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A scanning transmission electron microscope (STEM) is a type of transmission electron microscope (TEM). Pronunciation is () or (). As with any transmission illumination scheme, the electrons pass through a sufficiently thin specimen. However, STEM is distinguished from conventional transmission electron microscopes (CTEM) by focusing the electron beam into a narrow spot which is scanned over the sample in a raster. The rastering of the beam across the sample makes these microscopes suitable for analysis techniques such as mapping by energy dispersive X-ray (EDX) spectroscopy, electron energy loss spectroscopy (EELS) and annular dark-field imaging (ADF). These signals can be obtained simultaneously, allowing direct correlation of image and quantitative data. By using a STEM and a high-angle detector, it is possible to form atomic resolution images where the contrast is directly related to the atomic number (z-contrast image). The directly interpretable z-contrast image makes STEM imaging with a high-angle detector appealing. This is in contrast to the conventional high resolution electron microscopy technique, which uses phase-contrast, and therefore produces results which need interpretation by simulation. Usually a STEM is a conventional transmission electron microscope equipped with additional scanning coils, detectors and needed circuitry; however, dedicated STEMs are also manufactured. ==History== In 1925, Louis de Broglie first theorized the wave-like properties of an electron, with a wavelength substantially smaller than visible light. This would allow the use of electrons to image objects much smaller than the previous diffraction limit set by visible light. The first STEM was built in 1938 by Baron Manfred von Ardenne, working in Berlin for Siemens. However, at the time the results were inferior to those of transmission electron microscopy, and von Ardenne only spent two years working on the problem. The microscope was destroyed in an air raid in 1944, and von Ardenne did not return to his work after WWII.〔(D. McMullan, SEM 1928 - 1965 )〕 The technique was not developed further until the 1970s, when Albert Crewe at the University of Chicago developed the field emission gun and added a high quality objective lens to create a modern STEM. He demonstrated the ability to image atoms using an annular dark field detector. Crewe and coworkers at the University of Chicago developed the cold field emission electron source and built a STEM able to visualize single heavy atoms on thin carbon substrates. Aberration-corrected STEM was demonstrated with 1.9 angstrom resolution in 1997 and soon after in 2000 with roughly 1.36 angstrom resolution. Aberration-corrected STEM provided the added resolution and beam current critical to the implementation of atomic resolution chemical mapping with spectroscopic techniques. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「scanning transmission electron microscopy」の詳細全文を読む スポンサード リンク
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