Magazine Articles |
Le Moal, E., Boer-Duchemin, E. (2020). La nano-optique sous la pointe d’un microscope à effet tunnel. Photoniques, 102, 31–34.
Résumé: Le microscope à effet tunnel (STM) n’est pas seulement un outil de sciences des surfaces qui produit de magnifiques images résolues à l’échelle atomique. Le courant tunnel sous la pointe du STM est également une source d’excitation optique extrêmement locale, ce qui en fait un extraordinaire outil de la nano-optique. Ici, nous donnons un aperçu des possibilités de cet outil en plasmonique et en électroluminescence, lorsque STM et microscopie optique sont associés dans un même instrument.
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Peer-reviewed Publications |
Aguillon, F., Marinica, D. C., & Borisov, A. G. (2020). Molecule Detection with Graphene Dimer Nanoantennas. J. Phys. Chem. C, 124(51), 28210–28219.
Résumé: Using the tight binding description of the electronic structure of graphene and a time-dependent quantum approach, we address the vibrational excitation of molecules in the near field of a graphene nanoantenna. The possibility of tuning the graphene plasmon frequency by electrostatic doping allows an efficient resonant excitation of the infrared (IR)-active vibrational modes via the coupling between the molecular dipole and plasmon near field. We show that for the carbon monoxide CO molecules placed in the gap of a dimer antenna formed by the 20 nm size graphene patches, an excitation of the υ=1←0 transition leads to a distinct molecular signature in the IR absorption spectrum of the system. A very small number of molecules down to a single molecule placed in the antenna gap can thus be detected. Along with IR-active vibrations, the inhomogeneity of the plasmonic near field allows vibrational excitation of IR-inactive molecules via molecular quadrupole. The resonant excitation of the N2 molecule vibration is thus observed in the calculated absorption spectra, albeit the molecule signature is essentially smaller than for the CO molecule. Obtained with molecules described on the ab initio quantum chemistry level, our results provide quantitative insights into the performance of graphene nanoflakes and their dimers for molecular sensing.
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Alyabyeva, N., Ouvrard, A., Bavencoffe, M., Lindfors-Vrejoiu, I., Kolomiytsev, A., Solodovnik, M., Ageev, O., & McGrouther, D. (2020). Control of binary states of ferroic orders in bi-domain BiFeO3 nanoislands. Appl. Phys. Lett., 116(19), 192904.
Résumé: Understanding switching mechanisms in multiferroics such as BiFeO3 (BFO) is an important challenge to control ferroic orders (ferroelectric or ferroelastic) as it could lead to the design of non-volatile memories based on magnetoelectric coupling. Here, we demonstrate an alternative way to control the binary states of ferroic orders by locally applying pressure and electric field in ferroelectric bi-domains confined in single BFO nanoislands. The study of the electronic transport properties and domain orientations using atomic force microscopy (AFM) based techniques enabled us to determine the electric and mechanical parameters at which ferroelectric and ferroelastic resistive switching can be observed. Nanoislands exhibited binary high and low resistance states without scaling effect, with high performance switching characteristics. Positive-forward rectifying behavior at high tip force was interpreted by the formation of a subsurface non-conductive interface due to the strain gradient. Ferroelastic switching at the surface was associated with a symmetry-breaking induced by electromechanical coupling between the AFM tip and the BFO thin film. It led to out-of-plane polarization pinning that allows performing only in-plane switching accompanied by nucleation and propagation of a conductive domain wall. The control of ferroic binary states by the electric field and pressure may pave the way for multilevel data storage devices.
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Babaze, A., Esteban, R., Aizpurua, J., & Borisov, A. G. (2020). Second-Harmonic Generation from a Quantum Emitter Coupled to a Metallic Nanoantenna. ACS Photonics, 7(3), 701–713.
Résumé: We use time-dependent density functional theory and a semiclassical model to study second-harmonic generation in a system comprising a quantum emitter and a spherical metallic nanoparticle, where the transition frequency of the quantum emitter is set to be resonant with the second harmonic of the incident frequency. The quantum emitter is shown to enable strong second-harmonic generation, which is otherwise forbidden because of symmetry constraints. The time-dependent density functional theory calculations allow one to identify the main mechanism driving this nonlinear effect, where the quantum emitter plays the role of an optical resonator that experiences the nonlinear near fields generated by the metallic nanoantenna located nearby. The influence of the intrinsic properties of the quantum emitter and the nanoantenna, together with the relative position of both in the coupled system, allows for a high degree of control of the nonlinear light emission. The main effects and contributions to this nonlinear process can be correctly captured by a semiclassical description developed in this work.
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Bocan, G. A., Breiss, H., Szilasi, S., Momeni, A., Staicu Casagrande, E. M., Gravielle, M. S., Sánchez, E. A., & Khemliche, H. (2020). Anomalous KCl(001) Surface Corrugation from Fast He Diffraction at Very Grazing Incidence. Phys. Rev. Lett., 125, 096101.
Résumé: We present theoretical and experimental evidence of an anomalous surface corrugation behavior in He-KCl(001) for incidence along ⟨110⟩. When the He normal energy decreases below 100 meV, i.e., He-surface distances Z>2 Å, the corrugation unexpectedly increases up to an impressive ≳85%. This is not due to van der Waals interactions but to the combination of soft potential effects and the evolution of He-cation and He-anion interactions with Z. This feature, not previously analyzed on alkali-halide surfaces, may favor the alignment properties of weakly interacting overlayers.
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Cao, S., Zapata-Herrera, M., Campos, A., Le Moal, E., Marguet, S., Dujardin, G., Kociak, M., Aizpurua, J., Borisov, A. G., & Boer-Duchemin, E. (2020). Probing the Radiative Electromagnetic Local Density of States in Nanostructures with a Scanning Tunneling Microscope. ACS Photonics, 7(5), 1280–1289.
Résumé: A novel technique for the investigation of the radiative contribution to the electromagnetic local density of states is presented. The inelastic tunneling current from a scanning tunneling microscope (STM) is used to locally and electrically excite the plasmonic modes of a triangular gold platelet. The radiative decay of these modes is detected through the transparent substrate in the far field. Emission spectra, which depend on the position of the STM excitation, as well as energy-filtered emission maps for particular spectral windows are acquired using this technique. The STM-nanosource spectroscopy and microscopy results are compared to those obtained from spatially resolved electron energy loss spectroscopy (EELS) maps on similar platelets. While EELS is known to be related to the total projected electromagnetic local density of states, the light emission from the STM-nanosource is shown here to select the radiative contribution. Full electromagnetic calculations are carried out to explain the experimental STM data and provide valuable insight into the radiative nature of the different contributions of the breathing and edge plasmon modes of the nanoparticles. Our results introduce the STM-nanosource as a tool to investigate and engineer light emission at the nanoscale.
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Debiossac, M., Roncin, P., & Borisov, A. G. (2020). Refraction of Fast Ne Atoms in the Attractive Well of a LiF(001) Surface. J. Phys. Chem. Lett., 11, 4564–4569.
Résumé: Ne atoms with energies of </=3 keV are diffracted under grazing angles of incidence from a LiF(001) surface. For a small momentum component of the incident beam perpendicular to the surface, we observe an increase in the elastic rainbow angle together with a broadening of the inelastic scattering profile. We interpret these two effects as the refraction of the atomic wave in the attractive part of the surface potential. We use a fast, rigorous dynamical diffraction calculation to find a projectile-surface potential model that enables a quantitative reproduction of the experimental data for </=10 diffraction orders. This allows us to extract an attractive potential well depth of 10.4 meV. Our results set a benchmark for more refined surface potential models that include the weak van der Waals region, a long-standing challenge in the study of atom-surface interactions.
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Duverger, E., Boyer, A. - G., Sauriat-Dorizon, H., Sonnet, P., Stephan, R., Hanf, M. - C., & Riedel, D. (2020). Two-Dimensional Functionalized Ultrathin Semi-Insulating CaF2 Layer on the Si(100) Surface at a Low Temperature for Molecular Electronic Decoupling. ACS Appl. Mater. Interfaces, 12(26), 29661–29670.
Résumé: The ability to precisely control the electronic coupling/decoupling of adsorbates from surfaces is an essential goal. It is important for fundamental studies not only in surface science but also in several applied domains including, for example, miniaturized molecular electronic or for the development of various devices such as nanoscale biosensors or photovoltaic cells. Here, we provide atomic-scale experimental and theoretical investigations of a semi-insulating layer grown on a silicon surface via its epitaxy with CaF2. We show that, following the formation of a wetting layer, the ensuing organized unit cells are coupled to additional physisorbed CaF2 molecules, periodically located in their surroundings. This configuration shapes the formation of ribbons of stripes that functionalize the semiconductor surface. The obtained assembly, having a monolayer thickness, reveals a surface gap energy of ∼3.2 eV. The adsorption of iron tetraphenylporphyrin molecules on the ribbons of stripes is used to estimate the electronic insulating properties of this structure via differential conductance measurements. Density functional theory (DFT) including several levels of complexity (annealing, DFT + U, and nonlocal van der Waals functionals) is employed to reproduce our experimental observations. Our findings offer a unique and robust template that brings an alternative solution to electronic semi-insulating layers on metal surfaces such as NaCl. Hence, CaF2/Si(100) ribbon of stripe structures, whose lengths can reach more than 100 nm, can be used as a versatile surface platform for various atomic-scale studies of molecular devices.
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Humberg, N., Bretel, R., Eslam, A., Le Moal, E., & Sokolowski, M. (2020). Hydrogen-Bonded One-Dimensional Chains of Quinacridone on Ag(100) and Cu(111): The Role of Chirality and Surface Bonding. J. Phys. Chem. C, 124(45), 24861–24873.
Résumé: The adsorption and ordering of the prochiral molecule quinacridone (QA) on the Ag(100) and Cu(111) surfaces were studied by low-energy electron diffraction and scanning tunneling microscopy. Upon adsorption, the molecules form parallel homochiral chains of flat-lying molecules linked together via hydrogen bonds on both surfaces, but these chains show significant surface-dependent differences concerning their lateral order. On both substrates, the chains are not thermodynamically stable but only metastable and stabilized by kinetic barriers. On the Ag(100) surface, annealing induces a phase transition to a highly ordered and heterochiral structure with a reduced density of hydrogen bonds. The related loss of bonding energy is overcompensated by a stronger bonding to the substrate, yielding a commensurate structure. For QA on Ag(100), we propose that during the initial chain formation and the phase transition upon annealing, the molecules can change their handedness by rotating around their long axes. In contrast, the initial chain formation and the phase transitions of QA on the Cu(111) surface appear to be subject to stronger kinetic limitations. These are explained by stronger substrate molecule interactions on Cu(111), which reduce the diffusion and the possibility for a change of handedness in comparison to QA on Ag(100). We discuss how the intermolecular hydrogen bonds, the 2D chirality, and the different chemical reactivities of the two surfaces [Ag(100) and Cu(111)] influence the structural formation of QA aggregates. We compare our results to the results for QA on Ag(111) reported previously by Wagner et al. [JPCC2014, 118, 10911-10920].
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Ludwig, M., Aguirregabiria, G., Ritzkowsky, F., Rybka, T., Marinica, D. C., Aizpurua, J., Borisov, A. G., Leitenstorfer, A., & Brida D. (2020). Sub-femtosecond electron transport in a nanoscale gap. Nat. Phys., 16, 341–345.
Résumé: The strong fields associated with few-cycle pulses can drive highly nonlinear phenomena, allowing the direct control of electrons in condensed matter systems. In this context, by employing near-infrared single-cycle pulse pairs, we measure interferometric autocorrelations of the ultrafast currents induced by optical field emission at the nanogap of a single plasmonic nanocircuit. The dynamics of this ultrafast electron nanotransport depends on the precise temporal field profile of the optical driving pulse. Current autocorrelations are acquired with sub-femtosecond temporal resolution as a function of both pulse delay and absolute carrier-envelope phase. Quantitative modelling of the experiments enables us to monitor the spatiotemporal evolution of the electron density and currents induced in the system and to elucidate the physics underlying the electron transfer driven by strong optical fields in plasmonic gaps. Specifically, we clarify the interplay between the carrier-envelope phase of the driving pulse, plasmonic resonance and quiver motion.
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Ludwig, M., Kazansky, A. K., Aguirregabiria, G., Marinica, D. C., Falk, M., Leitenstorfer, A., Brida, D., Aizpurua, J., & Borisov, A. G. (2020). Active control of ultrafast electron dynamics in plasmonic gaps using an applied bias. Phys. Rev. B, 101(24), 241412.
Résumé: In this joint experimental and theoretical study we demonstrate coherent control of the optical field emission and electron transport in plasmonic gaps subjected to intense single-cycle laser pulses. Our results show that an external THz field or a minor dc bias, orders of magnitude smaller than the optical bias owing to the laser field, allows one to modulate and direct the electron photocurrents in the gap of a connected nanoantenna operating as an ultrafast nanoscale vacuum diode for lightwave electronics. Using time-dependent density functional theory calculations we elucidate the main physical mechanisms behind the observed effects and show that an applied dc field significantly modifies the optical field emission and quiver motion of photoemitted electrons within the gap. The quantum many-body theory reproduces the measured net electron transport in the experimental device, which allows us to establish a paradigm for controlling nanocircuits at petahertz frequencies.
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Raseev, G., Achlan, M. (2020). MIM thin film stack: flux enhancement due to coupling of surface plasmon polariton with wave guide modes. J. Phys. D: Appl. Phys., 53(50), 505303.
Résumé: A theoretical study is presented of the dispersion of surface plasmon polariton (SPP) and wave guide (WG) modes of a metal-insulator-metal (MIM) thin film stack. We study the dispersion of the reflectance and of the transmitted flux, originating from a local excitation source, of an asymmetric MIM air-Au-SiO2-Au-Ti-glass material system in the infrared and visible spectral region for a wide range of SiO2 and gold thicknesses, $d{\mathrm{SiO}2}$ and $d{\mathrm{Au}}$. In comparison to reference stacks of air-Au-glass or air-SiO2-glass, between 1.4 and 2.0 eV, the transmitted flux intensity is enhanced 12 or 25 times, in the emission direction of the in-plane wave vector $k\rho/k0\approx$1.05 and for a thickness of $d{\mathrm{SiO}2}\in$[300–700] nm, respectively. This enhancement is attributed to the coupling, through the avoided crossings, between the SPP${\mathrm{air}}$ and WG modes. As the fields of the SPP$_{\mathrm{air}}$ and WG modes are located in different regions of space the enhancement is nearly independent of the number of nodes in the WG mode. In summary we have identified sets of parameters giving rise to the observables enhancement. Therefore the present MIM thin film stack is a simple and a versatile system for the use in applications.
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Actes de Conférences |
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Aguilar-Galindo, F., Díaz-Tendero, S., & Borisov, A. G. (2020). Resonant anionic states of organic molecules adsorbed on metal surfaces. In Journal of Physics: Conference Series (Vol. 1412, 202015).
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Staicu Casagrande, E. M., Momeni, A., & Khemliche, H. (2020). Fast atom interaction with surfaces at grazing incidence: classical and quantum scattering applied to thin film growth. In Journal of Physics: Conference Series (Vol. 1412, 202010). IOP.
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