Electrochemical systems EXAFS studies

In order to simplify the discussion, the EXAFS studies on electrochemical systems reported to date will be divided into the categories listed below ... 

A number of cell designs have been employed in EXAFS studies of electrochemical systems. Of these, two general types can be identified depending on whether a transmission or a fluorescence mode of detection is employed. In a transmission mode, cells should be designed so as to minimize absorption losses due to the window material, elecrolyte, and the electrode itself. As a result, the windows are typically made of thin films (25/an) of low absorbing materials such as polyethylene and polyimide (Kapton). The electrolyte layer thickness is typically small, and electrodes are generally metal films evaporated on a thin polymer film or small particles dispersed in a low Z matrix. Carbon can be employed in a variety of forms and shapes because of its low absorption. 

The discussion of EXAFS studies of electrochemical systems will be divided into ... 

While X-ray diffraction is well suited to the study of the structure of crystalline samples, it is less well suited to amorphous or disordered ones. In this area, the availability of synchrotron radiation has again led to the development of new techniques, in particular, extended X-ray absorption fine structure (EXAFS). In EXAFS, structural information is derived from an analysis of the oscillations that appear above an X-ray absorption edge, and this technique is now widely applied. The conventional EXAFS experiment is not surface sensitive but some variants are. Under HV conditions, the electron yield is a measure of the absorption, and since these electrons can only escape from a thin layer at the surface, this detection method is surface sensitive. This is the basis of SEXAFS. " Clearly, this cannot be used for in situ studies, but in these cases the fluorescent X-ray yield (which is also a measure of the absorption) can be measured and, particularly when this is coupled with a glancing incidence geometry, reasonable surface sensitivity is achieved. Some initial studies of this type on electrochemical systems have now been made, and these will be described in greater detail later. 

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