Near-field microscopy with a scanning nitrogen-vacancy color center in a diamond nanocrystal: A brief review

We review our recent developments of near-field scanning optical microscopy (NSOM) that uses an active tip made of a single fluorescent nanodiamond (ND) grafted onto the apex of a substrate fiber tip. The ND hosting a limited number of nitrogen-vacancy (NV) color centers, such a tip is a scanning quantum source of light. The method for preparing the ND-based tips and their basic properties are summarized. Then we discuss theoretically the concept of spatial resolution that is achievable in this special NSOM configuration and find it to be only limited by the scan height over the imaged system, in contrast with the standard aperture-tip NSOM whose resolution depends critically on both the scan height and aperture diameter. Finally, we describe a scheme we have introduced recently for high-resolution imaging of nanoplasmonic structures with ND-based tips that is capable of approaching the ultimate resolution anticipated by theory.Comment: AD, AC, OM, MB and SH wish to dedicate this brief review article to their co-author and colleague Yannick Sonnefraud who passed away in September 2014. Yannick initiated this research in 200

Boundary effects in finite size plasmonic crystals: Focusing and routing of plasmonic beams for optical communications

Plasmonic crystals, which consist of periodic arrangements of surface features at a metal-dielectric interface, allow the manipulation of optical information in the form of surface plasmon polaritons. Here we investigate the excitation and propagation of plasmonic beams in and around finite size plasmonic crystals at telecom wavelengths, highlighting the effects of the crystal boundary shape and illumination conditions. Significant differences in broad plasmonic beam generation by crystals of different shapes are demonstrated, while for narrow beams, the propagation onto the smooth metal film is less sensitive to the crystal boundary shape. We show that by controlling the boundary shape, the size and the excitation beam parameters, directional control of propagating plasmonic modes and associated beam parameters such as angular beam splitting, focusing power and beam width can be efficiently achieved. This provides a promising route for robust and alignment-independent integration of plasmonic crystals with optical communication components

Fluorescent oxide nanoparticles adapted to active tips for near-field optics

We present a new kind of fluorescent oxide nanoparticles with properties well suited to active-tip based near-field optics. These particles with an average diameter in the range 5-10 nm are produced by Low Energy Cluster Beam Deposition (LECBD) from a YAG:Ce3+ target. They are studied by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), classical photoluminescence, cathodoluminescence and near-field scanning optical microscopy (NSOM). Particles of extreme photo-stability as small as 10 nm in size are observed. These emitters are validated as building blocks of active NSOM tips by coating a standard optical tip with a 10 nm thick layer of YAG:Ce3+ particles directly in the LECBD reactor and by subsequently performing NSOM imaging of test surfaces.Comment: Changes made following Referee's comments; added references; one added figure. See story on this article at: http://nanotechweb.org/cws/article/tech/3606

Engineering Tunable Plasmonic Nanostructures To Enhance Upconversion Luminescence

Plasmonic nanostructures, which can confine and manipulate light below the diffraction limit, are becoming increasingly important in many areas of optical physics and devices. One of the areas that can greatly benefit from surface-plasmon mediated confinement of optical fields is the enhancement of emission in low quantum yield materials. The resonant wavelength for plasmonic structures used for emission enhancement is either the excitation or emission wavelengths of the luminescent material. Therefore, a key component in designing plasmonic structures used in luminescent enhancement applications is the ability to engineer and tune plasmonic building blocks to create structures resonant at the desired wavelength. In this thesis, we have used two approaches to build tunable structures for luminescent enhancement: 1) using already synthesized metallic nanocrystals resonant at the desired wavelengths as building blocks, we designed structures that would result in maximum emission enhancement. 2) Designing arrays of plasmonic nanostructures with the help of simulation software to be resonant at the desired wavelength and then fabricating them with top-down nanoscale fabrication techniques. In either approach, the resulting large area structures were macroscopically studied by steady state and time-resolved photoluminescence measurements to quantify the plasmonic effects on enhancement. We were able to achieve high enhancement factors in almost all of the structures and designs. Furthermore, we were able to identify and study various effects that play a role in plasmonic enhancement processes

Nanowire-Intensified MEF in Hybrid Polymer-Plasmonic Electrospun Filaments

Hybrid polymer-plasmonic nanostructures might combine high enhancement of localized fields from metal nanoparticles with light confinement and long-range transport in subwavelength dielectric structures. Here we report on the complex behavior of fluorophores coupling to Au nanoparticles within polymer nanowires, which features localized metal-enhanced fluorescence (MEF) with unique characteristics compared to conventional structures. The intensification effect when the particle is placed in the organic filaments is remarkably higher with respect to thin films of comparable thickness, thus highlighting a specific, nanowire-related enhancement of MEF effects. A dependence on the confinement volume in the dielectric nanowire is also evidenced, with MEF significantly increasing upon reducing the wire diameter. These findings are rationalized by finite element simulations, predicting a position-dependent enhancement of the quantum yield of fluorophores embedded in the fibers. Calculation of the ensemble-averaged fluorescence enhancement unveils the possibility of strongly enhancing the overall emission intensity for structures with size twice the diameter of the embedded metal particles. These new, hybrid fluorescent systems with localized enhanced emission, as well as the general Nanowire-Intensified MEF effect associated to them, are highly relevant for developing nanoscale light-emitting devices with high efficiency and inter-coupled through nanofiber networks, highly sensitive optical sensors, and novel laser architectures.Comment: 29 pages, 12 figures, Small (2018

Nanoantennas for visible and infrared radiation

Nanoantennas for visible and infrared radiation can strongly enhance the interaction of light with nanoscale matter by their ability to efficiently link propagating and spatially localized optical fields. This ability unlocks an enormous potential for applications ranging from nanoscale optical microscopy and spectroscopy over solar energy conversion, integrated optical nanocircuitry, opto-electronics and density-ofstates engineering to ultra-sensing as well as enhancement of optical nonlinearities. Here we review the current understanding of optical antennas based on the background of both well-developed radiowave antenna engineering and the emerging field of plasmonics. In particular, we address the plasmonic behavior that emerges due to the very high optical frequencies involved and the limitations in the choice of antenna materials and geometrical parameters imposed by nanofabrication. Finally, we give a brief account of the current status of the field and the major established and emerging lines of investigation in this vivid area of research.Comment: Review article with 76 pages, 21 figure

Light matter interaction in hybrid plasmonic/photonic nanogaps

The aim of this thesis is to study the processes of light matter interaction at the nanoscale in hybrid nano gaps that are made from both metals and dielectrics. This approach enables the possibility to use both the optical properties of a dielectric, such as low losses and high-quality factor, with the small mode volume typical of a metal. High quality factor and small modal volume together make a high Purcell factor, which is the enhancement of the spontaneous emission rate due to the surrounding cavity environment. Both the size and the time scales involved in this study range in the nanometre and nano second, respectively.The architecture used for the study of the hybrid nano gaps consists of a substrate containing a Distributed Bragg Reflector (DBR) and a 10 nm thick emitting layer. On top of this layer lies a small concentration of gold nano spheres. Two different emitting dipole orientations have been studied, vertical and horizontal. The vertical orientation is parallel to the nano gap dipole moment while in the case of the horizontal orientation, it is perpendicular to it. These two emitting dipole orientations have been used to perform two different experiments exploiting different properties of the DBR. DBRs have been used for two purposes, reflectors and 1-d photonic crystals. These two applications are used to investigate different properties of the hybrid nano gaps. Indeed, DBRs have a highly reflective spectral region called photonic stopband, outside of it there are some highly localised reflectivity minima called Bragg modes.The first hybrid nano gap application explored is the directional nano antenna. In this approach the DBR is used as a reflector and the nano cavity is used to control the direction of the emission. Because of the Fermi golden rule, the dipole moment of the emitter and the nano gap must be parallel to achieve the largest coupling possible. The dipole orientation parallel to the cavity dipole moment is called vertical and it has been probed using the emitter Lumogen Red. This dye exhibits a high quantum yield, low photo bleaching and a good vertical orientability when spun on a surface in form of a film. In this configuration, the light is emitted by the layer at very large angle compared to the surface, roughly 60 degrees. The system can measure up to 64 degrees since the objective numerical aperture is 0.9/1. In this nanogap the nanoparticle acts like a directional antenna and 65% of the emitted light gets redirected at angles not accessible by emitters on their own. Spectrally dispersed k-space imaging has been used to perform such a measurement. This study has demonstrated how the light emission cone is a function of the nano particle size. The narrowest emission cone observed was found to occur for a 500 nm diameter particle size. This configuration showed an enhancement emission factor ranging from 30 up to 60.The second nano gap configuration used the DBR as photonic crystal to achieve localised Tamm plasmon generation. These results are described in chapter 6. The minimum in the reflectivity spectrum of the DBR is called the 1st Bragg mode. In this mode the impinging radiation can penetrate inside the stack and not propagate outside. Tamm states are surface states that can be excited at the interface between a DBR stack and a metal film. Super Tamm are more localised Tamm states that can be excited only by replacing the metallic film with a finite structure such as a micro disk. In this thesis, a new form of localised super Tamm states has been excited. This novelty state has been named Isolated super Tamm modes. The disk has been replaced with a gold nano sphere. Isolated super Tamm modes have been proved to have an intermediate spectral position between the 1st Bragg mode and the super Tamm