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Self‐Powered Chemical Sensing Driven by Graphene‐Based Photovoltaic Heterojunctions with Chemically Tunable Built‐In Potentials

2018-12-16T00:33:48+00:00December 15th, 2018|Categories: Publications|Tags: , |

Graphene (Gr)‐based photovoltaic heterojunctions capable of self‐powered chemical sensing are presented. Owing to the chemically tunable electrochemical potential of Gr, the built‐in electric field at the junction is effectively modulated by absorbed gas molecules, enabling photovoltaic‐driven sensing without electric power consumption. An innovative strategy to realize extremely energy‐efficient sensors provides an important advancement for future ubiquitous sensing. Abstract Ultralow power chemical sensing is essential toward realizing the Internet of Things. However, electrically driven sensors must consume power to generate an electrical readout. Here, a different class of self‐powered chemical sensing platform based on unconventional photovoltaic heterojunctions consisting of a top graphene (Gr) layer in contact with underlying photoactive semiconductors including bulk silicon and layered transition metal dichalcogenides is proposed. Owing to the chemically tunable electrochemical potential of Gr, the built‐in potential at the junction is effectively modulated by absorbed gas molecules in a predictable manner depending on their redox characteristics. Such ability distinctive from bulk photovoltaic counterparts enables photovoltaic‐driven chemical sensing without electric power consumption. Furthermore, it is demonstrated that the hydrogen (H2) sensing properties are independent of the light intensity, but sensitive to the gas concentration down to the 1 ppm level at room temperature. These results present an innovative strategy to realize extremely energy‐efficient sensors, providing an important advancement for future ubiquitous sensing.

Published in: "Small".

Recent Advances in 3D Graphene Architectures and Their Composites for Energy Storage Applications

2018-12-16T00:33:47+00:00December 15th, 2018|Categories: Publications|Tags: , |

Here, recent advances in synthesizing 3D graphene architectures and their composites as well as their application in different energy storage devices are reviewed, including various battery systems and supercapacitors. In addition, their challenges for application at the current stage are discussed, and future development prospects are indicated. Abstract Graphene is widely applied as an electrode material in energy storage fields. However, the strong π–π interaction between graphene layers and the stacking issues lead to a great loss of electrochemically active surface area, damaging the performance of graphene electrodes. Developing 3D graphene architectures that are constructed of graphene sheet subunits is an effective strategy to solve this problem. The graphene architectures can be directly utilized as binder‐free electrodes for energy storage devices. Furthermore, they can be used as a matrix to support active materials and further improve their electrochemical performance. Here, recent advances in synthesizing 3D graphene architectures and their composites as well as their application in different energy storage devices, including various battery systems and supercapacitors are reviewed. In addition, their challenges for application at the current stage are discussed and future development prospects are indicated.

Published in: "Small".

Site‐Selective and van der Waals Epitaxial Growth of Rhenium Disulfide on Graphene

2018-12-16T00:33:45+00:00December 15th, 2018|Categories: Publications|Tags: , , , |

Vertical van der Waals heterostructure of graphene/rhenium disulfide (ReS2) is synthesized by chemical vapor deposition. The rhenium disulfide is successfully grown along the in‐plane direction on an atomically smooth and chemically inert graphene surface without developing any structural defects, resulting in the high‐quality graphene/rhenium disulfide heterostructure. In addition, the patterning of vertical heterostructure is achieved through the site‐specific growth of ReS2. Abstract The surface property of growth substrate imposes significant influence in the growth behaviors of 2D materials. Rhenium disulfide (ReS2) is a new family of 2D transition metal dichalcogenides with unique distorted 1T crystal structure and thickness‐independent direct bandgap. The role of growth substrate is more critical for ReS2 owing to its weak interlayer coupling property, which leads to preferred growth along the out‐of‐plane direction while suppressing the uniform in‐plane growth. Herein, graphene is introduced as the growth substrate for ReS2 and the synthesis of graphene/ReS2 vertical heterostructure is demonstrated via chemical vapor deposition. Compared with the rough surface of SiO2/Si substrate with dangling bonds which hinders the uniform growth of ReS2, the inert and smooth surface nature of graphene sheet provides a lower energy barrier for migration of the adatoms, thereby promoting the growth of ReS2 on the graphene surface along the in‐plane direction. Furthermore, patterning of the graphene/ReS2 heterostructure is achieved by the selective growth of ReS2, which is attributed to the strong binding energy between sulfur atoms and graphene surface. The fundamental studies in the role of graphene as the growth template in the formation of

Published in: "Small".

3D Gold‐Modified Cerium and Cobalt Oxide Catalyst on a Graphene Aerogel for Highly Efficient Catalytic Formaldehyde Oxidation

2018-12-16T00:33:41+00:00December 15th, 2018|Categories: Publications|Tags: , |

Au‐Ce xCo y catalyst and graphene oxide are well formed to aerogel through a diamine cross‐linker for formaldehyde catalytic oxidation. The porous structure of graphene aerogels provides pathways to allow the access of reactants to the catalyst particles. The interaction between CeO2 and Co3O4 supports effectively promotes the migration of oxygen species and activation of gold catalysts. Abstract A hard template method is used to prepare porous gold‐doped cerium and cobalt oxide (Au‐Ce xCo y) materials. A series of 3D Au‐Ce xCo y/graphene aerogel (GA) composites is then fabricated by a facile heating method. The obtained catalysts possess a well‐defined structure of ordered arrays of nanotubes and good performance in formaldehyde (HCHO) oxidation. The composition and surface elemental valence states of the catalysts are modulated by the Ce/Co molar ratio. The Au‐Ce xCo y catalyst and graphene oxide sheets are well compounded within 60 s through a diamine cross‐linker to form 3D Au‐Ce xCo y/GA composites. In addition, the resulting catalyst of 3 wt% Au‐Ce3Co/GA achieves ≈55% conversion at room temperature and 100% conversion when the reaction temperature is raised at 60 °C. The synergistic effect between CeO2 and Co3O4 promotes the migration of oxygen species and the activation of Au, which facilitates HCHO oxidation. The method used to prepare the 3D catalyst could be used to produce other catalytic materials with good replication of the template. In addition, these findings provide a simple method for rapid fabrication of catalyst/GA composites. The superior activity and stability of the 3D Au‐Ce3Co/GA

Published in: "Small".

High‐Performance Photoinduced Memory with Ultrafast Charge Transfer Based on MoS2/SWCNTs Network Van Der Waals Heterostructure

2018-12-16T00:33:38+00:00December 15th, 2018|Categories: Publications|Tags: , |

A high‐speed photoinduced memory device is achieved based on the MoS2/single‐walled carbon nanotube network mixed‐dimensional van der Waals heterostructure. It demonstrates the multibit storage capacity, and meets all needs of an ideal photoinduced memory simultaneously—a record fast program/erase operation of 32/0.4 ms, a high program/erase ratio (106), appropriate storage time (103 s), and simple program/erase operation at room temperature. Abstract Photoinduced memory devices with fast program/erase operations are crucial for modern communication technology, especially for high‐throughput data storage and transfer. Although some photoinduced memories based on 2D materials have already demonstrated desirable performance, the program/erase speed is still limited to hundreds of micro‐seconds. A high‐speed photoinduced memory based on MoS2/single‐walled carbon nanotubes (SWCNTs) network mixed‐dimensional van der Waals heterostructure is demonstrated here. An intrinsic ultrafast charge transfer occurs at the heterostructure interface between MoS2 and SWCNTs (below 50 fs), therefore enabling a record program/erase speed of ≈32/0.4 ms, which is faster than that of the previous reports. Furthermore, benefiting from the unique device structure and material properties, while achieving high‐speed program/erase operation, the device can simultaneously obtain high program/erase ratio (≈106), appropriate storage time (≈103 s), record‐breaking detectivity (≈1016 Jones) and multibit storage capacity with a simple program/erase operation. It even has a potential application as a flexible optoelectronic device. Therefore, the designed concept here opens an avenue for high‐throughput fast data communications.

Published in: "Small".

Molecule‐Driven Nanoenergy Generator

2018-12-16T00:33:33+00:00December 15th, 2018|Categories: Publications|Tags: , |

A nanoenergy generator that comprises half‐sealed single‐crystalline ZnO nanowires (NWs) can generate electricity from various organic molecules including gaseous species from human breath. The magnitude of the voltage generated by ZnO NWs is about one‐order of magnitude larger than the typical streaming or piezoelectric potentials, and is powerful enough to directly drive a single carbon nanotube field‐effect transistor. Abstract A large potential can be generated when one end of 1D and/or 2D semiconducting nanostructures such as zinc oxide (ZnO) and molybdenum disulfide is exposed to a wide spectrum of chemical molecules. A nanoenergy generator that comprises vertically aligned ZnO nanowires and poly(vinyl chloride‐co‐vinyl‐co‐2‐hydroxypropyl acrylate) is fabricated, and it can generate electricity from various molecules including gaseous species exhaled from human breath. The generated voltage, which depends sensitively on the molecular dipole moment of adsorbed chemical species and surface coverage, is significantly larger than the streaming or piezoelectric potentials and is powerful enough to directly drive a single carbon nanotube field‐effect transistor. It is demonstrated that the notion of voltage generation through molecule‐surface interactions bears general implications to other semiconducting materials, and has the advantages of simplicity, cost‐effectiveness, fast response to a wide range of molecules, and high power output, making our approach a promising tool for energy conversion and sensing applications.

Published in: "Small".

Synthesis of P‐Doped and NiCo‐Hybridized Graphene‐Based Fibers for Flexible Asymmetrical Solid‐State Micro‐Energy Storage Device

2018-12-16T00:33:25+00:00December 15th, 2018|Categories: Publications|Tags: , , |

An all‐solid‐state P‐doped graphene oxide/carbon fiber (PGO/CF)//NiCo2O4‐based graphene oxide/carbon fiber (NCGO/CF) flexible asymmetric fiber supercapacitor (AFSC) with favorable flexibility and electrochemical properties is successfully assembled based on the PGO/CF and NCGO/CF electrodes. Interestingly, the introduction of the double reference electrode system provides a promising method for the study of the electrochemical performances of two‐electrode systems. Abstract Fiber supercapacitors (FSCs) are promising energy storage devices in portable and wearable smart electronics. Currently, a major challenge for FSCs is simultaneously achieving high volumetric energy and power densities. Herein, the microscale fiber electrode is designed by using carbon fibers as substrates and capillary channels as microreactors to space‐confined hydrothermal assembling. As P‐doped graphene oxide/carbon fiber (PGO/CF) and NiCo2O4‐based graphene oxide/carbon fiber (NCGO/CF) electrodes are successfully prepared, their unique hybrid structures exhibit a satisfactory electrochemical performance. An all‐solid‐state PGO/CF//NCGO/CF flexible asymmetric fiber supercapacitor (AFSC) based on the PGO/CF as the negative electrode, NCGO/CF hybrid electrode as the positive electrode, and poly(vinyl alcohol)/potassium hydroxide as the electrolyte is successfully assembled. The AFSC device delivers a higher volumetric energy density of 36.77 mW h cm−3 at a power density of 142.5 mW cm−3. In addition, a double reference electrode system is adopted to analyze and reduce the IR drop, as well as effectively matching negative and positive electrodes, which is conducive for the optimization and improvement of energy density. For the AFSC device, its better flexibility and electrochemical properties create a promising potential for high‐performance micro‐supercapacitors. Furthermore, the introduction of the double reference electrode system provides

Published in: "Small".

Superior Compatibility of C2N with Human Red Blood Cell Membranes and the Underlying Mechanism

2018-12-16T00:33:20+00:00December 15th, 2018|Categories: Publications|Tags: , , |

A combined experimental and theoretical study reveals that C2N exerts a negligible hemolysis effect on the blood cells with a superior biocompatibility. This arises from the unique electrostatic potential of the nanosheets, which enables it to exhibit neither phospholipid extraction nor a penetration effect on lipid membranes. Abstract The widespread use of nanomaterials, such as carbon based 2D nanomaterials, in biomedical applications, has been accompanied by a growing concern on their biocompatibility, and in particular, on how they may affect the integrity of cell membranes. Herein, the interactions between C2N, a novel 2D nanomaterial, and human red blood cell membranes are explored using a combined experimental and theoretical approach. The experimental microscopies show that C2N exerts a negligible hemolysis effect on the blood cells with a superior compatibility to their cell membranes, when compared with the control system, reduced graphene oxide (rGO), which is found to be highly hemolytic. The molecular dynamics simulations further reveal the underlying molecular mechanisms, which indicate that C2N prefers to be adsorbed flat on the water–membrane interface. Interaction energy analyses demonstrate the crucial role of Coulombic contributions, originating from the unique electrostatic potential surface of C2N, in preventing C2N from penetrating into cell membranes. These findings indicate a high compatibility of C2N with cell membranes, which may provide useful foundation for the future exploration of this 2D nanomaterial in related biomedical applications.

Published in: "Small".

2D MoS2‐Based Nanomaterials for Therapeutic, Bioimaging, and Biosensing Applications

2018-12-16T00:33:18+00:00December 15th, 2018|Categories: Publications|Tags: |

2D MoS2‐based nanomaterials have emerged as a new class of material for biomedical applications. This review article discusses the growth of MoS2 as a nanomaterial in the field of biomedicine by highlighting its diverse applications in drug/gene delivery, phototherapy, imaging, sensing, and theranostics, which demonstrates the potential of this 2D material to evolve as a new class of nanomedicine. Abstract Molybdenum disulfide (MoS2), a typical layered 2D transition metal dichalcogenide, has received colossal interest in the past few years due to its unique structural, physicochemical, optical, and biological properties. While MoS2 is mostly applied in traditional industries such as dry lubricants, intercalation agents, and negative electrode material in lithium‐ion batteries, its 2D and 0D forms have led to diverse applications in sensing, catalysis, therapy, and imaging. Herein, a systematic overview of the progress that is made in the field of MoS2 research with an emphasis on its different biomedical applications is presented. This article provides a general discussion on the basic structure and property of MoS2 and gives a detailed description of its different morphologies that are synthesized so far, namely, nanosheets, nanotubes, and quantum dots along with synthesis strategies. The biomedical applications of MoS2‐based nanocomposites are also described in detail and categorically, such as in varied therapeutic and diagnostic modalities like drug delivery, gene delivery, phototherapy, combined therapy, bioimaging, theranostics, and biosensing. Finally, a brief commentary on the current challenges and limitations being faced is provided, along with a discussion of some future perspectives for the overall improvement of

Published in: "Small".

MoS2/NiS Yolk–Shell Microsphere‐Based Electrodes for Overall Water Splitting and Asymmetric Supercapacitor

2018-12-16T00:33:16+00:00December 15th, 2018|Categories: Publications|Tags: , |

MoS2/NiS yolk–shell microspheres exhibit prominent electrochemical performance for both overall water splitting and asymmetric supercapacitors, which can be attributed to the advanced structural features of the interface effect and hollow structure. Abstract Rational designing of the composition and structure of electrode material is of great significance for achieving highly efficient energy storage and conversion in electrochemical energy devices. Herein, MoS2/NiS yolk–shell microspheres are successfully synthesized via a facile ionic liquid‐assisted one‐step hydrothermal method. With the favorable interface effect and hollow structure, the electrodes assembled with MoS2/NiS hybrid microspheres present remarkably enhanced electrochemical performance for both overall water splitting and asymmetric supercapacitors. In particular, to deliver a current density of 10 mA cm−2, the MoS2/NiS‐based electrolysis cell for overall water splitting only needs an output voltage of 1.64 V in the alkaline medium, lower than that of Pt/C–IrO2‐based electrolysis cells (1.70 V). As an electrode for supercapacitors, the MoS2/NiS hybrid microspheres exhibit a specific capacitance of 1493 F g−1 at current density of 0.2 A g−1, and remain 1165 F g−1 even at a large current density of 2 A g−1, implying outstanding charge storage capacity and excellent rate performance. The MoS2/NiS‐ and active carbon‐based asymmetric supercapacitor manifests a maximum energy density of 31 Wh kg−1 at a power density of 155.7 W kg−1, and remarkable cycling stability with a capacitance retention of approximately 100% after 10 000 cycles.

Published in: "Small".

Bioinspired Photonic Barcodes with Graphene Oxide Encapsulation for Multiplexed MicroRNA Quantification

2018-12-16T00:33:13+00:00December 15th, 2018|Categories: Publications|Tags: , |

A novel mussel‐inspired photonic crystal (PhC) barcode with graphene oxide (GO) encapsulation are presented for the multiplex miRNAs detection. The GO‐based hybridization chain reaction (HCR) strategy can realize low abundance and high sensitivity miRNA quantification. At the same time, multiplex detection can be achieved by employing different GO‐decorated PhC barcodes with high accuracy and reproducibility. Abstract Multiplexed microRNA (miRNA) quantification has a demonstrated value in clinical diagnosis. In this paper, novel mussel‐inspired photonic crystal (PhC) barcodes with graphene oxide (GO) encapsulation for multiplexed miRNA detection are presented. Using the excellent adhesion capability of polydopamine, the dispersed GO particles can be immobilized on the surfaces of the PhC barcodes to form an additional functional layer. The GO‐decorated PhC barcodes have constant characteristic reflection peaks because the GO immobilization process not only maintains their periodic microstructure but also enhances their stability and anti‐incoherent light‐scattering capability. The immobilized GO particles are shown to enable high‐sensitivity miRNA screening on the surface of the PhC barcodes by integration with a hybridization chain reaction amplification strategy. Because the PhC barcodes have stable encoding reflection peaks, multiplexed low‐abundance miRNA quantification can also be achieved rapidly, accurately, and reproducibly by employing different GO‐decorated PhC barcodes. These features should make GO‐encapsulated PhC barcodes ideal for many practical applications.

Published in: "Small".

A Salt‐Templated Strategy toward Hollow Iron Selenides‐Graphitic Carbon Composite Microspheres with Interconnected Multicavities as High‐Performance Anode Materials for Sodium‐Ion Batteries

2018-12-16T00:33:12+00:00December 15th, 2018|Categories: Publications|Tags: |

Hollow FeSe2/graphitic carbon composite microspheres with interconnected multicavities are introduced as anodes for high‐performance sodium‐ion batteries. The synergistic effect between the hollow cavities within FeSe2 and the porous carbon matrix is responsible for superior performances of the composite microspheres for sodium‐ion batteries. Abstract In this work, a facile salt‐templated approach is developed for the preparation of hollow FeSe2/graphitic carbon composite microspheres as sodium‐ion battery anodes; these are composed of interconnected multicavities and an enclosed surface in‐plane embedded with uniform hollow FeSe2 nanoparticles. As the precursor, Fe2O3/carbon microspheres containing NaCl nanocrystals are obtained using one‐pot ultrasonic spray pyrolysis in which inexpensive NaCl and dextrin are used as a porogen and carbon source, respectively, enabling mass production of the composites. During post‐treatment, Fe2O3 nanoparticles in the composites transform into hollow FeSe2 nanospheres via the Kirkendall effect. These rational structures provide numerous conductive channels to facilitate ion/electron transport and enhance the capacitive contribution. Moreover, the synergistic effect between the hollow cavities within FeSe2 and the outstanding mechanical strength of the porous carbon matrix can effectively accommodate the large volume changes during cycling. Correspondingly, the composite microsphere exhibits high discharge capacity of 510 mA h g−1 after 200 cycles at 0.2 A g−1 with capacity retention of 88% when calculated from the second cycle. Even at a high current density of 5.0 A g−1, a high discharge capacity of 417 mA h g−1 can be achieved.

Published in: "Small".

Micro‐Nano Fabrication: Fabrication of Sub‐Micrometer‐Sized MoS2 Thin‐Film Transistor by Phase Mode AFM Lithography (Small 49/2018)

2018-12-16T00:33:09+00:00December 15th, 2018|Categories: Publications|Tags: |

In article number 1803273, Lianqing Liu and co‐workers propose a unique mask‐free and marker‐free lithography technique to fabricate a sub‐micrometer‐sized 2D material thin‐film transistor using the phase mode of atomic force microscopy. This method does not change the chemical, physical, and electrical properties of 2D materials. It offers a flexible, easy, effective, and low‐cost way to fabricate prototypes of sub‐micrometer‐sized devices, and provides the opportunity to explore the potential performance of 2D materials.

Published in: "Small".

Tension‐Induced Raman Enhancement of Graphene Membranes in the Stretched State

2018-12-16T00:33:07+00:00December 15th, 2018|Categories: Publications|Tags: |

An interesting tension‐induced Raman enhancement phenomenon, where the intensity ratios I 2D/I G are significantly enhanced up to 16.74 and increased by more than 670%, is observed in substrate‐supported graphene membranes near the wells. The microscopic mechanism of this phenomenon is the depression effect of built‐in stresses on the intensity of the G band. Abstract The intensity ratio of the 2D band to the G band, I 2D/I G, is a good criterion in selecting high quality monolayer graphene samples; however, the evaluation of the ultimate value of I 2D/I G for intrinsic monolayer graphene is a challenging yet interesting issue. Here, an interesting tension‐induced Raman enhancement phenomenon is reported in supported graphene membranes, which show a transition from the corrugated state to the stretched state in the vicinity of wells. The I 2D/I G of substrate‐supported graphene membranes near wells are significantly enhanced up to 16.74, which is the highest experimental value to the best of knowledge, increasing by more than 600% when the testing points approach the well edges.The macroscopic origin of this phenomenon is that corrugated graphene membranes are stretched by built‐in tensions. A lattice dynamic model is proposed to successfully reveal the microscopic mechanism of this phenomenon. The theoretical results agree well with the experimental data, demonstrating that tensile stresses can depress the amplitude of in‐plane vibration of sp2‐bonded carbon atoms and result in the decrease in the G band intensity. This work can be helpful in furthering the development of the method of suppressing small

Published in: "Small".

Facile Fabrication of Large‐Area Atomically Thin Membranes by Direct Synthesis of Graphene with Nanoscale Porosity

2018-12-15T22:34:17+00:00December 15th, 2018|Categories: Publications|Tags: |

Facile fabrication of large‐area atomically thin membranes by bottom‐up synthesis of nanoporous monolayer graphene is reported. A simple reduction in graphene growth temperature enables facile synthesis of nanoporous graphene. By solution‐casting a hierarchically porous support on the as‐grown nanoporous graphene, large‐area (>5 cm2) nanoporous atomically thin membranes for dialysis applications are demonstrated. Abstract Direct synthesis of graphene with well‐defined nanoscale pores over large areas can transform the fabrication of nanoporous atomically thin membranes (NATMs) and greatly enhance their potential for practical applications. However, scalable bottom‐up synthesis of continuous sheets of nanoporous graphene that maintain integrity over large areas has not been demonstrated. Here, it is shown that a simple reduction in temperature during chemical vapor deposition (CVD) on Cu induces in‐situ formation of nanoscale defects (≤2–3 nm) in the graphene lattice, enabling direct and scalable synthesis of nanoporous monolayer graphene. By solution‐casting of hierarchically porous polyether sulfone supports on the as‐grown nanoporous CVD graphene, large‐area (>5 cm2) NATMs for dialysis applications are demonstrated. The synthesized NATMs show size‐selective diffusive transport and effective separation of small molecules and salts from a model protein, with ≈2–100× increase in permeance along with selectivity better than or comparable to state‐of‐the‐art commercially available polymeric dialysis membranes. The membranes constitute the largest fully functional NATMs fabricated via bottom‐up nanopore formation, and can be easily scaled up to larger sizes permitted by CVD synthesis. The results highlight synergistic benefits in blending traditional membrane casting with bottom‐up pore creation during graphene CVD for advancing NATMs toward practical applications.

Published in: "Advanced Materials".

Room‐Temperature Ultrabroadband Photodetection with MoS2 by Electronic‐Structure Engineering Strategy

2018-12-15T22:34:14+00:00December 15th, 2018|Categories: Publications|Tags: , |

Based on a proposed novel electronicstructure strategy, layered MoS2 is designed, which realizes ultrabroadband photodetection at room temperature. By introducing defect energy levels, the bandgap and electronic state density are modulated suitably. The prototype photodetector is investigated from 445 nm (blue) to 9536 nm (far‐IR) and offers a record high photoresponsivity of 21.8 mA W−1 (7.79 µm). Abstract Photodetection using semiconductors is critical for capture, identification, and processing of optical information. Nowadays, broadband photodetection is limited by the underdeveloped mid‐IR photodetection at room temperature (RT), primarily as a result of the large dark currents unavoidably generated by the Fermi–Dirac distribution in narrow‐bandgap semiconductors, which constrains the development of some modern technologies and systems. Here, an electronic‐structure strategy is proposed for designing ultrabroadband covering mid‐ and even far‐IR photodetection materials operating at RT and a layered MoS2 is manifested with an engineered bandgap of 0.13 eV and modulated electronic state density. The sample is designed by introducing defect energy levels into layered MoS2 and its RT photodetection is demonstrated for wavelengths from 445 nm to 9.5 µm with an electronic state density‐dependent peak photoresponsivity of 21.8 mA W−1 in the mid‐IR region, the highest value among all known photodetectors. This material should be a promising candidate for modern optoelectronic devices and offers inspiration for the design of other optoelectronic materials.

Published in: "Advanced Materials".

Gas‐Permeable, Multifunctional On‐Skin Electronics Based on Laser‐Induced Porous Graphene and Sugar‐Templated Elastomer Sponges

2018-12-15T22:34:12+00:00December 15th, 2018|Categories: Publications|Tags: |

A simple, versatile, and effective approach for making multifunctional, on‐skin bioelectronic sensing systems using laser‐induced porous graphene as the sensing components and sugar‐templated elastomer sponges as the substrates is reported. The porous structures of the devices can facilitate perspiration transport and evaporation, and minimize discomfort and inflammation risks, thereby improving their long‐term feasibility. Abstract Soft on‐skin electronics have broad applications in human healthcare, human–machine interface, robotics, and others. However, most current on‐skin electronic devices are made of materials with limited gas permeability, which constrain perspiration evaporation, resulting in adverse physiological and psychological effects, limiting their long‐term feasibility. In addition, the device fabrication process usually involves e‐beam or photolithography, thin‐film deposition, etching, and/or other complicated procedures, which are costly and time‐consuming, constraining their practical applications. Here, a simple, general, and effective approach for making multifunctional on‐skin electronics using porous materials with high‐gas permeability, consisting of laser‐patterned porous graphene as the sensing components and sugar‐templated silicone elastomer sponges as the substrates, is reported. The prototype device examples include electrophysiological sensors, hydration sensors, temperature sensors, and joule‐heating elements, showing signal qualities comparable to conventional, rigid, gas‐impermeable devices. Moreover, the devices exhibit high water‐vapor permeability (≈18 mg cm−2 h−1), ≈18 times higher than that of the silicone elastomers without pores, and also show high water‐wicking rates after polydopamine treatment, up to 1 cm per 30 s, which is comparable to that of cotton. The on‐skin devices with such attributes could facilitate perspiration transport and evaporation, and minimize discomfort and inflammation risks, thereby improving their long‐term

Published in: "Advanced Materials".

Probing the Physical Origin of Anisotropic Thermal Transport in Black Phosphorus Nanoribbons

2018-12-15T22:34:10+00:00December 15th, 2018|Categories: Publications|Tags: |

The anisotropic thermal transport of black phosphorus nanoribbons is studied. Direct evidence is provided that the origin of this anisotropy is dominated by the anisotropic phonon group velocity, verified by Young’s modulus measurements along different directions. These results provide fundamental insight into the anisotropic thermal transport in low‐symmetry crystals. Abstract Black phosphorus (BP) has emerged as a promising candidate for next‐generation electronics and optoelectronics among the 2D family materials due to its extraordinary electrical/optical/optoelectronic properties. Interestingly, BP shows strong anisotropic transport behavior because of its puckered honeycomb structure. Previous studies have demonstrated the thermal transport anisotropy of BP and theoretically attribute this to the anisotropy in both the phonon dispersion relation and the phonon relaxation time. However, the exact origin of such strong anisotropy lacks clarity and has yet to be proven experimentally. Here, the thermal transport anisotropy of BP nanoribbons is probed by an electron beam technique. Direct evidence is provided that the origin of this anisotropy is dominated by the anisotropic phonon group velocity, verified by Young’s modulus measurements along different directions. It turns out that the ratio of the thermal conductivity between zigzag (ZZ) and armchair (AC) ribbons is almost same as that of the corresponding Young modulus values. The results from first‐principles calculation are consistent with this experimental observation, where the anisotropic phonon group velocity between ZZ and AC is shown. These results provide fundamental insight into the anisotropic thermal transport in low‐symmetry crystals.

Published in: "Advanced Materials".

Edge‐Functionalized Graphene Nanoplatelets as Metal‐Free Electrocatalysts for Dye‐Sensitized Solar Cells

2018-12-15T22:34:07+00:00December 15th, 2018|Categories: Publications|Tags: , , |

Edge‐functionalized graphene nanoplatelets (EFGnPs), as counter electrode (CE) materials, have demonstrated an excellent performance for dye‐sensitized solar cells (DSSCs). Specific edge groups can provide electrocatalytic active sites for iodine and cobalt reduction reactions. Given the promising potential in metal‐free CEs, research directions are suggested to discover more efficient functional groups and to realize metal‐free‐carbon‐based DSSCs. Abstract A scalable and low‐cost production of graphene nanoplatelets (GnPs) is one of the most important challenges for their commercialization. A simple mechanochemical reaction has been developed and applied to prepare various edge‐functionalized GnPs (EFGnPs). EFGnPs can be produced in a simple and ecofriendly manner by ball milling of graphite with target substances (X = nonmetals, halogens, semimetals, or metalloids). The unique feature of this method is its use of kinetic energy, which can generate active carbon species by unzipping of graphitic CC bonds in dry conditions (no solvent). The active carbon species efficiently pick up X substance(s), leading to the formation of graphitic CX bonds along the broken edges and the delamination of graphitic layers into EFGnPs. Unlike graphene oxide (GO) and reduced GO (rGO), the preparation of EFGnPs does not involve toxic chemicals, such as corrosive acids and toxic reducing agents. Furthermore, the prepared EFGnPs preserve high crystallinity in the basal area due to their edge‐selective functionalization. Considering the available edge X groups that can be selectively employed, the potential applications of EFGnPs are unlimited. In this context, the synthesis, characterizations, and applications of EFGnPs, specifically, as metal‐free carbon‐based electrocatalysts for dye‐sensitized solar

Published in: "Advanced Materials".

Controllable Growth of Graphene on Liquid Surfaces

2018-12-15T22:34:04+00:00December 15th, 2018|Categories: Publications|Tags: |

Recent advancement in the controllable growth of graphene on liquid surfaces is comprehensively reviewed. Melted liquids offer a smooth surface, which enables uniformly tailoring the morphologies of graphene, and a rheological surface, which allows for self‐adjusted movement of graphene grains. The exciting progress in controlled growth behaviors of graphene on the liquid surface is presented and discussed in depth. Abstract Controllable fabrication of graphene is necessary for its practical application. Chemical vapor deposition (CVD) approaches based on solid metal substrates with morphology‐rich surfaces, such as copper (Cu) and nickel (Ni), suffer from the drawbacks of inhomogeneous nucleation and uncontrollable carbon precipitation. Liquid substrates offer a quasiatomically smooth surface, which enables the growth of uniform graphene layers. The fast surface diffusion rates also lead to unique growth and etching kinetics for achieving graphene grains with novel morphologies. The rheological surface endows the graphene grains with self‐adjusted rotation, alignment, and movement that are driven by specific interactions. The intermediary‐free transfer or the direct growth of graphene on insulated substrates is demonstrated using liquid metals. Here, the controllable growth process of graphene on a liquid surface to promote the development of attractive liquid CVD strategies is in focus. The exciting progress in controlled growth, etching, self‐assembly, and delivery of graphene on a liquid surface is presented and discussed in depth. In addition, prospects and further developments in these exciting fields of graphene growth on a liquid surface are discussed.

Published in: "Advanced Materials".

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