J. A. Sawicki

Hyperfine interactions of iron implanted into aluminium

Stable57Fe implanted into Al at energies of 20 to 70 keV and doses of 1014 to 2·1017 ions/cm2 was studied with conversion electron Mössbauer spectroscopy at room and liquid nitrogen temperatures. Spectra composed of a single line and a doublet were observed. Similarly as in the splat-quenched FeAl alloys iron monomers and iron associations, mostly dimers, are observed. The isomer shifts of both components differ considerably and do not change with iron concentration. The splitting of the doublet increases with iron concentration, the increase being reproduced by computer simulations of electric field gradients in lattices with a random distribution of charge defects. The observed probability of formation of iron associates is higher than in random systems, especially at high iron doses.

Conversion electron Mössbauer spectroscopy at low temperatures

Abstract A proportional counter operating at low temperatures has been constructed and applied to the conversion electron Mossbauer spectroscopy of 57 Fe.

Resonant emission of secondary electrons associated with recoilless nuclear absorption of gamma rays in solids

Abstract Secondary electrons generated in polycrystalline iron samples due to nuclear resonant absorption of 14.4 keV gamma-rays in 57 Fe and subsequent reemission of internal conversion and Auger electrons were investigated for an energy range between 0 and 100 eV with a cylindrical mirror analyzer. It was found that the resonance absorption of gamma-rays is accompanied by an intensive emission of secondary electrons, particularly at energies about 5–10 eV. It was shown that those electrons can be utilized for more efficient registration of conversion electron Mossbauer spectra due to their large collection and detection efficiency in equipment using channel electron multipliers.

Conversion electron Mossbauer spectroscopy with the use of channel electron multipliers operating at low temperatures

Abstract A simple method of measuring the conversion electron Mossbauer spectra at low temperatures down to 4.2 K is presented. The method utilizes channel electron multipliers as high performance detectors of low-energy electrons at cryogenic conditions. A versatile low-cost insert unit for Mossbauer effect measurements with the source, resonant scatterer and channel electron detector cooled down to liquid helium temperature is also described.

Conversion electron Mössbauer study of LiF implanted with 57Fe ions

Abstract Lithium fluoride crystals implanted with 57Fe ions at doses from 5×1015 at/cm2 to 6×1016 at/cm2 have been studied with conversion electron Mossbauer spectroscopy. It was found that iron enters the implanted zone in three well defined charge states: Fe3+, Fe2+ and Fe0 (metal). At low doses the relative fractions of Fe3+ and Fe2+ are close to 80% and 20%, which corresponds to the respective ionic fractions in an iron doped LiF sample obtained by vacuum co-deposition. With the increase in the implantation dose the Fe2+ and Fe0 fractions increase to about 40% and 30%, respectively. Annealing in vacuum results in a growth of metallic iron precipitates, whereas annealing in the presence of oxygen leads to precipitation of superparamagnetic particles of some, still unidentified, ferric compound. The Mossbauer data were related to the role of F- and F2-centres observed by optical absorption measurements. Good agreement has been achieved between the quadrupole splitting data for Fe3+ in fluorides LiF, NaF and KF and the calculated values in frames of the model of V−-Fe3+-V− defect clusters presented in our earlier work.

Site localization, aggregation and atomic size effects for implanted iron alloys — correlation with the miedema model of alloying

Abstract In this paper we discuss the applicability of various metallurgical parametrizations, and, in particular, of the Miedema model, in the analysis of site characterization for implanted atoms. In this aspect the results of conversion electron Mossbauer spectroscopy (CEMS) investigations of iron ion implantation in metals and metalloids are discussed. The localization of impurities, aggregation and amorphization effects in iron-implanted matrices of 3d, 4d and 5d series metals, 4f metals and sp-elements are considered. It is shown that the cellular model, proposed by Miedema for explaining the heat of alloy formation and various other energy effects for binary metallic systems formed at thermal equilibrium, also allows for a better understanding of the atomic processes which occur in binary systems formed in athermal conditions of high-dose ion implantation. In particular, the behaviour of iron in various matrices can be described using thermochemical coordinates and the basic concepts of charge transfer and electron density mismatch between impurity and host atoms. A possibility for making predictions of interstitial and substitutional locations for various impurities in various hosts, based on Miedema calculations of volume contraction upon alloying, is discussed.

Determination of the valence state of Eu atoms in implanted EuSi microalloy by low-temperature conversion electron Mössbauer spectroscopy

Abstract We improved the sensitivity of conversion electron Mossbauer spectroscopy to an extent sufficient for measurements on materials implanted with the stable 151 Eu isotope at doses above 10 16 atoms/cm 2 . The measurements can be performed down to liquid-helium temperature using a single-channel electron multiplier in a close to sample geometry. It is shown that europium implanted at high dose in silicon enters mostly in a divalent state Eu 2+ , the trivalent Eu 3+ contribution being smaller than 5%.

Temperature‐dependent conversion electron Mössbauer measurements of 57Fe implanted in silicon and germanium

Conversion electron Mossbauer spectra of 3 at% Fe implanted in silicon and germanium are measured at temperatures between 78 and 550 K. Helium counters of electrons are used in back-scattering geometry. The results indicate a temperature-independent s-electron density at the iron nuclei. A rather small temperature dependence of the electric field gradient is observed and is interpreted in terms of the T3/2-relationship. The possible location of iron implanted in amorphous silicon and germanium is discussed. Es werden die Elektronenkonversions-Mosbauerspektren von 3 At% Fe, das in Silizium und Germanium implantiert wurde, bei Temperaturen zwischen 78 und 550 K gemessen. Heliumelektronenzahler werden in Ruckstreugeometrie benutzt. Die Ergebnisse zeigen eine temperaturunabhangige s-Elektronendichte am Eisenkern. Eine ziemlich kleine Temperaturabhangigkeit des elektrischen Feldgradienten wird beobachtet und mit der T3/2-Beziehung interpretiert. Die mogliche Lokalisierung des implantierten Eisens in amorphem Silizium und Germanium wird diskutiert.

Cryogenic helium counter of particles

Abstract A proportional, miniature helium-gas counter has been constructed and examined above 15 K with low-energy electrons. A gas density was shown to be a chief parameter which determines the counter performance in the function of the temperature.

Conversion electron Mössbauer spectroscopy of 197Au

Abstract The Mossbauer spectra of 77.3 keV γ-transition in 197Au have been measured for the first time in the conversion electron scattering mode, with the use of a channel electron multiplier at low temperatures. The high magnitude of the resonant effect obtained makes the investigations of various phenomena in very thin gold films feasible. The application of the technique in studying other high-energy Mossbauer transitions is also possible.