We investigated the hyperfine interactions of 57Fe ions implanted into diamond crystals that were heated to 830 K during implantation. The implantation of radioactive parent 57Co ions was performed to a fluence of 2 × 10 13 ions/cm 2, using the 50 kV isotope separator. The Mössbauer emission spectra were measured in the temperature range between 4 and 300 K. using a helium flow cryostat. About 20% of the implanted ions end up in high-symmetry (HS, presumably substitutional) sites, with the remaining 80% of ions appearing in low-symmetry (LS, presumably hexagonal interstitial) sites. The HS sites are characterized by very high Debye temperature θ D ~ 1300 K and by high s-electron density characteristic for Fe 4+ (3d 4sp 3) electron configuration. Impurities at LS sites exhibit a Debye temperature of 550 ± 50 K and a very large electric field gradient, V zz = 1.2 × 10 18 V cm 2 . An anomalous rise of the recoil-free factor for LS sites below 100 K was observed. This effect can be an evidence of localized jumps of interstitial impurity atoms between adjacent tetrahedral and hexagonal positions in the host lattice. The values of the s-electron densities and electric field gradients at Fe nuclei implanted in diamond are compared with the corresponding values in other IV-group matrices and are found to be correlated with the atomic volumes of the corresponding host elements.