ELNES structure

EXEEES Extended Electron Energy Eoss Elne Structure Thin films Electrons (100-400 keV) Electrons energies 0-30 eV above edge <200 nm 1-100nm Density of states of valence electrons (above Eermi level) 27,32... 

Figure 4 Correspondence between the fine ELNES structure and the DOS in the empty part of the conduction band.

The occurrence of fine structures has already been noted in the sections on spectral information and ionization losses (Sects. 2.5.3 and 2.5.3.2). In the following text some principal considerations are made about the physical background and possible applications of both types of feature, i. e. near-edge and extended energy-loss fine structures (ELNES/EXELFS). A wealth of more detailed information on their usage is available, especially in textbooks [2.171, 2.173] and monographs [2.210-2.212]. 

Fig. 2.39. Fi ne structures of inner-shell edges (A) Al-K edge of AI4C3 exhibiting ELNES and EXELFS, (B) O-K ELNES of different titanates and Ti-containing silicates.

It should be noted that a comprehensive ELNES study is possible only by comparing experimentally observed structures with those calculated [2.210-2.212]. This is an extra field of investigation and different procedures based on molecular orbital approaches [2.214—2.216], multiple-scattering theory [2.217, 2.218], or band structure calculations [2.219, 2.220] can be used to compute the densities of electronic states in the valence and conduction bands. 

The Fine Structure Before and After Each Edge. ELNES is the term use to describe the energy-loss near edge structure, and this can be quite different for an element in different compounds. For example the shape of the aluminium L edges are quite different in EELS spectra from metallic aluminium and aluminium oxide, so that the chemical form of a given element may be indentified from these small variations in intensity after the edge. 

In solid state physics, the sensitivity of the EELS spectrum to the density of unoccupied states, reflected in the near-edge fine structure, makes it possible to study bonding, local coordination and local electronic properties of materials. One recent trend in ATEM is to compare ELNES data quantitatively with the results of band structure calculations. Furthermore, the ELNES data can directly be compared to X-ray absorption near edge structures (XANES) or to data obtained with other spectroscopic techniques. However, TEM offers by far the highest spatial resolution in the study of the densities of states (DOS). 

Figure 2. Schematic representation of two models for the origin of electron energy-loss nearedge structures (ELNES) for the core-ionization edges, (a) Transition of strongly bound core electrons into unoccupied states (b) multiple scattering description of ELNES.

ELNES Electron energy-Loss Near-Edge Structure Similar to NEXAFS, except monoenergetic high-energy electrons 60-300 KeV excite core-holes. 

Electron Energy Loss Near-Edge Structure (ELNES)... 

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