Electron microscopy - oxides high resolution

A special mention is in order of high-resolution electron microscopy (HREM), a variant that permits columns of atoms normal to the specimen surface to be imaged the resolution is better than an atomic diameter, but the nature of the image is not safely interpretable without the use of computer simulation of images to check whether the assumed interpretation matches what is actually seen. Solid-state chemists studying complex, non-stoichiometric oxides found this image simulation approach essential for their work. The technique has proved immensely powerful, especially with respect to the many types of defect that are found in microstructures. 

S lijima. High resolution electron microscopy of crystal lattice of titanium-niobium oxide. JApplPhys42 5891 - 5893,1971. 

The structures of iron oxides have been determined principally by single crystal X-ray diffraction or neutron diffraction with supplementary information coming from infrared spectroscopy, electron diffraction and high resolution electron microscopy. A few years after the first successful application of X-ray diffraction to crystal structure determination, this technique was used to establish the major features of the structures of magnetite (Bragg, 1915 Nishikawa, 1915) and hematite (Bragg Bragg, 1918). 

In 1995, Crespi et al. used high-resolution electron microscopy to investigate the structure of slightly silver-deficient Ag2 vV40, [58], During the discharge reaction, silver particles were observed on the outside of the needle-shaped SVO particles, which confirmed that the first step in the lithiation of this material was reduction of silver. The stacking of the vanadium oxide layers was also found to become random in this process. 

Crespi, A.M., PM. Skarstad, and H.W. Zandbergen. 1995. Characterization of silver vanadium oxide cathode material by high-resolution electron microscopy. J. Power Sources. 54 68-71. 

Hardacre el al. (7 75, 174) investigated the properties, structure, and composition of cerium oxide films prepared by cerium deposition on Pt(lll), finding that the activity for CO oxidation is enhanced on Pt(lll) that is partially covered by ceria. It was suggested that new sites at the Pt-oxide interface become available for reaction. A remarkable observation is the high activity for CO oxidation when the Pt(lll) sample is fully encapsulated by ceria (Pt was undetectable by XPS and AES). It was proposed that an ultrathin, disordered ceria film becomes the active catalyst. It was also demonstrated by XPS and AES that Pt dramatically increases the reducibility of cerium oxide that is in intimate contact with Pt. This result suggests that intimate contact between the noble metal and oxide phases is indeed crucial to facile oxygen release from ceria. High-resolution electron microscopy demonstrated the presence of direct contact between ceria and noble metal for supported Pt-Rh catalysts (775). Hardacre et al. (173,174) related the catalytic activity of the ceria phase to partially reduced cerium oxide. 

High Resolution Electron Microscopy (HREM) has proven as a very useful technique in the structural characterisation of supported metal catalysts (383-386) in general and, in particular, of noble metal catalysts supported on ceria-based oxides (52,70,72,97,105,109,117,124,135,137,139,144,147,155,171,182-184.194.203,209, 210,218,226,234,235,387) ... 

A. Carlsson, T. Oku, J.O. Bovin, G. Karlsson, Y. Okamoto, N. Ohnishi, and O. Terasaki, The Structure of Iron Oxide Implanted Zeolite Y, Determined by High-resolution Electron Microscopy and Refined with Selected Area Electron Diffraction Amplitudes. Chem. Eur. J., 1999, 5, 244-249. 

The catalyst employed in this work was a commercial Ru/C catalyst (Aldrich, ref 20,618-0). Inductive coupled plasma-atomic emission spectroscopy (ICP-AES) was used to measure the ruthenium content in the catalyst after dissolution of the solid in an acidic solution, and for the determination of the concentration of various metal ions in the solution after the oxidation treatment. The sizes of ruthenium particles were measured by high resolution electron microscopy (JEOL JEM 2010). 

---