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 to be 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 more flexible in terms of mounting positions. 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.

Important online forms (like those for ESRA or lab-booking) need connection to MAX IV using a VPN. Please find more information in the IT Services page.

6-8 weeks before beamtime:
  • Start planning early: Get in touch with your local contact early if it is your first time at Balder. In the email from MAX IV user-office, it will be specified about who is your LC. For complex experiments it is recommended to have a (virtual) planning meeting. 
  • In-situ equipment, gases: If the experiment involves in-situ equipment, specialized sample delivery systems or hazardous chemicals, complete the ESRA and/or get in touch with the experimental safety team well ahead of the experiment if there are questions. The LC can answer specific questions concerning the layout of equipment at the beamline and provide tips based on experience. Inert gases (N2, Ar, He) are available at the beamline as standard. Toxic, flammable, special gases including mixtures are procured by MAX IV on a case-by-case basis. Delivery times can vary and hence, it is essential to complete the ESRA early in case of complex experiments. The policy regarding expenditure and invoicing is updated here. Please note that the gas mixing system at Balder will not be available for general users at least until mid-2027.
  • Chemicals, sample holders: Ordering chemicals/reagents, capillaries or specialized sample holders from external suppliers. Delivery times can be surprisingly long. Ask your LC if the beamline has all necessary supplies in stock and figure out who procures the missing supplies.
  • Specialized adapters, mounts etc: Ordering adapters/mounts for user sample environment (if designed/ordered at MAX IV).
  • Borrowing/reserving equipment: The beamline has a collection of standard equipment listed here. Reserving space in the common chemical/bio labs and borrowing equipment from the MAX IV equipment pool is done via the iLab system. More information on the support labs page.
  • Note: It might not be permitted to handle some chemicals or gases in certain ways. If you are unsure, contact experimental safety team to discuss possible ways forward. 
2-4 weeks before beamtime:
  • Samples: Register all samples in DUO and ESRA (make it exhaustive, include all standards/ex-situ references you would like to measure (including plan B samples)) 
  • ESRA, gases, engineering support: Make sure the ESRA is approved – for experiments involving hazardous substances, the experimental team sometimes organizes a virtual meeting before doing so. If your experiment needs any engineering support from MAX IV or needs delivery of reactive gases, make sure to specify this in ESRA. These requests are handled by safety and engineering teams and typically needs at least 4 weeks to schedule and to ensure support. Please note that your LC cannot view the ESRA form until it is approved, so anything that needs to be organized at the beamline should be communicated to the LC separately.
  • Beamtime plan: This is especially important if the beamtime involves multiple absorption edges which need complete realignment of the beamline or other activities like changing setups which needs support not available during evenings/weekends.   
  • Lab access and training: Make sure lab access and training is scheduled based on arrival time of participants. This is especially important for beamtimes that happen during weekends.
  • Pre-beamtime tests: Discuss with LC possibilities for setting up equipment or performing offline tests in the lab before the official start of beamtime. Mondays are machine days and hence, access to Balder experimental hutch may be possible on Monday nights (not guaranteed, please discuss with LC). It is also possible to use chemistry labs at MAX IV a few days before/after the beamtime for sample preparation or offline-analysis purposes.
3-5 days before beamtime:
  • User information: Please review the beamline-specific user information. An overview of the experiment control system interface and some standard data handling protocols can be found here. Modern beamlines have complex interfaces that can be overwhelming to some users, and some degree of familiarization is strongly recommended.
  • 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). For experiments involving hazardous samples and user-supplied equipment, it is also a safety requirement that all team members are aware of potential risks and mitigation strategies.
  • 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 facility during the days and also to data files during/after beamtime. 
  • Shift plan for personnel: For multi-day beamtimes, it is mandatory that all 24 hours are used for measurements. For experiments classified under safety categories yellow and red, there is a requirement for round-the-clock physical monitoring at the beamline. Experimental safety team will inform you of what is relevant for your beamtime.
  • Tip: The control system and many in-house developed analysis tools at Balder are built using Python. Though not a strict requirement, we increasingly notice that users familiar with  python coding have an advantage during/after beamtime.
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, filters used for the fluorescence measurements and other beamline settings). Some essential parameters (like position of certain motors, temperature of in-situ cells etc) may not be logged in data files as standard and would need to be configured. Make sure your LC does this at the beginning of the beamtime.
  • Get software ready for data viewing/treatment (ask LC for suitable programs). This is especially important for in-situ/operando experiments where live plotting is not suitable to view trends over time.
  • 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

 

This information has been moved here.