Angular Distribution Auger

ADAM Angular-distribution Auger microscopy [85] Surface atoms silhouetted by Auger electrons from atoms in bulk Surface structure... 

Auger Electron Diffraction, AED, is an exact analogy to XPD, providing basically the same information. Instead of measuring the angular distribution of the ejected photoelectrons one uses the Auger electrons (Chapter 5). 

Auger electrons can also have anisotropic angular distributions (see [Meh68a, CMe74, FMS72]). These can be parametrized by the same expression as given for the photoelectrons except for some formal replacements necessary for the characterization of the Auger transition (see Section 3.5). 

From the expressions for Mj and M2 one can see immediately that the Auger electrons of this transition do not possess an anisotropic angular distribution, because T00(k) is a constant. (The same result follows for the other K-LL transitions it is a consequence of the vanishing alignment of the initial state for the Auger decay, see below equ. (3.30c).) The total transition rate P then follows from... 

Auger electrons can also possess an angular distribution (see the discussion in connection with equ. (1.30)). For Auger transitions induced by arbitrary polarized light this angular distribution is parametrized by an expression similar to equ. (1.53) for photoelectrons ... 

As a consequence of the two-step model for photoionization and subsequent Auger decay, there is a factorization of all observables. For the intensity, the product between the photoionization cross section Auger yield oja has already been discussed in connection with equ. (3.22), and for the angular distribution parameter fiA one has [BKa77]... 

The dynamics are contained in the photoionization cross section <7ph(2p3/2), in the Auger yield oja(L3-M1M1) and in the angular distribution parameters j ph(2p3/2) and j9A(L3-M1M1) of the non-coincident photo- and Auger electrons (see Section 5.2). For convenience, a ratio r is used in equ. (4.86b) which, however, is not a new parameter since in the present case it depends on j9A(L3-M1M1) (see equ. (8.133g)) ... 

Figure 4.45 Illustration of the content of equ. (4.90) which describes the angular distribution of Auger electrons (eb) in coincidence with the preceding photoelectron (ea). The data refer to 2p3/2 ionization of magnesium by linearly polarized photons of 80 eV and subsequent L3-M1M1 Auger decay, with emission of both electrons in a plane perpendicular to the photon beam direction. The alignment tensor a,

Note a2 = — 1 and the sign compensation in s/2-i( a) with 2-i(A>)-) The resulting angular distribution of coincident Auger electrons is then determined, according to the square bracket in equ. (4.90), by the properly weighted contribu-... 

Hence, the emission of Lj-MjMj Auger electrons is isotropic, while that of Auger electrons has an angular distribution coefficient proportional to the alignment parameter. Therefore, a measurement of (Lj-N Mj) is equivalent to a determination of the alignment of the photoionized state, and this quantity can be included in the list of observables in 2p photoionization of magnesium. 

Angular distribution of non-coincident L3-M1M1 Auger electrons (linearly... 

Angular distribution and alignment of L3-M,M, Auger electrons in magnesium... 

In the case of a non-coincident angular distribution of Auger electrons it is the angular distribution parameter / A, introduced in equ. (3.29) as... 

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