If you happen to find yourself in the Canadian Centre for Electron Microscopy (CCEM), tucked away in the basement of McMaster’s Arthur Bourns Building, you’ll likely find Mehdi Mosayebi studying things most other humans will never be able to see.
Mehdi is a postdoctoral fellow in Nabil Bassim’s group. He joined the team as a PhD student in 2021, when his interest in understanding how materials behave and fail at the microscopic scale, as well as a desire to learn from Bassim, brought him to McMaster from Iran.
Though he initially was interested in metallurgical materials, his research has shifted over time, becoming increasingly focused on the relationships between microstructure, processing and material performance.
But the materials he studies aren’t the most impressive thing about his work — it’s the scale at which it happens.
Most engineering materials look the same to the naked eye, Mehdi explains. But hidden inside them are a series of complex microscopic structures that we can’t see without highly sophisticated equipment that magnifies them to an atomic level.
And it’s at this nanoscale that Mehdi does his best work.
Working alongside Bassim, Mehdi uses advanced electron, ion and X-ray microscopy techniques at the CCEM to visualize these tiny structures in three dimensions. These visualizations are used to create detailed three-dimensional maps of materials that allow researchers to better understand why certain materials behave the way they do, how they fail and, most importantly, how they can be improved.
With use cases ranging from energy systems and transportation to advanced manufacturing and semiconductor technologies, Mehdi’s research projects are as varied in impact as they are microscopic in scale.
One of these projects was a collaboration with HydroQuebec. It involved the study of steel used in hydroelectric turbines and a three-dimensional analysis of a microstructure found in it called lath martensite. This structure is composed of microscopic crystals that form when stainless steel is cooled rapidly.
To better understand how this works, explains Mehdi, you can think of it like Lego blocks. Though a piece of steel might look solid and uniform, its internal structure is actually made up of tiny building blocks. And much like Lego structures, the arrangement and shape of these blocks, and the boundaries between them, determine how the steel will hold up under stress.
For decades, these microstructures were only visible in flat, two-dimensional slices, almost like an aerial view of a neighbourhood on Google Maps.
Using plasma focused ion beam serial section tomography and electron backscatter diffraction, two sophisticated imaging techniques made possible by the equipment in the CCEM, Mehdi was able to map the entire internal structure in three dimensions, at a scale large enough to see subtle imperfections that weren’t visible before. The study further revealed how the internal boundaries between the building blocks form and why they form the way they do.
These imperfections, though microscopic, matter a lot, explains Mehdi. They can act as weak points where cracks start, where hydrogen gets trapped or where fatigue damage accumulates over time.
“When this material is used in the energy infrastructure that millions of people rely on, understanding where these imperfections come from and how they form is vital,” says Mehdi.
“This work can help engineers design better heat treatments, improve manufacturing processes and ultimately build components that last longer and fail less.”
For this work, Mehdi was recently recognized with the 2025 Acta Student Award from Acta Materialia, one of the most influential journals in materials science.
Each year, the Acta Student Awards recognize a small number of outstanding students and the work they do to develop new ways of understanding complex materials in three dimensions.
Receiving this award, says Mehdi, is both rewarding and motivating.
While it recognizes years of hard work and dedication, he explains, it also reflects the value of the advanced microscopy and characterization research being carried out by the entire team at CCEM.
“Research often involves years of experimentation, analysis and problem-solving before the final results come together,” says Mehdi. “It’s nice to be recognized for both the scientific impact of the work and the strength of the overall research contribution.”
And this recognition reflects the quality of work coming out of CCEM more than anything, he says.
“Knowing that my work has been recognized by researchers in the field is encouraging, especially because it reflects the efforts of many people along the way,” he says. “I see this award as recognition of a collective effort as much as a personal achievement.”