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      Multifunctional structural design of graphene thermoelectrics by Bayesian optimization

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          Abstract

          Efficient multifunctional materials informatics enables the design of optimal graphene thermoelectrics.

          Abstract

          Materials development often confronts a dilemma as it needs to satisfy multifunctional, often conflicting, demands. For example, thermoelectric conversion requires high electrical conductivity, a high Seebeck coefficient, and low thermal conductivity, despite the fact that these three properties are normally closely correlated. Nanostructuring techniques have been shown to break the correlations to some extent; however, optimal design has been a major challenge due to the extraordinarily large degrees of freedom in the structures. By taking graphene nanoribbons (GNRs) as a representative thermoelectric material, we carried out structural optimization by alternating multifunctional (phonon and electron) transport calculations and Bayesian optimization to resolve the trade-off. As a result, we have achieved multifunctional structural optimization with an efficiency more than five times that achieved by random search. The obtained GNRs with optimized antidots significantly enhance the thermoelectric figure of merit by up to 11 times that of the pristine GNR. Knowledge of the optimal structure further provides new physical insights that independent tuning of electron and phonon transport properties can be realized by making use of zigzag edge states and aperiodic nanostructuring. The demonstrated optimization framework is also useful for other multifunctional problems in various applications.

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          Electric Field Effect in Atomically Thin Carbon Films

          We report a naturally-occurring two-dimensional material (graphene that can be viewed as a gigantic flat fullerene molecule, describe its electronic properties and demonstrate all-metallic field-effect transistor, which uniquely exhibits ballistic transport at submicron distances even at room temperature.
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            Edge state in graphene ribbons: Nanometer size effect and edge shape dependence

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              Ultrahigh electron mobility in suspended graphene

              We have achieved mobilities in excess of 200,000 cm^2/Vs at electron densities of ~2*10^11 cm^-2 by suspending single layer graphene. Suspension ~150 nm above a Si/SiO_2 gate electrode and electrical contacts to the graphene was achieved by a combination of electron beam lithography and etching. The specimens were cleaned in situ by employing current-induced heating, directly resulting in a significant improvement of electrical transport. Concomitant with large mobility enhancement, the widths of the characteristic Dirac peaks are reduced by a factor of 10 compared to traditional, non-suspended devices. This advance should allow for accessing the intrinsic transport properties of graphene.
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                Author and article information

                Journal
                Sci Adv
                Sci Adv
                SciAdv
                advances
                Science Advances
                American Association for the Advancement of Science
                2375-2548
                June 2018
                15 June 2018
                : 4
                : 6
                Affiliations
                [1 ]Department of Mechanical Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo 113-8654, Japan.
                [2 ]National Institute for Materials Science, 1-2-1 Sengen, Tsukuba 305-0047, Japan.
                [3 ]Japan Science and Technology Agency, Core Research for Evolutional Science and Technology, 4-1-8, Kawaguchi, Saitama 332-0012, Japan.
                [4 ]RIKEN Center for Advanced Intelligence Project, 1-4-1 Nihonbashi Chuo-ku, Tokyo 103-0027, Japan.
                Author notes
                [* ]Corresponding author. Email: shiomi@ 123456photon.t.u-tokyo.ac.jp
                Article
                aar4192
                10.1126/sciadv.aar4192
                6003749
                Copyright © 2018 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC).

                This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial license, which permits use, distribution, and reproduction in any medium, so long as the resultant use is not for commercial advantage and provided the original work is properly cited.

                Funding
                Funded by: doi http://dx.doi.org/10.13039/501100001691, Japan Society for the Promotion of Science;
                Award ID: 16H04274
                Funded by: doi http://dx.doi.org/10.13039/501100002241, Japan Science and Technology Agency;
                Award ID: JPMJCR16Q5
                Categories
                Research Article
                Research Articles
                SciAdv r-articles
                Condensed Matter Physics
                Condensed Matter Physics
                Custom metadata
                Judith Urtula

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