Beamtime Guide - XAS

Proposal guidelines

Summary: Beamtime at the XAS beamline is highly competitive.

Beamtime applications will be scored and ranked according to scientific merit, track record, need for synchrotron radiation, and technical feasibility and clarity. Please ensure that you read the entire proposal guidelines document. Failure to follow these guidelines is likely to render your proposal uncompetitive.

All potential new users to the beamline must contact the beamline scientists well in advance of submitting their proposal in order to discuss feasibility and maximise their chances of success. Applicants seeking to use Hutch C are requested to do the same.

Prior to submitting your proposal, please consider the following:

Does the experimental plan include a table of samples and experimental conditions as outlined in the guidelines?
If you have not used the XAS beamline over the past 3 years, have you contacted the beamline scientist team to discuss the feasibility of your experiment?
If you are proposing an experiment for Hutch C (non-standard experimental set-ups), have you contacted the beamline scientist team to discuss the feasibility of your experiment?
If you are applying for more than 6 shifts (2 days), are at least 3 people listed as attending?

If you answered 'no' to any of these questions, please reconsider before you submit. Your chances of being awarded time will depend on a well-prepared proposal.

Data / analysis

Step 1: Raw data conversion

All raw data collected are automatically saved in a binary .mda format, which requires conversion into ascii format prior to analysis.

For fluorescence data conversion please use Sakura (available for download here).
For transmission data conversion you can use mda display which is available at the beamline (instructions).

Step 2: Analysis

You may choose to use any data package that you are familiar with / desire. At the beamline we often use the IFEFFIT package for data reduction (Athena) and data analysis (Artemis). Further information and downloads can be found here: http://cars9.uchicago.edu/ifeffit/.

The beamline scientists are experienced in XAS data analysis and can provide some general advice in this regard. Please note, however, that it is not a specific task of the beamline scientists to analyse data for users and thus, should you wish to, please pursue their assistance in a reasonable manner.

Samples

Sample preparation

Generally speaking, both liquid and solid samples can be measured at the XAS beamline. Solid samples can be in the form of e.g. films, crushed powder, or homogeneous pastes, whilst liquids can be measured at room temperature or, more commonly, frozen in the 10K cryostat using a suitable glassing agent (to prevent diffraction of the X-ray beam). Please note that generally speaking, we do freeze liquids in order to avoid gas / bubble formation during exposure, which may otherwise distort the spectra.

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 a small, but noticeable, beam motion demands highly uniform samples as their homogeneity is directly related to obtained data quality.

You are encouraged to review the general information on sample preparation, the filter method for preparing certain samples (developed by one of our expert users), and our poster on sample homogeneity.

In the documents referred to above, we use XAFSMass for calculating ideal sample mass / thickness for transmission. This program can be downloaded here.

Sample holders

Please see this document for information on sample holders.

Reference metal foils and filter range

The attached metal foils and filters are available for use.

Transport and disposal

Please navigate to the User Information pages to find information on safe transport and handling of samples and the disposal of chemical waste.