A plasmon-induced current loop in gold semi-shells

We perform a computational investigation of the optical properties of nanoscale gold 'semi-shells' and show how additional plasmon resonances develop as the shape is successively mutated from 'nanoshell' to 'nano-cup', 'half-shell' and finally to 'nano-cap'. The effects of aspect ratio, surface roughness and cut-off height are explored. Of special interest is a new longitudinal resonance that generates an electric current loop. We predict that this will induce an orthogonal magnetic component that will sum with the magnetic component of incident light at certain orientations. Exploitation of this phenomenon in an ordered array of semi-shells may produce anomalous optical effects due to an altered magnetic permeability. © IOP Publishing Ltd

Control of plasmon resonance in coatings of gold nanorods

Gold nanorods manifest a tunable plasmon resonance with light in the visible to near-infrared regions of the spectrum, and have been proposed for use in spectrally selective coatings on glass. However, details of shape and packing density have a significant effect on the optical properties of these nanoparticle coatings. Here we show how these effects can be controlled and exploited to produce a flexible spectral response. © 2006 IEEE

Metal-insulator-metal (MIM) nanocapacitors and effects of material properties on their operation

Metal-insulator-metal (MIM) capacitors play an important part in many integrated electronic circuits in the areas of analog, microwave, and radio frequency systems. However the transverse dimensions of current MIM capacitors are in the micrometer scale. If integrated circuits continue to be miniaturized, the capacitor, alongside other components, must also be miniaturized to realize nanoelectronic circuits and systems. This article presents a novel device, the nanocapacitor, of which the dimensions are constrained to nanoscale in longitudinal and transverse directions, and discusses the effects of material properties on their operation. In particular, this work discusses the effects of dielectric constant, dielectric strength, and quantum electrical phenomena on achieving relatively high capacitances and capacitance densities in nanocapacitors. © Institute of Materials Engineering Australasia Ltd - Materials Forum Volume 27 - Published 2004

Effect of glass pre-treatment on the nucleation of semi-transparent gold coatings

Coatings of gold nanoparticles with a uniform film texture and a neutral blue hue may be applied to glass by an aqueous process and such coatings have recently been proposed for architectural applications. Here, we show that the optical transmission spectrum of these coatings is directly related to the interplay between the nucleation, growth and aggregation of the particles. In particular, prior treatments of the glass substrate in 1:1 sulfuric acid (H 2SO4), 98% H2SO4 and buffered hydrofluoric acid (HF) exerted a strong influence on the subsequent particle size and coverage, which is explained here in terms of contact angle and its effect on rates of nucleation. The rate of nucleation on the surface treated with HF is estimated to be twice that of the surface treated with 98% H 2SO4. The color of the coatings is the result of inter-particle plasmonic interactions and is, therefore, also controlled by the nature of nucleation and growth process. © 2005 Elsevier B.V. All rights reserved

Local electromagnetic fields surrounding gold nano-cap particles

Using the discrete dipole approximation (DDA) the local electromagnetic fields surrounding gold nano-cap particles are investigated. Suitable k-vectors and polarization vectors of the incident light are used to determine the largest local electric field enhancement. The largest enhancement can be found for the 864 nm dipole resonance; where the field enhancement is approximately 30 000 times the applied field. The electric field contours surrounding the particle are used to assign the order of the surface plasmon resonances. © 2006 IEEE

Aqueous pathways for the formation of zinc oxide nanoparticles

We examine the effect of reactant concentrations, temperatures and feeding methods on the morphology of ZnO formed when reacting solutions of ZnSO 4 and NaOH. The catalytic effect of hydroxide in excess relative to the stoichiometric ratio is considered. It is shown that, having fixed other reaction conditions, the end-products, particle structures and size strongly depend on the mole ratio of the precursors. The presence of zinc salt hydroxide species was confirmed at sub-stoichiometric ratios in slightly acidic conditions. At the stoichiometric ratio both zinc hydroxide and zinc oxide are formed, while only zinc oxide forms in an excess of hydroxide. The method of feeding the reactants into the reaction vessel also has a strong influence on the end-product properties, as does the reaction temperature. By control of these parameters the specific surface area could be varied from 10 to 33 m 2 g-1, the particle shape could be varied from equiaxed, through to star-like and needle-like, and the particle size may be varied from 50 to over 300 nm. © 2011 The Royal Society of Chemistry

The application of gold surfaces and particles in nanotechnology

Gold is widely used in nanotechnology, for example as a substrate in forming self-assembled monolayers or as nanoparticles for their unique optical and chemical properties. In this paper we give an overview of the properties of gold relevant to its potential application in molecular-scale devices and present some of our recent computational predictions. Density functional calculations of molecular adsorption onto gold surfaces were used to investigate the effect of surface symmetry and identify new linking schemes for self-assembled monolayers. Adsorption energies of methythiolate (SCH3) onto the (111), 9100) and (110) surfaces of gold are predicted to be 39.3, 48.4 and 51.1 kcal/mol respectively and demonstrate that selective functionalisation of the surfaces is possible. Phosphine molecules with at least two hydrogen atoms substituted for methyl groups are predicted to form Au-P surface bonds with energies of about 13-20 kcal/mol

Effect of multimodal plasmon resonances on the optical properties of five-pointed nanostars

© 2015 Author(s). The optical transmission and electric field distribution of plasmonic nanostructures dictate their performance in nano-optics and nano-biosensors. Here, we consider the use of hollow, five-pointed, star-shaped nanostructures made of Al, Ag, Au or Cu. We use simulations based on finite-difference time-domain and the discrete dipole approximation to identify the strongest plasmon resonances in these structures. In particular, we were seeking plasmon resonances within the visible part of the spectrum. The silver pentagrams exhibited the strongest such resonance, at a wavelength of about 530 nm. The visiblelight resonances of Au and Cu pentagrams were relatively weaker and red-shifted by about 50 nm. The main resonances of the Al pentagrams were in the ultra-violet. All the nanostars also showed a broad, dipolar-like resonance at about 1000 nm. Surprisingly, the maximum field intensities for the visible light modes were greatest along the flanks of the stars rather than at their tips, whereas those of the dipolar-like modes in the near-infrared were greatest at the tips of the star. These findings have practical implications for sensor design. The inclusion of a conformally hollow interior is beneficial because it provides additional 'hot spots'

Nanophotonics-enabled smart windows, buildings and wearables

© 2016 Geoff Smith et al., published by De Gruyter Open. Design and production of spectrally smart windows, walls, roofs and fabrics has a long history, which includes early examples of applied nanophotonics. Evolving nanoscience has a special role to play as it provides the means to improve the functionality of these everyday materials. Improvement in the quality of human experience in any location at any time of year is the goal. Energy savings, thermal and visual comfort indoors and outdoors, visual experience, air quality and better health are all made possible by materials, whose "smartness" is aimed at designed responses to environmental energy flows. The spectral and angle of incidence responses of these nanomaterials must thus take account of the spectral and directional aspects of solar energy and of atmospheric thermal radiation plus the visible and color sensitivity of the human eye. The structures required may use resonant absorption, multilayer stacks, optical anisotropy and scattering to achieve their functionality. These structures are, in turn, constructed out of particles, columns, ultrathin layers, voids, wires, pure and doped oxides, metals, polymers or transparent conductors (TCs). The need to cater for wavelengths stretching from 0.3 to 35 μm including ultraviolet-visible, near-infrared (IR) and thermal or Planck radiation, with a spectrally and directionally complex atmosphere, and both being dynamic, means that hierarchical and graded nanostructures often feature. Nature has evolved to deal with the same energy flows, so biomimicry is sometimes a useful guide

Fabrication of double nano-cup assemblies and their anomalous plasmon absorption

Double-cup assemblies of nanoscale gold semi-shells have been synthesized using a combination of thermal evaporation and chemical etching. The optical extinction of these structures peaked at 740 nm, but there was also evidence of additional extinction maxima at 560, 940 and 1110 nm. Numerical simulations of the optical properties revealed that the extinction was due mainly to scattering rather than to absorption In contrast, the extinction in simple single-shell nanocups was strongly absorptive in nature. Multiple plasmon resonances were identified in the double-cup structures, including an interesting quadrupole resonance in which oscillations of the inner and outer shells should operate 180° out-of-phase. © 2008 IEEE