Epitaxial growth of and silicide formation in Fe/FeSi multilayers

Abstract

The structural properties of multilayers consisting of Fe layers separated by Si or FeSi layers grown with molecular beam epitaxy on MgO(001) and Si(111) are reported. Rutherford backscattering and ion channeling are used to determine the crystallinity of the layers. We find evidence for epitaxy, alloying effects, and structural coherence. Conversion electron Mössbauer spectroscopy is utilized to investigate the silicide formation in the spacer layer of Fe/FeSi multilayers and at the interface of Fe/Si layers. The silicide formed in Fe/FeSi multilayers is characterized by a broad single line Mössbauer resonance which is characteristic for the metastable CsCl–FeSi phase. For Fe/Si multilayers the Mössbauer results indicate that FeSi compounds with clearly other hyperfine parameters than the CsCl phase are formed in the spacer.

Structures and physical properties of ∊-FeSi-type and CsCl-type RuSi studied by first-principles pseudopotential calculations

“…In a recent paper (Voc Ïadlo et al, 1999) we have used ®rstprinciples pseudopotential calculations to examine the stability and physical properties of the sevenfold-coordinated 4-FeSi structure relative to various hypothetical polymorphs, concluding that a CsCl-type structure would be the thermodynamically most stable phase for pressures greater than 13 GPa (a similar transition pressure, $15 GPa, has also been reported recently by Moroni et al 1999). However, FeSi with the CsCl structure has not yet been observed in bulk material, experimental studies to date having failed to detect any phase transitions from the 4-FeSi form under conditions of high pressure and temperature (Knittle & Williams, 1995;Guyot et al, 1997), although it has been reported in thin ®lms of FeSi grown on silicon substrates (von Ka È nel et al, 1992(von Ka È nel et al, , 1994Kafader et al, 1993;Dekoster et al, 1997). The compressibility of FeSi is of considerable interest to Earth scientists, silicon being a possible alloying element in the Earth's outer core.…”

Crystal structure, compressibility and possible phase transitions in \boldvarepsilon-FeSi studied by first-principles pseudopotential calculations

“…Calculation of the enthalpies for the two phases con®rmed this result. Experimental evidence for the stability of a CsCl-type phase is provided by the observation that thin ®lms of FeSi with the CsCl-type structure may be grown on silicon substrates (von Ka È nel et al, 1992;Kafader et al, 1993;von Ka È nel et al, 1994;Dekoster et al, 1997). It has been suggested that formation of this material as an epitaxic layer on Si is associated with a compressive strain, equivalent to an applied pressure of about 25 GPa (von Ka È nel et al, 1992;Girlanda et al, 1994).…”

“…Lattice-parameter measurements to much higher pressures (50 GPa) by powder X-ray diffraction (Knittle & Williams, 1995) did not suggest the presence of any structural phase transitions, even after laser-heating to about 1500 K at 49 GPa (the published data do, however, contain one point, at 36 GPa, which lies well away from the PV curve on which the rest of the data lie). Similarly, powder neutron diffraction studies both above and below room temperature (Watanabe et al, 1963) suggested that there was little change in the structure between 79 and 573 K. Recently, however, experiments on thin ®lms of FeSi grown on silicon substrates (von Ka È nel et al, 1992;Kafader et al, 1993;von Ka È nel et al, 1994;Dekoster et al, 1997) have indicated the formation of a CsCl-type structure, stable for layers thinner than 890 A Ê , and it is known that RuSi undergoes a transition from an FeSi-type to a CsCl-type structure at 1578 (AE15) K (Buschinger et al, 1997).…”

Formation of nonmagneticc−Fe1−xSiin antiferromagnetically coupled epitaxial Fe/Si/Fe

“…The measurements were performed on separately grown samples with 6 Å 57 Fe probe layers at various positions in an 56 Fe matrix, guaranteeing that the Fe in the iron silicide of the spacer layer can be clearly discriminated from the rest of the Fe, in contrast to earlier studies. 2,16,9 A first sample was designed to give information about the iron silicide spacer layer only, with the following nominal composition: Ge͑100͒ϩ68 Å 56 Feϩ3ϫ͑16 Å Siϩ6 Å 57 Feϩ19 Å 56 Fe) ϩ30 Å Si, schematically sketched in the inset of Fig. 4.…”