X-ray standing waves

Cowan P L, Golovchenko J L and Robbins M F 1980 X-ray standing waves at crystal surfaces Rhys. Rev.L44 1680-3... 

Woodruff D P, Cowie B C C and Ettem a A R H F 1994 Surface structure determination using x-ray standing waves a simple view J. Rhys.. Condens. 6 10 633—45... 

In this chapter, I will try to present an introduction to these various techniques with emphasis on EXAFS and X-ray standing waves and their application to the study of electrochemical interfaces. Each technique will be treated from theoretical and experimental points of view, and selected examples from the literature will be employed to illustrate their application to the study of electrochemical interfaces. 

Figure 31. Depiction of the X-ray standing wave field formed by the interference between incident and Bragg reflected beams.

Figure 33. Experimental setup for X-ray standing wave measurements on an LSM.

Figure 35. Electrochemical cell for in situ X-ray standing wave measurements. (From Ref. 120, with permission.)...

Figure 38. Experimental setup for back-reflection X-ray standing wave...

In addition to surface EXAFS and X-ray standing waves, X-ray diffraction can be employed in the study of electrochemical interfaces. Although an extensive treatment of X-ray diffraction techniques is beyond the scope of this chapter, some brief statements are appropriate. 

Kijute 2.71 IIImttalion erf the X-ray standing wave held formed by the interference between the incident and reflected plane waves above a mirror surface t ee teat for detail ) After Bedivk ei cl (1990) Copyright 1990 by the AAAS... 

The X-ray standing wave intensity at an angle of incidence 0 and distance r above the mirror surface is ... 

Mineral-liquid or mineral-gas interfaces under reactive conditions cannot be studied easily using standard UHV surface science methods. To overcome the pressure gap between ex situ UHV measurements and the in situ reactivity of surfaces under atmospheric pressure or in contact with a liquid, new approaches are required, some of which have only been introduced in the last 20 years, including scanning tunneling microscopy [28,29], atomic force microscopy [30,31], non-linear optical methods [32,33], synchrotron-based surface scattering [34—38], synchrotron-based X-ray absorption fine structure spectroscopy [39,40], X-ray standing wave... 

Macroscopic experiments allow determination of the capacitances, potentials, and binding constants by fitting titration data to a particular model of the surface complexation reaction [105,106,110-121] however, this approach does not allow direct microscopic determination of the inter-layer spacing or the dielectric constant in the inter-layer region. While discrimination between inner-sphere and outer-sphere sorption complexes may be presumed from macroscopic experiments [122,123], direct determination of the structure and nature of surface complexes and the structure of the diffuse layer is not possible by these methods alone [40,124]. Nor is it clear that ideas from the chemistry of isolated species in solution (e.g., outer-vs. inner-sphere complexes) are directly transferable to the surface layer or if additional short- to mid-range structural ordering is important. Instead, in situ (in the presence of bulk water) molecular-scale probes such as X-ray absorption fine structure spectroscopy (XAFS) and X-ray standing wave (XSW) methods are needed to provide this information (see Section 3.4). To date, however, there have been very few molecular-scale experimental studies of the EDL at the metal oxide-aqueous solution interface (see, e.g., [125,126]). 

X-ray standing wave studies of the electrical double layer at solid-aqueous solution interfaces and in situ measurements of surface reactivity... 

Effect of organic coatings and microbial biofilms on metal oxide surface reactivity - X-ray standing wave studies of metal ion partitioning between coating and surface... 

---