Advanced Materials

/Advanced Materials

Efficient and Robust Carbon Dioxide Electroreduction Enabled by Atomically Dispersed Snδ+ Sites

2019-02-22T06:37:14+00:00February 22nd, 2019|Categories: Publications|Tags: , |

A positively charged single‐atom metal electrocatalyst to largely reduce the overpotentials for carbon dioxide electroreduction is fabricated. Synchrotron‐radiation X‐ray absorption fine structure and high‐angle annular dark‐field scanning transmission electron microscopy demonstrate that atomically dispersed tin atoms are positively charged, which enables carbon dioxide activation and protonation proceed spontaneously, affirmed by in situ Fourier transform infrared spectra and Gibbs free energy calculations. Abstract Electrocatalytic CO2 reduction at considerably low overpotentials still remains a great challenge. Here, a positively charged single‐atom metal electrocatalyst to largely reduce the overpotentials is designed and hence CO2 electroreduction performance is accelerated. Taking the metal Sn as an example, kilogram‐scale single‐atom Sn δ + on N‐doped graphene is first fabricated by a quick freeze–vacuum drying–calcination method. Synchrotron‐radiation X‐ray absorption fine structure and high‐angle annular dark‐field scanning transmission electron microscopy demonstrate the atomically dispersed Sn atoms are positively charged, which enables CO2 activation and protonation to proceed spontaneously through stabilizing CO2•−* and HCOO−*, affirmed by in situ Fourier transform infrared spectra and Gibbs free energy calculations. Furthermore, N‐doping facilitates the rate‐limiting formate desorption step, verified by the decreased desorption energy from 2.16 to 1.01 eV and the elongated SnHCOO− bond length. As an result, single‐atom Sn δ + on N‐doped graphene exhibits a very low onset overpotential down to 60 mV for formate production and shows a very large turnover frequency up to 11930 h−1, while its electroreduction activity proceeds without deactivation even after 200 h. This work offers a new pathway for manipulating electrocatalytic performance.

Published in: "Advanced Materials".

Thinnest Nonvolatile Memory Based on Monolayer h‐BN

2019-02-21T00:38:34+00:00February 20th, 2019|Categories: Publications|Tags: |

The existence of nonvolatile resistance switching behavior is first demonstrated in monolayer hexagonal boron nitride (h‐BN) atomristors, with large on/off current ratio and fast switching speed (<15 ns) via pulse operation, representing a record thickness for memory materials (0.33 nm). Simulation results based on ab‐initio method reveal substitution of metal ions into h‐BN vacancies during electrical switching. Abstract 2D materials have attracted much interest over the past decade in nanoelectronics. However, it was believed that the atomically thin layered materials are not able to show memristive effect in vertically stacked structure, until the recent discovery of monolayer transition metal dichalcogenide (TMD) atomristors, overcoming the scaling limit to sub‐nanometer. Herein, the nonvolatile resistance switching (NVRS) phenomenon in monolayer hexagonal boron nitride (h‐BN), a typical 2D insulator, is reported. The h‐BN atomristors are studied using different electrodes and structures, featuring forming‐free switching in both unipolar and bipolar operations, with large on/off ratio (up to 107). Moreover, fast switching speed (<15 ns) is demonstrated via pulse operation. Compared with monolayer TMDs, the one‐atom‐thin h‐BN sheet reduces the vertical scaling to ≈0.33 nm, representing a record thickness for memory materials. Simulation results based on ab‐initio method reveal that substitution of metal ions into h‐BN vacancies during electrical switching is a likely mechanism. The existence of NVRS in monolayer h‐BN indicates fruitful interactions between defects, metal ions and interfaces, and can advance emerging applications on ultrathin flexible memory, printed electronics, neuromorphic computing, and radio frequency switches.

Published in: "Advanced Materials".

Exploring Approaches for the Synthesis of Few‐Layered Graphdiyne

2019-02-21T00:38:30+00:00February 20th, 2019|Categories: Publications|Tags: , |

The state‐of‐art research of graphdiyne (GDY) and focus on exploring approaches for few‐layered GDY synthesis are critically summarized. The obstacles and challenges of GDY synthesis are also analyzed in detail. The advantages and limitations of different methods are analyzed comprehensively. These synthetic methods provide considerable inspiration to approaching the synthesis of single/few‐layered GDY film. Abstract Graphdiyne (GDY) is an emerging carbon allotrope in the graphyne (GY) family, demonstrating extensive potential applications in the fields of electronic devices, catalysis, electrochemical energy storage, and nonlinear optics. Synthesis of few‐layered GDY is especially important for both electronic applications and structural characterization. This work critically summarizes the state‐of‐art of GDY and focuses on exploring approaches for few‐layered GDY synthesis. The obstacles and challenges of GDY synthesis are also analyzed in detail. Recently developed synthetic methods are discussed such as i) the copper substrate‐based method, ii) the chemical vapor deposition (CVD) method, iii) the interfacial construction method, and iv) the graphene‐templated method. Throughout the discussion, the superiorities and limitations of different methods are analyzed comprehensively. These synthetic methods have provided considerable inspiration approaching synthesis of few‐layered or single‐layered GDY film. The work concludes with a perspective on promising research directions and remaining barriers for layer‐controlled and morphology‐controlled synthesis of GDY with higher crystalline quality.

Published in: "Advanced Materials".

Progress and Prospects of Graphdiyne‐Based Materials in Biomedical Applications

2019-02-21T00:38:27+00:00February 20th, 2019|Categories: Publications|Tags: |

Current research progress indicates that graphdiyne‐based materials are useful in the biomedical field, including biosensing, radiation protection, and cancer therapy. In these applications, graphdiyne (GDY) is proven to be better than other carbon‐based materials. Though the biomedical applications of GDY are still rare and some difficulties need to be solved, graphdiyne has great potential in its future applications. Abstract Graphdiyne is a new member of the family of carbon‐based nanomaterials that possess two types of carbon atoms, sp‐ and sp2‐hybridized carbon atoms. As a novel 2D carbon‐based nanomaterial with unique planar structure, such as uniformly distributed nanopores and large conjugated structure, graphdiyne has shown many fascinating properties in mechanics, electronics, and optics since it was first experimentally synthesized in 2010. Up to now, graphdiyne and its derivatives have been reported to be successfully applied in many areas, such as catalysis, energy, environment, and biomedicine, due to these excellent properties. Herein, the current research progress of graphdiyne‐based materials in biomedical fields is summarized, including biosensing, biological protection, cancer therapy, tissue engineering, etc. The advantages of graphdiyne and its derivatives are presented and compared with other carbon‐based materials. Considering the potential biomedical and clinical applications of graphdiyne‐based materials, the toxicity and biocompatibility are also discussed based on current studies. Finally, future perspectives and possible biomedical applications of graphdiyne‐based materials are also discussed.

Published in: "Advanced Materials".

2D–Organic Hybrid Heterostructures for Optoelectronic Applications

2019-02-21T00:37:56+00:00February 20th, 2019|Categories: Publications|Tags: |

The hybridization of 2D materials and organic materials represents a promising domain for the realization of improved or unprecedented features in comparison to those of semiconductor devices. This comprehensive review focuses on emerging 2D–organic heterostructures (from their synthesis and fabrication to their state‐of‐the‐art optoelectronic applications) and highlights the future challenges and opportunities associated with these heterostructures. Abstract The unique properties of hybrid heterostructures have motivated the integration of two or more different types of nanomaterials into a single optoelectronic device structure. Despite the promising features of organic semiconductors, such as their acceptable optoelectronic properties, availability of low‐cost processes for their fabrication, and flexibility, further optimization of both material properties and device performances remains to be achieved. With the emergence of atomically thin 2D materials, they have been integrated with conventional organic semiconductors to form multidimensional heterostructures that overcome the present limitations and provide further opportunities in the field of optoelectronics. Herein, a comprehensive review of emerging 2D–organic heterostructures—from their synthesis and fabrication to their state‐of‐the‐art optoelectronic applications—is presented. Future challenges and opportunities associated with these heterostructures are highlighted.

Published in: "Advanced Materials".

Ultrathin Cobalt Oxide Layers as Electrocatalysts for High‐Performance Flexible Zn–Air Batteries

2019-02-21T00:37:54+00:00February 20th, 2019|Categories: Publications|Tags: , |

Ultrathin cobalt oxide layers on the surface of a metallic cobalt/N‐doped graphene substrate synergistically enhance the electrical conductivity and catalytic activity, leading to high performance in oxygen reactions under alkaline conditoins. A flexible Zn‐air battery built with this electrocatalyst has an ultrahigh output power capability and a record‐high specific power of 300 W gcat−1, which is essential for portable devices. Abstract Synergistic improvements in the electrical conductivity and catalytic activity for the oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) are of paramount importance for rechargeable metal–air batteries. In this study, one‐nanometer‐scale ultrathin cobalt oxide (CoOx) layers are fabricated on a conducting substrate (i.e., a metallic Co/N‐doped graphene substrate) to achieve superior bifunctional activity in both the ORR and OER and ultrahigh output power for flexible Zn–air batteries. Specifically, at the atomic scale, the ultrathin CoOx layers effectively accelerate electron conduction and provide abundant active sites. X‐ray absorption spectroscopy reveals that the metallic Co/N‐doped graphene substrate contributes to electron transfer toward the ultrathin CoOx layer, which is beneficial for the electrocatalytic process. The as‐obtained electrocatalyst exhibits ultrahigh electrochemical activity with a positive half‐wave potential of 0.896 V for ORR and a low overpotential of 370 mV at 10 mA cm−2 for OER. The flexible Zn–air battery built with this catalyst exhibits an ultrahigh specific power of 300 W gcat−1, which is essential for portable devices. This work provides a new design pathway for electrocatalysts for high‐performance rechargeable metal–air battery systems.

Published in: "Advanced Materials".

Interface‐Driven Partial Dislocation Formation in 2D Heterostructures

2019-02-21T00:37:52+00:00February 20th, 2019|Categories: Publications|Tags: , , |

Herein, extended 1D AB–AC stacking boundaries in WS2 are fabricated by using morphological defects on graphene substrates, such as graphene wrinkles. When the perfect basal dislocation direction is more perpendicular to the wrinkles, high‐density stacking boundaries are induced, due to the anisotropic friction of wrinkles. Abstract Van der Waals (vdW) epitaxy allows the fabrication of various heterostructures with dramatically released lattice matching conditions. This study demonstrates interface‐driven stacking boundaries in WS2 using epitaxially grown tungsten disulfide (WS2) on wrinkled graphene. Graphene wrinkles function as highly reactive nucleation sites on WS2 epilayers; however, they impede lateral growth and induce additional stress in the epilayer due to anisotropic friction. Moreover, partial dislocation‐driven in‐plane strain facilitates out‐of‐plane buckling with a height of 1 nm to release in‐plane strain. Remarkably, in‐plane strain relaxation at partial dislocations restores the bandgap to that of monolayer WS2 due to reduced interlayer interaction. These findings clarify significant substrate morphology effects even in vdW epitaxy and are potentially useful for various applications involving modifying optical and electronic properties by manipulating extended 1D defects via substrate morphology control.

Published in: "Advanced Materials".

Recent Advances in 2D Inorganic Nanomaterials for SERS Sensing

2019-02-21T00:37:49+00:00February 20th, 2019|Categories: Publications|Tags: , |

Layered 2D inorganic nanomaterials are emerging as high‐performance materials for surface‐enhanced Raman scattering (SERS)‐based chemical sensors, due to their tunable physicochemical and enhanced charge‐transfer properties. Recent advances in the application of various layered 2D nanomaterials for SERS chemical sensing are reviewed, and the perspectives for the future development of SERS chemical sensors using 2D nanomaterials are discussed. Abstract Surface‐enhanced Raman spectroscopy is a powerful and sensitive analytical tool that has found application in chemical and biomolecule analysis and environmental monitoring. Since its discovery in the early 1970s, a variety of materials ranging from noble metals to nanostructured materials have been employed as surface enhanced Raman scattering (SERS) substrates. In recent years, 2D inorganic materials have found wide use in the development of SERS‐based chemical sensors owing to their unique thickness dependent physico‐chemical properties with enhanced chemical‐based charge‐transfer processes. Here, recent advances in the application of various 2D inorganic nanomaterials, including graphene, boron nitride, semiconducting metal oxides, and transition metal chalcogenides, in chemical detection via SERS are presented. The background of the SERS concept, including its basic theory and sensing mechanism, along with the salient features of different nanomaterials used as substrates in SERS, extending from monometallic nanoparticles to nanometal oxides, is comprehensively discussed. The importance of 2D inorganic nanomaterials in SERS enhancement, along with their application toward chemical detection, is explained in detail with suitable examples and illustrations. In conclusion, some guidelines are presented for the development of this promising field in the future.

Published in: "Advanced Materials".

Graphene Oxide: Realizing Ultralow Concentration Gelation of Graphene Oxide with Artificial Interfaces (Adv. Mater. 8/2019)

2019-02-21T00:37:46+00:00February 20th, 2019|Categories: Publications|Tags: , |

A cocktail preparation is employed by Wei Lv, Jia Li, Quan‐Hong Yang, and co‐workers in article number 1805075 to demonstrate the ultralow‐concentration gelation of graphene oxide (GO) in a water–isopropyl‐alcohol mixture, where the two different colored liquids represent water and isopropyl alcohol respectively. Microphase separation takes place, due to the different intercalation energies of the GO in the two liquids, generating artificial liquid–liquid interfaces that facilitate interactions between the sheets and the formation of a three‐dimensional graphene network.

Published in: "Advanced Materials".

2D–Organic Hybrid Heterostructures for Optoelectronic Applications

2019-02-20T22:35:18+00:00February 20th, 2019|Categories: Publications|Tags: |

The hybridization of 2D materials and organic materials represents a promising domain for the realization of improved or unprecedented features in comparison to those of semiconductor devices. This comprehensive review focuses on emerging 2D–organic heterostructures (from their synthesis and fabrication to their state‐of‐the‐art optoelectronic applications) and highlights the future challenges and opportunities associated with these heterostructures. Abstract The unique properties of hybrid heterostructures have motivated the integration of two or more different types of nanomaterials into a single optoelectronic device structure. Despite the promising features of organic semiconductors, such as their acceptable optoelectronic properties, availability of low‐cost processes for their fabrication, and flexibility, further optimization of both material properties and device performances remains to be achieved. With the emergence of atomically thin 2D materials, they have been integrated with conventional organic semiconductors to form multidimensional heterostructures that overcome the present limitations and provide further opportunities in the field of optoelectronics. Herein, a comprehensive review of emerging 2D–organic heterostructures—from their synthesis and fabrication to their state‐of‐the‐art optoelectronic applications—is presented. Future challenges and opportunities associated with these heterostructures are highlighted.

Published in: "Advanced Materials".

Ultrathin Cobalt Oxide Layers as Electrocatalysts for High‐Performance Flexible Zn–Air Batteries

2019-02-20T12:36:41+00:00February 20th, 2019|Categories: Publications|Tags: , |

Ultrathin cobalt oxide layers on the surface of a metallic cobalt/N‐doped graphene substrate synergistically enhance the electrical conductivity and catalytic activity, leading to high performance in oxygen reactions under alkaline conditoins. A flexible Zn‐air battery built with this electrocatalyst has an ultrahigh output power capability and a record‐high specific power of 300 W gcat−1, which is essential for portable devices. Abstract Synergistic improvements in the electrical conductivity and catalytic activity for the oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) are of paramount importance for rechargeable metal–air batteries. In this study, one‐nanometer‐scale ultrathin cobalt oxide (CoOx) layers are fabricated on a conducting substrate (i.e., a metallic Co/N‐doped graphene substrate) to achieve superior bifunctional activity in both the ORR and OER and ultrahigh output power for flexible Zn–air batteries. Specifically, at the atomic scale, the ultrathin CoOx layers effectively accelerate electron conduction and provide abundant active sites. X‐ray absorption spectroscopy reveals that the metallic Co/N‐doped graphene substrate contributes to electron transfer toward the ultrathin CoOx layer, which is beneficial for the electrocatalytic process. The as‐obtained electrocatalyst exhibits ultrahigh electrochemical activity with a positive half‐wave potential of 0.896 V for ORR and a low overpotential of 370 mV at 10 mA cm−2 for OER. The flexible Zn–air battery built with this catalyst exhibits an ultrahigh specific power of 300 W gcat−1, which is essential for portable devices. This work provides a new design pathway for electrocatalysts for high‐performance rechargeable metal–air battery systems.

Published in: "Advanced Materials".

Interface‐Driven Partial Dislocation Formation in 2D Heterostructures

2019-02-20T10:45:43+00:00February 20th, 2019|Categories: Publications|Tags: , , |

Herein, extended 1D AB–AC stacking boundaries in WS2 are fabricated by using morphological defects on graphene substrates, such as graphene wrinkles. When the perfect basal dislocation direction is more perpendicular to the wrinkles, high‐density stacking boundaries are induced, due to the anisotropic friction of wrinkles. Abstract Van der Waals (vdW) epitaxy allows the fabrication of various heterostructures with dramatically released lattice matching conditions. This study demonstrates interface‐driven stacking boundaries in WS2 using epitaxially grown tungsten disulfide (WS2) on wrinkled graphene. Graphene wrinkles function as highly reactive nucleation sites on WS2 epilayers; however, they impede lateral growth and induce additional stress in the epilayer due to anisotropic friction. Moreover, partial dislocation‐driven in‐plane strain facilitates out‐of‐plane buckling with a height of 1 nm to release in‐plane strain. Remarkably, in‐plane strain relaxation at partial dislocations restores the bandgap to that of monolayer WS2 due to reduced interlayer interaction. These findings clarify significant substrate morphology effects even in vdW epitaxy and are potentially useful for various applications involving modifying optical and electronic properties by manipulating extended 1D defects via substrate morphology control.

Published in: "Advanced Materials".

Graphene Oxide: Realizing Ultralow Concentration Gelation of Graphene Oxide with Artificial Interfaces (Adv. Mater. 8/2019)

2019-02-19T18:38:25+00:00February 19th, 2019|Categories: Publications|Tags: , |

A cocktail preparation is employed by Wei Lv, Jia Li, Quan‐Hong Yang, and co‐workers in article number 1805075 to demonstrate the ultralow‐concentration gelation of graphene oxide (GO) in a water–isopropyl‐alcohol mixture, where the two different colored liquids represent water and isopropyl alcohol respectively. Microphase separation takes place, due to the different intercalation energies of the GO in the two liquids, generating artificial liquid–liquid interfaces that facilitate interactions between the sheets and the formation of a three‐dimensional graphene network.

Published in: "Advanced Materials".

Exploring Approaches for the Synthesis of Few‐Layered Graphdiyne

2019-02-19T10:46:39+00:00February 19th, 2019|Categories: Publications|Tags: , |

The state‐of‐art research of graphdiyne (GDY) and focus on exploring approaches for few‐layered GDY synthesis are critically summarized. The obstacles and challenges of GDY synthesis are also analyzed in detail. The advantages and limitations of different methods are analyzed comprehensively. These synthetic methods provide considerable inspiration to approaching the synthesis of single/few‐layered GDY film. Abstract Graphdiyne (GDY) is an emerging carbon allotrope in the graphyne (GY) family, demonstrating extensive potential applications in the fields of electronic devices, catalysis, electrochemical energy storage, and nonlinear optics. Synthesis of few‐layered GDY is especially important for both electronic applications and structural characterization. This work critically summarizes the state‐of‐art of GDY and focuses on exploring approaches for few‐layered GDY synthesis. The obstacles and challenges of GDY synthesis are also analyzed in detail. Recently developed synthetic methods are discussed such as i) the copper substrate‐based method, ii) the chemical vapor deposition (CVD) method, iii) the interfacial construction method, and iv) the graphene‐templated method. Throughout the discussion, the superiorities and limitations of different methods are analyzed comprehensively. These synthetic methods have provided considerable inspiration approaching synthesis of few‐layered or single‐layered GDY film. The work concludes with a perspective on promising research directions and remaining barriers for layer‐controlled and morphology‐controlled synthesis of GDY with higher crystalline quality.

Published in: "Advanced Materials".

Progress and Prospects of Graphdiyne‐Based Materials in Biomedical Applications

2019-02-19T10:46:35+00:00February 19th, 2019|Categories: Publications|Tags: |

Current research progress indicates that graphdiyne‐based materials are useful in the biomedical field, including biosensing, radiation protection, and cancer therapy. In these applications, graphdiyne (GDY) is proven to be better than other carbon‐based materials. Though the biomedical applications of GDY are still rare and some difficulties need to be solved, graphdiyne has great potential in its future applications. Abstract Graphdiyne is a new member of the family of carbon‐based nanomaterials that possess two types of carbon atoms, sp‐ and sp2‐hybridized carbon atoms. As a novel 2D carbon‐based nanomaterial with unique planar structure, such as uniformly distributed nanopores and large conjugated structure, graphdiyne has shown many fascinating properties in mechanics, electronics, and optics since it was first experimentally synthesized in 2010. Up to now, graphdiyne and its derivatives have been reported to be successfully applied in many areas, such as catalysis, energy, environment, and biomedicine, due to these excellent properties. Herein, the current research progress of graphdiyne‐based materials in biomedical fields is summarized, including biosensing, biological protection, cancer therapy, tissue engineering, etc. The advantages of graphdiyne and its derivatives are presented and compared with other carbon‐based materials. Considering the potential biomedical and clinical applications of graphdiyne‐based materials, the toxicity and biocompatibility are also discussed based on current studies. Finally, future perspectives and possible biomedical applications of graphdiyne‐based materials are also discussed.

Published in: "Advanced Materials".

Recent Advances in 2D Inorganic Nanomaterials for SERS Sensing

2019-02-19T10:45:49+00:00February 19th, 2019|Categories: Publications|Tags: , |

Layered 2D inorganic nanomaterials are emerging as high‐performance materials for surface‐enhanced Raman scattering (SERS)‐based chemical sensors, due to their tunable physicochemical and enhanced charge‐transfer properties. Recent advances in the application of various layered 2D nanomaterials for SERS chemical sensing are reviewed, and the perspectives for the future development of SERS chemical sensors using 2D nanomaterials are discussed. Abstract Surface‐enhanced Raman spectroscopy is a powerful and sensitive analytical tool that has found application in chemical and biomolecule analysis and environmental monitoring. Since its discovery in the early 1970s, a variety of materials ranging from noble metals to nanostructured materials have been employed as surface enhanced Raman scattering (SERS) substrates. In recent years, 2D inorganic materials have found wide use in the development of SERS‐based chemical sensors owing to their unique thickness dependent physico‐chemical properties with enhanced chemical‐based charge‐transfer processes. Here, recent advances in the application of various 2D inorganic nanomaterials, including graphene, boron nitride, semiconducting metal oxides, and transition metal chalcogenides, in chemical detection via SERS are presented. The background of the SERS concept, including its basic theory and sensing mechanism, along with the salient features of different nanomaterials used as substrates in SERS, extending from monometallic nanoparticles to nanometal oxides, is comprehensively discussed. The importance of 2D inorganic nanomaterials in SERS enhancement, along with their application toward chemical detection, is explained in detail with suitable examples and illustrations. In conclusion, some guidelines are presented for the development of this promising field in the future.

Published in: "Advanced Materials".

Thinnest Nonvolatile Memory Based on Monolayer h‐BN

2019-02-18T08:53:58+00:00February 18th, 2019|Categories: Publications|Tags: |

The existence of nonvolatile resistance switching behavior is first demonstrated in monolayer hexagonal boron nitride (h‐BN) atomristors, with large on/off current ratio and fast switching speed (<15 ns) via pulse operation, representing a record thickness for memory materials (0.33 nm). Simulation results based on ab‐initio method reveal substitution of metal ions into h‐BN vacancies during electrical switching. Abstract 2D materials have attracted much interest over the past decade in nanoelectronics. However, it was believed that the atomically thin layered materials are not able to show memristive effect in vertically stacked structure, until the recent discovery of monolayer transition metal dichalcogenide (TMD) atomristors, overcoming the scaling limit to sub‐nanometer. Herein, the nonvolatile resistance switching (NVRS) phenomenon in monolayer hexagonal boron nitride (h‐BN), a typical 2D insulator, is reported. The h‐BN atomristors are studied using different electrodes and structures, featuring forming‐free switching in both unipolar and bipolar operations, with large on/off ratio (up to 107). Moreover, fast switching speed (<15 ns) is demonstrated via pulse operation. Compared with monolayer TMDs, the one‐atom‐thin h‐BN sheet reduces the vertical scaling to ≈0.33 nm, representing a record thickness for memory materials. Simulation results based on ab‐initio method reveal that substitution of metal ions into h‐BN vacancies during electrical switching is a likely mechanism. The existence of NVRS in monolayer h‐BN indicates fruitful interactions between defects, metal ions and interfaces, and can advance emerging applications on ultrathin flexible memory, printed electronics, neuromorphic computing, and radio frequency switches.

Published in: "Advanced Materials".

Graphene on Group‐IV Elementary Semiconductors: The Direct Growth Approach and Its Applications

2019-02-16T22:37:40+00:00February 16th, 2019|Categories: Publications|Tags: , |

Research on the integration of graphene with group‐IV elementary semiconductors, which can complement and enhance the intrinsic properties of the semiconductor through graphene’s superior and unique properties, is actively under way. The recent progress in the direct growth of graphene on the Si and Ge surface and its applications are comprehensively summarized. Abstract Since the first development of large‐area graphene synthesis by the chemical vapor deposition (CVD) method in 2009, CVD‐graphene has been considered to be a key material in the future electronics, energy, and display industries, which require transparent, flexible, and stretchable characteristics. Although many graphene‐based prototype applications have been demonstrated, several important issues must be addressed in order for them to be compatible with current complementary metal‐oxide‐semiconductor (CMOS)‐based manufacturing processes. In particular, metal contamination and mechanical damage, caused by the metal catalyst for graphene growth, are known to cause severe and irreversible deterioration in the performance of devices. The most effective way to solve the problems is to grow the graphene directly on the semiconductor substrate. Herein, recent advances in the direct growth of graphene on group‐IV semiconductors are reviewed, focusing mainly on the growth mechanism and initial growth behavior when graphene is synthesized on Si and Ge. Furthermore, recent progress in the device applications of graphene with Si and Ge are presented. Finally, perspectives for future research in graphene with a semiconductor are discussed.

Published in: "Advanced Materials".

Improved Charge Extraction Beyond Diffusion Length by Layer‐by‐Layer Multistacking Intercalation of Graphene Layers inside Quantum Dots Films

2019-02-16T22:37:33+00:00February 16th, 2019|Categories: Publications|Tags: |

A novel architecture based on layer‐by‐layer multistacking intercalation of graphene inside quantum dot (QD) films is studied. The intercalated graphene layers ensure improved charge extraction beyond the diffusion length of the QDs, offering superior quantum efficiency over single‐bottom graphene/QD devices, and overcoming the restriction that the diffusion length imposes on film thickness. Abstract Charge collection is critical in any photodetector or photovoltaic device. Novel materials such as quantum dots (QDs) have extraordinary light absorption properties, but their poor mobility and short diffusion length limit efficient charge collection using conventional top/bottom contacts. In this work, a novel architecture based on multiple intercalated chemical vapor deposition graphene monolayers distributed in an orderly manner inside a QD film is studied. The intercalated graphene layers ensure that at any point in the absorbing material, photocarriers will be efficiently collected and transported. The devices with intercalated graphene layers have superior quantum efficiency over single‐bottom graphene/QD devices, overcoming the known restriction that the diffusion length imposes on film thickness. QD film with increased thickness shows efficient charge collection over the entire λ ≈ 500–1000 nm spectrum. This architecture could be applied to boost the performance of other low‐cost materials with poor mobility, allowing efficient collection for films thicker than their diffusion length.

Published in: "Advanced Materials".

Graphene Electrodes: Quantitative Principles for Precise Engineering of Sensitivity in Graphene Electrochemical Sensors (Adv. Mater. 6/2019)

2019-02-16T22:37:27+00:00February 16th, 2019|Categories: Publications|Tags: |

In article number 1805752, Davood Shahrjerdi and co‐workers reveal the quantitative relationships between the structural defects of graphene and the sensitivity of electrodes made of it. Using the physics of point defects in graphene, a microscopic model is proposed, which can quantitatively explain the relationship between sensitivity and average density of point defects in graphene electrodes. In addition, the model is shown to accurately guide nanoengineering of the structure of graphene, resulting in homogeneous miniaturized sensors with unprecedented sensitivity.

Published in: "Advanced Materials".

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