1,720,978 research outputs found
Optical investigation of degradation of graphene oxide in alkaline environment: Evidence of two distinct photon-emitting phases in visible region
Full text linkIn this work we show a procedure of treating of the graphene oxide in alkaline environment as a function of the treatment time in order to obtain novel structures with strong luminescence properties, water-stable, useful as potential replacement for critical raw materials employed as example in optical and optoelectronic devices or for diagnostic and therapeutic technology. These structures have distinct blue and green-luminescence properties which derived most likely from different structural conformations, one associable with that of carbon quantum dots (or as an alternative to that of the Oxidative Debris), the other, lighter and more similar to organic compounds, reported in literature as fulvic-like molecules, but whose nature has to be further investigated. We show that the lighter fraction has a dual mechanism of photoemission: the excitation-independent PL for excitation wavelength within 350 nm and the excitation-dependent component for excitation wavelength ranging in the visible spectrum. The PL dual behaviour could depend on fluorescent nanoclusters composed by specific organic fluorophores with a carbonaceous core. FTIR analysis shows reasonably the same functional groups unless of some difference discussed in the text, meanwhile UV–Vis and PL analysis clearly highlight two distinct emissions (450 nm and 530 nm) in the visible region of the electromagnetic spectrum. Excitation-dependent photoluminescence, water stability and organic fluorescent nanostructures are issues particularly required for application in the biological field but also in materials science
RESEARCH ACTIVITY ON PV WASTE RECYCLING IN ENEA
No full textENEA is dedicating significant efforts to the research activity concerning the treatment of End-of-Life (EoL) photovoltaic panels (PVs), which is a worldwide emergent issue to be urgently solved. With PVs typically having a lifespan of 25 years, the volume of PV waste is projected to increase rapidly by 2030. This issue is compounded by the composition of photovoltaics, which includes hazardous materials, necessi-tating the development of technological solutions to mitigate the environmental impact of commonly used recycling methods. Additionally, strategic materials present in PVs make the valorization of recovered materials highly advantageous. ENEA is actively involved in several research projects focused on EoL PVs recycling. This article will outline the main objectives of these projects and present the key findings achieved by ENEA’s research team
MgF2 films deposited by ion assisted electron beam evaporation for high power UV laser applications
No full textOptical characterisation of silver mirrors protected with transparent overcoats
No full textTime durability and environmental stability of silver-coated glass mirrors improve if silver layer is protected by a transparent thin film coating. The choice of the protecting layer material and of the methods for mirror manufacturing influences the mirror optical and mechanical properties. This work reports on a systematic study of silver mirrors overcoated by silicon oxide, nitride and oxy-nitrides. Variable angle spectroscopic ellipsometry was implemented to get an insight on metal-dielectric interface of the coatings. The results have been analyzed considering the coating deposition conditions and physical-chemical properties of the dielectric materials used as protective layers. © 2018 COPYRIGHT SPIE
On the Representativeness of Proton Radiation Resistance Tests on Optical Coatings for Interplanetary Missions
Full text linkOptical instrumentation used in space normally employs optical coatings. Future interplanetary space missions will be characterized by ever longer stays in environmental conditions where low energy protons represent one of the main types of radiation impacting the coating longevity and performance. To ensure the reliability of coated optics, environmental resistance tests should be accurately planned to be representative for a mission. To this end, the existing standards for coating tests and the test results interpretation have been constantly improved. In this study, we analyze the relevant standards of the European Space Agency (ESA) and of the Chinese Space Agency (CSA) for testing coated optics for interplanetary missions, and in particular for the missions at the Lagrange points. We focus in particular on the applicability of these standards and hence on their possible refinement when specifically implemented to the optical thin films and coatings. We proceed with the development of a methodology for reliable interpretation of the proton irradiation tests for the optical coatings for interplanetary missions, first briefly overviewing the existing tools which allow for space environment simulation and hence deriving the test conditions for the Lagrange points. Furthermore, we apply the approach to testing of aluminum oxide optical coatings for applications in the visible spectral range, concluding on the representativeness of the proposed approach and on possible refinement of the existing standards for coating tests when they are specifically developed for optical applications
Flexible Humidity Sensor Based on Chemically Reduced Graphene Oxide
Full text linkThe accurate measurement of moisture content in pure gases and in gas mixtures, such as air, has great relevance in many industrial processes. In the present study, graphene oxide reduced through a mild alkaline treatment was used as a humidity sensing material to fabricate a flexible chemiresistive device operating at room temperature. The active layer was deposited by solution casting on a substrate of bimatted polyester, previously coated with inkjet-printed interdigitated electrodes made of silver. Structural investigations were performed by means of X-ray diffraction, Raman spectroscopy, and FTIR spectroscopy, while the optical properties were investigated using UV-VIS absorption and photoluminescence excitation spectroscopy. With increasing relative hu-midity from 0 to 80%, the electrical resistance decreased from about 1.4 GΩ to 2.5 MΩ. The ex-traordinarily large range of resistance values highlights the ultrahigh humidity sensitivity of re-duced graphene oxide, which acquires a fair amount of electrical conductivity after physisorption of water molecules but results in a highly resistive material in dry air. The high sensitivity at room temperature, the response’s repeatability, the wide relative humidity range detected, and the fast response time are the main advantages of the proposed humidity sensor, while the presence of some hysteresis, mainly at low relative humidity, and the recovery time need further improve-ment. Finally, the sensing mechanisms are briefly discussed
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
Changing the Microstructural and Chemical Properties of Graphene Oxide Through a Chemical Route
No full textThe aim of this work is to investigate the possibility of engineering desired molecular sp2 structures in graphene oxide, via controlled oxidation of graphite powder, in order to achieve tunable chemical and microstructural properties useful for optoelectronics or sensing applications. Specifically, GO powder is obtained by a modified Hummers method, by using different concentrations of potassium permanganate (KMnO4) in order to change the number of oxygen functionalities in the graphitic structure. Then, a successive alkaline treatment is performed by increasing the KOH concentration. The alkaline treatment induces a noticeable variation of the GO microstructural and chemical properties, which is accompanied by a strong enhancement of photoluminecence. PL and PLE measurements reveal that the configuration of electronic energy states changes as a function of the KMnO4 and KOH concentration, by introducing further electronic n levels available for n→π* transitions. In particular, the number of sp2 small domains embedded among oxygen–sp3 domains, increases under the KOH treatment, due to the addition of OH groups. Most of these sp2 domains are lifted-off from GO and thrown away in the surnatant giving it high blue photoluminescence excited at λexc ∼ 319 nm. The employ of combined spectroscopy techniques allows a deep investigation of the microstructural and chemical changes induced by chemical treatments, opening the way to the fine tuning of GO functional properties
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
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