The Department of Materials Engineering at the Faculty of Mechanical Engineering of the University of Žilina (UNIZA) is one of Slovakia’s leading centres for materials research. Its history in electron microscopy dates back to 1966. Today, under the leadership of Prof. Peter Palček, Ph.D., the department combines decades of experience with state-of-the-art instrumentation, recently expanded with a Tescan MIRA XR system. “A material carries a record of everything that has happened to it. Our task is to read that story - with the help of electrons,” says Prof. Palček in this interview.
Our experience with electron microscopy is indeed extensive and began in 1966 with the acquisition of our first transmission electron microscope (TEM). It was a Tesla Brno BS 513 instrument with an accelerating voltage of 100 kV. We still keep this microscope today as a historical artefact and an educational tool for students.
A major step forward came in 1980, when we purchased a scanning electron microscope, also manufactured by Tesla Brno, specifically the BS 350 model. For its time, it was an advanced ultra-high-vacuum system with a field-emission gun (FEG), offering high resolution.
After 1990, we naturally continued our collaboration with Tesla’s successor company, Tescan. We used one of their early models, informally known as “Perla”, with which we experienced the evolution from analogue photography of screen images, through video printers, all the way to digital interfaces. This was followed by a long and reliable era of the Tescan VEGA system, which is still in operation at our department today.
When selecting the new system, we were looking for the optimal intersection of resolution, equipment versatility, and the available budget. The MIRA XR model was chosen within our financial limits for its higher resolution and its ability to work at much higher magnifications compared with the VEGA. The two systems therefore, complement each other, and our research capacity has been significantly expanded.
Installation took place around the turn of December and January. We gradually added extensions to the system; after the initial training, the spectrometer was installed, and minor technical details related to the compressor were resolved. The instrument is now fully fine-tuned and used for more advanced research tasks as well as for teaching.
We have divided the capacity according to the complexity of the tasks. The Tescan VEGA serves as a robust tool for bachelor’s and master’s students, who use it to learn the basics of microscopy and perform routine analyses. The MIRA XR is dedicated to more detailed scientific work and doctoral research.
One of the enormous benefits of modern systems, like MIRA XR, is their efficiency. With older ultra-high-vacuum instruments, changing a sample could take up to two hours. Today, we can exchange samples and begin analysis within three to five minutes. The digital environment also enables simultaneous imaging from multiple detectors - secondary and backscattered electrons - as well as signal addition or subtraction and precise navigation to saved sample positions. The benefit of the MIRA XR electron microscope is therefore not only its higher resolution, but also the significant acceleration of our work. And that is an equally important advance.
We analyse a broad spectrum of materials, from light metals such as calcium and magnesium to precious metals. The key area, however, is the analysis of structure, degradation and changes in properties. We observe structural changes, inclusions, precipitates and phase composition.
Fractography - the study of fracture surfaces - plays a dominant role. Under the microscope, we can precisely distinguish between overload fractures, fatigue fractures, creep fractures, and fractures caused by a combination of corrosion and mechanical loading. Fatigue fractures in particular carry a unique record: so-called beach marks, which correlate with cyclic loading of the material in real operation. It is fascinating when you realize that a material preserves its own history - and we are able to read it.
It may surprise you that metal analysis is also relevant in a field that might at first seem quite distant: biomedical engineering. We often analyse implant failures, such as hip endoprostheses and fixation plates.
In one case, we identified a fatigue fracture in a femoral plate in a 74-year-old patient, accelerated by electrochemical corrosion caused by the presence of a hip replacement. The combination of two different materials — the plate and the endoprosthesis — in the conductive environment of the human body caused significant structural changes in the material. Together with unsuitable heat treatment of the steel, this led to fracture. On the fracture surface, we could actually see how the crack had progressively propagated as the patient walked and loaded the plate.
This issue concerns austenitic stainless steels, which are primarily paramagnetic. During plastic deformation, however, deformation-induced, or twinned, martensite forms in their structure, and this martensite is ferromagnetic.
In the microscope, we use the interaction of the electron beam, as electromagnetic radiation, with the local magnetic field of the material. The magnetic field of the domains slightly affects the reflection angle of the electrons, which appears as a change in contrast when detecting secondary and backscattered electrons (BSE). In this way, we can imagine the domain structure. We have successfully applied this, for example, in the analysis of ferromagnetic control valves for hydrogen storage systems.
Our collaboration covers almost the whole of Slovakia and extends into sectors ranging from railways and energy to nuclear power plants. For the nuclear energy sector, for example, we are developing methods for producing crack standards by combining stress, chemical exposure, and temperature. These standards are used for the precise calibration of defectoscopy detectors.
Right now, I have in the MIRA XR an approximately ten-centimetre piece of a railway wagon bearing that failed after less than 200 kilometres of operation. These multi-tonne wagons travel at speeds of 160 kilometres per hour, so the material stress is truly extreme.
Read more: Understanding Electron Microscopy Fundamentals
I cannot tell you that. The interpretation of acquired data will take us several weeks, and in such cases we also maintain confidentiality.
Polymers and ceramics make up a smaller part of our research, but the new instrument expands our possibilities. With the VEGA system, non-conductive samples often had to be coated with metal, which could affect the authenticity of the surface. The MIRA XR allows observation at lower accelerating voltages and with short imaging times, which eliminates sample charging and in many cases makes analysis possible without coating.
This is crucial, for example, when studying concrete or corundum ceramics. We are therefore also able to analyse these materials, although I personally remain most fascinated by metals, which I consider a truly fundamental material in modern history.
In terms of resolution, we have already approached the physical limits. I see the future primarily in the integration of artificial intelligence into evaluation processes. AI will play a key role in sorting, classifying and interpreting large datasets.
Young people handle today’s control systems very quickly and naturally. I have to learn them more than they do, because I have habits from older instruments. On the other hand, although work with the microscope becomes faster and more intuitive, a deep understanding of the physics of electron–material interaction will remain essential for the scientific interpretation of results.
Many things will become simpler, and microscopy will become accessible to a broader range of users. But mastering it fully will still require a deeper knowledge of the physics behind the entire process. There will be people who truly understand it in depth, alongside the commercial sphere, where the need is often to perform routine measurements quickly.
Thank you for the interview, and I wish you many more successes in your work.