A Mossbauer-efFect experiment, with y-ray wave vector k directed both along and normal to the c axis of a siderite (FeCO3) single-crystal platelet, has been systematically performed in the temperature range 50& T & 300 K. The T dependence of the integrated area S(T) =S (T)+S (T) under the quadrupole doublet reveals that at 300 K the Debye-%aller factors are f, =0. 72(2) and f "=0. 75(2). Independently, the area ratios S /S under the n. and 0 quadrupole components, measured at 300 K, confirm the lack of a spatial anisotropy of the f factor but, more significantly, confirm the theoretically predicted polarization-dependent resonant-absorption cross section in transmission through the crystal.
Nanocrystalline Si particles of 10 nm size, doped with traces (1 at. %) of Sn, are prepared by mechanical attrition in an inert ambient. After stain-etching, the particles photoluminesce at room temperature. 119Sn Mössbauer spectroscopy, Raman scattering, photoluminesce, and Fourier transform infrared spectroscopy measurements performed as a function of stain-etching time reveal systematic changes, and suggest that the molecular structure of porous Si consists of nanocrystalline Si particles with surfaces passivated by H and/or O atoms.
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