We present a study on the interpretation of conversion electron Mössbauer spectra reflecting an infinite number of sites, in casu Mössbauer spectroscopy on Fe 1−x Si layers on Si, synthesized by pulsed laser annealing. These spectra display a broad double-peaked resonance, reflecting the numerous different environments of the 57 Fe probe due to a distribution of vacancies on the Fe sublattice. The spectra can be fitted in many different ways; hence finding a reliable physical interpretation is not straightforward. Therefore ab initio calculations have been performed in order to obtain a priori information about the hyperfine interaction parameter distributions. For this material, the electric-field gradient on the 57 Fe atoms turns out to depend on details in the configuration of neighbors as far as the sixth neighbor shell. The isomer shift appears to be determined by the number of Fe atoms in the first and second Fe neighbor shells only. This leads to the construction of an ab initio based model predicting the mean isomer shift and its distribution for a given Fe 1−x Si layer with a known Fe concentration profile. By applying this model new information from the experimental data can be extracted: we show that after applying one or two laser pulses, the Fe atoms are not completely randomized at an atomic scale. The relation of this model to other approaches of analyzing Mössbauer spectra with a distribution of sites is discussed, as well as the difference between the present results on ͓CsCl͔Fe 1−x Si and earlier interpretations in the literature. This work reveals how a combination of Mössbauer experiments and ab initio calculations leads to a more reliable interpretation of Mössbauer spectra reflecting an infinite number of sites.

No abstract

Thin films of ε-FeSi were grown by deposition of Fe on a Si〈111〉 substrate under ultrahigh vacuum conditions, followed by in situ annealing at 450 °C. These ε-FeSi films were subjected to irradiation from a pulsed excimer laser in the energy density range 0.30–0.90 J/cm2, in order to study the phase formation and crystallization processes of metastable [CsCl]Fe1−xSi phases. The samples were analyzed by Rutherford backscattering and channeling spectrometry and by cross-sectional transmission electron microscopy. Considerable diffusion of silicon into the silicide film was found to occur during the pulsed laser annealing, resulting in a film with nonstochiometric composition. In contrast to solid phase reaction, epitaxial ordering in the iron silicide film is observed during pulsed laser annealing when the film’s composition approaches that of FeSi2. Analysis by cross-sectional transmission electron microscopy confirmed that the phase which exhibits epitaxial ordering corresponds to the metastable [CsCl]Fe1−xSi phase. Upon annealing at 600 °C for 1 h, this metastable phase converts into the semiconducting β-FeSi2.

No abstract

Perturbed angular correlation experiments using soft-landed 111 Ag probe atoms on a Ag(100) surface allow monitoring of the self-diffusion of Ag on the surface. In total, three different sites are observed as a function of substrate temperature: the adatomic terrace site in the temperature interval between 80 and 150 K, the adatomic step site between 130 and 180 K, and the substitutional terrace site starting from 150 K, where adatoms are still present on the surface. These data could be explained only by assuming that the hopping diffusion mechanism is active at low temperatures, while the exchange diffusion mechanism is responsible for the observed substitutional terrace site at 150 K.[ S0031-9007(98)07711-4]