X-Ray Fluorescence Spectroscopy (XRF) – Basics

The energy dispersive X-ray fluorescence spectroscopy (XRF) is a method for measuring the thickness of coatings and for analysing materials. It can be used for the qualitative and quantitative determination of the elemental composition of a material sample as well as for measuring coatings and coating systems. In both laboratory and industrial environments, the fluorescence spectroscopy (XRF) is now well established and can be readily utilised with modern equipment. FISCHERSCOPE^® XRF instruments have the following advantages:

• Non-destructive: The X-radiation has absolutely no lasting influence on the material; it fully retains its quality.
• Fast: The XRF method needs very simple sample preparation and short measurement times range in the seconds, rarely longer than one minute.
• Clean: No chemicals are used.
• Safe: Method without the use of environmentally hazardous chemicals, X-radiation poses no risk for operator due to the protective instrument design.
• Universally applicable: The XRF method is suitable for material analysis and conting thickness measurment in a very broad range of applications.

The Principle of the X-Ray Fluorescence Spectroscopy (XRF)

The specimen is excited with the primary X-radiation. In the process electrons from the inner electron shells are knocked. Electrons from outer electron shells fill the resultant voids emitting a fluorescence radiation that is characteristic in its energy distribution for a particular material. This fluorescence radiation is evaluated by the detector.

The generation of the X-ray fluorescence radiation is shown simplified in the figure above. One electron from the K shell is knocked. The resultant void is filled by either an electron from the L shell or an electron from the M shell. In the process the K_α and K_β radiation is generated, which is characteristic for the particular material.

For further information see the Wikipedia page about XRF.

Functional Principle of a FISCHERSCOPE^® X-Ray Fluorescence Spectroscopy (XRF) Instrument

1. The X-ray tube generates the primary X-radiation. The electrically heated cathode emits electrons. Accelerated by the applied high voltage to very high speeds, the electrons bombard the anode material. This generates the primary X-radiation.
2. The shutter serves as a safety device and closes the access of the primary X-radiation to the measurement chamber, if needed.
3. A light source (not shown in the figure) illuminates the sample. A mirror and lens direct the image of the measurement location to a color video camera. The mirror has a hole in its center for the primary radiation to pass through.
4. The aperture (collimator) limits the cross-section of the primary beam in order to excite a measurement spot of a defined size.
5. The primary X-radiation impacts the atoms on the sample surface (coating layer and base material) and in the process knocks electrons from the inner electron shell. Electrons from outer electron shells fill the resultant voids emitting a fluorescence radiation that is characteristic in its energy distribution for a particular material.
6. The energy dispersive detector measures the energy distribution of the fluorescence radiation. A multistage electronics circuit processes the measurement signals.
7. The measured spectrum shows lines or peaks that are characteristic for the chemical elements in the sample.
8. The WinFTM Software computes the thickness of the coating(s) and/or the analysis result. The video image of the sample is shown in the WinFTM window. The precise position of the measurement location and the measurement spot is possible due to the special design of the optical and the x-ray guidance systems.