X-ray Standing Waves

The Bragg X-ray standing wave approach measures the modulation of X-ray fluorescence as the crystal is rotated through a substrate Bragg reflection. Due to the coherent superposition of the incident and reflected Bragg beams, an X-ray standing wave (XSW) is formed both above and below the crystal surface. The modulation of X-ray fluorescence by the XSW field is directly sensitive the location of the fluorescing atoms and provides a powerful probe of interfacial ion site distributions. With a known substrate lattice, the fluorescent yield, Y(θ), can be described by two parameters: coherent fraction, F_H, and coherent position, P_H, where H = (hkl) indicates the Bragg reflection. Because the fluorescing atom is located in the near field, the XSW measurement does not suffer from the well-known ‘phase problem’ of X-ray crystallography.

Reference: Bedzyk M. J. and Cheng L. (2002) X-ray standing wave studies of minerals and mineral surfaces: Principles and applications. Reviews in Mineralogy & Geochemistry 49, 221-266.