Electron attenuation

Fig. 8. A universal curve (or band) of electron attenuation length vs. electron kinetic energy, as resulting from an inspection of many experimental results on heavy metals. The energy of different laboratory sources, representing the maximal kinetic energy of the electron, is drawn for comparison in the figure (from Ref. 5)...

Splitting the flow serves as a means of diluting the adsorption and desorption concentration peaks in order to continuously adjust the signal height using needle valve N 3. The electronic attenuator shown in Fig. 15.8 adjusts the signal by factors of two for each step. 

Mean free path values are often approximated by a calculating them from a general formula [24], but data which take material properties into account are available also [25]. That this is important is illustrated by the mean free path of Si 2p photoelectrons in SiC>2 (3.7 nm) and in pure silicon (3.2 nm, valid when using A1 Ka radiation) the 2-values differ considerably, although the kinetic energies of the electrons are the same. In a recent review, Jablonski and Powell discussed developments in the understanding of electron attenuation lengths [26]. 

In this formula A and Aj are the spin-dependent hot electron attenuation lengths, which have been measured by various experimental techniques for different ferromagnetic materials [135-145]. The SVT and MTT have also successfully been used to measure Af and for 3d transition metal alloys [146-148], In these experiments the collector current is measured as a function of the ferromagnetic base layer thickness. 

Quantification is simple if the atoms are homogeneously distributed with depth since the intensity of each XPS peak is then directly related to the abundance of that particular element at the specimen surface. The peak intensity will usually be reported as a peak area and this will be normalized using atomic sensitivity factors (the intensity of the photoelectron transition of interest, I, is related to the concentration of that element within the XPS analysis volume, and the sensitivity factor, S, in the following way F= concentrationxS). Such atomic sensitivity factors are a function of the basic physical parameters, such as the relative photoelectron cross-sections of the different elements, electron attenuation lengths, and instrumental parameters, such as analyzer transmission functions, of the XPS experiment. The ratio of normalized peak area to the sum of normalized peak areas for the major peaks of all elements detected in the spectrum provides an analysis as an atomic fraction (or when multiplied by 100, atomic %). 

Electronic absorption consumes both the recoiled 1 — fs) and the recoilless fraction (fs) of photons. Their attenuation is described by the coefficients ps and for the source and the absorber, respectively. The electronic attenuation coefficients can be considered constant over the whole Doppler-velocity range. 

This means that the faster electrons contribute to the amplification of the incident laser wave, whereas the slower electrons attenuate it. This stimulated emission of the faster electrons and the absorption of photons by the slower electrons leads to a velocity bunching of the electrons toward the critical velocity Vc and enhances the coherent superposition of their contributions to the radiation field. The energy pumped by the electrons into the radiation field comes from their kinetic energy and has to be replaced by acceleration in RE cavities, if the same electrons in storage rings are to be used for multiple traversions through the wiggler. 

Table 3. Photoelectron Ionization Cross Sections a and Electron Attenuation Length X of Self-Assembled ODP Monolayer on Ta205, from Data Given in Refs 15 and 16...

The electron attenuation length (mean free path length X) in the various layers was calculated using the general expressions given by Seah ... 

Applications of WRs include automatic gain control (AGC) circuits, electronic attenuators, electronically variable filters, and oscillator ampHtude control circuits. 

FIGURE 3. Electron attenuation length as a function of kinetic energy. (Adapted from Reference 25.)... 

Another useful quantity for the description of the purity of a liquid is the electron attenuation leng, atf If No electrons start at x = 0 their number is reduced to Ng/e after traversing the distance att. This quantity is equivalent to the schubweg in solid-state physics. 

This means that the faster electrons contribute to the amplification of the incident laser wave, whereas the slower electrons attenuate it. This stimulated emission of the faster electrons and the absorption of photons by the slower... 

Figure 21. Electron attenuation lengths (AL) and electron e.scape depths (D, takeoff angle = 20°) of the XPS transitions and XAES transitions recorded from silica. The asterisk marks the AL for Si 2p electrons emitted in SRPS experiments. (Reproduced from Ref. 83 by permission of the American Institute of Physics.)...

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