Innovative patternable materials for micro- and nano- fabrication

The research activity of this thesis is focused on the development and optimization of new directly patternable organically modified TiO2, Al2O3 and ZrO2 based sol-gel materials whose peculiar characteristics and performances were optimized and exploited for the final specific application. In particular, the main strategy that lies at the basis of all the thesis work is the combination of top down and- bottom up approach for the final device realization. In fact, special attention has been set to materials design and synthesis (bottom up) and subsequently to the micro- and nano- fabrication of patterns on the corresponding film surface with different lithographic techniques (top down) in order to achieve the required properties, according to the final application. As it concerns the bottom up approach, the sol-gel has been assumed as the main synthetic method since, by mixing different organic-inorganic precursors, new materials with unique properties and microstructures can be created. In fact, by using organically modified precursors (such as trimethoxyphenylsilane, 3-glycidoxypropyltrimethoxysilane, 3-(Trimethoxysilyl)propyl methacrylate) or organic monomers it was possible to produce hybrid materials with the organic and inorganic components intimately mixed at a molecular scale, with the twofold effect of obtaining new properties and conferring them the patternability. Moreover, the addition of tetrafunctional precursors (Titanium isopropoxide, Zirconium butoxide, Aluminum-tri-sec-butoxide) allowed to increase the reticulation degree, taking part to the inorganic network formation, to improve the material mechanical properties (such as scratch, abrasion, plasma etching resistance) and to confer particular characteristics to the final materials, i.e. to modulate the refractive index. On the other hand, as it regards the top down approach, different lithographic techniques (photolithography, X-ray lithography, electron beam lithography and nanoimprint lithography) have been exploited in the realization of high refractive index patterns, high selective etching masks features, adaptive-optics devices and stamps for microinjection moulding directly with the synthesized materials. The structural and chemical changes induced inside the material by the interactions with the source used in the lithographic process have been deeply investigated in order to optimize both the synthesis of the best sol-gel systems and the final lithographic procedures. In conclusion the development of all the above mentioned advanced materials and innovative processing was pushed by the main target of improving, simplifying and decreasing costs and time of the overall micro- and nano- fabrication process in order to obtain better final features quality, with respect to traditional lithographic procedures

Innovative patternable materials for micro- and nano- fabrication

The research activity of this thesis is focused on the development and optimization of new directly patternable organically modified TiO2, Al2O3 and ZrO2 based sol-gel materials whose peculiar characteristics and performances were optimized and exploited for the final specific application. In particular, the main strategy that lies at the basis of all the thesis work is the combination of top down and- bottom up approach for the final device realization. In fact, special attention has been set to materials design and synthesis (bottom up) and subsequently to the micro- and nano- fabrication of patterns on the corresponding film surface with different lithographic techniques (top down) in order to achieve the required properties, according to the final application. As it concerns the bottom up approach, the sol-gel has been assumed as the main synthetic method since, by mixing different organic-inorganic precursors, new materials with unique properties and microstructures can be created. In fact, by using organically modified precursors (such as trimethoxyphenylsilane, 3-glycidoxypropyltrimethoxysilane, 3-(Trimethoxysilyl)propyl methacrylate) or organic monomers it was possible to produce hybrid materials with the organic and inorganic components intimately mixed at a molecular scale, with the twofold effect of obtaining new properties and conferring them the patternability. Moreover, the addition of tetrafunctional precursors (Titanium isopropoxide, Zirconium butoxide, Aluminum-tri-sec-butoxide) allowed to increase the reticulation degree, taking part to the inorganic network formation, to improve the material mechanical properties (such as scratch, abrasion, plasma etching resistance) and to confer particular characteristics to the final materials, i.e. to modulate the refractive index. On the other hand, as it regards the top down approach, different lithographic techniques (photolithography, X-ray lithography, electron beam lithography and nanoimprint lithography) have been exploited in the realization of high refractive index patterns, high selective etching masks features, adaptive-optics devices and stamps for microinjection moulding directly with the synthesized materials. The structural and chemical changes induced inside the material by the interactions with the source used in the lithographic process have been deeply investigated in order to optimize both the synthesis of the best sol-gel systems and the final lithographic procedures. In conclusion the development of all the above mentioned advanced materials and innovative processing was pushed by the main target of improving, simplifying and decreasing costs and time of the overall micro- and nano- fabrication process in order to obtain better final features quality, with respect to traditional lithographic procedures.L’attività di ricerca del presente lavoro di tesi è stata finalizzata allo sviluppo e all’ottimizzazione di nuovi materiali sol-gel a base di ossidi di TiO2, Al2O3 e ZrO2, organicamente modificati, per diverse applicazioni, sfruttando alcune delle loro caratteristiche peculiari e ottimizzandone le prestazioni. Nella fase iniziale del lavoro particolare attenzione è stata rivolta alla sintesi e all’ingegnerizzazione dei materiali stessi (approccio bottom up). Nella fase successiva i materiali sviluppati sono stati micro- e nano- strutturati mediante tecniche litografiche differenti (approccio top down) al fine di valorizzarne proprietà specifiche a seconda della particolare applicazione finale. La combinazione tra l’approccio top down e quello bottom up è stata dunque la principale strategia adottata al fine di raggiungere gli obiettivi prefissati. Per quanto riguarda l’approccio bottom up, la strategia di sintesi adottata è stata il metodo sol-gel. Infatti, l’utilizzo di precursori organico-inorganici permette di sintetizzare nuovi materiali con proprietà e microstrutture uniche. Utilizzando precursori organicamente modificati, come ad esempio trimetossifenilsilano, glicidossipropiltrimetossisilano, metacrilossipropiltrimtossisilano, è stato possibile infatti ottenere materiali ibridi avanzati le cui componenti, organica e inorganica, sono intimemente mescolate a livello molecolare. Inoltre, in fase di sintesi, possono essere aggiunti precursori tetra funzionali, tra cui Titanio isopropossido, Zirconio butossido, Alluminio-tri-sec-butossido, per: aumentare il grado di reticolazione, poiché partecipano alla formazione del network inorganico, con relativo incremento delle proprietà meccaniche del materiale (resistenza al graffio, all’abrasione, all’attacco con plasma), e conferire particolari caratteristiche al materiale finale, come ad esempio la modulazione dell’indice di rifrazione. I materiali così sintetizzati sono stati quindi direttamente micro- e nano- strutturati mediante tecniche litografiche differenti (fotolitografia, litografia a raggi X e a elettroni, litografia nanoimprint), approccio top down, al fine di ottenere pattern ad elevato indice di rifrazione, maschere per il silicio altamente selettive, dispositivi per ottica adattiva e stampi per micro-iniezione. Uno studio approfondito dell’interazione del materiale con le sorgenti utilizzate nei vari processi litografici ha permesso inoltre di ottimizzare sia la sintesi dei sistemi sol-gel stessi sia i parametri di processo litografico. Quindi, lo sviluppo e l’ottimizzazione contemporanei dei materiali avanzati e dei processi litografici innovativi appena citati hanno permesso di ridurre in termini di costi e tempo l’intero processo di micro- e nano- fabbricazione dei dispositivi finali realizzati, rispetto al processo litografico tradizionale, ottenendo strutture qualitativamente superiori

Direct pattern by UV lithography of High refractive index double tone titania resist

A direct one-step and low temperature micro-fabrication process, enabling to realize large area totally inorganic TiO2 micro-patterns from a spin-on resist, is presented. High refractive index structures (up to 2 at 632 nm) without the need for transfer processes have been obtained by mask assisted UV lithography, exploiting photocatalytic titania properties. A distinctive feature not shared by any of the known available resists and boosting the material versatility, is that the system behaves either as a positive or as negative tone resist, depending on the process parameters and on the development chemistry. In order to explain the resist double tone behavior, deep comprehension of the lithographic process parameters optimization and of the resist chemistry and structure evolution during the lithographic process, generally uncommon in literature, is reported. Another striking property of the presented resist is that the negative tone shows a high contrast up to 19, allowing to obtain structures resolution down to 2 \u3bcm wide. The presented process and material permit to directly fabricate different titania geometries of great importance for solar cells, photo-catalysis, and photonic crystals applications

Development of osteoinductive micro-structured polymer surfaces for mesenchymal stem cells differentiation

In this work the injection molding of micro-structured polystyrene surfaces and their application in stimulating growth of osteoblastic MC3T3-E1 cells is described. The experimental results obtained from micro-pillared surfaces show that among the physicochemical parameters of the biomaterial surface, such as surface energy, surface charges or chemical composition, micro-topography is one of the most crucial factor influencing cell adhesion and proliferation. Furthermore, the molding process parameters have been optimized to increase the degree of micro pillars replication and to induce cell growth. MTS results showed a better correlation of cell proliferation with micro pillars diameter and spacing than with their height or aspect ratio

Hybrid materials: a bottom-up approach for nanotechnology applications

Engineered organic-inorganic hybrid materials, HyMat, offer new opportunities for the easy, fast and cheap development of miniaturized functional devices. The integration of inorganic oxide networks, organic functional groups and optically active molecules or nanoparticles allows to obtain combinations of properties and structures otherwise impossible with traditional materials. In particular, a simple and highly versatile synthesis platform enabling preparation of HyMat is presented, which is built up by a bottom-up sol-gel approach at low processing temperatures. A few types of key building blocks pave the way for accessing HyMat and make up their formulation, providing a means to synthesize innovative materials enabling to get: - optically active micro and nanostructures; - miniaturized sensors for analytes in gaseous or liquid media; - direct patternability with a range of lithographic techniques; - variable inorganic and organic compositions, and controlled porosity. Examples of micro and nanostructures based on these spin-on materials with ceramic (i.e. SiO2, GeO2, Al2O3, ZrO2, TiO2,) and hybrid compositions will be presented for different applications including plasmonic or fluorescent sensors, dry-etching masks with outstanding resistance, optically active micro and nanostructured platforms and high resolution patterns

Hybrid materials: a bottom-up approach for nanotechnology applications

Engineered organic-inorganic hybrid materials, HyMat, offer new opportunities for the easy, fast and cheap development of miniaturized functional devices. The integration of inorganic oxide networks, organic functional groups and optically active molecules or nanoparticles allows to obtain combinations of properties and structures otherwise impossible with traditional materials. In particular, a simple and highly versatile synthesis platform enabling preparation of HyMat is presented, which is built up by a bottom-up sol-gel approach at low processing temperatures. A few types of key building blocks pave the way for accessing HyMat and make up their formulation, providing a means to synthesize innovative materials enabling to get: - optically active micro and nanostructures; - miniaturized sensors for analytes in gaseous or liquid media; - direct patternability with a range of lithographic techniques; - variable inorganic and organic compositions, and controlled porosity. Examples of micro and nanostructures based on these spin-on materials with ceramic (i.e. SiO2, GeO2, Al2O3, ZrO2, TiO2,) and hybrid compositions will be presented for different applications including plasmonic or fluorescent sensors, dry-etching masks with outstanding resistance, optically active micro and nanostructured platforms and high resolution patterns

Corpora@DipInTra (Interface to the CoLiTec corpora)

Corpora@DipInTra is a sharing hub giving unified access to the textual databases developed at the Corpora, Linguistics, Technology Research centre (CoLiTec corpora). Through this interface, the CoLiTec corpora are made widely available to the academic community, as well as other interested stakeholders, like students, language professionals and companies. These include large web-derived corpora and small but highly specialised ones, e.g.: a) acWaC (academic Web-as-Corpus), a pool of corpus resources to study institutional-academic language; b) WaCky (Web-As-Corpus Kool Yinitiative), a collection of large corpora built by automatically downloading texts from the English, French, German and Italian web; and c) La Repubblica, a corpus of Italian newspaper texts published between 1985 and 2000. The interface itself is based on the NoSketch Engine platform, a state-of-the-art, open-source tool for corpus management, providing a powerful and user-friendly interface to perform corpus searches, generate word/keyword lists and retrieve collocations based on several statistical measures

BootCaT v. 0.8 (Simple utilities to Bootstrap Corpora and Terms from the Web)

The BootCaT front-end is a graphical interface for the BootCaT toolkit (Baroni and Bernardini 2004). It automates the process of finding reference texts on the web and collating them in a single corpus. The pipeline allows varying levels of control. In the first step, users provide a list of single- or multi-word terms to be used as seeds for text collection. These are then combined into \u201ctuples\u201d of varying length and sent as queries to a search engine, which returns a list of potentially relevant URLs. At this point the user has the option of inspecting the URLs and trimming them; the actual web pages are then retrieved, converted to plain text and saved in "txt" format. The corpus can thus be interrogated using most concordancers. Using BootCat one can build a relatively large quick-and-dirty corpus (typically of about 80 texts, with default parameters and no manual quality checks) in less than half an hour. This flexible approach to the task makes BootCaT a very useful tool for translators and translation students, which has been used in the translation and terminology classroom to build small DIY corpora of varying size and specialization. As of June 2017, the software has been downloaded and installed by over 2800 single users, from 74 countries