The research field of nanophotonics has made tremendous progress in the past 10 years. Many of these achievements result from the increasing degree of control over nanofabrication and nanocharacterization that has evolved in the past years. Taking advantage of the extreme control over nanophotonic light fields that we have today, we are now in an ideal position to bring the photonics field a next step further, and to investigate the coupling of light with other degrees of freedom such as nanoscale mechanical motion, acoustic phonons, electron spins and excitons.
We will illustrate this emerging new trend of hybrid nanophotonics with several characteristic examples:
- plasmonic optomechanical oscillators: we demonstrate the integration of optically resonant plasmonic nanocavities with silicon-nitride-membrane mechanical oscillators. In these hybrid structures mechanical motion is transduced to scattered optical fields, enabling measurements of displacement sensitivity down to the picometer level.
- plasmonic transparent conductors: we shows how resonant plasmonic nanowire networks serve both as efficient light coupling/trapping geometries and low-resistivity electrical current collectors. We show the integration of nano-imprinted silver nanowire networks with high-efficiency silicon heterojunction solar cells, polymer solar cells, and present their possible use in touch-screen displays.
- cathodoluminescence microscopy: the high-energy electron beam in an electron microscope is coupled to resonant modes in photonic nanostructures, enabling spatial mapping of optical modes with deep-subwavelength resolution, as we will show. This technique provides the “purest” form of optical excitation spectroscopy, as a single electron drives individual polarizable nanophotonic building blocks.
Hybrid nanophotonic concepts will lead to new devices and functionality such as mechanical sensors, RF signal processing, bio-sensors, quantum information processing, ultra-high efficiency solar cells, light-emitting diodes, opto-electronic integrated circuits, imaging systems, and much more.

Classical polarized light carries spin and reveals spin-orbit coupling when propagating along a curved trajectory, however this interaction typically is weak. Utilizing a large phase-gradient, a metasurface can greatly enhance this interaction because it can bend light abruptly within an extremely small thickness due to the large induced momentum. Conceivably, this strong photonic spin-orbit coupling on a metasurface could drive the electrons collectively and lead to direct electric Hall currents flowing transversely to the light-bending direction, even at normal incidence and without external magnetic fields. Yet such a photon-spin-induced electric Hall effect has never until now been demonstrated. Here we report the first observation of this direct coupling between photon spin and electron orbital momenta on a metallic metasurface consisting of complementary nanoantennas. By inputting opposite photonic spins, we directly detect the changes inversion of the transverse current direction, with the longitudinal current (induced by the photon-drag effect) being constant. This effect enables an electrical way of detecting photonic spin-orbit interactions and provides a viable route to directly integrate conventional electronic chips with the additional degrees of freedom from the spin and orbital angular momenta of light for future information processing and communication applications

Optical matter is a unique class of materials. Typical optical matter is consisting of dielectric microparticles that are self-organized and stabilized by optical binding forces in an optical field. Noble metal nanoparticles usually exhibit strong scattering in the visible light spectrum, resulting in strong optical binding forces that offer the opportunity to construct optical matter from nanoparticles. Here we report our recent work on controlling and tailoring the self-organization of plasmonic nanoparticles in structured optical fields. Structurally stable 2D and 3D clusters with various geometries have been photonically synthesized from Ag nanoparticles with nanometer scale precision in their inter-particle separations. In particular, we show how Ag nanoparticles organize themselves in response to the optical trap shape, intensity gradient, phase gradient, polarization of light, and even the spatial assembly pathways. Our work paves the way for rational design of photonic clusters in optical fields, and we envision that these photonic clusters will find applications in various areas, such as sensing and quantum optics.

Enantiomers are pairs of chiral molecules that are non-superimposable mirror images of each other. The handedness of enantiomers is highly related to their biological function, and effective separation of enantiomers is crucial for the development of functional drugs. Since enantiomers are identical in their chemical composition and mass, existing methods of enantiomer separation largely rely on the unique ways in which each molecule in an enantiomeric pair interacts with other chiral reagents. Here we introduce a novel method of separating enantiomers using optical forces. To generate forces of sufficient strength to trap single molecules, we use a plasmonic coaxial optical trap composed of a 120-nm-diameter silver core and a 25-nm silicon dioxide channel. The coaxial resonator thickness is 150 nm, which provides two strong transmission peaks at 487 nm and 702 nm, corresponding to the Fabry-Perot resonances of the resonator. When light is scattered from the aperture, a large field gradient is generated close to it; linearly-polarized light can provide up to 1.8 pN of lateral force per 100 mW of transmitted power, sufficient to capture dielectric nanoparticles as small as 10 nm in diameter at 20 nm above the coaxial aperture. Interestingly, the near-fields of our coaxial aperture also generate forces that can differentiate between different chiral structures. The two distinct lateral forces arising from chiral molecules interacting with the coaxial aperture are related to the optical rotation dispersion and the circular dichroism of the molecule, and can be derived from electromagnetic chiral density and the energy flow vortex. To calculate the optical forces exerted selectively on R and S enantiomers, we use a combination of finite difference time domain simulations and analytic methods. We consider a 10-nm-diameter dielectric chiral particle (similar in size to a typical large protein) placed 20 nm away from the aperture. Our calculations indicate that, for left-handed circularly polarized illumination, the total maximum transverse force can reach 0.9pN/100mW for the S enantiomer and 0.3pN/100mW for the R entantiomer. Importantly, these forces are in opposite directions: the S enantiomer is attracted toward the trap, while the R enantiomer is repelled. Such significant differences in both magnitude and sign of the transverse forces for the enantiomer pairs result in large differences in trapping potentials: we observe a maximum trapping potential depth of -7.6kT per 100mW transmitted power for the S-enantiomer and a positive trapping potential for the R enantiomer. On-going experiments are employing atomic force microscopy to directly measure these forces and to maneuver single chiral molecules with a specific handedness by switching polarization states. Our presentation will describe this theoretical and experimental work and discuss optimized coaxial arrays for all-optical enantiomer-pure chemical synthesis and chiral drug purification.

Fundamentally plasmon oscillations are an opto-mechanical phenomenon. Incident optical fields induce the coherent motion of electrons that produce large fluctuations of charge density at ‘hot spots&’ in resonant structures. Despite these large fluctuations, during linearly polarized illumination a resonant structure, e.g. a metallic nanorod, will necessarily assume a uniform charge distribution twice during each optical cycle. This behavior mimics the electrical field vector of the linearly polarized excitation, which must also have zero magnitude in the plane perpendicular to the direction of propagation twice during an optical cycle. In contrast, the electrical field vector of circularly polarized light has constant magnitude. During an optical cycle, the electric field vector rotates in the plane normal to the wave propagation. Consequently, if plasmonic structures are resonant with circularly polarized excitation, they can exhibit regions of strongly modified carrier density for the duration of the optical cycle.
Here, we study a class of achiral toroid and ‘sun burst&’ patterned resonant plasmonic nanostructures that show persistent, circulating charge density waves during circularly polarized illumination. The direction of the continuously circulating wave (clockwise or counterclockwise) depends on the handedness of the incident beam. Our interest stems from whether these charge density waves can support circular electric currents (DC) manifest experimentally as static magnetic fields during illumination. Using full-wave optical modeling (FDTD method), and mechanistic calculations of the circulating potential acting on the electronic density of states in the toroid resonators, we outline the conditions that maximize optical excitation of circulating electric currents for the case of Au and Ag resonators. We show that in the limit of very weak coupling to the solenoid-like electron transport, or when < 1 x 10^-6 % of the electron population that contributes to the charge density wave enters the circular transport modes, relatively strong magnetic fields, > 1 G, can be expected. We discuss scanning probe measurements for monitoring the induced magnetic field, as well as the relationship between this phenomenon and the inverse faraday effect observed in continuous media.

The recent demonstration of resistless nano-imprint lithography (RNIL) as a scalable technique for the fabrication of nanoscale structures in metallic films provides great promise for the mass production of plasmonic devices. Computational and experimental studies indicate that nanocavities in a metallic film exhibit distinct localized resonances. These cavity resonances are accompanied by strongly enhanced and localized electric and magnetic fields and can modify the lifetime and other emission properties of quantum sources such as quantum dots, NV centers in nanodiamond and fluorescent molecules. Furthermore, cavities produced by RNIL support a higher energy, lowest-order, localized surface plasmon mode than a similarly sized dielectric-backed aperture. Applications for these nanocavities include plasmonic color filters, enhanced solar energy harvesting and the production of novel polarization states. Here we demonstrate enhanced fluorescence of CdSe/CdS/ZnS core-shell quantum dots (QDs) via coupling to plasmonic nanocavities imprinted using RNIL into a silver film.
A silicon master template was patterned using electron beam lithography and reactive ion etching. The pattern consisted of rectangular nanorods in a periodic array, with a period of 300 nm. The pattern was transferred to a 360 nm thick silver film on a silicon substrate using RNIL with a force of 19 kN at room temperature. The resulting cavities were 200 nm long by 60 nm wide by 40 nm deep. The QDs were mixed with SU8 2005 and then drop-cast over the sample and cured.
Fluorescence microscopy was performed on the sample by pumping the QDs with a 532 nm pulsed laser and collecting the 650 nm emission. Time correlated single photon counting (TCSPC) lifetime measurements indicate that excited state lifetimes of the QDs in the vicinity of the nano-imprinted plasmonic nanocavities are reduced. Preliminary results indicate around a 4-fold brightness enhancement and a lifetime reduction of around 70%, when compared to the QD-SU8 matrix on an unpatterned Ag film.
This work was performed in part at the Melbourne Centre for Nanofabrication (MCN) in the Victorian Node of the Australian National Fabrication Facility (ANFF). This research was supported under the Australian Research Council's Discovery Projects funding scheme (project number DP110100221) and a Melbourne Centre for Nanofabrication Technical Fellowship.

We study the optical properties of molecules deposited metallic nanostructures with respect to the free molecules. We show theoretically and experimentally that molecular excited states can be strongly coupled to plasmonic modes. Upon coupling new hybrid states are form, the lower and the higher polariton. These modes have the characteristic of both molecular and plasmonic states. As the coupling strength grows, a new mode emerges, which is attributed to long-range molecular interactions mediated by the plasmonic field. The new, molecular-like mode repels the polariton states, and leads to an opening of energy gaps. By tuning the plasmonic modes to be on/off resonance with respect to molecular system excited state, one can shift these hybrid modes and by that modify the photophysical and even the chemical properties of these molecules, and form a new kind of tunable hybrid materials.
In the same aspect, we study and demonstrate coupling between plasmonic modes of metallic nanocavities (holes). The metallic nanocavities display long range coupling at distances of hundreds of nanometers for selected hole distance/wavelength combinations. Such strong coupling drastically changes the symmetry of the charge distribution around the nanocavities as is evidenced by the nonlinear optical response of the medium. Upon coupling, the emission intensity is strongly dependent on the fundamental beam polarization, and is either suppressed or enhanced.
References
middot; From Individual to coupled metallic nanocavities. Salomon, A.; Prior, Y. ; Kolkowski, R.; Zyss,J.; Journal of optics, accepted 2014
middot; Role of mode degeneracy in molecule-surface plasmon strong coupling. Salomon A. Wang, S. Hutchison, J.A., Genet, C. Ebbesen, T.W. accepted ChemPhysChem 2013
J. Phys. Chem. C, 2013, 117 (43), pp 22377-22382
middot; Collective Plasmonic-Molecular Modes in the Strong Coupling Regime Salomon, A.; Gordon R.J.; Prior, Y.; Seideman, T.; Sukharev, M.;
Phys. Rev. Lett 109, 073002, 2012
middot; Molecule - light complex: dynamics of hybrid molecule - surface plasmon states. Salomon, A. Genet, C. and Ebbesen, TW. Angewandte Chemie, 48, Pages: 8749-8751, 2009.

Quantum optics involves the coupling of quantum emitters to their electromagnetic environment. Because this coupling is related to the concentration of the optical field, it is typically constrained by the diffraction limit of light. One way to circumvent this limitation is by moving to quantum plasmonics, which uses surface plasmon polaritons (SPPs) instead of photons. However, despite the advantages of this approach, quantum plasmonics has not yet been fully explored, largely due to the difficulty of creating the necessary structures. We address this problem by combining state-of-the-art quantum emitters with plasmonic structures (waveguides and reflectors) that approach theoretical performance limits. We synthesize highly luminescent colloidal quantum dots (photoluminescence quantum yields >90%) and precisely place them on template-stripped silver wedge waveguides. We demonstrate efficient coupling of the quantum-dot emission into guided plasmonic modes in the waveguide. In addition, by adding efficient reflectors, high-Q plasmonic resonators are obtained. More generally, the flexibility and fidelity of the resulting quantum plasmonic systems indicates that they will enable a broad set of nanoscale quantum optical measurements and devices.

Light-matter interaction probed at the nanoscale attracts much attention nowadays, both for its fundamental interest and potential applications, ranging from all-integrated optics to single photon sources [1].
Hybrid plasmo-photonic 2D crystals exhibit a complex resonance pattern, which has been characterised using both numerical simulations and measurements of the electric near-field patterns obtained with a scattering scanning near-field optical microscope (s-SNOM) [2]. We show that the resonance modes exhibited by such a hybrid nanostructure can be recovered in the far-field by using narrow-band fluorescence nano-reporters. To this end, different types of semiconductor quantum dots (QDs), acting as nanoreporters of the local interactions, were dispersed on top of these hybrid structures. We show that the emission rates are affected, in a unique way, by the complex interaction occurring between the plasmo-photonic modes and the excitons.
We also report on the experimental observation of an asymmetric wavelength-dependence of the emission rate enhancement in such 2D crystals [3]. This feature strongly contrasts with the traditional Lorentzian line shape exhibited at a resonance by the Purcell factor. This unusual dispersive behavior is shown to be reproducible for different combinations of emitters and structures. It is further retrieved from FDTD simulations. It is mainly due to the fact that a hybridized mode, resulting from the coupling of a Bragg and a SPP modes, is coupled to the emitters. Further studies of the emission detuning by hybrid plasmo-photonic structures are expected to benefit many related fields and notably sensing and bio-sensing technologies.
Furthermore, we show experimentally that frequency-bin entangled photons can propagate through these plasmo-photonic nanostructures [4]. Our measurements clearly show the robustness of frequency-bin entanglement, which survives after interactions with the plasmo-photonic structures, offering possibilities for a variety of applications in which quantum states can be encoded into the collective motion of a many-body electronic system without demolishing their quantum nature.
Finally, we show some recent investigations of the strong coupling regime between excitons and the resonances modes of such plasmo-photonics structures, the so-called "excimons".
[1] W.L. Barnes, A. Dereux and T.W. Ebbesen, Nature 424, 824 (2003)
[2] S. Ungureanu, B. Kolaric, J. Chen, R. Hillenbrand and R.A.L. Vallée, Nanophotonics, 2, 173, (2013)
[3] P. Fauché, S. Ungureanu, B. Kolaric, R.A.L. Vallée, Journal of Materials Chemistry C, 2014, DOI: 10.1039/C4TC01787K
[4] L. Olislager, B. Kolaric, W. Kubo, T. Tanaka, S. Ungureanu, R.A.L. Vallée, P. Emplit, S. Massar, in preparation.

Semiconductor nanowires (NWs) are filamentary crystals with a diameter of few tens of nanometers. Thanks to their dimensions and high refractive index, have the ability to collect and trap the light into a sub-wavelength volume ^[1]. Metal nanostructures have shown in the past the ability of modifying and enhancing light response of nanoscale objects^[2]. The realization of this hybrid system opens a way to novel applications and the use optical fields to manipulate and enhance the light interaction with semiconducting materials^[3,4].
We demonstrate for the first time how, by hybridizing a single nanowire photo#8208;detector with a bow#8208;tie antenna structure, it is possible to control the polarization response of a nanowire. Bow#8208; tie antenna concentrate radiation inside the body of the nanowire, thereby increasing the absorption of light polarized across the nanowire axis. The amount of light absorbed is strictly dependent on the antenna design and density. We demonstrate enhancement in light absorption, as well as for second order phenomena such as the generation of second harmonics and Raman scattering ^[3]. We perform photoconductivity measurements demonstrating that a hybrid structure formed by GaAs NWs and an array of bow-tie antennas is able to modify the polarization response of a NW^[5]. The large increase in light absorption for transverse polarized light changes the NW polarization response, including the inversion.
This study constitutes an important step for the understanding of light coupling in engineered nanodevices. It opens a path to applications aiming to combine the semiconducting properties of nanostructures with the plasmonic properties of metal. Hybrid nanoantenna-NW systems can certainly bring progress to the use of nanowires for next generation photo#8208;detectors and solar cells.
References
^[1]P. Krogstrup, et al., Nature Photonics, vol 7, 306-310 (2013)
^[2]C. Forestiere, et al., Nano Letters, vol 12, 2037-2044 (2012)
^[3]A. Casadei, et al., Nano Letters, vol 14, 2271-2278 (2014)
^[4]S. Heeg, et al., Nano Letters, vol 14, 1762-1768 (2014)
^[5]A. Casadei, et al, Scientific Report, (under review)

The “plasmon hybridization”concept,[1] shows that the plasmon resonances in complex metallic nanostructures interact and hybridize in an analogous manner as atomic wavefunctions in molecules. The insight gained from this concept provides an important conceptual foundation for the development of new plasmonic structures that can serve as substrates for surface enhanced spectroscopies, chemical and biosensing, and subwavelength plasmonic waveguiding and other applications. The talk is comprised of basic overview material interspersed with a few more specialized “hot topics” such quantum plasmonics,[2] molecular plasmonics,[3] active plasmonic nanoantennas for enhanced light harvesting,[4] plasmon induced hot carrier generation,[5] and chemical reactions.[6]
[1] N.J. Halas et al., Adv. Mat. 24(2012)4842
[2] T.V. Teperik et al., PRL 110(2013)263901; Opt. Express 21(2013)27306
[3] A. Manjavacas et al., ACS Nano 7(2013)3635
[4] M. W. Knight et al., NL 13(2013)1687; A. Sobhani et al., Nature Comm. 4(2013)1643
[5] A. Manjavacas et al., ACS Nano 8(2014)7630
[6] S. Mukherjee et al., JACS 136(2014)64; Y. Kang et al., Adv. Mat. 26(2014)6467

We report the large-area assembly of gold anisotropic nanoparticles into lithographically defined templates with control over their angular position using a capillary-based approach. We elucidate the role of the geometry of the templates in the assembly of anisotropic nanoparticles consisting of different shapes and sizes. These insights allow us to design templates that immobilize individual triangular nanoprisms and concave nanocubes in a shape-selective manner, and filter undesired impurity particles from a mixture of triangular prisms and other polyhedra. Furthermore, by studying the assembly of two particles in the same trench, we elucidate the importance of interparticle forces with this novel method. These advances allow for the construction of face-to-face and edge-to-edge nanocube dimers as well as triangular nanoprism bowties. As an example of the fundamental studies enabled by this assembly method, we investigate the surface enhanced Raman scattering (SERS) of face-to-face concave cube dimers both experimentally and theoretically, and reveal a strong polarization dependence of the local field enhancement.

We fabricated coatings with a silver nanocube aggregation gradient by applying different surface pressures during slow Langmuir-Blodgett deposition. The randomly distributed nanocube aggregates with gradually changing surface coverage open up new ways to continuously control the absorption and phase of the incoming light over a broad optical spectrum, while being polarization sensitive. Optical characterization under total internal reflection conditions (TIR) reveals that the broadband light absorption depends on the relative orientation of the particle aggregations to the polarization of the incoming light, which has not been investigated yet. By using electromagnetic simulations, we found that the electric field vector of the s-polarized light matches with the different types of silver nanocube aggregations to excite variable plasmonic resonances. Based on this matching conditions, the s-polarization shows an outstanding tunablility of the plasmonic resonance by the angle of incidence (64nm per 10° angle of incidence). Further observation of these modes with spectral ellipsometry reveals a steep phase change at the plasmonic resonances. With a very low surface coverage below 25%, we observed a polarization-selective absorption of 80% (theoretical 98% at peak value) of the incoming light over a broad optical range in the visible region from 400 to 700 nm. This low cost, large area, gradiental variable and easily scalable assembled plasmonic material designs is of particular interest for broadband light absorption, phase-sensitive sensors, and imaging.

Optical metasurfaces are ultrathin, two-dimensional arrays of subwavelength resonators that have been demonstrated to control the flow of light in ways that are otherwise unattainable with natural materials. However, metasurfaces pose major challenges in their nanofabrication, prominently in terms of minimum reliable feature size, high throughput and large area fabrication, which can be prohibitively expensive and time-consuming using conventional lithography techniques. Optical metasurfaces that operate in the visible are inherently challenging to fabricate due to their multi-scale architecture, and requirement for deeply sub-wavelength features, often requiring dielectric spacing of a few nanometers.
Self-assembly provides an alternative fabrication approach that overcomes these limitations in scalability and design. Here we show that colloidal, single-crystalline anisotropic nanocrystals can be organized into metasurface architectures with nanometer-precision using robust, scalable assembly methods. These metasurfaces exhibit extreme in- and out-of-plane electromagnetic coupling that is strongly dependent on nanocrystal size, shape, and spacing. We show that this fabrication approach enables plasmonic metamaterials to be tuned for diverse applications ranging from metasurfaces that display near-ideal electromagnetic absorption--up to 99.8%--tunable from the visible into mid- IR wavelengths, to quasi-2D metasurfaces that demonstrate photoluminescent enhancement of over 120x, for an active region less than 150 nm thick.

Laser induced mechanical shockwave was developed as an effective tool to tailor multi-crystalline Au nanostructures and tune nanogaps in plasmonic nanoantennas. The shock wave generation during laser shock irradiation of graphite was explained using Fabbro's model. Atomic movement of plasmonic gold structure under shockwave compression was investigated using molecular dynamic simulations. Force - displacement relationship was monitored to analyze mechanical property change of nanostructures during laser shock compression. Atoms were found to move in radial direction and nanodisks were found to keep their symmetry after severe plastic deformation. Geometrical changes at different laser energies were quantitatively measured using SEM and AFM images. Surface roughness was found to be decreased after laser shock compression. Different nanogaps down to sub-10 nm could be effectively controlled by varying laser fluences. Optical response of the processed nanostructures were compared with initial structures by numerical simulations and experiments. It was found that after laser shock, nanodisks were enlarged, brought closer, and field enhancement at the center of two adjunct nanodisks was hugely increased. The processed nanostructures had higher sensitivity in low- concentration molecular sensing experiment. Optical dark field spectroscopy experiment showed that the resonance of these processed structures had a red shift compared to the initial structures. Laser induced mechanical shockwave is an effective tool to improve optical properties of multi-crystalline plasmonic nanoantennas.

The origin of unique optical properties of gold nanorods such as distinctive extinction bands in the upper visible or near-infrared region is surface plasmon (SP) oscillation of free electrons. Surface electrostatics of gold nanorod is tremendously important to understand how electrons interact with optical waves. Electrostatic property of gold nanorods has been known to be centrosymetric, however, we have shown that gold nanorods have anisotropic charge accumulation on their surface, which can be defined as a polarized surface charge density. By using off-axis electron holography, we have observed anisotropic electrostatic potential of gold nanorods experimentally. We believe that their anisotropic potential is from different distribution of cetyltrimethylammonium bromide (CTAB), capping ligand having positive charge, on the gold nanorod surface. This anisotropic distribution of CTAB is identified by high resolution scanning electron microscopy (SEM), implementing secondary electron detector in high resolution transmission electron microscopy (TEM) system. We believe that this anisotropic potential formed by CTAB layer results in anisotropic charge accumulation on the gold surface as compensate the potential gradient. As the result, the inner potential of gold nanorod itself has no gradient as well known the fact that the electric field anywhere beneath the surface of a charged conductor is zero. Computation of electrostatic potential of gold nanorod considering this charge distribution from CTAB is well matched with experimental hologram that we observed.

As our society become progress, the possibility of people to be exposing to various hazardous environments. The needs to develop high sensitive and selective bio/chemical sensor have been increased. The π-conjugate polymers are a good candidate for the developing sensor applications because of their specific detection capability through a large change in the electrical and optical signals. In this study, we present a high performance optical sensing using core-shell hybrid nanostructure consist of silver (Ag) nanoparticles (NPs) and polydiacetylene (PDA). Our ultimate aims are improvement and control in the detection ability of selectivity and sensitivity by means of surface plasmon resonance (SPR) coupling effect. We fabricate a core-shell NP in deionized (DI) water solution through sequentially processes of reprecipitation and hydrothermal thermal method. The formation of the Ag/PDA core-shell hybrid NPs was visualized through scanning electron microscope (SEM) and high resolution-transmission electron microscope (HR-TEM) images. The nanometer-scale photoluminescence (PL) and Raman characteristics of core-shell NP were studied by using a laser confocal microscope (LCM) with a help of color charged-coupled device (CCD) images. The variation of light emission color and intensities of the core-shell hybrid nanostructure were observed depending on the amounts and kinds of target materials. Our results show that the PL intensity of Ag/PDA core-shell hybrid NP considerably increased compare to pristine PDA materials when the attachment of target bio/chemical materials because of the strong SPR coupling effect.

Recently, plasmonic coupled optical cavity has gained much attention due to its attractive properties in light manipulation, e.g. high Q optical resonance,[1] local field enhancements[2,3] and extraordinary transmission.[3] The strongly enhanced local filed originated from the plasmonic resonance hybridizing with the optical cavity mode has great potential applications. Therefore, it has been widely proposed to be used in enhancing semiconductor emission,[4] plasmonic laser,[1] WGM resonator based bio-sensor,[2] SERS detecting[5] and other related fields requiring superior optical performances.
In this work, the coupling effect between plasmonic mode and optical cavity mode has been demonstrated in self-assembled metal/dielectric hollow-nanosphere (HNS) arrays. The further employment of the strongly enhanced local filed originated from the inter-coupling of the plasmonic cavities for high sensitive SERS sensing was proposed. Large scale, two-dimensional (2D) metal/dielectric HNS arrays were successfully fabricated using the self-assembled polystyrene (PS) nanospheres as the template. Series orders of whispering gallery mode (WGM) resonances in the HNSs and plasmonic coupled WGM resonances in the double-shell HNSs have been experimentally and theoretically demonstrated by the transmission spectroscopy and simulated resonance spectra and near field patterns in FDTD method. Highly localized near field around the HNS cavities originated from the plasmonic WGM resonance and its strong multiple coupling effect between the HNS arrays ensure this plasmonic cavity arrays to be a suitable SERS substrate. Extraordinary SERS performances were then achieved on the HNS arrays with optimized size and gaps. Additionally, more significant photocatalytic self-cleaning process can be effectively accomplished on this recyclable SERS chips under visible light irradiation rather than conventional UV illumination.

The study of catalytic processes and redox reactions on metal nanocrystal surfaces is extremely challenging. Rates of reaction are highly sensitive to a variety of parameters including the particle size and shape, the degree of crystal faceting, the occurrence of underpotential deposition (UPD) and the role of substrate interactions. These factors are all convoluted in ensemble electrochemical measurements and consequently, one approach for obviating these problems is to study redox processes on single metal nanoparticles. We report the electrodeposition of metallic silver onto single gold nanostars adsorbed to indium tin oxide (ITO) electrodes. The electrochemical process was studied in-situ by correlated dark field spectroscopy and scanning electron microscopy (SEM). We demonstrate that bulk nucleation and growth on the ITO can be circumvented by careful application of chronoamperometry enabling controlled, selective growth of small amounts of silver onto single gold nanocrystals. This is possible because the binding energy for silver to gold is large enough to enable selective deposition at very low overpotentials. In order to increase the probability of UPD and hence control the deposition process, we have used gold nanostars which present a wide range of crystal facets and possess a high double-layer capacitance, due to their high surface-to-volume ratios. We carry out chronoamperometry at very low silver ion concentrations (0.5 micromolar) in 0.1 M NaNO₃ as the supporting electrolyte. SEM proves that deposition occurs preferentially on less atomically coordinated gold sites at the tips. The surface plasmon resonance blue-shifts by several tens of nanometers following the formation of spherical deposits of silver on the star tips, moving the scattered colour from the near infrared to red. The spectral shifts can be accurately modelled using finite element simulations. These results demonstrate that the morphological properties of individual bimetallic particles can be engineered electrochemically by monitoring optical changes.

Chiral structures are ubiquitous in nature, such as DNA, peptides and amino acids, which exhibit very small chiroptical effects. However, chiral nanoplasmonic structures exhibit strong chiroptical effects, which are not only due to the chiral geometry of nanoparticles, but also to nanoplasma used to manipulate the local electric and magnetic fields. In our study, silver nano-spirals (AgNSs) with adjustable geometric parameters have been fabricated in wafer scale by glancing angle deposition (GLAD) under controlled low temperature. When AgNSs are dispersed in ethanol, it has been demonstrated that circular dichroism of individual AgNSs can be tuned by adjusting a set of spiral dimensional parameters. In addition, a gigantic chiroptical response is obtained from the array of randomly distributed AgNSs deposited on sapphires in the UV-visible range, which has not been reported before to our best knowledge.

Materials with narrow-band high absorption ef#64257;ciency are particularly desirable for various applications including monochromatic photodetectors, sensors and thermal emitters. Previous theoretical work suggests that ideal narrow-band absorbers can be fabricated based on ordered two-dimensional arrays of metallodielectric core-shell microspheres on a gold substrate.^[1] In contrast to absorbers prepared by lithography, a low-cost fabrication method based on colloidal crystals is proposed to produce large area structures with almost perfect light absorption.
Here, we present a facile approach for the preparation and assembly of sub-micron metallodielectric particles on metallic substrates. The particles consist of a silica core surrounded by a platinum shell and a second shell made of silica. In this work, we developed a fabrication method for the production of almost perfectly smooth metallic shells of different thicknesses (3-30 nm) by a seeded growth method. Furthermore, we optimized the coating of the metallic surface with SiO₂, so that very homogeneous and smooth insulating shells in a range of 30 nm down to very thin shells of 2 nm were accessible. The metallic character of the core-shell SiO₂@Pt particles as well as the insulating character of the SiO₂-shells of the core-shell-shell SiO₂@Pt@SiO₂ particles could successfully be demonstrated by low-temperature conductivity measurements. Finally, we established a drop-casting method for self-assembly of high density particles with diameters of 350-400 nm, which enabled the formation of at least partially ordered monolayers of the core-shell-shell SiO₂@Pt@SiO₂ particles on metallic substrates. Optical measurements of these monolayers show a structurally related absorption in the IR region.

Metamaterial structures composed of ordered arrays of metallic nanoparticles and nanocavities are able to support strong plasmon and Fano resonances in the optical frequencies, where the appeared Fano dips can be utilized in bio/chemical sensing and spectroscopic purposes with a significant sensitivity. Herein, we utilize two concentric compositional nanoshells (Al/Al₂O₃) to design nanomatryushka structures in periodic arrays, where each one of Aluminum nanoparticles is covered by a certain thickness of the oxide layer. Depositing studied Aluminum nanomatryushka arrays on metasurfaces, we determined the optical response of the structure by calculating and drawing the extinction cross-sectional profiles. It is shown that the proposed structure is able to support multiple strong Fano resonances in the visible spectrum. Evaluating the plasmon response of the metamaterial configuration for the presence of various semiconductor metasurfaces (Silicon and GaN), the quality of Fano dips is analyzed for different regimes. Ultimately, we investigated the behavior of the appeared Fano dips for perturbations in the refractive index of the surrounding medium. In this method, we measured the accuracy and sensitivity of the metamaterial structure by plotting the linear figure of merit (FoM) and quantifying this parameter. This understanding paves a method to utilize entirely Aluminum nanoparticles in designing metamaterials structures that can be employed in designing ultra-sensitive bio/chemical sensors with low-cost and high efficiency.

Anisotropic linear assemblies of plasmonic NPs are highly interesting for their potential applications in the fields of sensing, metamaterials, wave guiding and light harvesting, due to their anisotropic optical properties. In this work, we present protein capped gold nanoparticles, which exhibit extremely high colloidal stability, even at super high NP concentrations and remarkable physicochemical and wettability properties[1-3]. In this work, we present highly ordered macroscopic (cm²) linear arrays of protein coated gold NPs via wrinkle assisted assembly.[4] The resulting anisotropic and nanostructured assemblies exhibit sophisticated polarization dependent optical properties.
[1] M. Chanana, M.A. Correa-Duarte, and L.M. Liz-Marzán, Small, 2011, 7, 2650
[2] M. S. Strozyk, M. Chanana, I. Pastoriza-Santos, J. Pérez-Juste and L. M. Liz-Marzán, Adv. Funct. Mater., 2012, 22, 1436.
[3] M. Chanana, P. Rivera_Gil, M. A. Correa-Duarte, L. M. Liz-Marzán and W. J. Parak, Angew. Chem. Int. Ed., 2013, 52, 4179
[4] Alexandra Schweikart, Nicolás Pazos-Pérez, Ramoacute;n A. Alvarez-Puebla and Andreas Fery, Soft Matter, 2011,7, 4093-4100

It is well known that the interface between a smooth silver surface and a dielectric enables propagation of surface plasmon polaritons (SPPs). Unfortunately, the direct excitation of SPPs from incident light is not possible at this smooth interface. Instead a surface structure providing a lateral impulse is needed, e.g. nanoparticles or gratings. The resulting roughened silver surfaces allow photons to be absorbed into SPPs which reduces reflection and enables improved photovoltaics and thermo-photovoltaics.
In our study we investigate the interface between a silver surface and air. Specifically, we introduce a facile approach that enables the large-area preparation of sophisticated metal nanostructures which allow for an efficient excitation of SPPs. Polydimethylsiloxane (PDMS) stamps containing nano-relief surface structures are prepared by cast and cure replication of wafer-based nano-templates.
The stamp surface is then coated with an ultra-thin silver island film. We have found that with exposure to humidity or liquid water the coalescence of the silver islands can be tuned from initially separated islands to smooth continuous films. After this tuning of the nanoparticle morphology the ultrathin silver film is transfer-printed on a smooth silver surface. Hence, the local roughness at the silver surface created after printing can be well controlled. Moreover, the ultrathin silver film is transferred only from the top regions of the nano-patterned stamp surface providing well controlled superimposed nanopatterns, e.g. gratings.
The resulting silver surfaces are analyzed by optical spectroscopy. We demonstrate blackened silver surfaces providing a large absorption of around 80% in the entire visible spectrum and for any incident angle. Moreover, the studies enable a new experimental access to the interaction of localized plasmons and delocalized SPPs.

Since the discovery of the effect named "Surface Enhanced Raman Spectroscopy" [1], a lot of work has been made to understand and control this effect [2], and making a complete list is now impossible. This work led to the construction of new scanning probe microscopes, microscope TERS (Tip Enhanced Raman Spectroscopy) [3] which have supplanted systems coupled with near-field optical spectrometers with low imaging capability [4]. Beautiful studies of nanoresonant objects could then be conducted with this TERS technique as well as molecular monolayers [5].
However, the TERS effect is not simply used for all of our samples, depending on its physical properties, leading us to propose a fundamental study coupling the ability to manipulate silver or gold nano-particles under a confocal Raman microscope, with multi-wavelength excitation laser. Our goal is to produce nano-assemblies of nano-particles in the vicinity of the single object or molecular materials [6] to be studied: this allows obtaining a plasmon spectrum with tunable resonance, according to the assembly structure [7]. Chemical contact with the molecule is avoided as well.
In this work, we are developing different nanostructures of metal nanoparticles (gold or silver) by AFM, coupled with a confocal micro-Raman spectrometer, allowing us to observe step by step the evolution of the vibrational spectrum of a sensor system (typically the advanced characterization of a single carbon nanotube, CNT).
These experimental data are associated with finite element models of far and local electromagnetic fields. Thus we achieve to a better understanding about the tunning of plasmon resonance modes of our nanostructures, including sensitive breaks symmetry modes. On the other hand, the consequences of their interactions with a substrate or molecule dipole moment, depending on the excitation wavelength (especially inelastic scattering), are studied. All this allows us to understand and to predict the phenomena observed experimentally.
[1] D.L. Jeanmaire, R.P. Van Duyne, J. Electroanal. Chem., 66 (1975), p. 235
[2]A.Bouvrée, A. D&’Orlando, S. Martin, G. Louarn, J.Y. Mévellec and B. Humbert, Nanostructured Gold surfaces: applications to the SERS and to the lightening rod effect, Gold Bulletin (2013), Vol 46, Issue 4, pp 283-290
[3] A. Hartschuh, N. Anderson, L.Novotny, Near-field Raman spectroscopy using a sharp metal tip, Journal of Microscopy, vol.210, Issue3, pages 234-240, June 2003
[4] Grausem, J., Humbert, B., Spajer, M., Courjon, D., Burneau, A., & Oswalt, J. (1999), Journal of Raman spectroscopy, 30(9), 833-840.
[5] G Picardi, M Chaigneau, R Ossikovski, C Licitra, G Delapierre, Journal of Raman Spectroscopy, 40 (10), 1407-1412, 2009
[6]Tong, L., Li, Z., Zhu, T., Xu, H., & Liu, Z. (2008), JPC C, 112(18), 7119-7123.
[7]Chuntonov, L. & Haran, G., Effect of Symmetry Breaking on the Mode Structure of Trimeric Plasmonic Molecules, JPC C 115(40):19488-19495, (2011)

Aluminum is the most abundant metal on the earth and recently has attracted much interest in nanophotonics because of its optical properties in the UV and visible regions. Single nanoparticles of aluminum, however, have broad, highly-damped plasmonic resonances at wavelengths longer than ~500 nm because of high optical losses. Here we show that the resonant lineshape narrows by a factor of three throughout the entire visible region by placing the nanocrystals on a thin film of aluminum. The nanocrystals and the film are separated by a self-terminating oxide, which is only a few nanometers thick. This results in a strong interaction between the two systems, counteracting the intrinsic optical losses of aluminum and increasing the radiative and non-radiative lifetimes of the nanocrystal plasmon. This capability expands the practicality of aluminum for nanophotonics in the visible range, resulting in vividly colored samples that enable applications ranging from full-color printing to sensing and surface enhanced microscopies.

We present the correlation between structural and optical properties of truly three-dimensionally gold/air percolated nanoparticles, nanosponges. The nanosponges provide a variation of the local dielectric function on the nanoscale, due to the size of the interior filaments, which is well below 20 nm. The inner morphology, i.e. the three-dimensionally gold/air percolation, can be adjusted changing the fabrication parameters.
Here, we report that the scattering spectra of single nanosponges are mainly determined by the three-dimensional percolation of each individual nanosponge. In addition, our experiments, in agreement with numerical calculations, indicate that the nanosponges are less lossy than solid gold nanoparticles, supporting our original aim to find a novel low loss plasmonic material.
Consequently, this, together with their large surface-to-volume ratio and the very small size of the interior filaments, renders single nanosponges as promising candidates for metamaterials in the visible range, for sensing applications and for photo-catalysis.
Financial support was provided by the ERC grant 257158 “ActiveNP” and Deutsche Forschungsgemeinschaft (DFG, grant SCHA 632/20-1).

In the present investigation SERS sensitivity and plasmonic-photonic interference coupling (P-PIC) in amorphous TiO₂ nanotube (A[TNT]) and crystalline silver (Ag) nanoparticles was studied. TNT were synthesized by two step anodization on titanium (Ti) substrate. Using thermal evaporation, 20 nm Ag film overcoating on TNT structures was synthesized, which coalescence to form Ag nanoparticles, acting as a three dimensional (3D) surface enhanced raman spectroscopy (SERS) substrate for rhodamine 6G (R6G) molecule detection. The current decay time studied under 1 sun condition in potassium hydroxide (KOH) electrolyte using two electrode system for A[TNT] samples is larger as compared to C[TNT] samples. The nanoarchitecture phase formation is confirmed by X-ray diffraction (XRD) analysis, Raman spectroscopy and Energy Dispersive X ray (EDAX) analysis. Surface morphology and the salient features are studied by scanning electron microscopy (SEM). Current decay time is also studied and compared for the samples respectively which show large current decay time for A[TNT]-Ag as compared to C[TNT-Ag]. UV- visible absorption studies shows larger red shift in the absorption band gap edge of A[TNT]-Ag samples as compared to C[TNT-Ag] samples. Moreover the TNT length variation in A[TNT]-Ag samples results into constructive or destructive interference, which in turn affect the P-PIC and R6G molecule detection as well as SERS intensity which was approximately three time higher than C[TNT-Ag].

Recent advances in plasmonic metamaterials have defied common sense in optics, where the optical properits of an artificial material can be tailored at will. Metamaterial absorbers have recently been demonstrated to exhibit a large or even perfect absorption within a certain frequency range. Since the metamaterial absorbers offer a unique surface condition with tailored absorption properties as well as strong plasmonic enhancement, a wide variety of potential applications have been proposed, such as high-efficiency thermal emitter and high-sensitive bio-chemical sensing. Here, we demonstrate a high-sensitive surface-enhanced molecular detection technique by utilizing the resonant coupling of plasmonic modes of a metamaterial absorber and infrared (IR) vibrational modes of a molecular self-assembled monolayer (SAM). IR absorption spectroscopy of molecular vibrations is of importance in material/medical science and security detection, since it provides essential information of the molecular structure, composition, and orientation. For direct (far-field) detection of extremely small amounts of molecules, surface enhanced IR absorption (SEIRA) using a tailored plasmonic nanostructures has been extensively studied to dramatically improve the sensitivity by several orders of magnitude. Our metamaterial approach offers not only significant plasmonic enhancement but also a low-background detection scheme, thus further lowering the detection limit of direct IR absorption spectroscopy. The fabricated metamaterial consisted of 1D array of Au micro-ribbons on a thick Au film separated by an MgF₂ gap layer. The surface structures were designed to exhibit an anomalous IR absorption at ~ 3000 cm^-1, which spectrally overlapped with C-H stretching vibrational modes. 16-Mercaptohexadecanoic acid (16-MHDA) was used as a test molecule, which formed a 2-nm thick SAM with their thiol head-group chemisorbed on the Au surface. In the FTIR measurements, the symmetric and asymmetric C-H stretching modes were clearly observed as reflection peaks within a broad plasmonic absorption of the metamaterial. The low-background detection scheme with tailored plasmonic enhancement by the metamaterial absorber dramatically improved the sensitivity down to ~ 1.8 attomoles within the diffraction-limited IR beam spot. Our metamaterial approach thus may open up new avenues for realizing ultrasensitive IR inspection technologies.

Over the last few decades, researches in the field of surface enhanced Raman scattering (SERS) have been dramatically developed due to its powerful analytic performance to biological and chemical analytes. Especially, the microfluidic systems coupled with SERS have been recently demonstrated for in-situ monitoring of chemical reactions and detect analytes. However, in-situ SERS measurement in microfluidic systems have limitations due to the destruction or contamination of SERS-active metallic nanostructure in the fluid channel by fluidic force.
Droplet-based open-channel microfluidic systems have several advantages compared with conventional microfluidics systems in terms of low cost, and simple manufacture. In particular, open-channel microfluidic systems on superhydrophobic surfaces with extremely low adhesion have a key advantage that the droplet can be easily roll-off without surface contamination.
Here, we demonstrate a novel droplet-based open-channel SERS measurement system on superhydrophobic guiding track. SERS-active structures were fabricated on a copper plate with a shallow groove via galvanic displacement reaction, and extreme water repellent properties were achieved through self-assembled monolayer coating. Droplet can be successfully guided along the pre-defined groove on the superhydrophobic surface, and transported to the laser spot for Raman measurement. By using this novel system, successive manipulation and SERS measurement on the same surface can be achieved using Rhodamine 6G droplet with a low concentration of 10^-7M without any contamination.

Metallic nanomaterials exhibiting distinct surface-plasmon-resonance effects have gained increasing attention over the past few years due to their broad applications in photonics, biological imaging, drug delivery, sensors and surface enhanced Raman scattering (SERS) ¹. One of the main drivers for the development of plasmonic materials is the desire to improve the sensitivity of SERS for exploring structure and reaction pathways at surfaces as well as for sensing ². The development of nanofabrication methodologies for tailoring both particle shape and size has been intensified recently, giving special attention to the preparation of noble metal nanoparticles (Cu, Ag, Pt, Pd, and Au). ³ Over a wide range of studies, the challenge is to develop metallic substrates combining high sensitivity, reproducibility, stability and easy of preparation. ⁴ The sensing feature of MNPs results from their collective charge density oscillations and is known as localized surface plasmon resonance (LSPR). ² In recent studies, we reported a new method of fabrication of MNPS based on the self assembly of metallic precursor-loaded homopolymer dispersion. Then, the deposition of this dispersion on a given substrate (glass, silicon, etc.) allows the formation of highly sensitive nano-objects particularly relevant for sensing and SERS (figure 1). Herein we report a facile way to detect few biomolecules (picomol) the LSPR and SERS features of a highly sensitive biosensor. In the present projet, we aim to investigate the physico-chemical mechanism of formation of MNPs in order tune their physical and optical properties, which is essential for applications. We highlight the possibility to measure few molecules of bacteria, which is an un-preceded result using a plasmonic sensor.
1. Akil S., Jradi S., Plain J, Adam P.-M., Bijeon, J.-L., Sanchez C., Bachelot R. and Royer P. , Chemical communications, 2011, 47, 2444.
2. Akil S., Jradi S., Plain J, Adam P.-M., Bijeon, J.-L., Bachelot R. and Royer P. (2012), RSC Advances, 2, 7837.
3. Jradi S., Balan L., Zeng X., Plain, J., Lougnot D., Royer P., Bachelot R., Akil S., Soppera O., Vidal L. (2010), Nanotechnology, Volume 21, 095605.
4. Seung Joon Lee, Brian D. Piorek, Carl D. Meinhart and Martin Moskovits. Nano Lett., 2010, 10, 1329.

Plasmonic optical biosensors have become an important area of research because they are extremely sensitive to surface changes within subwavelength dimensions and show significant potential for on-chip integration, low cost processing, and massive parallelization. Pushing this trend, the discovery of plasmon-enhanced optical transmission through an array of nano-structured holes has led to the development of an entirely new generation of optical biosensors. While nanoholes have been typically used in a liquid environment, plasmonic sensing of gas-phase analytes is also an important area of research and development. In this paper, we employ a template stripping method to produce plasmonic nanohole arrays on analyte-sensitive substrates for real-time vapor sensing. Template stripping involves cleaning a silicon master template, depositing a thin metal film, and then stripping the film from the template with an adhesive backing layer. The resultant surfaces are very smooth, and dozens of identical chips can be created by reusing the same template. While many fabrication methods are available, template stripping is ideal in our current case by offering the ability to chemically pattern the substrate before stripping from the template. Indeed, our device is designed to operate by explicitly exploiting simultaneous plasmonic resonances within the substrate as well as within the vapor being tested. Because the substrate is in contact with vapor due to the open-hole geometry, red-shifts (air-side plasmon resonances) and blue-shifts (substrate-side plasmon resonances) are seen at the same time during exposure to <10 ppm ethanol vapor in nitrogen. We also show negative control experiments with similar concentrations of m-xylene. Since we are able to chemically pattern the substrate prior to template stripping, our devices have potential for multiplex sensing. Initially, we demonstrated these sensors utilizing an inverted microscope and an imaging spectrometer system. While useful for sensor characterization, this setup requires bulky optics, microscope objectives, and large spectrometers and cannot lead to a compact, on-chip solution. To resolve this issue, in this paper we also show that by placing our nanohole chips directly onto the front window of a commercially available, low-cost CMOS imager, all of these optical components can be circumvented. By properly positioning the nanoholes, an illumination source (e.g., an LED), and a suitable spacer layer, transmitted light will diffract from the nanohole array, spread into a spectrum over the space of a few millimeters, and land on the imager as a full spectrum. This spectrum, with plasmon-enhanced transmission peaks, is monitored in real-time and used for vapor sensing as before. This on-chip solution circumvents the bulky components (e.g. microscopes, coupling optics, and spectrometers) needed for traditional plasmonic biosensing setups while maintaining high sensitivity and multiplexing capability.

Simultaneous LSPR and electrical detection using ultrathin gold films with incorporated nanoholes is presented. The sensor is electrochemically accessible and enables label-free sensing in a controlled fashion.
Films with dimensions smaller than the electron mean free path are essential to measure large resistance changes due to small alterations in thickness or close proximity of charged species [1]. Additionally, nanoholes within thin films enable optical sensing based on localized surface plasmon resonance. Our device is fabricated on a glass wafer coated with 12 nm of niobium pentoxide (Nb₂O₅). Colloidal lithography was used to generate nanoholes. The evaporated gold films are 20 nm thick, contacted by 100 nm thick gold traces, and (apart of the central sensing region of the film) covered by SU8. This chip is fully integrated into a custom-made flow cell. The design of both the flow cell and the chip allows for reproducible and accurate measurements with ideal fluid exchange behavior.
Iodide sensing is one of the possible applications for this device. Iodide is an essential element for humans and animals, but insufficient intake is still a major problem. Most current detection methods are costly and require both a sample pretreatment and a long analysis time [2,3]. However, for determining iodide concentrations of human samples in developing countries or for comprehensive and long-term studies in environmental waters, low cost and simplicity are becoming increasingly important.
Our device takes up on these issues with sensing based on iodide induced electrochemical etching of ultrathin gold films. For example potassium iodide (KI) dissociates in aqueous buffer and the iodide anions can be attracted using voltage. The resulting etching can be measured by a change in the impedance of the thin film. The underlying mechanism is demonstrated by simultaneous cyclic voltammetry experiments and by measuring resistance change in buffer solution. As sensing methodology, an amperometric multistep method is presented in buffer as well as in an environmentally relevant fluid (lake water) with limits of detection in the range of 1 µM (127 µg L^-1) and 2 µM (254 µg L^-1), respectively.
The versatility of this sensing platform is also shown with binding studies. Attachment of thiolated single-stranded DNA demonstrates this concept. Iodide etching can thereby be used as a controlled cleaning step, enabling the reuse of the device.
We believe this sensor not only enables low cost measurements of iodide concentrations and binding events, but also opens up opportunities for a variety of biosensing applications.
References
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2. Shelor CP, Dasgupta PK. Anal Chim Acta2011, 702, 16-36.
3. Khazan M, Azizi F, Hedayati M. Scimetr2013, 1, 1-9.

Plasmonic materials and devices aim to exploit the unique optical properties of metallic nanostructures to enable routing and manipulation of light at the nanoscale. A critical parameter in delivering the plasmonic devices is the materials&’ preparation methods, which should allow for the production of nanostructures with tunable plasmonic properties. Two issues, however, emerge: Firstly, as far as specific applications are concerned, such as plasmonic writing, the protection of these structures from environmental poisoning is of paramount importance; any production process should be able to form plasmonic nanoparticles (PNPs) below the dielectric surface. In that context, laser annealing (LA) of Ceramic:Ag nanocomposites is proposed as a promising route for the production of buried PNPs for optical encoding, lens coloration and decorative purposes. LA is a simple patterning tool providing freedom of design, fast processing, compatibility with large-scale manufacturing and allows for the use of inexpensive flexible and organic substrates such PET and polycarbonate. Secondly, the scale of the production process would dictate the maximum size of the envisaged devices and their application range in everyday life. Large-scale and simultaneously cold processes are still required for the effective production of buried PNPs. The sputter deposition of ceramic/metal nanocomposites and multilayers would address both the aforementioned limitations, as they are capable of producing metals buried into dielectric ceramics with fascinating optical response, while they are compatible with a variety of large-scale deposition configurations such as in-line, roll-to-roll, or close-field sputtering, which are becoming nowadays the manufacturing routes of choice. In the present work, we present a new entirely-cold route by combining the deposition of ceramic/metal nanocomposites and multilayers (in particular, AlN:Ag, AlN/Ag, Y2O3/Ag and CeO2/Ag) multilayers with one ultra-short UV LA step. We demonstrate that this LA step is capable of driving the subsurface modification of plasmonic metal/dielectric films and multilayers, and delivers tunable LSPR behavior from Ag nanoparticles that are formed and dispersed in a depth of several nm away from the free surface. This large-scale entirely-cold process is very unlike previous attempts dealing with the treatment of thin monolayered films on top of a rigid substrate. We perform an extensive, thorough and in depth investigation of the laser-matter interactions considering the morphological and microstructural features of the films. The experimental results are complemented by detailed photo-thermal calculations, which are used to identify the fundamental light-matter interactions and heat diffusion mechanisms in the films and multilayers, and obtain insights on the basic mechanisms of morphology changes upon LA.

Colorimetric sensor provides a way to sense and analyze various chemicals and biomaterial targets based on local refractive index changes. However, pre-existing colorimetric sensors, which incorporates one of the optical phenomena such as photonic crystal, whispering gallery mode and localized surface plasmon, shows limited resonance peak shifts which makes it hard to analyze and thus requires extra instruments. Furthermore often the structural color comes from superposition of several different colors rather than a single color, which makes it harder to talk about the sensitivity. Many approaches to increase the sensitivity of colorimetric sensors are usually focused on the structure that interacts with the light and produces plasmonic colors such as extra ordinary transmission from nano holes. However, another important aspect of colorimetric sensor is signal amplification since the density of target molecule in the environment is often far below the concentration that can induce the detectable color shift.
Here we demonstrate sandwich type plasmonic ELISA which incorporates glucose-glucose oxidase reaction for the signal amplification based on the aluminum anodized oxide structure and provide computational analysis of effective 3D colorimetric plasmon sensor structure on a novel aluminum anodized oxide (AAO) by FEM optical simulation. As the target molecules are anchored to capture antibody on substrate, the detection antibody with glucose oxidase attaches to target molecule thus inducing reduction of Au ions in solutions of ELISA. The reduced Au is deposited on the thin Au deposited AAO nanostructure resulting shift of plasmonic color. Furthermore color shift is calculated through FEM method and the nanostructure is optimized in terms of pore depth, pore size, etc. When the incident white beam is reflected from the Al mirror at the bottom of AAO structure, the interference between incoming wave and reflected wave forms and the wave is absorbed on the top Au layer due to the localized surface plasmon effect. As more Au is deposited on the nanostructure stronger color change occurs.

Plasmon excitation in metal nanostructures decays into short-lived hot-electrons and hot-holes. It is possible to harness the energy of these hot-carriers before they thermalize and are dissipated as heat. Here, we describe a scheme to extract the energy of hot-carriers into an optical form. Our novel scheme allows photon upconversion, i.e. emission of higher energy photons by absorbing low energy photons. While current state-of-the-art solid-state upconverters suffer from low efficiency, narrow-band operation, and lack of tunability, our hot-carrier upconversion overcomes these limitations. Specifically, we consider a metal/semiconductor quantum well heterostructure where the electrical current generated by hot-carriers in the metal nanostructure drives the adjacent quantum well emitter. When metal injects both hot-electrons and hot-holes into the quantum well, charge neutrality is maintained and a current loop is established to continuously drive the quantum well. This balanced injection allows the semiconductor quantum well to emit photons corresponding to its energy bandgap, which, importantly, can be higher than the energy of the photons exciting plasmons in the metal. First, we develop a theoretical model to determine the upconversion efficiency. We consider a small metallic cube placed adjacent to an ideal quantum well emitter. Upon plasmon excitation, the hot-carrier distribution in the metal cube is computed using Fermi&’s golden rule. Small metal cubes (less than 10 nm on a side) generate hot-carriers with efficiency greater than 80%. Injection of these carriers into the quantum well limits total upconversion quantum efficiency, but 5 nm silver cubes can still exhibit upconversion efficiencies exceeding 20%. Gold nanoparticles are less efficient, but can still generate upconverted photons with an efficiency of 10%. We then verify this scheme experimentally using blue emitting InGaN/GaN multiquantum wells adjacent to gold nanodisks. Electron beam lithography is used to fabricate 10 thick gold nanodisks of various diameters, ranging from 10 to 50 nm, on the InGaN/GaN quantum wells. These disks absorb at a wavelength of 530 nm, and following hot-carrier injection, enable emission from a three stack multi-quantum well (5 nm GaN and 3 nm In_0.13Ga_0.87N) at 423 nm. Our presentation will describe the efficiency of upconversion, its dependence on illumination intensity and its dependence on shape and size of gold nanostructures. Interestingly, the proposed hot-electron upconversion scheme does not require coherent illumination, can be quite broadband, is tunable-by-design, and more efficient than the existing lanthanide and molecular upconversion schemes.

The decay of surface plasmon resonances is usually a detriment in the field of plasmonics, but the possibility to capture the energy normally lost to heat would open new opportunities in photon sensors and energy conversion devices. In the context of hot-electron devices, the large extinction cross-section at a surface plasmon resonance enables nanostructures to absorb a significant fraction of the solar spectrum in very thin films. Despite the significant experimental work in this direction, a complete theoretical understanding of plasmon-driven hot carrier generation with electronic structure details has been evasive. Theoretical studies of plasmonic systems have traditionally focused on their optical response, including quantum jellium models of nanostructured systems. While extremely valuable, these models do not capture the material dependence of this process and miss interband transitions in noble metals.
Recently we analyzed the quantum decay of surface plasmon polaritons and found that the prompt distribution of generated carriers is extremely sensitive to the energy band structure of the plasmonic material. In this context, we have developed a general theoretical and computational framework using a multi-scale model that combines long-range electromagentic solvers for the plasmons with density functional theory in a maximally-localized Wannier basis for the electrons. With a Feynman diagram approach to processes involving plasmons, electrons and phonons built upon this model, we present realistic first principles calculations for nanostructured plasmonic systems including transport of plasmonic hot carriers to the surface and injection over a barrier. Additionally, using this diagrammatic approach we present results on higher order processes such as multi-plasmon decays in metals which are critical for plasmon-driven upconversion.

Cooling is a significant end-use of energy globally and a major driver of peak electricity demand. Air conditioning of buildings, for example, accounts for 15% of the primary energy used to generate electricity in the United States. Moreover, global energy use for cooling buildings is predicted to grow to be ten times what it is today by 2050, with most of the growth coming from the developing world. A passive cooling strategy that cools without any electricity input could therefore have a significant impact on global energy consumption. To achieve cooling one needs to be able to reach and maintain a temperature below the ambient air. At night, passive cooling below ambient air temperature has been demonstrated using a technique known as radiative cooling or night-sky cooling, where one uses a device exposed to the sky to radiatively emit heat to outer space through a transparency window in the atmosphere between 8-13 µm. Peak cooling demand however occurs during the daytime. Daytime radiative cooling below ambient under direct sunlight has never before been achieved because sky access during the day results in heating of the radiative cooler by the sun.
We show how thermal nanophotonic approaches and designs enable one, for the first time, to achieve passive radiative cooling below ambient air temperature during peak daylight hours. We first highlight the theoretical requirements necessary for daytime radiative cooling and discuss the need for a photonic approach. We then present a nanophotonic design that has the required spectral characteristics to achieve daytime radiative cooling: it is strongly reflective over visible and near-IR wavelengths but strongly emissive between 8 and 13 µm. We then present results of the first experimental demonstration of daytime radiative cooling, where we achieve a temperature of nearly 5°C below the ambient air temperature under direct sunlight. Using a thermal nanophotonic approach, we design and fabricate an integrated photonic solar reflector and thermal emitter consisting of 7 layers of HfO₂ and SiO₂ that reflects 97% of incident sunlight while emitting strongly and selectively in the atmospheric transparency window. Even when exposed to direct solar irradiance of greater than 850 W/m² on a rooftop, the photonic radiative cooler achieves an average of 4.9°C below ambient air temperature over one hour, and has a cooling power of 40.1 W/m² at ambient. Furthermore, we develop a theoretical model capable of accurately predicting the photonic radiative cooler's performance as a function of time of day, based on ambient conditions and the spectral absorption/emission characteristics of the radiative cooler.
These results demonstrate that a tailored, nanophotonic approach can fundamentally enable new technological possibilities for energy efficiency, and further indicate that the cold darkness of the universe can be used as a renewable thermodynamic resource, even during the hottest hours of the day.

Thermophotovoltaic (TPV) devices are highly attractive in harvesting and converting thermal energies, including solar energy and wasted energies from internal combustion engines, fuel sources, etc, into electricity at a very high efficiency. Solar thermophotovoltaics (sTPV) seek to overperform the Shockley-Quiesser limit for single junction solar cells by converting the broadband solar spectrum of sun light into much narrower emission wavelengths so that the photon energies can be more efficiently absorbed by the photovoltaic cells. 3D metallic photonic crystals (MPhCs) are promising candidates for the choice of sTPV emitters as they exhibit strong selectivity in absorption due to the tailoring of the photonic density of states by the periodic structures. However, reasons preventing the 3D MPhCs emitters being widely used in the sTPV devices are that the thermal stability of the materials being currently studied (i.e. W and Ta) and their fabrication process are still far from satisfactory. Therefore, it is necessary to find better material systems that can both potentially meet the requirements for having superior thermal stability and simultaneously being easily processed. Rhenium (Re) and its alloys, as another well-known refractory metal system, are highly reputed for the outstanding thermal and other physical properties in terms of non-structured architectures and have been broadly used in extreme conditions as bulk materials. However, the reported work in studying the engineered microstructures of Re and their optical responses are rare. In this work, we have been pursuing the development of the first rhenium nickel alloy based MPhC via electrodeposition from low temperature nontoxic aqueous electrolyte. The resulting 3D mesostructures are showing outstanding thermal stabilities for at least 1000 C annealing for extended hours, much better compared to the tungsten MPhCs fabricated via similar electrochemical approaches. The flexibility in adjusting the Re and Ni composition ratio also allows comprehensive studies of the metallurgy aspects of the heavily structured metallic microstructures, which could bring significant insights on the optimization of the 3D architectures under high temperature applications. Analysis on the selection of surface protective coatings from transparent dielectrics and the optical response of the MPhCs are also performed.

We will show that composite photo-catalysts combing plasmonic metallic nanoparticles of noble metals and semiconductor nanostructures exhibit improved photo-chemical activity compared to conventional photo-catalytic materials.^1,2 We will also show that plasmonic silver nanoparticles, optically excited with low intensity visible light, exhibit direct photo-catalytic activity. We will discuss underlying mechanisms associated with these phenomena.^2,3,4 We propose that this new family of photo-catalysts could prove useful for many heterogeneous catalytic processes that cannot be activated using conventional thermal processes on metals or photo-catalytic processes on semiconductors. I will show an example of such a process.⁵
D. B. Ingram, S. Linic, JACS, 133, 5202, 2011
Suljo Linic, Phillip Christopher and David B., Nature Materials,10, 911, 2011.
Ingram P. Christopher, H. Xin, S. Linic, Nature Chemistry, 3, 467, 2011.
P. Christopher, H. Xin, M. Andiappan, S. Linic, Nature Materials, 11, 1044, 2012.

We present new spectroscopic techniques that enable visualization of nanoparticle phase transitions in reactive environments and light-matter interactions with nanometer-scale resolution. First, we directly monitor hydrogen absorption and desorption in individual palladium nanocrystals. Our approach is based on in-situ electron energy-loss spectroscopy (EELS) in an environmental transmission electron microscope. By probing hydrogen-induced shifts of the palladium plasmon resonance, we find that hydrogen loading and unloading isotherms are characterized by abrupt phase transitions and macroscopic hysteresis gaps. These results suggest that alpha and beta phases do not coexist in single-crystalline nanoparticles, in striking contrast with conventional phase transitions and ensemble measurements of Pd nanoparticles. Then, we then extend these techniques to monitor nanoparticle reactions in a liquid environment. By constructing a flow chamber, we directly monitor growth and assembly of colloidal plasmonic metamaterial constituents induced by chemical catalysts. Lastly, we introduce a novel tomographic technique, cathodoluminescence spectroscopic tomography, to probe optical properties in three dimensions with nanometer-scale spatial and spectral resolution. Particular attention is given to reconstructing a 3D metamaterial resonator supporting broadband electric and magnetic resonances at optical frequencies. Our tomograms allow us to locate regions of efficient cathodoluminescence across visible and near-infrared wavelengths, with contributions from material luminescence and radiative decay of electromagnetic eigenmodes. The experimental signal can further be correlated with the radiative local density of optical states in particular regions of the reconstruction. Our results provide a general framework for visualizing chemical reactions and light-matter interactions in plasmonic materials and metamaterials, with sub-nanometer-scale resolution, and in three-dimensions.

Due to their unique optical properties, plasmonic nanostructures find a broad range of applications including sensing, subwavelength optical components and light management structures in photovoltaics. For such applications, structures with well-defined plasmon resonances are required, i.e. the plasmon resonance needs to occur in a certain energy range. At the same time substrate-supported systems are typically needed, which is a particularly important challenge with respect to tailoring optical properties since plasmon resonances are strongly sensitive to the refractive index environment. Consequently the introduction of an interface will alter the optical properties of the plasmonic nanostructures. In addition structural control such as adjustable inter-particle distances and surface coverage are of utmost importance for the preparation of optically functional superstructures since these can strongly affect the optical performance. The steady developments in wet-chemical synthesis of plasmonic nanoparticles with control over particle size, shape and their distribution as well as the particle functionalization provide a nearly infinite toolbox of optical building blocks. However, typically a single distribution of particles sizes is realized which omits the effective screening of a range of plasmon resonances.
In this presentation we demonstrate a versatile approach to prepare substrate-supported, macroscopic arrays of plasmonic gold nanoparticles with locally varying particle size and hence plasmonic properties[1]. The arrays are based on polymer-encapsulated gold nanoparticles[2], which were deposited on glass substrates by simple spin-coating. A controlled growing protocol was used to overgrow the gold cores in-situ, i.e. directly using the substrate-supported particle array. Analysis of the kinetics of overgrowth revealed diffusion-limited growth. This allowed us to control the size of the gold cores by adjusting the duration of growth, yielding a continuous gradient in particle size. The size of the particles was investigated by electron microscopy and atomic force microscopy, while absorbance spectroscopy was used to analyze the plasmonic properties of the array at different positions. Simulations based on Mie theory were used to support the experimental findings and to investigate the size and refractive index dependent plasmonic features of our particle superstructure.
[1] M.B. Müller, C. Kuttner, T.A.F. König, V.V. Tsukruk, S. Förster, M. Karg, A. Fery, ACS Nano2014, 8 (9), 9410-9421.
[2] M. Karg, S. Jaber, T. Hellweg, P. Mulvaney, Langmuir2011, 27, 820-827

It is well known that the plasmon resonance frequency of metal nanostructures depends on the free carrier density in the metal. Earlier work has shown that the plasmon resonance can be tuned by electrostatically controlling the carrier density: increasing the carrier density leads to a blueshift of the resonance, while decreasing it leads to a redshift. Interestingly, the reverse effect, the optical generation of an electrostatic potential, has so far not been observed. Thermodynamically, however, such a plasmoelectric effect is expected to occur. Here, we demonstrate direct experimental evidence of plasmoelectric potentials in the range 10-100 mV on colloidal assemblies and plasmonic hole-array device geometries.
When positioned on a grounded conductive substrate, metal nanoparticles can exchange electrons with the substrate, causing small shifts in the plasmon resonance absorption spectrum. Under monochromatic illumination detuned from the resonance peak wavelength, such electron transfer is thermodynamically favorable when it increases the particle absorption as that leads to a minute temperature increase corresponding to an increase in entropy. As a result, in steady state, an electrochemical potential builds up that is negative when the particle illuminated on the blue side of the plasmon resonance, and positive when it is illuminated on the red side.
To test this experimentally, 60 nm Au colloids were dropcasted on an ITO/glass substrate. Next, a dark-field scattering spectrum was measured, showing a clear plasmon resonance peak around lambda; = 550 nm. Kelvin probe force microscopy (KPFM) was used in non-contact mode to measure the potential difference between tip and substrate. The tip is positioned close to the colloids, and the sample is illuminated from the bottom with monochromatic radiation while the wavelength is scanned from 480 - 640 nm (1 W cm^-2). We observe a clear negative light-induced surface potential up to -12 mV for illumination below the resonance wavelength; a positive potential up to 14 mV is observed above the resonance, in agreement with the thermodynamic model.
Next, we studied optically-induced plasmoelectric potentials on sub-wavelength hole arrays in a 20 nm thin Au film that were fabricated on a glass substrate using e-beam lithography. The hole arrays with different collective absorption resonances are made by varying the array pitch from 175 - 300 nm, resulting into spectrally controlled absorption resonances between 580 - 710 nm. Surface potentials as high as 100 mV are observed (100 mW cm^-2 illumination intensity), changing from negative to positive at the plasmon resonance. By varying the array geometry the plasmo-electric potential spectrum is tuned over a broad spectral range. The hole arrays are a first step towards plasmo-electric circuitry in which power can be harvested.
M.T. Sheldon, J. van de Groep, A.M. Brown, A. Polman, H.A. Atwater, Science 346, in press (2014), published October 30, 2014

Nanomaterials exhibiting plasmonic resonances have been attracting intense attention for their tunable optical properties. Via control of the interaction of the nanoparticles (and surrounding media) with designed shapes such as nanospheres and nanorods, plasmonic resonances can be tuned to achieve unique optical properties such as Fano resonances and transparency windows. Such complex nanostructures have been traditionally fabricated using the electron-beam lithographic methods. In this work, we demonstrate the self-assembly of plasmonic nanoparticles via simple aerosol processing. Two kinds of typical plasmonic nanoparticles are used as model materials. The first type of nanoparticles is boron-doped silicon (Si) nanocrystals (NC), which are synthesized using a nonthermal plasma technique and show B-doping-induced plasmonic absorption in the infrared (IR) region. By aerosolizing and drying droplets of a mixture of small B-doped Si NCs and larger polystyrene latex (PSL) spheres, assembly of mesoscopic particles consisting of a hexagonally stacked PSL sphere scaffold with B-doped Si NCs infilling the voids in between is achieved.