A fully quantum mechanical investigation using time-dependent density functional theory reveals that the field enhancement in a coupled nanoparticle dimer can be strongly affected by nonlinear effects. We show that both classical as well as linear quantum mechanical descriptions of the system fail even for moderate incident light intensities. We present a novel approach, the quantum-corrected model (QCM), that incorporates quantum-mechanical effects within a classical electrodynamic framework. The QCM predicts optical properties in excellent agreement with fully quantum mechanical calculations for small interacting systems.
Nature Comm. 3, 825 (2012) / Nano Lett. 13, 5873 (2013)
Nanoantennas are key optical components for light harvesting; photodiodes convert light into a current of electrons for photodetection. We show that these two distinct, independent functions can be combined into the same structure. Photons coupled into a metallic nanoantenna excite resonant plasmons, which decay into energetic, “hot” electrons injected over a potential barrier at the nanoantenna-semiconductor interface, resulting in a photocurrent. This dual-function structure is a highly compact, wavelength-resonant, and polarization-specific light detector, with a spectral response extending to energies well below the semiconductor band edge.
Science 332, 702 (2011) / ACS Nano 7, 2388 (2013)
Surface Enhanced Spectroscopies
Here we design novel nanostructures for surface enhanced spectroscopies: SERS and SEIRA. For instance, we examine the near-field properties of individual Fano resonant plasmonic clusters using surface-enhanced Raman scattering (SERS) both from molecules distributed randomly on the structure and from dielectric nanoparticles deposited at specific locations within the cluster. We also design and optimize micrometer scale nanoantenna for SEIRA applications.
Nano Lett. 12, 1660 (2012) / J. Am. Chem. Soc. 135, 3688 (2013)
Neighboring fused heptamers can support magnetic plasmons due to the generation of antiphase ring currents in the metallic nanoclusters. We use such artificial plasmonic molecules as basic elements to construct low-loss plasmonic waveguides and devices. We also focus on rectangular and cylindrical nanowires as well as on nanowire with more complex cross-section shapes (stars,...).
ACS Nano 6, 5482 (2012) / Nano Lett. 13, 6256 (2013)
Plasmonic Fano Resonances
While the far-field properties of Fano resonances are well-known, clusters of plasmonic nanoparticles also possess Fano resonances with unique and spatially complex near-field properties. This interference effect is of high interest for sensing application due the extremely narrow Fano resonances. We design novel structures where dark and bright modes interact leading to the formation of a Fano resonance.
Science 328, 1135 (2010) / Nano Lett. 12, 4977 (2012) [highlight in Nature Photonics 6, 716 (2012)]