2018 
Aguirregabiria, G., Marinica, D. C., Esteban, R., Kazansky, A. K., Aizpurua, J., & Borisov, A. G. (2018). Role of electron tunneling in the nonlinear response of plasmonic nanogaps. Phys. Rev. B, 97(11), 115430.


2017 
Aguirregabiria, G., Marinica, D. C., Esteban, R., Kazansky, A. K., Aizpurua, J., & Borisov, A. G. (2017). Electric FieldInduced High Order Nonlinearity in Plasmonic Nanoparticles Retrieved with TimeDependent Density Functional Theory. ACS Photonics, 4(3), 613–620.


Debiossac, M., Atkinson, P., Zugarramurdi, A., Eddrief, M., Finocchi, F., Etgens, V. H., Momeni, A., Khemliche, H., Borisov, A. G., & Roncin, P. (2017). Fast atom diffraction inside a molecular beam epitaxy chamber, a rich combination. Applied Surface Science, 391, 53–58.
Résumé: brief oveview of the benefit of having a grazing incidence fast atom diffraction (GIFAD) setup inside a molecular beam eppitaxy setup.


Herrera, M. Z., Kazansky, A. K., Aizpurua, J., & Borisov, A. G. (2017). Quantum description of the optical response of charged monolayer–thick metallic patch nanoantennas. Phys. Rev. B, 95(24), 245413.


Koval, N. E., Borisov, A. G., Rosa, L. F. S., Stori, E. M., Dias, J. F., Grande, P. L., SánchezPortal, D., & Muiño, R. D. (2017). Vicinage effect in the energy loss of H2 dimers: Experiment and calculations based on timedependent densityfunctional theory. Phys. Rev. A, 95(6), 062707.


Marinica, D. C., Kazansky, A. K., & Borisov, A. G. (2017). Electrical control of the light absorption in quantumwell functionalized junctions between thin metallic films. Phys. Rev. B, 96(24), 245407.


Matias, F., Fadanelli, R. C., Grande, P. L., Koval, N. E., Muiño, R. D., Borisov, A. G., Arista, N. R., & Schiwietz, G. (2017). Ground and excitedstate scattering potentials for the stopping of protons in an electron gas. J. Phys. B: At. Mol. Opt. Phys., 50(18), 185201.


2016 
Gruber, E., Wilhelm, R. A., Petuya, R., Smejkal, V., Kozubek, R., Hierzenberger, A., Bayer, B. C., Aldazabal, I., Kazansky, A. K., Libisch, F., Krasheninnikov, A. V., Schleberger, M., Facsko, S., Borisov, A. G., Arnau, A., & Aumayr, F. (2016). Ultrafast electronic response of graphene to a strong and localized electric field. Nat Commun, 7, 13948.
Résumé: The way conduction electrons respond to ultrafast external perturbations in low dimensional materials is at the core of the design of future devices for (opto)electronics, photodetection and spintronics. Highly charged ions provide a tool for probing the electronic response of solids to extremely strong electric fields localized down to nanometresized areas. With ion transmission times in the order of femtoseconds, we can directly probe the local electronic dynamics of an ultrathin foil on this timescale. Here we report on the ability of freestanding single layer graphene to provide tens of electrons for charge neutralization of a slow highly charged ion within a few femtoseconds. With values higher than 10(12) A cm(2), the resulting local current density in graphene exceeds previously measured breakdown currents by three orders of magnitude. Surprisingly, the passing ion does not tear nanometresized holes into the single layer graphene. We use timedependent density functional theory to gain insight into the multielectron dynamics.


Marinica, D.  C., Aizpurua, J., & Borisov, A. G. (2016). Quantum effects in the plasmon response of bimetallic coreshell nanostructures. Opt Express, 24(21), 23941–23956.
Résumé: We report a quantum mechanical study of the plasmonic response of bimetallic spherical core/shell nanoparticles. The systems comprise up to 10<sup>4</sup> electrons and their optical response is addressed with Time Dependent Density Functional Theory calculations. These quantum results are compared with classical electromagnetic calculations for core/shell systems formed by Al/Na, Al/Au and Ag/Na, as representative examples of bimetallic systems. We show that for shell widths in the nanometer range, the system cannot be described as a simple stack of two metals. The finite size effect and the transition layer formed between the core and the shell strongly modify the optical properties of the compound nanoparticle. In particular this configuration leads to a frequency shift of the plasmon resonance with shell character and an increased plasmon decay into electronhole pairs which eventually quenches this resonance for very thin shells. This effect is difficult to capture with a classical theory even upon adjustment of the parameters of a combination of metallic dielectric functions.


Teperik, T. V., Kazansky, A. K., & Borisov, A. G. (2016). Electron tunneling through water layer in nanogaps probed by plasmon resonances. Phys. Rev. B, 93(15), 155431.


Zapata Herrera, M., Aizpurua, J., Kazansky, A. K., & Borisov, A. G. (2016). Plasmon Response and Electron Dynamics in Charged Metallic Nanoparticles. Langmuir, 32(11), 2829–2840.
Résumé: Using the timedependent density functional theory, we perform quantum calculations of the electron dynamics in small charged metallic nanoparticles (clusters) of spherical geometry. We show that the excess charge is accumulated at the surface of the nanoparticle within a narrow layer given by the typical screening distance of the electronic system. As a consequence, for nanoparticles in vacuum, the dipolar plasmon mode displays only a small frequency shift upon charging. We obtain a blue shift for positively charged clusters and a red shift for negatively charged clusters, consistent with the change of the electron spillout from the nanoparticle boundaries. For negatively charged clusters, the Fermi level is eventually promoted above the vacuum level leading to the decay of the excess charge via resonant electron transfer into the continuum. We show that, depending on the charge, the process of electron loss can be very fast, on the femtosecond time scale. Our results are of great relevance to correctly interpret the optical response of the nanoparticles obtained in electrochemistry, and demonstrate that the measured shift of the plasmon resonances upon charging of nanoparticles cannot be explained without account for the surface chemistry and the dielectric environment.


Zhu, W., Esteban, R., Borisov, A. G., Baumberg, J. J., Nordlander, P., Lezec, H. J., Aizpurua, J., & Crozier, K. B. (2016). Quantum mechanical effects in plasmonic structures with subnanometre gaps. Nat Commun, 7, 11495.
Résumé: Metallic structures with nanogap features have proven highly effective as building blocks for plasmonic systems, as they can provide a wide tuning range of operating frequencies and large nearfield enhancements. Recent work has shown that quantum mechanical effects such as electron tunnelling and nonlocal screening become important as the gap distances approach the subnanometre lengthscale. Such quantum effects challenge the classical picture of nanogap plasmons and have stimulated a number of theoretical and experimental studies. This review outlines the findings of many groups into quantum mechanical effects in nanogap plasmons, and discusses outstanding challenges and future directions.


2015 
Barbry, M., Koval, P., Marchesin, F., Esteban, R., Borisov, A. G., Aizpurua, J., & SanchezPortal, D. (2015). Atomistic nearfield nanoplasmonics: reaching atomicscale resolution in nanooptics. Nano Lett, 15(5), 3410–3419.
Résumé: Electromagnetic field localization in nanoantennas is one of the leitmotivs that drives the development of plasmonics. The nearfields in these plasmonic nanoantennas are commonly addressed theoretically within classical frameworks that neglect atomicscale features. This approach is often appropriate since the irregularities produced at the atomic scale are typically hidden in farfield optical spectroscopies. However, a variety of physical and chemical processes rely on the fine distribution of the local fields at this ultraconfined scale. We use timedependent density functional theory and perform atomistic quantum mechanical calculations of the optical response of plasmonic nanoparticles, and their dimers, characterized by the presence of crystallographic planes, facets, vertices, and steps. Using sodium clusters as an example, we show that the atomistic details of the nanoparticles morphologies determine the presence of subnanometric nearfield hot spots that are further enhanced by the action of the underlying nanometric plasmonic fields. This situation is analogue to a selfsimilar nanoantenna cascade effect, scaled down to atomic dimensions, and it provides new insights into the limits of field enhancement and confinement, with important implications in the optical resolution of fieldenhanced spectroscopies and microscopies.


Esteban, R., Aguirregabiria, G., Borisov, A. G., Wang, Y. M., Nordlander, P., Bryant, G. W., & Aizpurua, J. (2015). The Morphology of Narrow Gaps Modifies the Plasmonic Response. ACS Photonics, 2(2), 295–305.


Esteban, R., Zugarramurdi, A., Zhang, P., Nordlander, P., GarciaVidal, F. J., Borisov, A. G., & Aizpurua, J. (2015). A classical treatment of optical tunneling in plasmonic gaps: extending the quantum corrected model to practical situations. Faraday Discuss, 178, 151–183.
Résumé: The optical response of plasmonic nanogaps is challenging to address when the separation between the two nanoparticles forming the gap is reduced to a few nanometers or even subnanometer distances. We have compared results of the plasmon response within different levels of approximation, and identified a classical local regime, a nonlocal regime and a quantum regime of interaction. For separations of a few Angstroms, in the quantum regime, optical tunneling can occur, strongly modifying the optics of the nanogap. We have considered a classical effective model, so called Quantum Corrected Model (QCM), that has been introduced to correctly describe the main features of optical transport in plasmonic nanogaps. The basics of this model are explained in detail, and its implementation is extended to include nonlocal effects and address practical situations involving different materials and temperatures of operation.


Lin, L., Zapata, M., Xiong, M., Liu, Z., Wang, S., Xu, H., Borisov, A. G., Gu, H., Nordlander, P., Aizpurua, J., & Ye, J. (2015). Nanooptics of Plasmonic Nanomatryoshkas: Shrinking the Size of a CoreShell Junction to Subnanometer. Nano Lett, 15(10), 6419–6428.
Résumé: Quantum effects in plasmonic systems play an important role in defining the optical response of structures with subnanometer gaps. Electron tunneling across the gaps can occur, altering both the farfield optical response and the nearfield confinement and enhancement. In this study, we experimentally and theoretically investigate plasmon coupling in gold “nanomatryoshka” (NM) nanoparticles with different coreshell separations. Plasmon coupling effects between the core and the shell become significant when their separation decreases to 15 nm. When their separation decreases to below 1 nm, the near and farfield properties can no longer be described by classical approaches but require the inclusion of quantum mechanical effects such as electron transport through the selfassembled monolayer of molecular junction. In addition, surfaceenhanced Raman scattering measurements indicate strong electrontransport induced charge transfer across the molecular junction. Our quantum modeling provides an estimate for the AC conductances of molecules in the junction. The insights acquired from this work pave the way for the development of novel quantum plasmonic devices and substrates for surfaceenhanced Raman scattering.


Marinica, D. C., Zapata, M., Nordlander, P., Kazansky, A. K., M Echenique, P., Aizpurua, J., & Borisov, A. G. (2015). Active quantum plasmonics. Sci Adv, 1(11), e1501095.
Résumé: The ability of localized surface plasmons to squeeze light and engineer nanoscale electromagnetic fields through electronphoton coupling at dimensions below the wavelength has turned plasmonics into a driving tool in a variety of technological applications, targeting novel and more efficient optoelectronic processes. In this context, the development of active control of plasmon excitations is a major fundamental and practical challenge. We propose a mechanism for fast and active control of the optical response of metallic nanostructures based on exploiting quantum effects in subnanometric plasmonic gaps. By applying an external dc bias across a narrow gap, a substantial change in the tunneling conductance across the junction can be induced at optical frequencies, which modifies the plasmonic resonances of the system in a reversible manner. We demonstrate the feasibility of the concept using timedependent density functional theory calculations. Thus, along with twodimensional structures, metal nanoparticle plasmonics can benefit from the reversibility, fast response time, and versatility of an active control strategy based on applied bias. The proposed electrical manipulation of light using quantum plasmonics establishes a new platform for many practical applications in optoelectronics.


Zapata, M., Camacho Beltran, A. S., Borisov, A. G., & Aizpurua, J. (2015). Quantum effects in the optical response of extended plasmonic gaps: validation of the quantum corrected model in coreshell nanomatryushkas. Opt Express, 23(6), 8134–8149.
Résumé: Electron tunneling through narrow gaps between metal nanoparticles can strongly affect the plasmonic response of the hybrid nanostructure. Although quantum mechanical in nature, this effect can be properly taken into account within a classical framework of Maxwell equations using the socalled Quantum Corrected Model (QCM). We extend previous studies on spherical cluster and cylindrical nanowire dimers where the tunneling current occurs in the extremely localized gap regions, and perform quantum mechanical time dependent density functional theory (TDDFT) calculations of the plasmonic response of cylindrical coreshell nanoparticles (nanomatryushkas). In this axially symmetric situation, the tunneling region extends over the entire gap between the metal core and the metallic shell. For coreshell separations below 0.5 nm, the standard classical calculations fail to describe the plasmonic response of the cylindrical nanomatryushka, while the QCM can reproduce the quantum results. Using the QCM we also retrieve the quantum results for the absorption cross section of the spherical nanomatryushka calculated by V. Kulkarni et al. [Nano Lett. 13, 5873 (2013)]. The comparison between the model and the full quantum calculations establishes the applicability of the QCM for a wider range of geometries that hold tunneling gaps.


2014 
Debiossac, M., Zugarramurdi, A., LuncaPopa, P., Momeni, A., Khemliche, H., Borisov, A. G., & Roncin, P. (2014). Transient Quantum Trapping of Fast Atoms at Surfaces. PHYSICAL REVIEW LETTERS, 112(2).
Résumé: We report on the experimental observation and theoretical study of the bound state resonances in fast atom diffraction at surfaces. In our studies, the He4 atom beam has been scattered from a highquality LiF(001) surface at very small grazing incidence angles. In this regime, the reciprocal lattice vector exchange with the surface allows transient trapping of the 0.30.5 keV projectiles into the quasistationary states bound by the attractive atomsurface potential well which is only 10 meV deep. Analysis of the linewidths of the calculated and measured resonances reveals that prior to their release, the trapped projectiles preserve their coherence over travel distances along the surface as large as 0.2 μm, while being in average only at some angstroms in front of the last atomic plane.


Debiossac, M. and Z., A. and Khemliche, H. and Roncin, P. and Borisov, A. G. and Momeni, A. and Atkinson, P. and Eddrief, M. and Finocchi, F. and Etgens, V. H. (2014). Combined experimental and theoretical study of fast atom diffraction on the β2(2×4) reconstructed GaAs(001) surface. Phys. Rev. B, 90(15), 155308.
Résumé: A grazing incidence fast atom diffraction (GIFAD or FAD) setup, installed on a molecular beam epitaxy chamber, has been used to characterize the β2(2×4) reconstruction of a GaAs(001) surface at 530∘C under an As4 overpressure. Using a 400eV 4He beam, highresolution diffraction patterns with up to eighty wellresolved diffraction orders are observed simultaneously, providing a detailed fingerprint of the surface structure. Experimental diffraction data are in good agreement with results from quantum scattering calculations based on an ab initio projectilesurface interaction potential. Along with exact calculations, we show that a straightforward semiclassical analysis allows the features of the diffraction chart to be linked to the main characteristics of the surface reconstruction topography. Our results demonstrate that GIFAD is a technique suitable for measuring in situ the subtle details of complex surface reconstructions. We have performed measurements at very small incidence angles, where the kinetic energy of the projectile motion perpendicular to the surface can be reduced to less than 1 meV. This allowed the depth of the attractive van der Waals potential well to be estimated as −8.7 meV in very good agreement with results reported in literature.


2013 
Borisov, A. G., SanchezPortal, D., Kazansky, A. K., & Echenique, P. M. (2013). Resonant and nonresonant processes in attosecond streaking from metals. PHYSICAL REVIEW B, 87(12), 121110.
Résumé: We report on the theoretical study of laserassisted attosecond photoemission from metals. The full timedependent quantum approach reveals the role of the resonant interband and nonresonant surface emission processes in formation of final attostreaking spectra. The present results explain recent experimental data on magnesium and show that the valence band streaking essentially reflects the respective weight of surface and resonant bulk electron ejection. DOI: 10.1103/PhysRevB.87.121110


Koval, N. E., SánchezPortal, D., Borisov, A. G., & Díez Muiño, R. (2013). Dynamic screening and energy loss of antiprotons colliding with excited Al clusters. Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and , 317, 56–60.


Marinica, D. C., LourencoMartins, H., Aizpurua, J., & Borisov, A. G. (2013). Plexciton quenching by resonant electron transfer from quantum emitter to metallic nanoantenna. Nano Lett, 13(12), 5972–5978.
Résumé: Coupling molecular excitons and localized surface plasmons in hybrid nanostructures leads to appealing, tunable optical properties. In this respect, the knowledge about the excitation dynamics of a quantum emitter close to a plasmonic nanoantenna is of importance from fundamental and practical points of view. We address here the effect of the excited electron tunneling from the emitter into a metallic nanoparticle(s) in the optical response. When close to a plasmonic nanoparticle, the excited state localized on a quantum emitter becomes shortlived because of the electronic coupling with metal conduction band states. We show that as a consequence, the characteristic features associated with the quantum emitter disappear from the optical absorption spectrum. Thus, for the hybrid nanostructure studied here and comprising quantum emitter in the narrow gap of a plasmonic dimer nanoantenna, the quantum tunneling might quench the plexcitonic states. Under certain conditions the optical response of the system approaches that of the individual plasmonic dimer. Excitation decay via resonant electron transfer can play an important role in many situations of interest such as in surfaceenhanced spectroscopies, photovoltaics, catalysis, or quantum information, among others.


Teperik, T. V., Nordlander, P., Aizpurua, J., & Borisov, A. G. (2013). Quantum effects and nonlocality in strongly coupled plasmonic nanowire dimers. Opt. Express, 21(22), 27306.


Zugarramurdi, A., & Borisov, A. G. (2013). When fast atom diffraction turns 3D. Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and , 317, 83–89.


2012 
Borisov, A. G., Echenique, P. M., & Kazansky, A. K. (2012). Attostreaking with metallic nanoobjects. NEW JOURNAL OF PHYSICS, 14, 023036.
Résumé: The application of attosecond streaking spectroscopy (ASS) to direct timedomain studies of the plasmonic excitations in metallic nanoobjects is addressed theoretically. The streaking spectrograms for a rectangular gold nanoantenna and spherical gold clusters are obtained within strong field approximation using classical electron trajectory calculations. The results reported here for spherical clusters are also representative of spherical nanoshells. This study demonstrates that ASS allows for detailed characterization of plasmonic modes, including nearfield enhancement, frequency and decay rate. The role of the inhomogeneity of the induced electric fields is also demonstrated.


Esteban, R., Borisov, A. G., Nordlander, P., & Aizpurua, J. (2012). Bridging quantum and classical plasmonics with a quantumcorrected model. NATURE COMMUNICATIONS, 3, 825.
Résumé: Electromagnetic coupling between plasmonic resonances in metallic nanoparticles allows for engineering of the optical response and generation of strong localized nearfields. Classical electrodynamics fails to describe this coupling across subnanometer gaps, where quantum effects become important owing to nonlocal screening and the spillout of electrons. However, full quantum simulations are not presently feasible for realistically sized systems. Here we present a novel approach, the quantumcorrected model (QCM), that incorporates quantummechanical effects within a classical electrodynamic framework. The QCM approach models the junction between adjacent nanoparticles by means of a local dielectric response that includes electron tunnelling and tunnelling resistivity at the gap and can be integrated within a classical electrodynamical description of large and complex structures. The QCM predicts optical properties in excellent agreement with fully quantum mechanical calculations for small interacting systems, opening a new venue for addressing quantum effects in realistic plasmonic systems.


Marinica, D. C., Kazansky, A. K., Nordlander, P., Aizpurua, J., & Borisov, A. G. (2012). Quantum Plasmonics: Nonlinear Effects in the Field Enhancement of a Plasmonic Nanoparticle Dimer. NANO LETTERS, 12(3), 1333–1339.
Résumé: A fully quantum mechanical investigation using timedependent density functional theory reveals that the field enhancement in a coupled nanoparticle dimer can be strongly affected by nonlinear effects. We show that both classical as well as linear quantum mechanical descriptions of the system fail even for moderate incident light intensities. An interparticle current resulting from the strong field photo emission tends to neutralize the plasmoninduced surface charge densities on the opposite sides of the nanoparticle junction. Thus, the coupling between the two nanoparticles and the field enhancement is reduced as compared to linear theory. A substantial nonlinear effect is revealed already at incident powers of 10(9) W/cm(2) for interparticle separation distances as large as 1 nm and down to the touching limit.


Savage, K. J., Hawkeye, M. M., Esteban, R., Borisov, A. G., Aizpurua, J., & Baumberg, J. J. (2012). Revealing the quantum regime in tunnelling plasmonics. NATURE, 491(7425), 574–577.
Résumé: When two metal nanostructures are placed nanometres apart, their optically driven free electrons couple electrically across the gap. The resulting plasmons have enhanced optical fields of a specific colour tightly confined inside the gap. Many emerging nanophotonic technologies depend on the careful control of this plasmonic coupling, including optical nanoantennas for highsensitivity chemical and biological sensors(1), nanoscale control of active devices(24), and improved photovoltaic devices(5). But for subnanometre gaps, coherent quantum tunnelling becomes possible and the system enters a regime of extreme nonlocality in which previous classical treatments(614) fail. Electron correlations across the gap that are driven by quantum tunnelling require a new description of nonlocal transport, which is crucial in nanoscale optoelectronics and singlemolecule electronics. Here, by simultaneously measuring both the electrical and optical properties of two gold nanostructures with controllable subnanometre separation, we reveal the quantum regime of tunnelling plasmonics in unprecedented detail. All observed phenomena are in good agreement with recent quantumbased models of plasmonic systems(15), which eliminate the singularities predicted by classical theories. These findings imply that tunnelling establishes a quantum limit for plasmonic field confinement of about 10(8) lambda(3) for visible light (of wavelength lambda). Our work thus prompts new theoretical and experimental investigations into quantumdomain plasmonic systems, and will affect the future of nanoplasmonic device engineering and nanoscale photochemistry.


Schubert, K., Damm, A., Eremeev, S. V., Marks, M., Shibuta, M., Berthold, W., Guedde, J., Borisov, A. G., Tsirkin, S. S., Chulkov, E. V., & Hoefer, U. (2012). Momentumresolved electron dynamics of imagepotential states on Cu and Ag surfaces. PHYSICAL REVIEW B, 85(20), 205431.
Résumé: The dependence of the inelastic lifetime of electrons in the first n = 1 imagepotential state of clean and raregas covered Ag(111), Cu(111), and Cu(100) surfaces on their momentum parallel to the surface has been studied experimentally by means of timeand angleresolved twophoton photoemission spectroscopy (2PPE) and theoretically by calculations based on the manybody theory within the selfenergy formalism. Similar to the previously studied clean Cu(100) surface, the theoretical results are in excellent agreement with the experiment findings for Cu(111). For Ag(111), the theory overestimates the decay rate and its momentum dependence, which is attributed to the neglect of surface plasmon excitations. With increasing parallel momentum, the n = 1 state shifts out of the projected bulk band gap on both surfaces and turns into an imagepotential resonance. This opens an additional decay channel by resonant electron transfer into the bulk, which is theoretically treated by the application of the wave packet propagation approach. The expected stronger increase of the decay rate upon crossing the edge of the band gap, however, is not observed in the experiment. The decoupling of the imagepotential states from the metal surface upon adsorption of raregas layers results in a decrease of the decay rate as well as of its momentum dependence by a similar factor, which can be successfully explained by the change of interband and intraband contributions to the total decay rate.


Zugarramurdi, A., Zabala, N., Silkin, V. M., Chulkov, E. V., & Borisov, A. G. (2012). Quantumwell states with image state character for Pb overlayers on Cu(111). PHYSICAL REVIEW B, 86(7), 075434.
Résumé: We study theoretically the quantum well states (QWSs) localized in Pb overlayers on Cu(111) surface. Particular emphasis is given to the states with energies close to the vacuum level. Inclusion of the longrange image potential tail into the model potential description of the system allows us to show the effect of hybridization between QWSs and image potential states (ISs). The particleinabox energy sequence characteristic for QWSs evolves into the Rydberg series converging towards the vacuum level. The electron density of the corresponding states is partially moved from inside the metal overlayer into the vacuum. The decay rates due to the inelastic electronelectron scattering decrease with increasing energy, opposite to “conventional” QWSs and similar to the ISs. Manybody and wave packet propagation calculations of the inelastic decay rates are supplemented by simple analysis based on the phase accumulation model and wavefunction penetration approximation. This allows an analytical description of the dependence of the QWS/ISs hybridization on different parameters and, in particular, on the overlayer thickness.


2011 
Stepanow, S., Mugarza, A., Ceballos, G., Gambardella, P., Aldazabal, I., Borisov, A. G., & Arnau, A. (2011). Localization, splitting, and mixing of field emission resonances induced by alkali metal clusters on Cu(100). PHYSICAL REVIEW B, 83(11), 115101.
Résumé: We report on a joint scanning tunneling microscopy (STM) and theoretical wave packet propagation study of field emission resonances (FER's) of nanosized alkali metal clusters deposited on a Cu(100) surface. In addition to FER's of the pristine Cu(100) surface, we observe the appearance of islandinduced resonances that are particularly well resolved for STM bias voltage values corresponding to electron energies inside the projected band gap of the substrate. The corresponding dI/dV maps reveal islandinduced resonances of different nature. Their electronic densities are localized either inside the alkali cluster or on its boundaries. Our model calculations allow us to explain the experimental results as due to the coexistence and mixing of two kinds of islandinduced states. On the one side, since the alkali work function is lower than that of the substrate, the nanosized alkali metal clusters introduce intrinsic localized electronic states pinned to the vacuum level above the cluster. These states can be seen as the FER's of the complete alkali overlayer quantized by the cluster boundaries. On the other side, the attractive potential well due to the alkali metal cluster leads to twodimensional (2D) localization of the FER's of the Cu(100) surface, the corresponding split component of the resonances appearing below the bottom of the parent continuum. Our main conclusions are based on the attractive nature of the alkali adisland potential. They are of general validity and, therefore, significant to understand electron confinement in 2D.


Zugarramurdi, A., Borisov, A. G., Zabala, N., Chulkov, E. V., & Puska, M. J. (2011). Clustering and conductance in breakage of sodium nanowires. PHYSICAL REVIEW B, 83(3), 035402.
Résumé: We study the conductance during the elongation and breakage of Na nanowires described with the ultimate jellium model. A combined approach is used where the nanowire breakage is simulated selfconsistently within the densityfunctional theory, and the wave packet propagation technique is applied for ballistic electron transport. For certain conditions the breakage of the nanowire is preceded by formation of clusters of magic size in the break junction. This affects the conductance G, in particular the shape of the G = 3G(0) to G = G(0) (=2e(2)/h) step upon elongation. The observed trends can be explained as due to the transient trapping of ballistic electrons inside the cluster, leading to a resonant character of the electron transport through the break junction. The clusterderived resonances appear as peak structures in the differential conductance which may serve as an experimental signature of clustering.


Zugarramurdi, A., Zabala, N., Borisov, A. G., & Chulkov, E. V. (2011). Comment on “Phase Contribution of Image Potential on Empty Quantum Well States in Pb Islands on the Cu(111) Surface”. PHYSICAL REVIEW LETTERS, 106(24), 249601.


Zugarramurdi, A., Zabala, N., Borisov, A. G., & Chulkov, E. V. (2011). Theoretical study of constant current scanning tunneling spectroscopy in Pb overlayers. PHYSICAL REVIEW B, 84(11), 115422.
Résumé: We present a theoretical study of the constant current scanning tunneling spectroscopy of quantum well states localized in Pb(111) overlayers on Cu(111) surfaces. The distancevoltage characteristic of the tunneling junction is obtained with a mixed approach. The wave packet propagation technique is applied to describe electron tunneling from the tip into the sample, and the density functional calculations provide the necessary inputs for the onedimensional model potential representation of the system. The excitedstate population decay mechanisms via inelastic electronelectron and electronphonon interactions are taken into account with a biasdependent absorbing potential introduced in the metal. Our results are in good agreement with recent experimental studies [Phys. Rev. Lett. 102, 196102 (2009), Phys. Rev. B 81, 205438 (2010)] over the energy range where the freeelectron description of the Pb overlayer used here applies. We find that at high bias the quantum well states experience a Stark energy shift and partially acquire a character of field emission resonances. The present model study also sheds light at the experimentally observed departure of the energies of the quantum well states from the particleinabox prediction for the bias above 4 eV. The measured trend can be consistently explained as due to the departure of the realistic Pb band structure in the GammaL direction from freeelectron parabola when the electron momentum approaches the Gamma point.


2010 
PerezGonzalez, O., Zabala, N., Borisov, A. G., Halas, N. J., Nordlander, P., & Aizpurua, J. (2010). Optical Spectroscopy of Conductive Junctions in Plasmonic Cavities. NANO LETTERS, 10(8), 3090–3095.
Résumé: The optical properties of a nanoparticle dimer bridged by a conductive junction depend strongly on the junction conductivity. As the conductivity increases, the bonding dimer plasmon blueshifts and broadens. For large conductance, a low energy charge transfer plasmon also appears in the spectra with a line width that decreases with increasing conductance. A simple physical model for the understanding of the spectral feature is presented. Our finding of a strong influence of junction conductivity on the optical spectrum suggests that plasmonic cavities might serve as probes of molecular conductance at elevated frequencies not accessible through electrical measurements.


Quijada, M., Diez Muino, R., Borisov, A. G., Alonso, J. A., & Echenique, P. M. (2010). Lifetime of electronic excitations in metal nanoparticles. NEW JOURNAL OF PHYSICS, 12, 053023.
Résumé: Electronic excitations in metal particles with sizes up to a few nanometers are shown to have a oneelectron character when a laser pulse is applied off the plasmon resonance. The calculated lifetimes of these excitations are in the femtosecond timescale but their values are substantially different from those in bulk. This deviation can be explained from the large weight of the excitation wave function in the nanoparticle surface region, where dynamic screening is significantly reduced. The wellknown quadratic dependence of the lifetime with the excitation energy in bulk breaks down in these finitesize systems.


Riedel, D., Delattre, R., Borisov, A. G., & Teperik, T. V. (2010). A Scanning Tunneling Microscope as a Tunable Nanoantenna for Atomic Scale Control of OpticalField Enhancement. NANO LETTERS, 10(10), 3857–3862.
Résumé: The high stability of a low temperature (9 K) scanning tunneling microscope junction is used to precisely adjust the enhancement of an external pulsed vacuum ultraviolet (VUV) laser The ensuing VUV opticalfield strength is mapped on an hydrogenated Si(100) surface by imprinting locally onephoton atomic scale hydrogen desorption Subsequent to irradiation, topography of the Si(100) H surface at the reacted area revealed a desorption spot with unprecedented atomic precision Our results show that the shapes. positions. and sizes of the desorption spots are correlated to the calculated opticalfield structure, offering real control of the opticalheld distribution at molecular scale


2009 
Teperik, T. V., & Borisov, A. G. (2009). Optical resonances in the scattering of light from a nanostructured metal surface: A threedimensional numerical study. PHYSICAL REVIEW B, 79(24), 245409.
Résumé: We present the full threedimensional numerical study of the scattering of light by the gold substrate composed of square periodic array of inverted pyramidal pits. The timedependent wavepacketpropagation approach was used to extract the complete scattering matrix as well as the near fields. The role of the pitlocalized and surfacesupported plasmonic modes in resonant reflection spectra and field enhancement is revealed. We show that the resonances in the specular reflection arise because of the excitation of the pitlocalized plasmons while resonant absorption is linked with excitation of the surfaceplasmon polaritons. For certain structure parameters absorption can reach 100%. Our theoretical results are in a good agreement with recently published experimental data [N. M. B. Perney , Opt. Express 14, 847 (2006); Phys. Rev. B 76, 035426 (2007)]. We also show that present structure allows one to obtain zero specular reflection where all scattered intensity is redirected into the grazing beams.</p>.


Zugarramurdi, A., Zabala, N., Silkin, V. M., Borisov, A. G., & Chulkov, E. V. (2009). Lifetimes of quantum well states and resonances in Pb overlayers on Cu(111). PHYSICAL REVIEW B, 80(11), 115425.
Résumé: We present results of calculations of the lifetimes of excited electrons (holes) in quantum well states and quantum well resonances in Pb overlayers supported on Cu(111). Manybody decay via inelastic energy relaxation and oneelectron decay via energyconserving oneelectron transfer into the substrate are considered. Oneelectron energies and wave functions have been computed for different coverages of the Pb overlayer (from 1 to 18 monolayers) by using a onedimensional pseudopotential for the entire overlayersubstrate system in the framework of density functional theory within the local density approximation. The elastic (energyconserving resonant electron transfer) contribution to the total lifetime broadening of quantum well resonances has been calculated within the wave packet propagation method. The inelastic electronelectron (manybody) contribution to the lifetime broadening of both occupied and unoccupied quantum well states has been evaluated using GW approximation. The decay mechanisms of both quantum well states and quantum well resonances in thick overlayers are discussed.


2008 
Marinica, D. C., Borisov, A. G., & Shabanov, S. V. (2008). Bound States in the continuum in photonics. PHYSICAL REVIEW LETTERS, 100(18), 183902.
Résumé: With examples of two parallel dielectric gratings and two arrays of thin parallel dielectric cylinders, it is shown that the interaction between trapped electromagnetic modes can lead to scattering resonances with practically zero width. Such resonances are the bound states in the radiation continuum first discovered in quantum systems by von Neumann and Wigner. Potential applications of such photonic systems include: large amplification of electromagnetic fields within photonic structures and, hence, enhancement of nonlinear phenomena, biosensing, as well as perfect filters and waveguides for a particular frequency, and impurity detection.


Quijada, M., Borisov, A. G., & Muino, R. D. (2008). Timedependent density functional calculation of the energy loss of antiprotons colliding with metallic nanoshells. PHYSICA STATUS SOLIDI AAPPLICATIONS AND MATERIALS SCIENCE, 205(6), 1312–1316.
Résumé: Timedependent density functional theory is used to study the interaction between antiprotons and metallic nanoshells. The ground state electronic properties of the nanoshell are obtained in the jellium approximation. The energy lost by the antiproton during the collision is calculated and compared to that suffered by antiprotons traveling in metal clusters. The resulting energy loss per unit path length of material in thin nanoshells is larger than the corresponding quantity for clusters. It is shown that the collision process can be interpreted as the antiproton crossing of two nearly bidimensional independent metallic systems. (C) 2008 WILEYVCH Verlag GmbH & Co. KGaA, Weinheim.


Teperik, T. V., Garcia de Abajo, F. J., Borisov, A. G., Abdelsalam, M., Bartlett, P. N., Sugawara, Y., & Baumberg, J. J. (2008). Omnidirectional absorption in nanostructured metal surfaces. NATURE PHOTONICS, 2(5), 299–301.
Résumé: Light absorbers available at present provide far from optimal blackbody performance. The need for more efficient absorbers is particularly acute on the microscale, where they can play a significant role in preventing crosstalk between optical interconnects, and also as thermal lightemitting sources. Several efforts have been made in this context to achieve neartotal but directionally dependent absorption using periodic grating structures(17). However, the ability to absorb light completely for any incident direction of light remains a challenge. Here we show that total omnidirectional absorption of light can be achieved in nanostructured metal surfaces that sustain localized optical excitations. The effect is realized over a full range of incident angles and can be tuned throughout the visible and nearinfrared regimes by scaling the nanostructure dimensions. We suggest that surfaces displaying omnidirectional absorption will play a key role in devising efficient photovoltaic cells in which the absorbed light leads to electronhole pair production.


2003 
Borisov, A. G., Sidis, V., Roncin, P., Momeni, A., Khemliche, H., Mertens, A., & Winter, H. (2003). F formation via simultaneous twoelectron capture during grazing scattering of F+ ions from a LiF(001) surface. PHYSICAL REVIEW B, 67(11), 115403.
Résumé: For slow F+ ions (v<0.05 a.u.) scattered from a clean and flat LiF(001) surface under a grazing angle of incidence, large fractions of negative F ions have recently been observed in the reflected beam, while for neutral F0 projectiles no negative F ions are produced in the same velocity range [P. Roncin , Phys. Rev. Lett. 89, 043201 (2002)]. From detailed studies on projectile energy loss and charge fractions, the conclusion was drawn that the F ions are formed from F+ via a simultaneous capture of two electrons from adjacent F sites at the surface. We present a theoretical description of the doubleelectroncapture process leading to F formation from F+ projectiles grazingly scattered from the LiF(001) surface. We use quantum chemistry calculations to determine the relevant Hamiltonian matrix and closecoupling solution of the timedependent Schrodinger equation. The theoretical results are in good agreement with experimental observations.


2002 
Khemliche, H., Borisov, A. G., Momeni, A., & Roncin, P. (2002). Exciton and trion formation during neutralization of Ne+ at a LiF(001) surface. NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION BBEAM INTERACTIONS WITH MATERIALS AND ATOMS, 191, 221–225.
Résumé: The grazing angle interaction of 2 keV Ne+ projectiles with a LiF(0 0 1) surface is studied with the combination, in coincidence, of projectile and electron timeofflight spectroscopy. The measurements reveal that besides the standard Auger neutralization process that leads to electron ejection, there is another neutralization mechanism that does not result in electron emission. The latter process has been identified as the formation of an electronbihole complex termed trion. We report here the detailed study of the scattering angle dependence of these two neutralization channels, with comparison with the process leading to population of surface excitons. (C) 2002 Published by Elsevier Science B.V.

