Techniques relevant to HRTEM

1 Electron-optical conditions to obtain an HRTEM image 

In this section, some recent results on the structure analysis of HTSCs are shown in order to demonstrate the usefulness of HRTEM. In all cases mentioned here small blocks of specimens were lightly crushed in an agate mortar and the fragments obtained were observed in a high-resolution, high-voltage 

Electron diffraction patterns were taken from many crystal fragments of Ga-2434. Some typical patterns are shown in Fig. 1.3. From the reflection conditions (h - - k = 2n for hkO, I = 2n for Okl, hOl and 00/, h = 2n for 00 and k = 2n for 0 0) the space group is uniquely determined to be Pccn (56). The lattice parameters are a = 5.46, 6 = 5.54 and c = 51.3A, being in agreement with those obtained from X-ray diffraction. Weak diffuse streaks along [010] in Fig. 1.3(a) must be due to stacking faults, which have been observed locally as intergrowth defects. 

When we examine the image contrast of Fig. 1.4 in more detail, we note that there are two kinds of darkness for the SrO planes, i.e. the atom column sites of SrO plane, marked by arrow 1, are slightly darker than those of the SrO  

These possibilities were opened up by the development of a coherent field-emission electron beam [2.4] which is indispensable for forming high-quality electron holograms. In fact, an electron hologram formed with this type of electron beam can have such high contrast and precision that a phase distribution can be reconstructed within an accuracy of 1/100 of its electron wavelength [2.5]. Furthermore, since the field-emission beam has a high current 

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