Reflection high-energy electron diffraction: Difference between revisions

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A RHEED system requires an electron source (gun), photoluminescent detector screen and a sample with a clean surface, although modern RHEED systems have additional parts to optimize the technique.<ref name="ichimiya2004">{{cite book|author=Ichimiya A|author2=Cohen P I|name-list-style=amp|title=Reflection High Energy Electron Diffraction|publisher=Cambridge University Press: Cambridge, UK|date=2004|pages=1,13,16,98,130,161|url=https://books.google.com/books?id=AUVbPerNxTcC|isbn=0-521-45373-9}}</ref><ref name="horio1996">{{cite journal|author=Horio Y|author2= Hashimoto Y|author3=Ichimaya A|name-list-style=amp|title=A new type of RHEED apparatus equipped with an energy filter| journal=Appl. Surf. Sci.|volume=100|pages=292–6|date=1996|doi=10.1016/0169-4332(96)00229-2|bibcode = 1996ApSS..100..292H }}</ref> The electron gun generates a beam of electrons which strike the sample at a very small angle relative to the sample surface. Incident electrons diffract from atoms at the surface of the sample, and a small fraction of the diffracted electrons interfere constructively at specific angles and form regular patterns on the detector. The electrons interfere according to the position of atoms on the sample surface, so the diffraction pattern at the detector is a function of the sample surface. Figure 1 shows the most basic setup of a RHEED system.

[[File:RHEED.svg|thumbnail|400px|'''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.]]

==Surface diffraction==

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===Dynamic scattering analysis===

The dynamically, or inelastically, scattered electrons provide several types of information about the sample as well. The brightness or intensity at a point on the detector depends on dynamic scattering, so all analysis involving the intensity must account for dynamic scattering.<ref name="ichimiya2004"/><ref name="braun1999"/> Some inelastically scattered electrons penetrate the bulk crystal and fulfill Bragg diffraction conditions. These inelastically scattered electrons can reach the detector to yield kikuchiKikuchi diffraction patterns, which are useful for calculating diffraction conditions.<ref name="braun1999"/> Kikuchi patterns are characterized by lines connecting the intense diffraction points on a RHEED pattern. Figure 6 shows a RHEED pattern with visible [[Kikuchi line (solid state physics)|Kikuchi lines]].

[[File:TiO2 Surface with Kikuchi Lines.gif|thumbnail|400px|'''Figure 6'''. A RHEED pattern from a TiO₂ (110) surface with visible Kikuchi lines. The Kikuchi lines pass through the Laue circles and appear to radiate from the center of the pattern.]]