Introduction to µ-XRF
Hey everyone and welcome to my introduction to micro–X-ray fluoresce spectrometry (µ-XRF). Feel free to ask me questions and let me know what you would like to learn about (I will endavour to address your queries in future posts). In time, I will be covering several analytical techniques, not just µ-XRF, so stay tuned if you are interested.
Please note:
The instrumentation/equipment I talk about in these training blogs is purely what I have access to. There is no financial support or promotion from various companies that I mention.
Also, the procedures I discuss are equipment specific and furthermore laboratory specific. Each lab around the world will run their instrument slightly different, so always get in contact with the technical staff member who runs the instrument that you are interested in to find out how to get access and get trained.
Above is the µ-XRF that I work on to do research, training, and microanalysis.
It is a Bruker M4 Tornado µ-XRF Spectrometer.
Introduction to micro–X-ray Fluoresce spectrometry (µ-XRF)
The µ-XRF is an energy dispersive X-ray spectrometer that can be used for elemental analysis. The strength of the instrument is its ability to study small sample areas and particles. However, we can do this over a relatively large area if needed. You have flexibility to work on highly prepared samples such as thin sections, resin mounts or electron microscope stubs; or you can study whole irregular shaped objects such as fossils, artworks, jewellery for example (if it fits inside the chamber, and is stable under the experimental conditions, we can study the material).
From a safety perspective, the instrument is shielded from ionising radiation, unlike portable handheld systems where you need to be cautious to not harm yourself or others (training and use of handheld systems come under the Environmental Protection Agency (EPA), therefore check up on the rules for your local, state, or federal laws in your country).
The main forms of analysis that we can carry out in the µ-XRF are point analyses, where we look at a single spot, particle or an inclusion on the surface of a sample. We can also carry out elemental distribution analyses along a line scan or on areas through X-ray Mapping.
3D Printed stage to accommodate drill core samples.
Let’s look at the specs of the instrument so that we can start to recognise the possible samples we can study. This µ-XRF has a large vacuum sample chamber which is 600 mm x 350 mm x 260 mm which is a phenomenal amount of space to work with. The sample stage can hold up to 5 kg in weight. The system also allows for the stage to swap in and out. You can either use premade stages which are made by the equipment supplier or make custom stages yourself, like I have done for diamond drill core samples.
In front of the X-ray source is a polycapillary X-ray optic. This creates a 25 µm excitation spot to conduct analysis on small samples and particles which are 25 µm in size or bigger. The system runs a point, multipoint and auto point mode.
The inclusion of a fast and precise XYZ stage, which is controlled through the graphical user interface (GUI), helps with locating and focusing your sample relatively quickly. Focusing on your sample is aided using two optical video modes which include a x10 and a x100 magnification setting as well as image stitching using the mosaic mode in the software for large sample areas.
The use of silicon drift detector (SDD) technology for the energy dispersive spectrometer (EDS) allows you to run your samples at a high count-rate and great spectroscopic resolution. My specific system employs two EDS spectrometers, which enhances the captured solid angle of fluorescence radiation. This means we improve our counting statistics, the detection limit can be lower, and we can capture data faster.
The instrument is controlled via the GUI on the computer, this is used to set up the following parameters for an analysis:
The optical camera, specifically what magnification you would like to run (x10 or x100), sample and chamber illumination, and mosaic stitching of large or multiple samples.
The experiment excitation conditions; we can set up the voltage and current of the rhodium (Rh) X-ray tube, and the use of specific X-ray filters.
Calibration and detector settings, and setting the dwell time for your analysis.
Stage control, to position and mark points of interest.
Inside the u-XRF chamber
The key strength of µ-XRF is that the results can tell us the element distribution in the sample from the captured spectra. The software that comes with the instrument can display the different data types such as spectra for point analysis, X-ray maps, and line profiles.
Quantification of data can be carried via the standardless Fundamental-Parameter method for homogeneous samples (we will dive into this later). The instrument also allows for the quantification of layer systems based on Fundamental-Parameter method too. From this quick overview of the system, we can demonstrate several sample types and applications for which this instrument can be used.
Below are a few quick examples of samples and analyses that take place in our µ-XRF:
