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

Designing oxynitride nanostructured thin films to enhance europium white light emission for efficient solid state emitters

CLEO®/Europe-EQEC 2015, Munich (ICM), Germany, June 21st, - 25th, 2015; http://2015.cleoeurope.org/In the present work we study the visible light emission of europium (Eu) ions embedded in two different matrices (amorphous aluminum oxide (a-Al2O3) and ceramic SiAlON) as a function of the Eu distribution and concentration. Eu-doped thin films were produced using the pulsed laser deposition technique by the alternating ablation of the matrix target and the Eu target; as a result nanostructured Eu-doped multilayers were formed. The Eu in-depth distribution was modified by varying the host inter-layer thickness, which ranged from 1 to 15 nm, and the Eu content per layer was modified by varying the number of pulses on the Eu target. Under UV excitation (355 nm), the as-deposited films of both matrices showed a broadband emission (FWHM ¿200 nm), that has been related to the superposition of the 5d levels to the 4f levels of the Eu2+, which is rarely found in pure oxides. This broad emission was further enhanced keeping the same spectral distribution upon annealing treatments up to 500 oC for the a-Al2O3 (Fig. 1a) and 700 oC for the SiAlON (Fig. 1c). However for samples with higher Eu content and at the higher annealing temperatures the spectral shape emission changed and the emission spectra showed narrow and well-defined emission peaks. These have been identified as resulting from the 4f ¿ 4f transitions of Eu3+ (Fig. 1b). Therefore, it has been found that two distinct and efficient Eu-related emissions can be obtained by a suitable design of the Eu distribution and concentration. This is due to a change of oxidation state of Eu in the films, which will be discussed. These Eu-doped films have a high potential for the development of either solid state lighting LEDs with broadband emission, or integrated lasers with narrow emission lines. Acknowledgements. This work has been financially supported by the Spanish Ministry of Economy and Competitiveness through the project TEC2012_38901-C02-01. I.C. acknowledges the financial support through JAE-Pre-2011_00578. A.M. acknowledges the financial support through BES-2013-062593.This work has been financially supported by the Spanish Ministry of Economy and Competitiveness through the project TEC2012_38901-C02-01. I.C. acknowledges the financial support through JAE-Pre-2011_00578. A.M. acknowledges the financial support through BES-2013-062593.Peer Reviewe

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

UV Plasmonic Metamaterial from Vertical Non-Conventional Nanoantennas

Boston, Massachusetts, November 29-December 4, 2015Metallic nanoantennas have been used as nanophotonic detectors of infrared and visible radiation [1] [2]. The extension of these elements to the ultraviolet (UV) range has not been satisfactory due to the poor optical absorption showed by metals at these frequencies. The low values of electrical conductivity of metals at UV frequencies compromise the generation of currents along the resonant geometries. In change, several non-conventional materials show a larger value of electrical conductivity, increasing notably the absorption of nanoantennas in the UV [3]. This electrical conductivity increment is more noticeable in liquid semimetals as Bismuth or Gallium. Another way to improve optical absorption of these resonant elements is to arrange them with a high spatial density of semimetal nanoantennas. In this contribution we evaluate numerically, using multiphysics simulation, the light to heat conversion performance of a vertical nanoantenna arrangement embedded in a dielectric matrix. The so-obtained UV metamaterial enabling strong electromagnetic plasmonic absorption and heating effects. The use of nanoantennas allows a polarization and frequency selectivity that can be adequate to generate ultraviolet sensors. These selectivities are strongly related with the shape of the resonant elements. Furthermore, since the vertical antennas are embedded within a robust dielectric matrix, this arrangement allows to change from solid to liquid phase maintaining the nanoantenna geometry. This is possible for materials as Bismuth or Gallium which show a lower melting temperature than dielectric substrates [4]. This phase transition makes the metamaterial active upon control of temperature. [1] L. Novotny and N. van Hulst, ¿Antennas for light,¿ Nat. Photon. 5 (2), 83-90, (2011). [2] A. Cuadrado, E. Briones, F.J. González, J. Alda, ¿Polarimetric Pixel using Seebeck Nanoantenna¿. Opt Exp, 22, No 11, 13835-13845, (2014). [3] J.Toudert, R.Serna, and M. Jiménez de Castro, ¿Exploring the optical potencial of nano-Bismuth: Tunable surface Plasmon resonances in the near Ultraviolet-to-Near Infrared range¿, J. Phys. Chem. C, 116 (38), pp 20530-20539, (2012). [4] M. Jiménez de Castro, F. Cabello, J. Toudert, R. Serna and E.Haro-Poniatowski, ¿Potential of bismuth nanoparticles embedded in a glass matrix for spectral-selective thermo-optical devices¿ Appl. Phys. Lett. 105, 113102 (2014).Peer Reviewe

Multifractal patterns formed by laser irradiation in GeAl thin multilayer films

Structures induced in GeAl thin multilayer films by laser irradiation are studied. We compute their multifractal spectra from digitized transmission-electron micrographs. The results show that the patterns, which arise from a diffusion process followed by rapid solidification, are fractal, and that they cannot be described by a unique scaling exponent. © 1992 The American Physical Society.This work was partially supported by the Comision Interrninisterial de Ciencia y Tecnologia (CICyT) of Spain under Project Nos. MAT88-0437 and MAT90-0544.Peer Reviewe

Multifractal patterns formed by laser irradiation in GeAl thin multilayer films

Structures induced in GeA1 thin multilayer films by laser irradiation are studied. We compute their multifractal spectra from digitized transmission-electron micrographs. The results show that the patterns, which arise from a diH'usion process followed by rapid solidification, are fractal, and that they cannot be described by a unique scaling exponentThis work was partially supported by the Comision Interrninisterial de Ciencia y Tecnologia (CICyT) of Spain under Project Nos. MAT88-0437 and MAT90-0544.Publicad

Temperature dependence and quenching processes of the intra-4f luminescence of Er in crystalline Si

8 págs.; 7 figs.The luminescence quenching of Er in crystalline Si at temperatures between 77 and 300 K is investigated. Samples were prepared by solid-phase epitaxy of Er-implanted amorphous Si layers with or without O codoping. After epitaxial regrowth at 620°C, thermal annealing at 900°C for 30 sec was performed in order to eliminate residual defects in the regrown layer and electrically and optically activate the Er ions. Measurements of photoluminescence intensity and time decay were performed as a function of temperature and pump power. By increasing the temperature from 77 K to room temperature the luminescence intensity decreases by ~ three orders of magnitude in the Er-doped sample without O codoping, but only by a factor of 30 in the O-doped sample. In this sample room-temperature photo-luminescence and electroluminescence have been observed. Time-decay curves show a fast initial decay (~100 ¿sec) followed by a slow decay (~1 msec), with the relative intensity of these two components depending on temperature, pump power, and O codoping. The decay curves can be fitted by a sum of two exponential functions revealing the existence, in both samples, of two different classes of optically active Er sites. The concentration of excitable sites belonging to the slow-decaying class is similar for the samples with or without O codoping and rapidly decreases when temperature is increased. At temperatures above 150 K the Er luminescence is dominated by the fast-decaying centers the concentration of which is greatly increased by the presence of O. It is found that in the absence of oxygen room-temperature luminescence is hampered by the limited amount of excitable Er ions. In contrast, in O-doped samples the nonradiative decay of excited Er is the main quenching mechanism. The main factors determining the temperature quenching of Er luminescence and the crucial role of oxygen are discussed. © 1994 The American Physical Society.This work has been partially supported by GNSM-CNR. Work at the FOM Institute is part of the research program of the foundation for Fundamental Research on Matter (FOM), and was made possible by financial support from the Dutch organization for the Advancement of Research (NWO}, the Foundation for Technical Research (STW}, and the IC Technology Program (IOP Electro-optics) of the Ministry of Economic Affairs.Peer Reviewe

Nanocrystal size dependence of the third-order nonlinear optical response of Cu:Al2O3 thin films

3 pages, 3 figures.Metal nanocomposite thin films formed by Cu nanocrystals embedded in an amorphous Al2O3 host have been synthesized by pulsed laser deposition. The mean nanocrystal diameter d was varied in the range 3.0 ± 0.6 to 6 ± 1 nm. The linear and nonlinear optical properties of the films were studied in the vicinity of the surface plasmon resonance and the size dependence of the third-order nonlinear optical susceptibility of the metal nanocrystals has been determined. The observed dependence (1/d3) indicates that in the studied diameter interval, the nonlinear response is due to quantum confinement effects in which the major contribution is associated with electronic intraband transitions.This work has been partially supported by CICYT (Spain) under TIC 96-0467 project and by the EU under BRPR-CT98-0616 project. We acknowledge Dr. I. Vickridge (University of Paris VI et VII, France) for his assistance with RBS techniques.Peer reviewe

Segregation and trapping of erbium during silicon molecular beam epitaxy

3 pages, 4 figures.Erbium surface segregation is observed during growth of Er-doped Si by molecular beam epitaxy on Si(100) at 600 °C. Once a critical Er surface areal density of 2 × 1014 Er/cm2 is reached, enhanced Er trapping is observed, possibly due to the formation of silicide precipitates. Er segregation on Si(100) is fully avoided when growth is performed in an oxygen background pressure of ~ 10 – 10 mbar, due to the formation of Er-O complexes. No Er segregation is observed on Si(111), which is attributed to the formation of epitaxial Er3Si5 precipitates.This work is part of the research program of FOM and was made possible by financial support from NWO, STW, and IOP Electro-Optics. R. Serna acknowledges financial support from CSIC, Spain.Peer reviewe