Choosing scan parameters

Transmission or Fluorescence?

Transmission measurement is preferred, however the decision comes down to your sample composition. Fluorescence measurement allows analysis of low concentration samples, down to a few ppm (sometimes even less).
Most importantly, you should analyse all of your samples in the same way so they are directly comparable. If a few of your samples have concentrations too low for transmission analysis, you should dilute your other samples and analyse your entire dateset by fluorescence.

Here is a link on how to calculate whether your samples are suitable for transmission: Sample Preparation for Transmission Mode

Note: fluorescence scans take a little longer than transmission scans due to detector overheads.

XANES or EXAFS?

XANES - the region around the edge.
Contains information about valance state, chemical shifts.

EXAFS - the oscillations after the edge.
Contains information about local coordination and structure.

Depending on what information you need, you will spend more time collecting data points within either region.

A XANES scan will still scan the EXAFS region, but may spend less time, and will not extend as far. An EXAFS scan will still include the XANES region, but will spend a greater proportion of time sampling towards higher energies.

How far in k should I scan?

It is common to use the terminology k (wave number of the photoelecton) instead of energy (eV) when we talk about the EXAFS. k is equivalent to the energy range, so this is just another way of saying how far in energy range we want to scan past the edge.

A XANES-focused scan may extend to a maximum k of between 8 to 12, in order to include sufficient post-edge for normalisation.

An EXAFS-focused scan may extend to a maximum k of between 12 and 20, in order to capture oscillations after the edge. Noise will increase the further out we go, so measurement time will be increased in proportion to k.

Another consideration may be what other elements are in your sample. If there is a contaminant edge within the energy range you want to scan, it will probably not be useful to go any further past that energy.

Longer scans or multiple quick scans?

If your samples tend to be heterogeneous, you may prefer to collect multiple scans at different locations on the sample, to increase confidence about whether data is representative.

If your samples are radiation sensitive, you may prefer to collect multiple quick scans at different locations on the sample, to minimise radiation damage effects in the data.

If you are interested in a particular region (e.g. long range EXAFS), you may prefer to do a longer scan so that you spend more time measuring the EXAFS, and avoid duplicating time spent in regions you are not so interested in (e.g. pre-edge and edge).

A common strategy is to analyse two scans on the same spot, followed by an additional scan on a different spot, so that you can get an idea of any variation between duplicate scans, and between different spots.