Statistical model on the optical properties of silicon nanowire mats

Randomly grown silicon nanowire (SiNW) mats show a high light absorption even for long wavelengths despite the small volume of silicon. We present a statistical model that gives a physical understanding of the mechanisms of the absorption and scattering of light in such SiNW mats. According to this model the two main mechanisms of the effective absorption of light are (i) resonant optical antenna effects of the absorption within the individual SiNWs and (ii) the interaction of the light with several SiNWs in the mat due to strong light scattering. The results of this model are in good agreement with the experimental reflection, transmission, and absorption spectra taken with an integrating sphere

A STABLE SIMPLE SEQUENCE REPEAT MARKER FOR RESISTANCE TO WHITE MOULD IN TOBACCO

White mould, caused by Golovinomyces cichoracearum, is a major fungal disease of tobacco. Breeding for resistance to white mould is slow due to the intensive labour needed in artificial screening and the huge effect of the environment. In order to improve selection efficiency, molecular markers need to be identified to help in the rapid selection of germplasm resistant to white mould. The purpose of this study was, therefore, to identify the neutral, simple sequence repeat markers that can assist breeders in selecting for resistant plants. Two resistant parental lines XZ and STNCB, and three susceptible parental lines XSR, K51 and T71, were used in this study. Backcrosses of the hybrid from XZ and XSR were grown in a greenhouse, and DNA was extracted for molecular analysis. Eight simple sequence repeat markers and ten inter-simple sequence repeat markers were used. These markers were screened on the parental lines and the backcross generations for the differences between resistant (score 1) and susceptible (score 5) material. Single marker analysis was done using a t-test and significant (P<0.001) differences were found between the means of resistant and susceptible plants based on the marker PT30021. Marker PT30021 showed linkage to the white mould resistance gene, and thus managed to distinguish between resistant and susceptible materials in parental and advanced generations. Locus PT30021 has the potential of being used to identify white mould resistant germplasm in marker assisted backcrossing

Evaluation of gold nanowire pairs as a potential negative index material

A metamaterial consisting of pairs of metallic nanowires, separated by a dielectric spacer, has been fabricated and spectrally characterized in the visible and near-infrared spectral domain. It is shown, that the structure exhibits both a plasmonic and a magnetic resonance depending on its geometry and orientation with respect to the illuminating wave field. In particular, we investigate the influence of the thickness of the spacer layer on the spectral position of the resonances and show that, for an appropriate adjustment, both resonances coincide. Measurements of the amplitude and the phase of the transmitted wave are presented. It is also shown that the material is highly anisotropic with respect to the angle of incidence, as the plasmonic resonance wavelength depends strongly on it whereas the magnetic resonance does not show this sensitivity. All experimental results are supported by numerical simulations

Design of a scalable AuNP catalyst system for plasmon-driven photocatalysis

In this work we present a simple, fast and cost-efficient synthesis of a metal nanoparticle catalyst on a glass support for plasmon driven heterogeneous photocatalysis. It is based on efficient mixing of metal salts as particle precursors with porous glass as the supporting material in a mixer ball mill, and the subsequent realization of a complete catalyst system by laser sintering the obtained powder on a glass plate as the support. By this, we could obtain catalyst systems with a high particle proportion and an even spatial particle distribution in a rapid process, which could be applied to various kinds of metal salt resulting in plasmon active metal nanoparticles. Furthermore, the catalyst production process presented here is easily scalable to any size of area that is to be coated. Finally, we demonstrate the catalytic performance of our catalysts by a model reaction of ethanol degradation in a self-designed lab-scale reactor

Plasmonically Enhanced Electron Escape from Gold Nanoparticles and Their Polarization-Dependent Excitation Transfer along DNA Nanowires

Here we show plasmon mediated excitation transfer along DNA nanowires over up to one micrometer. Apparently, an electron excitation is initiated by a femtosecond laser pulse that illuminates gold nanoparticles (AuNP) on double stranded DNA (dsDNA). The dependency of this excitation on laser wavelength and polarization are investigated. Excitation of the plasmon resonance of the AuNPs via one- and two-photon absorption at 520 and 1030 nm, respectively, was explored. We demonstrate an excitation transfer along dsDNA molecules at plasmon supported four-photon excitation of AuNP cluster or at laser field driven nanoparticle electron tunneling for an alignment of the attached dsDNA to the polarization of the electric field of the laser light. These results extend the previously observed plasmonically induced three-photon excitation transfer along DNA nanowires to another nanoparticle material (gold) and the adapted irradiation wavelengths

Bi-directional terahertz emission from gold-coated nanogratings by excitation via femtosecond laser pulses

We report on the investigation of terahertz (THz) emission from gold-coated nanogratings (500 nm grating constant) upon femtosecond laser irradiation (785 nm, 150 fs, 1 kHz, a parts per thousand currency sign1 mJ/pulse). Unlike common assumptions, THz emission is not only observed in case of rear side irradiation (through substrate (Welsh et al. in Phys. Rev. Lett. 98:026803, 2007; Welsh and Wynne in Opt. Express 17:2470-2480, 2009)) of the nanograting, but also in case of front side excitation (through air). Furthermore in both cases, THz emission propagates in the direction of laser beam propagation and reverse. Based on these findings, we suggest a new approach to describe the newly observed phenomena. Using a highly sensitive and fast superconducting transition edge sensor (TES) as calorimeter, it was possible to directly measure the absolute energy of the emitted THz pulses in a defined spectral and spatial range, enabling for the first time a quantitative analysis of the THz emission process

Tuning of Spectral and Angular Distribution of Scattering from Single Gold Nanoparticles by Subwavelength Interference Layers

Localized surface plasmon resonance (LSPR) as the resonant oscillation of conduction electrons in metal nanostructures upon light irradiation is widely used for sensing as well as nanoscale manipulation. The spectral resonance band position can be controlled mainly by nanoparticle composition, size, and geometry and is slightly influenced by the local refractive index of the near-field environment. Here we introduce another approach for tuning, based on interference modulation of the light scattered by the nanostructure. Thereby, the incoming electric field is wavelength-dependent modulated in strength and direction by interference due to a subwavelength spacer layer between nanoparticle and a gold film. Hence, the wavelength of the scattering maximum is tuned with respect to the original nanoparticle LSPR. The scattering wavelength can be adjusted by a metallic mirror layer located 100–200 nm away from the nanoparticle, in contrast to near-field gap mode techniques that work at distances up to 50 nm in the nanoparticle environment. Thereby we demonstrate, for the first time at the single nanoparticle level, that dependent on the interference spacer layer thickness, different distributions of the scattered signal can be observed, such as bell-shaped or doughnut-shaped point spread functions (PSF). The tuning effect by interference is furthermore applied to anisotropic particles (dimers), which exhibit more than one resonance peak, and to particles which are moved from air into the polymeric spacer layer to study the influence of the distance to the gold film in combination with a change of the surrounding refractive index