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Compact Assembly and Programmable Integration of Supercapacitors

2019-12-18T16:33:22+00:00December 18th, 2019|Categories: Publications|Tags: , , |

A versatile self‐shrinkage assembling strategy is developed to directly construct a compact microsized supercapacitor (CmSC) from hydrogels of reduced graphene oxide. A single CmSC features a low volume of only 0.0023 cm3 but an unprecedented capacitance. The CmSCs can be shaped into various geometries and work effectively as building blocks for programmable integration toward mSC systems. Abstract Microsized supercapacitors (mSCs) with small volume, rapid charge–discharge rate, and ultralong cyclic lifetime are urgently needed to meet the demand of miniaturized portable electronic devices. A versatile self‐shrinkage assembling (SSA) strategy to directly construct the compact mSCs (CmSCs) from hydrogels of reduced graphene oxide is reported. A single CmSC is only 0.0023 cm3 in volume, which is significantly smaller than most reported mSCs in fiber/yarn and planar interdigital forms. It exhibits a high capacitance of up to 68.3 F cm−3 and a superior cycling stability with 98% capacitance retention after 25 000 cycles. Most importantly, the SSA technique enables the CmSC as the building block to realize arbitrary, programmable, and multi‐dimensional integration for adaptable and complicated power systems. By design on mortise and tenon joint connection, autologous integrated 3D interdigital CmSCs are fabricated in a self‐holding‐on manner, which thus dramatically reduces the whole device volume to achieve the high‐performance capacitive behavior. Consequently, the SSA technique offers a universal and versatile approach for large‐scale on‐demand integration of mSCs as flexible and transformable power sources.

Published in: "Advanced Materials".

Graphene Quantum Dots and Their Applications in Bioimaging, Biosensing, and Therapy

2019-12-13T12:34:46+00:00December 13th, 2019|Categories: Publications|Tags: |

Recent advancements in the development of graphene quantum dots (GQDs) in the field of nanomedicine are reviewed. Following an overview of the properties of GQDs, progress in top‐down and bottom‐up synthesis methods are presented. Application of GQDs in various modes of bioimaging, biosensing, and therapy are also discussed, with a subsequent discussion of future directions. Abstract Graphene quantum dots (GQDs) are carbon‐based, nanoscale particles that exhibit excellent chemical, physical, and biological properties that allow them to excel in a wide range of applications in nanomedicine. The unique electronic structure of GQDs confers functional attributes onto these nanomaterials such as strong and tunable photoluminescence for use in fluorescence bioimaging and biosensing, a high loading capacity of aromatic compounds for small‐molecule drug delivery, and the ability to absorb incident radiation for use in the cancer‐killing techniques of photothermal and photodynamic therapy. Recent advances in the development of GQDs as novel, multifunctional biomaterials are presented with a focus on their physicochemical, electronic, magnetic, and biological properties, along with a discussion of technical progress in the synthesis of GQDs. Progress toward the application of GQDs in bioimaging, biosensing, and therapy is reviewed, along with a discussion of the current limitations and future directions of this exciting material.

Published in: "Advanced Materials".

Modified Engineering of Graphene Nanoribbons Prepared via On‐Surface Synthesis

2019-12-12T20:32:58+00:00December 12th, 2019|Categories: Publications|Tags: |

Recent advances in modification engineering of graphene nanoribbons prepared via on‐surface synthesis are comprehensively reviewed. The varieties of graphene nanoribbons (GNRs) with narrow widths and specific edge/backbone structures and the electrical applications are presented. The GNR preparation strategy holds a bright future in both tailoring their bandgaps and the ultimate applications. Abstract 1D graphene nanoribbons (GNRs) have a bright future in the fabrication of next‐generation nanodevices because of their nontrivial electronic properties and tunable bandgaps. To promote the application of GNRs, preparation strategies of miscellaneous GNRs have to be developed. The GNRs prepared by top‐down approaches are accompanied by uncontrolled edges and structures. In order to overcome the difficulties, bottom‐up methods are widely used in the growth of various GNRs due to controllability of GNRs’ features. Among those bottom‐up methods, the on‐surface synthesis is a promising approach to prepare GNRs with distinct widths, edge/backbone structures, and so forth. Therefore, modified engineering of the GNRs prepared via on‐surface synthesis is of great significance in controllable preparation of GNRs and their potential applications. In the past decade, there have been a lot of reports on controllable preparation of GNRs using on‐surface synthesis approach. Herein, the advances of GNRs grown via on‐surface growth strategy are described. Several growth parameters, the latest advances in the modification of the GNR structure and width, the GNR doping/co‐doping with heteroatoms, a variety of GNR heterojunctions, and the device application of GNRs are reviewed. Finally, the opportunities and challenges are discussed.

Published in: "Advanced Materials".

Theory and Ab Initio Calculation of Optically Excited States—Recent Advances in 2D Materials

2019-12-12T04:33:50+00:00December 12th, 2019|Categories: Publications|

2D materials exhibit unique physical phenomena and features that are absent in conventional bulk semiconductors. The theoretical and ab initio methods that yield the optically excited states in 2D materials are reviewed. Several analytical and numerical approaches are introduced and their results are compared with experiments. Abstract Recent studies of the optical properties of 2D materials have reported unique phenomena and features that are absent in conventional bulk semiconductors. Many of these interesting properties, such as enhanced light‐matter coupling, gate‐tunable photoluminescence, and unusual excitonic optical selection rules arise from the nature of the two‐ and multi‐particle excited states such as strongly bound Wannier excitons and charged excitons. The theory, modeling, and ab initio calculations of these optically excited states in 2D materials are reviewed. Several analytical and ab initio approaches are introduced. These methods are compared with each other, revealing their relative strength and limitations. Recent works that apply these methods to a variety of 2D materials and material‐defect systems are then highlighted. Understanding of the optically excited states in these systems is relevant not only for fundamental scientific research of electronic excitations and correlations, but also plays an important role in the future development of quantum information science and nano‐photonics.

Published in: "Advanced Materials".

Confinement Catalysis with 2D Materials for Energy Conversion

2019-12-12T04:33:49+00:00December 12th, 2019|Categories: Publications|Tags: |

The recent advances in the design, applications, and structure–performance analysis of confinement catalysis with two‐dimensional materials are highlighted, with a focus on tuning the electronic states of active sites. Such confinement catalysis with 2D materials offers unique solutions for improving catalytic performance in heterogeneous systems for energy conversion and utilization. Abstract The unique electronic and structural properties of 2D materials have triggered wide research interest in catalysis. The lattice of 2D materials and the interface between 2D covers and other substrates provide intriguing confinement environments for active sites, which has stimulated a rising area of “confinement catalysis with 2D materials.” Fundamental understanding of confinement catalysis with 2D materials will favor the rational design of high‐performance 2D nanocatalysts. Confinement catalysis with 2D materials has found extensive applications in energy‐related reaction processes, especially in the conversion of small energy‐related molecules such as O2, CH4, CO, CO2, H2O, and CH3OH. Two representative strategies, i.e., 2D lattice‐confined single atoms and 2D cover‐confined metals, have been applied to construct 2D confinement catalytic systems with superior catalytic activity and stability. Herein, the recent advances in the design, applications, and structure–performance analysis of two 2D confinement catalytic systems are summarized. The different routes for tuning the electronic states of 2D confinement catalysts are highlighted and perspectives on confinement catalysis with 2D materials toward energy conversion and utilization in the future are provided.

Published in: "Advanced Materials".

Large‐Scale Synthesis of Strain‐Tunable Semiconducting Antimonene on Copper Oxide

2019-12-12T04:33:48+00:00December 12th, 2019|Categories: Publications|Tags: |

High‐quality antimonene with semiconducting nature is fabricated by molecular beam epitaxy on a dielectric oxide substrate. The evolution process and strain‐tunable band structures are revealed by scanning tunneling (ST) microscopy/ST spectroscopy measurements and theoretical calculations. The oxide substrate allows both decoupled electronic properties and direct integration of 2D systems into well‐established fabrication lines, a great advantage for large‐scale synthesis and practical application. Abstract Controlled synthesis of 2D structures on nonmetallic substrate is challenging, yet an attractive approach for the integration of 2D systems into current semiconductor technologies. Herein, the direct synthesis of high‐quality 2D antimony, or antimonene, on dielectric copper oxide substrate by molecular beam epitaxy is reported. Delicate scanning tunneling microscopy imaging on the evolution intermediates reveals a segregation growth process on Cu3O2/Cu(111), from ordered dimer chains to packed dot arrays, and finally to monolayer antimonene. First‐principles calculations demonstrate the strain‐modulated band structures in antimonene, which interacts weakly with the oxide surface so that its semiconducting nature is preserved, in perfect agreement with spectroscopic measurements. This work paves the way for large‐scale growth and processing of antimonene for practical implementation.

Published in: "Advanced Materials".

Controlled Growth and Thickness‐Dependent Conduction‐Type Transition of 2D Ferrimagnetic Cr2S3 Semiconductors

2019-12-12T04:33:46+00:00December 12th, 2019|Categories: Publications|

The thickness‐tunable synthesis of rhombohedral Cr2S3 flakes is first achieved via a facile chemical vapor deposition route by a unique design of the metal precursor and a precise control of the growth temperature. Particularly, the conduction behavior of the nanothick Cr2S3 is variable with increasing thickness, i.e., from p‐type to ambipolar, and then to n‐type. Abstract 2D magnetic materials have attracted intense attention as ideal platforms for constructing multifunctional electronic and spintronic devices. However, most of the reported 2D magnetic materials are mainly achieved by the mechanical exfoliation route. The direct synthesis of such materials is still rarely reported, especially toward thickness‐controlled synthesis down to the 2D limit. Herein, the thickness‐tunable synthesis of nanothick rhombohedral Cr2S3 flakes (from ≈1.9 nm to tens of nanometers) on a chemically inert mica substrate via a facile chemical vapor deposition route is demonstrated. This is accomplished by an accurate control of the feeding rate of the Cr precursor and the growth temperature. Furthermore, it is revealed that the conduction behavior of the nanothick Cr2S3 is variable with increasing thickness (from 2.6 to 4.8 nm and >7 nm) from p‐type to ambipolar and then to n‐type. Hereby, this work can shed light on the scalable synthesis, transport, and magnetic properties explorations of 2D magnetic materials.

Published in: "Advanced Materials".

Graphene/Half‐Metallic Heusler Alloy: A Novel Heterostructure toward High‐Performance Graphene Spintronic Devices

2019-12-12T04:33:38+00:00December 12th, 2019|Categories: Publications|Tags: , |

A novel heterostructure consisting of high‐quality single‐layer graphene (SLG) and a half‐metallic Heusler alloy Co2Fe(Ge0.5Ga0.5) (CFGG) is developed. This new heterostructure shows unusual weak interfacial interaction, which leads to distinctive features such as preservation of the robust magnetism and half‐metallic characteristic of CFGG near the interface, and the quasi‐free‐standing nature of SLG, providing a new platform for future development of advanced graphene spintronic devices. Abstract Graphene‐based vertical spin valves (SVs) are expected to offer a large magnetoresistance effect without impairing the electrical conductivity, which can pave the way for the next generation of high‐speed and low‐power‐consumption storage and memory technologies. However, the graphene‐based vertical SV has failed to prove its competence due to the lack of a graphene/ferromagnet heterostructure, which can provide highly efficient spin transport. Herein, the synthesis and spin‐dependent electronic properties of a novel heterostructure consisting of single‐layer graphene (SLG) and a half‐metallic Co2Fe(Ge0.5Ga0.5) (CFGG) Heusler alloy ferromagnet are reported. The growth of high‐quality SLG with complete coverage by ultrahigh‐vacuum chemical vapor deposition on a magnetron‐sputtered single‐crystalline CFGG thin film is demonstrated. The quasi‐free‐standing nature of SLG and robust magnetism of CFGG at the SLG/CFGG interface are revealed through depth‐resolved X‐ray magnetic circular dichroism spectroscopy. Density functional theory (DFT) calculation results indicate that the inherent electronic properties of SLG and CFGG such as the linear Dirac band and half‐metallic band structure are preserved in the vicinity of the interface. These exciting findings suggest that the SLG/CFGG heterostructure possesses distinctive advantages over other reported graphene/ferromagnet heterostructures, for realizing effective

Published in: "Advanced Materials".

Large‐Scale Synthesis of Strain‐Tunable Semiconducting Antimonene on Copper Oxide

2019-12-12T02:37:32+00:00December 12th, 2019|Categories: Publications|Tags: |

High‐quality antimonene with semiconducting nature is fabricated by molecular beam epitaxy on a dielectric oxide substrate. The evolution process and strain‐tunable band structures are revealed by scanning tunneling (ST) microscopy/ST spectroscopy measurements and theoretical calculations. The oxide substrate allows both decoupled electronic properties and direct integration of 2D systems into well‐established fabrication lines, a great advantage for large‐scale synthesis and practical application. Abstract Controlled synthesis of 2D structures on nonmetallic substrate is challenging, yet an attractive approach for the integration of 2D systems into current semiconductor technologies. Herein, the direct synthesis of high‐quality 2D antimony, or antimonene, on dielectric copper oxide substrate by molecular beam epitaxy is reported. Delicate scanning tunneling microscopy imaging on the evolution intermediates reveals a segregation growth process on Cu3O2/Cu(111), from ordered dimer chains to packed dot arrays, and finally to monolayer antimonene. First‐principles calculations demonstrate the strain‐modulated band structures in antimonene, which interacts weakly with the oxide surface so that its semiconducting nature is preserved, in perfect agreement with spectroscopic measurements. This work paves the way for large‐scale growth and processing of antimonene for practical implementation.

Published in: "Advanced Materials".

Controlled Growth and Thickness‐Dependent Conduction‐Type Transition of 2D Ferrimagnetic Cr2S3 Semiconductors

2019-12-12T02:37:29+00:00December 12th, 2019|Categories: Publications|

The thickness‐tunable synthesis of rhombohedral Cr2S3 flakes is first achieved via a facile chemical vapor deposition route by a unique design of the metal precursor and a precise control of the growth temperature. Particularly, the conduction behavior of the nanothick Cr2S3 is variable with increasing thickness, i.e., from p‐type to ambipolar, and then to n‐type. Abstract 2D magnetic materials have attracted intense attention as ideal platforms for constructing multifunctional electronic and spintronic devices. However, most of the reported 2D magnetic materials are mainly achieved by the mechanical exfoliation route. The direct synthesis of such materials is still rarely reported, especially toward thickness‐controlled synthesis down to the 2D limit. Herein, the thickness‐tunable synthesis of nanothick rhombohedral Cr2S3 flakes (from ≈1.9 nm to tens of nanometers) on a chemically inert mica substrate via a facile chemical vapor deposition route is demonstrated. This is accomplished by an accurate control of the feeding rate of the Cr precursor and the growth temperature. Furthermore, it is revealed that the conduction behavior of the nanothick Cr2S3 is variable with increasing thickness (from 2.6 to 4.8 nm and >7 nm) from p‐type to ambipolar and then to n‐type. Hereby, this work can shed light on the scalable synthesis, transport, and magnetic properties explorations of 2D magnetic materials.

Published in: "Advanced Materials".

Confinement Catalysis with 2D Materials for Energy Conversion

2019-12-12T00:35:16+00:00December 11th, 2019|Categories: Publications|Tags: |

The recent advances in the design, applications, and structure–performance analysis of confinement catalysis with two‐dimensional materials are highlighted, with a focus on tuning the electronic states of active sites. Such confinement catalysis with 2D materials offers unique solutions for improving catalytic performance in heterogeneous systems for energy conversion and utilization. Abstract The unique electronic and structural properties of 2D materials have triggered wide research interest in catalysis. The lattice of 2D materials and the interface between 2D covers and other substrates provide intriguing confinement environments for active sites, which has stimulated a rising area of “confinement catalysis with 2D materials.” Fundamental understanding of confinement catalysis with 2D materials will favor the rational design of high‐performance 2D nanocatalysts. Confinement catalysis with 2D materials has found extensive applications in energy‐related reaction processes, especially in the conversion of small energy‐related molecules such as O2, CH4, CO, CO2, H2O, and CH3OH. Two representative strategies, i.e., 2D lattice‐confined single atoms and 2D cover‐confined metals, have been applied to construct 2D confinement catalytic systems with superior catalytic activity and stability. Herein, the recent advances in the design, applications, and structure–performance analysis of two 2D confinement catalytic systems are summarized. The different routes for tuning the electronic states of 2D confinement catalysts are highlighted and perspectives on confinement catalysis with 2D materials toward energy conversion and utilization in the future are provided.

Published in: "Advanced Materials".

Large‐Scale Synthesis of Strain‐Tunable Semiconducting Antimonene on Copper Oxide

2019-12-12T00:35:13+00:00December 11th, 2019|Categories: Publications|Tags: |

High‐quality antimonene with semiconducting nature is fabricated by molecular beam epitaxy on a dielectric oxide substrate. The evolution process and strain‐tunable band structures are revealed by scanning tunneling (ST) microscopy/ST spectroscopy measurements and theoretical calculations. The oxide substrate allows both decoupled electronic properties and direct integration of 2D systems into well‐established fabrication lines, a great advantage for large‐scale synthesis and practical application. Abstract Controlled synthesis of 2D structures on nonmetallic substrate is challenging, yet an attractive approach for the integration of 2D systems into current semiconductor technologies. Herein, the direct synthesis of high‐quality 2D antimony, or antimonene, on dielectric copper oxide substrate by molecular beam epitaxy is reported. Delicate scanning tunneling microscopy imaging on the evolution intermediates reveals a segregation growth process on Cu3O2/Cu(111), from ordered dimer chains to packed dot arrays, and finally to monolayer antimonene. First‐principles calculations demonstrate the strain‐modulated band structures in antimonene, which interacts weakly with the oxide surface so that its semiconducting nature is preserved, in perfect agreement with spectroscopic measurements. This work paves the way for large‐scale growth and processing of antimonene for practical implementation.

Published in: "Advanced Materials".

Controlled Growth and Thickness‐Dependent Conduction‐Type Transition of 2D Ferrimagnetic Cr2S3 Semiconductors

2019-12-12T00:35:10+00:00December 11th, 2019|Categories: Publications|

The thickness‐tunable synthesis of rhombohedral Cr2S3 flakes is first achieved via a facile chemical vapor deposition route by a unique design of the metal precursor and a precise control of the growth temperature. Particularly, the conduction behavior of the nanothick Cr2S3 is variable with increasing thickness, i.e., from p‐type to ambipolar, and then to n‐type. Abstract 2D magnetic materials have attracted intense attention as ideal platforms for constructing multifunctional electronic and spintronic devices. However, most of the reported 2D magnetic materials are mainly achieved by the mechanical exfoliation route. The direct synthesis of such materials is still rarely reported, especially toward thickness‐controlled synthesis down to the 2D limit. Herein, the thickness‐tunable synthesis of nanothick rhombohedral Cr2S3 flakes (from ≈1.9 nm to tens of nanometers) on a chemically inert mica substrate via a facile chemical vapor deposition route is demonstrated. This is accomplished by an accurate control of the feeding rate of the Cr precursor and the growth temperature. Furthermore, it is revealed that the conduction behavior of the nanothick Cr2S3 is variable with increasing thickness (from 2.6 to 4.8 nm and >7 nm) from p‐type to ambipolar and then to n‐type. Hereby, this work can shed light on the scalable synthesis, transport, and magnetic properties explorations of 2D magnetic materials.

Published in: "Advanced Materials".

Theory and Ab Initio Calculation of Optically Excited States—Recent Advances in 2D Materials

2019-12-08T12:33:35+00:00December 8th, 2019|Categories: Publications|

2D materials exhibit unique physical phenomena and features that are absent in conventional bulk semiconductors. The theoretical and ab initio methods that yield the optically excited states in 2D materials are reviewed. Several analytical and numerical approaches are introduced and their results are compared with experiments. Abstract Recent studies of the optical properties of 2D materials have reported unique phenomena and features that are absent in conventional bulk semiconductors. Many of these interesting properties, such as enhanced light‐matter coupling, gate‐tunable photoluminescence, and unusual excitonic optical selection rules arise from the nature of the two‐ and multi‐particle excited states such as strongly bound Wannier excitons and charged excitons. The theory, modeling, and ab initio calculations of these optically excited states in 2D materials are reviewed. Several analytical and ab initio approaches are introduced. These methods are compared with each other, revealing their relative strength and limitations. Recent works that apply these methods to a variety of 2D materials and material‐defect systems are then highlighted. Understanding of the optically excited states in these systems is relevant not only for fundamental scientific research of electronic excitations and correlations, but also plays an important role in the future development of quantum information science and nano‐photonics.

Published in: "Advanced Materials".

Theory and Ab Initio Calculation of Optically Excited States—Recent Advances in 2D Materials

2019-12-06T20:37:32+00:00December 6th, 2019|Categories: Publications|

2D materials exhibit unique physical phenomena and features that are absent in conventional bulk semiconductors. The theoretical and ab initio methods that yield the optically excited states in 2D materials are reviewed. Several analytical and numerical approaches are introduced and their results are compared with experiments. Abstract Recent studies of the optical properties of 2D materials have reported unique phenomena and features that are absent in conventional bulk semiconductors. Many of these interesting properties, such as enhanced light‐matter coupling, gate‐tunable photoluminescence, and unusual excitonic optical selection rules arise from the nature of the two‐ and multi‐particle excited states such as strongly bound Wannier excitons and charged excitons. The theory, modeling, and ab initio calculations of these optically excited states in 2D materials are reviewed. Several analytical and ab initio approaches are introduced. These methods are compared with each other, revealing their relative strength and limitations. Recent works that apply these methods to a variety of 2D materials and material‐defect systems are then highlighted. Understanding of the optically excited states in these systems is relevant not only for fundamental scientific research of electronic excitations and correlations, but also plays an important role in the future development of quantum information science and nano‐photonics.

Published in: "Advanced Materials".

Theory and Ab Initio Calculation of Optically Excited States—Recent Advances in 2D Materials

2019-12-06T20:37:29+00:00December 6th, 2019|Categories: Publications|

2D materials exhibit unique physical phenomena and features that are absent in conventional bulk semiconductors. The theoretical and ab initio methods that yield the optically excited states in 2D materials are reviewed. Several analytical and numerical approaches are introduced and their results are compared with experiments. Abstract Recent studies of the optical properties of 2D materials have reported unique phenomena and features that are absent in conventional bulk semiconductors. Many of these interesting properties, such as enhanced light‐matter coupling, gate‐tunable photoluminescence, and unusual excitonic optical selection rules arise from the nature of the two‐ and multi‐particle excited states such as strongly bound Wannier excitons and charged excitons. The theory, modeling, and ab initio calculations of these optically excited states in 2D materials are reviewed. Several analytical and ab initio approaches are introduced. These methods are compared with each other, revealing their relative strength and limitations. Recent works that apply these methods to a variety of 2D materials and material‐defect systems are then highlighted. Understanding of the optically excited states in these systems is relevant not only for fundamental scientific research of electronic excitations and correlations, but also plays an important role in the future development of quantum information science and nano‐photonics.

Published in: "Advanced Materials".

Theory and Ab Initio Calculation of Optically Excited States—Recent Advances in 2D Materials

2019-12-06T20:37:28+00:00December 6th, 2019|Categories: Publications|

2D materials exhibit unique physical phenomena and features that are absent in conventional bulk semiconductors. The theoretical and ab initio methods that yield the optically excited states in 2D materials are reviewed. Several analytical and numerical approaches are introduced and their results are compared with experiments. Abstract Recent studies of the optical properties of 2D materials have reported unique phenomena and features that are absent in conventional bulk semiconductors. Many of these interesting properties, such as enhanced light‐matter coupling, gate‐tunable photoluminescence, and unusual excitonic optical selection rules arise from the nature of the two‐ and multi‐particle excited states such as strongly bound Wannier excitons and charged excitons. The theory, modeling, and ab initio calculations of these optically excited states in 2D materials are reviewed. Several analytical and ab initio approaches are introduced. These methods are compared with each other, revealing their relative strength and limitations. Recent works that apply these methods to a variety of 2D materials and material‐defect systems are then highlighted. Understanding of the optically excited states in these systems is relevant not only for fundamental scientific research of electronic excitations and correlations, but also plays an important role in the future development of quantum information science and nano‐photonics.

Published in: "Advanced Materials".

Graphene/Half‐Metallic Heusler Alloy: A Novel Heterostructure toward High‐Performance Graphene Spintronic Devices

2019-12-04T00:34:40+00:00December 3rd, 2019|Categories: Publications|Tags: , |

A novel heterostructure consisting of high‐quality single‐layer graphene (SLG) and a half‐metallic Heusler alloy Co2Fe(Ge0.5Ga0.5) (CFGG) is developed. This new heterostructure shows unusual weak interfacial interaction, which leads to distinctive features such as preservation of the robust magnetism and half‐metallic characteristic of CFGG near the interface, and the quasi‐free‐standing nature of SLG, providing a new platform for future development of advanced graphene spintronic devices. Abstract Graphene‐based vertical spin valves (SVs) are expected to offer a large magnetoresistance effect without impairing the electrical conductivity, which can pave the way for the next generation of high‐speed and low‐power‐consumption storage and memory technologies. However, the graphene‐based vertical SV has failed to prove its competence due to the lack of a graphene/ferromagnet heterostructure, which can provide highly efficient spin transport. Herein, the synthesis and spin‐dependent electronic properties of a novel heterostructure consisting of single‐layer graphene (SLG) and a half‐metallic Co2Fe(Ge0.5Ga0.5) (CFGG) Heusler alloy ferromagnet are reported. The growth of high‐quality SLG with complete coverage by ultrahigh‐vacuum chemical vapor deposition on a magnetron‐sputtered single‐crystalline CFGG thin film is demonstrated. The quasi‐free‐standing nature of SLG and robust magnetism of CFGG at the SLG/CFGG interface are revealed through depth‐resolved X‐ray magnetic circular dichroism spectroscopy. Density functional theory (DFT) calculation results indicate that the inherent electronic properties of SLG and CFGG such as the linear Dirac band and half‐metallic band structure are preserved in the vicinity of the interface. These exciting findings suggest that the SLG/CFGG heterostructure possesses distinctive advantages over other reported graphene/ferromagnet heterostructures, for realizing effective

Published in: "Advanced Materials".

Directional Janus Metasurface

2019-12-04T00:34:20+00:00December 3rd, 2019|Categories: Publications|

Direction‐encoded wave manipulations are experimentally achieved through the use of Janus metasurfaces composed of cascaded metasheets. By introducing a rotational twist in metasurface geometry, asymmetric electromagnetic wavefront manipulation can be realized. This is demonstrated both theoretically and experimentally by a series of passive metadevices, which enable functionalities including one‐way anomalous refraction, one‐way focusing, asymmetric focusing, and direction‐controlled holograms. Abstract Janus monolayers, a class of two‐faced 2D materials, have received significant attention in electronics, due to their unusual conduction properties stemming from their inherent out‐of‐plane asymmetry. Their photonic counterparts recently allowed for the control of hydrogenation/dehydrogenation processes, yielding drastically different responses for opposite light excitation spins. A passive Janus metasurface composed of cascaded subwavelength anisotropic impedance sheets is demonstrated. By introducing a rotational twist in their geometry, asymmetric transmission with the desired phase function is realized. Their broken out‐of‐plane symmetry realizes different functions for opposite propagation directions, enabling direction‐dependent versatile functionalities. A series of passive Janus metasurfaces that enable functionalities including one‐way anomalous refraction, one‐way focusing, asymmetric focusing, and direction‐controlled holograms are experimentally demonstrated.

Published in: "Advanced Materials".

Supersonic Cold Spraying for Energy and Environmental Applications: One‐Step Scalable Coating Technology for Advanced Micro‐ and Nanotextured Materials

2019-12-04T00:34:17+00:00December 3rd, 2019|Categories: Publications|Tags: , , |

Supersonic cold spraying, which can deposit various nanoscale materials onto nearly any substrate rapidly and economically, is emerging as a new coating technique for energy and environmental products. Fundamentals of the supersonic cold spraying technique and recent progress in its development are briefly discussed and reviewed, illustrating its advantages and utility for energy and environmental applications. Abstract Supersonic cold spraying is an emerging technique for rapid deposition of films of materials including micrometer‐size and sub‐micrometer metal particles, nanoscale ceramic particles, clays, polymers, hybrid materials composed of polymers and particulates, reduced graphene oxide (rGO), and metal–organic frameworks. In this method, particles are accelerated to a high velocity and then impact a substrate at near ambient temperature, where dissipation of their kinetic energy produces strong adhesion. Here, recent progress in fundamentals and applications of cold spraying is reviewed. High‐velocity impact with the substrate results in significant deformation, which not only produces adhesion, but can change the particles’ internal structure. Cold‐sprayed coatings can also exhibit micro‐ and nanotextured morphologies not achievable by other means. Suspending micro‐ or nanoparticles in a liquid and cold‐spraying the suspension produces fine atomization and even deposition of materials that could not otherwise be processed. The scalability and low cost of this method and its compatibility with roll‐to‐roll processing make it promising for many applications, including ultrathin flexible materials, solar cells, touch‐screen panels, nanotextured surfaces for enhanced heat transfer, thermal and electrical insulation films, transparent conductive films, materials for energy storage (e.g., Li‐ion battery electrodes), heaters, sensors, photoelectrodes for

Published in: "Advanced Materials".

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