Perhaps every phone owner has noticed that his or her phone gets hot when charging, for example. But when researchers want to study the heating of nanostructures and small components more closely, they run into technological limitations. "We would like to investigate heating, heat transfer and heat propagation at these small scales. But it's problematic. Conventional mercury thermometers are too big. If we wanted to use infrared thermometers, for example, we would hit the diffraction limit of light and we would not able to get down to the nanoscale," says Jiří Kabát from CEITEC BUT. He therefore decided to try to study heat propagation not with thermometers but with an electron microscope. "The idea is to use the interaction of the electron beam with heated samples on the nanoscale to measure temperature or to reveal constants such as thermal conductivity," he explains.

However, the interaction between the heated objects and the electron beam has a downside. It is impossible to study heating with an electron microscope without accounting for the effect of the microscope itself. "When we have heated structures, they affect our probe, which may just be the electron beam, for example. The magnetic lenses in an electron microscope are basically these large coils that focus the electrons so that we can use them to probe the nanostructures. In addition, the electron beam passes through other metal components. And all these components, when they reach a certain temperature, can affect the electron beam and degrade the resolution," explains Jiří.

The first part of the research, therefore, focuses on the use of thermal phenomena to measure temperature, and the second part investigates the extent to which these thermal phenomena affect the distortion of spatial and spectral resolution when using an electron microscope. "In a nutshell, I'm trying to investigate both the positive and negative effects of how electrons interact on a very small scale. The positive is that we can measure temperature with a resolution never seen before. The negative is that there's a so-called temperature noise that affects the electrons. And I am interested in how to theoretically describe this interaction between an electromagnetic field – for example, from temperature noise or a nanoparticle – and electrons," Jiří adds.

The research is still in its early stages. "Some experiments have already been conducted. But these were more to show that it is possible to measure temperature using an electron microscope. Our first task now is to find a suitable system to investigate. For example, to look at parts of chips or microtransistors and what problems researchers have with heating them up and measuring their temperature. They can see that it's heating up, but they don't know exactly where – whether it's some kind of joint between two materials, whether it's related to those particular materials, and so on," says Jiří Kabát, adding that he would like to follow up on the work of his PhD thesis supervisor. "Andrea Konečná has already made some models, but we are not yet able to describe exactly what we see in the experiment. So now we would like to continue their development and delve deeper into temperature noise and other effects that may play a role," he adds.

He has been close to theoretical physics and microscopes since his undergraduate studies. "For the first two years, I didn't know what I wanted to do in the future. Whether to focus on experiments, which are at the top level both at the Institute of Physical Engineering at the Faculty of Mechanical Engineering (FME) of BUT and at CEITEC, or to focus on theory. I have been interested in physics since childhood, I enjoy mathematics, and I like science fiction. So I thought theory would be a good path. And in my second year, we had a course in theoretical physics, which made me decide to go in this direction," says Jiří Kabát. Third year into his studies, under the guidance of Andrea Konečná, he focused on electron microscope spectroscopy and the study of phase transformation materials. "Then I went to Erasmus, where I took a bit of a detour and researched nano-optics. When I came back, I combined optical and electron microscopy and in my master's thesis, I tried to show that they are quite similar and from a theoretical point of view we can use the same formalism to describe them," says Jiří, adding that thermal effects are essentially a direct fcontinuation of his previous studies.

His doctoral research also caught the attention of the Brno Ph.D. Talent jury, from whom he eventually received the scholarship. "I entered the competition thinking it was an ambitious project, but I didn't know what to expect – whether the jury would be physicists, electron microscopy experts, or people from companies. I had no idea if they would be interested in my work. Plus, there was a lot of competition, and many projects were on hot topics such as the use of AI or curing diseases. Although my research is basic, a better understanding of electron microscopes has implications for many other fields," says Jiří Kabát, who would like to stay in academia for the foreseeable future. "I find what I do very fulfilling. Moreover, this puts me in a very inspiring environment full of top researchers," he concludes.

(zeh)