104 research outputs found
Optical emission near a high-impedance mirror
Solid state light emitters rely on metallic contacts with high
sheet-conductivity for effective charge injection. Unfortunately, such contacts
also support surface plasmon polariton (SPP) excitations that dissipate optical
energy into the metal and limit the external quantum efficiency. Here, inspired
by the concept of radio-frequency (RF) high-impedance surfaces and their use in
conformal antennas we illustrate how electrodes can be nanopatterned to
simultaneously provide a high DC electrical conductivity and high-impedance at
optical frequencies. Such electrodes do not support SPPs across the visible
spectrum and greatly suppress dissipative losses while facilitating a desirable
Lambertian emission profile. We verify this concept by studying the emission
enhancement and photoluminescence lifetime for a dye emitter layer deposited on
the electrodes
Strong antenna-enhanced fluorescence of a single light-harvesting complex shows photon antibunching
The nature of the highly efficient energy transfer in photosynthetic light-harvesting complexes is a subject of intense research. Unfortunately, the low fluorescence efficiency and limited photostability hampers the study of individual light-harvesting complexes at ambient conditions. Here we demonstrate an over 500-fold fluorescence enhancement of light-harvesting complex 2 (LH2) at the single-molecule level by coupling to a gold nanoantenna. The resonant antenna produces an excitation enhancement of circa 100 times and a fluorescence lifetime shortening to ~\n20 ps. The radiative rate enhancement results in a 5.5-fold-improved fluorescence quantum efficiency. Exploiting the unique brightness, we have recorded the first photon antibunching of a single light-harvesting complex under ambient conditions, showing that the 27 bacteriochlorophylls coordinated by LH2 act as a non-classical single-photon emitter. The presented bright antenna-enhanced LH2 emission is a highly promising system to study energy transfer and the role of quantum coherence at the level of single complexes
Contrast in spin-valley polarization due to competing indirect transitions in few-layer WS and WSe
Controlling the momentum of carriers in semiconductors, known as valley
polarization, is a new resource for optoelectronics and information
technologies. Materials exhibiting high polarization are needed for
valley-based devices. Few-layer WS shows a remarkable spin-valley
polarization above 90%, even at room temperature. In stark contrast,
polarization is absent for few-layer WSe despite the expected material
similarities. Here, we explain the origin of valley polarization in both
materials due to the interplay between two indirect optical transitions. We
show that the relative energy minima at the - and K-valleys in the
conduction band determine the spin-valley polarization of the K-K transition.
Polarization appears as the energy of the K-valley rises above the
-valley as a function of temperature and number of layers. Our results
advance the understanding of the high spin-valley polarization in WS. This
insight will impact the design of both passive and tunable valleytronic devices
operating at room temperature.Comment: 22 pages, 6 figures, 2 table
Enhanced light emission by magnetic and electric resonances in dielectric metasurfaces
We demonstrate an enhanced emission of high quantum yield molecules coupled
to dielectric metasurfaces formed by periodic arrays of polycrystalline silicon
nanoparticles. Radiative coupling of the nanoparticles, mediated by in-plane
diffraction, leads to the formation of collective Mie scattering resonances or
Mie surface lattice resonances (M-SLRs), with remarkable narrow line widths.
These narrow line widths and the intrinsic electric and magnetic dipole moments
of the individual Si nanoparticles allow to resolve electric and magnetic
M-SLRs. Incidence angle- and polarization-dependent extinction measurements and
high-accuracy surface integral simulations show unambiguously that magnetic
M-SLRs arise from in- and out-of-plane magnetic dipoles, while electric M-SLRs
are due to in-plane electric dipoles. Pronounced changes in the emission
spectrum of the molecules are observed, with almost a 20-fold enhancement of
the emission in defined directions of molecules coupled to electric M-SLRs, and
a 5-fold enhancement of the emission of molecules coupled to magnetic M-SLRs.
These measurements demonstrate the potential of dielectric metasurfaces for
emission control and enhancement, and open new opportunities to induce
asymmetric scattering and emission using collective electric and magnetic
resonances.Comment: 27 pages with 9 figure
Collective Mie Exciton-Polaritons in an Atomically Thin Semiconductor
Optically induced Mie resonances in dielectric nanoantennas feature low
dissipative losses and large resonant enhancement of both electric and magnetic
fields. They offer an alternative platform to plasmonic resonances to study
light-matter interactions from the weak to the strong coupling regimes. Here,
we experimentally demonstrate the strong coupling of bright excitons in
monolayer WS with Mie surface lattice resonances (Mie-SLRs). We resolve
both electric and magnetic Mie-SLRs of a Si nanoparticle array in angular
dispersion measurements. At the zero detuning condition, the dispersion of
electric Mie-SLRs (e-SLRs) exhibits a clear anti-crossing and a Rabi-splitting
of 32 meV between the upper and lower polariton bands. The magnetic Mie-SLRs
(m-SLRs) nearly cross the energy band of excitons. These results suggest that
the field of m-SLRs is dominated by out-of-plane components that do not
efficiently couple with the in-plane excitonic dipoles of the monolayer WS.
In contrast, e-SLRs in dielectric nanoparticle arrays with relatively high
quality factors (Q 120) facilitate the formation of collective Mie
exciton-polaritons, and may allow the development of novel polaritonic devices
which can tailor the optoelectronic properties of atomically thin
two-dimensional semiconductors.Comment: 27 pages, 7 figure
Silicon Mie Resonators for Highly Directional Light Emission from monolayer MoS2
Controlling light emission from quantum emitters has important applications
ranging from solid-state lighting and displays to nanoscale single-photon
sources. Optical antennas have emerged as promising tools to achieve such
control right at the location of the emitter, without the need for bulky,
external optics. Semiconductor nanoantennas are particularly practical for this
purpose because simple geometries, such as wires and spheres, support multiple,
degenerate optical resonances. Here, we start by modifying Mie scattering
theory developed for plane wave illumination to describe scattering of dipole
emission. We then use this theory and experiments to demonstrate several
pathways to achieve control over the directionality, polarization state, and
spectral emission that rely on a coherent coupling of an emitting dipole to
optical resonances of a Si nanowire. A forward-to-backward ratio of 20 was
demonstrated for the electric dipole emission at 680 nm from a monolayer MoS2
by optically coupling it to a Si nanowire
Broadband Linear-Dichroic Photodetector in a Black Phosphorus Vertical p-n Junction
The ability to detect light over a broad spectral range is central for
practical optoelectronic applications, and has been successfully demonstrated
with photodetectors of two-dimensional layered crystals such as graphene and
MoS2. However, polarization sensitivity within such a photodetector remains
elusive. Here we demonstrate a linear-dichroic broadband photodetector with
layered black phosphorus transistors, using the strong intrinsic linear
dichroism arising from the in-plane optical anisotropy with respect to the
atom-buckled direction, which is polarization sensitive over a broad bandwidth
from 400 nm to 3750 nm. Especially, a perpendicular build-in electric field
induced by gating in black phosphorus transistors can spatially separate the
photo-generated electrons and holes in the channel, effectively reducing their
recombination rate, and thus enhancing the efficiency and performance for
linear dichroism photodetection. This provides new functionality using
anisotropic layered black phosphorus, thereby enabling novel optical and
optoelectronic device applications.Comment: 18 pages, 5 figures in Nature Nanotechnology 201
Seroprevalencia de leptospirosis en cabras (Capra hircus) en dos áreas de la región Cuyana de la Argentina
La Leptospirosis es una infección bacteriana causada por diferentes serovares de Leptospira patógenas que afecta a diversas especies de animales y accidentamente al hombre. Es una de las enfermedades zoonóticas reemergentes de mayor prevalencia, con una amplia distribución a nivel global, compromete la salud humana y animal, alterando la producción animal y la economÃa de las regiones afectadas. La transmisión de la infección del animal al animal y al hombre ocurre a través del contacto con lÃquidos, tejidos y principalmente orina de animales infectados y, más comúnmente, por contacto con un ambiente contaminado. Algunos autores señalan que, el ganado caprino es menos susceptible que el bovino frente a la leptospirosis y que aún cuando la infección puede ser asintomática podrÃa presentarse de forma aguda. El objetivo del presente estudio fue investigar la seroprevalencia de leptospirosis en cabras en dos áreas cuyana de la capital de la provincia de San Luis y en Jáchal provincia de San Juan.Facultad de Ciencias Veterinaria
- …