Publication on 2D research

Promoted Glycerol Oxidation Reaction in an Interface‐Confined Hierarchically Structured Catalyst

2018-11-18T00:34:15+00:00November 17th, 2018|Categories: Publications|Tags: , |

The confinement of Pt nanosheets is realized in a vertically erected graphene array with hierarchically porous architecture to address the mass‐diffusion limitation in interface‐confined catalysis. Such a confined 3D catalyst exhibits a much stronger oxidation and CC bond cleaving ability for the glycerol oxidation reaction, leading to a superior mass activity and selectivity toward C1 products than commercial Pt/C catalysts. Abstract Confined catalysis in a 2D system is of particular interest owing to the facet control of the catalysts and the anisotropic kinetics of reactants, which suppress side reactions and improve selectivity. Here, a 2D‐confined system consisting of intercalated Pt nanosheets within few‐layered graphene is demonstrated. The strong metal–substrate interaction between the Pt nanosheets and the graphene leads to the quasi‐2D growth of Pt with a unique (100)/(111)/(100) faceted structure, thus providing excellent catalytic activity and selectivity toward one‐carbon (C1) products for the glycerol oxidation reaction. A hierarchically porous graphene architecture, grown on carbon cloth, is used to fabricate the confined catalyst bed in order to enhance the mass‐diffusion limitation in interface‐confined reactions. Owing to its unique 3D porous structure, this graphene‐confined Pt catalyst exhibits an extraordinary mass activity of 2910 mA mgPt−1 together with a formate selectivity of 79% at 60 °C. This paves the way toward rational designs of heterogeneous catalysts for energy‐related applications.

Published in: "Advanced Materials".

Electronic and Optical Properties of 2D Materials Constructed from Light Atoms

2018-11-18T00:34:12+00:00November 17th, 2018|Categories: Publications|Tags: |

2D materials constructed from boron, carbon, nitrogen, and oxygen atoms show a rich structural diversity. This makes possible engineering of their electronic and optical properties through a refined structural control. Abstract Boron, carbon, nitrogen, and oxygen atoms can form various building blocks for further construction of structurally well‐defined 2D materials (2DMs). Both in theory and experiment, it has been documented that the electronic structures and optical properties of 2DMs are well tunable through a rational design of the material structure. Here, the recent progress on 2DMs that are composed of B, C, N, and O elements is introduced, including borophene, graphene, h‐BN, g‐C3N4, organic 2D polymers (2DPs), etc. Attention is put on the band structure/bandgap engineering for these materials through a variety of methodologies, such as chemical modifications, layer number and atomic structure control, change of conjugation degree, etc. The optical properties, such as photoluminescence, thermoluminescence, single photon emission, as well as the associated applications in bioimaging and sensing, are discussed in detail and highlighted.

Published in: "Advanced Materials".

An Ambipolar Superconducting Field‐Effect Transistor Operating above Liquid Helium Temperature

2018-11-18T00:34:08+00:00November 17th, 2018|Categories: Publications|Tags: |

An ambipolar superconducting field‐effect transistor is developed using a strongly correlated molecular system laminated on a SiO2/Si substrate. The low‐temperature electronic state is fine tuned in the vicinity of the superconductor‐to‐Mott‐insulator transition, utilizing the negative pressure effect from the substrate, which allows a small dose of hole or electron injection by the SiO2 dielectric to control the superconductivity above 4.2 K. Abstract Superconducting (SC) devices are attracting renewed attention as the demands for quantum‐information processing, meteorology, and sensing become advanced. The SC field‐effect transistor (FET) is one of the elements that can control the SC state, but its variety is still limited. Superconductors at the strong‐coupling limit tend to require a higher carrier density when the critical temperature (T C) becomes higher. Therefore, field‐effect control of superconductivity by a solid gate dielectric has been limited only to low temperatures. However, recent efforts have resulted in achieving n‐type and p‐type SC FETs based on organic superconductors whose T C exceed liquid He temperature (4.2 K). Here, a novel “ambipolar” SC FET operating at normally OFF mode with T C of around 6 K is reported. Although this is the second example of an SC FET with such an operation mode, the operation temperature exceeds that of the first example, or magic‐angle twisted‐bilayer graphene that operates at around 1 K. Because the superconductivity in this SC FET is of unconventional type, the performance of the present device will contribute not only to fabricating SC circuits, but also to elucidating phase transitions

Published in: "Advanced Materials".

Lowering the Schottky Barrier Height by Graphene/Ag Electrodes for High‐Mobility MoS2 Field‐Effect Transistors

2018-11-18T00:34:06+00:00November 17th, 2018|Categories: Publications|Tags: , |

Contact resistance between the channel and electrodes in MoS2 devices is significantly reduced using a low work function metal (Ag) and graphene as an interfacial layer between MoS2 and Ag because the Schottky barrier height is lowered at the contacts. Using graphene/Ag contacts instead of Ti/Au improves the field‐effect mobility, on/off current ratio, and photoresponsivity of the devices. Abstract 2D transition metal dichalcogenides (TMDCs) have emerged as promising candidates for post‐silicon nanoelectronics owing to their unique and outstanding semiconducting properties. However, contact engineering for these materials to create high‐performance devices while adapting for large‐area fabrication is still in its nascent stages. In this study, graphene/Ag contacts are introduced into MoS2 devices, for which a graphene film synthesized by chemical vapor deposition (CVD) is inserted between a CVD‐grown MoS2 film and a Ag electrode as an interfacial layer. The MoS2 field‐effect transistors with graphene/Ag contacts show improved electrical and photoelectrical properties, achieving a field‐effect mobility of 35 cm2 V−1 s−1, an on/off current ratio of 4 × 108, and a photoresponsivity of 2160 A W−1, compared to those of devices with conventional Ti/Au contacts. These improvements are attributed to the low work function of Ag and the tunability of graphene Fermi level; the n‐doping of Ag in graphene decreases its Fermi level, thereby reducing the Schottky barrier height and contact resistance between the MoS2 and electrodes. This demonstration of contact interface engineering with CVD‐grown MoS2 and graphene is a key step toward the practical application of atomically thin TMDC‐based devices

Published in: "Advanced Materials".

Ultrasensitive 2D Bi2O2Se Phototransistors on Silicon Substrates

2018-11-18T00:34:04+00:00November 17th, 2018|Categories: Publications|

Ultrasensitive Bi2O2Se phototransistors are demonstrated by utilizing a unique method to transfer CVD‐grown Bi2O2Se from mica onto silicon substrates. Compared with devices on mica, photodetectors on silicon maintain high photoresponsivity, high photoconductive gain, fast response rate, and at the same time, the dark current is much lowered, which yields ultrahigh on/off ratio and specific detectivity. Abstract 2D materials are considered as intriguing building blocks for next‐generation optoelectronic devices. However, their photoresponse performance still needs to be improved for practical applications. Here, ultrasensitive 2D phototransistors are reported employing chemical vapor deposition (CVD)‐grown 2D Bi2O2Se transferred onto silicon substrates with a noncorrosive transfer method. The as‐transferred Bi2O2Se preserves high quality in contrast to the serious quality degradation in hydrofluoric‐acid‐assisted transfer. The phototransistors show a responsivity of 3.5 × 104 A W−1, a photoconductive gain of more than 104, and a time response in the order of sub‐millisecond. With back gating of the silicon substrate, the dark current can be reduced to several pA. This yields an ultrahigh sensitivity with a specific detectivity of 9.0 × 1013 Jones, which is one of the highest values among 2D material photodetectors and two orders of magnitude higher than that of other CVD‐grown 2D materials. The high performance of the phototransistor shown here together with the developed unique transfer technique are promising for the development of novel 2D‐material‐based optoelectronic applications as well as integrating with state‐of‐the‐art silicon photonic and electronic technologies.

Published in: "Advanced Materials".

Direct CVD Growth of Graphene on Traditional Glass: Methods and Mechanisms

2018-11-18T00:34:01+00:00November 17th, 2018|Categories: Publications|Tags: |

A summary of the chemical vapor deposition (CVD) growth techniques of graphene on traditional glass as well as the growth mechanisms is provided. Direct thermal CVD growth, molten‐bed CVD growth, metal‐catalyst‐assisted growth, and plasma‐enhanced growth are covered. Emphasis is laid on the strategy of growth corresponding to the different natures of glass substrates. Abstract Chemical vapor deposition (CVD) on catalytic metal surfaces is considered to be the most effective way to obtain large‐area, high‐quality graphene films. For practical applications, a transfer process from metal catalysts to target substrates (e.g., poly(ethylene terephthalate) (PET), glass, and SiO2/Si) is unavoidable and severely degrades the quality of graphene. In particular, the direct growth of graphene on glass can avoid the tedious transfer process and endow traditional glass with prominent electrical and thermal conductivities. Such a combination of graphene and glass creates a new type of glass, the so‐called “super graphene glass,” which has attracted great interest from the viewpoints of both fundamental research and daily‐life applications. In the last few years, great progress has been achieved in pursuit of this goal. Here, these growth methods as well as the specific growth mechanisms of graphene on glass surfaces are summarized. The typical techniques developed include direct thermal CVD growth, molten‐bed CVD growth, metal‐catalyst‐assisted growth, and plasma‐enhanced growth. Emphasis is placed on the strategy of growth corresponding to the different natures of glass substrates. A comprehensive understanding of graphene growth on nonmetal glass substrates and the latest status of “super graphene glass” production are provided.

Published in: "Advanced Materials".

Rollable, Stretchable, and Reconfigurable Graphene Hygroelectric Generators

2018-11-18T00:33:59+00:00November 17th, 2018|Categories: Publications|Tags: |

Rollable, stretchable, and 3D space‐deformable graphene‐based hygroelectric generators are developed by a laser processing strategy, which exhibit excellent electricity‐generation ability without any significant performance loss despite being deformed arbitrarily, and are promising as power supply for applications in complicated conditions. Abstract Moisture‐triggered electricity generation has attracted much attention because of the effective utilization of the water‐molecule diffusion process widely existing in atmosphere. However, the monotonous and rigid structures of previously developed generators have heavily restricted their applications in complex and highly deformable working conditions. Herein, by a rational configuration design with a versatile laser processing strategy, graphene‐based hygroelectric generators (GHEGs) of sophisticated architectures with diversified functions such as rollable, stretchable, and even multidimensional transformation are achieved for the first time. More importantly, a wide range of 3D deformable generators that can automatically assemble and transform from planar geometries into spacial architectures are also successfully fabricated, including cubic boxes, pyramids, Miura‐ori, and footballs. These GHEGs demonstrate excellent electricity‐generation performance in curling and elongating states. The generated voltages are easily up to 1.5 V under humidity variation in atmosphere, powering a variety of commercial electronic components. These deformable GHEGs can be applied on complicated surfaces, human bodies, and many more beyond those demonstrated in this work.

Published in: "Advanced Materials".

Surface Effect on 2D Hybrid Perovskite Crystals: Perovskites Using an Ethanolamine Organic Layer as an Example

2018-11-18T00:33:58+00:00November 17th, 2018|Categories: Publications|

The influence of the surface effect of 2D layered perovskites before and after mechanical exfoliation is studied. The smooth 2D perovskite is less sensitive to ambient moisture and exhibits a considerably low dark current. This work reveals the strong dependence of the surface condition of 2D hybrid perovskite crystals on their moisture stability and optoelectronic properties. Abstract Despite the remarkable progress of optoelectronic devices based on hybrid perovskites, there are significant drawbacks, which have largely hindered their development as an alternative of silicon. For instance, hybrid perovskites are well‐known to suffer from moisture instability which leads to surface degradation. Nonetheless, the dependence of the surface effect on the moisture stability and optoelectronic properties of hybrid perovskites has not been fully investigated. In this work, the influence of the surface effect of 2D layered perovskites before and after mechanical exfoliation, representing rough and smooth surfaces of perovskite crystals, are studied. It is found that the smooth 2D perovskite is less sensitive to ambient moisture and exhibits a considerably low dark current, which outperforms the rough perovskites by 23.6 times in terms of photodetectivity. The superior moisture stability of the smooth perovskites over the rough perovskites is demonstrated. Additionally, ethanolamine is employed as an organic linker of the 2D layered perovskite, which further improves the moisture stability. This work reveals the strong dependence of the surface conditions of 2D hybrid perovskite crystals on their moisture stability and optoelectronic properties, which are of utmost importance to the design of practical optoelectronic devices

Published in: "Advanced Materials".

Stimuli‐Responsive Materials: Self‐Adapting Wettability of ReS2 under a Constant Stimulus (Adv. Mater. 46/2018)

2018-11-18T00:33:56+00:00November 17th, 2018|Categories: Publications|Tags: |

In article number 1804559, Lei Fu and co‐workers enforce a smart self‐adapting wettability (SAQ) of ReS2 under sustained light irradiation, which breaks the stereotype that a single stimulus leads to a monotonic change in properties or structure. This unique SAW provides a brand‐new insight to broaden the applications of responsive materials, which will undoubtedly pave a novel way in further device optimization.

Published in: "Advanced Materials".

2D Layered Perovskites: Surface Effect on 2D Hybrid Perovskite Crystals: Perovskites Using an Ethanolamine Organic Layer as an Example (Adv. Mater. 46/2018)

2018-11-18T00:33:53+00:00November 17th, 2018|Categories: Publications|

In article number 1804372, Jr‐Hau He and co‐workers study the influences of the surface effect of 2D layered perovskites before and after mechanical exfoliation. The smooth 2D perovskite is less sensitive to ambient moisture and exhibits a considerably low dark current. This work reveals the strong dependence of the surface condition of 2D hybrid perovskite crystals on their moisture stability and optoelectronic properties.

Published in: "Advanced Materials".

Deactivating Defects in Graphenes with Al2O3 Nanoclusters to Produce Long‐Life and High‐Rate Sodium‐Ion Batteries

2018-11-18T00:32:36+00:00November 17th, 2018|Categories: Publications|Tags: , |

The defects in graphene are deactivated by the coverage of Al2O3 nanoclusters, which suppress the irreversible decomposition of the sodium conductive salt in sodium‐ion battery electrolytes. An ion‐conducting, thin and homogenous solid electrolyte interphase is formed, resulting in high initial Coulombic efficiency, good rate capability, and cyclic stability for sodium‐ion storage. Abstract Carbon materials are the most promising anodes for sodium‐ion batteries (SIBs), but low initial Coulombic efficiency (ICE) and poor cyclic stability hinder their practical use. It is shown herein, that an effective but simple remedy for these problems can be achieved by deactivating defects in the carbon with Al2O3 nanocluster coverage. A 3D porous graphene monolith (PGM) is used as the model material and Al2O3 nanoclusters around 1 nm are grown on the defects of graphene. It is shown that these Al2O3 nanoclusters suppress the decomposition of conductive sodium salt in the electrolyte, resulting in the formation of a thin and homogenous solid electrolyte interphase (SEI). In addition, Al2O3 nanoclusters appear to reduce the detrimental etching of the SEI by hydrogen fluoride (HF) and improve its stability. Therefore, after the introduction of Al2O3 nanoclusters, the ICE, cyclic stability, and rate capability of the PGM are greatly improved. A higher ICE (70.2%) and capacity retention (82.9% after 500 cycles at 0.5 A g−1) than those of normally reported for large surface area carbons are achieved. This work indicates a new way to deactivate defects and modify the SEI of carbon materials, and hopefully accelerate the commercialization of carbon

Published in: "Advanced Energy Materials".

Carbon Nanodots as Feedstock for a Uniform Hematite‐Graphene Nanocomposite

2018-11-17T22:34:21+00:00November 17th, 2018|Categories: Publications|Tags: |

Finely dispersed hematite nanoparticles in a carbon nanodot‐derived 3D‐graphene matrix show enhanced electrochemical performance in electrochemical double layer capacitors. Abstract High degrees of dispersion are a prerequisite for functional composite materials for applications in electronics such as sensors, charge and data storage, and catalysis. The use of small precursor materials can be a decisive factor in achieving a high degree of dispersion. In this study, carbon nanodots are used to fabricate a homogeneous, finely dispersed Fe2O3‐graphene composite aerogel in a one‐step conversion process from a precursor mixture. The laser‐assisted conversion of small size carbon nanodots enables a uniform distribution of 6.5 nm Fe2O3 nanoparticles during the formation of a highly conductive carbon matrix. Structural and electrochemical characterization shows that the features of both material entities are maintained and successfully integrated. The presence of Fe2O3 nanoparticles has a positive effect on the active surface area of the carbon aerogel and thus on the capacitance of the material. This is demonstrated by testing the performance of the composite in supercapacitors. Faradaic reactions are exploited in an aqueous electrolyte through the high accessible surface of the incorporated small Fe2O3 nanoparticles boosting the specific capacitance of the 3D turbostratic graphene network significantly.

Published in: "Small".

Phosphorus‐Mediated MoS2 Nanowires as a High‐Performance Electrode Material for Quasi‐Solid‐State Sodium‐Ion Intercalation Supercapacitors

2018-11-17T22:34:20+00:00November 17th, 2018|Categories: Publications|Tags: , |

We propose an efficient P‐anion doping strategy to enhance the electrochemical performance of the MoS2 nanowires by increasing the number of electrochemically active sites, improving the electrical conductivity, and decreasing the energy barrier of Na+ ion diffusion. The P‐doped MoS2 delivers remarkable specific capacitance and rate capability. This study highlights the dominating role of P dopants in electrode materials for supercapacitors. Abstract Molybdenum disulfide (MoS2) is a promising electrode material for electrochemical energy storage owing to its high theoretical specific capacity and fascinating 2D layered structure. However, its sluggish kinetics for ionic diffusion and charge transfer limits its practical applications. Here, a promising strategy is reported for enhancing the Na+‐ion charge storage kinetics of MoS2 for supercapacitors. In this strategy, electrical conductivity is enhanced and the diffusion barrier of Na+ ion is lowered by a facile phosphorus‐doping treatment. Density functional theory results reveal that the lowest energy barrier of dilute Na‐vacancy diffusion on P‐doped MoS2 (0.11 eV) is considerably lower than that on pure MoS2 (0.19 eV), thereby signifying a prominent rate performance at high Na intercalation stages upon P‐doping. Moreover, the Na‐vacancy diffusion coefficient of the P‐doped MoS2 at room temperatures can be enhanced substantially by approximately two orders of magnitude (10−6–10−4 cm2 s−1) compared with pure MoS2. Finally, the quasi‐solid‐state asymmetrical supercapacitor assembled with P‐doped MoS2 and MnO2, as the positive and negative electrode materials, respectively, exhibits an ultrahigh energy density of 67.4 W h kg−1 at 850 W kg−1 and excellent cycling stability with 93.4% capacitance

Published in: "Small".

Intrinsic Carrier Transport of Phase‐Pure Homologous 2D Organolead Halide Hybrid Perovskite Single Crystals

2018-11-17T22:34:18+00:00November 17th, 2018|Categories: Publications|

2D organolead halide perovskite field effect transistors, which are fabricated based on phase‐pure homologous (n = 1, 2, and 3) Ruddelsden–Popper perovskite (BA)2(MA) n− 1Pb nI3 n +1 single crystals are demonstrated. A strong dependence of carrier transport behavior of the 2D organolead halide hybrid perovskites on the n value is revealed. Abstract This work reveals the intrinsic carrier transport behavior of 2D organolead halide perovskites based on phase‐pure homologous (n = 1, 2, and 3) Ruddelsden–Popper perovskite (RPP) (BA)2(MA) n −1Pb nI3n+1 single crystals. The 2D perovskite field effect transistors with high‐quality exfoliated 2D perovskite bulk crystals are fabricated, and characteristic output and transfer curves are measured from individual single‐crystal flakes with various n values under different temperatures. Unipolar n‐type transport dominated the electrical properties of all these 2D RPP single crystals. The transport behavior of the 2D organolead halide hybrid perovskites exhibits a strong dependence on the n value and the mobility substantially increases as the ratio of the number of inorganic perovskite slabs per organic spacer increases. By extracting the effect of contact resistances, the corrected mobility values for n = 1, 2, and 3 are 2 × 10−3, 8.3 × 10−2, and 1.25 cm2 V−1 s−1 at 77 K, respectively. Furthermore, by combining temperature‐dependent electrical transport and optical measurements, it is found that the origin of the carrier mobility dependence on the phase transition for 2D organolead halide perovskites is very different from that of their 3D counterparts. Our findings offer insight into fundamental carrier

Published in: "Small".

Van der Waals Heterostructure Devices with Dynamically Controlled Conduction Polarity and Multifunctionality

2018-11-17T22:32:33+00:00November 17th, 2018|Categories: Publications|Tags: , , |

A new application of vdWHs to dynamically control and optimize the electronic and optoelectronic properties of 2D materials is demonstrated. The semivertical MoTe2/MoS2 structure allows for a desirable multifunctional integration of field effect transistorswith on/off ratio >107 and diode with rectification ratio >106. Moreover, the devices exhibit strong capability of suppressing the widely observed trap states–related negative photoresponse effect. Abstract Controlling the conduction behavior of 2D materials is an important prerequisite to achieve their electronic and optoelectronic applications. However, most of the reported approaches are aware of the shortcomings of inflexibility and complexity, which limits the possibility of multifunctional integration. Here, taking advantage of van der Waals heterostructure engineering, a simple method to achieve a dynamically controlled binary channel in a semivertical MoTe2/MoS2 field effect transistor is proposed. It is enabled by the high switchability between tunneling and thermal transports through simply changing the sign of voltage bias. In addition, the proposed system allows for multifunctional integration of transistor with on/off ratio >107 and diode with rectification ratio >106. Moreover, the devices show screen capability to negative photoresponse effect that is widely observed in ambipolar materials, hence improving the photodetection reliability and sensitivity. This study broadens the functionalities of van der Waals heterostructures and opens up more possibilities to realize multifunctional devices.

Published in: "Advanced Functional Materials".

Planar Alignment of Graphene Sheets by a Rotating Magnetic Field for Full Exploitation of Graphene as a 2D Material

2018-11-17T22:32:30+00:00November 17th, 2018|Categories: Publications|Tags: |

Planar alignment of suspended graphene sheets is realized with a near‐perfect order parameter and high optical anisotropy by using a rotating magnetic field produced by a pair of small NdFeB magnets, and can be further patterned and immobilized by photolithography. The arbitrary orientational and spatial control has enabled a wide range of device applications of graphene and related materials. Abstract Planar alignment of disc‐like nanomaterials is required to transfer their superior anisotropic properties from microscopic individual structures to macroscopic collective assemblies. However, such alignment by electrical or magnetic field is challenging due to their additional degrees of orientational freedom compared to that of rod‐like nanostructures. Here, the realization of planar alignment of suspended graphene sheets using a rotating magnetic field produced by a pair of small NdFeB magnets and subsequent demonstration of high optical anisotropy and potential novel device applications is reported. Compared to partially aligned sheets with a static magnetic field, planar aligned graphene suspensions exhibit a near‐perfect order parameter, much higher birefringence and anisotropic absorption/transmission. A unique feature of discotic nanomaterial assemblies is that the observed order parameter and optical property can vary from isotropic to partial and complete alignment depending on the experimental configuration. By immobilizing and patterning aligned graphene in a UV‐curable polymer resin, we further demonstrated an all‐graphene permanent display, which exhibits wide‐angle, high dark‐bright contrast in either transmission or reflection mode without any polarizing optics. The ability to control and pattern graphene orientation in all three dimensions opens up new exploration and broad

Published in: "Advanced Functional Materials".

Saddle‐Point Excitons and Their Extraordinary Light Absorption in 2D β‐Phase Group‐IV Monochalcogenides

2018-11-17T22:32:26+00:00November 17th, 2018|Categories: Publications|Tags: |

Monolayer β‐phase group‐IV monochalcogenides possess saddle‐points in the joint density of states, which leads to a remarkable absorption peak within the fundamental gap. Accordingly, the power conversion efficiencies for monolayer β‐GeSe and β‐SnSe are significantly higher than reported high‐performance ultrathin solar cells using transition metal dichalcogenides. Abstract In 2D materials, saddle‐points in the electronic structure give rise to diverging density of states, which leads to intriguing physical phenomena useful for applications, including magnetism, superconductivity, charge density wave, as well as enhanced optical absorption. Using first‐principles calculations, monolayer β‐phase group‐IV monochalcogenides (MX, M = Ge or Sn; X = S or Se) are shown to be a new class of 2D materials that possess saddle‐points in both the lowest conduction band and the highest valence band as well as in the joint density of states. Due to the existence of saddle‐points, a remarkable absorption peak within the fundamental gap is found in these materials when the light polarization is along the armchair (y) direction. The properties of saddle‐point excitons can be effectively tuned by both the strain and thickness of these materials. Importantly, the strong optical absorbance induced by saddle‐point exciton absorptions and the appropriate bandgap give ideal power conversion efficiencies as large as 1.11% for monolayer β‐SnSe, significantly higher than reported high‐performance ultrathin solar cells using transition metal dichalcogenides. These results not only open new avenues for exploring novel many‐body physics, but also suggest β‐phase MXs could be promising candidates for future optoelectronic devices.

Published in: "Advanced Functional Materials".

Stable Sulfur‐Intercalated 1T′ MoS2 on Graphitic Nanoribbons as Hydrogen Evolution Electrocatalyst

2018-11-17T22:32:24+00:00November 17th, 2018|Categories: Publications|Tags: |

The metastable 1T′ polymorph of MoS2 is an excellent catalyst toward the hydrogen evolution reaction. However, its production is limited by its lower energetic stability compared to the semiconductor 2H MoS2 phase. Stabilization of the 1T′ polymorph can be achieved through intercalation of sulfur‐based compounds without adversely affecting its catalytic properties. Abstract The metastable 1T′ polymorph of molybdenum disulfide (MoS2) has shown excellent catalytic activity toward the hydrogen evolution reaction (HER) in water‐splitting applications. Its basal plane exhibits high catalytic activity comparable to the edges in 2H MoS2 and noble metal platinum. However, the production and application of this polymorph are limited by its lower energetic stability compared to the semiconducting 2H MoS2 phase. Here, the production of stable intercalated 1T′ MoS2 nanosheets attached on graphitic nanoribbons is reported. The intercalated 1T′ MoS2 exhibits a stoichiometric S:Mo ratio of 2.3 (±0.1):1 with an expanded interlayer distance of 10 Å caused by a sulfur‐rich intercalation agent and is stable at room temperature for several months even after drying. The composition, structure, and catalytic activity toward HER are investigated both experimentally and theoretically. It is concluded that the 1T′ MoS2 phase is stabilized by the intercalated agents, which further improves the basal planes′ catalytic activity toward HER.

Published in: "Advanced Functional Materials".

Dipole Formation at the MoO3/Conjugated Polymer Interface

2018-11-17T22:32:20+00:00November 17th, 2018|Categories: Publications|Tags: |

MoO3 forms a strong dipole at the interface to P3HT/PC61BM. The dipole increases with increasing thickness of the MoO3 layer and saturates at 2.2 eV at a thickness around 3 nm of MoO3. The formation of the strong dipole is of high importance for the charge transport over the MoO3/polymer interface. Abstract MoO3 is known as high work function (WF) transparent metal oxides. It is used as anode buffer layer in organic based solar cells because of its capability to extract electrons and inject holes from the active layer due to its high WF. Here a broad range of techniques is used to determine the energy levels of the bulk heterojunction (BHJ) and MoO3 to determine that the minimum deposition thickness to achieve a closed layer is 1 nm due to penetration of the evaporated MoO3 into the BHJ. The investigation shows that upon evaporation of the MoO3, a strong dipole is formed at the extended interface between the active layer and the MoO3 and that the strength of the dipole increases with increasing thickness of the MoO3 layer and saturates at 2.2 eV at a thickness around 3 nm.

Published in: "Advanced Functional Materials".

Ultralight Conductive and Elastic Aerogel for Skeletal Muscle Atrophy Regeneration

2018-11-17T22:32:16+00:00November 17th, 2018|Categories: Publications|

Methacrylic anhydride–tannic acid (TA–MA), dopamine (DOPA), graphite oxide, and hydrothermal reduction are employed to produce an ultralight conductive and elastic aerogel in multistep base reduction. This aerogel can provide a favorable microenvironment for myogenic differentiation, and its transplantation‐combined electrical stimulation (ES) is proved to be a safe and effective strategy for retarding the disuse muscle atrophy. Abstract Cell‐free materials that can transmit both mechanical and electrical stimulations provide a promising strategy for myoinjury repair. Skeletal muscle is sensitive to electrical stimulation (ES), and accordingly, materials are required to transmit the electrical signal while maintaining their elasticity to build the cellular communication network in denervated muscle for retarding muscle atrophy. Here, tannic acid functionalized with methacrylate group (TA–MA), dopamine, and hydrothermal reduction are employed in multistep base reduction to fabricate a polydopamine (PDA)/reduced graphite oxide (rGO) aerogel. This mussel‐inspired PDA/rGO aerogel possesses good conductivity, electromechanical stability, and appropriate Young’s modulus, which are favorable for the growth and differentiation of C2C12 myoblasts. After the cell‐free PDA/rGO aerogel‐transplanted denervated muscle is loaded with cyclic ES for 3 weeks, the mean muscle fiber size increases by 90% and the maximum contraction force of denervated muscle elevates by 50%, accompanied with a slight inflammation infiltration in muscle. In conclusion, PDA/rGO aerogel is a safe and effective implant for retarding the disuse muscle atrophy.

Published in: "Advanced Functional Materials".

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