62 research outputs found
Large area TMD-based van der Waals heterostructures featuring enhanced photoconversion in the flat optics regime
No full textOne of the most urgent technological needs of this century concerns the research of innovative nanomaterials for applications in optoelectronics, nanophotonics and photovoltaics for renewable energy conversion. In fact, downscaling of the silicon-based devices (e.g. field-effect transistors) has come to an end due to intrinsic physical limitations such as size, inadequate carrier mobility, short channel effects, atomic-scale interactions, heat generation, and energy consumption at atomic scale thickness, requiring innovative materials to overcome such difficulties.
Graphene discovery in 2004 by Novoselov and Geim arose a tremendous interest for the two-dimensional (2D) materials, in which the reduced dimensionality brings new properties with respect to their bulk counterparts. Despite the extraordinary properties exhibited by graphene, its gapless nature strongly limits the fabrication of graphene-based optoelectronic devices. For this reason, the interest of researchers shifted towards the class of 2D semiconductors. Among these materials, Transition Metal Dichalcogenides (TMDs) represent the most important family due to suitable bandgap energy values which match the Schockley-Queisser efficiency criterion for solar photoconversion, and to their extraordinary optical absorption coefficient.
Additionally, 2D materials can be vertically stacked to form the so-called van der Waals heterostructures that are endowed by pristine interface thanks to the relatively weak van der Waals interactions that keep the stack together. This offers the opportunity to fabricate heterostructures of arbitrary 2D materials, independently by their crystal structure, with no limitations on the engineering of the optoelectronic and photonic properties of the new stacked metamaterial. In particular, the possibility to realize van der Waals p-n junctions by coupling 2D-TMDs layers is very intriguing for photoconversion and photovoltaic applications.
So far, TMDs employment has been mostly limited to the fabrication of prototypical devices such as field-effect transistors and photodetectors, most of which were realized via mechanical exfoliation from single crystal of flakes with thickness ranging from one to few atomic layers. Despite their intriguing properties, these materials do not represent an industrially relevant alternative to traditional semiconductors, being the exfoliation a randomic process with very low yields and limited areas in the micrometer range. Consequently, one of the key frontiers of TMDs research is the large area growth of homogeneous ultra-thin layers with controlled thickness over macroscopic areas. To meet this requirement, several large area techniques have been studied to synthesize TMDs layers extending over cm2 areas. However, in contrast with the exfoliation process, these techniques result in polycrystalline layers where the high concentration of grain boundaries degrades the macroscopic conduction.
The second crucial issue to be solved for ultra-thin TMD-based devices to be used in photoconductive and photodetection applications is the maximization of the optical absorption. Despite the excellent optical absorption coefficient, an ultra-thin TMD film indeed cannot absorb efficiently the incoming light due to the ultimately reduced thickness, which means a nanometric optical path. It is thus evident that new strategies for the optical absorption amplification in ultra-thin 2D semiconductors need to be developed to allow proper performances in TMD-based photodetection and photovoltaics applications. Because of the atomic thickness of the 2D layer, traditional solutions developed for the light harvesting amplification in conventional silicon-based photovoltaic devices, based on pyramidal microstructuring or on the addition of antireflective coatings, cannot be transferred to these materials.
Recently, the research group where I carried out my activity worked on large area ultra-thin MoS2 films conformally grown on self-organized rippled substrate fabricated by ion beam sputtering. Their results clearly showed a modification of the TMD optical and electronic properties grown on the nanostructured substrate with respect to a flat one. This observation was explained with the stress induced by the substrate morphology in the MoS2 layer in correspondence to the high curvature regions given by the crests and valleys of the ripples, meaning that by control of the substrate morphology it is possible to engineer the material intrinsic properties.
Additionally, the nanostructures anisotropy adds a polarization-dependent optical response, offering a way to engineer the optical absorption of the 2D material in view of photoconversion applications. However, self-organized nanostructures suffer from a relevant size dispersion and long range disorder, whereas more interesting optical effects are expected for periodic nanogratings in which the subwavelength TMD layers reshaping provide them the functionality of flat optic diffractive elements.
Starting from here, I devoted the most of my research activity to face the two main challenges described above: developing a growth process for large area ultra-thin TMD films, and studying an efficient light harvesting strategy to maximize the optical absorption in few-layer semiconductor films. An overview of the state-of-the-art regarding 2D materials and nanophotonics approaches for light harvesting in ultra-thin films is given in Chapter 1, while the growth synthesis techniques are postponed in Chapter 2.
At the beginning of my PhD, MoS2 films were grown by external collaborators of my group, thus limiting the activities. In the first phase of my research activity, I developed a novel large area growth process based on the physical deposition of solid precursor films and sulfurization, as I will describe in Chapter 2. This novel technique enabled not only the in-house growth of ultra-thin MoS2 films for the first time, but also allowed to extend the process to ultra-thin WS2 layers.
Having now the capability to control the deposition of two different TMDs layers, I moved to the growth of large area van der Waals heterostructures. Due to the type-II heterojunction formed by the band structure coupling of MoS2 and WS2, such heterostructures are expected to have a high potential in photoconversion applications. In Chapter 3 I will show the nanofabrication of planar MoS2/WS2 heterostacks, and their application in photocatalytic experiments and in a prototype of photonic device, featuring first evidence of photovoltage and photocurrent under illumination. This latter application also required me to develop large area transparent electrodes, so that I will dedicate a part of the chapter to indium tin oxide thin films and large area graphene.
In the second phase of my research activity, I focused on light harvesting in ultra-thin TMDs layers. Thanks to the conformality achieved by the physical deposition process, I explored a nanophotonic approach based on the optical anomalies arising from periodic modulation of the TMD layer at the subwavelength scale, obtained by conformal growth of the TMD layers onto nanostructured substrates. To this end, periodic nanogratings have been used as a template for the growth of ultra-thin MoS2 layers. Differently from the self-organized nanostructures mentioned before, the periodicity induces diffractive effects that are exploited to steer the light parallel to the active 2D material enhancing the optical absorption, as demonstrated in Chapter 4 both directly by absorption measurements and indirectly by a photo-to-chemical energy conversion experiment where we detected enhanced photocatalytic performances.
In the final part of my project, I started preliminary studies on the elastic scattering properties of subwavelength periodical lattices based on nanostructured tilted TMD layers. By defocused ion beam sputtering, I was able to reshape the morphology of the initial nanograting templates to further engineer the TMD optical response. In particular, by off-normal incidence sputtering it is possible to tailor a specific slope of the tilted nanofacets, on top of which I deposited laterally disconnected MoS2 nanostripes by grazing angle physical deposition. By developing a custom-made scatterometer, optical characterization of ultra-thin MoS2 nanostripes and thicker MoS2 films was performed, giving interesting preliminary results on the directional light scattering properties of these reshaped layers, as reported in Chapter 5. Finally, I adopted a similar deposition approach for the nanofabrication of large area heterostructures nanoarrays based on few-layer WS2 nanostripes coated by a conformal MoS2 layer, demonstrating further engineering of the optical response of few-layer TMD films with impact in photoconversion
Gardella/l’abitare: lo spazio temporaneo
No full textabstractLo studio dell’opera di Ignazio Gardella inerente il progetto di strutture alberghiere, consente di ampliare la conoscenza sull’attività di un autore molto considerato dalla critica, ma di cui manca completamente una trattazione sistematica dell’argomento. Dalle numerose e ben documentate fonti a disposizione, non solo relative a documenti di progetto o provenienti dagli archivi di famiglia, ma anche riferibili ad una vasta letteratura sul tema del turismo, la figura del progettista emerge come una personalità di riferimento del settore, di grande rilevanza per lo sviluppo del paese, nell’immediato secondo dopoguerra, prima, e ancor più negli anni del boom economico, poi, come testimoniano alcuni dei committenti di questi progetti
Ignazio Gardella, method and language in the house project
No full textLa ricerca inquadra all’interno dell’opera dell’autore, lo specifico tema della residenza.
Esso costituisce il campo di applicazione del progetto di architettura, in cui più efficacemente ricercare i tratti caratteristici del metodo progettuale dell’architetto, chiave di lettura dello studio proposto. Il processo che giunge alla costituzione materiale dell’architettura, viene considerato nelle fasi in cui è scomposto, negli strumenti che adotta, negli obbiettivi che si pone, nel rapporto con i sistemi produttivi, per come affronta il tema della forma e del programma e confrontato con la vasta letteratura presente nel pensiero di alcuni autori vicini a Ignazio Gardella.
Si definiscono in tal modo i tratti di una metodologia fortemente connotata dal realismo, che rende coerente una ricerca empirica e razionale, legata ad un’idea di architettura classica, di matrice illuministica e attenta alle istanze della modernità, all’interno della quale si realizza l’eteronomia linguistica che caratterizza uno dei tratti caratteristici delle architetture di Ignazio Gardella; aspetto più volte interpretato come appartenenza ai movimenti del novecento, che intersecano costantemente la lunga carriera dell’architetto.
L’analisi dell’opera della residenza è condotta non per casi esemplari, ma sulla totalità dei progetti che si avvale anche di contributi inediti. Essa è intesa come percorso di ricerca personale sui processi compositivi e sull’uso del linguaggio e permette un riposizionamento della figura di Gardella, in relazione al farsi dell’architettura, della sua realizzazione e non alla volontà di assecondare stili o norme a-priori. E’ la dimensione pratica, del mestiere, quella che meglio si presta all’interpretazione dei progetti di Gardella. Le residenze dell’architetto si mostrano per la capacità di adattarsi ai vincoli del luogo, del committente, della tecnologia, attraverso la re-interpretazione formale e il trasferimento da un tema all’altro, degli elementi essenziali che mostrano attraverso la loro immagine, una precisa idea di casa e di architettura, non autoriale, ma riconoscibile e a-temporale.The research fits within specific issue of the residence in the work of one of the most important italian contemporary architects.
It is the scope of architectural design, in which more effectively search for characteristic features of the design method of the architect, key to the proposed study. Projects are analyzed, starting from the search of the method that rules the process from creation to costruction,
The architecture of the author can be read as relationship between an empiric method and an eclectic language. It is formed by a realism that connect classic and rational methodolgy, with the modern shapes and the contents of the twentieth century architectur
Practically, project can be defined as a succession of operations, directed to solve problems, coming from three main generals binds: place, as a cultural and fisical environment, client and building technology. Each ones influenced by specific conditions of site, inhabitants and social - economical condition of the time.
Considering the all Gardella’s production about dwellings, that also makes use of new contributions, not only master pieces, architect does not research a style.
His buildings are products of the constant re-definition and adaptability of the essentials parts that respond to problems and concretely builds house and architecture as well.
So the Gardella’s work appears more complex than an interpretation based on twentieth century movements or styles.
In this way, it's possibile recognize same elements that form a personal, not authorship, but recognizable and a-temporal, idea of liveble spaces, and image of home, applied through the re-interpretation and the formal transfer from one theme to another, to different types of houses: collectives or individuals, to different users, bourgeois, middle or popular class, to different places and repeated in the different moments of the author’s long carrer
Aromatase inhibitors in the pharmacotherapy of endometriosis
No full textIntroduction: Endometriosis is a benign chronic inflammatory disease responsible for debilitating pain and decreased quality of life. The traditional treatment is based on estroprogestins, progestins, GnRH analogs, and surgery. Recently, aromatase inhibitors (AIs) demonstrated good efficacy in controlling symptoms and size of endometriotic implants, mostly because they suppress extraovarian estrogen synthesis, which can enhance the hypoestrogenic state ameliorating symptoms of endometriosis. Areas covered: Phase I, II, III and IV trials, on the use of AIs used for the treatment of endometriosis, have been retrieved. The pharmacokinetics and pharmacodynamics of third-generation non-steroidal AIs have also been investigated. A MEDLINE search has been performed using the following MeSH keywords: ‘endometriosis,’ aromatase inhibitors,’ ‘therapy,’ and ‘treatment’. The timeframe was from 2010 up to November 2022 including reviews, systematic reviews, reports, case series, and retrospective or prospective trials. Expert opinion: AIs have shown good clinical efficacy in combination with hormonal therapy in disease control, and they represent a promising second-line therapy in selected patients, yet more research is needed on alternative drug delivery systems and better control of adverse effects. In postmenopausal women in which surgery is contraindicated, AIs represent an excellent treatment option. Their application in routine clinical practice remains limited by adverse effects
Da condição do lugar à harmonia compositiva. Casa al Parco, Ignazio Gardella
Get PDFPartindo da reflexão do Movimento Moderno, como âncora no pensamento
e no fazer contemporâneo, procura-se focar a presente investigação no estudo de
uma obra singular e no seu autor, o projeto da Casa al Parco, em Milão, do arquiteto
Ignazio Gardella.
O estudo propõe, a partir do arquivo pessoal do arquiteto, compreender a
evolução do processo de desenho, analisar e interpretar as diferentes fases de desenvolvimento,
opções de projeto, seus princípios orientadores e temas de composição
arquitetónica. O aprofundamento dessas noções visa compreender os métodos e estratégias
de desenho do arquiteto, tendo em vista a intemporalidade do seu modo de
pensar e do seu desenho, procurando evidenciar a influência da arquitetura moderna
nas narrativas contemporâneas.Nestled at the reflection of the Modern Movement, an anchor in the contemporary
way of thinking and working, the present investigation focuses on the analysis
of a unique piece of architecture and its author - Casa al Parco, in Milan, by the
architect Ignazio Gardella.
The personal archive of the architect was set as a starting point while the study
intends to understand the evolution of the design process, to analyse and clarify the
different phases of development, its design options, guiding principles and architectural
composition themes.
As the investigation develops, the purpose is to fully understand the architect's
design methods and strategies, as Gardella became an icon of a timelessness way of
thinking and designing which played a crucial role on the influence of modern architecture
in the contemporary narratives
Flat-optics hybrid MoS2/polymer films for photochemical conversion
No full textNovel light harvesting platforms and strategies are crucial to develop renewable photon to energy conversion technologies that overcome the current global energy and environmental challenges. Two-dimensional (2D) transition metal dichalcogenide (TMD) semiconductor layers are particularly attractive for photoconversion applications but new ultra-compact photon harvesting schemes are urgently required to mitigate their poor photon absorption properties. Here, we propose a flat-optics scheme based on nanogrooved ultra-thin MoS2 layers conformally grown onto large area (cm2 scale) nanopatterned templates. The subwavelength re-shaping of the 2D-TMD layers promotes the excitation of photonic Rayleigh anomaly (RA) modes, uniquely boosting a strong in-plane electromagnetic confinement. By tailoring the illumination conditions, we demonstrate effective tuning of the photonic anomalies over a broadband visible spectrum across the absorption band of relevant polluting dye molecules. Thanks to the strong photonic in-plane confinement, we achieve a resonant enhancement of the photodissociation rate of methylene blue (MB) molecules, well above a factor of 2. These results highlight the potential of flat-optics photon harvesting schemes for boosting photoconversion efficiency in large-scale hybrid 2D-TMD/polymer layers, with a strong impact in various applications ranging from new-generation photonics to waste water remediation and renewable energy storage
Large area nanostructuring of van der Waals materials for photon harvesting in the flat optics regime
No full textITO-free transparent plasmonic nano-electrodes via Ar Plasma irradiation for large area and flexible architectures
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