Electron excited Auger spectra

Figxjre 15.9. Electron-excited Auger spectra from a 150-A nichrome film deposited on a silicon substrate. The spectra represent a profile of the film from the surface down to a depth of 200 A as various amounts of the material have been sputtered off. Note that the unit on the ordinate is the derivative of the electron intensity, dN(E)/dE, rather than the intensity N(E). From R. E. Weber, J. Crystal Growth, 17, 342 (1972), by permission of the author and the North Holland Publishing Company. 

Figure 7. Schematic electron-beam excited Auger spectrum in the direct mode.

Figure 1. X-ray excited Auger spectrum of polyethylene. Top trace raw data with secondary electron background subtracted (Ref. 3,5). Bottom trace Auger spectrum corrected for electron energy loss functions to the solid (Ref. 10). The corrected spectrum has a width of V 50 eV, compared to the 40 eV predicted by independent particle theory (see text).

Figure Al.7.12. Secondary electron kinetic energy distribution, obtained by measuring the scadered electrons produced by bombardment of Al(lOO) with a 170 eV electron beam. The spectrum shows the elastic peak, loss features due to the excitation of plasmons, a signal due to the emission of Al LMM Auger electrons and the inelastic tail. The exact position of the cutoff at 0 eV depends on die surface work fimction.

A typical x-ray photoelectron spectrum consists of a plot of the intensity of photoelectrons as a function of electron EB or E A sample is shown in Figure 8 for Ag (21). In this spectrum, discrete photoelectron responses from the core and valence electron eneigy levels of the Ag atoms are observed. These electrons are superimposed on a significant background from the Bremsstrahlung radiation inherent in nonmonochromatic x-ray sources (see below) which produces an increasing number of photoelectrons as EK decreases. Also observed in the spectrum are lines due to x-ray excited Auger electrons. 

Fig. 33. Ba 5p - 6s2ep (O23P1P1) electron-excited atomic Auger spectrum (AES)54-55) giving a direct picture of the 5 p hole spectrum (see text)...

In most instruments, an electron beam, which can be focused to a smaller spot size than an X-ray beam (see Figure 17.3.2), is used to excite the sample. The spectrum of emitted and scattered electrons, including Auger electrons, is analyzed according to kinetic energy in a manner that produces a derivative readout, so that the sharp Auger structure is more easily seen on the broad continuum (Figure 17.3.10). 

Fig. 34. Three of the corrected measured electron excited Cu LMM Auger spectra (dotted lines) for different primary energies. The background due to the secondary electron cascade and the backscattered primary electrons has been subtracted prior to correction. The reference from the X-ray excited Cu LMM Auger spectrum (see Fig. 26) is represented by the solid line [113]. Reprinted with permission from M. Schleberger, D. Fujita, and S. Tougaard, J. Electr. Spectr. 82, 173 (1996), 1996, Elsevier Science.

X-ray excited Auger Electron Spectroscopy (XAES) is limited by the flux density of the X-ray source, but conveniently accompanies the photoelectron emission spectrum produced in an X-ray Photoelectron Spectrometer. XAES was used by Desimoni and co-workers [54,55],... 

Associated with prominent features in an Auger spectrum are the same types of energy loss feature, the plasmon losses, that are found associated with photoelectron peaks in an XPS spectrum. As described in Section 27.2.3, plasmon energy losses arise from excitation of modes of collective oscillation of the conduction electrons by outgoing secondary electrons of sufficient energy. Successive plasmon losses suffered by the backscattered... 

The peaks observed in a XPS spectrum can be grouped into two basic types peaks due to photoemission from core levels and valence levels (levels occupied by electrons of low binding energy (0-20 eV), which are involved in de-localized bonding orbitals), and peaks due to X-ray-excited Auger emission. 

Fig. 13. L2 3-4s Auger spectrum of Ca excited by 2 keV electrons (from Breuckmann ). The energy splitting of the pairs of lines a/c and b/d correspond to the fine structure splitting of the initial L3 and L2 levels.

X-ray-excited Auger emission A secondary electron emission process that follows the photoionization and appears as a peak in the X-ray photoelectron spectrum. After the initial photoemission, an upper level valence electron relaxes into the vacant core-level state, followed by an ejection of another electron in the valence level. 

Figure Bl.25.6. Energy spectrum of electrons coming off a surface irradiated with a primary electron beam. Electrons have lost energy to vibrations and electronic transitions (loss electrons), to collective excitations of the electron sea (plasmons) and to all kinds of inelastic process (secondary electrons). The element-specific Auger electrons appear as small peaks on an intense background and are more visible in a derivative spectrum.

If the work function is smaller than the ionization potential of metastable state (see. Fig. 5.18b), then the process of resonance ionization becomes impossible and the major way of de-excitation is a direct Auger-deactivation process similar to the Penning Effect ionization a valence electron of metal moves to an unoccupied orbital of the atom ground state, and the excited electron from a higher orbital of the atom is ejected into the gaseous phase. The energy spectrum of secondary electrons is characterized by a marked maximum corresponding to the... 

---