Silver nanowires with optimized silica coating as versatile plasmonic resonators

Metal nanoparticles are the most frequently used nanostructures in plasmonics. However, besides nanoparticles, metal nanowires feature several advantages for applications. Their elongation offers a larger interaction volume, their resonances can reach higher quality factors, and their mode structure provides better coupling into integrated hybrid dielectric plasmonic circuits. It is crucial though, to control the distance of the wire to a supporting substrate, to another metal layer or to active materials with sub nanometer precision. A dielectric coating can be utilized for distance control, but it must not degrade the plasmonic properties. In this paper, we introduce a controlled synthesis and coating approach for silver nanowires to fulfill these demands. We synthesize and characterize silver nanowires of around 70 amp; 8201;nm in diameter. These nanowires are coated with nm sized silica shells using a modified Stöber method to achieve a homogeneous and smooth surface quality. We use transmission electron microscopy, dark field microscopy and electron energy loss spectroscopy to study morphology and plasmonic resonances of individual nanowires and quantify the influence of the silica coating. Thorough numerical simulations support the experimental findings showing that the coating does not deteriorate the plasmonic properties and thus introduce silver nanowires as usable building blocks for integrated hybrid plasmonic system

Self Assembly of Plasmonic Nanoantenna Waveguide Structures for Subdiffractional Chiral Sensing

Spin momentum locking is a peculiar effect in thenear field of guided optical or plasmonic modes. It can beutilized to map the spinning or handedness of electromagneticfields onto the propagation direction. This motivates a methodto probe the circular dichroism of an illuminated chiral object.In this work, we demonstrate local, subdiffraction limited chiralcoupling of light and propagating surface plasmon polaritons ina self assembled system of a gold nanoantenna and a silvernanowire. A thin silica shell around the nanowire providesprecise distance control and also serves as a host forfluorescentmolecules, which indicate the direction of plasmon propaga tion. We characterize our nanoantenna amp; 8722;nanowire systems comprehensively through correlated electron microscopy, energy dispersive X ray spectroscopy, dark field, andfluorescence imaging. Three dimensional numerical simulations support theexperimentalfindings. Besides our measurement of far field polarization, we estimate sensing capabilities and derive not only asensitivity of 1 mdeg for the ellipticity of the lightfield, but alsofind 103deg cm2 dmol for the circular dichroism of an analytelocally introduced in the hot spot of the antenna amp; 8722;wire system. Thorough modeling of a prototypical design predicts on chipsensing of chiral analytes. This introduces our system as an ultracompact sensor for chiral response far below the diffractio

Micro-concave waveguide antenna for high photon extraction from nitrogen vacancy centers in nanodiamond

The negatively charged nitrogen-vacancy colour center (NV(-) center) in nanodiamond is an excellent single photon source due to its stable photon generation in ambient conditions, optically addressable nuclear spin state, high quantum yield and its availability in nanometer sized crystals. In order to make practical devices using nanodiamond, highly efficient and directional emission of single photons in well-defined modes, either collimated into free space or waveguides are essential. This is a Herculean task as the photoluminescence of the NV centers is associated with two orthogonal dipoles arranged in a plane perpendicular to the NV defect symmetry axis. Here, we report on a micro-concave waveguide antenna design, which can effectively direct single photons from any emitter into either free space or into waveguides in a narrow cone angle with more than 80% collection efficiency irrespective of the dipole orientation. The device also enhances the spontaneous emission rate which further increases the number of photons available for collection. The waveguide antenna has potential applications in quantum cryptography, quantum computation, spectroscopy and metrology

Direct measurement of quantum efficiency of single-photon emitters in hexagonal boron nitride

© 2019 Optical Society of America. Single-photon emitters (SPEs) in two-dimensional materials are promising candidates for the future generation of quantum photonic technologies. In this work, we experimentally determine the quantum efficiency (QE) of SPEs in few-layer hexagonal boron nitride (h-BN). We employ a metal hemisphere that is attached to the tip of an atomic force microscope to directly measure the lifetime variation of the SPEs as the tip approaches the h-BN. This technique enables nondestructive, yet direct and absolute measurement of the QE of SPEs. We find that the emitters exhibit very high QEs approaching (87 ± 7)% at wavelengths of ≈580 nm, which is among the highest QEs recorded for a solid-state SPE

Photostable Molecules on Chip: Integrated Sources of Nonclassical Light

The on-chip integration of quantum light sources and nonlinear elements constitutes a major step toward scalable photon-based quantum information processing and communication. In this work we demonstrate the potential of a hybrid technology that combines organic-molecule-based quantum emitters and dielectric chips consisting of ridge waveguides and grating far-field couplers. In particular, dibenzoterrylene molecules in thin anthracene crystals are used as single-photon sources, exhibiting long-term photostability, easy fabrication methods, almost unitary quantum yield, and lifetime-limited emission at cryogenic temperatures. We couple such single emitters to silicon nitride ridge waveguides, showing a coupling efficiency of up to 42 ± 2% over both propagation directions. Our results open a novel path toward a fully integrated and scalable photon-processing platform