ASTM E984-12(R2020) pdf free download

ASTM E984-12(R2020) pdf free download.Standard Guide for Identifying Chemical Effects and Matrix Effects in Auger Electron Spectroscopy
4. Significance and Use
4.1 Auger electron spectroscopy is often capable ofyielding information concerning the chemical and physical environment of atoms in the near-surface region of a solid as well as giving elemental and quantitative information. This information is manifested as changes in the observedAuger electron spectrum for a particular element in the specimen under study compared to the Auger spectrum produced by the same element when it is in some reference form. The differences in the two spectra are said to be due to a chemical effect or a matrix effect. Despite sometimes making elemental identification and quan- titative measurements more difficult, these effects in the Auger spectrum are considered valuable tools for characterizing the environment of the near-surface atoms in a solid.
5. Defining Auger Chemical Effects and Matrix Effects
5.1 In general, Auger chemical and matrix effects may result in (a) a shift in the energy ofanAuger peak, (b) a change in the shape of an Auger electron energy distribution, (c) a change in the shape of the electron energy loss distribution associated with an Auger peak, or (d) a change in the Auger signal strengths of an Auger transition. The above changes may be due to the bonding or chemical environment of the element (chemical effect) or to the distribution of the element or compound within the specimen (matrix effect). 5.2 The Auger chemical shift is one of the most commonly observed chemical effects. A comparison can be made to the more familiar chemical shifts in XPS (X-ray photoelectron spectroscopy) photoelectron lines, where energy shifts are caused by changes in the ionic charge on an atom, the lattice potential at that atomic site, and the final-state relaxation energy contributed by adjacent atoms (1 and 2). 4 Frequently an Auger chemical shift is larger than an XPS chemical shift (see Fig. 1) because the Auger process involves a two-hole final state for the atom which is more strongly influenced by extra-atomic relaxation. Coverage by gas adsorbates on metal surfaces may also cause shifts in the metal Auger peak energies (3). Band bending across junctions between p- and n-type materials shift the energy levels of each material relative to the Fermi level resulting in an apparent shift in the Auger line energies. This effect has been observed for p-n junctions of silicon (see Fig. 2) (4) and those of heteroepitaxial layers such as GaN/AlGaN (see Fig. 3) (5).5.2.1 Related to chemical shifts is the (modified) Auger parameter, defined as the sum of the photoelectron binding energy and the Auger electron kinetic energy (7). Because the Auger parameter is the difference between two line energies of the same element of the same specimen, it is independent of any electrical charging of the specimen and spectrometer energy reference level, making it easier to identify chemical states of elements in insulating specimens. Naturally, since both photoelectron lines andAuger lines must be measured, the Auger parameter can only be used with X-ray excited spectra. 5.3 The second category of chemical information from Auger spectroscopy is the Auger lineshapes observed for transitions involving valence electron orbitals. Shown in Fig. 4 are variations in the lineshapes for electron-excited carbon KLL for different phases of carbon, in Fig. 5 are lineshapes for carbon KLL for different chemical environments of carbon, and in Fig. 6 are lineshapes for aluminum LVV for different levels of oxidation. While it is possible to relate the prominent peaks in the Auger spectrum to transitions from particular bands in the density of states (for solids) or to particular molecular orbitals (for molecules) (8), this is not an easy task. The large number of possible two-hole final states, taken together with shake-up and shake-off transitions and uncer- tainty on all their final energies and intensities make the job of constructing a valence orbital density map from the Auger spectrum next to impossible for all but the simplest systems.