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单词 Reflection high energy electron diffraction
释义

Reflection high energy electron diffraction

英语百科

Reflection high-energy electron diffraction

Figure 1. Systematic setup of the electron gun, sample and detector /CCD components of a RHEED system. Electrons follow the path indicated by the arrow and approach the sample at angle θ. The sample surface diffracts electrons, and some of these diffracted electrons reach the detector and form the RHEED pattern. The reflected (specular) beam follows the path from the sample to the detector.
Figure 2. A RHEED pattern obtained from electron diffraction from a clean TiO2 (110) surface. The bright spots indicate where many electrons reach the detector.
Figure 3. The RHEED construction of the Ewald's Sphere at the sample surface. The radius of the Ewald's sphere is equal to the magnitude of the k0 vector, which is the reciprocal of the wavelength of the incident electrons. The k vector, corresponds to an allowed diffraction condition, and the G vector is the difference between the k and k0 vectors. In this figure, the k vector is the specular beam.
Figure 4. Diffraction from a row of atoms a Laue circle on the surface of the Ewald's sphere. The reciprocal lattice rods are so closely space, that they comprise the plane cutting the sphere. Diffraction conditions are fulfilled on the perimeter of the Laue circle. The vectors are all equal to the reciprocal of the incident vector, k.

Reflection high-energy electron diffraction (RHEED) is a technique used to characterize the surface of crystalline materials. RHEED systems gather information only from the surface layer of the sample, which distinguishes RHEED from other materials characterization methods that also rely on diffraction of high-energy electrons. Transmission electron microscopy, another common electron diffraction method samples the bulk of the sample due to the geometry of the system. Low-energy electron diffraction (LEED) is also surface sensitive, but LEED achieves surface sensitivity through the use of low energy electrons.

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