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THE FRESNEL DIFFRACTION : A STORY OF LIGHT AND DARKNESS
THE FRESNEL DIFFRACTION : A STORY OF LIGHT AND DARKNESS

... circular screen should give rise in the center of its shadow of a bright spot of the same intensity as if the screen does not exist. The experiment was soon realized by Arago, another jury’s member, who indeed brilliantly confirmed Fresnel’s theory. This bright spot is now called after Poisson, Arag ...
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Low-energy electron diffraction



Low-energy electron diffraction (LEED) is a technique for the determination of the surface structure of single-crystalline materials by bombardment with a collimated beam of low energy electrons (20–200 eV) and observation of diffracted electrons as spots on a fluorescent screen.LEED may be used in one of two ways: Qualitatively, where the diffraction pattern is recorded and analysis of the spot positions gives information on the symmetry of the surface structure. In the presence of an adsorbate the qualitative analysis may reveal information about the size and rotational alignment of the adsorbate unit cell with respect to the substrate unit cell. Quantitatively, where the intensities of diffracted beams are recorded as a function of incident electron beam energy to generate the so-called I-V curves. By comparison with theoretical curves, these may provide accurate information on atomic positions on the surface at hand.↑
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