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

Sample type	Mounting

Sample type	Mounting
Powder	Powdered samples are typically prepared as rectangular or circular pellets and sealed between Kapton tape.
Liquids	Solutions can be injected into sample plate well that has Kapton tape sealing both sides.
Coin cells	Ex-situ: Can be directly affixed to our sample holders. In-operando: Three coin cell holder with Neware clips. See MEX1 In-operando
Films	Can be directly affixed to our sample holders.
Minerals	Can be directly affixed to our sample holders.
Cryogenic	See MEX1 Cryostat
Microprobe	See MEX1 µProbe (µMEX)

Analysis Mode and Pellet Preparation

There are two ways your data can be collected that is dependent on your sample type: Transmission- or fluorescence mode.

Transmission-mode > 6 keV: for highly concentrated samples that can be diluted

Aim for an edge step of approximately 1. An edge step below 0.3 will not be suitable, especially if you want EXAFS information. We use XAFSmass to estimate the edge step of samples based on their composition.

Read https://asuserwiki.atlassian.net/wiki/x/AYAEbQ on how to use XAFSmass to calculate your sample edge step and total absorption. A modern version of XAFSMass is available from github, pypi and anaconda.
Mix together your sample and inert matrix, such as cellulose, and grind together as homogeneously as possible using a mortar and pestle or ball mill. A ball mill will provide superior homogenity.
Use a hand pellet press to transform your mixture into a pellet (7 mm pellet is 40 mg; 13 mm pellet is 90 mg).
Mount the pressed pellet into a sample holder.

Transmission-mode: light in vs light out X-Ray Absorption Spectroscopy Study of Battery Materials | IntechOpen

Pellet sample mounting examples:

Round 7 or 13 mm pellet sample mounting examples. For low energy edges or cryostat samples, you will need to make a window around your sample. Do not completely cover both sides with tape.

An example of the RT sample holder with 7 mm pellet plates mounted.

Sample holder mount for high throughput transmission only measurements

Fluorescence-mode < 6 keV: for samples inherently low in concentration i.e. <2000 ppm

Transmission-mode samples will provide higher quality EXAFS data. Only prepare samples for fluorescence-mode if they cannot be prepared for transmission-mode

Fluorescence-mode sample mounting examples: Biological, mineral and medicinal samples that you cannot dilute.

Fluorescence-mode. Light in causes your sample to emit photons, i.e fluorescence, which is detected.

How to make a pelleted fluorescence sample: Skip XAFSmass. Instead, dilute your sample to ~1000 ppm in an inert matrix, then follow the same grinding and pelleting procedure for preparing a transmission sample (steps 2-4 above).

Aim to achieve a concentration of approximately 1000 ppm. Exceeding 2000 ppm will increase self-absorption effects. We commonly use cellulose to dilute samples to an appropriate concentration.

We appreciate that guidance on the limits of detection and quantitation at MEX1 would be very useful. Robustly providing this information is a complex task that the beamline team is working on. However, to provide some sense of what is achievable, the Transmission VS Fluorescence spectra below show the Ti (top) and Zn (bottom) XANES measured from ZnTiO₃ at various concentrations.

Fluorescence VS Transmission EXAFS

Fluorescence VS Transmission XANES

Transmission VS Fluorescence XANES spectra for ZnTiO3. Top: Ti K edge. Bottom: Zn K edge. Note: these samples were very homogenous (vide infra).

Equipment required to make a pellet sample

To make sample pellets, you will need the following equipment available in the Chemistry Lab:

For a superior grinding and pellet pressing method the automatic sample mill/grinder and hydraulic press below should be used. Contact the Chemistry Lab technicians as-labs@ansto.gov.au for training.

A balance to weigh out the amount of sample and diluent

A mortar and pestle for grinding up your sample or grinding together your sample and diluent

A hand pellet press with a 7 mm die set to form pellets from your powder samples Operating the PIKE Hand Press

Sample mill/grinder Mixer Mill MM 400 Introduction - Retsch

Hydraulic press to make pellets

Homogeneity

If movement of the sample occurs (e.g. due to vibrations), or when the beam moves over the course of a scan (it moves vertically), you will be measuring different parts of the sample. If the sample is not homogenous, spectra can be detrimentally impacted. Below are spectra from iron oxide in cellulose samples, one prepared simply by mixing, one by grinding in a mortar and pestle for 5 revolutions, and one by grinding in a mortar and pestle for 15 revolution. Clearly the longer grinding produced a more homogeneous sample and optimal spectra.

Please do not take the data in the plot below to suggest that 15 revolutions is a sufficient amount of grinding to prepare a sample for transmission. When using a mortar and pestle 15-30 minutes grinding time is recommended. A superior and less tedious solution is to use a ball mill.

Sample Holders

MEX1 uses sample holders described in the technical drawings below.

The round sample holders can hold samples with 13mm (one hole) or 7mm (two holes) diameters or smaller.

The rectangular sample holders (3 holes) are 6mm x 3mm.

MEX1 Sample Preparation