Performance of Ultrahigh Resolution Electron Microscope JEM-4000EX and some Applications of High Tc Superconductor
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PERFORMANCE OF ULTRAHIGH RESOLUTION ELECTRON MICROSCOPE JEM-4000EX AND SOME APPLICATIONS OF HIGH Tc SUPERCONDUCTOR. TOSHIKAZU HONDA*, KATSUHIKO IBE*, YUKIHISA ISHIDA* AND MICHAEL M. KERSKER**
*JEOL LTD., 1-2 Musashino 3-chome, Akishima, Tokyo 196, Japan **JEOL (U.S.A.) Inc., 11 Dearborn Road, Peabody, MA01960, U.S.A. ABSTRACT The high resolution electron microscope is powerful for modern materials science, because of its direct observation capability for the atomic structu. of materials. The JEM-4000EX, a 400 kV accelerating voltage electron microscope whose objective lens has a I mmspherical aberration coefficient, has a 0.168 nm theoretical resolving power. Using this microscope, atomic structure images of high Tc superconductor such as Y-Ba-Cu-0, Bi-Ca-Sr-Cu-O and TI -Ca-Ba-Cu-O were observed. INSTRUMENT The JEM-4000EX, a 400 kV accelerating voltage electron microscope whose objective lens has a I mmspherical aberration coefficient, was used for the present study. A high voltage electron microscope having the short wave length (0) is extremely advantageous for observing the high resolution images because the theoretical resolution (d) is given by 4 It must d=O.65(Cs')') . Here Cs is the spherical aberration constant. be noticed that d is more strongly dependent on 4 than Cs. Therefore, it A as well as decreasing Cs for obtaining the is important to decrease high resolution images. This idea was proposed and brought into function by Uyeda et al. [1 using a cOO kV electron microscope and by Iloriuchi et al. [2] using a 1 MVelectron microscope. As is well known, a resolution of less than 0.2 nm is necessary for the structural analysis of metallic crystals. The divergence angle of the incident beam and the stability of the high voltage as well as chromatic aberration have a direct bearing on the resolution limit as seen from an analysis of an envelope function [3, 4] of the phase contrast transfer function. Several considerations were paid to the fundamental design of this microscope; (1) Minimizing the aberration coefficients of the objective lens by using the finite element method calculation, (2) developing a highly stabilized and bright electron gun, (3) minimizing astigmatism change due to magnification change, and (4) improving the operability of the goniometer device for ease of operation. (1) The viewing area and the tilting angle of the specimen depend on the outer diameter of the tip of the specimen holder. The specimen holder for normal temperature use has a tip of less than 6 mmouter diameter, while the three-axis tilting heating holder, provided with a built-in heater, has a tip of 9 mmouter diameter. Using the finite element method, we have designed three types of polepieces for ultrahigh resolution observation; the UHP40, which allows observation of a 2 mm diameter area in the center of a 3 mm diameter specimen, the UHP-40H, which is used for observation of a 1.4 mmdiameter area, and the UHP4OX, which allows specimen heating up to 8O0t. The UHP40 was already reported at the EMAG '85.[5] The UHP40H wa
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