M. Neubauer

The new cubic iron-nitride phase FeN prepared by reactive magnetron sputtering

Abstract Films of the recently discovered cubic FeN phase have been produced via RF magnetron sputtering. Their properties have been investigated as a function of the deposition parameters (substrate temperature, N 2 and Ar flows, bias voltage and RF power) in order to optimize their purity and structure. The analyses of the typically 200 nm thick films have been carried out using ion-beam analysis (Rutherford Backscattering Spectroscopy, Nuclear Reaction Analysis, and Time-Of-Flight Elastic Recoil Detection Analysis) as well as phase analysis (via X-Ray Diffraction, Conversion Electron Mossbauer Spectroscopy, and Transmission Electron Microscopy). We achieved samples with about 90% single-phase cubic FeN. The stability of the films when heated in vacuum, H 2 and ammonia up to 723 K, has also been investigated.

Preparation of ion-implanted and sub-monolayer 111In-tracer layers for perturbed angular correlation analysis

Abstract Some 10 12 radioactive 111 In-tracer atoms are routinely implanted at 400 keV into different samples to perform Perturbed Angular Correlation (PAC) measurements. The experimental details and the tricks used during the preparation and implantation are summarized. As an alternative to ion-implantation, a method to deposit submonolayer 111 In-tracer films into metallic multilayers is described. The different applications and benefits of both techniques are compared.

The production of the new cubic FeN phase by reactive magnetron sputtering

Abstract FeNy films with a nitrogen content of nearly 50 at.% (y≈1) were prepared by reactive magnetron sputtering. Their properties were studied as a function of several sputtering parameters (gas-flow rates, substrate temperature and bias voltage), using ion-beam analytical methods, Mossbauer spectroscopy as well as transmission electron microscopy (TEM) and X-ray diffraction (XRD). In order to highlight the role of light contaminant elements (H,C,O) in the production of single-phase cubic FeN films, the concentration profiles of all the elements of the films were measured by Time of Flight Elastic Recoil Detection Analysis (TOF-ERDA).

Ion-beam induced magnetic anisotropies in iron films

Abstract 100–300 nm thin Fe layers evaporated onto crystalline and amorphous Si or SiO2 substrates were irradiated, at 77 K, with 1014–1016 Xe+-ions/cm2 at 450 keV beam energy. The magnetizations in the films were measured by means of Perturbed Angular Correlation (PAC) spectroscopy with implanted 111In tracer ions, or the Magneto-Optic Kerr Effect (MOKE). Upon ion implantation, dramatic changes of the magnetic anisotropy were observed which are attributed to ion-beam enhanced lateral grain growth. Very little influence of the deposition parameters (type and cristallinity of substrate, evaporation rate) on the anisotropic magnetization was found.

Laser nitriding of iron: influence of the spatial laser intensity distribution

Abstract Laser nitriding of metals and alloys has attracted technological interest. Nevertheless, the basic nitriding mechanisms are hardly understood. Here, a detailed analysis of the nitrogen profiles, laterally and in depth, the surface profiles and the microhardness is given in their respective dependence on the spatial laser intensity profile. Irradiation with a homogenised laser beam results in a more homogeneous lateral nitrogen distribution and a smooth surface as compared to irradiation with the inhomogeneous raw beam. Furthermore, the nitrogen saturation concentrations reach over 10 at.% in the case of the homogenised beam, which is significantly higher than the 3–4 at.% found for the raw beam. On the other hand, the hardness and the hardening depth are considerably larger for the raw beam treatment, which is explained by the high amount of the e-nitride phase formed only in this case.

PAC and CEMS study of ion-irradiated Ag/Fe and In/Fe layers

Ion-beam mixing of the thermally immiscible systems Ag/Fe and In/Fe by 450 and 600 keV Xe ions was investigated by means of perturbed angular correlation and conversion electron Mossbauer spectroscopy. Different magnetic hyperfine fields associated with one or two Ag atoms close to the hyperfine probe were identified with both methods. The results are compared with those obtained for a supersaturated Fe(Ag) alloy.

Perturbed angular correlations in metal oxides with radioactive tracer beams

Abstract The perturbed γγ-angular correlation method (PAC) allows an investigation of microscopic environments of probe nuclei in solids through the hyperfine interaction. By implantation of radioactive tracer ions below the ppm level the properties of the host material in most cases remain unchanged. The multiple advantages of using an ion implanter to insert the radioactive tracer ions are illustrated by our systematic PAC investigations in oxides. The examples chosen are the annealing of radiation induced defects (e.g. in NiO, CoO); phase transformations between different crystalline structures (Mn3O4 → Mn2O3), a refinement of ionic positions (bixbyite oxides) and dynamics of electronic defects on a 10−9–10−6 s time scale (Cr2O3). In insulating compounds the probe ion itself introduces excited electronic defect levels (La2O3).

Doping of sapphire single crystals with 111In and 111Cd detected by perturbed angular correlation

The electric hyperfine interaction of ion beam implanted 111In and 111Cd probe atoms in sapphire (Al2O3) single crystals has been investigated using perturbed angular correlation spectroscopy. For both probe atoms the same distinctive electric field gradient was found, indicating that nearly all the implanted probe atoms form a stable substitutional configuration in the temperature range between 77 K and 873 K on the aluminum sublattice. A comparative study between 111In and 111Cd-measurements points to a dynamic interaction initiated by the electron-capture of 111In(EC)111Cd similar to In2O3 and La2O3. Size and orientation of the EFG are discussed in comparison to experimental results in Cr2O3 single crystals.

Phase transitions in the SrHfO3 perovskite measured with 111In/111Cd PAC

The temperature dependence of the hyperfine parameters in SrHfO3 powder samples has been investigated by means of Perturbed Angular Correlation spectroscopy using implanted 111In probes. Three quadrupole interactions have been established, with the largest fraction showing a pronounced dynamic interaction. We assign this fraction to 111In / 111Cd probe atoms on substitutional Hf sites. The temperature dependence of the dynamic interaction has been associated to the Pnma↔Imma phase transition at ∼700 K. We discuss the results in relation to those obtained for 181Hf / 111Ta-probes in AHfO3 (A=Ba, Sr, Ca) and for 111In / 111Cd-probes in PbZrO3 and BaTiO3.

Indium solubility in iron studied with perturbed angular correlations

Segregation of In in Fe-based alloys containing 0.11–2.12 at.% In has been studied by measuring the perturbed angular correlations of γ-rays emitted in the nuclear decay of 111In. The probe atoms were introduced into the alloys by either adding the carrier-free 111In during melting or via ion implantation. Ageing of the samples at elevated temperatures followed by a slow cooling to room temperature allowed us to determine the upper limit of the solubility at room temperature, S(300 K)≤ 30 at. ppm. This value is far below the one reported in the published phase diagram. Quenching of the samples in water from 973–1373 K resulted in the determination of the indium solubility in iron at these elevated temperatures.