Cross-sectional bright-field TEM images (panels (a), (b)) and the corresponding electron diffraction pattern (panel (c)) (sample PAA/S-15 min/Si). In this sample the anodization was stopped before the abrupt current increase in the anodization current. In panel (a), we reveal an amorphous layer (indicated by 2) on the Si substrate (indicated by 1). On top of this thin amorphous layer, there is another layer (layer 3) in which we identify different round-shaped multi-phase clusters of Pt-Al-Si (indicated by b) and Al nanocrystals (indicated by a). In panel (b), the pores of the PAA film are shown in larger magnification, while the inset illustrates the barrier layer at the bottom of the pores. The electron diffraction pattern of panel (c) reveals that some of the Al nanocrystals are in very good epitaxial relationship with the Si substrate.