Peer-reviewed Publications |
Aguilar-Galindo, F., Diaz-Tendero, S., & Borisov, A. G. (2019). Electronic Structure Effects in the Coupling of a Single Molecule with a Plasmonic Antenna. J. Phys. Chem. C, 123(7), 4446–4456.
Résumé: Miniaturization of plasmonic devices and the possibility to address single-molecule quantum emitters (QEs) in plasmonic cavities allow one to approach a regime where the characteristic sizes of the system are on the scale of molecular dimensions. In such a situation, the actual spatial profile of the transition electron density associated with a molecular exciton affects the coupling between molecular excitons and metal (nano)objects. Using a quantum approach, we address the energies and lifetimes of the excited states of the zinc phthalocyanine dye molecule placed in the nanometer vicinity of a plasmonic antenna. We demonstrate that the interaction between the molecular excitons and a metal nanoparticle reflects the gross features of the atomic structure in the molecule. The possibility to “look” inside the molecule does not require the presence of atomic scale probes on the surfaces of plasmonic nanoparticles, which would lead to the corresponding localization of the optical field. We show that the QE itself simultaneously generates highly localized fields and probes them via self-interaction.
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Aguirregabiria, G., Marinica, D. C., Ludwig, M., Brida, D., Leitenstorfer, A., Aizpurua, J., & Borisov, A. G. (2019). Dynamics of electron-emission currents in plasmonic gaps induced by strong fields. Faraday Discus., 214, 147–157.
Résumé: The dynamics of ultrafast electron currents triggered by femtosecond laser pulse irradiation of narrow gaps in a plasmonic dimer is studied using quantum mechanical Time-Dependent Density Functional Theory (TDDFT). The electrons are injected into the gap due to the optical field emission from the surfaces of the metal nanoparticles across the junction. Further evolution of the electron currents in the gap is governed by the locally enhanced electric fields. The combination of TDDFT and classical modelling of the electron trajectories allows us to study the quiver motion of the electrons in the gap region as a function of the Carrier Envelope Phase (CEP) of the incident pulse. In particular, we demonstrate the role of the quiver motion in establishing the CEP-sensitive net electric transport between nanoparticles.
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Alyabyeva, N., Ouvrard, A., Lazzari, R., & Bourguignon B. (2019). Ordered Hybrid Assembly of Palladium Nanoparticles and Perylene Molecules on an Alumina Template. J. Phys. Chem. C, 123(31), 19175–19182.
Résumé: Combining in a synergic way inorganic and organic matter at a nanometer level has become a key research pathway for nanoelectronics, light harvesting, energy storage, or sensing. Herein, we demonstrate the nanoscale ordering at room temperature of a two-dimensional hybrid assembly combining a long-range ordered array of Pd nanoparticles (NPs) with perylene molecules. The ordering, driven by the periodic superstructure of the Al2O3 ultrathin layer support, has been achieved for 0.9 nm diameter NPs and flat-lying molecules with a 2:1 perylene/NP relative ratio. At a larger NP size and perylene coverage, molecules tilt up on alumina and adsorb on NPs. Combined near-field microscopy and optical spectroscopies provide a detailed understanding of the structural properties as a function of NP size and molecular coverage. This hybrid assembly opens the way to study at the molecular level the optical and electronic properties resulting from the coupling of organic molecules and nanoparticles using multiscale surface sensitive techniques.
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Alyabyeva, N., Ouvrard, A., Zakaria, A. M., & Bourguignon, B. (2019). Probing nanoparticle geometry down to subnanometer size: The benefits of vibrational spectroscopy. J. Phys. Chem. Lett., 10(3), 624–629.
Résumé: Understanding the role of nanoparticle size and shape in the binding of molecules is very relevant for heterogeneous catalysis and molecular electronics. The geometry of Pd nanoparticles (NPs) has been studied from very small clusters containing 4 atoms up to large (>500 atoms), well-faceted NPs. Their geometry was retrieved by combining scanning tunneling microscopy and vibrational sum frequency generation (SFG) spectroscopy of adsorbed CO. SFG has been revealed to be highly sensitive to the geometry of NPs smaller than 100 atoms by identifying the nature of CO adsorption sites. NP growth could be followed layer by layer in the critical size range corresponding to the transition from a nonmetallic to a metallic state and to oscillations of CO adsorption energy. NP height remained at two Pd planes up to 30 atoms, and adsorption energy minima correspond to the completion of successive layers.
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Brand, C., Debiossac, M., Susi, T., Aguillon, F., Kotakoski, J., Roncin P., & Arndt, M. (2019). Coherent diffraction of hydrogen through the 246 pm lattice of graphene. New J. Phys., 21, 033004.
Résumé: We study the diffraction of neutral hydrogen atoms through suspended single-layer graphene using molecular dynamics simulations based on density functional theory. Although the atoms have to overcome a transmission barrier, we find that the de Broglie wave function for H at 80 eV has a high probability to be coherently transmitted through about 18% of the graphene area, contrary to the case of He. We propose an experiment to realize the diffraction of atoms at the natural hexagon lattice period of 246 pm, leading to a more than 400-fold increase in beam separation of the coherently split atomic wave function compared to diffraction experiments at state-of-the art nano-machined masks. We expect this unusual wide coherent beam splitting to give rise to novel applications in atom interferometry.
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Cao, S., Achlan, M., Bryche, J. - F., Gogol, P., Dujardin, G., Raşeev, G., Le Moal, E., & Boer-Duchemin, E. (2019). An electrically induced probe of the modes of a plasmonic multilayer stack. Opt. Express, 27(23), 33011.
Résumé: A new single-image acquisition technique for the determination of the dispersion relation of the propagating modes of a plasmonic multilayer stack is introduced. This technique is based on an electrically-driven, spectrally broad excitation source which is nanoscale in size: the inelastic electron tunnel current between the tip of a scanning tunneling microscope (STM) and the sample. The resulting light from the excited modes of the system is collected in transmission using a microscope objective. The energy-momentum dispersion relation of the excited optical modes is then determined from the angle-resolved optical spectrum of the collected light. Experimental and theoretical results are obtained for metal-insulator-metal (MIM) stacks consisting of a silicon oxide layer (70, 190 or 310 nm thick) between two gold films (each with a thickness of 30 nm). The broadband characterization of hybrid plasmonic-photonic transverse magnetic (TM) modes involved in an avoided crossing is demonstrated and the advantages of this new technique over optical reflectivity measurements are evaluated
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Pommier, D., Bretel, R., López, L. E. P., Fabre, F., Mayne, A., Boer-Duchemin, E., Dujardin, G., Schull, G., Berciaud, S., & Le Moal, E. (2019). Scanning Tunneling Microscope-Induced Excitonic Luminescence of a Two-Dimensional Semiconductor. Phys. Rev. Lett., 123(2), 027402.
Résumé: The long sought-after goal of locally and spectroscopically probing the excitons of two-dimensional (2D) semiconductors is attained using a scanning tunneling microscope (STM). Excitonic luminescence from monolayer molybdenum diselenide (MoSe2) on a transparent conducting substrate is electrically excited in the tunnel junction of an STM under ambient conditions. By comparing the results with photoluminescence measurements, the emission mechanism is identified as the radiative recombination of bright A excitons. STM-induced luminescence is observed at bias voltages as low as those that correspond to the energy of the optical band gap of MoSe2. The proposed excitation mechanism is resonance energy transfer from the tunneling current to the excitons in the semiconductor, i.e., through virtual photon coupling. Additional mechanisms (e.g., charge injection) may come into play at bias voltages that are higher than the electronic band gap. Photon emission quantum efficiencies of up to 10−7 photons per electron are obtained, despite the lack of any participating plasmons. Our results demonstrate a new technique for investigating the excitonic and optoelectronic properties of 2D semiconductors and their heterostructures at the nanometer scale.
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Riemensberger, J., Neppl, S., Potamianos, D., Schaffer, M., Schnitzenbaumer, M., Ossiander, M., Schroder, C., Guggenmos, A., Kleineberg, U., Menzel, D., Allegretti, F., Barth, J. V., Kienberger, R., Feulner, P., Borisov, A. G., Echenique, P. M., & Kazansky A. K. (2019). Attosecond Dynamics of sp-Band Photoexcitation. Phys. Rev. Lett., 123(17), 176801.
Résumé: We report measurements of the temporal dynamics of the valence band photoemission from the magnesium (0001) surface across the resonance of the ¯Γ surface state at 134 eV and link them to observations of high-resolution synchrotron photoemission and numerical calculations of the time-dependent Schrödinger equation using an effective single-electron model potential. We observe a decrease in the time delay between photoemission from delocalized valence states and the localized core orbitals on resonance. Our approach to rigorously link excitation energy-resolved conventional steady-state photoemission with attosecond streaking spectroscopy reveals the connection between energy-space properties of bound electronic states and the temporal dynamics of the fundamental electronic excitations underlying the photoelectric effect.
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Yengui, M., Duverger, E., Sonnet, P., & Riedel, D. (2019). Translational Manipulation of Magnetic Cobalt Adatoms on the Si(100)-2 × 1 Surface at 9 K. J. Phys. Chem. C, 123(43), 26415–26423.
Résumé: The controlled motion of magnetic impurities on semiconductor (SC) surfaces is of crucial importance for atomic scale magnetic devices. Still challenging because of their strong reactivity with SCs, magnetic impurities are usually studied in bulk SCs, thus preventing their manipulation. Here, we show that a single Co adatom can be steadied on the bare Si(100)-2 × 1 surface in a pedestal configuration at low temperature, 9 K, and moved along the reconstructed silicon dimer rows via the use of a scanning tunneling microscope. The electronic characteristics of the Co adatom and its surroundings are investigated via topography and dI/dV measurements. Our findings reveal that the Si–Co bonding involves hybridization between the Si-p and the Co-pxpy orbitals. This configuration indicates that the Co-d orbitals remain weakly hybridized with the silicon atoms. These results are supported by density functional theory calculations where the role of the As dopant is discussed as well as the surface reconstruction. Therefore, we show that the motion direction of the Co adatom can be influenced by the surrounding c(4 × 2) or p(2 × 2) surface reconstruction phases, thus opening future interesting magnetic applications.
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