TRENDS AND FUTURE PROSPECTS - Total-Reflection X-Ray Fluorescence Analysis and Related Methods - page 465

Figure7.16. Experimental arrangement for X-ray reflectivity measurements in parallel to
GI-XRF. The sample is tilted by a small angle α , the detector tilted by 2 α for a geometry of
( α /180 ° 2 α ) in the total reflection regime. A simple gas-flow detector or a Si-Pin diode is used for

the detection of the reflected monochromatic beam. The fluorescence radiation of the sample is
detected in ( α /90 ° ) geometry by a Si(Li) detector or by an SDD.

in tandem to find the true model of a layered material. A combined piece of
equipment that allows for both TXRF and XRR measurements can easily be
assembled as demonstrated in Figure 7.16. It is commercially available from
Rigaku and ATI.
The additional experimental effort is small; only a second X-ray detector is
needed, positioned in the direction of the reflected beam. The detector can be a
simple ionization chamber, a gas-flow detector, and even a Si-PIN diode has
already been used. Only the intensity of the strong K α or L α peak of the
exciting X-ray beam has to be recorded depending on the glancing angle of the
incident beam. Weaker peaks, such as K β or L β peaks, can be filtered out by a
thin metal foil.
Multilayered systems of inorganic and organic materials show certain
oscillations of the intensity called Kiessig fringes. Their period is related to
the number N and thickness d of layers: Δ α = λ /(2 Nd ). The topic was actually
dealt with in Section 2.1.2. Three examples have been demonstrated and the
results were found simply and fast. Figure 2.2 shows the XRR profile for a
70 nm silicon layer on a gold substrate. The period Δ α of the Kiessig maxima or
minima of 0.028 ° leads to a thickness of 72.5 nm in accord with Equation 2.7.
Figure 2.3 represents the profile for a 30 nm cobalt layer on a silicon substrate.
The period of 0.065 ° corresponds to a thickness of 31.3 nm. Figure 2.6 was
recorded for a stack of 15 Pt/Co bilayers each 2.1 nm thick. The profile has 15
Kiessig fringes between two successive Bragg reflections with a period of
0.133 ° , which corresponds to a thickness of 2.2 nm. The results confirm that
number and thickness of several layers can simply be determined by the
number and period of Kiessig fringes. The results have an accuracy of about
4% and can help for different kinds of thin-layer analysis by GI-XRF as
mentioned in Section 5.4.8.2.