Electron Effective-Attenuation-Length

Fig. 12. Schematic representation of electron effective attenuation length as a function of electron energy.

C.J. PoweU and A. Jablonski, Electron Effective Attenuation Length Database, Version 1.0 (SRD 82), US Department of Commerce, National Institute of Standards and Technology, Gaithersburg, 2000. 

DDFs can be calculated from Eq. (3.2.3.2) by specifying the experimental configuration (the angle a and the angle P between the direction of the X-rays and the direction of the analyzer) and parameters for particular photoelectrons from a given solid (/3, Xin, and Xtr). Since the formalism is rather complex, DDFs can be obtained more conveniently from the NIST Electron Effective-Attenuation-Length Database (SRD 82) [41]. 

A. (2011) NIST Electron Effective-Attenuation-Length Database,... 

The effective attenuation length is a function of electron kinetic energy and of the medium density. However, when we represent A. in number of monolayers, an approximately universal curve is obtained [32] as displayed in Figure 12. 

Table 19-1. Attenuation length and effective cross section for strand breaks (SB) in SAM of oligonu-cleotides chemisorbed on gold as a function of electron energy...

Incident electron energy (eV) Attenuation length (nm) Effective cross section for SB (x 10 17 cm2)1 ... 

It seems to be possible to explain the polarization enhancement of secondary electrons by the spin dependence of the IMFP. This means, the different attenuation lengths act as a spin filter, majority electrons preferentially allowing to be transmitted. The spin asymmetry of the IMFP, given by A = (2+ — 2 )/(2+ + 2 ), amounts to about 20% for both systems and is confirmed by an investigation of Fe/Cu(100) [8] leading to the same value of A. A very effective spin filter can be realized by a graphene layer which was theoretically predicted [11] and experimentally verified for graphene on Ni(lll) [12]. 

As with any other analytical data, electron spectra are subject to statistical noise. In general, it is likely that for any particular spectrum the errors in quantification are dominated by systematic effects such as the uncertainty in the rclative sensitivity factor or in the attenuation length. However, if comparisons are to be made within. series of similar spectra, the random errors arising from the statistical noise in the data become important. Similarly, if a particular element is present in the specimen at a very low level it becomes necessary to consider the statistical nature of the detection limit of the technique. 

The linear attenuation coefficient is the sum of the probabilities of interaction per unit path length by each of the three scattering and absorption processes photoelectric effect, Compton effect, and electron-positron pair production. The reciprocal of p is defined as the mean-free path, which is the average distance the photon travels in an absorber before an interaction takes place. 

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