Figure 63. Ge 3d XPS spectra of the as-deposited and Ar+-sputtered Ge/GeO2 and GeO2 films. Reprinted with permission from [24], S. Mathur et al., Mafer. Sci. Forum 386-388, 341 (2002). © 2002, Trans Tech Publications.

then gradually decreased to the initial value (6.0 GPa); the hardness value at the maximum corresponds to the hardness of bulk Ge (7.6 GPa). The indented depth-dependent variation of hardness (Fig. 64) indicated that the composite was composed of a harder constituent at the core. The indented depth corresponding to the maximum hardness can be assigned to the center of a spherical particle, which indicates that the mean particle diameter is about the twice the indented depth (ca. 120 nm), a fact borne out by the AFM image (Fig. 64), which shows the average particle size to be ca. 120-130 nm.

The redox chemistry observed for divalent Ge, Sn, and Pb species is also valid in their heterometal compounds;

50 100 150 200 Contact depth (nm)

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