HAADF Imaging: An Effective Technique for the Study of NonhomogeneousNanostructures

Abstract

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.

Phytochelatin–cadmium–sulfide high‐molecular‐mass complexes of Euglena gracilis

“…Euglena gracilis cells cultured with 50 µ m Cd 2+ for 4 days were also analyzed with atomic‐resolution high‐angle annular dark‐field scanning‐transmission electron microscopy (HAADF‐STEM), a more sensitive method [30,31]. The intensity in HAADF‐STEM projection images is proportional to the square of the atomic number.…”

“…The intensity in HAADF‐STEM projection images is proportional to the square of the atomic number. Then, small particles can indeed be visualized by HAADF‐STEM tomography [30,31]. The high sensitivity of this technique does not allow the use of osmium (or other metal‐based postfixation) in the analyzed samples, although the samples were contrasted with lead and uranyl.…”

“…For HAADF‐STEM, specimens were not postfixed with OsO 4 , but they were processed with lead citrate plus uranyl acetate (2%) to generate images with high resolution. Thin sections were observed using the 210F‐UHR Jeol electron microscope (Gatan Inc., Pleasanton, CA, USA) [30]. Images were recorded with a bottom‐mounted slow‐scan CCD camera (Gatan Inc.).…”

The interaction of carbon nanotubes with an in vitro blood-brain barrier model and mouse brain in vivo

“…ADF images feature an inverse contrast that allows resolution of high electron dense structures, such as carbon nanotubes and metal catalysts with more detail. High angle annular dark field (HAADF) images are produced from scattered electrons that are collected on an annular dark field detector at higher angles; the intensity in HAADF images is directly related to the atomic number of the elements within the sample [13] . Finally, high-resolution TEM (HRTEM) images and STEM images (reported in SI) were obtained using a FEI Tecnai G2 F20 TEM running at 120 kV.…”

Surface-Bioengineered Extracellular Vesicles Seeking Molecular Biotargets in Lung Cancer Cells

“…The exemplary TEM results of both the nonfunctionalized EVs (reference system) and the EVs decorated with heptapeptide from the C end (PTHTRWA-EVs) are presented in Figure . Images A and E show EVs made with the HAADF detector (sensitive to atomic number (so-called Z-contrast)) . There is a difference in the appearance of the extracellular vesicles surface, indicating that successful deposition of PTHTRWA on the surface EDX investigation confirmed the existence of a shell containing O and C on the surface of the EVs, which is shown in Figure F–H.…”