HAADF imaging: an effective technique for the study of nonhomogeneous nanostructures.

Atomic number contrast (Z-contrast) imaging using high-angle annular dark field (HAADF) detector, along with high resolution electron microscopy (HREM), is used to study the nanostructured metal, semiconductor, mixed oxide, and soft matter composites of inhomogeneous nature. A comparison between the HREM and HAADF images for the analysis of crystal structure, defects, and compositional inhomogenity in those nanostructures has been made. While the HREM technique is efficient in determining bulk crystallinity and defect structures, the HAADF imaging technique is superior in determining the surface inhomogenity, defect structures in the interior of the nanostructures, even at atomic resolution. The efficiency of the HAADF imaging technique in determining the surface inhomogenity and defect structures is demonstrated for the Au-Pt bimetallic clusters, CdSe nanofibers and nanowires, Nb16W18O94 mixed oxide, and polystyrene-mormorillonite clay nanocomposites.