41 results found
In recent years, the possibility to induce chemical transformations by using tunable plasmonic modes has opened the question of whether we can control or create chemical hot spots in these systems. This can be rationalized as the reactive analogue of the well-established concept of optical hot spots, which have drawn a great deal of attention to plasmonic nanostructures for their ability to circumvent the far-field diffraction limit of conventional optical elements. Although optical hot spots can be mainly defined by the geometry and permittivity of the nanostructures, the degrees of freedom influencing their photocatalytic properties appear to be much more numerous. In fact, the reactivity of plasmonic systems are deeply influenced by the dynamics and interplay of photons, plasmon-polaritons, carriers, phonons, and molecular states. These degrees of freedom can affect the reaction rates, the product selectivity, or the spatial localization of a chemical reaction. In this Account, we discuss the oportunities to control chemical hot spots by tuning the cascade of events that follows the excitation and decay of plasmonic modes in nanostructures. We discuss a series of techniques to spatially map and image plasmonic nanoscale reactivity at the single photocatalyst level. We show how to optimize the reactivity of carriers by manipulating their excitation and decay mechanisms in plasmonic nanoparticles. In addition, the tailored generation of non-thermal phonons in metallic nanostructures and their dissipation is shown as a promise to understand and exploit thermal photocatalysis at the nanoscale. Understanding and controlling these processes is essential for the rational design of solar nanometric photocatalysts. Nevertheless, the ultimate capability of a plasmonic photocatalyst to trigger a chemical reaction is correlated to its ability to navigate through, or even modify, the potential energy surface of a given chemical reaction. Here we reuni
Guerra Hernandez LA, Huidobro PA, Cortes E, et al., 2019, Resonant Far- to Near-Field Channeling in Synergetic Multiscale Antennas, ACS PHOTONICS, Vol: 6, Pages: 1466-1473, ISSN: 2330-4022
Pensa E, Gargiulo J, Lauri A, et al., 2019, Spectral screening of the energy of hot holes over a particle plasmon resonance, Nano Letters, Vol: 19, Pages: 1867-1874, ISSN: 1530-6984
Plasmonic hot carriers have been recently identified as key elements for photocatalysis at visible wavelengths. The possibility to transfer energy between metal plasmonic nanoparticles and nearby molecules depends not only on carrier generation and collection efficiencies but also on their energy at the metal-molecule interface. Here an energy screening study was performed by monitoring the aniline electro-polymerization reaction via an illuminated 80 nm gold nanoparticle. Our results show that plasmon excitation reduces the energy required to start the polymerization reaction as much as 0.24 eV. Three possible photocatalytic mechanisms were explored: the enhanced near field of the illuminated particle, the temperature increase at the metal-liquid interface, and the excited electron-hole pairs. This last phenomenon is found to be the one contributing most prominently to the observed energy reduction.
Zaza C, Violi IL, Gargiulo J, et al., 2019, Size-selective optical printing of silicon nanoparticles through their dipolar magnetic resonance, ACS Photonics
© 2019 American Chemical Society. Silicon nanoparticles possess unique size-dependent optical properties due to their strong electric and magnetic resonances in the visible range. However, their widespread application has been limited, in comparison with other (e.g., metallic) nanoparticles, because their preparation on monodisperse colloids remains challenging. Exploiting the unique properties of Si nanoparticles in nano- A nd microdevices calls for methods able to sort and organize them from a colloidal suspension onto specific positions of solid substrates with nanometric precision. We demonstrate that surfactant-free silicon nanoparticles of a predefined and narrow (σ < 10 nm) size range can be selectively immobilized on a substrate by optical printing from a polydisperse colloidal suspension. The size selectivity is based on differential optical forces that can be applied on nanoparticles of different sizes by tuning the light wavelength to the size-dependent magnetic dipolar resonance of the nanoparticles.
Simoncelli S, Pensa EL, Brick T, et al., 2019, Monitoring plasmonic hot-carrier chemical reactions at the single particle level, Faraday Discussions, ISSN: 1359-6640
Plasmon excitation in metal nanoparticles triggers the generation of highly energetic charge carriers that, when properly manipulated and exploited, can mediate chemical reactions. Single-particle techniques are key to unearthing the underlying mechanisms of hot-carrier generation, transport and injection, as well as to disentangling the role of the temperature increase and the enhanced near-field at the nanoparticle-molecule interface. Gaining nanoscopic insight into these processes and their interplay could aid in the rational design of plasmonic photocatalysts. Here, we present three different approaches to monitor hot-carrier reactivity at the single-particle level. We use a combination of dark-field microscopy and photoelectrochemistry to track a hot-hole driven reaction on a single Au nanoparticle. We image hot-electron reactivity with sub-particle spatial resolution using nanoscopy techniques. Finally, we push the limits by looking for a hot-electron induced chemical reaction that generates a fluorescent product, which should enable imaging plasmonic photocatalysis at the single-particle and single-molecule levels.
Berte R, Della Picca F, Poblet M, et al., 2018, Acoustic far-field hypersonic surface wave detection with single plasmonic nanoantennas, Physical Review Letters, Vol: 121, ISSN: 0031-9007
The optical properties of small metallic particles allow us to bridge the gap between the myriad of subdiffraction local phenomena and macroscopic optical elements. The optomechanical coupling between mechanical vibrations of Au nanoparticles and their optical response due to collective electronic oscillations leads to the emission and the detection of surface acoustic waves (SAWs) by single metallic nanoantennas. We take two Au nanoparticles, one acting as a source and the other as a receptor of SAWs and, even though these antennas are separated by distances orders of magnitude larger than the characteristic subnanometric displacements of vibrations, we probe the frequency content, wave speed, and amplitude decay of SAWs originating from the damping of coherent mechanical modes of the source. Two-color pump-probe experiments and numerical methods reveal the characteristic Rayleigh wave behavior of emitted SAWs, and show that the SAW-induced optical modulation of the receptor antenna allows us to accurately probe the frequency of the source, even when the eigenmodes of source and receptor are detuned.
Cortes E, 2018, Activating plasmonic chemistry, SCIENCE, Vol: 362, Pages: 28-29, ISSN: 0036-8075
Simoncelli S, Li Y, Cortés E, et al., 2018, Imaging plasmon hybridization of fano resonances via hot-electron-mediated absorption mapping, Nano Letters, Vol: 18, Pages: 3400-3406, ISSN: 1530-6984
The inhibition of radiative losses in dark plasmon modes allows storing electromagnetic energy more efficiently than in far-field excitable bright-plasmon modes. As such, processes benefiting from the enhanced absorption of light in plasmonic materials could also take profit of dark plasmon modes to boost and control nanoscale energy collection, storage, and transfer. We experimentally probe this process by imaging with nanoscale precision the hot-electron driven desorption of thiolated molecules from the surface of gold Fano nanostructures, investigating the effect of wavelength and polarization of the incident light. Spatially resolved absorption maps allow us to show the contribution of each element of the nanoantenna in the hot-electron driven process and their interplay in exciting a dark plasmon mode. Plasmon-mode engineering allows control of nanoscale reactivity and offers a route to further enhance and manipulate hot-electron driven chemical reactions and energy-conversion and transfer at the nanoscale.
Cambiasso J, Koenig M, Cortes E, et al., 2018, Surface-Enhanced Spectroscopies of a Molecular Monolayer in an All-Dielectric Nanoantenna, ACS PHOTONICS, Vol: 5, Pages: 1546-1557, ISSN: 2330-4022
Torrelles X, Pensa E, Cortes E, et al., 2018, Solving the Long-Standing Controversy of Long-Chain Alkanethiols Surface Structure on Au(111), JOURNAL OF PHYSICAL CHEMISTRY C, Vol: 122, Pages: 3893-3902, ISSN: 1932-7447
Simoncelli S, Li Y, Cortés E, et al., 2018, Nanoscale control of molecular self-assembly induced by plasmonic hot-electron dynamics, ACS Nano, Vol: 12, Pages: 2184-2192, ISSN: 1936-0851
Self-assembly processes allow designing and creating complex nanostructures using molecules as building blocks and surfaces as scaffolds. This autonomous driven construction is possible due to a complex thermodynamic balance of molecule-surface interactions. As such, nanoscale guidance and control over this process is hard to achieve. Here we use the highly localized light-to-chemical-energy conversion of plasmonic materials to spatially cleave Au-S bonds on predetermined locations within a single nanoparticle, enabling a high degree of control over this archetypal system for molecular self-assembly. Our method offers nanoscale precision and high-throughput light-induced tailoring of the surface chemistry of individual and packed nanosized metallic structures by simply varying wavelength and polarization of the incident light. Assisted by single-molecule super-resolution fluorescence microscopy, we image, quantify, and shed light onto the plasmon-induced desorption mechanism. Our results point toward localized distribution of hot electrons, contrary to uniformly distributed lattice heating, as the mechanism inducing Au-S bond breaking. We demonstrate that plasmon-induced photodesorption enables subdiffraction and even subparticle multiplexing. Finally, we explore possible routes to further exploit these concepts for the selective positioning of nanomaterials and the sorting and purification of colloidal nanoparticles.
Gargiulo J, Violi IL, Cerrota S, et al., 2017, Accuracy and Mechanistic Details of Optical Printing of Single Au and Ag Nanoparticles, ACS NANO, Vol: 11, Pages: 9678-9688, ISSN: 1936-0851
lauri A, Velleman L, Xiao X, et al., 2017, 3D Confocal Raman Tomography to Probe Field Enhancements inside Supercluster Metamaterials, ACS Photonics, Vol: 4, Pages: 2070-2077, ISSN: 2330-4022
Spherical colloidal superclusters, composed from sub-100 nm plasmonic nanoparticles, have been proposed to possess collective plasmonic modes imbued with large field enhancements and tunable spectral response extending from the visible to infrared regions. Here, we report the experimental verification of collective near-IR plasmonic modes inside single superclusters, with dimensions ranging from 0.77 μm up to 2 μm. Raman reporters, coated onto the nanoparticle building blocks, were used as local probes of the electric field enhancement inside the metamaterial. By performing diffraction-limited 3D Raman tomography we were able to build up the electric field intensity distribution within the superclusters. We demonstrate that plasmonic responses of superclusters vary according to their size and excitation wavelength, in accordance with theoretical predictions of their tunable optical properties. The existence of three-dimensional internal collective modes in these superclusters enables the excitation of a large number of electromagnetic hot-spots, validating these self-assembled structures as promising candidates for molecular spectroscopy.
Gargiulo J, Brick T, Violi IL, et al., 2017, Understanding and Reducing Photothermal Forces for the Fabrication of Au Nanoparticle Dimers by Optical Printing, NANO LETTERS, Vol: 17, Pages: 5747-5755, ISSN: 1530-6984
Optical printing holds great potential to enable the use of the vast variety of colloidal nanoparticles (NPs) in nano- and microdevices and circuits. By means of optical forces, it enables the direct assembly of NPs, one by one, onto specific positions of solid surfaces with great flexibility of pattern design and no need of previous surface patterning. However, for unclear causes it was not possible to print identical NPs closer to each other than 300 nm. Here, we show that the repulsion restricting the optical printing of close by NPs arises from light absorption by the printed NPs and subsequent local heating. By optimizing heat dissipation, it is possible to reduce the minimum separation between NPs. Using a reduced graphene oxide layer on a sapphire substrate, we demonstrate for the first time the optical printing of Au—Au NP dimers. Modeling the experiments considering optical, thermophoretic, and thermo-osmotic forces we obtain a detailed understanding and a clear pathway for the optical printing fabrication of complex nano structures and circuits based on connected colloidal NPs.
Cortes E, 2017, Efﬁciency and bond selectivity in plasmon-induced photochemistry, Advanced Optical Materials, Vol: 5, ISSN: 2195-1071
Light-induced chemical reactions on bulk metal surfaces have been explored for more than 50 years. Light absorption at the metal surface plays a key role in inducing photochemical transformations of adsorbed molecules. Our current ability to control both the absorption cross-sections and the energy of absorbed light by metal plasmonic nanoparticles opens new pathways for the manipulation of photochemical reactions. Physical phenomena associated with the localized surface plasmon resonances, such as energetic surface states and intensified electric fields, force us to revisit our traditional understanding of photochemical reactions at metal surfaces. Long standing goals in the field – such as bond selectivity and increased efficiency of photocatalytic processes – might now be achievable, assisted by plasmonic nanoparticles. This Progress Report intends to examine some of the elementary concepts and mechanisms behind these processes in the context of the most recent advancements in the fields of plasmonic-assisted chemistry, charge transfer at the nanoscale, and surface photochemistry.
Cortes E, Xie W, Cambiasso J, et al., 2017, Plasmonic hot-electron transport drives nano-localized chemistry, Nature Communications, Vol: 8, ISSN: 2041-1723
Nanoscale localization of electromagnetic fields near metallic nanostructures underpins the fundamentals and applications of plasmonics.The unavoidable energy loss from plasmon decay, initially seen as a detriment, has now expanded the scope of plasmonic applications to exploit the generated hot carriers.However, quantitative understanding of the spatial localization of these hot carriers, akin to electromagnetic near-field maps, has been elusive. Here wespatially maphot-electron-driven reduction chemistry with 15 nanometre resolutionas a function of time and electromagnetic field polarization for different plasmonic nanostructures.We combine experiments employing asix-electron photo-recycling processthatmodify the terminal group of a self-assembledmonolayer on plasmonic silver nanoantennas,with theoretical predictions fromfirst-principles calculations of non-equilibrium hot-carrier transport in these systems. The resulting localization of reactive regions,determined by hot carrier transport fromhigh-field regions,paves the way for improving efficiency in hot-carrier extraction scienceandnanoscaleregio-selective surface chemistry.
Mack, Cortes, Giannini, et al., 2017, Decoupling absorption and emission processes in super-resolution localisation of emitters in a plasmonic hotspot, Nature Communications, Vol: 8, ISSN: 2041-1723
The absorption process of an emitter close to a plasmonic antenna is enhanced due to strong local electromagnetic (EM) fields. The emission process, if resonant with the plasmonic system, re-radiates to the far-field by coupling with the antenna due to the availability of plasmonic states. This increases the local density of states (LDOS), effectively providing more, or alternate, pathways for emission. Through the mapping of localized emission events from single molecules close to plasmonic antennas – performed using far-field data – one gains combined information on both the local EM field strength and the LDOS available. The localization from these emission-coupled events generally do not, therefore, report the real position of the molecules, nor the EM enhancement distribution at the illuminating wavelength. Here we propose the use of a fluorescent molecule with a large Stokes shift in order to spectrally decouple the emission process of the dye from the plasmonic system, leaving only the absorption strongly in resonance with the enhanced EM field in the antenna’s vicinity. We demonstrate that this technique provides an effective way of exploring either the EM field or the LDOS with nanometre spatial resolution.
Cambiasso J, Grinblat G, Li Y, et al., 2017, Bridging the gap between dielectric nanophotonics and the visible regime with effectively lossless gallium phosphide antennas, Nano Letters, Vol: 17, Pages: 1219-1225, ISSN: 1530-6992
We present all-dielectric gallium phosphide (GaP) nanoantennas as an efficient nanophotonic platform for surface-enhanced second harmonic generation (SHG) and fluorescence (SEF), showing negligible losses in the visible range. Employing single GaP nanodisks, we observe an increase of more than 3 orders of magnitude in the SHG conversion signal in comparison with the bulk. This constitutes an SHG efficiency as large as 0.0002%, which is to the best of our knowledge the highest yet achieved value for a single nano-object in the optical region. Furthermore, we show that GaP dimers with 35 nm gap can enhance up to 3600 times the fluorescence emission of dyes located in the gap of the nanoantenna. This is accomplished by a fluorescence lifetime reduction of at least 22 times, accompanied by a high-intensity field confinement in the gap region. These results open new avenues for low-loss nanophotonics in the optical regime.
Pellegrotti JV, Cortes E, Bordenave MD, et al., 2016, Plasmonic Photothermal Fluorescence Modulation for Homogeneous Biosensing, ACS SENSORS, Vol: 1, Pages: 1351-1357, ISSN: 2379-3694
Cortés E, Huidobro PA, Sinclair HG, et al., 2016, Plasmonic nanoprobes for stimulated emission depletion nanoscopy, ACS Nano, Vol: 10, Pages: 10454-10461, ISSN: 1936-0851
Plasmonic nanoparticles influence the absorption and emission processes of nearby emitters due to local enhancements of the illuminating radiation and the photonic density of states. Here, we use the plasmon resonance of metal nanoparticles in order to enhance the stimulated depletion of excited molecules for super-resolved nanoscopy. We demonstrate stimulated emission depletion (STED) nanoscopy with gold nanorods with a long axis of only 26 nm and a width of 8 nm. These particles provide an enhancement of up to 50% of the resolution compared to fluorescent-only probes without plasmonic components irradiated with the same depletion power. The nanoparticle-assisted STED probes reported here represent a ∼2 × 103 reduction in probe volume compared to previously used nanoparticles. Finally, we demonstrate their application toward plasmon-assisted STED cellular imaging at low-depletion powers, and we also discuss their current limitations.
Violi I, Gargiulo J, von Bilderling C, et al., 2016, Light-Induced Polarization-Directed Growth of Optically Printed Gold Nanoparticles, Nano Letters, Vol: 16, Pages: 6529-6533, ISSN: 1530-6992
Optical printing has been proved a versatile and simple method to fabricate arbitrary arrays of colloidal nanoparticles (NPs) on substrates. Here, we show that is also a powerful tool for studying chemical reactions at the single NP level. We demonstrate that 60 nm gold NPs immobilized by optical printing can be used as seeds to obtain larger NPs by plasmon-assisted reduction of aqueous HAuCl4. The final size of each NP is simply controlled by the irradiation time. Moreover, we show conditions for which the growth occurs preferentially in the direction of light polarization, enabling the in situ anisotropic reshaping of the NPs in predetermined orientations.
Ben-Jaber S, Peveler WJ, Quesada-Cabrera R, et al., 2016, Photo-induced enhanced Raman spectroscopy for universal ultra-trace detection of explosives, pollutants and biomolecules, Nature Communications, Vol: 7, ISSN: 2041-1723
Surface-enhanced Raman spectroscopy is one of the most sensitive spectroscopic techniques available, with single-molecule detection possible on a range of noble-metal substrates. It is widely used to detect molecules that have a strong Raman response at very low concentrations. Here we present photo-induced-enhanced Raman spectroscopy, where the combination of plasmonic nanoparticles with a photo-activated substrate gives rise to large signal enhancement (an order of magnitude) for a wide range of small molecules, even those with a typically low Raman cross-section. We show that the induced chemical enhancement is due to increased electron density at the noble-metal nanoparticles, and demonstrate the universality of this system with explosives, biomolecules and organic dyes, at trace levels. Our substrates are also easy to fabricate, self-cleaning and reusable.
Gargiulo J, Cerrota S, Cortes E, et al., 2016, Connecting Metallic Nanoparticles by Optical Printing, NANO LETTERS, Vol: 16, Pages: 1224-1229, ISSN: 1530-6984
Della Picca F, Berte R, Rahmani M, et al., 2016, Tailored Hypersound Generation in Single Plasmonic Nanoantennas., Nano Letters, Vol: 16, Pages: 1428-1434, ISSN: 1530-6992
Ultrashort laser pulses impinging on a plasmonic nanostructure trigger a highly dynamic scenario in the interplay of electronic relaxation with lattice vibrations, which can be experimentally probed via the generation of coherent phonons. In this Letter, we present studies of hypersound generation in the range of a few to tens of gigahertz on single gold plasmonic nanoantennas, which have additionally been subjected to predesigned mechanical constraints via silica bridges. Using these hybrid gold/silica nanoantennas, we demonstrate experimentally and via numerical simulations how mechanical constraints allow control over their vibrational mode spectrum. Degenerate pump-probe techniques with double modulation are performed in order to detect the small changes produced in the probe transmission by the mechanical oscillations of these single nanoantennas.
Guerra Hernández LA, Daza Millone MA, Cortés E, et al., 2015, Synergetic Light-Harvesting and Near-Field Enhancement in Multiscale Patterned Gold Substrates, ACS Photonics, Vol: 2, Pages: 1355-1365, ISSN: 2330-4022
Sphere-segment void (SSV) cavities have emerged as promising substrates for reproducible Surface Enhanced Raman Scattering (SERS), offering strong and uniform electromagnetic enhancement associated with the excitation of cavity-like localized surface plasmon resonances tunable across the UV–vis-near IR range, with a facile large-scale fabrication process. High-resolution electron micrographs of these structures reveal a considerable departure from the idealized smooth spherical cavity shape; notably, the electrochemical deposition of gold yields an important surface roughness. We investigate this contribution to the SERS activity of SSV substrates with a series of experiments, varying the degree of surface roughness using thermal annealing and gradual electrochemical roughening. Notably, we observe that both roughness features and cavity-like modes operate in conjunction as a multiscale antenna to provide larger SERS efficiency than the two mechanisms considered separately. We conclude that the main role of the ordered cavity structure is to increase the plasmonic mode density near rough surface features, thus, optimizing the coupling of far-field radiation (light harvesting) to locally enhanced near fields.
Baumberg J, Nielsen M, Bozhevolnyi S, et al., 2015, Surface plasmon enhanced spectroscopies and time and space resolved methods: general discussion, FARADAY DISCUSSIONS, Vol: 178, Pages: 253-279, ISSN: 1359-6640
Caldarola M, Albella P, Cortés E, et al., 2015, Non-plasmonic nanoantennas for surface enhanced spectroscopies with ultra-low heat conversion., Nature Communications, Vol: 6, Pages: 7915-7915, ISSN: 2041-1723
Nanoplasmonics has recently revolutionized our ability to control light on the nanoscale. Using metallic nanostructures with tailored shapes, it is possible to efficiently focus light into nanoscale field 'hot spots'. High field enhancement factors have been achieved in such optical nanoantennas, enabling transformative science in the areas of single molecule interactions, highly enhanced nonlinearities and nanoscale waveguiding. Unfortunately, these large enhancements come at the price of high optical losses due to absorption in the metal, severely limiting real-world applications. Via the realization of a novel nanophotonic platform based on dielectric nanostructures to form efficient nanoantennas with ultra-low light-into-heat conversion, here we demonstrate an approach that overcomes these limitations. We show that dimer-like silicon-based single nanoantennas produce both high surface enhanced fluorescence and surface enhanced Raman scattering, while at the same time generating a negligible temperature increase in their hot spots and surrounding environments.
Grinblat G, Rahmani M, Cortes E, et al., 2014, High-Efficiency Second Harmonic Generation from a Single Hybrid ZnO Nanowire/Au Plasmonic Nano-Oligomer, NANO LETTERS, Vol: 14, Pages: 6660-6665, ISSN: 1530-6984
Vericat C, Vela ME, Corthey G, et al., 2014, Self-assembled monolayers of thiolates on metals: a review article on sulfur-metal chemistry and surface structures, RSC ADVANCES, Vol: 4, Pages: 27730-27754, ISSN: 2046-2069
Cortes E, Etchegoin PG, Le Ru EC, et al., 2013, Strong Correlation between Molecular Configurations and Charge-Transfer Processes Probed at the Single-Molecule Level by Surface-Enhanced Raman Scattering, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, Vol: 135, Pages: 2809-2815, ISSN: 0002-7863
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