Numerous efforts have been recently undertaken towards the development of rectifying devices operating at high frequencies especially dedicated to light harvesting and photo detection applications. To this end various rectification strategies have been implemented, such as laser-induced STM tunneling, metal-insulator-metal (MIM) travelling wave diodes, plasmonic nanogap optical antennas, antenna-diode coupled planar MIM, and MIM point-contact sharp-tip or whisker diodes. However, developing high frequency rectifying antennas (rectennas) remains a major technological challenge, as only recent progresses enabled the fabrication of efficient tunable nano-antennas at near infrared and visible frequencies. Here we report on a new type of rectenna based on plasmonic carrier generation. The proposed rectifying structure consists of a broadly resonant gold conical nano-tip antenna in contact with a metal-oxide/metal sample surface, forming a point-contact tunneling diode. The nano-sized antenna apex, designed to maximize the Surface Plasmon Polaritons (SPPs) damping, allows for an efficient power conversion from the light field into excited charges above the Fermi level, the latter ones collectable from the point-contact location through an electronic tunneling process. We demonstrated rectification operation at 280 THz with a power conversion efficiency one order of magnitude higher than the state-of-the-art which we attribute to efficient plasmonic carrier generation and collection.
To enhance the Raman scattering efficiency of light by molecules, various techniques relying on either stimulated or surface enhanced Raman scattering (SERS) have been developed. But they are either limited by the poor control of the scattered light, narrow bandwidth of the resonance frequency, or restricted area of field enhancement. Here we present a unique waveguide approach to achieve broadband enhanced Raman scattering of molecules with precisely controlled propagation direction. We demonstrated 99% of the Raman photons can be coupled into the waveguide. The near unity couple efficiency is due to the largely enhanced spontaneous Raman scattering rate in waveguide.
We report recent studies of integrated plasmonic devices for nano-focusing and nano-defocusing, capable of drastically enhancing interactions between light and matter. Our approach is based on gap plasmonic waveguides, which enable efficient photonic-to-plasmonic mode conversion. Here, we demonstrate metallic components that focus light to a 10 nm scale and explore how linear and nonlinear processes are enhanced. We will initially discuss how to achieve low-loss conversion from photonic-like states to plasmonic gap modes. We will then focus on new studies that evaluate the enhancement of nonlinear frequency mixing, spontaneous emission and Raman scattering, all occurring at the nanofocus in these devices.
The combination of the AFM technique and the sphere-mediated microscopy (SMM) opens a new opportunity to the Atomic Force Microscopy (AFM). With the help of a tipless AFM cantilever is possible to place and scan a microspheres (MS) close to the surface. From the optical point of view, when a MS is close to a surface act as high NA nanolenses whose optical characteristics define the maximum attainable resolution.
By using the stages of a standard AFM, the microsphere can easily scan over the surface. The deflection of the cantilever could still be used to control the distance between microsphere and sample. With an optical detector and a low N.A. objective is so possible to obtain optical high resolution maps synchronized with the topography ones.
Despite microspheres do not to break the Abbe diffraction limit or produce super-resolution, they can be used as portable and cheap optical elements that can enhance the effective NA of a system. A systematic optical characterization of the system will be presented in parallel with some preliminary results of forthcoming applications of SMM in nanolithography, micro or nano Raman spectroscopy and Near Filed Optical Microscopy (SNOM).
Here, we propose easy and robust strategies for the versatile integration 2D material flakes on plasmonic nanoholes by means of site selective deposition of MoS2. The methods can be applied both to simple metallic flat nanostructures and to complex 3D metallic structures comprising nanoholes. The deposition methods allow the decoration of large ordered arrays of plasmonic structures with single or few layers of MoS2. We show that the plasmonic field generated by the nanohole can interact significantly with the 2D layer, thus representing an ideal system for hybrid 2DMaterial/ Plasmonic investigation. The controlled/ordered integration of 2D materials on plasmonic nanostructures opens a pathway towards new investigation of the following: enhanced light emission; strong coupling from plasmonic hybrid structures; hot electron generation; and sensors in general based on 2D materials.
Nanoporous gold is a very promising material platform for several plasmonic applications. Nanoporous gold can be
formed by dealloying Au–Ag alloys, previously grown by means of Ag-Au co-sputtering. The optical response is
completely determined by the nanostructured film features, that only depend on the initial alloy composition. It has been
extensively used as SERS substrate both as thin film and nanofabricated fancy designs. Here we explore the potential
application of nanoporous gold as SERS substrate as it is coupled and decorated with Ag nanoparticles. Significant
enhancement has been observed in comparison with bare nanoporous film.
Surface plasmon waves carry an intrinsic transverse spin angular momentum, which is locked to their propagation direction. On the other hand, helical plasmonic distributions may also carry an orbital angular momentum that is linked to the field topology. Apparently, when such a singular plasmonic mode propagates on a surface or is guided on a conic structure its helicity and the transverse spin can be coupled to the far-field spin and orbital angular momentum. We discuss the mechaism of such a coupling by using 2D and 3D guiding architetures. We analyze the coupling efficiency in each case as well as the intriguing spin-locking phenomenon occurring in our system. Finally we experimentally demonstrate the efficient beaming of a single-handed mode decorated by a desired orbital angular using accurately fabricated nanostructures.
In this work we show that the fabrication method introduced by De Angelis et al.1 is highly versatile and allows to
produce three-dimensional (3D) hollow plasmonic nanostructures with a precisely tunable shape and with large scale
capabilities. The fabrication process is comprehensively explained and some structure examples are introduced in order
to show the versatility of the method. The resulting plasmonic nanoantennas are characterized by Raman spectroscopy in
order to evaluate their plasmonic performance in respect to their features.
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