Coating Thickness Software for Eagle µ-EDXRF Systems

1.4.4 Multiple Layers Systems
In multi-layer systems, there are more complications introduced by the very presence of the adjacent layers,
in particular the layers above. The situation for a two-layer (double layer) system is illustrated in Figure 8.
Note: The convention in the FunMaster & ReCalib software packages is that the layer most
remote from the base (i.e. at the surface) is designated “layer #1”.
detector
detector
thin coating layer #1
thick coating layer #2
thick coating layer #1
thick coating layer #2
“base”
material
(a)
(b)
Figure 8. Illustrating the consequence of variations in the upper layer’s (#1) thickness and its
influence upon observed intensities for underlying layers (e.g. #2).
Thickness of sub-layer #2 is unchanged in Figures 8a & 8b, but the observed intensity (indicated by the
width of the emergent beam) in 8b is lower because the increased thickness of the top layer #1.
The variable thickness of layer #1 affects both:
a. the amount of incident radiation reaching layer #2 and hence available to excite its analyte line(s)
[an example of “Primary absorption”]
b. the degree of additional absorption of the emergent analyte beam from layer #2 and hence it’s
observed intensity [an example of “Secondary absorption”].
These effects are additional to the self absorption effects of the analyte line within its own layer.
FunMaster generated calibrations for multi-layer systems first determine the relevant calibrations for each
individual layer’s element/alloy. It then determines how these calibrations for the sub-layer components will
be modified by the presence and/or variable thickness of any upper layers. Typically, the presence of upper
layers reduces the working thickness-range of the underlying layers.
The standard-less procedures within FunMaster yield calibration accuracies of typically 5% for the first top
layer. Errors in calibrations of underlying layers will be larger. Contributions to errors include uncertainties
in the Fundamental Parameters, assumptions in the model, as well as the possibly incomplete description of
the instrument’s geometry. The recalibration procedure to be found in the stand alone ReCalib routine
makes it possible to reduce the influence of the foregoing errors and improve overall accuracy.
The recalibration procedure can become quite involved especially for multi-layer systems and alloy layers. It
is recommended, where data from suitable reference standards is available, to always fine tune the
theoretical calibration parameters computed within FunMaster by using such data within the ReCalib routine.
Any FunMaster generated calibration should be verified using the ReCalib routine.
1.4.1 “Bulk Sample” and “Thin Film” Intensities 14