| 1. |
- Benatto, L., et al.
(author)
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Understanding the effect of solvent additive in polymeric thin film : turning a bilayer into a bulk heterojunction-like photovoltaic device
- 2020
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In: Journal of Physics D. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 53:36
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Journal article (peer-reviewed)abstract
- Here we report the effect of an additive solvent, 1,8-diiodooctane (DIO), on the performance of a bilayer organic photovoltaic device in which the active layer comprises poly[2,7-(9,9-bis(2 ethylhexyl)-dibenzosilole)-alt-4,7-bis(thiophen-2-yl)benzo-2,1,3-thiadiazole] (PSiF-DBT) as the electron donor material and C60 as the electron acceptor material. We observed that when the donor layer was treated with 1% of DIO the power conversion efficiency (PCE) of the device increased by 138.4% in relation to the device with an untreated donor layer, and 21.3% in relation to the device containing a donor layer submitted to thermal annealing. The main effects that lead to this increase in PCE are the large interfacial area between donor and acceptor materials and the improved conductivity at low voltages. The increase in polymer surface roughness leads to a more effective PSiF-DBT/C60 interface for exciton dissociation. This effect, as well as the increase in the conductivity, raised the short circuit current density (JSC) to 13.89 mA cm−2 and the PCE to 4.84%. Our conclusions are supported by morphological analysis, chemical cross-sectional evaluations with advanced microscopy techniques, charge mobility measurements, as well as by theoretical simulations of the devices in which the changes on the donor/acceptor interfacial area were considered. The outcomes suggest that solvent additives could be an alternative treatment to replace the thermal annealing, which imposes further difficulties in performing lab-to-manufacturing upscaling.
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| 2. |
- Cazzaniga, C., et al.
(author)
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Light response of YAP:Ce and LaBr3:Ce scintillators to 4-30 MeV protons for applications to Telescope Proton Recoil neutron spectrometers
- 2016
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In: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 820, s. 85-88
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Journal article (peer-reviewed)abstract
- The light response of two thin inorganic scintillators based on YAP:Ce and LaBr3:Ce crystals has been measured with protons in the 4-8 MeV energy range at the Uppsala tandem accelerator and in the 826 MeV energy range at the Legnaro tandem accelerator. The crystals have been calibrated in situ with Cs-137 and Co-60 gamma-ray sources. The relative light yields of protons with respect to gammas have been measured and are here reported to be (96 +/- 2)% and (80 +/- 2)% for YAP:Ce and LaBr3:Ce, respectively. The results open up to the development of a Telescope Proton Recoil spectrometer based on either of the two crystals as alternative to a silicon based spectrometer for applications to high neutron fluxes.
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| 3. |
- Pereira, Cassia Ferreira Coutinho, et al.
(author)
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Inducing molecular orientation in solution-processed thin films of fluorene-bithiophene-based copolymer : thermal annealing vs. solvent additive
- 2024
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In: RSC Advances. - : Royal Society of Chemistry. - 2046-2069. ; 14:13, s. 9051-9061
-
Journal article (peer-reviewed)abstract
- A deep understanding of the factors influencing the morphology of thin films based on conjugated polymers is essential to boost their performance in optoelectronic devices. Herein, we investigated the electronic structure and morphology of thin films of the copolymer poly(9,9-dioctyl-fluorenyl-co-bithiophene) (F8T2) in its pristine form as well as samples processed with the solvent additive 1,8-diiodooctane (DIO) or post-processed through thermal annealing treatment. Measurements were carried out using angle-resolved S K-edge NEXAFS (near-edge X-ray absorption fine structure) in total electron yield (TEY) and fluorescence yield (FY) detection modes. Two main transitions were observed at the S 1s NEXAFS spectra: S 1s -> pi* and S 1s -> sigma* (S-C). The observed dichroism pointed to a face-on orientation of the conjugated backbone, which was significantly increased for F8T2 films processed with DIO. Resonant Auger decay spectra were obtained and analyzed using the core-hole clock (CHC) method. An enhancement in the charge transfer process was observed for thermally annealed films, especially for samples processed with DIO, corresponding to an increase in film ordering. Furthermore, the investigated films were characterized using X-ray photoelectron spectroscopy, attesting to the presence of the thiophene unit in the samples and demonstrating that some of its sulfur atoms were positively polarized in the F8T2 films. All these experimental findings were compared with molecular dynamics (MD) simulations of film evaporation with and without DIO. The use of MD, together with mathematical modeling, was able to explain the major effects found in the experiments, including the polarization of sulfur atoms. The simultaneous use of powerful spectroscopic techniques and theoretical methods shed light on key aspects linking film morphology with fabrication procedures.
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| 4. |
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| 5. |
- Aderne, Rian E., et al.
(author)
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On the energy gap determination of organic optoelectronic materials : the case of porphyrin derivatives
- 2022
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In: Materials Advances. - : Royal Society of Chemistry. - 2633-5409. ; :3, s. 1791-1803
-
Journal article (peer-reviewed)abstract
- The correct determination of the ionization potential (IP) and electron affinity (EA) as well as the energy gap is essential to properly characterize a series of key phenomena related to the applications of organic semiconductors. For example, energy offsets play an essential role in charge separation in organic photovoltaics. Yet there has been a lot of confusion involving the real physical meaning behind those quantities. Experimentally the energy gap can be measured by direct techniques such as UV-Vis absorption, or indirect techniques such as cyclic voltammetry (CV). Another spectroscopic method is the Reflection Electron Energy Loss Spectroscopy (REELS). Regarding data correlation, there is little consensus on how the REELS' energy gap can be interpreted in light of the energies obtained from other methodologies such as CV, UV-Vis, or photoemission. In addition, even data acquired using those traditional techniques has been misinterpreted or applied to derive conclusions beyond the limits imposed by the physics of the measurement. A similar situation also happens when different theoretical approaches are used to assess the energy gap or employed to explain outcomes from experiments. By using a set of porphyrin derivatives as model molecules, we discuss some key aspects of those important issues. The peculiar properties of these porphyrins demonstrate that even straightforward measurements or calculations performed in a group of very similar molecules need a careful interpretation of the outcomes. Differences up to 660 meV (similar to 190 meV) are found comparing REELS (electrochemical) measurements with UV-Vis energy gaps, for instance. From the theoretical point of view, a reasonable agreement with electrochemical measurements of the IP, EA, and the gap of the porphyrins is only obtained when the calculations involve the full thermodynamics of the redox processes. The purpose of this work is to shed light on the differences and similarities of those aforementioned characterization methods and provide some insight that might help one to develop a critical analysis of the different experimental and theoretical methodologies.
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| 6. |
- Cremona, C., et al.
(author)
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Improved Assessment Methods for Static and Fatigue Resistance of Old Steel Railway Bridges
- 2007
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Reports (peer-reviewed)abstract
- The present section of Deliverable D.4.3 is dedicated to the static and fatigue assess-ment of old metal bridges. It forms the basis of the Chapter 7 guideline developed in work package 4 (WP4) “Guideline for Load and Resistance Assessment of Existing European Railway Bridges”. This section is divided into four parts related to the four research activities of the WP4 metal subgroup:– Analysis of material properties of existing metal railway bridges, – Fatigue of riveted structure,– Updated assessment methods for riveted structures,– Enhanced non destructive techniques for inspecting riveted structures.
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| 7. |
- Cremona, F., et al.
(author)
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Hybrid Co-simulation : It's about time
- 2018
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In: Proceedings - 21st ACM/IEEE International Conference on Model Driven Engineering Languages and Systems, MODELS 2018. - New York, NY, USA : Association for Computing Machinery, Inc. - 9781450349499
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Conference paper (peer-reviewed)abstract
- Model-based design methodologies are commonly used in industry for the development of cyber-physical systems (CPSs). There are many different languages, tools, and formalisms for model-based design, each with its strengths and weaknesses. Instead of accepting the weaknesses of a particular tool, an alternative is to embrace heterogeneity and develop tool integration platforms and protocols to leverage the strengths from other environments. A fairly recent attempt in this direction is an open interface standard called Functional Mock-up Interface (FMI), which is focused on the convenient exchange and co-simulation of simulation models (Functional Mock-up Units, FMUs), primarily between component suppliers and OEMs. As it stands, FMI has reached acceptance in industry, but its specification (version 2.0) provides only limited support for hybrid co-simulation-simulating systems that mix continuous and discrete behaviors, which are commonly used to model CPSs. This paper identifies FMI's time representation based on floating-point numbers as a key problem, because it does not support well the discrete events that typically occur at the cyber-physical boundary; it is only suitable for modeling continuous dynamics without discrete behaviors. While time is a central concept in reasoning about the physical world, it is largely abstracted away when reasoning about the cyber world. As a result, the engineering methods for CPSs have misaligned abstractions between the physics domain, the mathematical domain used to model physics, the computational domain used to implement these mathematical abstractions for simulation, and the computational domain used on the cyber side of CPSs. The most common resolution for this conundrum is to adopt the naive Newtonian ideal model of time, where time is a real number known everywhere and advancing uniformly. But ironically, Newtonian time proves not so practical for hybrid co-simulation. The obvious reason is that digital computers do not work with real numbers. Whereas real numbers have infinite precision, their floating-point representation does not. This discrepancy leads to unpredictable quantization errors that may accumulate. Although real numbers can be compared for equality (e.g., to define “simultaneity”), it rarely makes sense to do so for floating-point numbers. We show that the approach taken in FMI (and many other modeling frameworks) that embraces a naive Newtonian physical model of time, and a cyber-approximation of this model using floating-point numbers, is inadequate for CPSs; it leads to models with unnecessarily inexplicable, nondeterministic, and complex behaviors. Our analysis concludes that a model of time that solely uses integers solves many of these problems. Specifically, we propose to use a 64-bit unsigned integer representation with arbitrary resolution, given as a power of ten, allowing model parameters specified in decimal to be represented exactly (granted ample resolution). Integer arithmetic is computationally efficient, and, for well-chosen resolutions, this representation will tolerate very long simulations without overflow. It is also easily converted to and from floating-point representations, albeit not losslessly. Given the vast range of time scales used across different simulation models, we believe that choosing a fixed universal time resolution does not make sense. Instead, we describe an algorithm that picks an adequate time resolution for a particular model and we provide procedures for time quantization needed to reconcile discrepacies between internal time representations of co-simulated FMUs. We propose concrete extensions to the FMI standard for the support of hybrid co-simulation that enable the use of integer time, automatic choice of time resolution, and the use of absent signals. We explain in detail how these extensions can be implemented mod-ularly within the frameworks of existing simulation environments and with support for legacy FMUs and superdense time.
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| 8. |
- Cremona, Fabio, et al.
(author)
-
Hybrid co-simulation : it's about time
- 2019
-
In: Software and Systems Modeling. - : Springer Nature. - 1619-1366 .- 1619-1374. ; 18:3, s. 1655-1679
-
Journal article (peer-reviewed)abstract
- Model-based design methodologies are commonly used in industry for the development of complex cyber-physical systems (CPSs). There are many different languages, tools, and formalisms for model-based design, each with its strengths and weaknesses. Instead of accepting some weaknesses of a particular tool, an alternative is to embrace heterogeneity, and to develop tool integration platforms and protocols to leverage the strengths from different environments. A fairly recent attempt in this direction is the functional mock-up interface (FMI) standard that includes support for co-simulation. Although this standard has reached acceptance in industry, it provides only limited support for simulating systems that mix continuous and discrete behavior, which are typical of CPS. This paper identifies the representation of time as a key problem, because the FMI representation does not support well the discrete events that typically occur at the cyber-physical boundary. We analyze alternatives for representing time in hybrid co-simulation and conclude that a superdense model of time using integers only solves many of these problems. We show how an execution engine can pick an adequate time resolution, and how disparities between time representations internal to co-simulated components and the resulting effects of time quantization can be managed. We propose a concrete extension to the FMI standard for supporting hybrid co-simulation that includes integer time, automatic choice of time resolution, and the use of absent signals. We explain how these extensions can be implemented modularly within the frameworks of existing simulation environments.
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| 9. |
- Gouvêa, P. M. P., et al.
(author)
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Characterization of a fiber optic sensor based on LSPR and specular reflection
- 2010
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In: Optical Sensors (Sensors) 2010. - 9781557528964
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Conference paper (peer-reviewed)abstract
- A fiber optic sensor based on Localized Surface Plasmon Resonance (LSPR) and specular reflection has been characterized as a function of refractive índex. The sensitivity has been obtained for the range from n=1.0 to n=2.0.
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| 10. |
- Laguardia, L., et al.
(author)
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Formation of dust in low-pressure magnetized hydrocarbon plasmas
- 2011
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In: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 13, s. 063006-
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Journal article (peer-reviewed)abstract
- The rapid formation of large molecules and the subsequent production of solid-state dust particles in a low-pressure discharge is unlikely, because of the low rates of the polymerization reactions and short lifetimes of the species. Here, we suggest that C dust particles can form in atypically low (10(-3) mbar)-pressure hydrocarbon plasmas if the dust charging time is much shorter than the gas residence time in the device; we present supporting experimental evidence for this. Such a condition can be obtained by the production of high-density plasmas. The results show that dust formation from the gaseous phase can occur in a much wider parameter range than is commonly assumed.
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