Chemistry Reference
In-Depth Information
Fig. 6.28 Mössbauer spectra of
57
Fe in n-type FZ-Si measured between 330 and 1,200 K. Notice
that the vertical scale for the region above 900 K is blown up with a factor of two, in order to
show the small and broad resonance effects more clearly [
42
]
usual temperature dependence of a spectrum component due to the SOD shift.
Both the interstitial and the substitutional components, however, do not simply
follow the SOD shift. The center shift of the interstitial component deviates from
the SOD shift, moving continuously to the substitutional position with increasing
temperature. This anomaly is accompanied by the strong decrease of the resonance
area. Furthermore, the center shifts of the substitutional singlet between 800 and
1,000 K are different from the extrapolation of the center shift, but above 1,100 K
the shift goes back to the position of the substitutional again. This is essential
observation to interpret the whole dynamical phenomena (Fig.
6.29
).
Above 500 K interstitial Fe atoms are supposed to start migrating within the
lifetime, subsequently finding vacancies. Consequently, the singlet between 800
and 1,000 K is thought to be a ''motional-averaged component'' due to substitu-
tional
57
Fe formation. Above 1,100 K the isomer shift of the broad singlet coin-
cides with that of substitutional Fe, indicating that Fe atoms stay dominantly on
