Kristy C. Vernon

Two-dimensionally localized modes of a nanoscale gap plasmon waveguide

We report numerical analysis and experimental observation of two dimensionally localized plasmonic modes guided by a nanogap in a thin metal film. Dispersion, dissipation, and field structure of these modes are analyzed using the finite-difference time-domain algorithm. The experimental observation is conducted by the end-fire excitation of the proposed gap plasmon waveguides and detection of the generated modes using their edge scattering and charge coupled device camera imaging. Physical interpretation of the obtained results is presented and origins of the described modes are discussed.

Surface Plasmon Mediated Strong Exciton−Photon Coupling in Semiconductor Nanocrystals

We present an experimental demonstration of strong coupling between a surface plasmon propagating on a planar silver thin film and the lowest excited state of CdSe nanocrystals. Attenuated total reflection measurements demonstrate the formation of plasmon-exciton mixed states, characterized by a Rabi splitting of approximately 112 meV at room temperature. Such a coherent interaction has the potential for the development of nonlinear plasmonic devices, and furthermore, this system is akin to those studied in cavity quantum electrodynamics, thus offering the possibility to study the regime of strong light-matter coupling in semiconductor nanocrystals under easily accessible experimental conditions.We present an experimental demonstration of strong coupling between a surface plasmon propagating on a planar silver substrate, and the lowest excited state of CdSe nanocrystals. Variable-angle spectroscopic ellipsometry measurements demonstrated the formation of plasmon-exciton mixed states, characterized by a Rabi splitting of ∼ 82 meV at room temperature. Such a coherent interaction has the potential for the development of plasmonic non-linear devices, and furthermore, this system is akin to those studied in cavity quantum electrodynamics, thus offering the possibility to study the regime of strong light-matter coupling in semiconductor nanocrystals at easily accessible experimental conditions.

Influence of Particle-Substrate Interaction on Localized Plasmon Resonances

We present a theory for determining the localized surface plasmon resonance shifts of arbitrarily shaped metal nanoparticles on a substrate. Using a pseudoparticle concept, an expression for the particle-substrate interaction is derived, providing both physical insight and formulas to estimate the shifted plasmon resonance. The theory is verified against measured scattering spectra of nanorods on substrates. Simple formulas are provided to calculate the resonance of nanorods, spheres, and ellipsoids on dielectric substrate.

Adiabatic nanofocusing of plasmons by a sharp metal wedge on a dielectric substrate

We demonstrate that efficient adiabatic nanofocusing of plasmons can be achieved using a sharp metal wedge (thin tapered film) on a dielectric substrate. It is shown that the quasisymmetric (with respect to the charge distribution across the wedge) plasmon mode can experience infinite adiabatic slowing down with both its phase and group velocities reducing to zero as the plasmon propagates towards the tip of the wedge. Conditions for strong local field enhancement near the tip are determined and analyzed. In particular, it is demonstrated that the electric field in the plasmon experiences much stronger local enhancement than the magnetic field. Two distinct asymptotic regimes with the electric field amplitude approaching either zero or infinity at the tip of the wedge (tapered film) are described. The results are compared to adiabatic nanofocusing of plasmons by metallic V grooves and sharp metal wedges in a uniform dielectric.

Channel plasmon-polariton modes in V grooves filled with dielectric

We investigated the effect of dielectric filling in a V groove on the propagation parameters of channel plasmon-polariton (CPP) modes. In particular, existence conditions and critical groove angles, mode localization, field structure, dispersion, and propagation distances of CPP modes are analyzed as functions of dielectric permittivity inside the groove. It is demonstrated that increasing dielectric permittivity in the groove results in a rapid increase of mode localization near the tip of the groove and increase of both the critical angles that determine a range of groove angles for which CPP modes can exist. Detailed analysis of the field structure has demonstrated that the maximum of the field in a CPP mode is typically reached at a small distance from the tip of the groove. The effect of rounded tip is also investigated.

Coherent superposition of exciton states in quantum dots induced by surface plasmons

We present an experimental demonstration of strong optical coupling between CdSequantum dots of different sizes which is induced by a surface plasmon propagating on a planar silver thin film. Attenuated total reflection measurements demonstrate the hybridization of exciton states, characterized by the observation of two avoided crossings in the energy dispersion measured for the interacting system.

A plasmonic “ac Wheatstone bridge” circuit for high-sensitivity phase measurement and single-molecule detection

In this paper, a plasmonic “ac Wheatstone bridge” circuit is proposed and theoretically modeled for the first time. The bridge circuit consists of three metallic nanoparticles, shaped as rectangular prisms, with two nanoparticles acting as parallel arms of a resonant circuit and the third bridging nanoparticle acting as an optical antenna providing an output signal. Polarized light excites localized surface plasmon resonances in the two arms of the circuit, which generate an optical signal dependent on the phase-sensitive excitations of surface plasmons in the antenna. The circuit is analyzed using a plasmonic coupling theory and numerical simulations. The analyses show that the plasmonic circuit is sensitive to phase shifts between the arms of the bridge and has the potential to detect the presence of single molecules.

Aligned linear arrays of crystalline nanoparticles

Fabrication of one-dimensional arrays of crystalline nanoparticles with tunable particle size and spacing (down to 20 nm) is demonstrated. The individual nanocrystals are pentagonal prisms, and the arrays are up to 11 μm in length, with some arrays containing >50 nanocrystals. Precise particle morphology and interparticle spacing can be maintained down the array. The far-field scattering spectra of the arrays show the near-fields of the nanocrystals are coupled. The method is fast and produces precise, well-defined, coupled plasmonic arrays with optical properties that match well to theory.

A RESONANCE TUNABLE AND DURABLE LSPR NANO-PARTICLE SENSOR: AL 2 O 3 CAPPED SILVER NANO-DISKS

Localized surface plasmon resonance (LSPR) biosensors are employed to detect target biomolecules which have particular resonance wavelengths. Accordingly, tunability of the LSPR wavelength is essential in designing LSPR devices. LSPR devices employing silver nano-particles present better efficiencies than those using other noble metals such as gold; however, silver nano-particles are easily oxidized when they come in contact with liquids, which is inevitable in biosensing applications. To attain both durability and tunabilty in a LSPR biosensor, this paper proposes alumina (AL2O3) capped silver nano-disks. It is shown that through controlling the thickness of the cap, the LSPR resonance frequency can be finely tuned over a wide range; and moreover, the cap protects silver nano-particles from oxidation and high temperature.

Synthesis and applications of carbon nanomaterials for energy generation and storage

Summary The world is facing an energy crisis due to exponential population growth and limited availability of fossil fuels. Over the last 20 years, carbon, one of the most abundant materials found on earth, and its allotrope forms such as fullerenes, carbon nanotubes and graphene have been proposed as sources of energy generation and storage because of their extraordinary properties and ease of production. Various approaches for the synthesis and incorporation of carbon nanomaterials in organic photovoltaics and supercapacitors have been reviewed and discussed in this work, highlighting their benefits as compared to other materials commonly used in these devices. The use of fullerenes, carbon nanotubes and graphene in organic photovoltaics and supercapacitors is described in detail, explaining how their remarkable properties can enhance the efficiency of solar cells and energy storage in supercapacitors. Fullerenes, carbon nanotubes and graphene have all been included in solar cells with interesting results, although a number of problems are still to be overcome in order to achieve high efficiency and stability. However, the flexibility and the low cost of these materials provide the opportunity for many applications such as wearable and disposable electronics or mobile charging. The application of carbon nanotubes and graphene to supercapacitors is also discussed and reviewed in this work. Carbon nanotubes, in combination with graphene, can create a more porous film with extraordinary capacitive performance, paving the way to many practical applications from mobile phones to electric cars. In conclusion, we show that carbon nanomaterials, developed by inexpensive synthesis and process methods such as printing and roll-to-roll techniques, are ideal for the development of flexible devices for energy generation and storage – the key to the portable electronics of the future.