High-resolution specimen, electron microscopy

The calcined samples are investigated by transmission electron microscopy (TEM) in a Philips EM 420 instrument operated at 120 kV. The specimens are deposited on a copper grid coated with a carbon film. High-resolution transmission electron microscopy (HRTEM) has been carried out at the Laboratory of Inorganic Chemistry, ETH Zurich, Switzerland, with a Philips CM20-ST microscope (accelerating voltage 300 kV). 

High-resolution transmission electron microscopy can be understood as a general information-transfer process. The incident electron wave, which for HRTEM is ideally a plane wave with its wave vector parallel to a zone axis of the crystal, is diffracted by the crystal and transferred to the exit plane of the specimen. The electron wave at the exit plane contains the structure information of the illuminated specimen area in both the phase and the amplitude.. This exit-plane wave is transferred, however affected by the objective lens, to the recording device. To describe this information transfer in the microscope, it is advantageous to work in Fourier space with the spatial frequency of the electron wave as the relevant variable. For a crystal, the frequency spectrum of the exit-plane wave is dominated by a few discrete values, which are given by the most strongly excited Bloch states, respectively, by the Bragg-diffracted beams. 

Figure 1.3 High-resolution transmission electron microscopy images of the grain boundaries of alumina samples sintered with 5 wt% calcium silicate additives. The numbers in the names ofthe specimens denote the molar...

Crystal phase structure was examined by a Rigaku X-ray diffraction (XRD) with CuKa radiation (X=1.5418A), scarmed from 20 to 80 and scanning speed was 4°/min. Microstructures were analyzed on a polished surface of the specimens by high resolution scanning electron microscopy (SEM). The relative density of piezoelectric ceramics was measured by an Archimedes s method. 

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. 

Analytical electron microscopy (AEM) can use several signals from the specimen to analyze volumes of catalyst material about a thousand times smaller than conventional techniques. X-ray emission spectroscopy (XES) is the most quantitative mode of chemical analyse in the AEM and is now also useful as a high resolution elemental mapping technique. Electron energy loss spectroscopy (EELS) vftiile not as well developed for quantitative analysis gives additional chemical information in the fine structure of the elemental absorption edges. EELS avoids the problem of spurious x-rays generated from areas of the spectrum remote from the analysis area. 

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