Low-energy cut off

Figure 4.19 The LEIS spectrum of a Cu/Al203 catalyst illustrates that ions lose more energy in collisions with light elements than with heavy elements. Note the step in the background at the low kinetic energy side of the peaks. The high peak at low energy is due to sputtered ions. The low energy cut-off of about 40 eV is indicative of a positively charged sample (courtesy of J.P. Jacobs and H.H. Bron-gersma, Eindhoven).

In acetonitrile at the concentrations of ArH and XPyNOT indicated. Ionization potential from Hanna and Lippert (1973). Low-energy cut-off ... 

Fig. 9.9. High harmonics in the spectrum of He. Note the high energy cut-off, which is real (the low energy cut-off is due to the optical arrangement), and how the harmonic spectrum remains essentially flat in intensity up to very high orders, which is a nonperturbative effect (data averaged over 18 shots) (after J.-P. Connerade et al. [482]).

An alternative wide bandpass system is to replace the soap film with an attenuator such as aluminium foil which gives a low energy cut-off and is sometimes used in Laue protein crystallography (chapter 7). 

Effective potentials also depend on the type of basis set used, hi atomic orbital calculations, they are sometimes referred to as frozen-core potentials. In most cases, only the highest-energy s, p and d electrons are included in the calculation. In plane-wave calculations, effective potentials are known as pseudopotentials They come in different varieties soft or ultrasoft pseudopotentials need only a relatively low energy cut-off as they involve a larger atomic core. ... 

Additionally, from Fig. 4.5, it can be seen that for both sizes the shift towards the low energy cut off is proportional to the amount of cluster coverage. The total shift of 0.9-1 eV is far above the resolution limit, and may allow for quantification with respect to coverage. 

Two words of caution are in order here. First, a high secondary peak at threshold is at best an indicator of a low and possibly negative EA. Whether x < 0 can be judged only from a quantitative analysis of the spectra. With reference to Figure 10.21b, it is apparent that NEA requires that hv—W = Eg, where W is the width of the spectrum taken from the high-energy threshold that must correspond to emission from the VBM E, to the low energy cut-off. Contrary to what has been claimed in some publications, hv—W cannot be smaller than Eg, and hence it is not possible... 

B) dehydrogenated and (C) plasma oxidized. Notice the different scaling of the spectra and the difference in energy and intensity of the low energy cut-off. Spectrum (A) is that of an NEA surface, whereas (B) and (C) correspond to surfaces with PEA [62]. (b) Schematic explanation for (a). On the left, the photoexcitation process leads to the emission of primary electrons that yield a replica of the occupied density of valence states in the kinetic energy distribution of... 

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