DIFFERENT FIELDS OF APPLICATIONS - Total-Reflection X-Ray Fluorescence Analysis and Related Methods - page 351

Krämer also studied thin films of a specific protein and a lipid. Cytochrome is
a colored chromo-protein and phosphor lipid was prepared as a bilayer by the
Langmuir-Blodgett technique [183]. Both films were shown to have only about
5 nm thickness.
A further example of GI-XRF deals with a one-element layer deposited on a
Si substrate and covered by a thin multielement layer [175,182]. Figure 5.20
represents intensity profiles of five elements Cr, Fe, Ni, Pd, and Si measured for
a layered sample at glancing angles up to 0.7 ° . From the similar course of the Cr,
Fe, and Ni curves, it can be concluded that there is a first layer consisting of a
Cr/Fe/Ni alloy. The course of these curves suggests a thin layer of about 10 nm
thickness. The course of the Pd curve refers to a second layer of pure palladium,
which in contrast to the first layer is thicker than 100 nm. The Si curve indicates
a pure silicon substrate.
This first qualitative impression of the curves is a rough estimate, as shown in
the inset of Figure 5.20. It serves as a starting point for the quantitative
calculations described in Section 4.6.4. The solid curves of Figure 5.20 represent
the best fit after several iterations. They are based on a model presented in
Table 5.6 as the final result. It contains the element composition, the thickness,
and the density of the two layers and the substrate, thereby making the first
Figure5.20. Fluorescence intensities of five elements measured on a layered sample by an angle
scan. Excitation was performed by the K α peak of a Mo X-ray tube. The solid curves do not
represent a regression line of the measuring points but are a best fit of calculations based on a model
as demonstrated in the inset on top, right. Figure from Ref. [182], reprinted with permission.
Copyright1992, American Chemical Society.