Jesus Giráldez-Cru  Manuel Chica  Oscar Cordón  Francisco Herrera 《国际智能系统杂志》2020,35(2):283-299

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Karl Ridier  Yuteng Zhang  Mario Piedrahita-Bello  Carlos M. Quintero  Lionel Salmon  Gábor Molnár  Christian Bergaud  Azzedine Bousseksou 《Advanced materials (Deerfield Beach, Fla.)》2020,32(21):2000987

The thermally induced spin-crossover (SCO) phenomenon in transition metal complexes is an entropy-driven process, which has been extensively studied through calorimetric methods. Yet, the excess heat capacity associated with the molecular spin-state switching has never been explored for practical applications. Herein, the thermal damping effect of an SCO film is experimentally assessed by monitoring the transient heating response of SCO-coated metallic microwires, Joule-heated by current pulses. A damping of the wire temperature, up to 10%, is evidenced on a time scale of tens of microseconds due to the spin-state switching of the molecular film. Fast heat-charging dynamics and negligible fatigability are demonstrated, which, together with the solid-solid nature of the spin transition, appear as promising features for achieving thermal energy management applications in functional devices.  相似文献   

    

Chao Wen  Alexander G. Banshchikov  Yury Y. Illarionov  Werner Frammelsberger  Theresia Knobloch  Fei Hui  Nikolai S. Sokolov  Tibor Grasser  Mario Lanza 《Advanced materials (Deerfield Beach, Fla.)》2020,32(34):2002525

Mechanically exfoliated 2D hexagonal boron nitride (h-BN) is currently the preferred dielectric material to interact with graphene and 2D transition metal dichalcogenides in nanoelectronic devices, as they form a clean van der Waals interface. However, h-BN has a low dielectric constant (≈3.9), which in ultrascaled devices results in high leakage current and premature dielectric breakdown. Furthermore, the synthesis of h-BN using scalable methods, such as chemical vapor deposition, requires very high temperatures (>900 °C) , and the resulting h-BN stacks contain abundant few-atoms-wide amorphous regions that decrease its homogeneity and dielectric strength. Here it is shown that ultrathin calcium fluoride (CaF₂) ionic crystals could be an excellent solution to mitigate these problems. By applying >3000 ramped voltage stresses and several current maps at different locations of the samples via conductive atomic force microscopy, it is statistically demonstrated that ultrathin CaF₂ shows much better dielectric performance (i.e., homogeneity, leakage current, and dielectric strength) than SiO₂, TiO₂, and h-BN. The main reason behind this behavior is that the cubic crystalline structure of CaF₂ is continuous and free of defects over large regions, which prevents the formation of electrically weak spots.  相似文献   

    

Eva Cortés-del Río  Pierre Mallet  Héctor González-Herrero  José Luis Lado  Joaquín Fernández-Rossier  José María Gómez-Rodríguez  Jean-Yves Veuillen  Iván Brihuega 《Advanced materials (Deerfield Beach, Fla.)》2020,32(30):2001119

Quantum confinement of graphene Dirac-like electrons in artificially crafted nanometer structures is a long sought goal that would provide a strategy to selectively tune the electronic properties of graphene, including bandgap opening or quantization of energy levels. However, creating confining structures with nanometer precision in shape, size, and location remains an experimental challenge, both for top-down and bottom-up approaches. Moreover, Klein tunneling, offering an escape route to graphene electrons, limits the efficiency of electrostatic confinement. Here, a scanning tunneling microscope (STM) is used to create graphene nanopatterns, with sub-nanometer precision, by the collective manipulation of a large number of H atoms. Individual graphene nanostructures are built at selected locations, with predetermined orientations and shapes, and with dimensions going all the way from 2 nm up to 1 µm. The method permits the patterns to be erased and rebuilt at will, and it can be implemented on different graphene substrates. STM experiments demonstrate that such graphene nanostructures confine very efficiently graphene Dirac quasiparticles, both in 0D and 1D structures. In graphene quantum dots, perfectly defined energy bandgaps up to 0.8 eV are found that scale as the inverse of the dot’s linear dimension, as expected for massless Dirac fermions.  相似文献   

    

Laura Barrutia  Ivn Lombardero  Mario Ochoa  Mercedes Gabs  Ivn García  Toms Palacios  Andrew Johnson  Ignacio Rey‐Stolle  Carlos Algora 《Progress in Photovoltaics: Research and Applications》2020,28(1):60-70

Graphene has been intensively studied in photovoltaics focusing on emerging solar cells based on thin films, dye‐sensitized solar cells, quantum dots, nanowires, and so forth. However, the typical efficiency of these solar cells incorporating graphene is below 16%. Therefore, the photovoltaic potential of graphene has not yet been shown. In this work, the use of graphene for concentration applications on III‐V multijunction solar cells, which indeed are the solar cells with the highest efficiency, is demonstrated. First, a wide optoelectronic characterization of graphene layers is carried out. Then, the graphene layer is incorporated onto triple‐junction solar cells, which decreases their series resistance by 35% (relative), leading to an increase in fill factor of 4% (absolute) at concentrations of 1000 suns. Simultaneously, the optical absorption of graphene produces a relative short‐circuit current density decrease in the range of 0% to 1.8%. As a result, an absolute efficiency improvement close to 1% at concentrations of 1000 suns was achieved with respect to triple‐junction solar cells without graphene. The impact of incorporating one and two graphene monolayers is also evaluated.  相似文献   

    

Xu Jing  Yury Illarionov  Eilam Yalon  Peng Zhou  Tibor Grasser  Yuanyuan Shi  Mario Lanza 《Advanced functional materials》2020,30(18)

The continuous miniaturization of field effect transistors (FETs) dictated by Moore's law has enabled continuous enhancement of their performance during the last four decades, allowing the fabrication of more powerful electronic products (e.g., computers and phones). However, as the size of FETs currently approaches interatomic distances, a general performance stagnation is expected, and new strategies to continue the performance enhancement trend are being thoroughly investigated. Among them, the use of 2D semiconducting materials as channels in FETs has raised a lot of interest in both academia and industry. However, after 15 years of intense research on 2D materials, there remain important limitations preventing their integration in solid‐state microelectronic devices. In this work, the main methods developed to fabricate FETs with 2D semiconducting channels are presented, and their scalability and compatibility with the requirements imposed by the semiconductor industry are discussed. The key factors that determine the performance of FETs with 2D semiconducting channels are carefully analyzed, and some recommendations to engineer them are proposed. This report presents a pathway for the integration of 2D semiconducting materials in FETs, and therefore, it may become a useful guide for materials scientists and engineers working in this field.  相似文献   

    

Pietro Cataldi  Marco Cassinelli  Jos A. Heredia‐Guerrero  Susana Guzman‐Puyol  Sara Naderizadeh  Athanassia Athanassiou  Mario Caironi 《Advanced functional materials》2020,30(3)

The materials commonly used to fabricate thermoelectric devices are tellurium, lead, and germanium. These materials ensure the best thermoelectric performance, but exhibit drawbacks in terms of availability, sustainability, cost, and manufacturing complexity. Moreover, they do not guarantee a safe and cheap implementation in wearable thermoelectric applications. Here, p‐Type and n‐type flexible thermoelectric textiles are produced with sustainable and low‐cost materials through green and scalable processes. Cotton is functionalized with inks made with biopolyester and carbon nanomaterials. Depending on the nanofiller, i.e., graphene nanoplatelets, carbon nanotubes, or carbon nanofibers, positive or negative Seebeck coefficient values are obtained, resulting in a remarkable electrical conductivity value of 55 S cm^?1 using carbon nanotubes. The best bending and washing stability are registered for the carbon nanofiber‐based biocomposites, which increase their electrical resistance by 5 times after repeated bending cycles and only by 30% after washing. Finally, in‐plane flexible thermoelectric generators coupling the best p‐ and n‐type materials are fabricated and analysed, resulting in an output voltage of ≈1.65 mV and a maximum output power of ≈1.0 nW by connecting only 2 p/n thermocouples at a temperature difference of 70 °C.  相似文献   

    

Leonardo Ataide Carniato  Alexandre Ataide Carniato  Marcelo Carvalho Minhoto Teixeira  Rodrigo Cardim  Edson Italo Mainardi Junior  Edvaldo Assunção 《International journal of control》2020,93(5):1127-1146

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Julio Moreno  Javier Gómez  Manuel A. Serrano  Eduardo B. Fernandez  Eduardo Fernández-Medina 《Software》2020,50(8):1520-1538

Big Data environments are typically very complex ecosystems; this means that implementing them is complicated. One possible technique with which to address this complexity is the use of abstraction. Reference architecture (RA) can be useful for an improved understanding of the main components of Big Data. Herein, we propose a security RA that includes the management of security concerns and provides the main elements of a Big Data ecosystem. Application of this architecture to real-world scenarios facilitates its refinement and improves its usefulness. In this article, we present a case study of a real-world Big Data ecosystem implemented in a banking environment. This ecosystem was developed by everis, an NTT company with which we collaborated for this study. To conduct this validation case study, a map was established between the elements of the Big Data ecosystem implemented and our proposal. Consequently, a series of valuable lessons that can improve both our architecture and the security of the Big Data environment were obtained. These include recommendations for a set of best practices such as the use of security patterns.  相似文献   

    

Antonio Caselles  David Soler  Maria T. Sanz  Joan C. Micó 《控制论与系统》2020,51(3):265-314

Abstract

A system methodology for modeling and optimizing social systems is presented. It allows constructing dynamical models formulated stochastically, i.e., their results are given by confidence intervals. The models provide optimal intervention ways to reach the stated objectives. Two optimization methods are used: (1) to test strategies and scenarios and (2) to optimize with a genetic algorithm. The application case presented is a small nonformal education Spanish business. First, the model is validated in the 2008–2012 period, and subsequently, the optimal way to obtain a maximum profit in the 2013–2025 period is obtained using the two methods.  相似文献