Optical Properties of Bismuth Nanostructures Towards the Ultrathin Film Regime

Bulk bismuth presents outstanding optical properties, such as a giant infrared refractive index (n near 10) and a negative ultraviolet visible permittivity induced by giant interband electronic transitions. Although such properties are very appealing for applications in nanophotonics, the dielectric function of bismuth nanostructures has been scarcely studied. Here, we determine by spectroscopic ellipsometry the far infrared to ultraviolet dielectric function of pulsed laser deposited bismuth thin films with nominal thickness tBi varied from near 10 nm to several tens of nm. For tBi above 15 nm, the films display a continuous structure and their dielectric function is comparable with that of bulk bismuth. For tBi below 15 nm, the film structure is discontinuous, and the dielectric function differs markedly from that of bulk bismuth. It is proposed from FDTD simulations that this marked difference arises mainly from effective medium effects induced by the discontinuous film structure, where quantum electronic confinement does not play a dominant role. This suggests that ultrathin and continuous bismuth films should present the same outstanding optical properties as bulk bismuth for high performance nanophotonic devices

Polarization - Selective Optical Darkness in Metamaterials built from Nano-Bismuth

META'15, City College of New York, New York City, NY, USA August 4, 2015 – August 7, 2015; http://metaconferences.org/ocs/index.php/META15/META15We extend the concept of polarization ¿ selective optical darkness to metamaterials based on bismuth nanostructures (nano-Bi). It will be shown that in nano-Bi based metamaterials, this phenomenon can be achieved due to the near UV ¿ visible polaritonic resonances permitted by the near IR interband transitions of Bi.Financial support from the European Commission (FP7 STREP BisNano Project), the Spanish Ministry for Economy and Competitiveness (TEC2012-38901-C02-01 AMALIE) are acknowledged.Peer Reviewe

Linear and non-linear light emission of Er-hybridized Si nanostructures in the ultrathin geometry

Lille Grand Palais, May 11-15, 2015Resume : Advanced integrated photonic devices will include active metamaterials in which plasmonic and photonic modes will be used to manipulate the light in nanoscale dimensions. Efficient, robust, and optically modulated nanoscale light emitters with high color purity are required as active building blocks for these metamaterials. A single ultrathin layer (few nanometers thick) formed by Er ions coupled to Si nanoparticles or nanostructures (NSs) is suitable for such a purpose, since RE ions provide a robust emission that can be enhanced by using the Si NSs as sensitizers. However, it is necessary to investigate the potential of these nanoscale systems for light emission and modulation. // In this work we report the light emission properties of ultrathin (< 8 nm) hybrid Er-Si NSs layers, in which all the Er ions are located at few nm of the Si NSs in order to obtain unprecedently high sensitization efficiency. Clear IR Er light emission from an ultrathin layer containing less than 2.5% of an atomic monolayer of Er under near-ultraviolet and visible excitation. Moreover it is found that the emission of the Er-Si NSs layers shows a complex non-linear behaviour as a function of the excitation photon flux. We will discuss how these Er-Si NSs layers possess a high functional versatility, and can be used as efficient nanoscale near IR light sources the emission of which can be modulated optically. - See more at: http://www.european-mrs.com/2015-spring-symposium-h-european-materials-research-society#sthash.kww6pbzm.dpufPeer Reviewe

Interband transitions in semi-metals, semiconductors, and topological insulators: A new driving force for plasmonics and nanophotonics

Plasmonic and Mie resonances in subwavelength nanostructures provide an efficient way to manipulate light below the diffraction limit that has fostered the growth of plasmonics and nanophotonics. Plasmonic resonances have been mainly related with the excitation of free charge carriers, initially in metals, and Mie resonances have been identified in Si nanostructures. Remarkably, although much less studied, semi-metals, semiconductors and topological insulators of the p-block enable plasmonic resonances without free charge carriers and Mie resonances with enhanced properties compared with Si. In this review, we explain how interband transitions in these materials show a major role in this duality. We evaluate the plasmonic and Mie performance of nanostructures made of relevant p-block elements and compounds, especially Bi, and discuss their promising potential for applications ranging from switchable plasmonics and nanophotonics to energy conversion, especially photocatalysis

Evaluation of the Physical Stability of Zinc Oxide Suspensions Containing Sodium Poly-(acrylate) and Sodium Dodecylsulfate.

The physical stability of zinc oxide (ZnO) aqueous suspensions has been monitored during two months by different methods of investigation. The suspensions were formulated with ZnO at a fixed concentration (5 wt%), sodium poly-(acrylate), as a viscosifier, and sodium dodecylsulfate (SDS), as a wetting agent. The rheological study shows that the suspensions exhibit a non-Newtonian, most often shear-thinning behavior and their apparent viscosity increases with polymer concentration. The rheograms of most of the ZnO suspensions do not vary during the experimental period. The viscoelastic properties of these suspensions, such as elastic or storage modulus (G′), viscous or loss modulus (G″) and phase angle (δ) were also examined. For% strains lower than 10%, all the formulations show strong elastic properties (G′ > G″, δ varies between 5 and 15°). Beyond 10% strain, the rheological behavior changes progressively from elastic to viscous (G″ > G′ for % strain >80%). Consistently, δ increases and reaches the 50–70° zone. Multiple light scattering (back-scattered intensity), measured with the Turbiscan ags, was used to characterize suspension physical stability (early detection of particle or aggregate size variations and particle/aggregate migration phenomena). Suspensions containing 0.4 and 0.6 wt% polymer remain stable and macroscopically homogeneous, without being affected by the change of particle size observed with a laser particle sizer. Sedimentation tests, pH, and ζ potential measurements versus time, also confirmed these findings

Exploring the Optical Resonances of Photocatalytic Bismuth Nanostructures

Symposium O—Plasmonic Nanomaterials for Energy Conversion, Boston, Massachusetts, November 29-December 4, 2015Nanostructures presenting optical resonances present a strong potential for energy applications. This potential has been first developed with noble metal nanostructures. At their plasmonic resonances, they can be used as scatterers for improved light trapping into photovoltaic photonic structures or as near-field enhancers boosting photocarrier excitation in photovoltaic media.1 Very recently, plasmoelectric potentials have been measured in resonant noble metal nanostructures, thus allowing a novel opto-electrical conversion scheme.2 Optical resonances can be excited in nanostructures beyond noble metals. Indeed, most of the metals of the periodic table can support plasmonic resonances.3 Moreover, non-Drude plasmonic-like resonances can also be achieved: for instance the so-called interband polaritonic resonances in nanostructures presenting sharp interband transitions, such as bismuth nanostructures.4,5 Based on such resonances, the potential of bismuth nanostructures for photocatalysis has been demonstrated.6,7 In the reported works, photocatalysis was achieved using bismuth nanospheres. At present, the underlying mechanism has to be discussed together with the photocatalytic potential of bismuth nanostructures in a broad range of sizes and shapes. In this presentation, we provide a detailed description of the optical response of bismuth nanostructures as a function of their size and shape, with dimensions ranging from 50 nm to 500 nm. We demonstrate a strong dependence of the absorption, scattering and extinction cross-sections, near-field, surface charges and currents that will impact the efficiency of photocatalytic solutions based on bismuth nanostructures. 1 Polman, A. et al.; Photonic design principles for ultrahigh efficiency photovoltaics, Nature Materials 2012, 11, 174 2 Sheldon, M.T. et al.; Plasmoelectric potentials in metal nanostructures, Science 2014, 346, 828 3 Naik, G. et al.; Alternative plasmonic materials: Beyond gold and silver, Advanced Materials 2013, 25, 3264 4 Toudert, J. et al.; Exploring the optical potential of nano-bismuth: tunable surface plasmon resonances in the near ultraviolet-to-near infrared range, Journal of Physical Chemistry C 2012, 116, 20530 4 Toudert, J. et al.; Spectroscopic ellipsometry for active nano- and meta- materials, Nanotechnology Reviews 2014, 3, 223 6 Wang, Z. et al.; Investigation of the optical and photocatalytic properties of bismuth nanospheres prepared by a facile thermolysis method, Journal of Physical Chemistry C 2014, 118, 1155 7 Dong, F.; A semimetal bismuth element as a direct plasmonic photocatalyst, Chemical Communications 2014, 50, 10386Peer Reviewe

LAI based trees selection for mid latitude urban developments: A microclimatic study in Cairo, Egypt

To study the leaf area index, LAI, based thermal performance in distinguishing trees for Cairo's urban developments, ENVI-met plants database was used as platform for a foliage modeling parameter, the leaf area density, LAD. Two Egyptian trees: Ficus elastica. and Peltophorum pterocarpum were simulated in 2 urban sites with one having no trees, whilst the second is having Ficus nitida trees. Trees LAD values were calculated using flat leaves' trees LAI definition to produce maximum ground solid shadow at peak time. An empirical value of 1 for LAI is applied to numerically introduce LAD values for ENVI-met. Basically, different meteorological records showed improvements for pedestrian comfort and ambient microclimate of the building using E elastica. About 40-50% interception of direct radiation, reductions in surfaces' fluxes around trees and in radiant temperature T-mrt in comparison to base cases gave preferability to E elastica. The lack of soil water prevented evapotranspiration to take place effectively and the reduced wind speeds concluded negligible air temperature differences from both base cases except slightly appeared with the F elastica. Results show that a flat leaves tree if does not validate LAI of 1, the ground shading would not fulfill about 50% direct radiation interception and this value can be used as a reference for urban trees selection. Further simulations were held to investigate LAI value of maximum direct radiation interception. Performing additional simulations, F elastica of LAI of 3 intercepted almost 84% of direct radiation and revealed implications about urban trees in practice and its actual LAI. (C) 2009 Elsevier Ltd. All rights reserved