Tamm plasmon modes on semi-infinite metallodielectric superlattices

We analyze the fundamental properties of optical waves referred to as Tamm plasmon modes (TPMs) which are tied to the interface of a semi-infinite two-phase metallodielectric superlattice with an arbitrary homogeneous capping medium. Such modes offer new ways of achieving high electromagnetic field localization and spontaneous emission enhancement in the vicinity of the interface in conjunction with absorption loss management, which is crucial for future applications. The homointerface, formed when the capping medium has the same permittivity as one of the superlattice constituents, is found to support a TPM whose dispersion overlaps the single-interface surface plasmon polariton (SPP) dispersion but which has a cut off at the topological transition point. In contrast, a heterointerface formed for an arbitrary capping medium, is found to support multiple TPMs whose origin can be traced by considering the interaction between a single-interface SPP and the homointerface TPM burried under the top layer of the superlattice. By carrying out a systematic comparison between TPMs and single-interface SPPs, we find that the deviations are most pronounced in the vicinity of the transition frequency for superlattices in which dielectric layers are thicker than metallic ones.Publisher correction: A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has been fixed in the paper

Coordinate transformation based design of confined metamaterial structures

The coordinate transformation method is applied to bounded domains to design metamaterial devices for steering spatially confined electromagnetic fields. Both waveguide and free-space beam applications are considered as these are analogous within the present approach. In particular, we describe devices that bend the propagation direction and squeeze confined electromagnetic fields. Two approaches in non-magnetic realization of these structures are examined. The first is based on using a reduced set of material parameters, and the second on finding non-magnetic transformation media. It is shown that transverse-magnetic fields can be bent or squeezed to an arbitrary extent and without reflection using only dielectric structures.Comment: The previous version has been revised and considerably expande

Magnetotunnelling in resonant tunnelling structures with spin-orbit interaction

Magnetotunnelling spectroscopy of resonant tunnelling structures provides information on the nature of the two-dimensional electron gas in the well. We describe a model based on nonequilibrium Green's functions that allows for a comprehensive study of the density of states, tunnelling currents and current spin polarization. The investigated effects include the electron-phonon interaction, interface roughness scattering, Zeeman effect and the Rashba spin-orbit interaction. A qualitative agreement with experimental data is found regarding the satellite peaks. The spin polarization is predicted to be larger than ten percent for magnetic fields above 2 Tesla and having a structure even at the satellite peaks. The Rashba effect is confirmed to be observable as a beating pattern in the density of states but found to be too small to affect the tunnelling current.Comment: 31 pages, 11 figure

Surface enhanced Raman spectroscopy of thiacyanine dye J-aggregates on single silver nanoaggregates

Dye-coated colloidal metal nanoparticles (NPs) exhibit interesting optical properties originating from the interaction between metal core and dye shell. Depending on the interaction mechanism between the two, optical properties of dyes or NPs can be changed separately or jointly within the dye-NP assembly [1]. Many of the recent studies are focused on dyes which are able to self-assemble in highly oriented structures called Jaggregates on the surface of metallic NPs [2,3]. Owing to the variety of mechanisms by which dyes and their J-aggregates can interact with metallic NPs, dye-NP assemblies can lead to applications ranging from nanoscale sensing [4] to advanced composite materials for novel active and nonlinear optical devices [5]. Here we study the influence of TC concentration on its J-aggregation on the surface of AgNPs assemblies using Raman mapping and atomic force microscopy (AFM). Aqueous solutions (colloids) of citrate stabilized AgNPs with an average diameter of ~10 nm are mixed with TC dye solution and then deposited onto freshly cleaved highly oriented pyrolytic graphite and mica surfaces. The spectral signature of citrate ions is identified by (i) the O-H band around 220 cm-1, (ii) the C-H band around 2950 cm-1 and (iii) pronounced blinking in the 1000-1800 cm-1 range. In contrast, dye molecules adsorbed on nanoparticles are recognized by several stable Raman bands between 200 and 1600 cm-1. In situ AFM measurements show that SERS 'hot spots' are formed either on large single nanoparticles (diameter > 100 nm) or within assemblies of small nanoparticles (with diameters in the 10 - 50 nm range). However, only the latter are found to yield a citrate or TC dye SERS signal. We find that the TC dye adsorbed on the surface of AgNP nanoassemblies always forms J-aggregates when the dye concentration in the TC-AgNP solution is varied between 0.5μM and 17μM. Even though, a clear SERS spectra of dye Jaggregates can be acquired for high dye concentration (17μM) the citrate ions always exist on the AgNP surface and so does their SERS signature in form of O-H (220 cm-1) and C-H (2960 cm-1) bands. Assemblies with low TC concentration (0.5μM) do not have a clear dye SERS spectra, but rather spectra similar to the one of citrate ions meaning that either not all AgNPs are dye coated, or rather that the amount of TC molecules adsorbed on the surface of the nanoparticle is small and hence not detectable. We are grateful to the Serbian Ministry of Education, Science and Technological Development for financial support through projects Nos. OI 171005, OI 172023. This work was performed in the context of the European COST Action MP1302 Nanospectroscopy.V International School and Conference on Photonics and COST actions: MP1204, BM1205 and MP1205 and the Second international workshop "Control of light and matter waves propagation and localization in photonic lattices" : PHOTONICA2015 : book of abstracts; August 24-28, 2015; Belgrad

Copper-Nickel heterometallic multilayer composites for plasmonic applications

Plasmonics and optical metamaterials offer possibilities for numerous applications in different fields, from transformation optics and chemical sensing to merging the beneficial properties of electronic and optical circuits. Crucial for their function are interfaces between materials of which one has to exhibit negative value of relative dielectric permittivity due to the existence of free electron plasma. However, the choice of convenient materials is rather limited and their performance is severely impaired by strong absorption losses. This is the reason why alternative plasmonic media are currently of an increasing interest. In this contribution we consider one such medium, the heterometallic multilayer consisting of copper and nickel. Copper is an excellent plasmonic material, but needs protection against surface oxidation, a role fulfilled by nickel layers which simultaneously form interfaces supporting surface waves. We describe our proposed heterometallics and consider their electromagnetic properties and experimental fabrication. Ab initio numerical simulations were done using the finite element method for Cu-Ni multilayers on a copper substrate. Laminate composite structures of alternately electrodeposited nanocrystalline Ni and Cu films on cold-rolled polycrystalline copper substrates were fabricated. Highly-densified parallel interfaces can be obtained by depositing layers at a very narrow spacing. Our results show that Cu-Ni pairs are a viable alternative to conventional plasmonic media, while the electrodeposition approach offers acceptable structural and electromagnetic parameters with large area and good uniformity at a low cost

Preparation of silver and copper nanoparticles in presence of ascorbic acid and investigation of their antibacterial activity

In this study, we present a synthesis of silver and copper nanoparticles (NPs) using ascorbic acid as stabilizing and sodium borohydride as reducing agents, respectively. Four colloidal dispersions were obtained, two of them additionally stabilized by gelatin. They were characterized by UV-Vis, AFM, DLS and zeta potential measurements. The size of both silver and copper NPs, determined by AFM measurements, was 10 nm before, and 15 nm after stabilization with gelatin. Antibacterial activity of synthesized NPs was tested using series of gram positive and gram negative bacteria. It was found that Ag and Cu NPs showed antibacterial activity in all case s

Tailorable spectral dispersion of copper-nickel 1D plasmonic crystals

Plasmonic nanocomposites are a new class of materials that offers unprecedented opportunities to tailor the optical response, including the possibility to design their spectral and spatial dispersion at will. This includes the optical parameters rarely or never met in nature, which opens a path toward plasmonic metamaterials and the wide new area of transformation optics. Responsible for such a unique behavior are bound surface modes propagating along interfaces between materials with different signs of relative dielectric permittivity known as surface plasmon polaritons (SPP). Most metals possess negative relative permittivity in optical range due to the existence of free electron plasma. However, they also exhibit large absorption losses and are bound to a given spectral range defined by the metal itself, which is the reason why alternative plasmonic materials are being actively sought upon. One possible way to extend the toolbox of available materials is to use alternating metal-dielectric or metal-metal layers – the one-dimensional plasmonic crystals. Typically gold and silver are used for the metal part due to their large conductance and generally favorable properties. In this contribution we perform an analysis of the suitability of the use of copper for plasmonic nanocomposites. Its oxidation, the main barricade towards its more widespread use in plasmonics, is avoided by combining it with nickel. We utilize ab initio analysis by 2D finite element modeling and realistic material parameters to assess different electromagnetic modes. Tailorability of the response is attained by simple changing of the Cu to Ni fill factor. The analyzed CuNi plasmonic crystals are convenient for simple, low cost biochemical sensors and superabsorbers