Tensile control of the thermal flow in plasmonic heaters realized on flexible substrates.

In this paper, we present a simple and robust numerical method capable of predicting, with high accuracy, the thermal effects occurring for different gold nanoparticle arrangements under externally applied strain. The physical system is numerically implemented in the COMSOL Multiphysics simulation platform. The photothermal response of different arrangements of gold nanoparticles, resonantly excited by linearly polarized light, is considered with the system at rest and under the action of mechanical stress. The generation of heat at the nanoscale is analyzed by considering how this is affected by the variation of the extinction cross section. We describe the peculiar conditions under which mechanically controlled gold nanoparticle arrangements can significantly increase the local temperature due to the formation of localized photothermal hot spots. The resulting systems are envisioned in applications as optomechanically tunable plasmonic heaters.

Quantum Dot Transfer from the Organic Phase to Acrylic Monomers for the Controlled Integration of Single-Photon Sources by Photopolymerization.

This paper reports on a new strategy for obtaining homogeneous dispersion of grafted quantum dots (QDs) in a photopolymer matrix and their use for the integration of single-photon sources by two-photon polymerization (TPP) with nanoscale precision. The method is based on phase transfer of QDs from organic solvents to an acrylic matrix. The detailed protocol is described, and the corresponding mechanism is investigated and revealed. The phase transfer is done by ligand exchange through the introduction of mono-2-(methacryloyloxy) ethyl succinate (MES) that replaces oleic acid (OA). Infrared (IR) measurements show the replacement of OA on the QD surface by MES after ligand exchange. This allows QDs to move from the hexane phase to the pentaerythritol triacrylate (PETA) phase. The QDs that are homogeneously dispersed in the photopolymer without any clusterization do not show any significant broadening in their photoluminescence spectra even after more than 3 years. The ability of the hybrid photopolymer to create micro- and nanostructures by two-photon polymerization is demonstrated. The homogeneity of emission from 2D and 3D microstructures is confirmed by confocal photoluminescence microscopy. The fabrication and integration of a single-photon source in a spatially controlled manner by TPP is achieved and confirmed by auto-correlation measurements.

Swarm of lightsail nanosatellites for Solar System exploration.

This paper presents a study for the realization of a space mission which employs nanosatellites driven by an external laser source impinging on an optimized lightsail, as a valuable technology to launch swarms of spacecrafts into the Solar System. Nanosatellites propelled by laser can be useful for heliosphere exploration and for planetary observation, if suitably equipped with sensors, or be adopted for the establishment of network systems when placed into specific orbits. By varying the area-to-mass ratio (i.e. the ratio between the sail area and the payload weight) and the laser power, it is possible to insert nanosatellites into different hyperbolic orbits with respect to Earth, thus reaching the target by means of controlled trajectories in a relatively short amount of time. A mission involving nanosatellites of the order of 1 kg of mass is envisioned, by describing all the on-board subsystems and satisfying all the requirements in terms of power and mass budget. Particular attention is paid to the telecommunication subsystem, which must offer all the necessary functionalities. To fabricate the lightsail, the thin films technology has been considered, by verifying the sail's thermal stability during the thrust phase. Moreover, the problem of mechanical stability of the lightsail has been tackled, showing that the distance between the ligthsail structure and the payload plays a pivotal role. Some potential applications of the proposed technology are discussed, such as the mapping of the heliospheric environment.

Stability of Film-Forming Dispersions: Affects the Morphology and Optical Properties of Polymeric Films.

Starch-based films are promising alternatives to synthetic films in food packaging. They were widely studied in terms of mechanical and optical properties. In food packaging, optical properties are of great interest because ultra violet (UV-light) protection is strictly required. Nevertheless, the characterization of film-forming dispersions was poorly addressed, especially regarding its correlation with the film produced. In this work, we characterized film-forming dispersions at different compositions of starch and carboxymethyl cellulose (CMC) by Turbiscan. This instrument is based on multiple light scattering and gives significant information about the miscibility of polymers in the dispersed phase. Indeed, it identifies the phenomena of destabilization and phase separation before their visibility to the unaided eye. This work aimed to study whether the homogeneous/inhomogeneous morphology of films could be forecast by the analysis of profiles obtained in the dispersed phase. The films produced were investigated by optical microscopy and absorbance analysis. As the CMC fraction increased, Turbiscan showed reduced phase separation. This implies better miscibility of mixture components and higher gelification degree. The related film was more homogeneous and presented higher UV absorbance. Consequently, film-forming dispersions and optical properties of films are strictly correlated and Turbiscan-based analysis is very useful to investigate the dispersion stability and predict the film quality.

Leveraging on ENZ Metamaterials to Achieve 2D and 3D Hyper-Resolution in Two-Photon Direct Laser Writing.

A novel technique is developed to improve the resolution of two-photon direct laser writing lithography. Thanks to the high collimation enabled by extraordinary εNZ (near-zero) metamaterial features, ultrathin dielectric hyper-resolute nanostructures are within reach. With respect to the standard direct laser writing approach, a size reduction of 89% and 50%, in height and width respectively, is achieved with the height of the structures adjustable between 5 and 50 nm. The retrieved 2D fabrication parameters are exploited for realizing extremely thin all-dielectric metalenses tailored through deep machine learning codes. The hyper-resolution achieved in the writing process enables the fabrication of a highly detailed dielectric 3D bas-relief (with full height of 500 nm) of Da Vinci's "Lady with an Ermine". The proof-of-concept results show intriguing cues for the current and trendsetting research scenario in anti-counterfeiting applications and ultracompact photonics, paving the way for the realization of all-dielectric and apochromatic ultrathin imaging systems.

A comprehensive optical analysis of nanoscale structures: from thin films to asymmetric nanocavities.

A simple and robust method able to evaluate and predict, with high accuracy, the optical properties of single and multi-layer nanostructures is presented. The method was implemented using a COMSOL Multiphysics simulation platform and it has been validated by four case studies with increasing numerical complexities: (i) a single thin layer (20 nm) of Ag deposited on a glass substrate; (ii) a metamaterial composed of five bi-layers of Ag/ITO (indium tin oxide), with a thickness of 20 nm each; (iii) a system based on a three-material unit cell (AZO/ITO/Ag), but without any thickness periodicity (AZO stands for Al2O3/zinc oxide); (iv) an asymmetric nanocavity (thin-ITO/Ag/thick-ITO/Ag). A thorough study of this latter configuration reveals peculiar metamaterial effects that can widen the actual scenario in nanophotonic applications. Numerical results have been compared with experimental data provided by real ellipsometric measurements performed on the above mentioned ad hoc fabricated nanostructures. The obtained agreement is excellent, suggesting this research as a valid design approach to realize multi-band metamaterials able to work in a broad spectral range.