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Improving the Thermionic Energy Conversion Efficiency Through Fine-Tuning Functional Characteristics of Multilayer Carbyne-Enriched Nano-Interfaces
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Anthropogenic emissions of carbon dioxide (CO 2 ), methane (CH 4 ) and nitrous oxide (N 2 O) have made significant contributions to global warming since the pre-industrial period and are therefore targeted in international climate policy. There is substantial interest in tracking and apportioning national contributions to climate change and informing equitable commitments to decarbonisation. Here, we introduce a new dataset of national contributions to global warming caused by historical emissions of carbon dioxide, methane, and nitrous oxide during the years 1851–2021, which are consistent with the latest findings of the IPCC. We calculate the global mean surface temperature response to historical emissions of the three gases, including recent refinements which account for the short atmospheric lifetime of CH 4 . We report national contributions to global warming resulting from emissions of each gas, including a disaggregation to fossil and land use sectors. This dataset will be updated annually as national emissions datasets are updated.
The recent rise of computational, data-driven research has significant potential to accelerate materials discovery. Automated workflows and materials databases are being rapidly developed, contributing to high-throughput data of bulk materials that are growing in quantity and complexity, allowing for correlation between structural-chemical features and functional properties. In contrast, computational data-driven approaches are still relatively rare for nanomaterials discovery due to the rapid scaling of computational cost for finite systems. However, the distinct behaviors at the nanoscale as compared to the parent bulk materials and the vast tunability space with respect to dimensionality and morphology motivate the development of data sets for nanometric materials. In this review, we discuss the recent progress in data-driven research in two aspects: functional materials design and guided synthesis, including commonly used metrics and approaches for designing materials properties and predicting synthesis routes. More importantly, we discuss the distinct behaviors of materials as a result of nanosizing and the implications for data-driven research. Finally, we share our perspectives on future directions for extending the current data-driven research into the nano realm.
Charging of dielectrics on contact and separation has puzzled scientists and engineers for centuries. In a conventional view, the charges emerging on the two surfaces derive from the properties of the contacting materials, are of opposite polarities and are distributed approximately uniformly. However, a body of evidence has been mounting that contact electrification can also produce heterogeneous charge distributions in the form of (+/-) charge mosaics on each of the surfaces—yet, despite many attempts, no predictive model explaining the formation of mosaics at different length scales has been proposed; the main line of thinking has been that they must reflect some spatial heterogeneity present in the contacting materials. Here we describe experiments and theoretical models that prove a fundamentally different origin of mosaic formation: namely, not due to the properties of the contacting materials but due to electrostatic discharges between the separating surfaces. In particular, as the gap between the contact-charging surfaces grows, the threshold of the electric-field magnitude required for electrostatic discharge by Paschen’s law decreases, and eventually becomes lower than the electric field created in the gap by surface charges. Once a discharge starts, it continues not only until neutralizing but also locally inverting the surface charges. It is then the cycles of such discharges along the delamination front that give rise to the bipolar charge mosaics. Under certain conditions, contact electrification can lead to heterogeneous surface charge distributions—charge mosaics. Experiments and theory now show that these arise from electrostatic discharges between disjoining surfaces.
Spatially resolved vibrational mapping of nanostructures is indispensable to the development and understanding of thermal nanodevices¹, modulation of thermal transport² and novel nanostructured thermoelectric materials3–5. Through the engineering of complex structures, such as alloys, nanostructures and superlattice interfaces, one can significantly alter the propagation of phonons and suppress material thermal conductivity while maintaining electrical conductivity². There have been no correlative experiments that spatially track the modulation of phonon properties in and around nanostructures due to spatial resolution limitations of conventional optical phonon detection techniques. Here we demonstrate two-dimensional spatial mapping of phonons in a single silicon–germanium (SiGe) quantum dot (QD) using monochromated electron energy loss spectroscopy in the transmission electron microscope. Tracking the variation of the Si optical mode in and around the QD, we observe the nanoscale modification of the composition-induced red shift. We observe non-equilibrium phonons that only exist near the interface and, furthermore, develop a novel technique to differentially map phonon momenta, providing direct evidence that the interplay between diffuse and specular reflection largely depends on the detailed atomistic structure: a major advancement in the field. Our work unveils the non-equilibrium phonon dynamics at nanoscale interfaces and can be used to study actual nanodevices and aid in the understanding of heat dissipation near nanoscale hotspots, which is crucial for future high-performance nanoelectronics.
As the length scales of materials decrease, the heterogeneities associated with interfaces become almost as important as the surrounding materials. This has led to extensive studies of emergent electronic and magnetic interface properties in superlattices1–9. However, the interfacial vibrations that affect the phonon-mediated properties, such as thermal conductivity10,11, are measured using macroscopic techniques that lack spatial resolution. Although it is accepted that intrinsic phonons change near boundaries12,13, the physical mechanisms and length scales through which interfacial effects influence materials remain unclear. Here we demonstrate the localized vibrational response of interfaces in strontium titanate–calcium titanate superlattices by combining advanced scanning transmission electron microscopy imaging and spectroscopy, density functional theory calculations and ultrafast optical spectroscopy. Structurally diffuse interfaces that bridge the bounding materials are observed and this local structure creates phonon modes that determine the global response of the superlattice once the spacing of the interfaces approaches the phonon spatial extent. Our results provide direct visualization of the progression of the local atomic structure and interface vibrations as they come to determine the vibrational response of an entire superlattice. Direct observation of such local atomic and vibrational phenomena demonstrates that their spatial extent needs to be quantified to understand macroscopic behaviour. Tailoring interfaces, and knowing their local vibrational response, provides a means of pursuing designer solids with emergent infrared and thermal responses.
Carbon nanomaterials with a different character of the chemical bond—graphene (sp2) and nanodiamond (sp3)—are the building bricks for a new class of all-carbon hybrid nanomaterials, where the two different carbon networks with sp3 and sp2 hybridization coexist, interacting and even transforming into one another. The extraordinary physiochemical properties defined by the unique electronic band structure of the two border nanoallotropes ensure the immense application potential and versatility of these all-carbon nanomaterials. The review summarizes the status quo of sp2 – sp3 nanomaterials, including graphene/graphene-oxide—nanodiamond composites and hybrids, graphene/graphene-oxide—diamond heterojunctions, and other sp2–sp3 nanocarbon hybrids for sensing, electronic, and other emergent applications. Novel sp2–sp3 transitional nanocarbon phases and architectures are also discussed. Furthermore, the two-way sp2 (graphene) to sp3 (diamond surface and nanodiamond) transformations at the nanoscale, essential for innovative fabrication, and stability and chemical reactivity assessment are discussed based on extensive theoretical, computational and experimental studies.
Thermionic energy converters are solid‐state heat engines that have the potential to produce electricity with efficiencies of over 30% and area‐specific power densities of 100 Wcm−2. Despite this prospect, no prototypes reported in the literature have achieved true efficiencies close to this target, and many of the most recent investigations report power densities on the order of mWcm−2 or less. These discrepancies stem in part from the low‐temperature (<1300 K) test conditions used to evaluate these devices, the large vacuum gap distances (25–100 µm) employed by these devices, and material challenges related to these devices' electrodes. This review will argue that, for feasible electrode work functions available today, efficient performance requires generating output power densities of >1 Wcm−2 and employing emitter temperatures of 1300 K or higher. With this result in mind, this review provides an overview of historical and current design architectures and comments on their capacity to realize the efficiency and power potential of thermionic energy converters. Also emphasized is the importance of using standardized efficiency metrics to report thermionic energy converter performance data. Thermionic energy converters transform heat into electricity using no moving parts. This review highlights recent developments that have the potential to achieve high power density outputs at high efficiencies for commercial operation. Also emphasized are two standardized efficiency metrics to evaluate converter performance.
Electrically contacting two‐dimensional (2D) materials is an inevitable process in the fabrication of devices for both the study of fundamental nanoscale charge transport physics and the design of high‐performance novel electronic and optoelectronic devices. The physics of electrical contact formation and interfacial charge injection critically underlies the performance, energy‐efficiency and the functionality of 2D‐material‐based devices, thus representing one of the key factors in determining whether 2D materials can be successfully implemented as a new material basis for the development of next‐generation beyond‐silicon solid‐state device technology. In this review, the recent developments in the theory and the computational simulation of electron emission, interfacial charge injection and electrical contact formation in 2D material interfaces, heterostructures, and devices are reviewed. Focusing on thermionic charge injection phenomena which are omnipresent in 2D‐materials‐based metal/semiconductor Schottky contacts, we summarize various transport models and scaling laws recently developed for 2D materials. Recent progress on the first‐principle density functional theory simulation of 2D‐material‐based electrical contacts are also reviewed. This review aims to provide a crystalized summary on the physics of charge injection in the 2D Flatlands for bridging the theoretical and the experimental research communities of 2D material device physics and technology.
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Modern nanotechnology research has generated numerous experimental data for various nanomaterials. However, the few nanomaterial databases available are not suitable for modeling studies due to the way they are curated. Here, we report the construction of a large nanomaterial database containing annotated nanostructures suited for modeling research. The database, which is publicly available through http://www.pubvinas.com/, contains 705 unique nanomaterials covering 11 material types. Each nanomaterial has up to six physicochemical properties and/or bioactivities, resulting in more than ten endpoints in the database. All the nanostructures are annotated and transformed into protein data bank files, which are downloadable by researchers worldwide. Furthermore, the nanostructure annotation procedure generates 2142 nanodescriptors for all nanomaterials for machine learning purposes, which are also available through the portal. This database provides a public resource for data-driven nanoinformatics modeling research aimed at rational nanomaterial design and other areas of modern computational nanotechnology. The low curation of existing nanomaterials’s databases is limiting their application in modeling studies. Here the authors report a publicly available nanomaterial database that contains annotated nanostructures of diverse nanomaterials immediately available for modeling research studies.
Thin carbon films prepared by pulsed plasma ion-assisted deposition of graphite in an atmosphere of a mixture of argon and nitrogen are studied. The results of characteristic electron energy loss spectroscopy and electron diffraction indicate the increase in the graphite component with increasing ion assistance energy. The use of ion assistance during the film deposition makes it possible to control their resistivity by changing it from 10⁵ to 10² Ω cm.
Thermionic energy conversion (TEC) is the direct conversion of heat into electricity by the mechanism of thermionic emission, the spontaneous ejection of hot electrons from a surface. Although the physical mechanism has been known for over a century, it has yet to be consistently realized in a manner practical for large-scale deployment. This perspective article provides an assessment of the potential of TEC systems for space and terrestrial applications in the twenty-first century, overviewing recent advances in the field and identifying key research challenges. Recent developments as well as persisting research needs in materials, device design, fundamental understanding, and testing and validation are discussed.
Carbon films 110–180 nm thick are fabricated on nickel substrates by the ion sputtering of graphite with simultaneous electron irradiation and subsequent ion irradiation. Irradiation leads to the formation of bonds in the films in various proportions due to the sp and sp³ hybridization of orbitals (sp-and sp³-bonds). Ion irradiation induces, to a greater extent, the formation of sp bonds, while concurrent electron irradiation increases the portion of sp³ bonds. Electron and ion irradiation increases the film microhardness which reaches a value of 12 GPa. A model of the kinetics of creating carbon allotropes in a deposited film is proposed, which is based on the competition between the formation and breakage of carbon bonds during hybridization of different types. Electron and ion irradiation influence the probabilities of the formation and breakage of carbon bonds in the deposited film. The model provides a qualitative interpretation of the observed content ratios of carbon phases in the deposited film.
Seeking for thermoelectric (TE) materials with high figure of merit (or ZT), which can directly converts low-grade wasted heat (400 to 500 K) into electricity, has been a big challenge. Inspired by the concept of multilayer thermionic devices, we propose and design a solid-state thermionic devices (as a power generator or a refrigerator) in using van der Waals (vdW) heterostructure sandwiched between two graphene electrodes, to achieve high energy conversion efficiency in the temperature range of 400 to 500 K. The vdW heterostructure is composed of suitable multiple layers of transition metal dichalcogenides (TMDs), such as MoS2, MoSe2, WS2 and WSe2. From our calculations, WSe2 and MoSe2 are identified as two ideal TMDs (using the reported experimental material’s properties), which can harvest waste heat at 400 K with efficiencies about 7% to 8%. To our best knowledge, this design is the first in combining the advantages of graphene electrodes and TMDs to function as a thermionic-based device.
This paper introduces Teslaphoresis, the directed motion and self-assembly of matter by a Tesla coil, and studies this electrokinetic phenomenon using single-walled carbon nanotubes (CNTs). Conventional directed self-assembly of matter using electric fields has been restricted to small scale structures, but with Teslaphoresis we exceed this limitation by using the Tesla coil's antenna to create a gradient high-voltage force field that projects into free space. CNTs placed within the Teslaphoretic (TEP) field polarize and self-assemble into wires that span from the nanoscale to the macroscale, the longest thus far being 15 cm. We show that the TEP field not only directs the self-assembly of long nanotube wires at remote distances (> 30 cm) but can also wirelessly power nanotube-based LED circuits. Furthermore, individualized CNTs self-organize to form long parallel arrays with high fidelity alignment to the TEP field. Thus, Teslaphoresis is effective for directed self-assembly from the bottom-up to the macroscale.
What are we going to do with the cornucopia of nanomaterials appearing in the open and patent literature, every day? Imagine the benefits of an intelligent and convenient means of categorizing, organizing, sifting, sorting, connecting, and utilizing this information in scientifically and technologically innovative ways by building a Nanomaterials Genome founded upon an all-purpose Periodic Table of Nanomaterials. In this Concept article, inspired by work on the Human Genome project, which began in 1989 together with motivation from the recent emergence of the Materials Genome project initiated in 2011 and the Nanoinformatics Roadmap 2020 instigated in 2010, we envision the development of a Nanomaterials Genome (NMG) database with the most advanced data-mining tools that leverage inference engines to help connect and interpret patterns of nanomaterials information. It will be equipped with state-of-the-art visualization techniques that rapidly organize and picture, categorize and interrelate the inherited behavior of complex nanomatter from the information programmed in its constituent nanomaterials building blocks. A Nanomaterials Genome Initiative (NMGI) of the type imagined herein has the potential to serve the global nanoscience community with an opportunity to speed up the development continuum of nanomaterials through the innovation process steps of discovery, structure determination and property optimization, functionality elucidation, system design and integration, certification and manufacturing to deployment in technologies that apply these versatile nanomaterials in environmentally responsible ways. The possibilities and limitations of this concept are critically evaluated in this article.
The secondary emission of thin films of the 2D-ordered linear-chain carbon (LCC) with a thickness of 100 nm are studied using transmission measurements at various energies of primary electrons. It is demonstrated that the coefficient of secondary emission of the LCC films substantially depends on the extraction field strength on the opposite side of the film and reaches a maximum value of 56 at a field strength of about 2 kV/cm.
Two-dimensional ordered linear-chain carbon films with different thicknesses (50 and 500 nm) have been studied by the tunneling spectroscopy method. The oscillatory dependence of the differential conductivity of the studied structures has been found. The obtained results have been interpreted with the use of the model of the formation of the charge density waves on the regular bends of the structure of linear-chain carbon.
The design of solid-state materials whose properties and functions can be manipulated in a controlled manner by the application of electron beam irradiation is important in modern materials chemistry and physics. In this paper, we present a progress in the development of scalable electron beam irradiation platform to obtain innovative materials for technological and industrial applications, since one of the problems to be solved in this research area is the scalability of these new nanomaterials induced by electron beam irradiation (EBI). In particular, we focus on carbon structures due to its excellent and exciting properties applied in the technological area in the last years, where we show for the first time a new strategy for carbon allotropic transformation through the portable EBI. This new platform is particularly effective, fast, versatile, clean and easy-to-use, facilitating the preparation of many types of nanomaterials that cannot be obtained by conventional chemical and physical methods. The EBI on flat graphite pellets resulted in a covering of it surface with rod-like particles composed of different allotropic forms of carbon. Furthermore, the developed system allowed the implantation of the Fe as a catalytic material through steel sputtering of the high voltage acceleration anode during the EBI process. It was observed by HRTEM analyses that the rod-like particles are preferentially composed of highly oriented graphite in its bottom, polycrystalline graphite in its middle and magnetite nanoparticles in its top.
Materials development has historically been driven by human needs and desires, and this is likely to continue in the foreseeable future. The global population is expected to reach ten billion by 2050, which will promote increasingly large demands for clean and high-efficiency energy, personalized consumer products, secure food supplies, and professional healthcare. New functional materials that are made and tailored for targeted properties or behaviors will be the key to tackling this challenge. Traditionally, advanced materials are found empirically or through experimental trial-and-error approaches. As big data generated by modern experimental and computational techniques is becoming more readily available, data-driven or machine learning (ML) methods have opened new paradigms for the discovery and rational design of materials. In this review article, we provide a brief introduction on various ML methods and related software or tools. Main ideas and basic procedures for employing ML approaches in materials research are highlighted. We then summarize recent important applications of ML for the large-scale screening and optimal design of polymer and porous materials, catalytic materials, and energetic materials. Finally, concluding remarks and an outlook are provided. Keywords: Big data, Data-driven, Machine learning, Materials screening, Materials design
Carbon films 50–180 nm thick on nickel substrates are fabricated by the ion sputtering of graphite and the deposition of heavy hydrocarbons from the gas phase with simultaneous electron irradiation. Irradiation results in the formation of bonds in carbon films due to the sp and sp³ hybridization of orbitals (sp and sp³ bonds), mainly, sp³ bonds. A fraction of these bonds does not change with growth in the electron energy; it increases three-fold with a reduction in the temperature and an increase in the electron current density. Electron irradiation enhances the film microhardness which exceeds 12 GPa. The films, prepared by heavy hydrocarbon deposition, contain CHn bonds and a small fraction of sp³ bonds. The maximum value of the microhardness of the hydrocarbon films is no more than 4.5 GPa. The analysis of the proposed model of the kinetics of forming different allotropic phases in a carbon film to be deposited shows that a temperature reduction changes the specific volume of an atom in the lattice, while under conditions of simultaneous electron irradiation, it appreciably increases the content of the phase with sp³ bonds. The effect of spⁱ-bond breakage during electron-beam-assisted deposition weakly depends on the electron energy. The weak excitations of electrons of carbon atoms can also result in the formation of sp³ bonds and increases their concentration with growth in the electron current density.
This article focuses on the acoustic-wave enhancement of chemisorption and surface reactions. Acoustic waves generated by a piezoelectric phenomenon on ferroelectric crystals by the application of radio frequency electric power produce periodic lattice distortions at the surface. The effects of surface acoustic waves (SAWs) and the resonance oscillation (RO) of bulk acoustic waves on thin films of metals or metal oxides are described herein. Both SAWs and RO can modify the work functions of thin Ag, Au, or Pd films, and this effect is highly dependent on the surface structures. These changes in the work function can, in turn, affect the adsorptive characteristics of the metals as well as surface reactions and properties such as catalysis. The importance of periodic lattice displacement vertical to the surface is examined in this article, and the acoustic-wave enhancement of metal and metal oxide surfaces as a means of tuning electronic states and chemical properties is discussed.
Besides graphite and diamond, the solid allotropes of carbon in sp2 and sp3 hybridization, the possible existence of a third allotrope based on the sp-carbon linear chain, the Carbyne, has stimulated researchers for a long time. The advent of fullerenes, nanotubes and graphene has opened new opportunities and nurtured the interest in novel carbon allotropes including linear structures. The efforts made in this direction produced a number of interesting sp-hybridized carbon molecules and nanostructures in the form of carbon-atom wires. We here discuss some of the new perspectives opened by the recent advancements in the research on sp-carbon systems.
Electron emission represents the key mechanism enabling the development of devices that have revolutionized modern science and technology. Today, science still relies on advanced electron-emission devices for imaging, electronics, sensing, and high-energy physics. New generations of emission devices are continuously being improved based on innovative materials and the introduction of novel physical concepts. Recent advances are highlighted by emerging low-work-function and low-dimensional materials with unusual electronic and thermal properties. Nanotubes, nanowires, graphene, and electron-emission models are discussed in this issue, as well as original mechanisms, such as the thermoelectronic effect, thermionic emission, and heat trap processes. Advances in electron-emission materials and physics are driving a renaissance in the field, both opening up new applications, such as energy conversion and ultrafast electronics, as well as improving traditional applications in electron imaging and high-energy science.
Field emission (FE) phenomena are generally explained in the frame-work of Fowler Nordheim (FN) theory which was given for flat metal surfaces. In this work, an effort has been made to present the field emission mechanism in carbon nanotubes (CNTs) which have tip type geometry at nanoscale. High aspect ratio of CNTs leads to large field enhancement factor and lower operating voltages because the electric field strength in the vicinity of the nanotubes tip can be enhanced by thousand times. The work function of nanostructure by using FN plot has been calculated with reverse engineering. With the help of modified FN equation, an important formula for effective emitting area (active area for emission of electrons) has been derived and employed to calculate the active emitting area for CNT field emitters. Therefore, it is of great interest to present a state of art study on the complete solution of FN equation for CNTs based field emitter displays. This manuscript will also provide a better understanding of calculation of different FE parameters of CNTs field emitters using FN equation.
Advances in theoretical, computational and experimental materials science and engineering offer not only the promise to accelerate the pace at which new materials are discovered, but also to reduce the time required to bring new products to market. The so-called Materials Genome Initiative seeks to capitalize on that promise by identifying innovative research paradigms that integrate theory, computation, synthesis, and characterization in manners that, until recently, were not possible. A workshop was held at the National Science Foundation in December of 2013 to identify some of the central challenges and opportunities facing materials research within the context of that initiative. This article summarizes the findings of the workshop, and presents a series of concrete recommendations with the potential to facilitate its implementation. It also provides an overview of timely fundamental, technical and logistical challenges, organized according to distinct classes of materials, whose solution could have significant practical and societal benefits.
The structure of amorphous linear-chain carbon (LCC) during the structure formation under conditions of vacuum annealing was studied by electron diffraction and Raman spectroscopy methods. It was shown that the determining factor of lowering the work function of the LCC coating is the formation of nanoclusters of mutually misoriented short carbon chains.