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

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

Active analog tuning of the phase of light in the visible regime by bismuth-based metamaterials

Active and analog tuning of the phase of light is needed to boost the switching performance of photonic devices. However, demonstrations of this type of tuning in the pivotal visible spectral region are still scarce. Herein we report active analog tuning of the phase of visible light reflected by a bismuth-based metamaterial, enabled by a reversible solid-liquid transition. This metamaterial, fabricated by a lithography-free approach, consists of two-dimensional assemblies of polydisperse plasmonic bismuth nanostructures embedded in a refractory and transparent aluminum oxide matrix. Analog tuning of the phase is achieved by controlled heating of the metamaterial to melt a fraction of the nanostructures. A maximum tuning of 320 deg (1.8pi) is observed upon complete melting of the nanostructures at 230 degrees Celsius. This tuning is reversible by cooling to 25 degrees Celsius. In addition, it presents a wide hysteretic character due to liquid bismuth undercooling. This enables the phase achieved by this analog approach to remain stable over a broad temperature range upon cooling and until re-solidification occurs around 100 degrees Celsius. Therefore, bismuth-based metamaterials are appealing for applications including optical data storage with enhanced information density or bistable photonic switching with a tunable "on" state

An all optical nanometric switch

[Poster of]: ¿SINFOTONes en el Año de la Luz?: Reunión de Jóvenes Investigadores SINFOTON: 1ª Feria de Otoño 2015, 23 de Octubre.Current requirements on information transfer, computation and storage demand new counterparts to the electronic components. In particular, full-optical components are currently explored. Different phenomena observed in the interaction of light with nanoparticles allow the development of this concept. In this work, we explored the possibility of creating a full optical nanometric switch to be the simplest part of the future family of components in optical nanocircuits. In 80's, Kerker et al [1] showed that the scattering of sub-wavelength particles can be directed under certain conditions. In fact, a nanoparticle can accomplish a zero backscattering (ZB) or minimum forward scattering (MF) depending on the relationship between its material, size and incident wavelength. We have demonstrated that the Kerker conditions can be found in the visible range for several usual semiconductor materials, as Silicon, Germanium, TiO2, GaAs, etc [2]. Playing with sizes, it is possible to obtain nanoparticles satisfying either the ZB or the MF at the same wavelength. Then, we have proposed a dimer of silicon nanoparticles [3] presenting such combination of directional scattering in the visible range. This set can produce either a maximum or a minimum of the scattered field in the area between the nanoparticles. As Kerkers' conditions are very dependent on the wavelength, we propose that a modulation of the incident wavelength can be used as switching parameter (Fig. 1). We have searched the optimum parameters of the dimer setup, in wavelength, distance between particles and their sizes, in order to make easier the fabrication for the Research Community to get an experimental Proof of Technology of these simple designs.This work has been supported by Ministerio de Economía y Competitividad of Spain (grants no. TEC2013-47342-C2-2-R, TEC2012-38901-C02-01 and no.TEC2013-50138-EXP) and the R&D Program SINFOTON S2013/MIT-2790 of the Comunidad de Madrid.Publicad

Strain-Tuning of the Optical Properties of Semiconductor Nanomaterials by Integration onto Piezoelectric Actuators

The tailoring of the physical properties of semiconductor nanomaterials by strain has been gaining increasing attention over the last years for a wide range of applications such as electronics, optoelectronics and photonics. The ability to introduce deliberate strain fields with controlled magnitude and in a reversible manner is essential for fundamental studies of novel materials and may lead to the realization of advanced multi-functional devices. A prominent approach consists in the integration of active nanomaterials, in thin epitaxial films or embedded within carrier nanomembranes, onto Pb(Mg1/3Nb2/3)O3-PbTiO3-based piezoelectric actuators, which convert electrical signals into mechanical deformation (strain). In this review, we mainly focus on recent advances in strain-tunable properties of self-assembled InAs quantum dots embedded in semiconductor nanomembranes and photonic structures. Additionally, recent works on other nanomaterials like rare-earth and metal-ion doped thin films, graphene and MoS2 or WSe2 semiconductor two-dimensional materials are also reviewed. For the sake of completeness, a comprehensive comparison between different procedures employed throughout the literature to fabricate such hybrid piezoelectric-semiconductor devices is presented. Very recently, a novel class of micro-machined piezoelectric actuators have been demonstrated for a full control of in-plane stress fields in nanomembranes, which enables producing energy-tunable sources of polarization-entangled photons in arbitrary quantum dots. Future research directions and prospects are discussed.Comment: review manuscript, 78 pages, 27 figure

Copernicus Ocean State Report, issue 6

The 6th issue of the Copernicus OSR incorporates a large range of topics for the blue, white and green ocean for all European regional seas, and the global ocean over 1993–2020 with a special focus on 2020

Bismuth-based Metamaterials: Fundamentals and Applications

Bismuth shows outstanding optical properties, including a metal-like response in the ultraviolet-visible and a dielectric character with giant refractive index in the infrared. We explain how this enables bismuth-based metamaterials to show a remarkable optical response over these spectral regions. Such response can be tuned in a static way by suitable metamaterial design and in a dynamic way by harnessing the solid-liquid transition of bismuth. We discuss the application of such metamaterials to information technology, energy harvesting and sensing