Core-hole formation

After core hole formation, relaxation in the valence orbitals can give rise to promotion of valence electrons into unoccupied levels. If this reorganization is fast, and the energy required for this transition is not available to the primary photoelectron, shake-up satellites can show up on the low kinetic energy (high p) side of the main peak. Further loss lines can be created if the photoelectron passing the solid excites group oscillation of the conduction electrons (plasmon loss). 

A more complex example lies in the charge transfer that occms on 2p core hole formation in the Cu ion when bound within CuO. This process takes the form of electron transfer from the 2p level of an attached ion to the Cu-3d level (Note Such configurations are only noted during core hole formation). In full spectroscopic notation, this would be represented as ... 

Auger emission is preferred in the lower Z elements, whereas fluorescence is preferred in higher Z elements. This is illustrated in Figure 2.7 for Is (K level) core hole formation. The same general trend is noted for core holes formed in other... 

Figure 2.7 S chematic example of core hole relaxation via aKI L Auger process (top left) and TTttj X-ray fluorescence (top right), which can occur following Is core hole formation. Note XLjLj, and XL3L3 transitions can also occur. The probability (percentage yield) for Auger versus fluorescence as a function of Z is shown in the accompanying plot.

The incoming ion threshold energy required to induce core hole formation ( 900 eV for Ar impact on Aluminum (Valerie 1993)). Note This is ion and substrate specific... 

Stimulated desorption, whether photon, electron, or ion induced, is an inelastic sputtering process as it is the energy associated with the formation of a core hole that results in the emission of the element in question. Indeed, the formation of F " and Cl ions on electron irradiation of Aluminum and Silicon surfaces is accepted to arise through core hole formation followed by ejection through the Coulom-bic repulsion induced. In the case of ion-irradiated surfaces, it has been suggested that stimulated emission arises from Auger electrons formed in relatively distant neighbors (Williams 1981). 

Using the coaxial configuration, for a given stretch rate and equivalence ratio in the outer tube, the critical lean and rich limits of the inner-core mixture leading to the onset of the hole formation can be systematically identified. The boundaries between the existence of the flame hole and the possible reignition can also be measured. Furthermore, it would be of interest to explore whether the retreat of the flame edge leads to extinction of the surrounding flame. 

The heats of formation of CH4 and e are well known, but we cannot directly obtain the heat of formation of CH4 from ordinary thermodynamic data. However, we can do this if we apply the so-called equivalent cores approximation6 n> 2a 24 According to this approximation, the hypothetical process in which an electron is transferred from the nucleus of a core-ionized atom to the core hole has an energy which is independent of the chemical environment of the core-ionized atom. For example, in the case of carbon Is holes in CH4 and CO2, it is assumed that the following reactions have the same energy. 

The formation of a multiply charged ion following the ejection of a core electron often leads to decay of the molecule into several positive fragments, and, in the end, gives different final products than in photochemistry. An ion with a core hole can also make transitions into the highly excited states that cannot be occupied spectroscopically (for instance, into the C2S + state of the ion5 ). 

In Pd the 4 p width is considerably larger than the shift which means that during the formation of the tidal wave, the energy loss ( friction") is dominant and a maximum relaxation shift is not very probable. However, this does of course not violate the picture of a 4p hole as a stable excitation in the sense that the total width is still much smaller than the core-hole binding energy. However, in order to observe the Weisskopf-Wigner limit of exponential decay one may have to go back to the elements around 42Mo. 

Despite the potential, experimental spectra of ELNES and XANES have not been fully utilized in order to monitor the local structural and chemical environment. One of the major reasons is the presence of core-hole effects which leads to a redistribution of the PDOS features [10]. In other words, the presence of this effect has been considered as a bottleneck for the full interpretation of the experimental spectra. For example, O Brien et al. compared their XANES spectra of MgO, o -Al203 and MgAl204 at cation L2,3-edge with theoretical DOS obtained by band calculations, but their unoccupied DOS did not reproduce the experimental spectra [11]. Thus, the origin of the major spectral features was concluded to be the formation of a core exciton, i. e., a bound state of the excited electron due to the presence of a core hole. 

The localization due to the formation of a core hole is expected to be greater... 

Figure 1. Index map of Piceance basin showing location of core holes CR-2 and 01-A. Stippled area is underlain by the Green River Formation.

Figure 1. Map of portion of the Green River Formation showing the three core holes...

The availability of a complete range of photon energies from storage ring synchrotron emission has allowed the formation and decay of some exotic inner-shell hole states to be studied. The formation of double core-hole states, where two electrons are removed from the same inner shell by direct photoionization is expected to be weaker by several orders of magnitude than the formation of doubly charged ions with two vacancies in the valence shell... 

A different result occurred, however, when the GaAs surface was coated with each micelle containing one elementary gold particle of 0=12nm. Such a resist corresponds to the film shown in Figure lb in which case the Au was reduced to Au prior to film formation. Instead of formation of an elevation at the places where the substrate was shielded by the micellar core, holes of lOnm in depth and lOnm in diameter were obtained after sputtering (marked by B in Figure 5b). 

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