As described in Appendix 1: Merit Process of the Australian Synchrotron Access Model document, proposals for Merit Access to beamtime at the Australian Synchrotron undergo two reviews:

• peer review by external scientific reviewers, ranked according to criteria outlined here,

• technical feasibility review by beamline staff on a pass/fail basis.

This page provides guidelines to help users in developing technically feasible proposals for beamtime at the MEX1 and MEX2 beamlines.

Background

Each beamline receives a large number of proposals for beamtime each round, resulting in a large number of proposals for beamline staff to review. To make this process efficient, when conducting technical feasibility reviews, beamline staff focus almost all their attention on the Proposed Experiment section of the proposal. Thus, a successful proposal must include in this section all information necessary for the team to assess technical feasibility. The lack of a commonly accepted standard for the information required for technical feasibility assessment prompted the XAS beamline to develop and then MEX beamlines to adopt the sample table as a way for proposals to efficiently communicate the relevant technical details of their proposed experiment in a standardised way. Thus, it is a requirement that all proposals include a sample table conforming to the requirements outlined here.

Submitting to the correct beamline

Every round, the MEX beamline team marks perfectly good proposals as infeasible because they were submitted to the wrong beamline. Before starting a proposal you must be sure you understand which beamline is appropriate for your proposal. First, familiarise yourself with the x-ray absorption spectroscopy technique. Some straightforward ways to determine which beamline is appropriate are:

• researching the beamlines on the ANSTO website and the Australian Synchrotron User wiki

• talking to other experienced users of the Australian Synchrotron

• contacting the beamline team

As x-ray absorption spectroscopy is an element specific technique, your element(s) of interest and the energy range accessible at a beamline will be the main factors determining to which beamline you submit your proposal. The energy ranges covered by x-ray absorption spectroscopy beamlines at the Australian Synchrotron are provided in the table below:

You can determine the energies of the edges you wish to investigate by inspecting the periodic tables presented here.

See this handy flowchart for a method to choose amongst MEX1, MEX2 and XAS.

The Proposed Experiment section

The Proposed Experiment section is the place for you to describe the activities and measurements you intend to perform at the beamline. It comprises two equally important, necessary sections: the text and the sample table (see next section). The proposed experiment section is not an extension of the ‘Scientific Purpose’ or ‘National Benefit’ sections.

The Proposed Experiment text

The text of the Proposed Experiment section should give the reviewers and beamline team a sense of the experiment you intend to perform during your beamtime. The text, combined with the information presented in the sample table should demonstrate to the reviewers and beamline team that you have considered how best to prepare your samples for measurement, and have planned to use your beamtime efficiently. The text of the Proposed Experiment section should comprise several paragraphs describing your intended measurements, including information the nature of the samples you will be measuring, how they will be presented to the beam, the edges you intend to measure, etc.

Some examples of things to include in the text of the Proposed Experiment section (if relevant to your samples):

• A brief description of your samples. Description of the samples should be restricted to information that is relevant to the measurements and other activities performed on-site. For instance, the Proposed Experiment section is not the place for a description of how you synthesised your sample material, although you should describe the form of the sample when it is presented to the beam. If you are modifying your material for measurement, e.g. homogenisation by grinding, diluting with cellulose or boron nitride, pressing into a pellet you should detail that in the experiment section. If you are preparing your samples on-site in the chemistry lab, mention that in this section.

• If you are presenting your samples undiluted you can detail how you know the abundance of the element of interest, e.g. previous bulk analysis by XRF or ICP-MS, quantification via EPMA or SEM EDS.

• A justification of the energy range of your scans

• A request for a particular DCM crystal based on inspection of the MEX1 DCM glitch maps

• If you are planning on measuring particular samples as model compounds for linear combination fitting, you can explicitly mention that in this section, as it will help the reviewers assess if they are appropriate for your unknowns.

• The composition of the sample beyond the element of interest is important information, as is the presence of other elements in the sample have edges or fluorescence lines that interfere with the element of interest. For example, measuring fluorescence mode EXAFS of 5 ppm Co in soil with 30 wt% Fe₂O₃ is unlikely to produce publishable-quality results due to the overwhelming fluorescence from the Fe K emission lines. Similarly, it is not possible to measure Ni K-edge (8333 eV) EXAFS to k=16 in a Ni-Gd alloy as the Gd L1 edge (8376 eV) will contaminate the Ni EXAFS. It is important that you consider possible interference from other elements when designing your experiment. If you are aware of the presence of interfering elements in your samples, use this section to describe how you will mitigate the interference.

• If you do not know the composition of your samples, use this section to describe the strategy you will employ to measure samples of the appropriate concentration for x-ray absorption spectroscopy using your chosen analysis mode. The modes available at MEX1 are fluorescence or transmission. The modes available at MEX2 are fluorescence or drain current.

• If you are unable to homogenise your sample (e.g. grinding will destroy fundamental features of your sample), use this section to describe how the form of the sample may impact the quality of data you will collect (e.g. pinholes, grain size much greater than 1 absorption length) and any mitigation strategies you propose to employ.

• If you know your samples will exhibit significant over-absorption (a.k.a self-absorption), detail the methods you will use to correct over absorption, e.g. correlation with transmission or drain current, correction algorithms, grazing exit geometry.

• If you are intending to perform radiation hardness/beam damage testing, detail your approach in this section.

If you think your samples may possess characteristics that will make measurement difficult, but are unsure how to proceed, contact the beamline team for advice.

Example Proposed Experiment text

We propose to record Lu L3-edge XANES spectra of 34 samples of Na₂O-B₂O₃-SiO₂ glass doped with ~2000 ppm Lu. To determine the relationship between oxygen fugacity and Lu speciation, we have synthesised the glasses over 16 log units of oxygen fugacity at a constant temperature of 1400 ˚C, predicted to cover the entire Lu³⁺ to Lu⁴⁺ transition. The samples comprise glass beads cast in 13 mm discs, that have been sectioned and polished. The Lu content of all samples has been confirmed via LA-ICP-MS. A Lu content of ~2000 ppm is sufficiently low to avoid over-absorption effects. Samples will be presented to the beam for fluorescence mode measurement in the fluorescence RT box (FRT) a custom 3d-printed sample holder designed with input from beamline staff and employed in previous MEX1 experiments.

As reference materials we will prepare Lu₂O₃, LuO₂, Lu₂Si3O9, LuPO₄ as 13 mm pellets, diluted with cellulose to a nominal Lu concentration of 2000 ppm.

All samples and reference materials will be prepared off-site at our home institution and brought to site as either polished mounts or pellets sealed into MEX standard sample holders using kapton tape.

Beam induced changes in Lu oxidation state will be investigated by monitoring the Lu3+ white line as a function of time on a previously unexposed portion of a sample.

The Sample Table

The sample table is the heart of the Proposed Experiment section of the proposal. The importance of the sample table is that it avoids repetitive text by efficiently condensing all the following information into common format:

• the element and absorption edge you wish to analyse

• the number of samples you wish to analyse

• the analysis mode used to collect x-ray absorption spectroscopy data

• parameters related to the composition of your samples

  • the concentration/abundance of the element of interest in your sample if you are measuring in fluorescence or drain current

  • an edge step and total absorption if you are measuring in transmission

• the physical form of your samples

• the sample environment to be used for measurements

• the energy range you wish to scan

• for how long you will analyse each sample

• the number of repeat scans per sample

• the time devoted to activities such as radiation hardness testing and beamline setup

• the time budget for your entire beamtime

Column descriptions

Sample

A simple description of your sample. In this column each row represents a specific object, or group of similar objects that will be presented to the x-ray beam for measurement. For example, rows of the table could represent (but certainly not limited to):

• a pressed pellet of a model compound;

• an aliquot of solution;

• a series pellets where the treatment of the sample has been varied systematically;

• ex-situ electrodes representing various states of charge or a range of charge-discharge cycles;

• a series of liquids that form a concentration series;

• soil samples collected from a range of locations;

Avoid using discipline specific acronyms in the description of your sample unless you have defined them previously in the text of the Proposed Experiment section. Whilst everyone in your particular scientific sub-discipline might know what the acronyms mean, you cannot assume all reviewers or the beamline team will know.

Sample form

A brief description of the form of your sample. Examples include:

• 7 mm pellet

• 13 mm pellet

• 6 x 3 mm pellet

• powder spread on carbon tape

• liquid

At this stage liquid phase measurements at either MEX1 or MEX2 are to be discussed with the beamline scientists prior to submitting a proposal.

• MEX2 is yet to have a suitable cell for liquid measurements. Please note 25-micron Kapton film and Kapton tape strongly attenuates the X-ray beam at the S and P edges. ≤ 8-micron film is required.

Edge

The element and absorption edge you wish to investigate. Ensure the edge is within the energy range accessible by the beamline to which you are applying. See the table above for energy ranges of XAFS beamlines at the Australian Synchrotron.

Analysis mode

The measurement mode you wish to employ.

• MEX1 measurement modes:

  • F (fluorescence)

    • Fluorescence at MEX1 is available in both the cryostat and room temperature environments;

  • T (transmission)

    • Transmission at MEX1 is available in both the cryostat and room temperature environments;

  • You can use both modes during an experiment. You can even measure both transmission and fluorescence at the same time if your sample is suitable.

• MEX2 measurement modes:

  • F (fluorescence)

    • Fluorescence at MEX2 can be performed under vacuum or in helium atmosphere;

  • D (drain current)

    • Drain current analysis can only be performed under vacuum. Drain current is not compatible with helium atmosphere

    • The sample must have some degree of conductivity. If your samples are likely to be electrically insulating, please contact the beamline scientists.

  • You can use both modes during an experiment. You can even measure both drain current and fluorescence at the same time if your sample is suitable.

The measurement mode dictates what information you will report in the concentration column.

Concentration

For successful x-ray absorption measurements, it is vital you know the composition of your sample. This column, called "concentration" for brevity, reports parameters related to the composition of your sample that help communicate its suitability for the chosen analysis mode. The parameters presented in the “concentration” column of sample table depends on the analysis mode you wish you use. Note that only permissible concentration units are those listed below:

• Fluorescence - express the concentration of the element of interest in the sample as presented to the beam in one of the following units:

  • weight percent

  • part per million (ppm) by weight

  • millimolal (liquid samples only)

  • samples measured in fluorescence are susceptible to over-absorption (also referred to as self-absorption). Good fluorescence samples have 2000 ppm or less of the element of interest. If your samples have weight percent abundance, you will have to dilute them, or develop a strategy for correcting for over-absorption. This strategy should be discussed in the text of the proposed experiment section.

  • It is important that this column reports the concentration of the sample as presented to the beam, i.e. the concentration after any dilution

• Transmission

  • edge step (Δμd) and total absorption (μ_Td). It is insufficient to report only one of the two.

  • it is vital you understand the composition of your sample, and the properties that make a good transmission sample. See this comprehensive guide for how to calculate the appropriate dilution for transmission samples in pellet form.

• Drain current - express the concentration of the element of interest in one of the following units:

  • weight percent

  • part per million (ppm) by weight

  • Detection limit of 1 atomic % (e.g. 1 S atom in a matrix of 99 other atoms XANES is possible)

  • At concentrations > 1 atomic %, drain current is advantageous as it is a surface measurement, where the drain current signal is collected from a layer within 10 nm of the surface of the sample, thus eliminating over adsorption.

We stress that the concentration you report is the concentration of the sample as presented for analysis. If you are diluting your sample for analysis report the concentration after dilution, not the concentration of the element in the material prior to dilution.

K max

This column reports the energy of the end of your scan expressed in wavenumber, k. The definition of wavenumber can be found here, and a table of conversions between electron volts (eV) above the edge and wavenumber is provided below. e.g. a scan of the Cu K-edge to kmax = 20 would result in a maximum energy of 10503 eV (8979 eV + 1524 eV; where the energy of the Cu K-edge is 8979 eV). This value is helpful for the beamline team to assess your time estimates, and check if you will experience contamination of your EXAFS by the absorption edge of another element in your sample, though you should certainly try and check this yourself before submitting your proposal, as you will have the most information available to you regarding the composition of your sample. If you are only interested in collecting XANES data, it is sufficient to report “XANES only”.

You can calculate k using the expression below:

where E is the energy at the end of the scan, E0 is the energy of the absorption edge of interest, m is the electron mass, and h is Planck's constant.

Using the Gd L3 edge as an example, Gd L3 occurs at 7243 eV, and the Gd L2 edge occurs at 7930 eV. If you wanted to scan across the Gd L3 edge but end your scan at the Gd L2 edge the calculation would be as follows:

Where E is 7930 eV (the energy of the Gd L2 edge) and E0 is the energy of the Gd L3 edge (7243 eV). The difference between these energies is 687 eV, and the calculation above tells us that 687 eV corresponds to a wavenumber of 13.4 inverse angstroms, otherwise referred to as k=13.4.

k to eV conversion table

Environment

The sample environment you wish to use.

For MEX1:

• RT (room temperature)

• Cryo (top loading cryostat). You can employ both RT and cyro environments in the same experiment. There will be some time consumed to change between RT and cryo.

• Microprobe

For MEX2:

• vacuum

• helium

Scan time

The duration of a single scan, expressed in hours.

Number of scans

The number of scans you wish to perform per sample. If your row represents a collection of similar samples, you can represent this as number of samples x number of scans = total scans; i.e. if you have a concentration series of 10 samples, each of which you would like to perform 3 repeats, you would enter 10 x 3 = 30.

Total

The sum of the duration of a single scan, multiplied by any repeats.

Other activities

Use this row to add time dedicated to activities such as (but not restricted to):

• beamline setup (the MEX beamline team recommends 4-6 hours as a good estimate)

• radiation hardness/beam damage testing testing

Total time requested

The sum of the total time for each sample, plus the times for other activities. Beamtime is awarded in 24 hour blocks, and there are three 8-hour shifts per 24 hours. Report total time requested in hours, and the number of shifts in brackets, rounded to the nearest 3 shifts:

e.g. 46.5 hours (6 shifts)

Example sample tables

Use the tables below as inspiration for your own sample table. You can copy and paste one of the tables below into your proposal and modify it to suit your experiment.

MEX1 transmission samples examples

MEX1 fluorescence sample examples

MEX1 simultaneous fluorescence and transmission sample examples

MEX1 Microprobe sample table example (click here for more information)

MEX2 sample table example

FAQ

What is the difference between sample table and sample spreadsheet?

The sample spreadsheet and sample table are two different things:

• The sample spreadsheet is an excel sheet you download from the portal in fill in with the hazard/safety-related information regarding all chemicals you will use whilst on site

• The sample table is part of the Proposed Experiment section of the proposal that communicates information relevant to x-ray absorption spectroscopy measurements of your samples

Can I measure in fluorescence and transmission modes in the same beamtime at MEX1?

Yes! If you want to use both techniques during your experiment, we will usually configure the beamline to use the fluorescence room temperature (FRT) box.

Can I use the cryostat and RT environment in the same beamtime at MEX1?

Yes, but some beamtime will be consumed changing to/from the cryostat.

Can I measure a sample fluorescence and transmission at the same time at MEX1?

Yes! Though it is often tricky to make a sample with both a reasonable edge step AND a concentration of the element of interest low enough to avoid self-absorption.

When creating your sample table, you must report the concentration values relevant to both the transmission and fluorescence measurements, i.e. edge-step, total absorption and concentration (wt.%, ppm or mM). See the "MEX1 simultaneous fluorescence and transmission sample examples"

Can I measure fluorescence and drain current modes in the same beamtime at MEX2?

Yes!

Can I measure a sample fluorescence and drain current at the same time at MEX2?

Yes, but only in vacuum.

Can I measure in a vacuum and helium atmosphere in the same beamtime at MEX2?

Yes, but the beamline can accommodate only one change of atmosphere per day.

How do I include a sample table in my proposal?

There are two ways a table can be included in a proposal:

• as a table in the text of the “Proposed Experiment” section (this is by far the preferred method of the beamline team)

• attached to the proposal as a figure. This will not consume your word count.

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