X-ray crystal truncation rod

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

Theory

The Bragg equation predicts the existence of so-called Bragg peak for certain scattering angle in the X-ray diffraction. Mathematically, such a delta -like distribution of the leakage signal by summing over an infinite grid in three dimensions is calculated, i.e. it is assumed that the crystal is extended infinitely in all directions in space.

However, a real crystal is finite. As a result, the infinite sum in the direction to the surface needs to be converted into a semi- infinite sum vertically. This leads to a broadening of the Bragg peak along the reciprocal direction perpendicular to the surface. So you can measure a leakage signal between these Bragg peaks.

The now interconnected Bragg peaks are called Crystal Truncation Rods ( eng. for crystal - termination rod ). Since these CTRs, namely the existence of a surface have their origin in the demolition of the grid, 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 peak, this kind of measurements are performed at synchrotron.

Benefits of SXRD

In contrast to many spectroscopic methods, such as scanning tunneling microscopy and Auger electron spectroscopy, is not limited to SXRD conductive materials. Therefore SXRD is in materials science often one of the few ways for the determination of surface structures.