Principle
X-ray fluorescence analysis (XRF) is suitable for the
non-contact and non-destructive thickness measurement of thin
layers as well as for determining their chemical composition. For
this type of measurement, the X-ray source and detector are located
on the same side of the sample. When the layer on the substrate is
subjected to X-rays, the radiation will penetrate the layer, if it
is sufficiently thin, to a certain extent, depending on the
thickness, and in turn cause characteristic fluorescence radiation
in the material of the underlying substrate. On its way to the
detector, this fluorescence radiation will be attenuated by
absorption at the layer. The thickness of the layer can be
determined based on the intensity attenuation of the fluorescence
radiation of the substrate material.
Tasks
- Calibrate the semiconductor energy detector.
- Measure fluorescence spectrum of the iron substrate with
different numbers n of pieces of aluminium foil with the same
thickness placed on the substrate (including n = 0).
Determine the intensity of the Fe-Kα fluorescence
line.
- Plot the intensity of the Fe-Kα fluorescence line as a
function of the number of pieces of aluminium foil placed on the
substrate in linear and semilogarithmic way.
- Determine the intensity of the Fe-Kα fluorescence line
for various numbers of pieces of aluminium foil that are fastened
in front of the outlet of the tube of the energy detector.
- Calculate the thickness of the aluminium foil.
- Execute tasks 2 to 4 for copper foil on molybdenum or zinc
substrate.
What you can learn about
- Bremsstrahlung
- characteristic X-radiation
- fluorescent yield
- Auger effect
- coherent and incoherent photon scattering
- law of absorption
- mass attenuation coefficient
- saturation thickness
- matrix effects
- semiconductor
- energy detectors
- multi-channel analysers
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