Imperial College London

DrEmilianoCortes

Faculty of Natural SciencesDepartment of Physics

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e.cortes

 
 
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Blackett LaboratorySouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
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88 results found

Chen S, Luo T, Li X, Chen K, Fu J, Liu K, Cai C, Wang Q, Li H, Chen Y, Ma C, Zhu L, Lu Y-R, Chan T-S, Zhu M, Cortés E, Liu Met al., 2022, Identification of the Highly Active Co-N4 Coordination Motif for Selective Oxygen Reduction to Hydrogen Peroxide., J Am Chem Soc, Vol: 144, Pages: 14505-14516

Electrosynthesis of hydrogen peroxide (H2O2) through oxygen reduction reaction (ORR) is an environment-friendly and sustainable route for obtaining a fundamental product in the chemical industry. Co-N4 single-atom catalysts (SAC) have sparkled attention for being highly active in both 2e- ORR, leading to H2O2 and 4e- ORR, in which H2O is the main product. However, there is still a lack of fundamental insights into the structure-function relationship between CoN4 and the ORR mechanism over this family of catalysts. Here, by combining theoretical simulation and experiments, we unveil that pyrrole-type CoN4 (Co-N SACDp) is mainly responsible for the 2e- ORR, while pyridine-type CoN4 catalyzes the 4e- ORR. Indeed, Co-N SACDp exhibits a remarkable H2O2 selectivity of 94% and a superb H2O2 yield of 2032 mg for 90 h in a flow cell, outperforming most reported catalysts in acid media. Theoretical analysis and experimental investigations confirm that Co-N SACDp─with weakening O2/HOO* interaction─boosts the H2O2 production.

Journal article

Hu H, Weber T, Bienek O, Wester A, Huettenhofer L, Sharp ID, Maier SA, Tittl A, Cortes Eet al., 2022, Catalytic Metasurfaces Empowered by Bound States in the Continuum, ACS NANO, Vol: 16, Pages: 13057-13068, ISSN: 1936-0851

Journal article

Chen Q, Liu K, Zhou Y, Wang X, Wu K, Li H, Pensa E, Fu J, Miyauchi M, Cortes E, Liu Met al., 2022, Ordered Ag Nanoneedle Arrays with Enhanced Electrocatalytic CO2 Reduction via Structure-Induced Inhibition of Hydrogen Evolution, NANO LETTERS, Vol: 22, Pages: 6276-6284, ISSN: 1530-6984

Journal article

Yao K, Li J, Wang H, Lu R, Yang X, Luo M, Wang N, Wang Z, Liu C, Jing T, Chen S, Cortes E, Maier SA, Zhang S, Li T, Yu Y, Liu Y, Kang X, Liang Het al., 2022, Mechanistic Insights into OC-COH Coupling in CO2 Electroreduction on Fragmented Copper, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, ISSN: 0002-7863

Journal article

Herran M, Sousa-Castillo A, Fan C, Lee S, Xie W, Doeblinger M, Auguie B, Cortes Eet al., 2022, Tailoring Plasmonic Bimetallic Nanocatalysts Toward Sunlight-Driven H-2 Production, ADVANCED FUNCTIONAL MATERIALS, ISSN: 1616-301X

Journal article

Cortes E, Wendisch FJ, Sortino L, Mancini A, Ezendam S, Saris S, Menezes LDS, Tittl A, Ren H, Maier SAet al., 2022, Optical Metasurfaces for Energy Conversion, CHEMICAL REVIEWS, ISSN: 0009-2665

Journal article

Rosenberger P, Dagar R, Zhang W, Sousa-Castillo A, Neuhaus M, Cortes E, Maier SA, Costa-Vera C, Kling MF, Bergues Bet al., 2022, Imaging elliptically polarized infrared near-fields on nanoparticles by strong-field dissociation of functional surface groups, European Physical Journal D: Atomic, Molecular, Optical and Plasma Physics, Vol: 76, Pages: 1-9, ISSN: 0011-4626

We investigate the strong-field ion emission from the surface of isolated silica nanoparticles aerosolized from an alcoholic solution, and demonstrate the applicability of the recently reported near-field imaging at 720 nm [Rupp et al., Nat. Comm., 10(1):4655, 2019] to longer wavelength (2 μm) and polarizations with arbitrary ellipticity. Based on the experimental observations, we discuss the validity of a previously introduced semi-classical model, which is based on near-field driven charge generation by a Monte-Carlo approach and classical propagation. We furthermore clarify the role of the solvent in the surface composition of the nanoparticles in the interaction region. We find that upon injection of the nanoparticles into the vacuum, the alcoholic solvent evaporates on millisecond time scales, and that the generated ions originate predominantly from covalent bonds with the silica surface rather than from physisorbed solvent molecules. These findings have important implications for the development of future theoretical models of the strong-field ion emission from silica nanoparticles, and the application of near-field imaging and reaction dynamics of functional groups on isolated nanoparticles.

Journal article

Zhang W, Dagar R, Rosenberger P, Sousa-Castillo A, Neuhaus M, Li W, Khan SA, Alnaser AS, Cortes E, Maier SA, Costa-Vera C, Kling MF, Bergues Bet al., 2022, All-optical nanoscopic spatial control of molecular reaction yields on nanoparticles, OPTICA, Vol: 9, Pages: 551-560, ISSN: 2334-2536

Journal article

Stefancu A, Nan L, Zhu L, Chis V, Bald I, Liu M, Leopold N, Maier SA, Cortes Eet al., 2022, Controlling Plasmonic Chemistry Pathways through Specific Ion Effects, ADVANCED OPTICAL MATERIALS, Vol: 10, ISSN: 2195-1071

Journal article

Cortes E, Grzeschik R, Maier SA, Schluecker Set al., 2022, Experimental characterization techniques for plasmon-assisted chemistry, NATURE REVIEWS CHEMISTRY, Vol: 6, Pages: 259-274

Journal article

Chen K, Cao M, Lin Y, Fu J, Liao H, Zhou Y, Li H, Qiu X, Hu J, Zheng X, Shakouri M, Xiao Q, Hu Y, Li J, Liu J, Cortés E, Liu Met al., 2022, Ligand Engineering in Nickel Phthalocyanine to Boost the Electrocatalytic Reduction of CO<inf>2</inf>, Advanced Functional Materials, Vol: 32, ISSN: 1616-301X

Designing and synthesizing efficient molecular catalysts may unlock the great challenge of controlling the CO2 reduction reaction (CO2RR) with molecular precision. Nickel phthalocyanine (NiPc) appears as a promising candidate for this task due to its adjustable Ni active-site. However, the pristine NiPc suffers from poor activity and stability for CO2RR owing to the poor CO2 adsorption and activation at the bare Ni site. Here, a ligand-tuned strategy is developed to enhance the catalytic performance and unveil the ligand effect of NiPc on CO2RR. Theoretical calculations and experimental results indicate that NiPc with electron-donating substituents (hydroxyl or amino) can induce electronic localization at the Ni site which greatly enhances the CO2 adsorption and activation. Employing the optimal catalyst—an amino-substituted NiPc—to convert CO2 into CO in a flow cell can achieve an ultrahigh activity and selectivity of 99.8% at current densities up to −400 mA cm−2. This work offers a novel strategy to regulate the electronic structure of active sites by ligand design and discloses the ligand-directed catalysis of the tailored NiPc for highly efficient CO2RR.

Journal article

Yang B, Liu K, Li H, Liu C, Fu J, Li H, Huang JE, Ou P, Alkayyali T, Cai C, Duan Y, Liu H, An P, Zhang N, Li W, Qiu X, Jia C, Hu J, Chai L, Lin Z, Gao Y, Miyauchi M, Cortés E, Maier SA, Liu Met al., 2022, Accelerating CO2 electroreduction to multicarbon products via synergistic electric-thermal field on copper nanoneedles., Journal of the American Chemical Society, Vol: 144, Pages: 3039-3049, ISSN: 0002-7863

Electrochemical CO2 reduction is a promising way to mitigate CO2 emissions and close the anthropogenic carbon cycle. Among products from CO2RR, multicarbon chemicals, such as ethylene and ethanol with high energy density, are more valuable. However, the selectivity and reaction rate of C2 production are unsatisfactory due to the sluggish thermodynamics and kinetics of C-C coupling. The electric field and thermal field have been studied and utilized to promote catalytic reactions, as they can regulate the thermodynamic and kinetic barriers of reactions. Either raising the potential or heating the electrolyte can enhance C-C coupling, but these come at the cost of increasing side reactions, such as the hydrogen evolution reaction. Here, we present a generic strategy to enhance the local electric field and temperature simultaneously and dramatically improve the electric-thermal synergy desired in electrocatalysis. A conformal coating of ∼5 nm of polytetrafluoroethylene significantly improves the catalytic ability of copper nanoneedles (∼7-fold electric field and ∼40 K temperature enhancement at the tips compared with bare copper nanoneedles experimentally), resulting in an improved C2 Faradaic efficiency of over 86% at a partial current density of more than 250 mA cm-2 and a record-high C2 turnover frequency of 11.5 ± 0.3 s-1 Cu site-1. Combined with its low cost and scalability, the electric-thermal strategy for a state-of-the-art catalyst not only offers new insight into improving activity and selectivity of value-added C2 products as we demonstrated but also inspires advances in efficiency and/or selectivity of other valuable electro-/photocatalysis such as hydrogen evolution, nitrogen reduction, and hydrogen peroxide electrosynthesis.

Journal article

Zhou Y, Liang Y, Fu J, Liu K, Chen Q, Wang X, Li H, Zhu L, Hu J, Pan H, Miyauchi M, Jiang L, Cortés E, Liu Met al., 2022, Vertical cu nanoneedle arrays enhance the local electric field promoting C2 hydrocarbons in the CO2 electroreduction, Nano Letters: a journal dedicated to nanoscience and nanotechnology, Vol: 22, Pages: 1963-1970, ISSN: 1530-6984

Electrocatalytic reduction of CO2 to multicarbon products is a potential strategy to solve the energy crisis while achieving carbon neutrality. To improve the efficiency of multicarbon products in Cu-based catalysts, optimizing the *CO adsorption and reducing the energy barrier for carbon-carbon (C-C) coupling are essential features. In this work, a strong local electric field is obtained by regulating the arrangement of Cu nanoneedle arrays (CuNNAs). CO2 reduction performance tests indicate that an ordered nanoneedle array reaches a 59% Faraday efficiency for multicarbon products (FEC2) at -1.2 V (vs RHE), compared to a FEC2 of 20% for a disordered nanoneedle array (CuNNs). As such, the very high and local electric fields achieved by an ordered Cu nanoneedle array leads to the accumulation of K+ ions, which benefit both *CO adsorption and C-C coupling. Our results contribute to the design of highly efficient catalysts for multicarbon products.

Journal article

Ezendam S, Herran M, Nan L, Gruber C, Kang Y, Groebmeyer F, Lin R, Gargiulo J, Sousa-Castillo A, Cortes Eet al., 2022, Hybrid plasmonic nanomaterials for hydrogen generation and carbon dioxide reduction, ACS Energy Letters, Vol: 7, Pages: 778-815, ISSN: 2380-8195

The successful development of artificial photosynthesis requires finding new materials able to efficiently harvest sunlight and catalyze hydrogen generation and carbon dioxide reduction reactions. Plasmonic nanoparticles are promising candidates for these tasks, due to their ability to confine solar energy into molecular regions. Here, we review recent developments in hybrid plasmonic photocatalysis, including the combination of plasmonic nanomaterials with catalytic metals, semiconductors, perovskites, 2D materials, metal–organic frameworks, and electrochemical cells. We perform a quantitative comparison of the demonstrated activity and selectivity of these materials for solar fuel generation in the liquid phase. In this way, we critically assess the state-of-the-art of hybrid plasmonic photocatalysts for solar fuel production, allowing its benchmarking against other existing heterogeneous catalysts. Our analysis allows the identification of the best performing plasmonic systems, useful to design a new generation of plasmonic catalysts.

Journal article

Stefancu A, Biro OM, Todor-Boer O, Botiz I, Cortés E, Leopold Net al., 2022, Halide-metal complexes at plasmonic interfaces create new decay pathways for plasmons and excited molecules, ACS Photonics, Vol: 9, Pages: 895-904, ISSN: 2330-4022

We show that by modifying the chemical interface of silver nanoparticles (AgNPs) with halide ions, it is possible to tune the total decay rate of adsorbed excited molecules and the plasmon damping rate. Through single-molecule surface-enhanced Raman scattering and surface-enhanced fluorescence enhancement factors of crystal violet (CV) and rhodamine 6G (R6G), we show that I–-modified AgNPs (AgNPs@I) and Br–-modified AgNPs (AgNPs@Br) lead to an increase in the total decay rate of excited CV and R6G by a factor between ∼1.6–2.6, compared to Cl–-modified AgNPs (AgNPs@Cl). In addition, we found that the chemical interface damping, which characterizes the plasmon resonance decay into surface states, is stronger on AgNPs@I and AgNPs@Br when compared to AgNPs@Cl. These results point toward the formation of metal–halide surface complexes. These new interfacial states can accept electrons from both excited molecular orbitals and surface plasmon excitations, completely altering the electronic dynamics and reactivity of plasmonic interfaces.

Journal article

Violi IL, Martinez LP, Barella M, Zaza C, Chvatal L, Zemanek P, Gutierrez MV, Paredes MY, Scarpettini AF, Olmos-Trigo J, Pais VR, Noblega ID, Cortes E, Saenz JJ, Bragas AV, Gargiulo J, Stefani FDet al., 2022, Challenges on optical printing of colloidal nanoparticles, Journal of Chemical Physics, Vol: 156, ISSN: 0021-9606

While colloidal chemistry provides ways to obtain a great variety of nanoparticles with different shapes, sizes, material compositions, and surface functions, their controlled deposition and combination on arbitrary positions of substrates remain a considerable challenge. Over the last ten years, optical printing arose as a versatile method to achieve this purpose for different kinds of nanoparticles. In this article, we review the state of the art of optical printing of single nanoparticles and discuss its strengths, limitations, and future perspectives by focusing on four main challenges: printing accuracy, resolution, selectivity, and nanoparticle photostability

Journal article

Cai C, Liu K, Zhu Y, Li P, Wang Q, Liu B, Chen S, Li H, Zhu L, Li H, Fu J, Chen Y, Pensa E, Hu J, Lu Y-R, Chan T-S, Cortés E, Liu Met al., 2022, Optimizing hydrogen binding on Ru sites with RuCo alloy nanosheets for efficient alkaline hydrogen evolution, Angewandte Chemie International Edition, Vol: 61, Pages: e202113664-e202113664, ISSN: 1433-7851

Ruthenium (Ru)-based catalysts, with considerable performance and desirable cost, are becoming highly interesting candidates to replace platinum (Pt) in the alkaline hydrogen evolution reaction (HER). The hydrogen binding at Ru sites (Ru-H) is an important factor limiting the HER activity. Herein, density functional theory (DFT) simulations show that the essence of Ru-H binding energy is the strong interaction between the 4 d z 2 orbital of Ru and the 1s orbital of H. The charge transfer between Ru sites and substrates (Co and Ni) causes the appropriate downward shift of the 4 d z 2 -band center of Ru, which results in a Gibbs free energy of 0.022 eV for H* in the RuCo system, much lower than the 0.133 eV in the pure Ru system. This theoretical prediction has been experimentally confirmed using RuCo alloy-nanosheets (RuCo ANSs). They were prepared via a fast co-precipitation method followed with a mild electrochemical reduction. Structure characterizations reveal that the Ru atoms are embedded into the Co substrate as isolated active sites with a planar symmetric and Z-direction asymmetric coordination structure, obtaining an optimal 4 d z 2 modulated electronic structure. Hydrogen sensor and temperature program desorption (TPD) tests demonstrate the enhanced Ru-H interactions in RuCo ANSs compared to those in pure Ru nanoparticles. As a result, the RuCo ANSs reach an ultra-low overpotential of 10 mV at 10 mA cm-2 and a Tafel slope of 20.6 mV dec-1 in 1 M KOH, outperforming that of the commercial Pt/C. This holistic work provides a new insight to promote alkaline HER by optimizing the metal-H binding energy of active sites.

Journal article

Besteiro L, Movsesyan A, Avalos-Ovando O, Lee S, Cortes E, Correa-Duarte MA, Wang ZM, Govorov AOet al., 2021, Local Growth Mediated by Plasmonic Hot Carriers: Chirality from Achiral Nanocrystals Using Circularly Polarized Light, NANO LETTERS, Vol: 21, Pages: 10315-10324, ISSN: 1530-6984

Journal article

Moretti GQ, Cortes E, Maier SA, Bragas A, Grinblat Get al., 2021, Engineering gallium phosphide nanostructures for efficient nonlinear photonics and enhanced spectroscopies, Nanophotonics, Vol: 10, Pages: 4261-4271, ISSN: 2192-8606

Optical resonances arising from quasi-bound states in the continuum (QBICs) have been recently identified in nanostructured dielectrics, showing ultrahigh quality factors accompanied by very large electromagnetic field enhancements. In this work, we design a periodic array of gallium phosphide (GaP) elliptical cylinders supporting, concurrently, three spectrally separated QBIC resonances with in-plane magnetic dipole, out-of-plane magnetic dipole, and electric quadrupole characters. We numerically explore this system for second-harmonic generation and degenerate four-wave mixing, demonstrating giant per unit cell conversion efficiencies of up to ∼ 2 W−1 and ∼ 60 W−2, respectively, when considering realistic introduced asymmetries in the metasurface, compatible with current fabrication limitations. We find that this configuration outperforms by up to more than four orders of magnitude the response of low-Q Mie or anapole resonances in individual GaP nanoantennas with engineered nonlinear mode-matching conditions. Benefiting from the straight-oriented electric field of one of the examined high-Q resonances, we further propose a novel nanocavity design for enhanced spectroscopies by slotting the meta-atoms of the periodic array. We discover that the optical cavity sustains high-intensity fields homogeneously distributed inside the slot, delivering its best performance when the elliptical cylinders are cut from end to end forming a gap, which represents a convenient model for experimental investigations. When placing an electric point dipole inside the added aperture, we find that the metasurface offers ultrahigh radiative enhancements, exceeding the previously reported slotted dielectric nanodisk at the anapole excitation by more than two orders of magnitude.

Journal article

Glass D, Quesada-Cabrera R, Bardey S, Promdet P, Sapienza R, Keller V, Maier SA, Caps V, Parkin IP, Cortes Eet al., 2021, Probing the role of atomic defects in photocatalytic systems through photoinduced enhanced raman scattering, ACS Energy Letters, Vol: 6, Pages: 4273-4281, ISSN: 2380-8195

Even in ultralow quantities, oxygen vacancies (VO) drastically impact keyproperties of metal oxide semiconductors, such as charge transport, surface adsorption,and reactivity, playing central roles in functional materials performance. Currentmethods used to investigate VO often rely on specialized instrumentation under far fromideal reaction conditions. Hence, the influence of VO generated in situ during catalyticprocesses has yet to be probed. In this work, we assess in situ extrinsic surface VOformation and lifetime under photocatalytic conditions which we compare tophotocatalytic performance. We show for the first time that lifetimes of in situ generatedatomic VO play more significant roles in catalysis than their concentration, with strongcorrelations between longer-lived VO and higher photocatalytic activity. Our resultsindicate that enhanced photocatalytic efficiency correlates with goldilocks VOconcentrations, where VO densities must be just right to encourage carrier transportwhile avoiding charge carrier trapping.

Journal article

Huettenhofer L, Golibrzuch M, Bienek O, Wendisch FJ, Lin R, Becherer M, Sharp ID, Maier SA, Cortes Eet al., 2021, Metasurface photoelectrodes for enhanced solar fuel generation, Advanced Energy Materials, Vol: 11, ISSN: 1614-6832

Tailoring optical properties in photocatalysts by nanostructuring them can help increase solar light harvesting efficiencies in a wide range of materials. Whereas plasmon resonances are widely employed in metallic catalysts for this purpose, latest advances of nonradiative, dielectric nanophotonics also enable light confinement and enhanced visible light absorption in semiconductors. Here, a design procedure for large-scale nanofabrication of semiconductor photoelectrodes using imprint lithography is developed. Anapole excitations and metasurface lattice resonances are combined to enhance the absorption of the model material, amorphous gallium phosphide (a-GaP), over the visible spectrum. It is shown that cost-effective, high sample throughput is achieved while retaining the precise signature of the engineered photonic states. Photoelectrochemical measurements under hydrogen evolution reaction conditions and sunlight illumination reveal the contributions of the respective resonances and demonstrate an overall photocurrent enhancement of 5.7, compared to a planar film. These results are supported by optical and numerical analysis of single nanodisks and of the upscaled metasurface.https://onlinelibrary.wiley.com/doi/10.1002/aenm.202102877

Journal article

Poblet M, Berte R, Boggiano HD, Li Y, Cortes E, Grinblat G, Maier SA, Bragas Aet al., 2021, Acoustic coupling between plasmonic nanoantennas: detection and directionality of surface acoustic waves, ACS Photonics, Vol: 8, Pages: 2846-2852, ISSN: 2330-4022

Hypersound waves can be efficient mediators between optical signals at the nanoscale. Having phase velocities several orders of magnitude lower than the speed of light, they propagate with much shorter wavelengths and can be controlled, directed, and even focused in a very small region of space. This work shows how two optical nanoantennas can be coupled through an acoustic wave that propagates with a certain directionality. An “emitter” antenna is first optically excited to generate acoustic coherent phonons that launch surface acoustic waves through the underlying substrate. These waves travel until they are mechanically detected by a “receiver” nanoantenna whose oscillation produces a detectable optical signal. Generation and detection are studied in detail, and new designs are proposed to improve the directionality of the hypersonic surface acoustic wave.

Journal article

Dagdeviren OE, Glass D, Sapienza R, Cortes E, Maier SA, Parkin IP, Grutter P, Quesada-Cabrera Ret al., 2021, The effect of photoinduced surface oxygen vacancies on the charge carrier dynamics in TiO2 films, Nano Letters: a journal dedicated to nanoscience and nanotechnology, Vol: 21, Pages: 8348-8354, ISSN: 1530-6984

Metal-oxide semiconductors (MOS) are widely utilized for catalytic and photocatalytic applications in which the dynamics of charged carriers (e.g., electrons, holes) play important roles. Under operation conditions, photoinduced surface oxygen vacancies (PI-SOV) can greatly impact the dynamics of charge carriers. However, current knowledge regarding the effect of PI-SOV on the dynamics of hole migration in MOS films, such as titanium dioxide, is solely based upon volume-averaged measurements and/or vacuum conditions. This limits the basic understanding of hole-vacancy interactions, as they are not capable of revealing time-resolved variations during operation. Here, we measured the effect of PI-SOV on the dynamics of hole migration using time-resolved atomic force microscopy. Our findings demonstrate that the time constant associated with hole migration is strongly affected by PI-SOV, in a reversible manner. These results will nucleate an insightful understanding of the physics of hole dynamics and thus enable emerging technologies, facilitated by engineering hole-vacancy interactions.

Journal article

Zhu C, Fan C, Cortes E, Xie Wet al., 2021, In situ surface-enhanced Raman spectroelectrochemistry reveals the molecular conformation of electrolyte additives in Li-ion batteries, Journal of Materials Chemistry A, Vol: 9, Pages: 20024-20031, ISSN: 2050-7488

We report the mechanism of rhodamine B (RhB) acting as an electrolyte additive in Li/graphite cells. We show that the cycle performance and rate capability of graphite are enhanced in carbonate-based electrolytes containing 0.2 wt% RhB. By using silica-encapsulated Au nanoparticles, in situ surface-enhanced Raman spectroscopy (SERS) is applied to study the graphite/electrolyte interface. We find that the adsorption orientation of RhB molecules on the surface of graphite can be modulated by the applied potential: vertical adsorption at higher potentials while horizontal adsorption takes place at lower potentials. This behavior effectively suppresses the electrolyte solvent decomposition, as well as electrode corrosion while improving the Li+ diffusion. This work shows that SERS is a powerful tool for interfacial analysis of battery systems and provides new ideas for rational design of electrolyte additives.

Journal article

Stefancu A, Lee S, Zhu L, Liu M, Lucacel RC, Cortes E, Leopold Net al., 2021, Fermi level equilibration at the metal-molecule interface in plasmonic systems, Nano Letters: a journal dedicated to nanoscience and nanotechnology, Vol: 21, Pages: 6592-6599, ISSN: 1530-6984

We highlight a new metal–molecule charge transfer process by tuning the Fermi energy of plasmonic silver nanoparticles (AgNPs) in situ. The strong adsorption of halide ions upshifts the Fermi level of AgNPs by up to ∼0.3 eV in the order Cl– < Br– < I–, favoring the spontaneous charge transfer to aligned molecular acceptor orbitals until charge neutrality across the interface is achieved. By carefully quantifying, experimentally and theoretically, the Fermi level upshift, we show for the first time that this effect is comparable in energy to different plasmonic effects such as the plasmoelectric effect or hot-carriers production. Moreover, by monitoring in situ the adsorption dynamic of halide ions in different AgNP–molecule systems, we show for the first time that the catalytic role of halide ions in plasmonic nanostructures depends on the surface affinity of halide ions compared to that of the target molecule.

Journal article

Wang X, Liu C, Gao C, Yao K, Masouleh SSM, Berté R, Ren H, Menezes LDS, Cortés E, Bicket IC, Wang H, Li N, Zhang Z, Li M, Xie W, Yu Y, Fang Y, Zhang S, Xu H, Vomiero A, Liu Y, Botton GA, Maier SA, Liang Het al., 2021, Self-constructed multiple plasmonic hotspots on an individual fractal to amplify broadband hot electron generation., ACS Nano, Vol: 15, Pages: 10553-10564, ISSN: 1936-0851

Plasmonic nanoparticles are ideal candidates for hot-electron-assisted applications, but their narrow resonance region and limited hotspot number hindered the energy utilization of broadband solar energy. Inspired by tree branches, we designed and chemically synthesized silver fractals, which enable self-constructed hotspots and multiple plasmonic resonances, extending the broadband generation of hot electrons for better matching with the solar radiation spectrum. We directly revealed the plasmonic origin, the spatial distribution, and the decay dynamics of hot electrons on the single-particle level by using ab initio simulation, dark-field spectroscopy, pump-probe measurements, and electron energy loss spectroscopy. Our results show that fractals with acute tips and narrow gaps can support broadband resonances (400-1100 nm) and a large number of randomly distributed hotspots, which can provide unpolarized enhanced near field and promote hot electron generation. As a proof-of-concept, hot-electron-triggered dimerization of p-nitropthiophenol and hydrogen production are investigated under various irradiations, and the promoted hot electron generation on fractals was confirmed with significantly improved efficiency.

Journal article

Hüttenhofer L, Tittl A, Kühner L, Cortés E, Maier SAet al., 2021, Anapole-assisted absorption engineering in arrays of coupled amorphous gallium phosphide nanodisks, ACS Photonics, Vol: 8, Pages: 1469-1476, ISSN: 2330-4022

Broadband solar light harvesting plays a crucial role for efficient energy conversion. Anapole excitations and associated absorption engineering in dielectric nanoresonators are a focus of nanophotonic research due to the intricate combination of nonradiating modes and strong electromagnetic field confinement in the underlying material. The arising high field strengths are used for enhanced second-harmonic generation and photocatalysis, where devices require large areas with closely spaced nanoresonators for sizable photonic yields. However, most anapole studies have so far been carried out at the single-particle level, neglecting the influence of anapole–anapole interactions. Here, we present a systematic study of coupling mechanisms in rectangular arrays of amorphous GaP nanodisks that support anapole excitations at 600 nm, which is within the lossy spectral regime of the material. Our experimental findings show that maximum visible light extinction by the array and maximum absorption in the GaP are not achieved by the densest packing of resonators. Counterintuitively, increasing the array periodicities such that collective effects spectrally overlap with the anapole excitation of a single particle leads to an absorption enhancement of up to 300% compared to a single disk. An analysis of coupling in one- and two-dimensional arrays with polarization-dependent measurements and numerical simulations allows us to discriminate between coupling interactions parallel and perpendicular to the polarization axis and evaluate their strengths. Utilizing a multipolar decomposition of excitations in single nanodisks embedded in one-dimensional arrays, we can attribute the coupling to enhanced electric and toroidal dipoles under variation of the interparticle spacing. Our results provide a fundamental understanding of tailored light absorption in coupled anapole resonators and reveal important design guidelines for advanced metasurface approaches in a wide range of energy

Journal article

Besteiro LV, Cortes E, Ishii S, Narang P, Oulton RFet al., 2021, Hot electron physics and applications, JOURNAL OF APPLIED PHYSICS, Vol: 129, ISSN: 0021-8979

Journal article

Barella M, Violi IL, Gargiulo J, Martinez LP, Goschin F, Guglielmotti V, Pallarola D, Schluecker S, Pilo-Pais M, Acuna GP, Maier SA, Cortes E, Stefani FDet al., 2021, In situ photothermal response of single gold nanoparticles through hyperspectral imaging anti-stokes thermometry, ACS Nano, Vol: 15, Pages: 2458-2467, ISSN: 1936-0851

Several fields of applications require a reliable characterization of the photothermal response and heat dissipation of nanoscopic systems, which remains a challenging task for both modeling and experimental measurements. Here, we present an implementation of anti-Stokes thermometry that enables the in situ photothermal characterization of individual nanoparticles (NPs) from a single hyperspectral photoluminescence confocal image. The method is label-free, potentially applicable to any NP with detectable anti-Stokes emission, and does not require any prior information about the NP itself or the surrounding media. With it, we first studied the photothermal response of spherical gold NPs of different sizes on glass substrates, immersed in water, and found that heat dissipation is mainly dominated by the water for NPs larger than 50 nm. Then, the role of the substrate was studied by comparing the photothermal response of 80 nm gold NPs on glass with sapphire and graphene, two materials with high thermal conductivity. For a given irradiance level, the NPs reach temperatures 18% lower on sapphire and 24% higher on graphene than on bare glass. The fact that the presence of a highly conductive material such as graphene leads to a poorer thermal dissipation demonstrates that interfacial thermal resistances play a very significant role in nanoscopic systems and emphasize the need for in situ experimental thermometry techniques. The developed method will allow addressing several open questions about the role of temperature in plasmon-assisted applications, especially ones where NPs of arbitrary shapes are present in complex matrixes and environments.

Journal article

Li H, Liu K, Fu J, Chen K, Yang K, Lin Y, Yang B, Wang Q, Pan H, Cai Z, Li H, Cao M, Hu J, Lu Y-R, Chan T-S, Cortes E, Fratalocchi A, Liu Met al., 2021, Paired Ru-O-Mo ensemble for efficient and stable alkaline hydrogen evolution reaction, NANO ENERGY, Vol: 82, ISSN: 2211-2855

Journal article

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