Surface sensitive X-ray diffraction

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The surface-sensitive X-ray diffraction (English: Surface X-ray Diffraction, short SXRD) is a tool of surface physics to determine structures of surfaces with atomic resolution.

theory

The Bragg equation predicts the existence of so-called Bragg peaks for certain scattering angles in X-ray diffraction . Such a delta-like distribution of the scatter signal is mathematically calculated by summation over a grid that is infinite in three dimensions, i.e. H. it is assumed that the crystal is infinitely extended in all spatial directions.

However, a real crystal is finite. The consequence of this is that the infinite sum in the direction perpendicular to the surface must be converted into a semi-infinite sum. This leads to a broadening of the Bragg peaks along the reciprocal direction perpendicular to the surface. A scatter signal can therefore be measured between these Bragg peaks.

The now interconnected Bragg peaks are called Crystal Truncation Rods (for crystal truncation rods ). Since these CTRs originate in the abortion of the trellis, i. H. in the existence of a surface, its measurement is a very powerful tool to determine the atomic arrangement of ordered surfaces.

Because of the weak intensity of the CTRs between the Bragg peaks, these types of measurements are performed on synchrotrons .

Advantages of SXRD

In contrast to many spectroscopic methods, such as scanning tunneling microscopy or Auger electron spectroscopy , SXRD is not limited to conductive materials. In materials science, SXRD is therefore often one of the few options for determining surface structures.

literature

  • H. Dosch, Critical phenomena at surfaces and interfaces, Springer 1992
  • R. Feidenhans'l, Surface structure determination by X-ray diffraction, Surface Science Reports 10, 105-188 (1989)
  • IK Robinson, Physical Review B 33, 2830-3836 (1986)