FEBRUARY 26, 2025

CHTP 2024 Image of the Year Contest Winner

Akash Gondaliya with his supervisor, Dr. Johan Foster, outside the CHTP lab.

Congratulations to the 2024 CHTP Image of the Year contest winner, Akash Gondaliya! Akash’s false-coloured micrograph of wood with iron particles received the most votes from our users. Akash acquired the image using the Hitachi SU-3500 SEM. A print of the image is displayed on the wall outside the CHTP.

Akash Gondaliya is a PhD student researcher with Foster Research Group. For more information on his research, please see the article provided by Akash below.

Turning Wood Into a Magnetic Shield

SEM micrograph of a wood surface with α-Fe crystals, acquired by Akash Gondaliya with the Hitachi SU-3500 SEM.

Ever feel like we're drowning in invisible waves from all our gadgets? From smartphones to Wi-Fi routers, electromagnetic interference (EMI) is everywhere, causing concerns about health and messing with our tech. Typically, we rely on metals and plastics to block these waves, but these materials are expensive and far from eco-friendly as they require high-energy manufacturing processes and emit a large amount of greenhouse gases (GHGs).

To tackle this challenge, we synthesized a futuristic material made from...wood! Using a green process, we transformed ordinary wood into a magnetic, conductive material, creating tiny magnetic particles within the wood, enhancing its properties to effectively block EMI.

This material proved it could stand tall among traditional materials, making it perfect for protecting our devices, homes and even packaging—all while being lightweight, affordable and sustainable. It's a glimpse into a greener, smarter future. Who knew wood could outsmart metal?

FEI Helios NanoLab 650 FIB-SEM EDX Status Update

As mentioned in a previous newsletter, the EDX system on the FEI Helios NanoLab 650 FIB-SEM is down due to a hardware failure. The detector requires significant repair, which means that a return to active use is not imminent. All EDX analyses will need to be carried out on the Hitachi SU-3500 SEM for the foreseeable future. CHTP users requiring EDX analysis are encouraged to either seek training on the Hitachi system or look for alternate forms of analysis.

Is EDX the right tool for you?

Would you like to do a chemical analysis of your material? It is generally quick and simple to acquire data with EDX. But this means it often gets used for analyses that aren’t always optimal. In the worst-case scenario, the data obtained from the EDX could result in erroneous conclusions being drawn. Before deciding that EDX is the correct analysis choice, let’s review what information it can provide and how it works.

What information can EDX provide and how does it do this?

EDX is an acronym for energy dispersive X-ray analysis; it is an analysis technique in which X-rays are counted as a function of their energy. These X-rays are created as a result of a material being irradiated by the electron beam in a SEM (or TEM). There are two types of X-ray signals detected by an EDX detector: Bremsstrahlung X-rays and characteristic X-rays. The former make up the background signal in an EDX spectrum while the latter have very specific energies and cause the peaks in an X-ray spectrum. These characteristic X-rays are used to identify elements present in the material.

Figure 1: Example EDX Spectrum.

To explain how characteristic X-rays are produced, we will need to consider how the electrons from the electron beam interact with the atoms in a sample using a simplified core-shell atomic model, i.e., electrons sit in shells around a nucleus core. In this model, the electrons occupying the outer shells are less tightly bound and thus have the highest energy. The electrons occupying the innermost shell are tightly bound and have the lowest energy. The X-ray emission process is initiated when an electron from the incident beam of the SEM collides with an atom, causing an electron from the shell to be ejected. To return the atom to its lowest energy state, an electron from a higher-energy shell will drop down to the lower-energy shell to fill the vacancy created in the lower-energy shell, emitting an X-ray of energy equal to the energy difference between the two shells in the process. Thus, this X-ray has a characteristic energy specific to the difference between the originating electron shell and the electron shell to which the electron transitions. It’s because of this characteristic energy that these X-rays are useful. By identifying the energies at which X-ray count peaks occur in an EDX spectrum, the elements present in the EDX analysis area may be determined. The atomic composition of the analysis volume may be computed quantitatively from the spectral data. In addition, elemental mapping may be performed by scanning the incident electron beam over an area while acquiring X-ray spectra at each spot.

Figure 2: Example EDX Element Map.

What are the limitations of EDX? 

In principle, elemental analysis/mapping of a material with the spatial resolution of an SEM is an extremely useful tool. In practice, the following limitations should be considered: 

Size of analysis volume/resolution 

The volume from which an X-ray signal can escape the sample material is larger than that of secondary and backscattered electrons. Consequently, the spatial resolution of the X-ray signal is inherently less than that of the image. Consider the escape depths of each signal. Secondary electrons can typically escape from within the top ~100 nm of the sample while backscattered electrons can escape from deeper within the sample. The escape depth from which characteristic X-rays can escape from the sample is much larger, encompassing the full interaction volume of the beam with the sample (simulated in Figure 3).

Figure 3: Monte Carlo simulation of electron trajectories in aluminum with 10 kV accelerating voltage.

Consequently, for the same electron beam energy, the volume from which characteristic X-rays may originate is larger than the volume from which secondary and backscattered electrons, which make up the image, originate. Therefore, the spatial resolution of the X-ray map will always be worse than the resolution of the image. It is good practice to run a simulation, such as that shown in Figure 3, in advance of an EDX elemental map to give a better idea of what pixel size to use for the map (chosen based on simulated electron beam interaction volume). Such a simulation can be done using the freely available Win X-Ray software. 

Quantification accuracy 

Quantification using EDX is less accurate than new users typically assume. In the best-case scenario using quantification standards with a sample that is atomically flat, completely homogenous and defect-free, one might expect a quantification accuracy to ~0.1 atomic percent. In practice this is almost never the case. Standard-based analysis is time-consuming, expensive and, consequently, rarely done. The vast majority of EDX analysis quantification is standard-less quantification and significantly less accurate. Also, the sample surface is not going to be as flat or as homogenous as in the ideal case. Expectations should be set with this in mind, and one could reasonably expect accuracy within a few atomic percent on a decent-quality sample. 

Sensitivity/detection limits 

There is insufficient X-ray signal from elements in low concentrations to be detected using EDX analysis. This is especially true for lighter elements. Lithium, for example, can’t be detected in most EDX detectors due to the characteristic X-rays from lithium being so low energy that they are attenuated by the window in front of the EDX detector. Most detectors will have a sensitivity of ~0.1 atomic percent, so trace element analysis isn’t an option. 

Materials sensitive to EDX electron beam conditions 

Not all samples can withstand the beam conditions necessary for prolonged EDX analysis or, in some cases, even short EDX analysis. Specifically, polymers and biological samples tend to be challenging at best to analyze and impossible at worst. Polymer surfaces can be destroyed in seconds. This beam sensitivity coupled with the lack of spatial resolution and low X-ray yield makes this technique not recommended for polymers. Beam sensitivity is not just limited to organic samples. For example, some lithium battery materials can be very sensitive to electron beam irradiation, and even imaging in mild conditions can cause problems. If you’re unsure whether your material is suitable for EDX, please consult with CHTP staff.  

Is EDX a bulk analysis or a surface analysis? 

EDX is neither considered a bulk analysis nor a surface analysis owing to the size of the analysis volume. The analysis volume is too large for a surface analysis and not large enough to sample enough material to be a statistically representative bulk analysis. For compositional analyses of materials without any surface coatings, EDX can provide a quick, non-destructive analysis to give a reasonable estimate in many cases. 

What if I would like to analyze a surface/coating with EDX? 

Surface analysis applications of EDX are quite limited. EDX can be useful for determining the area coverage of a coating, assuming there is a sufficient X-ray signal from the coating (depending on the thickness of the coating). In some cases, the thickness of surface oxides/coatings may be estimated by acquiring EDX spectra at different electron beam accelerating voltages and comparing them with simulated spectra. In general, EDX is largely inadequate for surface analyses. The analysis volume is too large to be representative of a surface and the sensitivity is not high enough to detect monolayers/surface layers of only a few nanometers. For this kind of analysis, X-ray photoelectron spectroscopy (XPS)/auger electron spectroscopy (AES) is recommended. 

Corporate Sponsors

The CHTP is grateful to the following corporate sponsors for their significant in-kind Canada Foundation for Innovation support:

We acknowledge that the UBC Vancouver campus is situated on the traditional, ancestral, and unceded territory of the xʷməθkʷəy̓əm (Musqueam).