Transformation-optics description of nonlocal effects in plasmonic nanostructures

We develop an insightful transformation-optics approach to investigate the impact that nonlocality has on the optical properties of plasmonic nanostructures. The light-harvesting performance of a dimer of touching nanowires is studied by using the hydrodynamical Drude model, which reveals nonlocal resonances not predicted by previous local calculations. Our method clarifies the interplay between radiative and nonlocal effects in this nanoparticle configuration, which enables us to elucidate the optimum size that maximizes its absorption and field enhancement capabilities.     

Broadband light harvesting nanostructures robust to edge bluntness

Metallic structures with sharp corners harvest the energy of incident light through plasmonic resonances, concentrating it in the corners and greatly increasing the local energy density. Despite its wide array of applications, this effect is normally strongly dependent on how sharp the corners are, presenting problems for fabrication. In this Letter, an analytical approach is proposed, based on transformation optics, to investigate a general class of plasmonic nanostructures with blunt edges or corners. Comprehensive discussions are provided on how the geometry affects the local field enhancement as well as the frequency and energy of each plasmonic resonance. Remarkably, our results evidence the possibility of designing broadband light harvesting devices with an absorption property insensitive to the geometry bluntness.     

Theory of secondary electron emission

The fine structure in angle-resolved secondary electron spectra is shown to be related to the total reflectivity in low-energy electron diffraction (LEED). Theoretical results for tungsten are compared with experimental data. For non-normal emission, spin-orbit coupling is predicted to produce spin polarization of the emitted electrons.     

Multiple coincidences in surface structure determinations

We show that when the adsorbate is a weak scatterer of electrons, agreement of calculated LEED spectra with experiment is subject to approximate multiple coincidences in the vertical adsorbate-substrate spacing, with a periodicity of about 0.7 Å. Scrutiny of low energy spectra and the appearance of a compression or expansion of the theoretical energy scale with respect to experiment provide means to distinguish between the coincidences.     

SEXAFS without X-rays

Surface extended X-ray absorption fine structure provides a means of finding the structure of disordered adsorbate layers on a clean substrate, low energy electron diffraction techniques having been confined to well-ordered systems. Here we show how the diffuse patterns characteristic of disordered adsorbates can be analysed to yield structural information. The theory contains terms which are entirely analogous to SEXAFS theory, showing that all the information contained in a SEXAFS experiment is present in a diffuse scattering measurement. Not only that, but the amount and detail of information available for diffuse scattering is much greater than for SEXAFS. The interpretation of diffuse scattering is no more complex than for LEED from the clean well-ordered substrate.     

Hydrodynamic Model for Plasmonics: A Macroscopic Approach to a Microscopic Problem

In this concept, we present the basic assumptions and techniques underlying the hydrodynamic model of electron response in metals and demonstrate that the model can be easily incorporated into computational models. We discuss the role of the additional boundary conditions that arise due to nonlocal terms in the modified equation of motion and the ultimate impact on nanoplasmonic systems. The hydrodynamic model captures much of the microscopic dynamics relating to the fundamental quantum mechanical nature of the electrons and reveals intrinsic limitations to the confinement and enhancement of light around nanoscale features. The presence of such limits is investigated numerically for different configurations of plasmonic nanostructures.     

Symmetry and transport of waves in one-dimensional disordered systems

The transfer matrix approach to transport in one-dimensional systems is reviewed in detail with emphasis on the role of symmetrized products. First, the concept of a transfer matrix is introduced, and then generalized through the introduction of symmetrized products. The resulting formalism is successively applied to the problem of averaging: resistance, density of states, conductance (i.e. transmission coefficient), phases of transmission and reflection, and frequency response. Finally the problem of 1/f noise in disordered systems is addressed in the language of symmetrized transfer matrices.