How to: GeoPIXE: Generate a DA matrix for XANES spectra or XANES mapping

The basic idea is to use the XRF spectra from the highest beam energy you used to fine-tune the spectrum fitting and thereby fine-tune the DA matrix. Details for many of these steps will be found in previous tutorials on importing and fitting spectra.

You will need a XANES energy list (.csv file) before beginning this process.

If you are doing multiple XANES scans on a single sample, or very similar samples, you probably only need to this process once.

Video

Coming soon!

Steps

1. Load the XRF .spec file from the highest beam energy you used, or import the raw data to generate the XRF spectra following these steps:

• In the Spectrum Display window, use File> Import to choose the last spectra collected in the XANES experiment (highest energy map). Set output path to a folder of your choice in the analysis directory, and set Flux PV settings as usual (FC0, gain, units, etc.).

• Using the Spectrum select tool, delete all XYT.

• In the Spectrum Display window, use Display > Get ALL energy cals to calibrate the spectrum. Choose a .spec file where the energy calibration is good for your XANES maps.

• In the Spectrum Display window, use Process > Add (re-map cal) to sum your spectra, taking the energy calibration into account.

• Save the spectrum for your future reference, should you need to adjust the fit further in the future.

2. In the Spectrum Display window, use Window > Xray Spectrum Fit to open the main fitting window.

3. In the X-ray Spectrum Fit window, load a fit setup (.pcm file) that will be a reasonably close start for fitting your XANES data (e.g., a fit setup from an XRF map of the same sample).

4. Redo the yields calculation, changing the beam energy to the highest beam energy you used in your XANES experiment.

5. Adjust the fit of the spectrum, especially around the element of interest. Don't bother fitting any harmonics if they are present.

6. When you are satisfied with the fit, click "Generate DA matrix" and choose "XANES energy series DA matrix" from the drop-down menu.

7. Click the "Energies" button that appears, and navigate to your .csv file list of energies.

8. Set Merge E to the highest beam energy in your XANES experiment, then click OK.

9. Save the new "*-xanes.damx" file to your setup folder.

-- LouisaSmieska - 22 May 2016