Introduction to the themed issue in honour of Professor Dr Petra Rudolf

In this issue of Journal of Materials Chemistry A, B & C, we honour Prof. Dr Petra Rudolf on the occasion of her retirement and celebrate her remarkable contributions to surface and materials physics and to the cause of women in science.

Petra is a solid state physicist by training, with broad interest in the topics covering surface physics. Over the past three decades, Petra has worked on different aspects of surface analysis, studying electronic structure, surface crystalline structure and vibrational properties of adatoms and molecules, in particular C₆₀, on metallic surfaces.^1–6 While these techniques have been applied by Petra and her group to a wide range of materials, she has always maintained a special interest in carbon allotropes such as fullerene, graphite, graphene and graphene-based materials,^7–9 which gradually expanded into a wider exploration of two-dimensional materials.¹⁰

Petra's passion for surface physics dates back to 1988, when she attended the “Spring College in Condensed matter on interaction of atoms & molecules with solid surfaces” organised by the International Centre for Theoretical Physics in Trieste, Italy. This formative experience sparked a lifelong passion for surface science, one that she nurtured throughout her academic journey and carried forward into her distinguished career at the University of Groningen.

Petra earned her MSc in 1987 from Sapienza University of Rome, Italy, researching hydrogenated amorphous silicon.¹¹ She then worked at the National Surface Science Laboratory in Trieste,^3–5 with two research stays at Bell Labs, USA, focusing on the newly discovered fullerenes.^2,12,13

In 1995 she obtained a PhD in physics at the Facultés Universitaires Notre-Dame de la Paix de Namur, Belgium, under the supervision of Prof. Roland Caudano with a dissertation titled “Structural, vibrational and electronic properties of ultrathin C₆₀ films on metallic substrates”.¹⁴ She continued working in Namur as an associate professor until she joined the University of Groningen, The Netherlands, in 2003 as Professor of Experimental Solid State Physics, where she continued her pioneering work until her retirement in 2025.

As mentioned earlier, a large part of Petra's career has been connected to carbon and its allotropes,^{3–5,7–9,12,14–18} groundbreaking work conducted well before graphene captured worldwide attention.^15,16 Her early and sustained interest in low-dimensional carbon materials led to important advances in understanding their growth, structure, and electronic properties, establishing her as a true forerunner in the field.

Throughout her career, Petra has fostered strong collaborations across disciplines, particularly with colleagues in chemistry. Among these, her shared interest in carbon allotropes led to fruitful work with Prof. Maurizio Prato,⁸ as well as an extremely productive long-standing collaboration with Prof. Dimitrios Gournis^22,23 on carbon allotropes and clays. In this context, Petra coordinated a European project called CASSIUSCLAYS (acronym for Composites of Augmented Strength: Study of Intercalates of Uniquely Structured CLAYS), in which Maurizio Prato, Dimitrios Gournis, Francesco Zerbetto, Dirk Guldi and David Leigh participated.

The project idea was born in September 1999, the group convened in San Feliu de Guíxols (Costa Brava) at a EURESCO conference organized by Francesco Zerbetto. This meeting sparked both enduring collaborations and the concept for a project on polymer nanocomposites, utilizing novel tailored clay minerals – the oldest known 2D nanomaterials. The initiative secured EU funding shortly thereafter, with the kickoff meeting held in Namur, where Petra was based at the time.

Subsequent annual meetings in Corfu, Trieste, Maastricht, and Malta fostered productive scientific exchange and lasting friendships that have endured for over 25 years.

In another European project very important for Petra’s career, the SynNanoMotors project, conducted in collaboration with David Leigh, François Kajzar, Fabio Biscarini, Francesco Zerbetto, and Wybren Jan Buma, Petra made pioneering contributions to the field of molecular motors and surface functionalization. For this work, she received the prestigious Descartes Prize from the European Commission in 2007.

When discussing molecular motors, it is essential to recognize the rich collaboration between Petra, a distinguished surface scientist, and Prof. Ben L. Feringa, the 2016 Nobel Laureate in Chemistry. By combining their expertise – Petra's mastery of surface science with Feringa's pioneering work in synthetic chemistry – they have advanced the frontiers of molecular switches and machines, producing many contributions of great importance for the field.^8,19–21

In recent years, her research has increasingly bridged fundamental and applied science, with a particular focus on biomedical applications of advanced materials.^22–25 She has explored innovative ways to translate her findings, especially those on graphene-based systems, into practical technologies, and her seminal work on polydopamine has opened new directions for surface functionalization.²⁴

Among the honors she received, in 2010, Petra was elected a Fellow of the American Physical Society in recognition of her influential work on fullerenes, nanotubes, graphite, and graphene, as well as her studies on light-driven synthetic molecular motors. She is also a Fellow of the Institute of Physics and an honorary member of the Italian and the Dutch Physical Society. In 2016 Petra was elected as a Member of the German National Academy of Science and Engineering (acatech), and she was elected to the Academia Europaea in 2021.

In 2013, Petra received a Dutch royal decoration for her activities in favour of diversity in science and was appointed Officer of the Order of Orange-Nassau.

Those who have had the privilege of knowing Petra know that she is a true force of nature, and it comes as no surprise that her contributions extend far beyond her scientific achievements.

Petra's dedication to the field of physics and to physicists themselves has been unwavering throughout her career. Her leadership and advocacy have left a lasting impact on the scientific community, in Groningen and Europe.

Petra served as President of the Belgian Physical Society from 2000 to 2001, where she played a pivotal role in shaping the society's direction and fostering collaboration among Belgian physicists. Later, she took on the prestigious role of President of the European Physical Society from 2019 to 2020, further extending her influence across Europe and championing the advancement of physics on an international scale. Currently, she chairs the EPS Equal Opportunities Committee, continuing her commitment to promoting equity and inclusion within the physics community.

As a professor at the University of Groningen, Petra has been a driving force in increasing the representation of women in academic leadership. She has devoted considerable energy and innovative ideas to improving both the number of female professors and the well-being of those already in these roles. She served on the Rosalind Franklin hiring committee, which has hired a number of female scientists at the University of Groningen, but also in the Sleutelvrouwen group, which aimed to monitor diversity policies and give feedback to stakeholders. Furthermore, despite her demanding schedule, she has consistently made time to organize the annual dinner for female professors of the University of Groningen, fostering a sense of community and support.

Petra was also one of the key initiators of the Avril McDonald Dinner and Scholarship, an initiative that has provided vital support and recognition to female Master’s students. Her mentorship has touched the lives of countless young scientists, both women and men, guiding them through their academic and professional journeys.

In her capacity as Director of the Graduate School – both within the Faculty of Science and at the university level – she initiated significant reforms aimed at increasing the efficiency of doctoral research and improving the employability of graduates. Remarkably, she accomplished this without compromising her own scientific productivity, as evidenced by her retirement with a steadily rising citation record. With this themed issue, former students, colleagues, and friends come together to celebrate the remarkable career of an exceptionally original and dedicated scientist – a true powerhouse of commitment to making science a more inclusive, equitable, and inspiring place for all.

Guest Editors left to right: Antonija Grubišić-Čabo, Maria Antonietta Loi, Dimitrios Gournis, Francesco Zerbetto, Maurizio Prato, Rasmita Raval.

References

1. A. Bianconi, A. C. Castellano, M. De Santis, P. Rudolf, P. Lagarde, A. M. Flank and A. Marcelli, L_2,3 XANES of the High T_c Superconductor YBa₂Cu₃O_≈7 with Variable Oxygen Content, Solid State Commun., 1987, 63(11), 1009–1013,  DOI:10.1016/0038-1098(87)90650-8.
2. C. T. Chen, L. H. Tjeng, J. Kwo, H. L. Kao, P. Rudolf, F. Sette and R. M. Fleming, Out-of-plane Orbital Characters of Intrinsic and Doped Holes in La_2−xSr_xCuO₄, Phys. Rev. Lett., 1992, 68(16), 2543,  DOI:10.1103/PhysRevLett.68.2543.
3. S. Modesti, S. Cerasari and P. Rudolf, Determination of Charge States of C₆₀ Adsorbed on Metal Surfaces, Phys. Rev. Lett., 1993, 71(15), 2469,  DOI:10.1103/PhysRevLett.71.2469.
4. A. J. Maxwell, P. A. Brühwiler, A. Nilsson, N. Mårtensson and P. Rudolf, Photoemission, Autoionization, and X-Ray-Absorption Spectroscopy of Ultrathin-Film C₆₀ on Au(110), Phys. Rev. B: Condens. Matter Mater. Phys., 1994, 49(15), 10717,  DOI:10.1103/PhysRevB.49.10717.
5. M. R. C. Hunt, S. Modesti, P. Rudolf and R. E. Palmer, Charge Transfer and Structure in C₆₀ Adsorption on Metal Surfaces, Phys. Rev. B, 1995, 51(15), 10039,  DOI:10.1103/PhysRevB.51.10039.
6. J. Berna, D. A. Leigh, M. Lubomska, S. M. Mendoza, E. M. Pérez, P. Rudolf, G. Teobaldi and F. Zarbetto, Macroscopic Transport by Synthetic Molecular Machines, Nat. Mater., 2005, 4(9), 704–710,  DOI:10.1038/nmat1455.
7. F. Carbone, P. Baum, P. Rudolf and A. H. Zewail, Structural Preablation Dynamics of Graphite Observed by Ultrafast Electron Crystallography, Phys. Rev. Lett., 2008, 100(3), 035501,  DOI:10.1103/PhysRevLett.100.035501.
8. M. Quintana, K. Spyrou, M. Grzelczak, W. R. Browne, P. Rudolf and M. Prato, Functionalization of Graphene via 1,3-Dipolar Cycloaddition, ACS Nano, 2010, 4(6), 3527–3533,  DOI:10.1021/nn100883p.
9. X. Zhang, L. Hou, A. Cnossen, A. C. Coleman, O. Ivashenko, P. Rudolf, B. J. van Wees, W. R. Browne and B. L. Feringa, One-Pot Functionalization of Graphene with Porphyrin through Cycloaddition Reactions, Chem.–Eur. J., 2011, 17(32), 8957–8964,  DOI:10.1002/chem.201100980.
10. G. Feraco, O. De Luca, P. Przybysz, H. Jafari, O. Zheliuk, Y. Wang, P. Schädlich, P. Dudin, J. Avila, J. Ye, T. Seyller, P. Dąbrowski, P. J. Kowalczyk, J. Sławińska, P. Rudolf and A. Grubišić-Čabo, Nano-ARPES Investigation of Structural Relaxation in Small Angle Twisted Bilayer Tungsten Disulfide, Phys. Rev. Mater., 2024, 12(8), 124004,  DOI:10.1103/PhysRevMaterials.8.124004.
11. P. Rudolf, C. Coluzza, L. Mariucci and A. Frova, Properties of Amorphous Si:H Films Prepared by Dual Ion Beam Sputtering, Phys. Scr., 1998, 5(37), 828–830,  DOI:10.1088/0031-8949/37/5/033.
12. C. T. Chen, L. H. Tjeng, P. Rudolf, G. Meigs, J. E. Rowe, J. Chen, J. P. McCauley Jr, A. B. Smith III, A. R. McGhie, W. J. Romanow and E. W. Plummer, Electronic States and Phases of K_xC₆₀ from Photoemission and X-Ray Absorption Spectroscopy, Nature, 1991, 352(6336), 603–605,  DOI:10.1038/352603a0.
13. P. Kuiper, B. G. Searle, P. Rudolf, L. H. Tjeng and C. T. Chen, X-Ray Magnetic Dichroism of Antiferromagnet Fe₂O₃: The Orientation of Magnetic Moments Observed by Fe 2p X-Ray Absorption Spectroscopy, Phys. Rev. Lett., 1993, 70(10), 1549,  DOI:10.1103/PhysRevLett.70.1549.
14. K. Hevesi, C. A. Fustin, P. Rudolf, L. M. Yu, B.-Y. Han, G. Gensterblum, P. A. Thiry, J.-J. Pireaux and R. Caudano, Resonant Interaction of Low Energy Electrons with Intramolecular Vibrations in Solid C₆₀, J. Electron Spectrosc. Relat. Phenom., 1995, 76, 115–119,  DOI:10.1016/0368-2048(95)02512-X.
15. C. Puglia, P. Bennich, J. Hasselström, P. A. Brühwiler, A. Nilsson, A. J. Maxwell, N. Mårtensson and P. Rudolf, A Photoemission and XAS Study of Oxygen Coadsorbed with a (2 × 2) Layer of K on Graphite, Surf. Sci., 1997, 383, 149–161,  DOI:10.1016/S0039-6028(97)00139-8.
16. P. Bennich, C. Puglia, P. A. Brühwiler, A. Nilsson, A. J. Maxwell, A. Sandell, N. Mårtensson and P. Rudolf, Photoemission Study of K on Graphite, Phys. Rev. B: Condens. Matter Mater. Phys., 1999, 59, 8292–8304,  DOI:10.1103/PhysRevB.59.8292.
17. A. Grüneis, C. Attaccalite, T. Pichler, V. Zabolotnyy, H. Shiozawa, S. L. Molodtsov, D. Inosov, A. Koitzsch, M. Knupfer, J. Schiessling, R. Follath, R. Weber, P. Rudolf, L. Wirtz and A. Rubio, Electron-Electron Correlation in Graphite: A Combined Angle-Resolved Photoemission and First-Principles Study, Phys. Rev. Lett., 2008, 100(3), 037601,  DOI:10.1103/PhysRevLett.100.037601.
18. N. Karousis, G. E. Tsotsou, F. Evangelista, P. Rudolf, N. Ragoussis and N. Tagmatarchis, Carbon Nanotubes Decorated with Palladium Nanoparticles: Synthesis, Characterization, and Catalytic Activity, J. Phys. Chem. C, 2008, 112(35), 13463–13469,  DOI:10.1021/jp802920k.
19. N. Katsonis, M. Lubomska, M. M. Pollard, B. L. Feringa and P. Rudolf, Synthetic Light-Activated Molecular Switches and Motors on Surfaces, Prog. Surf. Sci., 2007, 82(7–8), 407–434,  DOI:10.1016/j.progsurf.2007.03.011.
20. G. Fioravanti, N. Haraszkiewicz, E. R. Kay, S. M. Mendoza, C. Bruno, M. Maraccio, P. G. Wiering, F. Paloucci, P. Rudolf, A. M. Brouwer and D. A. Leigh, Three State Redox-Active Molecular Shuttle That Switches in Solution and on a Surface, J. Am. Chem. Soc., 2008, 130(8), 2593–2601,  DOI:10.1021/ja077223a.
21. K. Y. Chen, O. Ivashenko, G. T. Carroll, J. Robertus, J. C. M. Kistemaker, G. London, W. R. Browne, P. Rudolf and B. L. Feringa, Control of Surface Wettability Using Tripodal Light-Activated Molecular Motors, J. Am. Chem. Soc., 2008, 136(8), 3219–3224,  DOI:10.1021/ja412110t.
22. I. V. Pavlidis, T. Vorhaben, T. Tsoufis, P. Rudolf, U. T. Bornscheuer, D. Gournis and H. Stamatis, Development of Effective Nanobiocatalytic Systems Through the Immobilization of Hydrolases on Functionalized Carbon-based Nanomaterials, Bioresour. Technol., 2012, 115, 164–171,  DOI:10.1016/j.biortech.2011.11.007.
23. P. Koutsogiannis, E. Thomou, H. Stamatis, D. Gournis and P. Rudolf, Advances in Fluorescent Carbon Dots for Biomedical Applications, Adv. Phys.: X, 2020, 5(1), 1758592,  DOI:10.1080/23746149.2020.1758592.
24. H. Hemmatpour, O. De Luca, D. Crestani, M. C. A. Stuart, A. Lasorsa, P. C. A. van der Wel, K. Loos, T. Giousis, V. Haddadi-Asl and P. Rudolf, New Insights in Polydopamine Formation via Surface Adsorption, Nat. Commun., 2023, 14(1), 664,  DOI:10.1038/s41467-023-36303-8.
25. L. A. T. W. Asri, M. Crismaru, S. Roest, Y. Chen, O. Ivashenko, P. Rudolf, J. C. Tiller, H. C. van der Mei, T. J. A. Loontjens and H. J. Busscher, A Shape-Adaptive, Antibacterial-Coating of Immobilized Quaternary-Ammonium Compounds Tethered on Hyperbranched Polyurea and its Mechanism of Action, Adv. Funct. Mater., 2014, 24(3), 346–355,  DOI:10.1002/adfm.201301686.

---