RECOIL IMPLANTATION MÖSSBAUER EXPERIMENT ON ⁵⁷Fe IN Ge IN THE PRESENCE OF AN EXTERNAL MAGNETIC FIELD

Abstract
The recoil implantation experiments of Latshaw (1) had an important influence on the later Mössbauer work on implanted atoms in semiconductors (2,3). It was believed that the observed doublet, with an intensity ratio that changed drastically with temperature, provided strong evidence for a two site hypothesis. However, it was recently shown for ⁵⁷Fe implanted in Si to a dose of 10¹⁶ atoms/cm² (4), and for ⁵⁷Fe in the decay of ⁵⁷Co, implanted to a dose of 10¹⁴ atoms/cm² (5), that the doublet is due to a quadrupole interaction. A dose dependence study (6) and annealing experiments (7) both support the idea that this doublet is associated with ⁵⁷Fe in amorphized Si or Ge. Although it is very tempting to extrapolate these results to the data of Latshaw, one has to be cautious as the experimental conditions are very different : the implantation energy is almost three orders of magnitude higher (20-30 MeV), but the implantation dose (10¹⁰ atoms/cm²) is at least four orders of magnitude lower. It is hard to make definite statements about amorphisation under these conditions. Therefore an experiment was set up to perform recoil implantation experiments in an external field. A 66 Mev³⁵Cl⁸⁺ beam was used to Coulomb excite the ⁵⁷Fe atoms from a 2.3 mg/cm^{2 57}Fe foil, and to recoil implant them into a Ge catcher. This catcher was placed in the gap of a 35 kGauss split coil superconducting magnet, with the field in the beam direction, and the gamma rays were detected perpendicular to this direction. The resulting Mössbauer spectrum shows strong evidence for a quadrupole interaction hypothesis. Differences between the spectra of ⁵⁷Fe in Si and Ge will be discussed.