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Notes: Ion beam induced atomic mixing at Fe-Mo interface has been studied by using the technique of conversion electron Mössbauer spectroscopy (CEMS). Use has been made of a thin (∼50 A(ring)) layer of Fe57 isotope (enriched to 95.4%) at the interface to obtain the Mössbauer information selectively from this region. A noninterface sensitive measurement has also been performed to reveal the magnetic hyperfine interactions in the entire region of the iron overlayer. It is shown that a deposition induced reaction between the molybdenum substrate (having a thin coating of native oxide) and the Fe57 layer renders a graded nature to the interface, which is transformed upon ion bombardment (100-keV Kr+, dose ∼1016 ions/cm2) into a disordered alloy. The dominant nonmagnetic component corresponding to the interface of the ion beam mixed sample happens to be a quadrupole doublet, which represents the presence of Fe57 atoms in Fe2+ charge state. The appearance of this contribution is attributed to formation of an oxygen coordinated ternary compound in the interface layer during ion bombardment. On the basis of the comparison of the results of the interface-sensitive and non-interface-sensitive studies it is established that the inclusion of oxygen in the ion mixed sample is mainly confined to the near interface region and that the region of the overlayer contains a metastable alloy of the binary Fe-Mo system. The influence of thermal annealing at various temperatures between 200 °C and 500 °C on the ion beam mixed state has also been studied by monitoring the changes in the hyperfine interaction parameters. It is shown that the oxygen-incorporated regions of the disordered alloy retain the nonmagnetic Fe2+ charge state subsequent to annealing at 500 °C, while other regions lead to precipitation of α-Fe and Fe2Mo phases.

Notes: A grazing incidence x-ray reflectivity technique has been used to determine electron density profile (EDP) as a function of depth in Nb-on-Si and Si-on-Nb bilayer, Nb–Si–Nb and Si–Nb–Si trilayer, and Nb/Si multilayer structures. In each case, films having layer thicknesses of 35 Å were deposited on float glass and Si(100) substrates under ultrahigh vacuum conditions using an electron beam evaporation technique. EDP determined in as-deposited bilayer films shows that the widths of Si-on-Nb and Nb-on-Si interfaces are 20 and 40 Å, respectively. The large difference observed in the widths is attributed to the different growth morphology of 35 Å Nb and 35 Å Si single layer films as revealed by atomic force microscopy investigations. In situ dc resistance measurements carried out on 35 Å single layer Nb films during growth show percolation at a thickness much less than the layer thickness. In case of as-deposited Nb–Si–Nb trilayer film, EDP shows a width of 21 Å at both the interfaces viz. Si-on-Nb and Nb-on-Si whereas in the case of as-deposited Si–Nb–Si trilayer films, the widths of Si-on-Nb and Nb-on-Si interfaces are 21 and 42 Å, respectively. The EDPs obtained from bilayer and trilayer films are used to determine layer-by-layer electron density variation in Nb/Si multilayer structures. The results corresponding to the as-deposited multilayer structure indicate that interdiffusion is larger in the bottom layers of the stack. To study the role of kinetic and thermodynamic factors in the interfacial reactions, the bilayer, trilayer, and multilayer samples were isochronally annealed in vacuum up to a temperature of 300 °C in steps of 50 °C for 1 h. EDP of annealed bilayer and trilayer films show an increase in interfacial width due to interdiffusion of Nb and Si and samples annealed at 250 and 300 °C show Nb-rich and Si-rich intermixed regions. In addition to this, plateau regions having an electron density of 1.8 e/Å3 are observed in the EDP of Nb–Si–Nb and Si–Nb–Si trilayer structures annealed at 300 °C which indicates the formation of a Nb3Si phase. Structural parameters obtained from EDP are extended to interpret the results in as-deposited and annealed multilayer structures. The observed contraction in a bilayer period of an annealed multilayer structure is interpreted in terms of formation of a dense Nb3Si phase confirmed by wide angle x-ray diffraction measurements. Consequently, the multilayer structure is fully destroyed between 250–300 °C. © 2000 American Institute of Physics.

Notes: New routes using laser and ion beam techniques are developed to synthesize iron oxide based magnetic materials. The first method, pulsed ruby laser treatment (pulse duration 30 ns, λ=0.694 μm) of thermally grown iron oxide (α-Fe2O3) under water, is shown to lead to the formation of FeO and Fe3O4 phases depending upon the choice of the treatment parameters. The other method, ion beam mixing to atomically mix a deposited overlayer of cobalt (400 A(ring) thick) on an α-Fe2O3 substrate with 100-keV Ar+ at a dose higher than 1×1016 ions/cm2, leads to ferrite formation. The surface layer sensitive technique of conversion electron Mössbauer spectroscopy (CEMS) was employed for characterization.

Notes: Abstract The effect of ion beam induced atomic mixing and subsequent thermal transformations at the Fe:Al2O3 interface have been investigated by means of conversion electron Mössbauer spectroscopy [CEMS]. It is shown that the asdeposited and ion beam mixed samples exhibit distinctly different features. In particular, the ion beam mixed sample in as-mixed state shows the presence of FeAl2O4 along with non-stoichiometric FeO. Upon annealing at 600°C it shows precipitation of α-Fe with reduced contribution of FeAl2O4. The study of dose dependence of ion beam mixing has also revealed interesting features regarding the ion beam induced interface reactions.

Notes: Abstract Magnetite (Fe3O4) has been synthesized for the first time by using pulsed ruby laser induced reactive quenching process at α-Fe2O3/H2O interface. Iron foils (99.99% pure) were oxidised at 450° C for four hours to form a thick layer of α-Fe2O3 on it. These oxidised samples were immersed in water and then treated with ruby laser pulses (λ=0.694 μm, pulse width = 30 ns, energy density = 10 J/cm2). The conversion electron Mössbauer spectroscopy (CEMS) has been used to characterize the laser induced surface modifications. It is shown that laser treated samples show the formation of Fe3O4 phase along with FeO. The stability of magnetite phase in laser treated sample against thermal treatment is also studied by investigating the changes in hyperfine interaction parameters upon vacuum annealing at 300° C.

Notes: Abstract The high temperature oxidation behavior of Fe50Ni50 alloy foils implanted with 100 KeV N2 + ions at a different dose values is studied by using the technique of conversion electron Mössbauer spectroscopy (CEMS). It has been shown that the implanted foils exhibit considerable adherence of scales and higher oxidation resistance as compared to the virgin foils. This excessive adherence of scales to the surface and higher resistance to oxidation of implanted samples is attributed to nickel enrichment in the surface layers. Various oxides of Fe, Ni and Fe−Ni are identified from the hyperfine interaction parameters of the corresponding CEMS spectra and also from x-ray diffraction measurements.