Hot charge carrier extraction from metallic nanostructures is a very promising approach for applications in photocatalysis, photovoltaics, and photodetection. One limitation is that many metallic nanostructures support a single plasmon resonance thus restricting the light-to-charge-carrier activity to a spectral band. Here we demonstrate that a monolayer of plasmonic nanoparticles can be assembled on a multistack layered configuration to achieve broadband, near-unit light absorption, which is spatially localized on the nanoparticle layer. We show that this enhanced light absorbance leads to ∼40-fold increases in the photon-to-electron conversion efficiency by the plasmonic nanostructures. We developed a model that successfully captures the essential physics of the plasmonic hot electron charge generation and separation in these structures. This model also allowed us to establish that efficient hot carrier extraction is limited to spectral regions where (i) the photons have energies higher than the Schottky junctions and (ii) the absorption of light is localized on the metal nanoparticles.

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We show how a combination of near- and far-field coupling of the localised surface plasmon resonances in aluminium nanoparticles deposited on TiO2 films greatly enhances the visible light photocatalytic activity of the semiconductor material. We demonstrate two orders of magnitude enhancement in the rate of decomposition of methylene blue under visible light illumination when the surface of TiO2 films is decorated with gratings of Al nanoparticle dimers.

wileyonlinelibrary.com FULL PAPERapproach to increase the effi ciency of the photoconversion processes consists on integrating plasmonic metal nanostructures with semiconductor materials [4][5][6][7] Plasmonic nanostructures can improve photocatalytic processes via: [ 8 ] (i) intrinsic charge separation mechanisms (builtin potentials) that occur at metal-semiconductor junctions (Schottky contacts), (ii) strong confi nement of electromagnetic energy at the surface of the metal nanoparticles, which leads to enormous energy densities at the near-fi eld regions of the metallic nanostructures and (iii) the emission of hot charge-carriers from the metal nanoparticles into the semiconductor material. [9][10][11] Plasmon related phenomena originate from the light-driven collective oscillation of electrons at the surface of metallic nanostructures. The resonance frequencies at which these oscillations take place are largely controlled by the geometry of the metallic nanostructures. One of the simplest structures that exhibits localized surface plasmon resonances are metal nanowires ( Figure 1 ): these structures consist of metal stripes with particle plasmon resonances that depend on the width and height of the wire in addition to the period of the wire array (gratings). These particle plasmon resonances can be excited with light polarized perpendicular to the wire length and occur in the visible region of the spectrum for width and heights in the order of a few tens of nanometers for Au.Under particular illumination conditions and for specifi c grating periods, these nanowire gratings can exhibit [ 12 ] resonances involving coupling of energy into complex waves supported by the grating and Rayleigh-type anomalies due to the emergence of a grating order at grazing angle.Rayleigh anomalies are easy to understand for the simple case of a 1D nanowire grating deposited on a substrate (see diagram of Figure 1 b). For normal incidence, conservation of momentum k inc on the incident medium dictates that 2 inc 2 2 k k k n t = − (1)where n and t denote the normal and transverse components of the total momentum resulting from the interaction of light with the grating (see diagram of Figure 1 ). The transverse component (for normal incidence) is given by integer multiples ( m ) of the momentum imparted by the grating (2π/ p ):One key process in plasmon-enhanced photocatalysis is the transfer of hot charge-carriers from metal nanostructures into photocatalytically active materials. This process is secondary to the initial step of light absorption by the metal nanostructures. Light absorption in these structures can be controlled by designing complex geometries with tailored optical cross-sections.Here, a study on one of the simplest nanostructures exhibiting plasmon resonances is presented: 1D gratings of metal wires. Results on the effect of the periodicity of these arrays are presented on the resonant absorption of light and on the hot charge-carrier transfer to a supporting TiO 2 thin fi lm. This charge transfer process is monitor...

Diffraction profiles were analysed from thermally deposited 111-oriented gold films, ranging in thickness from 300 to 1900 Å. The data were collected using the high-resolution powder diffractometer on beamline BM16 at the European Synchrotron Research Facility (ESRF) set at a wavelength of 0.3507 Å. The profiles were measured under conventional symmetric θ–2θ reflection conditions and by asymmetric transmission diffraction to ensure that only crystallites oriented normal to the substrate contribute to the diffraction. An analysis of the instrument profile shape of the diffractometer was undertaken using the SRM 660 LaB6line profile standard. A parallel study of the films using atomic force microscopy and transmission electron microscopy was also undertaken to provide information on the dimensions of the crystallite columns in the films and the presence of dislocations. All the films displayed diffraction broadening arising from both crystallite-size effects and dislocation-induced strain effects. Analysis of the magnitude and anisotropy of the dislocation-induced broadening withhklindicates that the dislocations have a mixed screw/edge character and tend to form primarily on (111) slip planes parallel to the substrate at densities of ∼1015to 1016 m−2.

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The preparation of ultra flat gold surfaces for use in chemical force microscopy (CFM) has been studied. The surfaces were studied in terms of substrate effects by comparing mica, Si (110) wafer and glass slides. The effect of different annealing regimes was also investigated. Measurements on these surfaces were made by both atomic force microscopy (AFM) (in contact and tapping mode) and by scanning tunneling microscopy (STM). The films contain different morphologies with respect to grain size and topography. Calculations of surface roughness present values less than 2.5 nm for all surfaces studied, making the choice of the flattest surface difficult if based on criteria of surface roughness alone. Additionally, it is shown that different acquisition parameters can produce dissimilar images that have stability and reproducibility.