Transmission XAS

Transmission is the most common and straightforward method to measure X-ray absorption spectra. For good data quality, it is recommended to have –

    • Total optical thickness µd~2.5. It can be twice less or twice more with some loss in S/N of ~30%.

    • Absorption step at the relevant absorption edge of Δµd>0.1. Note that absorption step is not an optimization parameter; a thicker sample would give a bigger Δµd but the total µd would also become big and non-optimal. If Δµd happens too small, one should consider going to fluorescence detection.

    • Sample homogeneous down to a length scale of an absorption length.
XAFSmass

A useful tool to calculate absorption lengths is XAFSmass. A windows executable with associated documentation is available here. The user manual for a more recent Qt implementation is found here. The recent Qt version itself is on GitHub and PyPI.

 

X-ray Fluorescence

In cases where transmission measurements are not possible (eg. thick substrates, light elements of interest in heavy matrices, low concentrations, geometrical constraints of sample environments etc.), we use X-ray fluorescence technique to measure XAFS. The physical location of the energy dispersive 7-element fluorescence detectors (SDD and Ge) is fixed 90 degree to the beam (sample in 45 degree), while the TFY detector (PIPS) is free to mount. While it is possible to combine them with all of the existing sample environments at the beamline, discuss with beamline staff to check if they can be combined with a user-developed sample environment.

The primary guidelines for the usage of MAX IV facilities is given here. This checklist only provides some supplementary information specific to users involved of the Balder beamline. Some parts may be relevant to only a subset of experiments.

8-12 weeks before beamtime:
  • Get in touch with your local contact. You received an email from MAX IV user-office about who is your LC when the proposal was scheduled. For complex experiments start with a (virtual) planning meeting. 
  • Ordering gases for your beamtime (if needed) (LC will do this for you, follow up periodically) 
  • Ordering chemicals/reagents, capillaries or specialized sample holders from external suppliers. Delivery times can be surprisingly long. 
  • Ordering adapters/mounts for user sample environment (if designed/ordered at MAX IV) 
  • Borrowing equipment from the MAX IV equipment pool (LC does this) 
  • Note: It might not be permitted to handle some chemicals or gases in certain ways. If you are unsure, contact experimental safety to discuss possible ways forward. 
4-6 weeks before beamtime:
  • Samples in DUO (make it exhaustive, include all standards/ex-situ references you would like to measure (including plan B samples)) 
  • ESRA – discuss with LC in case of doubts regarding possible risks/mitigation 
  • Talk about a global experiment plan with LC. 
  • Discuss need for any special cables, adapters, sample holders or 3D printed parts. 
  • Book chemical/bio labs, organize lab introduction/training before beamtime with the lab manager or specified contact-person 
  • Discuss with LC possibilities for setting up in-situ equipment earlier than the official start of beamtime. This is usually possible for beamtimes starting on Tuesdays). This helps plan your travel. 
3-5 days before beamtime:
  • Please review the beamline-specific user information.
  • Organize a team meeting. Ensure all team members are aware of the basics of the experiment, the samples that are being measured, basics of the measurement technique (XAS/XES/XRF). 
  • Register team members in DUO experiment session (to be done by proposer/PI or designated person). Only the users added to a session will have access to the data files. 
  • Create tentative shift plan for personnel (this is important to run experiments round the clock) 
  • Samples and ESRA are approved (if unsure, contact LC or safety team) 
Before start of beamtime:
  • Get introduction to the beamline, preparation lab(s), glove-box or other equipment (if needed) 
  • Create user directories for your session (LC does this). Decide on a naming convention and strategy (when to start a new file etc). 
  • Decide on how you keep experimental logs (MAXIV Elogy or another system) and make sure necessary beamline settings/conditions which are not available in data files are recorded there (like beam size, ion-chamber fillings, other beamline settings) 
  • Get software ready for data viewing/treatment (ask LC for suitable programs)
  • Find out from LC where to find additional beamline documentation specific to the experiment and general troubleshooting guides in print and electronic form (Elogy/Wiki). 
During beamtime:
  • Create a log of changes to beamline settings during your session like changes to detectors, acquisition parameters, sample environment etc. Be aware that some parameters are not stored in data files. It is recommended to use the MAX IV Elogy system to keep measurement logs including screenshots of live data, beamline settings etc. Your LC would create a page for your session and explain how to use this.  
  • Keep track of consumables used: capillaries, special sample holders, chemicals etc and keep LC updated if anything is in short supply 
  • Write down any issues with beamline control system or equipment. Pictorial logs and screenshots are strongly recommended to be documented in Elogy.
After beamtime:
  • Copied data, analysis scripts (if needed), electronic logs (Elogy etc.) 
  • Collected all samples and user equipment 
  • Waste sorted and labelled, handed over to LC 
  • Expt. hutch left clean, equipment/tools back in place

 

  • Samples: Include a comprehensive description of the sample – physical form, solvent/matrix/support, sample environment. This lets the reviewers estimate the X-ray transmission and edge jump at the relevant absorption edges and the suitability of the sample for transmission/fluorescence measurements.
  • Equipment: Include a schematic diagram of any in-house designed equipment you intend to bring to the experiment. For experiments involving gases, we are currently unable to provide mass flow controllers or a mass spectrometer (updated 20240821). Users need to organize these and be able to ship them to MAX IV if granted beamtime.
  • Experimental chemicals/gases/standards: In addition to the samples, add in DUO an exhaustive list of standards, chemicals and gases needed for in-situ experiments and on-site sample preparation (if applicable).
  • Time estimate: Transmission XAS measurements typically take between 1s (for XANES) and 10 s (for EXAFS) for good samples with optimal transmission. Energy changes within 2-3 keV range can sometimes be made automatic and takes less than a second (depending on the energy region and data quality needed). Sample changes in the cryostat typically need about 10 minutes + 5 min to reach set temperature. For in-situ measurements, switching between XAS and XRD is also automatic and takes less than a second. Large changes in energy might involve changing optical elements or monochromator crystals and need refilling of gases in ionization chambers – this typically is done by the beamline staff during office hours and requires 30-60 minutes.
  • XRD is only offered to XAS users as a complimentary technique for measurements which cannot be performed ex-situ.
  • Feasibility studies: If unsure whether a certain sample or a custom-built cell can be used for measurements at Balder, users can apply for a beamtime for feasibility check in the Fast Access mode. Contact beamline staff to discuss this possibility.
  • Ex-situ samples: If samples are all ex-situ and can be measured within 1-2 shifts (max. 8 hrs), Fast Access beamtime can be requested. Contact beamline staff to check whether this could be an option for you.