Range Of Applications In Nanophotonics Research Articles

Hyperspectral dark-field optical microscopy correlated to atomic force microscopy for the analysis of single plasmonic nanoparticles: tutorial

Plasmonic nanostructures are actively investigated for their optical properties and for a wide range of applications in nanophotonics, biosensing, photocatalysis, hot carrier physics, and advanced cancer therapies. The localized surface plasmon resonance (LSPR) can be excited in gold or silver nanoparticles or in more complex nanostructures and gives rise to a wide range of unique optical properties. It is often critical to be able to localize individual plasmonic nanoparticles and simultaneously measure their spectrum. This is known as hyperspectral microscopy. In this tutorial, we describe and carefully explain how to achieve this goal with an optical microscope equipped with a dark-field objective and an optical spectrometer. The images and the scattering spectra of spherical gold nanoparticles with diameters of 90, 70, 50, and 25 nm are recorded. We compare them with the scattering spectra predicted with the Mie formula (LSPR peaks measured at 553, 541, 535, and 534 nm, respectively). The optical images are limited by the diffraction, and this is discussed in the framework of the Abbe equation. We also describe a strategy to easily correlate the optical images with atomic force microscope images of the samples. This allows us to precisely relate the morphology of the nanoparticles with their optical images, their color, and their optical spectrum. The case of non-spherical nanostructures, namely, dimers of nanoparticles, is also discussed. This approach allows a relatively low-cost setup and efficient characterization method that will be helpful for teachers who want to introduce their students to the wide topics of plasmonics. This will also be useful for labs seeking an affordable method to investigate the plasmonic properties of single nanostructures.

Probing hyperbolic polaritons using infrared attenuated total reflectance micro-spectroscopy

Abstract

Microcavity enhanced single photon emission from two-dimensional WSe2

Atomically flat semiconducting materials such as monolayer WSe2 hold great promise for novel optoelectronic devices. Recently, quantum light emission has been observed from bound excitons in exfoliated WSe2. As part of developing optoelectronic devices, the control of the radiative properties of such emitters is an important step. Here, we report the coupling of a bound exciton in WSe2 to open microcavities. We use a range of radii of curvature in the plano-concave cavity geometry with mode volumes in the λ3 regime, giving Purcell factors of up to 8 while increasing the photon flux five-fold. Additionally, we determine the quantum efficiency of the single photon emitter to be η=0.46±0.03. Our findings pave the way to cavity-enhanced monolayer based single photon sources for a wide range of applications in nanophotonics and quantum information technologies.

Fabrication and optical properties of assembled gold nanoparticles film on elastomeric substrate

Abstract We report an easy, scalable and low cost interfacial self-assembly approach to fabricate dense metal nanoparticle monolayer films deposited on elastomeric substrate which exhibit tunable plasmonic responses to uniaxial mechanical stretching. The nanoparticle monolayers deposited on silicon substrate by water-in-oil self-assembling were quantitatively transferred to the elastic substrate by a wet lift-up soft lithography approach. By uniaxial stretching of the resulting nanoparticle film the plasmonic resonance peak experience a blue shift proportional to the applied strain. Numerical simulations were performed on the plasmon modes of the gold nanoparticles film under mechanical stress to explain the observed behaviors. Such metal nanoparticle film can be exploited in a wide range of applications in nanophotonics including strain sensors.

Electric and Magnetic Field Enhancement with Ultralow Heat Radiation Dielectric Nanoantennas: Considerations for Surface-Enhanced Spectroscopies

Plasmonic structures are known to offer strong local enhancements of the electric field for interaction with molecules and materials in their vicinity. However, they inherently suffer from high losses and absorption, which can occur in both surface plasmon polaritons and localized plasmons in particles, on which we shall focus. An effect of those losses, and an aspect often neglected, is the local heating of the nanoparticle due to the absorption of incident radiation and the transduction into thermal energy. This increase in the nanoparticle temperature, and in turn in the surrounding medium, can directly disrupt the response of the system due to changes in the optical properties of the medium and nanoparticle itself. This is especially a problem in the spectroscopic analysis of matter, where the advantage of field enhancement due to the plasmonic effect can be obstructed (or hampered) by a local temperature increase affecting the pure electromagnetic response of the sample. Here we investigate the use of subwavelength structures made of high refractive index dielectrics with ultralow losses in the optical and near-IR regime, gallium phosphide (GaP) in this case, as a novel way to approach applications that require near- and far-field enhancement, such as surface-enhanced Raman spectroscopy, but with the peculiarity of not perturbing the response of the sample under evaluation due to local heating. In particular, we show a comparison of the near- and far-field enhancing performance of plasmonic dimers with the one obtained from similar structures made of GaP. This study opens new possibilities to overcome losses and heat generation issues associated with plasmonic nanostructures in a range of applications in nanophotonics and metamaterials.

Recent Developments in Magneto-optic Garnet-type Thin-film Materials Synthesis

Magneto-optic (MO) garnets are used in a range of applications in nanophotonics, integrated optics, communications and imaging. Bi-substituted iron garnets of different compositions are the most useful class of materials in applied magneto- optics due to their excellent MO properties (large Faraday effect) and record-high MO figure of merit among all semi- transparent dielectrics. It is highly desirable to synthesise garnets which possess simultaneously a high MO figure of merit and large uniaxial magnetic anisotropy. However, the simultaneous optimization of several material properties and parameters can be difficult in single-layer garnet thin films, and it is also challenging to prepare films with high bismuth content using physical vapor deposition technologies. To meet the current challenge of developing next-generation functional MO materials, we design, develop and demonstrate the functionality of new magnetostatically-altered all-garnet multilayer heterostructures using two different garnet materials of dissimilar anisotropy types (out-of-plane and almost-in- plane). The multilayer structures possess simultaneously a high MO figure of merit and large uniaxial magnetic anisotropy together with low coercivity, if each of the layers is optimized in composition and annealed correctly. We prepare thin-film heterostructures by sandwiching a MO garnet layer with almost in-plane magnetization in-between two MO garnet layers with out-of-plane magnetization using RF sputtering. We apply customised high-temperature oven annealing processes (optimized in temperature and process durations after running many trials) for the as-deposited (amorphous) garnet multilayers to obtain the crystalline garnet phase in every layer. These structures then possess simultaneously a high optical/MO quality and low coercivity, which is very attractive for the development of magnetic photonic crystals, sensing devices and ultra-fast switches. Based on Bi-substituted ferrite garnets grown on garnet substrates, this new and unique method for the development of new magnetic materials, enables customized magnetic properties to be attained, and can be used to develop novel types of synthetic garnet materials.