Materials that can change their properties upon exposure to environmental stimuli are gaining an increasing interest, because they enable novel opportunities for the design and the realization of reconfigurable and adaptive objects and devices. The capabilities of these devices can be further enhanced by nanofabrication technologies, which allows complex and miniaturized architectures to be realized. Examples of complex nanostructured materials are polymer nanofibers, which have already found application in many fields including responsive systems [1-4]. In this presentation we will review our recent works aimed at realizing polymer nanofibers whose shape and function can be varied and controlled by external inputs in order to achieve intelligent complex materials. Electrospinning is here exploited for the nanofiber realization. Relevant applications in this framework include optical switching and logics. The research leading to these results has received funding from the Italian Minister of University and Research through the PRIN 201795SBA3, 2017PHRM8X and 20173L7W8K projects.
In this work we will review our activities on the realization of systems and networks of light-emitting nanofibers with complex topologies. The optical gain and lasing emission properties can be controlled in such systems through the concentration of the chromophores and the optical pumping features. The research leading to these results has received funding from the Italian Minister of University and Research through the PRIN 201795SBA3 and 2017PHRM8X projects.
Nanofibers based on polymers are widely used in different fields, including cosmetics, electronics, sensing, medicine, phtonics, energy and filtration. These materials have a 1D character and exhibit tailorable physico-chemical properties which enables their use in multifunctional devices. They are characterized by properties such as, high surface to volume ratio, large area coverage and low-cost manufacturing which makes their use already widespread in industry. Here I report on our research on nanofibers made by spinning technologies assisted by electric fields, which exhibits photonic functions and energy harvesting/sensing capabilities1. An additional exploited application relies on their use as photoprogrammable material, based on an epoxy-based negative photoresist. Intelligent, flexible, paper-based labels, capable to operate by visual contrast and indicate inappropriate time-temperature exposure of perishable food and drugs are demonstrated2.
The research leading to these results has received funding from the European Research Council under the European Union’s Horizon 2020 Research and Innovation Programme (Grant Agreement no. 682157, “xPRINT”) and the Italian Minister of University and Research PRIN 2017PHRM8X and 20173L7W8K projects.
References
1 L. Persano et al., Advanced Materials 2017, 29, 1701031, 10.1002/adma.201701031.
2 L. Romano et al. Nature Communications 2020, 11, 5991, https://doi.org/10.1038/s41467-020-19676-y.
Transient and smart functionalities can be obtained by devices that can physically disappear in a controlled way. Water-soluble polymers and materials that can dissolve/disintegrate offer self-degradable opportunities for use in various domains. Here we report on our recent results on combinatory, transient photonics based on water-soluble compounds and sublimating materials for application in full-field imaging and labelling. The research leading to these results has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No. 682157, “xPRINT”) and from the Italian Minister of University and Research PRIN 20173L7W8K project.
Miniaturized optical diagnostics might be greatly favored by the availability of effective, conformable UV light sources combining reduced size with mechanical flexibility. Here we report on our recent results on ZnO-incorporated nanofibers, exhibiting optical gain and polarized emission, used to obtain flexible UV lasers operating at room-temperature. The research leading to these results has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No. 682157, “xPRINT”), from the Italian Minister of University and Research (PRIN 2017PHRM8X) and from the University of Pisa (PRA “ANISE”).
Here we will review our current activities on the realization of photonic active structures based on biomaterials. Nanofibers of DNA incorporating light-emitting chromophores are reported with enhanced optical emission and lasing properties tailorable by the fiber size and architecture. The research leading to these results has received funding the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No. 682157, “xPRINT”) and from the Italian Minister of University and Research through the PRIN 201795SBA3 project.
Photonic components responsive to external optical stimuli are attracting increasing interest, because their properties can be manipulated by light with fast switching times, high spatial definition, and potentially remote control. These aspects can be further enhanced by novel architectures, which have been recently enabled by the availability of 3D printing and additive manufacturing technologies. However, current methods are still limited to passive optical materials, whereas photo-responsive materials would require the development of 3D printing techniques able to preserve the optical properties of photoactive compounds and to achieve high spatial resolution to precisely control the propagation of light. Also, optical losses in 3D printed materials are an issue to be addressed. Here we report on advanced additive manufacturing technologies, specifically designed to embed photo-responsive compounds in 3D optical devices. The properties of 3D printed devices can be controlled by external UV and visible light beams, with characteristic switching times in the range 1-10 s.
3D printing technologies are currently enabling the fabrication of objects with complex architectures and tailored properties. In such framework, the production of 3D optical structures, which are typically based on optical transparent matrices, optionally doped with active molecular compounds and nanoparticles, is still limited by the poor uniformity of the printed structures. Both bulk inhomogeneities and surface roughness of the printed structures can negatively affect the propagation of light in 3D printed optical components. Here we investigate photopolymerization-based printing processes by laser confocal microscopy. The experimental method we developed allows the printing process to be investigated in-situ, with microscale spatial resolution, and in real-time. The modelling of the photo-polymerization kinetics allows the different polymerization regimes to be investigated and the influence of process variables to be rationalized. In addition, the origin of the factors limiting light propagation in printed materials are rationalized, with the aim of envisaging effective experimental strategies to improve optical properties of printed materials.
Random optical media (ROM) are a novel class of photonic materials characterized by a disordered assembly of the elementary constituents (such as particles, wires and fibers), that determines unique scattering, absorption and emission properties. The propagation of light in ROM is affected by the size and optical properties (refractive index, absorption and emission wavelengths) of their components, as well as by the overall 3-dimensional architecture. So far, most of the investigated ROM have been realized using liquid dispersions or bulk samples embedding colloidal nanoparticles or porous systems. While nanowire-based ROM are poorly investigated, such materials can feature new optical effects related to the elongated shape of their building blocks and to their light-transport properties. Here we report on the fabrication and on the morphological and spectroscopic characterization of hybrid organic-inorganic nanowires, realized by doping polymers with dielectric nanoparticles. We investigate light diffusion and multi-scattering properties of 3- dimensional ROM formed by organic and hybrid nanowires, as well as field localization in 2-dimensional networks. The influence of nanowire geometry and composition on the scattering properties is also discussed.
The understanding of the phenomena underlying the interaction of photons with dielectric, metallic and hybrid microand nano-structures and the development of advanced fabrication tools have paved the way to the realization of complex, nanostructured photonic structures, with tailored and exotic absorption and emission properties. Among such nanostructured materials, polymer nanofibers have intriguing and specific properties: they can embed molecular and quantum dot light sources, they can transport light among distant emitters and they can be arranged in 2-dimensional and 3-dimensional architectures in a controlled fashion, forming complex networks of interacting light emitters. However, coupling of light with polymer nanofibers depends on many variables, being often limited by the arrangement and positioning of the nanoscale light-sources, and by the fiber geometry. Here we report on the fabrication of active polymer nanofibers with improved surface properties and controlled geometry by electrospinning. Polarization and momentum spectroscopy of light emitted by molecular compounds and single quantum dots embedded in electrospun polymer fibers, evidence that efficient, nanostructured photon sources with targeted polarization and coupling efficiency can be realized in nanofiber-based photonic environments.
The optomechanical properties of a silicon-nitride membrane mirror covered by Alq3 and Silver layers are investigated. Excitation at two laser wavelengths, 780 and 405 nm, corresponding to different absorptions of the multilayer, is examined. Such dual driving will lead to a more flexible optomechanical operation. Topographic reconstruction of the whole static membrane deformation and cooling of the membrane oscillations are reported. The cooling, observed for blue laser detuning and produced by bolometric forces, is deduced from the optomechanical damping of the membrane eigenfrequency. We determine the presence of different contributions to the photothermal response of the membrane.
Electrospinning technologies for the realization of active polymeric nanomaterials can be easily up-scaled, opening perspectives to industrial exploitation, and due to their versatility they can be employed to finely tailor the size, morphology and macroscopic assembly of fibers as well as their functional properties. Light-emitting or other active polymer nanofibers, made of conjugated polymers or of blends embedding chromophores or other functional dopants, are suitable for various applications in advanced photonics and sensing technologies. In particular, their almost onedimensional geometry and finely tunable composition make them interesting materials for developing novel lasing devices. However, electrospinning techniques rely on a large variety of parameters and possible experimental geometries, and they need to be carefully optimized in order to obtain suitable topographical and photonic properties in the resulting nanostructures. Targeted features include smooth and uniform fiber surface, dimensional control, as well as filament alignment, enhanced light emission, and stimulated emission. We here present various optimization strategies for electrospinning methods which have been implemented and developed by us for the realization of lasing architectures based on polymer nanofibers. The geometry of the resulting nanowires leads to peculiar light-scattering from spun filaments, and to controllable lasing characteristics.
Active nanowires and nanofibers can be realized by the electric-field induced stretching of polymer solutions with sufficient molecular entanglements. The resulting nanomaterials are attracting an increasing attention in view of their application in a wide variety of fields, including optoelectronics, photonics, energy harvesting, nanoelectronics, and microelectromechanical systems. Realizing nanocomposite nanofibers is especially interesting in this respect. In particular, methods suitable for embedding inorganic nanocrystals in electrified jets and then in active fiber systems allow for controlling light-scattering and refractive index properties in the realized fibrous materials. We here report on the design, realization, and morphological and spectroscopic characterization of new species of active, composite nanowires and nanofibers for nanophotonics. We focus on the properties of light-confinement and photon transport along the nanowire longitudinal axis, and on how these depend on nanoparticle incorporation. Optical losses mechanisms and their influence on device design and performances are also presented and discussed.
Light-emitting nanostructures made by conjugated polymers show interesting emission and electronic properties. In this work we report on novel approaches for the fabrication and control of light-emitting nanofibers by electrospinning. The shape, size and light-emitting properties of the fibers can be specifically tailored by acting on the composition of the solution used for the electrospinning process, an approach allowing for obtaining fibers ranging from micrometer-sized ribbons to almost cylindrical fibers with diameters down to few hundreds of nanometers. Moreover, following proper process optimization these fibers can also be precisely positioned in ordered arrays by near-field electrospinning, a method that exploits the stable region of the polymer jet. The possibility of precisely shaping the conjugated polymer fibers and of assembling the fiber in ordered arrays, combined with enhanced emission properties, opens interesting perspectives for developing novel emitting flexible nanomaterials suitable for light sourcing and optical sensing.
Polymer micro- and nano-fibers, made of organic light-emitting materials with optical gain, show interesting lasing properties. Fibers with diameters from few tens of nm to few microns can be fabricated by electrospinning, a method based on electrostatic fields applied to a polymer solution. The morphology and emission properties of these fibers, composed of optically inert polymers embedding laser dyes, are characterized by scanning electron and fluorescence microscopy, and lasing is observed under optical pumping for fluences of the order of 102 μJ cm-2. In addition, lightemitting fibers can be electrospun by conjugated polymers, their blends, and other active organics, and can be exploited in a range of photonic and electronic devices. In particular, waveguiding of light is observed and characterized, showing optical loss coefficient in the range of 102-103 cm-1. The reduced size of these novel laser systems, combined with the possibility of achieving wavelength tunability through transistor or other electrode-based architectures embedding nonlinear molecular layers, and with their peculiar mechanical robustness, open interesting perspectives for realizing miniaturized laser sources to integrate on-chip optical sensors and photonic circuits.
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