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RheedRHEED stands for Reflection High Energy Electron diffraction. RHEED is quite similar to LEED. RHEED uses an electron gun and a fluorescent screen for creating pictures showing the structure and/or morphology of a crystal surface. RHEED uses much higher electron energy (5-100keV) and lower impact angles (<5) than LEED. The higher energy sharpens the picture, while the lower angle makes the electrons just pass a few atomic layers into the crystal. This makes Rheed pictures represent the structure of the surface, not the whole crystal. In RHEED, the reciprocal lattice is 2-dimensional if the crystal is single crystalline and the surface is flat in nanometer scale. This characteristic makes the reciprocal lattice appear as lines instead of dots in 3-dimensional case. This way the reciprocal lattice lines touch the Ewald-sphere more often than normal and the Laue diffraction condition is fulfilled quite often in the forward direction of the electron beam, where the fluorescent screen is mounted. The diffraction image changes in other cases, depending on the crystallinity and the morphology of the crystal. Pros of RHEED: Real-Time Analysis: RHEED is often used for monitoring crystal growth, as it doesn't block the direction vertical to the surface of the crystal, which is observed. Especially for the crystals that can be easily damaged, MCP-RHEED is used.
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