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MEX-1 Sample Preparation
Well-considered sample preparation is an important pre-beamtime task. It has the potential to critically influence the experimental outcome and success. In summary, the small vertical beam size coupled with small but noticeable beam motion demands highly uniform samples, as sample homogeneity is directly related to obtained data quality.
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Powders
Powdered samples are commonly prepared as pellets and sealed in kapton tape.
Optimising powdered sample concentration for either transmission of fluorescence-mode measurements will help you maximise your data quality and consistency within your sample set.
For transmission, aim Transmission mode: for highly concentrated samples that can be diluted.
Aim for an edge step of approximately 1. An edge step below 0.3 will not be suitable, especially if you want EXAFS information. We use XAFSmass to estimate the edge step of samples based on their composition.
A guide to using XAFSmass for sample preparation is available here
A more modern version of XAFSMass is available for users familiar with python. It is available from github, pypi and anaconda. This is the recommended version of XAFSmass
Old version of XAFSMass for Windows can be downloaded from the link provided on this page. It is NOT recommended to use the old version of XAFSmass.
A guide to sample preparation using XAFSMass from the XAS beamline is available here.
For fluorescence, aim Fluorescence mode: for minimally concentrated samples i.e. <2000 ppm
Aim to achieve a concentration of approximately 1000 ppm. Exceeding 2000 ppm will increase self-absorption effects. We commonly use cellulose to dilute samples to an appropriate concentration.
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Please do not take the data in the plot below to suggest that 15 revolutions is a sufficient amount of grinding to prepare a sample for transmission. When using a mortar and pestle 15-30 minutes grinding time is recommended. A superior and less tedious solution is to use a ball mill.
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Films and coin cell batteries
These can be directly affixed to our sample holders.
Sample Holders
MEX1 uses sample holders described in the technical drawings below.
The round sample holders can hold samples with 13mm (one hole) or 7mm (two holes) diameters or smaller.
The rectangular sample holders (3 holes) are 6mm x 3mm.
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Sample holder mount for transmission only measurements