R. Proietti Zaccaria

Multi-scheme approach for efficient surface plasmon polariton generation in metallic conical tips on AFM-based cantilevers

We report on the possibility of realizing adiabatic surface plasmon polaritons compression on metallic conical tips built-in on AFM cantilevers by means of different approaches. The problem is faced considering the role of the source, when linear and radial polarizations are assumed, associated to different fabrication schemes. Nano-patterned devices properly combined with metallic conical tips can affect the adiabatic characteristic of the surface electric field. The results are analyzed in terms of tradeoff between fabrication difficulties and device performances. Suggestions on the best possible scheme are provided.

Plasmonic Moon: A Fano-Like Approach for Squeezing the Magnetic Field in the Infrared.

Outstanding results have been achieved in the localization of optical electric fields via ultrasmall plasmonic cavities, paving the way to the subdiffractive confinement of local electromagnetic fields. However, due to the intrinsic constraints related to conventional architectures, no comparable squeezing factors have been managed yet for the magnetic counterpart of radiation, practically hindering the detection and manipulation of magneto-optical effects at the nanoscale. Here, we observe a strong magnetic field nanofocusing in the infrared, promoted by the induction of a coil-type Fano resonance. By triggering the coil current via a quadrupole-like plasmonic mode, we straightforwardly boost the enhancement of the infrared magnetic field and perform its efficient squeezing in localized nanovolumes.

Stacked optical antennas for plasmon propagation in a 5 nm- confined cavity

The sub-wavelength concentration and propagation of electromagnetic energy are two complementary aspects of plasmonics that are not necessarily co-present in a single nanosystem. Here we exploit the strong nanofocusing properties of stacked optical antennas in order to highly concentrate the electromagnetic energy into a 5 nm metal-insulator-metal (MIM) cavity and convert free radiation into guided modes. The proposed nano-architecture combines the concentration properties of optical nanoantennas with the propagation capability of MIM systems, paving the way to highly miniaturized on-chip plasmonic waveguiding.

Dark and bright modes manipulation for plasmon-triggered photonic devices

In the last decade, several efforts have been spent in the study of near-field coupled systems, in order to induce hybridization of plasmonic modes. Within this context, particular attention has been recently paid on the possibility to couple conventional bright and dark modes. As a result of such phenomenon, a Fano resonance appears as a characteristic sharp dip in the scattering spectra. Here we show how, gradually coupling a single rod-like nanostructure to an aligned nanoantenna dimer, it is possible to induce the near-field activation of an anti-bonding dark mode. The high polarization sensitivity presented by the far-field response of T-shape trimer, combined with the sharp Fano resonance sustained by this plasmonic device, opens interesting perspectives towards a new era of photonic devices.

Plasmonics and Super-Hydrophobicity: A New Class of Nano-Bio-Devices

Early detection of diseases has great importance in terms of success of the disease treatment. In fact, it has a profound positive influence on the response provided by the patient, leading to shorter and less invasive treatment regimes. We consider here the Raman detection of low (atto-molar) concentrates of molecules by applying nanofabrication techniques in the fabrication of plasmonic devices fulfilling the requirement of superhydrophobicity. Plasmonic resonances will have the effect of substantially increasing the local electric field around the fabricated nano-device which, in turn, will positively affect the Raman signal. Similarly, the superhydrophobicity will play the crucial role in localizing the few molecules of the analyte around the plasmonic device, therefore allowing their detection in a manner otherwise impossible in diffusion-based devices. We will theoretically explain the concept of superhydrophobicity by providing also a roadmap for defining the optimal superhydrophobic device, then we will introduce the fabrication process to realize such a device and, finally, we will provide the Raman counting of a series of analytes together with electromagnetic simulations illustrating the role of the electric field in the formation of the Raman signal.

The magic of nanoplasmonics: from superhydrophobic and 3D suspended devices for SERS/TERS-like applications to hot-electrons based nanoscopy

The ability to confine light in small volumes, associated to low background signals, is an important technological achievement for a number of disciplines such as biology or electronics. In fact, decoupling the source position from the sample area allows an unprecedented sensitivity which can be exploited in different systems. The most direct implications are however related to either Surface Enhanced Raman Scattering (SERS) or Tip Enhanced Raman Scattering (TERS). Furthermore, while the combination with super-hydrophobic patterns can overcome the typical diffusion limit of sensors, focused surface plasmons decaying into hot electrons can be exploited to study the electronic properties of the sample by means of a Schottky junction. Within this paper these techniques will be briefly described and the key role played by both surface and localized plasmons will be highlighted.

Nanoscale chemical mapping through plasmonic tips on AFM-based cantilevers

Noble metal tapered waveguides supporting plasmon-polariton modes are able to localize the optical fields at nanometer level producing a remarkable local electromagnetic field enhancement, which enables the realization of highsensitivity biochemical sensing devices. Here we report on the design, fabrication and experimental test of a novel photonic-plasmonic device that can be operated as an Atomic Force Microscopy tip and simultaneously for local probing of Raman scattering spectra. This result has made possible by recent approaches in nano-fabrication methods, which allow 3D nanostructuring of metals down to the nanoscale. The device demonstrates label-free detection capabilities on single inorganic nanoparticles and on monolayers of organic compounds in label-free conditions and native environments, allowing a topographic and chemical mapping of the materials with spatial resolution of a few nanometers.

Superhydrophobicity, plasmonics and Raman spectroscopy for few/single molecule detection down to attomolar concentration

Few/single molecule detection is of great importance in fields including biomedicine, safety and eco-pollution in relation to rare and dangerous chemicals. Superhydrophobic surfaces incorporated with the nanoplasmonic structure enable this device to overcome the diffusion limit of molecules dissolved in water with the concentration down to 10 attomolar. In this paper demonstrated the fabrication of hydrophobic surfaces using optical lithography/reactive ion etching and its application to overcome the diffusion limit. Various experiments such as contact angle measurements, SEM, fluorescence, Raman and FTIR absorption spectroscopy were performed which indicate that utilizing this device it could be possible to perform the measurements for the sample with extremely low dilution. The major application of this novel family of devices would be the early detection of tumors or other important pathologies, with incredible advances in medicine.