PIXE and RBS spectroscopies

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PIXE (Particle Induced X-ray Emission) spectroscopy

Quantitative and multielemental analysis for all elements heavier than Na.
A non-destructive method (except in the case of very fragile materials which can be damaged due to a temperature rise during irradiation).
Limits of detection (LOD), in optimal conditions (light matrices, low concentrations of heavier elements), are in the range of 1 – 10 ppm for elements with atomic numbers 20 < Z < 40 (detection of K X-rays), and in the range 10 – 1000 ppm for all other elements.
Proton and He ion beams in the energy range between 1 and 3 MeV (typically 2 MeV) are used for the excitation of X-rays.
Elemental concentration maps can be measured with focused (1 μm) or collimated (1 mm) ion beams.

Analysis results

PIXE spectra are analyzed with the GUPIX program package. The results are given as a concentration table of elements, presented in the example.
If the samples are measured with a scanning ion beam at the nuclear microprobe, then the analysis results are given as qualitative distributions of the intensities of X-rays for certain elements (within the scanning area which is typically 1 x 1 mm² maximum).
Elemental concentration mapping is also possible for the In-air PIXE in which case the pixel size is 1 mm and the scanning procedure is done by moving the sample in the x and y planes.

Sample requirements

For PIXE analysis, samples of up to 3 cm in size can be placed in the vacuum chamber, optimally in the 1 – 2 cm range. Only flat surfaces of the sample, between 1 and 8 mm in size, can be analyzed.
For PIXE analysis with a focused ion beam at the nuclear microprobe, the maximum sample size that can be placed in the vacuum chamber is approximately 2 cm. Areas of the sample up to 1 mm in size can be scanned.
For In-air PIXE analysis, areas of the sample that can be exposed to the beam are approximately 1 mm in size. The sample is placed on a XYZ translator support and can be as large as several tens of centimeters, under the condition that the region for analysis can be placed directly in front the exit tube of the proton beam.

RBS (Rutherford Backscattering Spectrometry)

Quantitative analysis of major elements in the samples (heavier than He).
Elemental depth profiling under the condition that the elements of interest are heavier than the ones present in the substrate (e.g. thin metal films on silicon).
Proton or He ion beams in the energy range 1 – 3 MeV are used for the analysis.
Standards are not required.

Analysis results

Quantitative analysis of homogenous samples with RBS spectroscopy is done by a simulation of experimental results with the SIMNRA program package. The results are presented as atomic (stochiometric) ratio of detected elements in the sample.
For thin film samples, only the analysis of elemental composition in the surface layers is possible. The typical thickness of thin films is between 1 and 1000 nm. The results are presented as elemental ratios and thicknesses (in ng/cm2) in surface thin films.
For RBS analysis with a focused ion beam at the nuclear microprobe, certain positions within the scanning area can be quantitatively analyzed as well.

Sample requirements

Samples up to 3 cm in size can be placed in the vacuum chamber, optimally around 2 cm. Only flat surfaces of the sample, between 1 and 8 mm in size, can be analyzed.
For RBS analysis with a focused ion beam at the nuclear microprobe, the maximum sample size that can be placed in the vacuum chamber is approximately 2 cm. Areas of the sample up to 1 mm in size can be scanned.

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