Isolated 57Fe atoms were studied in MgO single-crystals by emission Mössbauer spectroscopy following implantation of 57Mn decaying to 57Fe. Four Mössbauer spectral components were found corresponding to different Fe lattice positions and/or charge states. Two components represent Fe atoms substituting Mg as Fe2+ and Fe3+, respectively; a third component is due to Fe in a strongly implantation-induced disturbed region. The fourth component, which is the focus of this paper, can be assigned to Fe at an interstitial site. Comparison of its measured isomer shift with ab initio calculations suggests that the interstitial Fe is located on, or close to, the face of the rock-salt MgO structure. To harmonize such an assignment with the measured near-zero quadrupole interaction a local motion process (cage motion) of the Fe has to be stipulated. The relation of such a local motion as a starting point for long range diffusion is discussed.

We have applied implantation of radioactive 57Mn + (T1/2 = 1.5 min) at the ISOLDE facility at CERN with 50–60 keV energy to fluences <1012 /cm2 to study the emission Mössbauer spectra from the 14.4 keV transition of the 57Fe daughter atoms. For fluences ≥5 × 1011 57Mn/cm2, the spectra are dominated by the Fe3 + state exhibiting a slow paramagnetic relaxation. We show that the Fe3 + state in ZnO saturated by <1012 57Mn/cm2 implantations is unstable. The crystals can be reset by annealing at T > 760 K or storage at room temperature for 12 months, after which they show dominantly the Fe2 + state for <2 × 1010 57Mn/cm2 implantations. These findings are discussed in terms of diffusion and/or annihilation of implantation-induced defects.

The influence of the ion implantation process on the charge state of dilute 57Fe impurities implanted as radioactive 57Mn in ZnO is investigated by 57Fe emission Mössbauer spectroscopy. One sample is additionally implanted with stable 23Na impurities. Both Fe2+ and Fe3+ charge states are observed, and the Fe3+/Fe2+ ratio is found to increase with the fluence of both 57Mn/57Fe and 23Na ions, demonstrating that the build-up of Fe3+ is not related to the chemical nature of the implanted ions. The results are interpreted in terms of radiation damage induced changes of the Fermi level, and illustrate that the Fe3+/Fe2+ ratio can be adjusted by ion implantation. The spin–lattice relaxation time for Fe3+ in ZnO is found to be independent of the implantation fluence, and is evidently an intrinsic property of the system.

In 2010, 15 shifts were awarded to the proposal entitled “Emission Mossbauer spectroscopy of advanced materials for opto- and nano- electronics”, for investigations on (1) Paramagnetic relaxations in compound semiconductors (2) Vacancy diffusion in group IV semiconductors. On both subjects, major progress has been made, but after two years, many questions are still open, and we wish to propose a continuation of our investigations to derive solid conclusions on many aspects of these investigations.

The spin-lattice relaxation rate of paramagnetic Fe3+ in single-crystalline ZnO has been determined following low-fluence (Phi < 10(12) cm(-2)) 60 keV implantation of Mn-57(+) (T-1/2 = 1.5 min) and emission Mossbauer spectroscopy on the Fe-57 daughter nucleus in the temperature range from 300 to 664 K. The spin-lattice relaxation of Fe3+ is found to follow a T-9 temperature dependence, in contrast to the T-2 dependence expected for a two-phonon Raman process determined in both single-crystal MgO and alpha-Al2O3 using the same analysis method of the Mossbauer spectra measured without an applied external magnetic field. This is an unexpected result since ZnO has a lower Debye temperature than both MgO and alpha-Al2O3.

Fe-57 Mossbauer spectroscopy studies, following implantation of radioactive Mn-57*, have been conducted on InP and n- and p-type InAs at temperatures above 300 K. The Mn-52* ions are produced at the ISOLDE facility at CERN, ionized and accelerated to 60 key energy and implanted with fluences of 2 x 10(12) ion/cm(2) into single crystal samples. Mossbauer spectra were collected with a parallel plate avalanche counter. Analysis of the Mossbauer spectra required three components: an asymmetric doublet attributed to Fe atoms in implantation induced damaged environments, a single line assigned to Fe on substitutional In sites and a weak symmetric doublet assigned to impurity-vacancy complexes. In InP the substitutional Fe component (Fe-S) becomes significant above 400 K; while in InAs the Fe-S fraction is already appreciable (>30%) after implantation at room temperature. The asymmetric doublet dominates the spectra of all samples but shows significant reduction in intensity with increasing temperatures. The radiation damage shows strong annealing above 400 K in the InAs samples and above 450 K in InP; the Fe-defect complex dissociates at 500 K, and the Fe-S component dominates the spectra at higher temperatures. There was no evidence of any magnetic components in the spectra, indicating that at the low concentrations used in our measurements, the Fe ions were predominantly in the Fe2+ state. (C) 2011 Elsevier B.V. All rights reserved.

The annealing of defects in Sb/Sn implanted diamond has been studied in 119Sn Mössbauer spectroscopy following the implantation of radioactive parent isotopes 119Xe and 119mSn. Our results show that after annealing above 1300K, 40% of the implanted ions are located at or near regular sites in the lattice. Significant implantation induced defects however remain.

Monoenergetic recoil of 29 eV on 111In atoms due to neutrino emission in combination with the microscoui PAC method is utilized to study single Frenkel pairs in materials. The 111In atoms serve as primary knock-on atoms and are simultaneously nuclear probes for PAC. In this way microscopic information on the Frenkel pair formation process and the thermal behavior of vacancies and interstitials in several fcc metals (Cu, Ag, Al) have been obtained. In semiconductor Ge an intrinsic defect - probably a monovacancy -is observed. No indication of Frenkel pair production was found in the intermetallic compound PdIn.

Prompted by the generally poor understanding of the nature of magnetic phenomena in 3d-metal doped ZnO, we have undertaken on-line F57e Mössbauer spectroscopy on ZnO single crystals in an external magnetic field of 0.6 T, following the implantation of radioactive M57n ions at room temperature. The Mössbauer spectra of the dilute Fe impurities are dominated by sextets whose angular dependence rules out an ordered magnetic state (which had been previously proposed) but are well accounted for on the basis of Fe3+ paramagnetic centers on substitutional Zn sites with unusually long relaxation times (>20 ns).

We present a method to describe the temperature dependence of emission Mössbauer spectra showing slow spin-lattice relaxations of Fe3 +  in MgO single crystals, obtained after implantation of 57Mn at ISOLDE/CERN. The analysis is based on the Blume-Tjon model for the line-shape of relaxing paramagnetic sextets with the spin relaxation rate, τ  − 1 as a parameter. The temperature dependent spin relaxation rate of Fe3 +  in MgO is found to increase to ~108 s − 1 at 647 K by assuming a relaxation rate of τ  − 1 < 106 s − 1 at 77 K. The results are in accordance with those obtained by electron paramagnetic resonance spectroscopy demonstrating the possibility of retrieving spin-lattice relaxation rates of dilute Fe3 +  from emission Mössbauer spectroscopy of Mn/Fe-implanted oxides.

Emission Mössbauer spectroscopy on 57Fe fed by 57Mn ions implanted in the metal oxides ZnO, MgO and Al2O3 has been performed. The implanted ions occupy different lattice sites and charge states. A magnetic part of the spectra in each oxide can be assigned to Fe3 +  ions in a paramagnetic state with unusually long relaxation time observable to temperatures up to several hundreds Kelvin. Earlier expectations that the magnetic spectra could correspond to an ordered magnetic state could not be confirmed. A clear decision for paramagnetism and against an ordered magnetic state was achieved by applying a strong magnetic field of 0.6 Tesla. The relaxation times deduced were compared to spin–lattice relaxation times from electron paramagnetic resonance (EPR).

Ion implantation provides a precise method of incorporating dopant atoms in semiconductors, provided lattice damage due to the implantation process can be annealed and the dopant atoms located on regular lattice sites. We have undertaken 57Fe emission Mössbauer spectroscopy measurements on GaAs and GaP single crystals following implantation of radioactive 57Mn +  ions, to study the lattice sites of the implanted ions, the annealing of implantation induced damage and impurity–vacancy complexes formed. The Mössbauer spectra were analyzed with four spectral components: an asymmetric doublet (D1) attributed to Fe atoms in distorted environments due to implantation damage, two single lines, S1 assigned to Fe on substitutional Ga sites, and S2 to Fe on interstitial sites, and a low intensity symmetric doublet (D2) assigned to impurity–vacancy complexes. The variations in the extracted hyperfine parameters of D1 for both materials at high temperatures (T > 400 K) suggests changes in the immediate environment of the Fe impurity atoms and different bonding mechanism to the Mössbauer probe atom. The results show that the annealing of the radiation induced damage is more prominent in GaAs compared to GaP.

The valence state and annealing reactions of Mn/Fe in single crystalline alpha-Al2O3 have been determined following low fluence (<10(12) cm(-2)) 60 keV implantations of Mn-57(+) (T-1/2 = 1.5 min) and emission Mossbauer spectroscopy on the Fe-57m daughter nuclei in the temperature range from 110-700 K. At 110 K, most probe atoms are found in the Fe2+ state in amorphous surroundings due to the implantation damage. A fraction of the Fe is found in cubic environment, possibly nano-precipitates of eta-Al2O3. This site is found to disappear from the spectra above 500 K. Annealing of the damage sites at increasing temperatures leads first to increased incorporation of the probe atoms as Fe3+ on Al sites, and, above room temperature, also as Fe4+. The Fe3+ sub-spectrum is masked by slow paramagnetic relaxations following a T-2 dependence, as expected for a two-phonon Raman process. Our data is consistent with data from Co-57 and Fe-57 implantations, suggesting a general increase in the average Fe valence state with lower implantation dose and negligible annealing reactions at room temperature.

The valence state and annealing reactions of Mn/Fe in single crystalline α-Al2O3 have been determined following low fluence (<1012 cm − 2) 60 keV implantations of 57Mn +  (T1/2 = 1.5 min) and emission Mössbauer spectroscopy on the 57m Fe daughter nuclei in the temperature range from 110–700 K. At 110 K, most probe atoms are found in the Fe2 +  state in amorphous surroundings due to the implantation damage. A fraction of the Fe is found in cubic environment, possibly nano-precipitates of η-Al2O3. This site is found to disappear from the spectra above 500 K. Annealing of the damage sites at increasing temperatures leads first to increased incorporation of the probe atoms as Fe3 +  on Al sites, and, above room temperature, also as Fe4 + . The Fe3 +  sub-spectrum is masked by slow paramagnetic relaxations following a T2 dependence, as expected for a two-phonon Raman process. Our data is consistent with data from 57Co and 57Fe implantations, suggesting a general increase in the average Fe valence state with lower implantation dose and negligible annealing reactions at room temperature.

Ion implantation provides a precise method of incorporating dopant atoms in semiconductors, provided lattice damage due to the implantation process can be annealed and the dopant atoms located on regular lattice sites. We have undertaken Fe-57 emission Mossbauer spectroscopy measurements on GaAs and GaP single crystals following implantation of radioactive Mn-57(+) ions, to study the lattice sites of the implanted ions, the annealing of implantation induced damage and impurity-vacancy complexes formed. The Mossbauer spectra were analyzed with four spectral components: an asymmetric doublet (D1) attributed to Fe atoms in distorted environments due to implantation damage, two single lines, S1 assigned to Fe on substitutional Ga sites, and S2 to Fe on interstitial sites, and a low intensity symmetric doublet (D2) assigned to impurity-vacancy complexes. The variations in the extracted hyperfine parameters of D1 for both materials at high temperatures (T > 400 K) suggests changes in the immediate environment of the Fe impurity atoms and different bonding mechanism to the Mossbauer probe atom. The results show that the annealing of the radiation induced damage is more prominent in GaAs compared to GaP.

57Fe Mössbauer spectroscopy following ion implantation of radioactive 57Mn+ ( T1/2=85.4s) has been applied to study the formation of Fe/Mn implantation-induced defects in ZnO at temperatures between 319 and 390K. The formation of ferric iron–vacancy complexes is found to depend strongly on the implanted dose and to be faster and more efficient at higher temperatures. The results at these temperatures suggest the mobility of the Zn vacancy, together with vacancy trapping at the substitutional Mn/Fe impurities are responsible for the formation of Fe–VZn complexes.

The theory for so-called Time-Delayed-Measurements is outlined. This method allows for isothermal annealing studies in emission Mössbauer spectroscopy utilizing radioactive beams. The usefulness of this method is illustrated by the example of the annealing of a magnetic defect in ZnO.

Mössbauer measurements have been performed on a GaAs single crystal sample following the implantation of radioactive 57Mn +  (\(T_{{\raise0.7ex\hbox{$1$} \!\mathord{\left/ {\vphantom {1 2}}\right.\kern-\nulldelimiterspace} \!\lower0.7ex\hbox{$2$}}} = 1.5\) min) ions. The Mn +  ions were implanted with 60 keV energy into a GaAs sample held at temperatures of 300–700 K in an implantation chamber. Implantation fluences were <2 × 1012 ions/cm2 which assured single ion implantations. Mössbauer spectra were measured with a resonance detector equipped with 57Fe enriched stainless steel foils mounted on a conventional drive system outside the implantation chamber. The spectra at the lower temperatures are dominated by an asymmetrically broadened quadrupole split doublet (FeD), assigned to Fe in implantation induced damaged surroundings; at higher temperatures a single line dominates, due to Fe at undisturbed substitutional sites (FeS). The spectra also required small contributions (approx. 13–5%) of a quadrupole split component, FeX, which may be due to interstitial Fe and Fe in vacancy complexes. A prominent annealing stage is evident in the temperature range 300–550 K, leading to substantial increase in the FeS fraction, and attributed to mobile Ga vacancies.