Absorption edge effect

Many elements, covering nearly the whole of the periodic table, show the absorption edge effects in the X-ray region (figure 9.3). The proliferation of the edges indicates the widespread opportunities of using optimised anomalous dispersion techniques. 

In certain cases the absorption edge effects may exhibit dichroism whereby there is a change as the crystal orientation is changed. Not only the XANES effects can change but also the edge position itself. Templeton and Templeton (1980, 1982) show these effects clearly in their... 

These aspects of the optical spectra of solids are illustrated in the upper portion of Figure 1, which displays the reflectance curve (R) at room temperature for a typical semiconductor, GaAs. The fundamental absorption edge around 1.4 eV produces only a weak shoulder. Some structure is apparent in the two features around 3 eV and the large, broad peak near 5 eV. However, the dominant aspect of the line shape is the slowly varyii background. The derivative namre of Modulation Spectroscopy suppresses the uninteresting background effects in favor of sharp, deriva-... 

The effective wavelength provides a useful way of characterizing polychromatic beams that are not appreciably affected by the presence of an absorption edge. One suspects intuitively that the presence of an absorption edge critically located could cause complications in absorptiometry with polychromatic beams. That this does happen has been demonstrated,13 and it limits the usefulness of the effective wavelength. 

The situation may be complicated further by the presence of absorption edges and by the filtering of a polychromatic beam if such is used for excitation. The filtering effect can be approximately treated by choosing a suitable effective wavelength for the polychromatic beam. Sherman10 has given the most complete theoretical treatment of the... 

Edges, absorption, see Absorption edges EDT (EDDT) as analyzing crystal, 116-118, 220, 257, 260, 318-327 Effective wavelength of a polychromatic x-ray beam, determination, 8, 72, 76-78... 

Figure 2.74 Schematic representation of the electron wave interference effects giving rise to the Kronig fine structure on X-ray absorption edges (sec text).

Figure 5.4 X-ray tube output spectrum, showing continuous emission and line spectra of the target material (in this case gold). The K absorption edges for major elements in silicate glasses are shown below the diagram, indicating that the gold M lines are particularly effective for the analysis of the light elements Na to P.

The effect of increased x-ray absorption on sensitivity was explored by conducting monochromatic exposures of a bromine-containing resist, poly(N-allyl maleimide-vinyl benzyl bromide), at photon energies which bracket the bromine absorption edges between 1.6 and 1.8 keV contrast curves obtained for these monochromatic exposures are shown in Figure 7. The results are also plotted as l/D "5 vs absorption coefficient in Figure 8 the data accurately follow the predicted inverse relationship defined by Equation 1. 

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