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Alessandra Bellissimo on the mysteries of plasmons

Alessandra Bellissimo, a solid-state physicist from the Vienna University of Technology, conducted measurements on the NanoESCA endstation of ELI ALPS for four weeks. In Vienna, she works in the same laboratory where the Nobel Prize winning physicist Ferenc Krausz did his research more than two decades ago.

Alessandra Bellissimo on the mysteries of plasmons

 

Dr Bellissimo is convinced that more and more physicists are asking questions that can be answered by attosecond physics.

 

Pierre Agostini, Anne L'Huillier and Ferenc Krausz were awarded the Nobel Prize in Physics in 2023 for experimental methods that generate attosecond pulses of light. Ferenc Krausz conducted the experiments that revolutionized attophysics at the Vienna University of Technology. Where you are currently working

And not only that! Last October, I found out that I am doing research in the very same spot where Ferenc Krausz had done his experiments more than twenty years ago. Of course, I now use different equipment, but the room is the same. The day after last year’s Nobel Prize laureates in physics were announced, Professor Krausz turned up unexpectedly at our institute. It was a fantastic experience. I had known about his achievements, but we had never met in person before. I was struck by his openness, directness and honesty, and that his colleagues can always count on his help. I am impressed that he finds time for physics despite his many administrative tasks.

 

How did you become a physicist?

The area around my hometown, Naples, is a special place. It is home to Mount Vesuvius and nearby stretches a special volcanic area known as Campi Flegrei (Phlegraean Fields). This could have steered me towards geology or archaeology, due to the presence of Pompeii, but it did not. Although my father was a doctor and my mother a fine artist, neither of them insisted that I follow their career paths. They left it up to me to decide what I would like be. I graduated in physics at the Vienna University of Technology and got my PhD degree in Rome. As a solid-state physicist, I am interested in the interaction of electrons with solid surfaces and I am eager to understand the mechanisms involved. I am fascinated by the transport and ejection of electrons in/from metal surfaces, and the underlying fundamental processes. I am especially intrigued by one phenomenon: the so-called “plasmons”, a collective excitation in which solid-state electrons oscillate in a wave-like pattern, as the electron density alternates between compression and rarefaction. The the details of this collective electron phenomenon are not yet fully known. Furthermore, due to their many-body nature, the processes involved are difficult to describe. That is why I want to study their evolution and dynamics.

 

 

Why did you use graphite to investigate this phenomenon?

“Plasmon excitation” is common to many materials. But I chose graphite because it is always preferable to explore the details of the formation, evolution and disruption of interactions in already well-known systems. During my PhD studies, I thoroughly investigated several electron interaction channels in graphite and aluminium, as well as relevant aspects related to the phenomenon of secondary electron emission. Graphite has a rather complex (and interesting) band structure and is a typical example of two-dimensional materials that are becoming increasingly important in modern technological applications. Aluminium is the simplest, almost free-electron metal, which also shows a significant plasmon spectral response. I have used these two materials for all possible spectroscopic studies, and although both have been extensively studied by many other researchers, for me they are ideal candidates for the in-depth investigation of plasmonic excitation.

 

What did an average working day look like?

I usually arrived at the laboratory between 08:30 and 09:00 in the morning, and together with my colleagues we decided what measurements we would focus on that day – however, the outline plan was clear already the night before. During the first week, we didn’t need a laser yet, so we usually finished work at around 6 pm. In the subsequent three weeks, we needed lasers for all types of measurements; we all worked hard during the experimental campaign. We conducted measurements from morning until late at night every single day. Everybody on the NanoESCA, beamline and TU Wien teams worked hard and harmoniously towards our scientific goal. It was exhausting for everyone involved, but we were all happy about what we achieved.

 

 

Was this your first time in Szeged?

I had already been here before; I attended a user workshop in 2021. It was then when I got acquainted with the laser facilities available here, the NanoEsca endstation and the colleagues who run it. Since then, I have kept it on my agenda that I should do some research in Szeged. I do have to take advantage of the opportunities offered by this institute, as it is clearly world-class in laser physics. My fellow researchers in Vienna are leading scientists in attosecond physics, but they mainly study the behaviour of molecules and gases. I am looking for answers to questions in solid state physics. And the infrastructure in Szeged is perfectly suited for this endeavour.

 

What does ELI ALPS mean for laser physics?

The cutting edge. More and more physicists are asking questions that may be answered with the help of attosecond physics. But universities do not generally have the resources to build their own attosecond laser sources. To them, ELI ALPS may provide a helping hand.

 

What can be the practical benefit of your research?

With the measurement campaign in Szeged, we aimed to investigate the dynamics of inelastic scattered electrons in relation to plasmon excitation – we focused on resolving the dynamics of photoemission events at different high symmetry points in the valence band of graphite. Although these types of studies focus on the fundamental aspects of these processes, understanding the details can have significant implications for the development of specific technologies and devices, for example, in the fields of plasmonics and energy-harvesting photovoltaic devices.

 

 

You are talking about your research in a clear and enjoyable way. Have you studied science communication?

No, but I have learned the importance of explaining, for example, physical phenomena to young people. I am convinced that we must sell our profession to the general public. We physicists understand one another, but when a lay person asks me a question, I scratch my head trying to explain my science in a clear and professional way. Last year, I gave a lecture on light, plasmons and attosecond lasers to master students at the University of Applied Arts in Vienna. Some of the questions I received were pertinent, while others were funny.

 

Will the work you did in Szeged continue?

Yes, definitely. The colleagues here are all helpful and, equally important, they are highly qualified. I am happy to recommend this facility – and of course the colleagues who run it – to the professional community. Just as I was happy to introduce it to three young colleagues in Vienna, who joined my experimental campaign and were also amazed by the opportunities available here. They may return to Szeged in a few years’ time, maybe as postdoctoral fellows, with their own project ideas. I am convinced that this research centre can contribute to important scientific discoveries.

 

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The NanoESCA endstation is a photoemission electron microscope (PEEM), where the electron structure of surfaces and solids is investigated partly with NanoESCA’s own light sources and partly with near-infrared and XUV pulses generated by the HR1 laser and the GHHG Condensed beamline. The endstation can be used to image condensed phase samples in both real and reciprocal space. Static and dynamic time-resolved studies reveal the electron structure of solid surfaces. Real-space imaging gives the photoelectron spectrum at each pixel of the surface. The system consists of a preparation chamber and an analysis chamber. The preparation of the surfaces to be analyzed is a complex task; the outer few-nanometre layer of the sample must be in a well-defined chemical and crystalline state.

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Photos: Gábor Balázs 

Author: Zoltán Ötvös

May

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