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TWO DIMENSIONAL SELF ASSEMBLY OF NANOSPHERES, A VERSATILE METHOD FOR NANOFABRICATION
Full text linkNanotechnology is one of the most innovative and multidisciplinary fields in modern research. Techniques to manipulate and control matter at the nanometric scale, giving the possibility to change the morphology and the physical and chemical properties are growing in number. At the nano scale, changing the morphology implies changing also the properties of matter: many properties are no longer intrinsic but they depend on the size, shape, and even on the environment. One of the most striking example is given by gold and silver colour when they are in the nanoparticle form. Gold, for example ould be vine-red or green, or bluish or black simply by changing the morphology of the particles. Appropriate manipulation of the matter could also give birth at new proprieties such as the transmission of light through holes much smaller that the light wavelength, allowing the possibility to control at a very intimate
scale the propagation of light. It is clear that to exploit the great potential of nanotechnology it is important to have nanofabrication techniques that have a very precise control on the production of nanometric materials or materials with nanometric structures. There are many technologies that can produce structures with an outstanding resolution of just a few nanometer (Electron Beam Lithography, Focused Ion Beam). These technologies are ”serial” fabrication tool, they can produce one object at time and this means high costs and low throughput. On the other hand parallel technologies derive from the semiconductor industry and are mostly optical lithographic methods that are limited by the diffraction limit of light (200nm).
In this thesis work the need for a nanofabrication tool that can allow the production of smaller nanostructures will be addressed by using a nanofabrication tool that meets the following criteria:
• parallel processing
• low cost
• large area processing (cm2)
• scalability
• reproducibility
• easy implementation
We choose to exploit the ability of self aggregation of matter in ordered structures. In particular we exploited the tendency of spherical monodisperse nanoparticles to assemble in ordered, close packed structures known as colloidal crystals. One monolayer of such colloidal crystal is a very interesting
structure because it has a well ordered array of pores among the particles that have a well defined size and shape, that could be tuned by simply changing the size of the self assembled colloidal particles. A simple and easy method to create and deposit on different substrate these self assembled monolayer of polystyrene nanoparticles will be presented. Monolayers
will be used to synthesize arrays of monodisperse plasmonic nanoparticles with a very good control on their size and shape, allowing the tuning of the plasmonic proprieties on the desired application. We will use the array of plasmonic nanoparticles to realize molecular sensors and to amplify the Raman
signal by the Surface Enhanced Raman Scattering effect. We will study the rise in temperature induced by illumination with a laser light resonant with the nanoparticle’s plasmonic transition. This information could be very interesting for the biological application of the nanoparticles arrays since temperature
variation in such a very complex environment could have relevant effect. Moreover we will use these 2D colloidal crystal to synthesize different kinds of nanostructures like an array of holes in a metal film. This nanostructure is very interesting since the discovery of its ability to transmit light even if
the hole size is much smaller than the light’s wavelength. A synthesis method based on self assembled nanospheres could be useful for the fabrication of such nanostructures because of its high flexibility in changing the nanoparticles size and so the array geometric parameters like hole size and the lattice period.
Self assembled monolayers will be used as a template for the synthesis of nanostructured thin films of TiO2. Titania is a semiconductor of great technological interest in many different fields: catalysis, energy conversion, gas sensing. We
will fabricate using the same technology two different nanostructured thin film: a macroporous thin films and a surface patterned with a nanobowl pattern. Finally we will demonstrate the use of self assembled monolayers coupled with
a standard technology used in the semiconductor industry such the ion implantation. Nanometric patterns will be produced on Si wafers using the ordered monolayer as a mask for the ion beam.Il campo delle nanotecnologie è uno dei più innovativi e multidisciplinari della ricerca moderna. Sempre pi`u numerose diventano le tecniche per manipolare la materia su scala nanometrica, modificando così le proprietà fisico, chimiche
e morfologiche a livelli mai raggiunti prima. Alla nano scala la manipolazione morfologica è accompagnata dal cambiamento delle proprietà che smettono di essere intrinseche della materia ma diventano dipendenti da altri fattori come la forma, la dimensione e l’ambiente in cui le nanostrutture sono immerse.
Uno dei casi più eclatanti è il colore dell’oro e dell’argento quando sono sottoforma di particelle nanometriche. L’oro, ad esempio, può essere di colore rosso-vino, verde, blu e nero, semplicemente cambiando la forma o l’ambiente
attorno ad esso. Manipolando la materia opportunamente possono comparire nuove proprietà come la trasmissione della luce attraverso aperture che sono molto più piccole della lunghezza d’onda della luce, dando la possibilità di ottenere il controllo della propagazione della luce ad un livello molto intimo. Si può capire quindi come per poter sfruttare le enormi potenzialità offerte dalle nanotecnologie sia importante avere tecnologie di fabbricazione che permettano un preciso controllo nella produzione di oggetti nanometrici o con strutture nanometriche. Le tecnologie al momento disponibili che permettono di creare strutture con precisione molto elevata (pochi nanometri) sono tecnologie ”seriali” come l’Electron Beam Lithography o il Focused Ion Beam.
Queste tecniche sono limitate alla produzione di un oggetto alla volta e quindi comportano costi elevati e lunghi tempi. Le tecnologie ”parallele” derivano dall’industria dei semiconduttori e sono tecniche litografiche che hanno come limite la risoluzione della luce utilizzata ( 200nm).
In questo lavoro di tesi si cercherà di dare risposta alla domanda di tecniche di fabbricazione di strutture nanometriche utilizzando una tecnica che abbia le seguenti caratteristiche:
• quickness
• low cost
• ability to synthesize very small nanostructures
• reproducibility
• easy implementation
Si è scelto di utilizzare la capacità della materia di organizzarsi spontaneamente in strutture ordinate. In particolare si è sfruttata la tendenza di nanoparticelle sferiche di polistirene ad impaccarsi in strutture compatte ed ordinate costituendo dei ”cristalli colloidali”. Un singolo strato di nanosfere autoassemblate è una struttura interessante perchè presenta dei pori tra le particelle di forma e dimensioni ben definite, che possono essere modificate cambiando le dimensioni delle sfere che costituiscono il cristallo bidimensionale.
Verrà illustrato un metodo semplice e rapido per ottenere questi monostrati di particelle ordinate e per poterli depositare su vari substrati. Questi cristalli bidimensionali verranno utilizzati per depositare una matrice ordinata di nanoparticelle
plasmoniche, con un ottimo controllo sulla loro forma e dimensioni, consentendo di realizzare particelle con proprietà su misura per l’applicazione desiderata. Verranno anche studiate applicazioni di queste nanoparticelle come
sensori di molecole e per amplificare il segnale Raman grazie all’effetto SERS. Verrà inoltre studiato l’aumento di temperatura di queste nanoparticelle quando vengono illuminate da un laser risonante con la loro risonanza di plasma di superficie.
Per applicazioni spettroscopiche applicate a sistemi biologici il cambiamento di temperatura può avere effetti rilevanti in un ambiente complesso come quello biologico.
In seguito verrà dimostrato come questi cristalli colloidali bidimensionali possono essere utilizzati per creare altre classi di nanostrutture, come ad esempio una matrice di buchi nanometrici in un film metallico. Queste strutture
sono studiate da quando è stato scoperta la loro capacità di far trasmettere attraverso strutture che sono molto minori del limite di diffrazione per le lunghezze d’onda trasmesse. Una sintesi che si basa sulle nanosfere autoassemblate può essere interessante per queste strutture grazie alla sua intrinseca
flessibilità. Si possono infatti cambiare in modo molto semplice i parametri geometrici che caratterizzano la matrice di buchi quali le dimensioni dei buchi e il periodo degli stessi.
Un’altra tipologia di nanostrutture che verrà realizzata sono film sottili nanostrutturati di TiO2. La titania è un semiconduttore di grande interesse tecnologico in molti campi diversi: dalla catalisi, alla conversione di energia ai sensori di gas. Verranno fabbricati, con la stessa tecnologia, dei film con una porosità ordinata e delle superfici nanostrutturate con un motivo a incavi.
Infine verrà dimostrata la possibilità di utilizzare i cristalli colloidali 2D accoppiati con una tecnologia molto utilizzata dall’industria dei semiconduttori quale l’impiantatore ionico. Pattern nanometrici verranno realizzati su silicio utilizzando le nanoparticelle autoassemblate come maschera per il fascio ionico
Patterned TiO2 nanostructures fabricated with a novel inorganic resist
No full textThe fabrication of nanostructures is a very intense field of research in material science over the last decades. Overcoming the limit imposed by the diffraction limit in lithography was addressed in several ways: shifting to smaller wavelength, changing radiation and using electrons or ions instead of photons or using non-conventional bottom up techniques like self-assembly. There are few studies on fabrication of ordered TiO2 nanostructures, mostly confined to non-scalable technologies, while nanostructured TiO 2 is a material used in many different fields of applications. In our work we present a hybrid nanofabrication technique based on self-assembly coupled with standard UV lithography. With this method we were able to fabricate in a single step and with the use of inexpensive equipment a 2D Nano Bowl Array of TiO2 with sub wavelength features and easily scalable pattern features
Hydrophobic and water resistant fish leather: a fully sustainable combination of discarded biomass and by-products of the food industry
Full text linkThe food industry produces a large amount of food byproducts that, when appropriately valorized, can become a renewable source of sustainable materials. The valorization of these byproducts requires a new set of green technologies. For example, fish farming, one of the fastest growing sectors, uses only 30% to 40% of the fish as food, with the remaining 60% to 70% being a byproduct. One example of valorization of fish byproducts is the upcycling of fish skin into leather. This new fish leather has interesting properties, in part due to its microstructure, but also has new shortcomings like the high hydrophilicity and water absorption. To mitigate these issues, a water protecting coating was developed using only two other food byproducts: epoxidized soybean oil and the fatty acid trimer Pripol. These two building blocks were deposited on leather and then crosslinked to create a strong network that made leather hydrophobic, with a water contact angle >120° without the need for fluorine or silicone chemistry or the use of nanoparticles. The coating was applied via dip-coating and was cured at low temperature as required by fish leather without the need for initiators, catalysts, which are mostly toxic, or UV light. The same strategy could also be applied to cotton, showing that its application is not limited only to leather. The coating showed good adhesion to the substrate and excellent water resistance, making the leather and the cotton hydrophobic and substantially reducing the water absorption, without changing the breathability, flexibility and microstructure of the substrate. This work demonstrates how high performing materials can be created within a green chemistry and circular economy framework, with results that can be relevant for other textile materials, contributing to the effort for developing sustainable alternatives for providing hydrophobicity
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
POMOPLA^2: A Bio‐Based Material Solution Valorizing Tomato By‐Products for Circular Packaging Applications
Full text linkThe depletion of fossil resources, increasing packaging pollution, and stricter regulations require the development of sustainable alternative materials. This study presents POMOPLA2, a fully bio-based composite that enhances circularity by valorizing industrial tomato peel by-products within a plasticized polylactic acid (PLA) matrix. A novel bio-based and biodegradable plasticizer derived from oils was used to successfully reduce PLA brittleness, providing higher toughness (+485%) and strain at break (+177%), a lower glass transition temperature, while enhancing the compatibility of the tomato peels, used as reinforcement. The incorporation of tomato peel biomass has the potential to reduce production costs, and we showed that it can be used to modulate mechanical performance as well as aesthetics-sensory attributes. Low percentages of tomato peels (5% w/w) maintained translucency for flexible film packaging applications, whereas higher contents (20% w/w) proved adequate mechanical properties for rigid packaging. POMOPLA2 might implement a local circular economy in line with the European Circular Economy Action Plan, that is, to produce tomatoes' packaging to be potentially reintegrated into the biological cycle as compost, fostering a seamless nature-to-nature cycle
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Functionalization of Titanates–Silk Nanocomposites via Cation Exchange for Optical Applications
No full textA simple and efficient method is developed to introduce plasmonic and luminescence functionalities in titanate nanosheets (TNSs)–silk nanocomposites by direct cation-exchange process. First, the cation exchange properties such as exchange kinetic and capacity are studied to verify the behavior of the material and determine the best condition of exchange. In particular, the effect of the valence on the kinetic is investigated through elemental analysis, focusing on three target cations (Ag+, Cu2+, and Eu3+) in water. It is demonstrated that the cation exchange capability of the composite is strictly dependent of the amount of TNSs. By acting on the time of ion exchange or by changing the TNSs concentration in the silk fibroin matrix it is possible to tune the metal ions doping. The process is applicable both on flexible free-standing membranes and thin films deposited on an appropriate substrate. By exposing the material to UV radiation, it is possible to synthesize in situ metallic nanoparticles, exhibiting a characteristic plasmonic peak in the visible spectrum. Furthermore, it is verified that the europium ions preserve their photoluminescence properties when introduced in the nanocomposite, showing a characteristic red emission under UV light
Rare-earth fluorescence thermometry of laser-induced plasmon heating in silver nanoparticles arrays
Full text linkThe laser-induced plasmon heating of an ordered array of silver nanoparticles, under continuous illumination with an Ar laser, was probed by rare-earth fluorescence thermometry. The rise in temperature in the samples was monitored by measuring the temperature-sensitive photoluminescent emission of a europium complex (EuTTA) embedded in PMMA thin-films, deposited onto the nanoparticles array. A maximum temperature increase of 19 °C was determined upon resonant illumination with the surface plasmon resonance of the nanoarray at the highest pump Ar laser power (173 mW). The experimental results were supported by finite elements method electrodynamic simulations, which provided also information on the temporal dynamics of the heating process. This method proved to be a facile and accurate approach to probe the actual temperature increase due to photo-induced plasmon heating in plasmonic nanosystems
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