Synchrotron radiation properties intensity

Work on EXAFS then progressed very little until the advent of the synchrotron radiation source (storage ring), described in Section 8.1.1.1. This type of source produces X-ray radiation of the order of 10 to 10 times as intense as that of a conventional source and is continuously tunable. These properties led to the establishment of EXAFS as an important structural tool for solid materials. 

The availability of high-intensity, tunable X-rays produced by synchrotron radiation has resulted in the development of new techniques to study both bulk and surface materials properties. XAS methods have been applied both in situ and ex situ to determine electronic and structural characteristics of electrodes and electrode materials [58, 59], XAS combined with electron-yield techniques can be used to distinguish between surface and bulk properties, In the latter procedure X-rays are used to produce high energy Auger electrons [60] which, because of their limited escape depth ( 150-200 A), can provide information regarding near surface composition. 

The properties which we require from an ideal source in UPS is good monochromaticity, defined by a line width better than 100 meV, high intensity and continuous wavelength selectivity. Unfortunately only synchrotron radiation together with a suitable monochromator offers us all these features. The rare gas discharge lamps or, alternatively, monochromators with continuum or many-line sources have generally been used hitherto, but have certain disadvantages. 

A more recent addition to the diverse array of x-ray based methods is x-ray absorption spectroscopy. In contrast to x-ray diffraction methods which derive their utility from the properties of well defined crystallites, x-ray absorption methods are atomic probes, capable of obtaining both electronic and structural information about a specific type of atom. The growing use of x-ray absorption methods is a result of the greater availability of synchrotron radiation sources which provide the intense broad band x-radiation required. In some instances laboratory based spectrometers utilizing either sealed tubes or rotating anode x-ray generators can also be used. 

Another very important property of synchrotron radiation is its very high degree of polarization. The radiation is predominantly polarized with the electric field vector parallel to the acceleration vector. Thus, in the plane of the orbit, the radiation is 100% plane-polarized. Elliptical polarization can be obtained by going away from the plane however, intensities also decrease significantly. 

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