Peer-reviewed Publications |
Aguillon, F., & Borisov, A. G. (2024). Nonlinear Response of Nanostructured Graphene to Circularly Polarized Light. J. Phys. Chem. C, 128(39), 16576–16587.
Résumé: Using the tight-binding description of graphene and the time-dependent density matrix approach, we theoretically address the nonlinear response of plasmonic graphene nanostructures to the circularly polarized light. The intensity and polarization of emitted harmonics depend on the symmetry of the system and can be analyzed by applying Neumann’s principle. We find that for the nanoflakes comprising thousands of carbon atoms, it is the symmetry of the carbon atom arrangement on the atomic scale that determines the nonlinear response. Therefore, it might be very different from the nonlinear response predicted using the macroscopic geometry. For the compound systems made of several nanoflakes, we reveal the role of the near-field interactions in intensity and circular polarization states of emitted harmonics. Finally, we show that symmetry break by, e.g., lattice defects strongly affects the nonlinear response of graphene nanoflakes to the circularly polarized light. Our work extends the theoretical studies of the nonlinear optical properties of graphene nanomaterials toward spin-carrying light beams.
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Borisov, A. G. (2024). Model description of electron transfer between PTCDA molecule and metal surface upon molecular adsorption and STM manipulation. Phys. Rev. B, 110, 075413.
Résumé: The coupling between the molecule-localized electronic states and continuum of the electronic states of the metal surface is of paramount importance for adsorption dynamics, surface reactivity, as well as for the electron- and photon-induced processes at metal surfaces. Here, using the model one-active-electron description and wave-packet propagation approach, we study the resonant electron transfer between the perylene-tetracarboxylic-dianhydride (PTCDA) molecule and metal substrate from 0.5 nm separations down to the adsorption distances. We also address the situation where the molecule is lifted up from the substrate using the scanning tunneling microscope. A detailed comparison with the large amount of available experimental data and ab initio calculations allows us to discuss the validity of the method and the main robust effects driving the lifetimes of molecule-localized states that it reveals. Thus we show that the symmetry of molecule-localized states strongly impacts the dependence of the electron transfer rates on the metal band structure and molecule-surface distance. In addition, in full agreement with recent experimental data on scanning tunneling microscopy manipulation where an adsorbed molecule is lifted into the vertical geometry, we find an order of magnitude reduction of the adsorbate-substrate coupling.
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Raseev, G. (2024). Optical intensity figures of merit of insulator-metal-insulator and metal-insulator-metal thin-film stacks. Phys. Scr., 99, 085535.
Résumé: Figures of merit (FoM) are used to characterise the mode intensity and leakage of reflection and plane-wave and locally excited transmitted fluxes of simple insulator-metal-insulator (IMI) and metal-insulator-metal (MIM) 2D planar thin-film stacks sustaining a single surface plasmon polariton (SPP) and multiple planar waveguide (PWG) modes. This first comparative study of the intensity FoM (IFoM) of IMI and MIM stack modes is carried out by analysing these observables 3D dispersion graph (observable dispersion/in-plane wave vector/frequency) along 2D cuts where one of the independent variables is fixed. In the spatial domain, the observable 2D dispersion curves along the in-plane wave vector at a given frequency are examined. In the frequency domain, these 2D dispersion curves are examined along the frequency at a given in-plane wave vector. Due to the lower leakage, the quality factors and IFoM of the IMI and MIM thin film stack modes are significantly larger in the spatial domain than in the frequency domain. Our optimized quality factors and IFoMs can be larger than those obtained in some 2D/3D nanoscale samples with an involved geometry.
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Zapata-Herrera, M., Rogez, B., Marguet, S., Dujardin, G., Boer-Duchemin, E., & Le Moal, E. (2024). Spectral shifts in tip-induced light from plasmonic nanoparticles in air. Phys. Rev. B, 109(15), 155433.
Résumé: In this article, we carry out an in-depth study of the scanning tunneling microscopy-induced luminescence spectra (STML) of individual plasmonic nanoparticles measured in air. When compared to the results of far-field light scattering measured under the same ambient conditions, the STML measurements show spectral shifts and peak broadening of hundreds of meV, even when a non-plasmonic tip is used for STML. We simulate the near-field excitation and the effect of the tip using the finite-element method and show that these effects alone cannot explain the spectral shifts and peak broadening observed for STML experiments in air. However, the experimental results are well reproduced in the numerical simulations if the screening effect of a water meniscus bridge present in the tip-nanoparticle gap is considered. Our results pave the way for finer interpretations of STML experiments in air, where ignoring this additional screening effect can lead to an incorrect mode assignment of the observed resonances.
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