Features
X-ray fluorescence (XRF) is a technique for analysing sample
composition by element. It is based on spectroscopic analysis of
characteristic X-rays generated by X-ray irradiation of the sample. XRF
has the following features:
Energies corresponding to atomic numbers 11 (Na) to 92 (U) can be
measured simultaneously in a short time (1-100 s)
Pre-treatment is not necessary except for special samples
Analysis in ambient atmosphere
Identification of elements in unknown samples
Application Examples
Visualization of elemental distribution on the sample surface
Elemental analysis of resin contaminants
Transmission X-ray imaging and image analysis
Plating film thickness measurement
Identification of residue components
Elemental analysis of liquids
Principle
When an atom in the ground state is irradiated with X-rays (1,
numbers refer to Figure 2), the inner shell
electrons (K shell example in
the figure) are excited to the vacuum level at a certain probability,
thereby resulting in vacancies in the inner K and L shells (2).
The atomic state with vacancies in the inner shell is energetically
unstable, so the outer shell electrons spontaneously transition to the
inner shell (3). This results in emission of characteristic X-rays
(fluorescence) corresponding to the energy difference between the
pre-and post-transition states (4). The fluorescence X-rays are then
spectroscopically analysed by energy dispersion X-ray spectroscopy (EDX)
using spectroscopic crystals, each of which has its own energy range.
Since the X-ray fluorescence spectral fingerprint is unique, the
elements constituting the sample can be identified. The strength of the
diffraction peaks also yields information about the relative amount of
the element.
Figure 2. Process of
X-ray fluorescence generation
Data examples
Figure 3. Optical microscopy image of a printed circuit board.
Figure 4. Transmissive X-ray image of a printed circuit board
Figure 5. Surface analysis of the electrode regions of a printed
circuit board
Figure 6. Line analysis of a printed circuit board electrode
Figure 7. Qualitative and semi-quantitative analysis of a bulk GaAs
sample (substrate). The analysis does not require calibration to any
elemental standard samples, i.e., it is standardless, and the
element concentration and film thickness (if a film sample) can be
calculated from the energy spectrum.
Figure 8. Semi-quantitative analysis of a thin Zn/Sn alloy
foil.
The Zn:Sn wt% ratio was found to be 30:70.
Photos, graphs, tables, compound reports: Portable document format
(PDF) files.
Photos: Joint photographic expert group (JPEG) files.
Graphs: Portable network graphics (PNG) or bitmap (BMP) files.
Spectral data: Excel file.
Measurement specifications
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Depends on element and tube voltage
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Point analysis. Depends on beam diameter and element
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Items for enquiries
Purpose and scope of the analysis
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Element of interest layer structure, film thickness, possibility of
destructive preparation of samples to fit the instrument.
Desired delivery dates of preliminary and final results.
Other relevant information.
Caution
Ambient atmosphere or vacuum (rotary pump) can be selected.
Gases cannot be analysed.
Due to its high transmission ability, X-rays may detect information
at depths of several mm in bulk samples or in substrates on which the
sample films are deposited.
Film thickness calculation requires specification of the thin-film
constituents. Analysing films containing the same elements as the
substrate may be difficult.
Calculated concentrations are semi-quantitative values obtained from
theoretical and actual X-ray intensity, and detector sensitivity.
The smallest resolvable energy difference is of about 150 eV or one
order of magnitude larger than that of wavelength dispersion X-ray
spectroscopy (WDX). Hence, it may be difficult to distinguish some
elements due to overlapping peaks.