Auger electron and X-ray fluorescence spectroscopy

Although it is conceptually useful to think of two successive processes following the initial ionization to A, the electron transfer and the generation of the Auger electron occur simultaneously. 

There is an important difference between the two techniques in that photons, produced by XRF, can pass through a relatively large thickness of a solid sample, typically 4000 nm, whereas electrons can penetrate only about 2 nm. This means that AES is more useful in the study of solid surfaces, whereas XRF gives information referring more to the bulk of a solid or liquid. 

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Various interactions occur when X-rays are irradiated to the samples. Figure 1 illustrates various interactions between X-rays and the samples. One part of incident X-rays is scattered and/or diffracted, and another part is absorbed to generate fluorescent X-rays and/or electrons (photoelectrons or Auger electrons), and the rest is transmitted. In this section, operating principles and characteristics of X-ray fluorescence analysis (XRF), X-ray diffraction analysis (XRD), and X-ray photoelectron spectroscopy (XPS), which are often used for the analyses of corrosion and surface finishing, are described. 

Acronyms abound in phofoelecfron and relafed specfroscopies buf we shall use only XPS, UPS and, in Sections 8.2 and 8.3, AES (Auger elecfron specfroscopy), XRF (X-ray fluorescence) and EXAFS (exfended X-ray absorption fine sfmcfure). In addition, ESCA is worth mentioning, briefly. If sfands for elecfron specfroscopy for chemical analysis in which elecfron specfroscopy refers fo fhe various branches of specfroscopy which involve fhe ejection of an elecfron from an atom or molecule. Flowever, because ESCA was an acronym infroduced by workers in fhe field of XPS if is mosf often used to refer to XPS rather than to electron spectroscopy in general. 

Accompanying the photoemission process, electron reorganisation can result in the ejection of a photon (X-ray fluorescence) or internal electronic reorganisation leading to the ejection of a second electron. The latter is referred to as the Auger process and is the basis of Auger electron spectroscopy (AES). It was Harris at General Electric s laboratories at Schenectady, USA, who first realised that a conventional LEED experiment could be modified easily to... 

The interaction of an electron with an atom gives rise to two types of X-rays characteristic emission lines and bremsstrahlung. The atom emits element-characteristic X-rays when the incident electron ejects a bound electron from an atomic orbital. The core-ionized atom is highly unstable and has two possibilities for decay X-ray fluorescence and Auger decay. The first is the basis for electron microprobe analysis, and the second is the basis of Auger electron spectroscopy, discussed in Chapter 3. 

All analytical methods that use some part of the electromagnetic spectrum have evolved into many highly specialized ways of extracting information. The interaction of X-rays with matter represents an excellent example of this diversity. In addition to straightforward X-ray absorption, diffraction, and fluorescence, there is a whole host of other techniques that are either directly X-ray-related or come about as a secondary result of X-ray interaction with matter, such as X-ray photoemission spectroscopy (XPS), surface-extended X-ray absorption fine structure (SEXAFS) spectroscopy, Auger electron spectroscopy (AES), and time-resolved X-ray diffraction techniques, to name only a few [1,2]. 

GD-OES (glow discharge optical emission spectrometry) are applied. AES (auger electron spectroscopy), AFM (atomic force microscopy) and TRXF (transmission reflection X-ray fluorescence analysis) have been successfully used, especially in the semiconductor industry and in materials research. 

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