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Slovensko   English2024-10-03

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Researchers from F3 and F7 Departments of the Jožef Stefan Institute in collaboration with researchers from the Faculty of Mechanical Engineering, University of Ljubljana and Coimbra University (Portugal) investigated in the picosecond excitation regime the photoacoustic (PA) response of composite material made of graphene or graphene decorated with gold nanoparticles (AuNP) and polydimethylsiloxane (PDMS). AuNP attached to graphene improve the dispersibility of the flakes in the polymer, increase the surface area in contact with the polymer, and prevent the re-adhesion. All of this leads to a better intercalation of the polymer with the graphene flakes and a more uniform and efficient generation of PA waves. By using picosecond excitation of the graphene-based composite, we measured PA waves with bandwidths of 70 MHz and 130 MHz at -6 dB and -20 dB. The peak pressures of the PA waves achieve values > 5 MPa. The bandwidth can be further increased to values of 85 MHz at -6 dB and 135 MHz at -20 dB by decorating the graphene with AuNP. The results of the research were published in the journal Nano Energy and EU patent was granted.

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Feynman diagrams are an important tool in modern theoretical physics, with applications in solid-state, high-energy physics, and quantum chemistry. Doc. dr. Denis Golež from the Department of Theoretical Physics and his colleagues from the Flatiron Institute (USA), Berkeley University (USA) and the University of Örebro (Sweden) discovered a new approach for using Feynman diagrams in quantum materials, published in Physical Review X. Higher-order Feynman diagrams are challenging in strongly correlated quantum systems due to their computational complexity. This study uncovered a 'hidden structure' within these high-order diagrams based on the separability of quantum propagators, see figure, significantly reducing computational demands. The algorithm was applied to non-perturbative problems where traditional quantum Monte Carlo methods would fail, offering a promising new tool for diagrammatic computations. This theoretical advancement is expected to greatly facilitate the discovery of new quantum collective states, such as excitonic magnetism and spin glasses.

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Researchers from the Department of Condensed Matter Physics (Venkata. S. R. Jampani, Miha Škarabot and Miha Ravnik) in collaboration with colleagues from Universities of Ljubljana, Sorbonne, Siegen and Luxembourg reported on the synthesis of water-based templating nanoscale thin films in Advanced Materials. These films are made from superglue (cyanoacrylate monomers) vapours and grow with a controlled rate of several nanometres per minute. Superglues (cyanoacrylate monomers) are otherwise well-known for their rapid reactivity, forming polycyanoacrylate chains that bond materials instantly. On the contrary, in this report the modulated polymerization of cyanoacrylates was introduced, which enable controlled growth of thin polymer films. Furthermore, the shape and color of the film are precisely controlled by the polymerization kinetics, wetting conditions, and/or exposure to patterned light. This study introduces simple, versatile and an eco-friendly approach analogous to existing chemical vapor deposition techniques. This approach facilitates the creation of water-templated films for gas encapsulation, liquid packaging, and in-situ chemical/biological cargo packaging.

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Researchers and collaborators of the Extreme Conditions Chemistry Laboratory (ECCL) at the "Jožef Stefan" Institute (Klemen Motaln, Anton Kokalj, Kristian Radan, Mirela Dragomir, Boris Žemva and Matic Lozinšek), in collaboration with partners from the Institute of Physics of the Czech Academy of Sciences (Kshitij Gurung, Petr Brázda and Lukáš Palatinus), have for the first time successfully employed 3D electron diffraction on nanocrystals to determine the crystal structures of reactive xenon compounds. To accomplish this, the team developed a specialized procedure for handling and transferring extremely reactive and air-sensitive substances, ensuring their safe introduction into a transmission electron microscope. This method paves the way for structural analysis of other reactive and sensitive compounds and materials, particularly those for which single-crystal growth is challenging, rendering traditional X-ray diffraction methods ineffective. This study, funded by GA ČR and ARIS as part of the CEUS joint research project, was published in ACS Central Science, where it was highlighted on the cover. The American Chemical Society (ACS) also featured the research in a press release.



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