Auger transitions

Fig. 15. Auger sensitivity factors relative to the Ag MNN Auger transition as a function of atomic number (19).

Once an inner shell vacancy is created in an atom the atom may then remrn toward its ground state via emission of a characteristic X ray or through a radiationless Auger transition. The probability of X-ray emission is called the fluorescence yield. 

In X-ray notation the Auger transition shown in Fig. 2.1 would therefore be labeled KL2L3. In this coupling scheme, six Auger transitions would be possible in the KLL series. Obviously, many other series are possible (e. g., KLM, LMM, MNN). These are discussed more fully in Sect. 2.2, dealing with AES. 

Considering that heavy elements have more levels than just K and L, Eq. (2.2) also indicates that the heavier the element, the more numerous are the possible Auger transitions. Fortunately, there are large differences between the probabilities of different Auger transitions, so that even for the heaviest elements, only a few intense transitions occur, and analysis is still possible. 

The nomenclature used in AES has also been mentioned in Sect. 2.1.1. The Auger transition in which initial ionization occurs in level X, followed by the filling of X by an electron from Y and ejection of an electron from Z, would therefore be labeled XYZ. In this rather restricted scheme, one would thus find in the KLL series the six possible transitions KLiLi, KL1L2, KL1L3, KL2L2, KL2L3, and KL3L3. Other combinations could be written for other series such as the LMM, MNN, etc. 

If ionization of a core level X in an atom A in a solid matrix M by a primary electron of energy Ep gives rise to the current Ij (XYZ) of electrons produced by the Auger transition XYZ, then the Auger current from A is... 

Similarly to Eq. (2.6), fCis a proportionality constant containing fixed operating conditions, for example incident electron current density, transmission of the analyzer at the kinetic energy Ea, efficiency of the detector at the kinetic energy Ea, and the probability of the Auger transition XYZ. 

Advantages of silicon x-radiation include the access of aluminum and magnesium core level (Is) lines and the corresponding (KLL) Auger transitions for chemical state identification and improved quantitation, because these lines are at least 10 times more intense than the corresponding (2p) or (2s) lines. The construction of an off-axis reactor has produced a simple, versatile and inexpensive system easily adapted to any vacuum system. The role of AES and SAM in catalyst research will also be highlighted by examples. 

Figure 4. Positions and relative intensities of XPS and Auger transitions using silicon, aluminum, and magnesium x-ray sources.

Ion neutralization (or Ion survival) can dominate this technique. A number of theories have arisen to account for this phenomenon, but all seem to Include both Auger transitions and resonance tunneling processes as the dominant means of Ion neutralization.(4,5) For very slow Ions, as In LEISS, Auger... 

Figure 7. Dependence of the kinetic energy of the Ag M4VV Auger-transition on BE of the Ag 3ds/2 core level during ion bombardment of the Ag islands. The characteristic energies of certain silver compounds and alloys are also shown for comparison. (Data compiled from Ref [163].)...

Auger atlases can be used in applied AES for rapid preliminary elemental identification, although comparison of the spectra from any two adjacent elements in such atlases reveals that the relative intensities of different Auger transitions within... 

The notation of Auger transitions uses the X-ray level nomenclature of Table 3.1. For example, KL L2 stands for a transition in which the initial core hole in the K-shell is filled from the L -shell, while the Auger electron is emitted from the L2-shell. Valence levels are indicated by V as in the carbon KVV transition. 

The energy of an Auger transition, for example KLM, is to a first approximation given by ... 

Figure 3.24 The spectrum of the carbon KVV Auger transition contains chemical information and can be used as a fingerprint of the state of the carbon.

Chemical bonding information is also obtained when the Auger transition involves valence levels, as with the KVV Auger transitions of carbon and oxygen. As Fig. 3.24 shows, the fine structure of the C KVV signal can be used as a fingerprint of the state of the carbon, but is difficult to interpret further. 

Auger electron spectroscopy (AES), 76 495 24 84-87, 94-97. See also AES instrumentation archaeological materials, 5 744 quantitative, 24 98 Auger sensitivity factors, 24 96 Auger spectra, 24 95-97, 98 Auger transitions, 24 95 Augite, in coal, 6 718 Au(III) halides, 72 706. See also Gold(III) entries... 

Fig.2 Adsorption of Ni on W(110) plotted as the ratio Ni(84S) W(179) Auger transitions versus Ni desorbed in TPD. Ni deposition was carried out at 100 K. From Rtf. 188.)...

Fig.l. Schematic illustration of electron transfer via (a) resonant, (b) quasi-resonant, (c) Auger transition. 

Auger transitions are due to the transfer of a solid electron to the ion, coupled with the excitation of a second electron into an Auger state of energy in the solid. Thus, the TDAN Hamiltonian is augmented by the terms ... 

In Auger transitions, incident electrons interact with the inner shell electrons E of the sample. The vacancy created by an ejected inner shell electron is filled by an outer shell electron (Ei), and a second outer shell electron ( 2) is ejected leaving the atom in a doubly ionized state. The electrons ejected from the outer shells are called Auger electrons, named after the Frenchman Pierre Auger, who discovered the effect. Thus, AES measures the energies of the Auger electrons ( a) emitted from the first 10 A of a sample surface. The energy equation is expressed as... 

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