When conducting PXRD on metal hydride nanoparticles. We often use Kapton tape to protect the materials. However, this gives a strong peak in the low-angle ranges. Is it appropriate to do a background subtraction, and how is this best done to eliminate slight variations of position and intensity so I do not get strong negative peaks?
Dear Charles Brewster ,
as you have experienced by yourself, taking a plane cover on top of the sample material will bring additional XRD peaks from that cover material. Background subtraction is critical; even in the case of having a pure Kapton XRD pattern. You may, however, fit the shift of the 'measured' Kapton background onto the strong peak in the low theta range according to the formula given in
Presentation XRD and XRR angular shifts due to sample height variations
With respect to the 'intensity' I do not expect any relevant differences, because in both cases the Kapton foil is directly exposed to the primary beam.
A way to avoid the superposition of the Kapton and the sample signal is to use a domed type of protective cover.
Examples are given in the following links:
https://mystore.malvernpanalytical.com/mystore/s/en-GB/product/domed-sample-holder/01t0Y000006V5SnQAK
and
https://rigaku.com/products/x-ray-diffraction-and-scattering/xrd/accessories/air-sensitive-sample-holder
Here the cover material is ouside the ROI and contributes only a bit of attenuation*) onto the x-ray beam(s); thus only scaling the XRD pattern by a constant factor close to 1.
*) without any theta/2theta dependence.
Best regards
G.M.
The main cause of peak shifts of PXRD was due to sample preparation, i.e. the surface height. The subtraction to remove the impact of a cover material is not a good practice regarding to the regulatory authorities. It can, however, merely be and is in fact used for academic publications.
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