Hot electron science in plasmonics and catalysis: what we argue about.

Hot electron photochemistry has made strong claims for improved control of chemical reactions. Here I discuss these claims in the light of a plethora of model experiments and theories, asking what are the key issues to solve. I particularly highlight the need to understand nanoscale thermal hot-spots, thermal gradients, and thermal transport, as well as the conventional optical confinement in plasmonics. I note how the 'direct electron transfer' process seems to dominate, and resembles well known 'indirect excitons' in semiconductor quantum wells. I believe a crucial advance still required is a prototype nano-confined geometry which allows reactants and products to access a well-controlled metallic atomic surface

Reality science

Another panel reviewing grants. Hours of argument when, with the funding available, only the top-rated one will get funded. I sigh. Surely there might be other ways..

Molecules in the mirror: how SERS backgrounds arise from the quantum method of images

The Raman coupling of light to molecular vibrations is strongly modified when they are placed near a plasmonic metal surface, with the appearance of a strong broad continuum background in addition to the normal surface-enhanced Raman scattering (SERS) peaks. Using a quantum method of images approach, we produce a simple but quantitative explanation of the inevitable presence of the background, due to the resistive damping of the image molecule. This model thus suggests new strategies for enhancing the SERS peak to background ratio

Accessing Plasmonic Hotspots Using Nanoparticle-on-Foil Constructs.

Funder: Trinity College, University of CambridgeMetal-insulator-metal (MIM) nanogaps in the canonical nanoparticle-on-mirror geometry (NPoM) provide deep-subwavelength confinement of light with mode volumes smaller than V/V λ < 10-6. However, access to these hotspots is limited by the impendence mismatch between the high in-plane k ∥ of trapped light and free-space plane-waves, making the in- and out-coupling of light difficult. Here, by constructing a nanoparticle-on-foil (NPoF) system with thin metal films, we show the mixing of insulator-metal-insulator (IMI) modes and MIM gap modes results in MIMI modes. This mixing provides multichannel access to the plasmonic nanocavity through light incident from both sides of the metal film. The red-tuning and near-field strength of MIMI modes for thinner foils is measured experimentally with white-light scattering and surface-enhanced Raman scattering from individual NPoFs. We discuss further the utility of NPoF systems, since the geometry allows tightly confined light to be accessed simply through different ports

Demonstrating photoluminescence from Au is electronic inelastic light scattering of a plasmonic metal: the origin of SERS backgrounds.

Temperature-dependent surface-enhanced Raman scattering (SERS) is used to investigate the photoluminescence and background continuum always present in SERS but whose origin remains controversial. Both the Stokes and anti-Stokes background is found to be dominated by inelastic light scattering (ILS) from the electrons in the noble metal nanostructures supporting the plasmon modes. The anti-Stokes background is highly temperature dependent and is shown to be related to the thermal occupation of electronic states within the metal via a simple model. This suggests new routes to enhance SERS sensitivities, as well as providing ubiquitous and calibrated real-time temperature measurements of nanostructures.The authors would like to thank EPSRC (EP/K028510/1, EP/ G060649/1, EP/H007024/1, EP/L027151/1), ERC LINASS 320503, EU CUBiHOLE, and Renishaw Diagnostics Ltd. for funding and samples.This is the final published version. It first appeared at http://pubs.acs.org/doi/abs/10.1021/acs.nanolett.5b00146

Tuning localized plasmons in nanostructured substrates for surface-enhanced Raman scattering

Comprehensive reflectivity mapping of the angular dispersion of nanostructured arrays comprising of inverted pyramidal pits is demonstrated. By comparing equivalently structured dielectric and metallic arrays, diffraction and plasmonic features are readily distinguished. While the diffraction features match expected theory, localised plasmons are also observed with severely flattened energy dispersions. Using pit arrays with identical pitch, but graded pit dimensions, energy scaling of the localised plasmon is observed. These localised plasmons are found to match a simple model which confines surface plasmons onto the pit sidewalls thus allowing an intuitive picture of the plasmons to be developed. This model agrees well with a 2D finite-difference time-domain simulation which shows the same dependence on pit dimensions. We believe these tuneable plasmons are responsible for the surface-enhancement of the Raman scattering (SERS) of an attached layer of benzenethiol molecules. Such SERS substrates have a wide range of applications both in security, chemical identification, environmental monitoring and healthcare

An experimental and theoretical determination of oscillatory shear-induced crystallization processes in viscoelastic photonic crystal media

A study is presented of the oscillatory shear-ordering dynamics of viscoelastic photonic crystal media, using an optical shear cell. The hard-sphere/“sticky”-shell design of these polymeric composite particles produces athermal, quasi-solid rubbery media, with a characteristic viscoelastic ensemble response to applied shear. Monotonic crystallization processes, as directly measured by the photonic stopband transmission, are tracked as a function of strain amplitude, oscillation frequency, and temperature. A complementary generic spatio-temporal model is developed of crystallization due to shear-dependent interlayer viscosity, giving propagating crystalline fronts with increasing applied strain, and a gradual transition from interparticle disorder to order. The introduction of a competing shear-induced flow degradation process, dependent on the global shear rate, gives solutions with both amplitude and frequency dependence. The extracted crystallization timescales show parametric trends which are in good qualitative agreement with experimental observations

Molecules in the mirror: how SERS backgrounds arise from the quantum method of images.

The Raman coupling of light to molecular vibrations is strongly modified when they are placed near a plasmonic metal surface, with the appearance of a strong broad continuum background in addition to the normal surface-enhanced Raman scattering (SERS) peaks. Using a quantum method of images approach, we produce a simple but quantitative explanation of the inevitable presence of the background, due to the resistive damping of the image molecule. This model thus suggests new strategies for enhancing the SERS peak to background ratio.This work was supported by UK EPSRC EP/C511786/1, EP/F011393, ERC 320503 LINASS, EU CUBIHOLES, 3M, the Royal Society and the Wolfson Foundation

Stamping colloidal photonic crystals: a facile way towards complex pixel colour patterns for sensing and displays.

Patterning of colloidal photonic crystals (CPCs) has been strongly investigated in recent years for sensing and image displays. Rather than using traditional template-directed approaches, here microimprint lithography along with convective self-assembly is applied to generate complex CPC patterns that can be adjusted to show single- or dual-colour patterns or composite CPC patterns possessing two different colours. These composite CPC patterns show different wettability with water because of the surface chemistry of the polymers and silica used. This dramatically transforms the structural colours upon liquid infiltration. By mixing different ethanol concentrations with water, the infiltration efficiency can be further improved and easily read out from changes in reflection intensity and spectral peak shifts. Integrating these nano-architectures into devices can thus yield function as image displays and as sensors for solvents.We acknowledge financial support from EPSRC grant EP/ G060649/1, EP/I012060/1, EP/J007552/1, EP/L027151/1, ERC grant LINASS 320503, EMATTER 280078.This is the final published version. The article first appeared at http://pubs.rsc.org/en/Content/ArticleLanding/2015/NR/C4NR05934D#!divAbstract