Spotlight: Controlling the optical properties of graphene with Eva Pogna

Eva Pogna began studying graphene at the Graphene Flagship Partner Polytechnic University of Milan in 2013, when she was a PhD student. Since then, she has focused her research on the optical properties of graphene – namely, how graphene absorbs, transmits and emits light, from the extreme ultraviolet to the far infrared [1-8]. Currently, she works as a researcher at the Institute for Photonics and Nanotechnologies - CNR in Italy.

In this interview, we explore Pogna’s interests in graphene and other aspects of her career.

Why are you interested in graphene’s optical properties?

Graphene’s optical response is interesting for two primary aspects. Scientifically, it is a unique playground of both quantum and relativistic physics. Technologically, graphene can absorb light over a broadband range and shows tunable absorption and fast recovery time after impulsive light excitation. These are highly desired properties for several applications related to the manipulation of the electromagnetic radiation.

Which applications are you referring to?

The possibility to actively and efficiently control how graphene absorbs or reflects light, and how fast it relaxes to its equilibrium after an external excitation, has implications for the engineering of graphene-based optoelectronic and photonic nano-devices, that can serve for light detection, modulation and emission. Examples of these devices, which include saturable absorbers, photo-detectors, optical modulators, photo-switches, light converters or emitters, can serve as building blocks for next-generation wireless communication technologies, enabling higher-data rates, or empower available instrumentations for material inspection and sensing using light.

What is your current research goal?

As part of a vast collaboration fostered by the Graphene Flagship, including the Graphene Flagship Partners Cambridge Graphene Centre, Polytechnic University of Milan, ICN2 and the University of Pisa, we have pushed forward our understanding of the optical properties of graphene, demonstrating the possibility to tune its out-of-equilibrium response to an unprecedented level, superior to what has been shown by any other known material.

We designed a transistor that exploits ionic liquid gating to apply large electrostatic fields to graphene, thus controlling and varying how graphene responds to ultrafast optical excitation. To follow the fast response of graphene, we used ultrafast spectroscopy, which exploit ultrashort light pulses, having time duration of hundreds of femtoseconds (<10^-12s). We are now working at developing photonics applications that take advantage of graphene’s tunability, for producing ultrafast laser sources and for boosting the efficiency of photodetectors and optical modulators based on graphene.

Why do you feel your research is important, and what benefits could it bring to society?  

The ability to manipulate light has revolutionised human life in various important ways, ranging from medicine (providing tools for non-invasive diagnosis and disease treatment), to communications (with the diffusion of wireless data communications) and energy production (with photovoltaics). It has also bolstered the development of fundamental science by providing unparalleled methods for inspecting our world, from astrophysical to cellular systems. The investigation of the light-matter interaction in graphene and related materials offers great opportunity to expand our understanding of condensed matter physics, as well as develop flexible and compact technologies for light manipulation.

What are the biggest milestones in your career – or your proudest moments?  

Joining the Graphene Flagship has been very important for my career as a researcher because it gave me great networking opportunities. Only with this unique concentration of resources could we have reached the level of understanding and knowledge that we now have on graphene. My research topic has been extremely motivating, and I feel I am close to the frontier of our understanding of condensed matter physics and a true technological breakthrough. I am also extremely grateful to my PhD supervisor, Prof. Giulio Cerullo of Graphene Flagship Partner Polytechnic University of Milan, for his expert and stimulating guidance, rigorous method and noble spirit. I would also like to thank Dr Miriam Vitiello, my scientific advisor at Istituto di Nanoscienze, CNR-Nano in Pisa, for her encouragement throughout my career and her brilliant passion for research.

What are your plans for the future?

I will continue studying the optoelectronic properties of graphene and layered materials to explore equilibrium and non-equilibrium properties, with particular interest in regimes of strong light-matter interaction, exploiting the unique possibilities offered by layered materials. I am interested in pursuing the application of layered materials in quantum technologies as building blocks of quantum objects in support of the second quantum revolution.

Have you ever had a role model, or someone who inspired you? If so, please tell us about them and how they influenced you.

I come from a family of researchers. My parents, Norberto Pogna and Annamaria Marzetti, have been my first and strongest inspiration: they have taught me the importance of knowledge and culture, instilled in me a lot of curiosity and drive to expand the understanding of the world. They conveyed the idea of the researcher as a very optimistic dreamer, whose mind is projected to the future and to progress. My family has always pushed me towards challenging myself, and what’s more challenging than STEM? I had the privilege of being able to pursue this career after completing my education in top-level Italian universities where I met extremely stimulating professors and supervisors. Their dedication helped me to overcome the discouragement once can feel before the unknown, trust rigorous methods and consult others with an open and humble mindset.

Why do you feel that diversity in science and technology is important for the Graphene Flagship's progress?

When I think about diversity in my work experience, I do not immediately think about gender or sexual orientation. The diversity that comes to mind first for me is an educational and cultural diversity: these two are the most tangible in my everyday life. I am an experimental physicist and I work most of the time with engineers and theoretical physicists and chemists. Even though we are supposed to have a similar background based on mathematic language, I often feel that we belong to different worlds, in how we think about, phrase and tackle our scientific problems. We get excited by different aspects. Deeply understanding each other, requires an open mindset, asking questions is key to advance and obtain a comprehensive picture. So diversity for me is a requirement.

Furthermore, encouraging gender diversity, helping women to break the so-called glass ceiling, can bring an important revitalizing drift to the scientific world. Women nowadays have more possibilities to access higher education and want to break all the boundaries that have unjustifiably constrained them, blocking their access to leading positions. In this context I like a quote from Rita Levi Montalcini that can be translated as: “The woman has been blocked for centuries. When she has access to culture, she is hungry and the food is more useful to whomever is hungry than to whomever is full.”

References

[1] Pogna, EAA, et al. “Electrically tunable nonequilibrium optical response of graphene.” ACS nano (2022) https://pubs.acs.org/doi/full/10.1021/acsnano.1c04937

[2] Pogna, EAA, et al. “Hot-Carrier Cooling in High-Quality Graphene Is Intrinsically Limited by Optical Phonons”. ACS Nano (2021) https://doi.org/10.1021/acsnano.0c10864

[3] Pogna, EAA, et al. “Angle-tunable intersubband photoabsorption and enhanced photobleaching in twisted bilayer graphene.” Nano Research (2021) https://doi.org/10.1007/s12274-021-3288-0

[4] Ghirardini, L, Pogna, EAA, Soavi, G et al. “Tunable broadband light emission from graphene.” 2D Materials (2021) https://doi.org/10.1088/2053-1583/abf08d

[5] Di Gaspare et al. “Tunable, Grating‐Gated, Graphene‐On‐Polyimide Terahertz Modulators.” Advanced Functional Materials (2021)  https://doi.org/10.1002/adfm.202008039

[6] G. Soavi et al. “Hot electrons modulation of third-harmonic generation in graphene.” ACS Photonics (2019) https://doi.org/10.1021/acsphotonics.9b00928

[7] Tielrooij, K et al. “Out-of-plane heat transfer in van der Waals stacks through electron–hyperbolic phonon coupling.” Nature Nanotechnology (2018) https://doi.org/10.1038/s41565-017-0008-8

[8] Cinquanta, E, Pogna EAA et al. “Charge carrier dynamics in 2D materials probed by ultrafast THzspectroscopy.” Advances Physics: X (2022) https://doi.org/10.1080/23746149.2022.2120416