Modified Auger parameter

Rather than the afore defined a parameter, of more convenient use is the so called modified Auger parameter a, defined as the sum of a plus the photon energy. In the following, we shall use this modified Auger parameter. 

At this point of the discussion, we would like just to mention the different behaviour of the modified Auger parameter between the two growth modes the evaporated films exhibit a singularity for both Al and Si KLL transitions around Al thicknesses 10-20 A while the sputtered films show this singularity only for a j with a monotonous increase of the a., parameter. We have no present explanation for these observations, But we want to present them as an experimental evidence for differences in long range electronic properties of these interfaces. 

One feature of these plots is of additional interest. The diagonal grid represents the sum of the Auger kinetic energy and the photoelectron binding energy, which we call the modified Auger Parameter (1 ), ... 

The chemical state of aluminum on the surface has a multitude of possible configuration designations. The state in the hydroxylated outer layer corresponds to various mineral phases such as AIO(OH) (boehmite), Al(OH)3, having a modified Auger parameter of 1460.6 on the acetone-cleaned surface and 1461.4 on both the (Aik) and (Dox) surfaces. When capped with a plasma polymer, depth profiles show that the state of the aluminum is seen to be consistent with the many oxides, as well as mixed states with plasma film components. 

Fig. 2. Comparison of modified Auger parameters for MgPc on Au foil and on Au(100). We distinguish between interface and bulk signal, the average difference Aa for the two components (1.8 eV) is similar in both cases.

In many cases, the Auger peaks present in the XPS spectrum also provide chemical-state information and can supplement energy shifts from the photoelectron peaks. The modified Auger parameter, a, defined as(70)... 

Defining a modified Auger parameter, a, as the sum of the kinetic energy of the Auger peak and the binding energy of the photoelcctron peak allows the change in a to be written as... 

A specific example of the use of the modified Auger parameter, a, in XPS is that of the study of silicate structures produced in thin oxide layers in metal surfaces arising from low-temperature plasma reactions [86.114]. Oxide layers of predetermined thickness can be produced with an HiO vapor plasma followed by reaction with silane H20 plasma products. Mass spectra [114] of the plasma have demonstrated the presence of reactive SiO entities that produce a... 

Figure 22. Modified Auger parameter plot for a number of silicates (from Ref. 137) and plasma-reacted (HnO silane) nickel surfaces % values show the atomic concentrations of Si measured by XPS. Note the transition from py-rosilicate to bulk silica species as the reaction progresses [1141.

Sample BE Cr 2/73/2 (eV) Cr 2/7 doublet spin-orbit split (eV) Satellite to main peak distance (eV) Satellite to main peak intensity ratio Modified Auger parameter a (eV)... 

Auger Kinetic Energies and Modified Auger Parameters for Some Chemical Elements in Various Compounds (all data are in electron-volts) ... 

FIGURE11 Wagner chemical state plot for arsenic. The modified Auger parameter is evaluated on the diagonal grid. [From Wagner, C. D., etal. (1979). Handbook of XPS, Perkin Elmer Corp, Eden Prairie. MN.]... 

FIGURE 10 Modified Auger parameter piot. [Reprinted with permission from C. D. Wagner and A. Joshi, Journal of Electron Spectroscopy and Related Phenomena, Vol. 47, p. 301, 1988 Copyright 1988, Elsevier Science.]... 

---