Atomic number imaging using STEM

Characterization techniques continue to develop and will impact their application to zeolitic systems. Aberration corrected electron microscopes are now being used to improve our understanding of catalysts and other nano-materials and will do the same for zeolites. For example, individual Pt atoms dispersed on a catalyst support are now able to be imaged in the STEM mode [252]. The application of this technique for imaging the location of rare-earth or other high atomic number cations in a zeolite would be expected to follow. Combining this with tomography... 

The main drawbacks of this approach are the low availability of such instruments in laboratories, and the fact that many samples are sensitive to ion beam damage, require specific preparation (95), and can induce low contrast. Moreover, the imaging between two milling periods is typically performed in the backscattered electrons mode, which is not always favorable this is the case for carbon nanotubes in a polymer matrix as the atomic number contrast is low. This is probably the reason why, even if the FIB/SEM approach is used on polymer nanocomposites, it not used in the literature for carbon nanotubes in polymer matrix. In this last application, the tomo-STEM technique is a good alternative to obtain images of relatively thick samples with high contrast and resolution (91). 

Small domains of high electronic density have been imaged in halato-telechelic ionomers by Scanning Transmission Electron Microscopy (STEM) using the technique of atomic number or Z-contrast. The possibility that these are ionic domains is evaluated and the morphology compared with that derived from recent SAXS experiments. 

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