Reflection high-energy electron diffraction: Difference between revisions

Revision as of 18:08, 6 May 2019

Revision as of 13:34, 11 July 2019

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[[File:TiO2 Terraced and Streaked RHEED Pattern.gif|thumbnail|400px|'''Figure 7'''. Streaked RHEED pattern from the TiO₂ (110) surface. The sample had a terraced surface, which caused noticeable streaking compared to the RHEED pattern from the flat TiO₂ (110) surface shown above.]]

Surface features and polycrystalline surfaces add complexity or change RHEED patterns from those from perfectly flat surfaces. Growing films, nucleating particles, crystal twinning, grains of varying size and adsorbed species add complicated diffraction conditions to those of a perfect surface.<ref name="bozovic2001">{{cite book|author=Bozovic I|author2=Eckstein J N|author3=Bozovic N|last-author-amp=yes|title=In Situ Real-Time Characterization of Thin Films|publisher=John Wiley and Sons: New York|date=2001|pages=29–56|editor=Auceillo O|editor2=Krauss A R|url=https://books.google.com/books?id=kmyVA1OYB_UC&pg=PA29|isbn=0-471-24141-5}}</ref><ref name="brewer2001">{{cite journal|author=Brewer R T|author2=Hartman J W|author3=Groves J R|author4=Arendt P N|author5=Yashar P C|author6=Atwater H A|last-author-amp=yes|title=Rheed in-plane rocking curve analysis of biaxially-textured polycrystalline MgO films on amorphous substrates grown by ion beam-assisted deposition|journal=Appl. Surf. Sci.|volume=175|issue=1–2|pages=691691–696|date=2001|doi=10.1016/S0169-4332(01)00106-4|bibcode = 2001ApSS..175..691B }}</ref> Superimposed patterns of the substrate and heterogeneous materials, complex interference patterns and degradation of the resolution are characteristic of complex surfaces or those partially covered with heterogeneous materials.

==Specialized RHEED techniques==

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===RHEED-TRAXS===

Reflection high energy electron diffraction - total reflection angle X-ray spectroscopy is a technique for monitoring the chemical composition of crystals.<ref>{{cite journal|last1=Hasegawa|first1=Shuji|last2=Ino|first2=Shozo|last3=Yamamoto|first3=Youiti|last4=Daimon|first4=Hiroshi|title=Chemical Analysis of Surfaces by Total-Reflection-Angle X-Ray Spectroscopy in RHEED Experiments (RHEED-TRAXS)|journal=Japanese Journal of Applied Physics|volume=24|issue=6|pages=L387L387–L390|date=1985|doi=10.1143/JJAP.24.L387|bibcode = 1985JaJAP..24L.387H }}</ref> RHEED-TRAXS analyzes X-ray spectral lines emitted from a crystal as a result of electrons from a RHEED gun colliding with the surface.

RHEED-TRAXS is preferential to X-ray microanalysis (XMA)(such as [[Energy-dispersive X-ray spectroscopy|EDS]] and [[Wavelength dispersive X-ray spectroscopy|WDS]]) because the incidence angle of the electrons on the surface is very small, typically less than 5°. As a result, the electrons do not penetrate deeply into the crystal, meaning the X-ray emission is restricted to the top of the crystal, allowing for real-time, in-situ monitoring of surface stoichiometry.