Browsing by Author "Giocondo, Michele"

Now showing 1 - 4 of 4

Atomic force microscopy study of physico-chemical and nanotribological properties of hydrophobin protein
(2009-11-09) Houmadi, M. Said; Giocondo, Michele; Lacaze, Emmanuelle
Hyper resolute laser writing mediated by tailored ENZ matematerials: the specifc case of all-dielectric broadband metalenses
(Università della Calabria, 2021-04-02) Lio, Giuseppe Emanuele; Cipparrone, Gabriella; Caputo, Roberto; Giocondo, Michele; De Luca, Antonio
Metamaterials are part of an emerging research field with a broad range of useful potential applications in cross-disciplinary fields spanning material science, optics, industrial applications, and last but not least, sensing from environmental hazards to cancer cells. Metamaterials present particular features especially when they are fabricated as multi-stack layered systems or optical nano-cavities. In fact, due to the particular features presented by this kind of materials as strong self-collimation and canalization effects, extraordinary transmittance and plasmonic behavior, they open a very wide scenario of nano-technological applications. The application that has been addressed in this thesis exploits the interesting and intriguing features of metal/ insulator/ metal/insulator systems, so-called MIMIs, in optical nano-cavities configuration tailored to drastically improve the resolution of a generic Two Photon Direct Laser Writing (TP-DLW) lithography process. The enhanced technique covers an important role in nanotechnology and especially in new nanomaterials frontiers for the possible realization of polymeric, thus completely dielectric, metasurfaces. For these reasons, the driving concept of the work presented in this research activity is to carry out the entire cycle of realization of MIMI devices, passing from their design, optimization, fabrication and characterization. Following their realization, the optimized MIMI are used to enhance the TP-DLW process in order to fabricate hyper-resolute test samples as 1D gratings, 2D metasurfaces and 3D complex objects. Given its self-collimation optical features, the MIMI metamaterial is used for the characterization of the realized structures as well. A specific, noticeable case that has been addressed in this thesis is the realization of ultra-flat all-dielectric apochromatic broadband metalenses assisted, during the design, by a Deep Machine Learning algorithm and, for their fabrication, by the above mentioned enhanced TP-DLW process. Finally, the realized metalenses have been optically characterized in the visible spectrum (300 − 1000 nm) confirming (as designed) fascinating features if compared with the already realized metalenses like the numerical aperture, extended focal length and depth of focus. Chapter 1 introduces the main aspects of metamaterials, as well as, the isofrequency surface describing the dispersion relations of hyperbolic metamaterials, and different geometrical configurations that allow exploiting particular physical effects and behaviors in light-matter interaction. Then, stacked multi-layer materials and a particular family of those, #psilon Near Zero, are presented. These metamaterials are a particular class of artificial optical structures consisting of a periodic arrangement of metallic and dielectric layers able to self-collimate and canalize light inside themselves. Finally, the chapter concludes with an overview of the plasmonic behavior in a simple metal/insulator interface that produces surface plasmon polaritons. Then it considers the bulk plasmon polaritons in multi-stacked metamaterials and the gap surface plasmon in Fabry-Perot nano-cavities. In Chapter 2, a simple and fast, yet robust, way to design metamaterials is evaluated as a function of their optical response and behavior. In fact, the first topic addressed in this chapter is ellipsometry and related advantages, to characterize nano-structures by retrieving the ellipsometric parameters Y and D, reflectance and transmittance and the complex refractive index n − ik. Then, the Transfer Matrix Method (TMM) has been detailed and used to code a homebuilt Matlab tool to predict the optical behavior as a function of the metamaterials design. On the same way, by using COMSOL Multiphysics, a Numerical Ellipsometer Analysis (NEA) has been realized. NEA covers the role of a robust tool to predict the optical response in much complex systems such as multi-layered materials with/without superstructures (gratings, holes, helices) placed above them. Some numerical simulations predicted by the NEA are experimentally validated by different cases with increasing system complexity. The plasmonic dispersion relations and the modal analysis have been addressed for dielectric cavities that support multi-spectral modes in the visible. Finally, in the last section, particular effects produced by MIMI cavities have been studied. Two key aspects related to the optical cavities are presented below. The first concerns the way they show hues / shades of color as a function of the cavity thickness and the involved material; the second one is a fast and effective way to identify the plasmons propagating inside these structures through the pseudo-dielectric function < ˜# >. These designed cavities present also particular effects like a large de-phasing well-known as Goos-Hänchen shift, that it is exploitable for extremely accurate sensing. Chapter 3 begins by introducing the main concepts of one and two-photon lithography and describing the state of the art of the Two-Photon Direct Laser Writing (TP-DLW) process. Then, as reported in the previous chapter, it shows detailed aspects of optical-nano cavities and leverages on the MIMI properties and features to design an embedded device able to work at the two photon lithography process wavelength (l = 780nm). The fabricated prototype is tested in terms of the incident beam waist modification by the evaluation of the Point Spread Function (PSF) reduction, measured by an homebuilt confocal setup equipped with a beam profiler. After its characterization, the MIMI device is used to realize 1D gratings compared with the ones fabricated through standard glass substrates. The reduction of 89% in height and 50% in width challenges our research product to reproduce the portrait "The Lady with an Ermine" by Leonardo Da Vinci that exhibits an high resolution level in terms of details and the nanoscale slicing in the 3D fabrication Chapter 4. The results obtained by the enhanced TP-DLW technique are exploited, in this chapter, to realize all-dielectric apochromatic broadband "flatland" metalenses with overall thickness less than 50nm. For their de facto two-dimensional nature, we call them "flatland" metalenses with the obvious reference to the famous Abbott’s novel ("Flatland: A Romance of Many Dimensions"). Next generation optics follow the trendsetting of miniaturized devices with extraordinary features as extended focal length and Depth of Focus (DOF), high Numerical Aperture and, last but not least, fast and easy way to produce them. In fact, this extremely flat design is the result of the novel two-photon direct laser writing (TP-DLW) process enhanced to hyper resolution performance by leveraging on the peculiar optical properties of our designed and developed ENZ metamaterials. Once fabricated, the characterization of the metalenses follows by means of a homebuilt setup equipped with beam-profiler and spectrometer. This measurement provided the characteristic values for these features like focal length f = 1.14mm, DOF in the range |50 − 150|μm and the numerical aperture NA = 0.087. In summary, the improved resolution of TP-DLWprocess presented in Chapter 3 is extremely significant for industrial applications in several fields such as anti-counterfeiting and flat optics, as shown in the last two Chapters of this Thesis work.
Materials and processes for the optical Additive Manufacturing of advanced organic/inorganic nanocomposites for the mask-less plating of insulator and semiconductor substrates, and microfluidic devices
(Università della Calabria, 2020) Di Cianni, Wera; Cipparrone, Gabriella; Giocondo, Michele; De Luca, Antonio; De Leon, Alberto Sanz
The research presented in this doctoral thesis is carried out in the nanotechnology and soft matter frameworks, under the 4.0 Industry paradigm, inspired by the need to find new strategies for the Additive Manufacturing (AM) and to obtain new processable nanocomposites with enhanced properties. The AM technologies allow to build 3D objects with complex geometries by adding layer-upon-layer of material without any mold and permits to fabricate structured objects and microfluidic systems with particular optical and mechanical properties which cannot be easily made with classical Subtractive Manufacturing (SM) techniques. This paves the way to large improvements in optoelectronics, biotechnology, diagnostic or medicine. Moreover, the combined employment of bottom-up and top-down fabrication approaches could lead to important advances in the field of nanotechnology, widening further the possible applications field, permitting high resolution repeatable nanofabrication of 3D complex objects with the possibility of immediate industrial applications. The first AM technique used in this work is Stereolithography (SL), a vat photopolymerization technique that uses UV light to produce objects with resolution in the range 10-100 μm. Here, the novelty consists in adding a metallic precursor (KAuCl4) to a typical photosensitive resin to produce nanocomposites with gold nanoparticles synthesized in situ via photo- and thermal reduction. Nanocomposites produced are rich in gold nanoparticles and have interesting optical and plasmonic properties. Moreover, a fine tuning of the concentration of the gold salt allows the resin polymerization without suffering any inhibition of the gold precursor. A similar approach, taking advantage of the combination with photoreduction of a gold precursor (HAuCl4), can be achieved using a different technique belonging to the vat photopolymerization category, namely the Two Photon Direct Laser Writing (TP-DLW). This technique exploits the optical, nonlinear multiphoton absorption process and allows for the fabrication of 3D objects featuring details below the diffraction limit, down to 100 nm or even less. Here, this multiphoton absorption process is exploited to trigger the photo-reduction of the gold precursor. The use of a transparent hydrogel matrix allows for a fine control of the nanoparticles’ growth on either transparent or opaque substrates, such as glass or silicon, without the need of using masks or molds. An in-depth study on the diffusive process underlying the nanoparticles growth and a control of the ionic concentration are done to prove the importance of having a polymeric network to hold the created nanoparticles at their place, which enhances the quality of the created nanostructures. The nanofabrication of fiber reinforced polymer nanocomposites by TP-DLW was also demonstrated. For these experiments, the classical glass or silicon substrates were replaced with a silicon substrate on which silica nanowires (SiO2 NWs) have been previously grown. This research allowed to achieve the best resolution offered by the TP-DLW technique, even with high loads of fillers of SiO2 NWs, up to 70 wt%. This was achieved by matching the refractive indices of the SiO2 NWs and of the photoresist used as polymeric matrix. These nanocomposite materials presented a noticeable improvement of nano-hardness and elastic modulus when compared to the pristine photoresist, indicating how the proposed technique is well-suited for nano-applications with higher structural requirements, as in advanced microfluidics. A final comparison of the AM technologies used in the thesis is done to elucidate the advantages and disadvantages of each one of these techniques to choose the most efficient, easiest and fastest, depending on the materials to be used or the required resolution.
Physical processes in single and multiple photons additive nano-manufacturing of three-dimensional polymeric and metallic structures for advanced optics
(2018-04-04) Ritacco, Tiziana; Carbone, Vincenzo; Giocondo, Michele; Pagliusi, Pasquale
In the field of nanotechnologies the Two-Photons Direct Laser Writing (TP-DLW) is the most advanced optical technique for creating arbitrarily complex 3D structures in organic resists, featuring details down to 50 nm, well below the diffraction limit. More recently, this technique has been used in “resists” containing a photosensitive metallic precursor, activated by the two-photon absorption (TPA) process, allowing for the creation of metallic nanoparticles clusters inside to the focus figure of a highly focused laser beam, where the TPA threshold intensity is reached. The aim of my PhD work was the elucidation of the physical processes involved in the realization of 3D nanostructures made in different materials for applications in micro-fluidics and advanced optics. In particular, I carried out studies on both isotropic and anisotropic photoresists, and on metallic precursors. Concerning the isotropic photoresists, I have investigated the capabilities and the limits of the TP-DLW technique, on the fabrication of microfluidic systems and elements of millimetric size, with micro- and nano-features printed inside the channels. The best results in printing such millimetric structures in terms of geometrical compliance and fabrication time are achieved, by combining the single (SPA) and the two-photon absorption (TPA) processes. The latter one allowed for the creation of a shell, an internal structural scaffold and eventual microscopic details, whereas the former one to polymerize the bulk of the object. However, the development step of microfluidic systems (i.e. the removal of the un-polymerized resist) is quite challenging in general, due to possible swellings and consequent distortions in the structure geometry. In my PhD, I developed an effective protocol to face this issue. The application of the TP-DLW technique to anisotropic reactive mesogens (RMs) resulted in very interesting achievements, as it allowed for the fabrication of 3D solid structures, maintaining the optical properties of liquid crystals, in combination with the mechanical properties of polymers. Effects of the direct laser writing on the internal molecular order of the reactive mesogens have been thoroughly investigated, to ensure a fine control on the optical properties of 3D objects made in liquid crystalline elastomers. Analyses of the physical processes, which occur during TP-DLW and allow for tuning of the optical response of the printed 3D solid structures are shown. Appropriate doping of the reactive mesogens with dyes and chiral dopant agents were performed to investigate different fields of applications. In particular, a chiral agent confers helical order to the RMs, which show selective Bragg reflection of the impinging light in both wavelength and polarization. Micro-fabrication of 3D chiral structures is a brand new field that is paving the way to the creation of photonic devices, such as micro-laser of defined shape, white light reflective object, anti-counterfeiting and data storage systems. I performed a series of experiments aimed at demonstrating the possibility to manipulate the helical structural order of the liquid crystals during TP-DLW. As a consequence, multi-colour three-dimensional structure can be created. Finally, the possibility to include metallic details in polymeric objects or even to create metallic structures would pave the way for the DLW of metallic/polymeric nano-composites. I performed experiments with polymeric or hydrogel matrices doped with a suitable metallic precursor, in a free surface drop cast, or in cell segregated thin film, onto a glass substrate. In such system, I was able to create 1D gratings made of GNPs stripes with single or multiple laser sweep. I demonstrated that the stripe width increases with the laser power and the exposure time, showing a behaviour similar to the photo-polymerization, as expected. I also analysed the influence of the exposure time over the nano-particles size distribution and density and showed that by suitably adjusting the exposure time it is possible to maximize the occurrence of a given diameter. The experiments were aimed at elucidating the involved physical phenomena, beyond the bare optical absorption. In particular, the key-role of thermal and diffusive processes have been analysed. TPA leads to the photo-reduction of ions of AuCl4 – and the creation of GNPs, but to a local heating of the sample as well. Due to the very fast heating, a thermal shock-wave is generated and is responsible of the local dehydration in the spot area. Due the concentration gradients of the ions of gold precursor and of water, different diffusive processes take place, occurring on different timescales. Therefore, different characteristic times are observed for the ion and the water diffusion, in the polymeric matrix. My experiments demonstrate that the diffusive effects can be exploited for controlling the NPs density and size when a given energy dose is delivered in multiple shots, by tuning the time interval between each shots. Preliminary experiments on the possibility to control the growth of GNPs through the application of specific electric field during TP-DLW were performed as well. Last but not least, the possibility to use TP-DLW of metal precursor to realize smart platform rich in GNPs suitable to different application is shown. In particular, I demonstrate that, controlling the pitch and the size of GNPs stripes, it is possible to create both thermo-platform whose thermal response to external light is tuneable, and detecting substrates for Surface-Enhanced Raman Spectroscopy (SERS). The Raman spectra were recorded from samples immersed in a solution of rhodamine-6G (R6G), as well as, after exposure of the samples in xylene. SERS enhancement factors of up to ~104 were obtained for both rhodamine-6G and xylene.