Correlation between Plasmonic and Thermal Properties of Metallic Nanoparticles.

Here, we investigate the correlation between the heat generated by gold nanoparticles, in particular nanospheres and nanobipyramids, and their plasmonic response manifested by the presence of Localized Surface Plasmon Resonances (LSPRs). Using a tunable laser and a thermal camera, we measure the temperature increase induced by colloidal nanoparticles in an aqueous solution as a function of the excitation wavelength in the optical regime. We demonstrate that the photothermal performances of the nanoparticles are strongly related not only to their plasmonic properties but also to the size and shape of the nanoparticles.

Janus-Nanojet as an efficient asymmetric photothermal source.

The combination of materials with radically different physical properties in the same nanostructure gives rise to the so-called Janus effects, allowing phenomena of a contrasting nature to occur in the same architecture. Interesting advantages can be taken from a thermal Janus effect for photoinduced hyperthermia cancer therapies. Such therapies have limitations associated to the heating control in terms of temperature stability and energy management.

Thermophoresis and thermal orientation of Janus nanoparticles in thermal fields.

Thermal fields provide a route to control the motion of nanoparticles and molecules and potentially modify the behaviour of soft matter systems. Janus nanoparticles have emerged as versatile building blocks for the self-assembly of materials with novel properties. Here we investigate using non-equilibrium molecular dynamics simulations the behaviour of coarse-grained models of Janus nanoparticles under thermal fields.

Enhanced Thermo-optical Response by Means of Anapole Excitation.

High refractive index (HRI) dielectric nanostructures offer a versatile platform to control the light-matter interaction at the nanoscale as they can easily support electric and magnetic modes with low losses. An additional property that makes them extraordinary is that they can support low radiative modes, so-called anapole modes. In this work, we propose a spectrally tunable anapole nanoheater based on the use of a dielectric anapole resonator.

Gold nanodoughnut as an outstanding nanoheater for photothermal applications.

Photoinduced hyperthermia is a cancer therapy technique that induces death to cancerous cells via heat generated by plasmonic nanoparticles. While previous studies have shown that some nanoparticles can be effective at killing cancer cells under certain conditions, there is still a necessity (or the need) to improve its heating efficiency. In this work, we perform a detailed theoretical study comparing the thermoplasmonic response of the most effective nanoparticle geometries up to now with a doughnut-shaped nanoparticle.

Spatial Control of Heat Flow at the Nanoscale Using Janus Particles.

Janus nanoparticles (JNPs) feature heterogeneous compositions, bringing opportunities in technological and medical applications. We introduce a theoretical approach based on nonequilibrium molecular dynamics simulations and heat transfer continuum theory to investigate the temperature fields generated around heated spherical JNPs covering a wide range of particle sizes, from a few nm to 100 nm. We assess the performance of these nanoparticles to generate anisotropic heating at the nanoscale.

Broadband Unidirectional Forward Scattering with High Refractive Index Nanostructures: Application in Solar Cells.

High refractive index dielectric (HRID) nanoparticles are a clear alternative to metals in nanophotonic applications due to their low losses and directional scattering properties. It has been demonstrated that HRID dimers are more efficient scattering units than single nanoparticles in redirecting the incident radiation towards the forward direction. This effect was recently reported and is known as the "near zero-backward" scattering condition, attained when nanoparticles forming dimers strongly interact with each other.

On the performance of a tunable grating-based high sensitivity unidirectional plasmonic sensor.

Optical biosensing is currently an intensively active research area, with an increasing demand of highly selective, sensitivity-enhanced and low-cost devices where different plasmonic approaches have been developed. In this work we propose a tunable optimized grating-based gold metasurface that can act both as a high sensitivity sensor device (up to 1500 nm/RIU) and as an unidirectional plasmon source. The theory behind surface plasmon polariton generation is recalled to thoroughly understand the influence that every parameter of the grating source has on the performance of the proposed device.

Polarization of acetonitrile under thermal fields via non-equilibrium molecular dynamics simulations.

We show that thermal gradients polarize liquid and supercritical acetonitrile. The polarization results in a stationary electrostatic potential that builds up between hot and cold regions. The strength of the field increases with the static dielectric constant or with decreasing temperature.

Plasmonic linear nanomotor using lateral optical forces.

Optical force is a powerful tool to actuate micromachines. Conventional approaches often require focusing and steering an incident laser beam, resulting in a bottleneck for the integration of the optically actuated machines. Here, we propose a linear nanomotor based on a plasmonic particle that generates, even when illuminated with a plane wave, a lateral optical force due to its directional side scattering.

All-Dielectric Chiral Metasurfaces Based on Crossed-Bowtie Nanoantennas.

Circular dichroism spectroscopy is a technique used to discriminate molecular chirality, which is essential in fields like biology, chemistry, or pharmacology where different chiral agents often show different biological activities. Nevertheless, due to the inherently weak molecular-chiroptical activity, this technique is limited to high concentrations or large analyte volumes. Finding novel ways to enhance the circular dichroism would boost the performance of these techniques.

Enhanced Transverse Magneto-Optical Kerr Effect in Magnetoplasmonic Crystals for the Design of Highly Sensitive Plasmonic (Bio)sensing Platforms.

We propose a highly sensitive sensor based on enhancing the transversal magneto-optical Kerr effect (TMOKE) through excitation of surface plasmon resonances in a novel and simple architecture, which consists of a metal grating on a metal magneto-optical layer. Detection of the change in the refractive index of the analyte medium is made by monitoring the angular shift of the Fano-like resonances associated with TMOKE. A higher resolution is obtained with this technique than with reflectance curves.

Understanding and Reducing Photothermal Forces for the Fabrication of Au Nanoparticle Dimers by Optical Printing.

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.

Efficient Third Harmonic Generation from Metal-Dielectric Hybrid Nanoantennas.

High refractive index dielectric nanoantennas are expected to become key elements for nonlinear nano-optics applications due to their large nonlinearities, low energy losses, and ability to produce high electric field enhancements in relatively large nanoscale volumes. In this work, we show that the nonlinear response from a high-index dielectric nanoantenna can be significantly improved by adding a metallic component to build a metal-dielectric hybrid nanostructure. We demonstrate that the plasmonic resonance of a Au nanoring can boost the anapole mode supported by a Si nanodisk, strongly enhancing the electric field inside the large third-order susceptibility dielectric.

Unidirectional light scattering with high efficiency at optical frequencies based on low-loss dielectric nanoantennas.

Dielectric nanoparticles offer low optical losses and access to both electric and magnetic Mie resonances. This enables unidirectional scattering along the incident axis of light, owing to the interference between these two resonances. Here we theoretically and experimentally demonstrate that an asymmetric dimer of dielectric nanoparticles can provide unidirectional forward scattering with high efficiency.

Tailored Hypersound Generation in Single Plasmonic Nanoantennas.

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.

Switchable directional scattering of electromagnetic radiation with subwavelength asymmetric silicon dimers.

High refractive index dielectric nanoparticles show high promise as a complementary nanophotonics platform due to compared with plasmonic nanostructures low absorption losses and the co-existence of magnetic and electric resonances. Here we explore their use as resonantly enhanced directional scatterers. We theoretically demonstrate that an asymmetric dimer of silicon nanoparticles shows tuneable directional scattering depending on the frequency of excitation.

Non-plasmonic nanoantennas for surface enhanced spectroscopies with ultra-low heat conversion.

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.

Plasmonic control of radiative properties of semiconductor quantum dots coupled to plasmonic ring cavities.

In recent years, a lot of effort has been made to achieve controlled delivery of target particles to the hotspots of plasmonic nanoantennas, in order to probe and/or exploit the extremely large field enhancements produced by such structures. While in many cases such high fields are advantageous, there are instances where they should be avoided. In this work, we consider the implications of using the standard nanoantenna geometries when colloidal quantum dots are employed as target entities.

Precise attoliter temperature control of nanopore sensors using a nanoplasmonic bullseye.

Targeted temperature control in nanopores is greatly important in further understanding biological molecules. Such control would extend the range of examinable molecules and facilitate advanced analysis, including the characterization of temperature-dependent molecule conformations. The work presented within details well-defined plasmonic gold bullseye and silicon nitride nanopore membranes.

Plasmon enhanced fluorescence with aggregated shell-isolated nanoparticles.

Shell-isolated nanoparticles (SHINs) nanostructures provide a versatile substrate where the localized surface plasmon resonances (LSPRs) are well-defined. For SHINEF, the silver (or gold) metal core is protected by the SiO2 coating, which is thicker than the critical distance for minimum quenching by the metal. In the present work, it is shown that an increase in the SHINEF enhancement factor may be achieved by inducing SHIN aggregation with electrolytes in solution.

Visualizing the near-field coupling and interference of bonding and anti-bonding modes in infrared dimer nanoantennas.

We directly visualize and identify the capacitive coupling of infrared dimer antennas in the near field by employing scattering-type scanning near-field optical microscopy (s-SNOM). The coupling is identified by (i) resolving the strongly enhanced nano-localized near fields in the antenna gap and by (ii) tracing the red shift of the dimer resonance when compared to the resonance of the single antenna constituents. Furthermore, by modifying the illumination geometry we break the symmetry, providing a means to excite both the bonding and the "dark" anti-bonding modes.

Interference, coupling, and nonlinear control of high-order modes in single asymmetric nanoantennas.

We investigate theoretically and experimentally the structure of plasmonic modes in individual asymmetric dimer antennas. Plasmonic near-field coupling of high-order modes results in hybridization of bright and dark modes of the individual nanorods, leading to an anticrossing of the coupled resonances. For two bright modes, hybridization results in a capacitive red shift and super-radiant broadening.

Detection of deep-subwavelength dielectric layers at terahertz frequencies using semiconductor plasmonic resonators.

Plasmonic bowtie antennas made of doped silicon can operate as plasmonic resonators at terahertz (THz) frequencies and provide large field enhancement close to their gap. We demonstrate both experimentally and theoretically that the field confinement close to the surface of the antenna enables the detection of ultrathin (100 nm) inorganic films, about 3750 times thinner than the free space wavelength. Based on model calculations, we conclude that the detection sensitivity and its variation with the thickness of the deposited layer are related to both the decay of the local THz field profile around the antenna and the local field enhancement in the gap of the bowtie antenna.