Ionization energy outer-level electrons

With AES, the sample is subjected to a high-energy (typically 2-20 KeV) electron beam that can cause ejection of a core electron from an atom to form an atomic inner shell vacancy. An outer-level electron will then fill the inner-level vacancy, which will induce an excited state. One of the ways that the atom can then relax is by emitting another electron to form a doubly ionized species. This electron is the Auger electron (named for Pierre Auger, who recognized the effect... 

X-ray energy is far more energetic than that in the ultraviolet range. If an X-ray photon has an energy that exceeds the ionization energy of an electron, absorption of that photon can eject the electron outright. Furthermore, the ejected electrons are from core levels—those closest to the nucleus. In terms of quantum numbers, these levels correspond to n = 1,2, and 3, which are usually referred to with the older shell notation K, L, and M. When an inner-shell electron is ejected, an outer-shell electron "falls" to fill the vacancy and release X-ray photons (fluorescence) in the process as shown in Figure 5.44. 

The relative position of the electronic level eo to the Fermi level depends on the electrode potential. We perform estimates for the case where there is no drop in the outer potential between the adsorbate and the metal - usually this situation is not far from the pzc. In this case we obtain for an alkali ion eo — Ep — where is the work function of the metal, and I the ionization energy of the alkali atom. For a halide ion eo — Ep = electron affinity of the atom. 

The unitary level of the surface ion referred to the standard gaseous ion S sTD) at the outer potential of the semiconductor is represented by the unitary real potential, Ug. (= - 7s). This unitary real potential is equivalent to the sum of the standard free enthalpy AG of sublimation of the semiconductor, the ionization energy Is of the gaseous atom S, and the electron energy sy at the upper edge level of the valence band as shown in Eqn. 3-14 ... 

Fig. 4-16. Energy levels of metal ion and electron in an ionic electrode of metal ion transfer 4Cjn i = sublimation energy of solid metal /m" = ionization energy of gaseous metal atoms > >s = outer potential of electrolyte solution E s electrode potential (absolute electrode potential).

Ionization energy tends to decrease down a group. This makes sense in terms of the energy level that the valence electrons occupy. Electrons in the outer energy level are farther from the positive force of the nucleus. Thus, they are easier to remove than electrons in lower energy levels. 

Ionization energy tends to increase across a period. As you go across a period, the attraction between the nucleus and the electrons in the outer energy level increases. Thus, more energy is needed to pull an electron away from its atom. For this trend to be true, you would expect a noble gas to have the highest ionization energy of all the elements in the same period. As you can see in Figure 2.16, they do. 

The position of an edge denotes the ionization threshold of the absorbing atom. The inflection in the initial absorption rise marks the energy value of the onset of allowed energy levels for the ejected inner electron (216). For a metal this represents the transition of an inner electron into the first empty level of the Fermi distribution (242) and in case of a compound the transition of an inner electron to the first available unoccupied outer level of proper symmetry. Chemical shifts in the absorption-edge position due to chemical combination (reflecting the initial density of states) were first observed by Bergergren (27). 

An isolated atom has a characteristic set of discrete energy levels. Then if one electron is removed from an inner shell of the atom, electronic relaxation occurs due to one of the outer shell electrons filling the electron hole left in the inner shell. This leads to the emission of a characteristic X-ray. In such cases, only one spectral line, originating from the X-ray transition between an inner shell and one of the discrete outer shells, can be observed. However, when multiple ionization occurs during a single excitation process, as in the case of enei etic ion impact, a fine structure or finger pattern is necessarily observed in the spectrum. In PIXE,... 

Auger electron spectroscopy is used mainly for determining the elemental composition of the outer layers of a solid. Each element, when excited by the ionization of an inner electron level, emits Auger electrons with energies characteristic of that element and virtually independent of the chemical environment of the atom concerned. 

Fig. 2 shows a diagram summarizing the various transitions which can be observed in the Mjjj and My spectra of a metal as well as in the 3 d Auger spectra. The Mjjj and My absorption transitions are shown in Fig. 2a and b the energy of the Mjjj discontinuity corresponds to the transfer of an inner 3p i2 electron to the Fermi level and its shape involves the 6d unoccupied distribution the energy of the My absorption line is exactly that of the 5/" -> SJjyj excitation transition. The My emission is shown in Fig. 2e an inner 3 d i2 hole is created and a 5/electron transits to this hole with the emission of a photon. In the corresponding non-radiative transition, there is simultaneously the 5/ electron transition, and the excitation or ionization of a 5/electron (or 6p or 6 s) (Fig. 2f). The My resonance line is represented in 2c the excited 5/electron drops back to the inner hole the corresponding emission line then coincides with an absorption line. The competing non-radiative transition is shown in 2d this is an Auger transition in the excited atom the final state has only one hole in an outer shell and the configuration is the same as in a photoemission process.

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