In this column of the sample table, each row represents a specific object, or a group of similar objects that will be presented to the X-ray beam for measurement. For example, rows of the table could represent (but certainly not limited to):

• A pressed pellet of a model compound;

• An aliquot of solution;

• A series of pellets where the treatment of the sample has been varied systematically;

• ex-situ Electrodes representing various states of charge or a range of charge-discharge cycles

• A series of liquids that form a concentration series;

• Soil samples collected from a range of locations;

Avoid using discipline-specific acronyms in the description of your sample unless you have defined them previously in the text of the Proposed Experiment section. Whilst everyone in your particular scientific sub-discipline might know what the acronyms mean, you cannot assume all reviewers or the beamline team will know.

A brief description of the form of your sample. Examples include:

• 7 mm diameter round pellet

• 13 mm diameter round pellet

• 6 x 3 mm rectangular pellet

• powder spread on carbon tape

• liquid

At this stage, liquid-phase measurements at either MEX1 or MEX2 are to be discussed with the beamline scientists before submitting a proposal.

• MEX2 lacks a suitable cell for liquid measurements. Please note that 25-micron Kapton film and Kapton tape strongly attenuate the X-ray beam at the S and P edges. ≤ 8-micron film is required.

The element and absorption edge you wish to investigate. Ensure the edge is within the energy range accessible by the beamline to which you are applying. See the table above for energy ranges of XAFS beamlines at the Australian Synchrotron.

The measurement mode you wish to employ.

MEX1 measurement modes:

• F (fluorescence-mode) For samples of low concentration, <1000 ppm or intact samples that cannot be ground up or diluted.

• T (transmission-mode) For concentrated samples that can be ground up and diluted to an edge step (Δμ) between 0.1 and 1.5 absorption units and total absorption (μ_Td) around 2 absorption units, and definitely <3 absorption units.

  • In X-ray absorption spectroscopy Δμ and μ_Td are critical parameters for sample preparation and data analysis. If you are unsure what Δμ or μ_Td describe, you are not ready to submit your proposal.

A note on F/T analysis mode

It is VERY (very) rare that a complex sample is well suited to simultaneous transmission and fluorescence measurement, as the two measurement modes are in opposition:

• Transmission requires a sufficiently concentrated sample to produce a large edge step, whereas

• Fluorescence requires a dilute sample to avoid over-absorption.

If you do choose combined F/T, think carefully as to whether you would be better served preparing your sample appropriately for one of the two analysis modes to ensure you get the best possible data, rather than choosing the least worst of two poor (likely unpublishable) datasets, as this is typically the outcome of most samples "prepared" for F/T analysis.

MEX2 measurement modes:

• F (fluorescence)

  • Fluorescence at MEX2 can be performed under vacuum or in a helium atmosphere.

• D (drain current)

  • Drain current analysis can only be performed under a vacuum. Drain current is not compatible with a helium atmosphere

  • The sample must have some degree of conductivity. If your samples are likely to be electrically insulating, please contact the beamline scientists.

• You can use both modes during an experiment. You can even measure both the drain current and fluorescence simultaneously if your sample is suitable.

The measurement mode dictates what information you will report in the concentration column.

For successful X-ray absorption measurements, it is vital that you know your sample's composition. This column, called "concentration" for brevity, reports parameters related to your sample's composition that help communicate its suitability for the chosen analysis mode. The parameters presented in the “concentration” column of the sample table depend on the analysis mode you wish to use. Note that only permissible concentration units are those listed below:

• Fluorescence - expresses the concentration of the element of interest in the sample as presented to the beam in one of the following units:

  • Weight percent

  • Part per million (ppm) by weight

  • Millimolar (liquid samples only)

  • Samples measured in fluorescence are susceptible to over- and self-absorption (two distinct effects that can be conflated in the literature - https://bruceravel.github.io/demeter/documents/Athena/process/sa.html?highlight=self%20absorption ). Good fluorescence samples have 2000 ppm or less of the element of interest. If your samples have weight-per-cent abundance, you will need to dilute them or develop a strategy to correct for over-absorption. This strategy should be discussed in the proposed experiment section of the text.

  • It is important that this column reports the concentration of the sample as presented to the beam, i.e. the concentration after any dilution.

• Transmission

  • edge step (Δμd) and total absorption (μ_Td). It is insufficient to report only one of the two.

  • It is vital that you understand the composition of your sample and the properties that make a good transmission sample. See this comprehensive guide for how to calculate the appropriate dilution for transmission samples in pellet form.

• Drain current - express the concentration of the element of interest in one of the following units:

  • Weight percent

  • Part per million (ppm) by weight

  • Detection limit of 1 atomic % (e.g. 1 S atom in a matrix of 99 other atoms XANES is possible)

  • At concentrations > 1 atomic %, drain current is advantageous as it is a surface measurement, where the drain current signal is collected from a layer within 10 nm of the surface of the sample, thus eliminating over adsorption.

We stress that the concentration you report is the concentration of the sample as presented for analysis. If you are diluting your sample for analysis report the concentration after dilution, not the concentration of the element in the material prior to dilution.

The definition of wavenumber can be found here, and a table of conversions between electron volts (eV) above the edge and wavenumber is provided below. e.g. a scan of the Cu K-edge to kmax = 20 would result in a maximum energy of 10503 eV (8979 eV + 1524 eV; where the energy of the Cu K-edge is 8979 eV).

This value is helpful for the beamline team to assess your time estimates, and check if you will experience contamination of your EXAFS by the absorption edge of another element in your sample. In fact, you should try and check this yourself before submitting your proposal, as you will have the most information available to you regarding the composition of your sample.

If you are only interested in collecting XANES data, it is sufficient to report “XANES only”.

You can calculate k using the expression below:

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Where E is the energy at the end of the scan, E0 is the energy of the absorption edge of interest, m is the electron mass, and h is Planck's constant.

Using the Gd L3 edge as an example, Gd L3 occurs at 7243 eV, and the Gd L2 edge occurs at 7930 eV. If you wanted to scan across the Gd L3 edge but end your scan at the Gd L2 edge, the calculation would be as follows:

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Where E is 7930 eV (the energy of the Gd L2 edge), and E0 is the energy of the Gd L3 edge (7243 eV). The difference between these energies is 687 eV, and the calculation above tells us that 687 eV corresponds to a wavenumber of 13.4 inverse angstroms, or k = 13.4.

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This table comes from the documentation for the XAS analysis package xraylarch, authored by Matt Newville - https://xraypy.github.io/xraylarch/index.html