High-resolution electron microscopy HREM

Flueli M, Buffat P A and Borel J P 1988 Real time observation by high resolution electron microscopy (HREM) of the coalescence of small gold particles in the electron beam Surf. Sc/. 202 343... 

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. 

In the present study, we synthesized in zeolite cavities Co-Mo binary sulfide clusters by using Co and Mo carbonyls and characterized the clusters by extended X-ray absorption fine structure (EXAFS), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and high resolution electron microscopy (HREM). The mechanism of catalytic synergy generation in HDS is discussed. 

Electron diffraction performed with a parallel incident beam, i.e. Selected-Area Electron Diffraction is used to obtain good electron micrographs. The two-beam condition allows the observation of defects. SAED is also used in High-Resolution Electron Microscopy (HREM) to set a crystal to a zone axis so that the atomic columns are vertical in the microscope. SAED is very useful for the identification of phases and the... 

In the early days of high resolution electron microscopy (HREM), some special classes of stmctures were solved by recognising basic units of a... 

High resolution electron microscopy (HREM) is also used extensively for structural examination of zeolites, particularly for intergrowths and faults. EXAFS has been used to determine the local coordination geometry of the exchangeable cations and how this changes on reaction or dehydration. 

In this paper we shall describe how high resolution electron microscopy (HREM) can be used in conjunction with selected area electron diffraction (SAED) to probe the local structure of zeolitic solids (2, 5 8) which are often microcrystalline, multi-phasic or twinned. We shall also refer to the application of optical diffractometry (4, 9-11) as a supplemental procedure either for interpretation of electron micrographs, or for analogue diffraction studies of model systems. 

The power spectrum of high-resolution electron microscopy (HREM) images contains usefiil diffraction information, which can be used for studying defects, small particles or other local structures that are difficult to study by diffraction alone. For thin specimens below a certain thickness, the Fourier transform of the image intensity (/ (5)) can be related to the Fourier transform of the potential (F (5), the structure factor) ... 

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) ... 

In the work reported in this chapter, oriented pyrolytic graphite was shock-loaded at pressures up to 15 GPa perpendicular or parallel to the basal plane of the graphite. The phase transitions of graphite to other carbon allotropes will be discussed using nanostructural data obtained by high-resolution electron microscopy (HREM). 

Modem high resolution electron microscopy (HREM) reveals how frequently these defects occur, and how they provide a setting and a mechanism for intergrowth between related structures. 

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