Imaging electric, magnetic microfields.Sprinkle iron filings Iron filings are very small pieces of iron that look like a dark powder. They are very often used in magnetism demonstrations, to show magnetic lines. Since iron is a magnetic material, it will align itself with the magnetic lines of a magnet in the same way a compass will align across a sheet of paper covering a bar magnet, and the filings align themselves to reveal the shape of the magnetic field around the magnet. But what do you do if the magnetized object itself is considerably smaller than an iron filing? Researchers have now developed a new method based on electron microscopy electron microscopy Technique that allows examination of samples too small to be seen with a light microscope. Electron beams have much smaller wavelengths than visible light and hence higher resolving power. for directly visualizing the fields surrounding tiny, electrically charged or magnetized particles. Akira Tonomura and Takayoshi Tanji of the Hitachi Advanced Research Laboratory in Saitama, Japan, and Tsukasa Hirayama of the Japan Fine Ceramics Center in Nagoya describe their novel imaging technique in the Aug. 28 Applied Physics Letters Applied Physics Letters is a weekly peer-reviewed scientific journal published by the American Institute of Physics devoted to the publication of new experimental and theoretical papers about applications of physics to science, engineering, and modern technology. . Tonomura and his coworkers rely on the fact that electrons can exhibit both particle and wave behavior. Using an electron microscope electron microscope: see microscope. , they generate three electron waves (see diagram), which combine to reinforce and cancel each other out at different places, creating a distinctive interference pattern interference pattern An overall pattern that results when two or more waves interfere with each other, generally showing regions of constructive and of destructive interference. . Placing an electrically charged or magnetized specimen in the path of the central beam distorts the pattern, revealing the field around the particle. Using this technique, the researchers have observed the electric field around a microscopic latex particle and magnetic field lines around a barium ferrite particle. |
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