Stress Controllability in Thermal and Electrical Conductivity of 3D Elastic Graphene‐Crosslinked Carbon Nanotube Sponge/Polyimide Nanocomposite

2019-06-19T20:57:39+00:00June 19th, 2019|Categories: Publications|Tags: |

An elasic, flexible, and stress controllable thermal and electrical conductivity of a graphene‐crosslinked carbon nanotube (Gw‐CNT)/polyimide (PI) nanocomposite is developed. A Gw‐CNT network is constructed to provide a continuous conductive network and an elastic template for the rigid PI. The elasticity, thermal conductivity, and electrical conductivity of the resulting composites can be effectively controlled by adjusting the amount of PI. Abstract Stress controllability in thermal and electrical conductivity is important for flexible piezoresistive devices. Due to the strength‐elasticity trade‐off, comprehensive investigation of stress‐controllable conduction in elastic high‐modulus polymers is challenging. Here presented is a 3D elastic graphene‐crosslinked carbon nanotube sponge/polyimide (Gw‐CNT/PI) nanocomposite. Graphene welding at the junction enables both phonon and electron transfer as well as avoids interfacial slippage during cyclic compression. The uniform Gw‐CNT/PI comprising a high‐modulus PI deposited on a porous templated network combines stress‐controllable thermal/electrical conductivity and cyclic elastic deformation. The uniform composites show different variation trends controlled by the porosity due to different phonon and electron conduction mechanisms. A relatively high k (3.24 W m−1 K−1, 1620% higher than PI) and suitable compressibility (16.5% under 1 MPa compression) enables the application of the composite in flexible elastic thermal interface conductors, which is further analyzed by finite element simulations. The interconnected network favors a high stress‐sensitive electrical conductivity (sensitivity, 973% at 9.6% strain). Thus, the Gw‐CNT/PI composite can be an important candidate material for piezoresistive sensors upon porosity optimization based on stress‐controllable thermal or electrical conductivity. The results provide insights toward controlling the stress‐induced thermal/electrical conductivities of

Published in: "Advanced Functional Materials".

High‐Performance Flexible Thermoelectric Devices Based on All‐Inorganic Hybrid Films for Harvesting Low‐Grade Heat

2019-06-19T20:57:36+00:00June 19th, 2019|Categories: Publications|Tags: , , |

A flexible thermoelectric generator based on all‐inorganic hybrid films of n‐type RGO/Bi2Te3 and p‐type SWCNTs/Sb2Te3 is fabricated. The prototypes of a wearable wrist band and a photovoltaic–thermoelectric integrated device are proven, which can be used for harvesting waste heat and stabilizing the photovoltaic performance. Abstract The fabrication of a flexible thermoelectric (TE) device that contains flexible, all‐inorganic hybrid thin films (p‐type single‐wall carbon nanotubes (SWCNTs)/Sb2Te3 and n‐type reduced graphene oxide (RGO)/Bi2Te3) is reported. The optimized power factors of the p‐type and n‐type hybrid thin films at ambient temperature are about 55 and 108 µW m−1 K−2, respectively. The high performance of these films that are fabricated through the combination of vacuum filtration and annealing can be attributed to their planar orientation and network structure. In addition, a TE device, with 10 couples of legs, shows an output power of 23.6 µW at a temperature gradient of 70 K. A prototype of an integrated photovoltaic‐TE (PV‐TE) device demonstrates the ability to harvest low‐grade “waste” thermal energy from the human body and solar irradiation. The flexible TE and PV‐TE device have great potential in wearable energy harvesting and management.

Published in: "Advanced Functional Materials".

Composite Networks: Stress Controllability in Thermal and Electrical Conductivity of 3D Elastic Graphene‐Crosslinked Carbon Nanotube Sponge/Polyimide Nanocomposite (Adv. Funct. Mater. 25/2019)

2019-06-19T20:57:26+00:00June 19th, 2019|Categories: Publications|Tags: |

In article number 1901383, Yiyu Feng, Wei Feng, and co‐workers report a flexible/elastic graphene‐crosslinked carbon nanotube sponge/polyimide nanocomposite. The 3D continuous graphene/carbon nanotube hybrid network can facilitate phonon and electron transmission through the polymer matrix. Under the action of force (water droplets), changes in thermal conductivity and electrical conductivity are caused.

Published in: "Advanced Functional Materials".

Anisotropic Thermal Conductive Composite by the Guided Assembly of Boron Nitride Nanosheets for Flexible and Stretchable Electronics

2019-06-19T18:55:47+00:00June 19th, 2019|Categories: Publications|Tags: |

The reported anisotropic thermal conductive composite film can serve as a flexible and stretchable heat sink for high‐performance electronics. The assembled BN layer on tetrahedral structure in composite guarantees anisotropic heat dissipation and flexibility and stretchability without degradation of thermal conductivity during the deformation of devices, overcoming the otherwise unsolvable trade‐off of high thermal conductivity against mechanical stability. Abstract Owing to the growing demand for highly integrated electronics, anisotropic heat dissipation of thermal management material is a challenging and promising technique. Moreover, to satisfy the needs for advancing flexible and stretchable electronic devices, maintaining high thermal conductivity during the deformation of electronic materials is at issue. Presented here is an effective assembly technique to realize a continuous array of boron nitride (BN) nanosheets on tetrahedral structures, creating 3D thermal paths for anisotropic dissipation integrated with deformable electronics. The tetrahedral structures, with a fancy wavy shaped cross‐section, guarantee flexibility and stretchability, without the degradation of thermal conductivity during the deformation of the composite film. The structured BN layer in the composites induces a high thermal conductivity of 1.15 W m−1 K−1 in the through‐plane and 11.05 W m−1 K−1 in the in‐plane direction at the low BN fraction of 16 wt%, which represent 145% and 83% increases over the randomly mixing method, respectively. Furthermore, this structured BN composite maintains thermal dissipation property with 50% strain of the original length of composite. Various electronic device demonstrations provide exceptional heat dissipation capabilities, including thin film silicon transistor and light‐emitting diode on flexible and

Published in: "Advanced Functional Materials".

Rapid and Sensitive Voltammetric Detection of Rhodamine B in Chili-Containing Foodstuffs Using MnO2 Nanorods/Electro-Reduced Graphene Oxide Composite

2019-06-19T18:45:37+00:00June 19th, 2019|Categories: Publications|Tags: , |

A facile voltammetric sensor based on MnO2 nanorods/electro-reduced graphene oxide composite modified glassy carbon electrode (MnO2NRs-ERGO/GCE) was proposed for the detection of Rhodamine B (RhB). The MnO2NRs-ERGO/GCE was fabricated by a facile drop-casting approach followed by a potentiostatic reduction technique. A well-shaped oxidation peak of RhB was observed at the MnO2NRs-ERGO/GCE, and the response peak current was 17-fold and 2-fold higher than that of bare GCE and ERGO/GCE respectively, attributing to the synergistic electrocatalytic effect from ERGO sheets and MnO2NRs. Under the optimal analytical conditions, the response peak currents linearly increased with the RhB concentrations varying from 0.02 μM to 1.0 μM and from 1.0 μM to 20 μM. The limit of detection (LOD, S/N = 3) was 6.0 nM. Furthermore, the MnO2NRs-ERGO/GCE showed good selectivity, repeatability, reproducibility and stability. Finally, the MnO2NRs-ERGO/GCE was successfully employed to detect RhB in different commercial chili-containing foodstuffs, and the results were in good accordance with the values that detected by high-performance liquid chromatography. Combining with low cost and portable electrochemical apparatus, the proposed sensor is especially suitable for the in-situ detection of RhB in actual food samples.

Published in: "Journal of the Electrochemical Society".

Enhanced intrinsic photovoltaic effect in tungsten disulfide nanotubes

2019-06-19T17:47:28+00:00June 19th, 2019|Categories: Publications|Tags: |

Nature, Published online: 19 June 2019; doi:10.1038/s41586-019-1303-3A bulk photovoltaic effect is observed in devices based on tungsten disulfide, and is enhanced if the devices take the form of polar nanotubes, showing the importance of reducing crystal symmetry to a polar structure in achieving higher efficiencies.

Published in: "Nature".

Quantum Interference Theory of Magnetoresistance in Dirac Materials

2019-06-19T15:33:01+00:00June 19th, 2019|Categories: Publications|

Author(s): Bo Fu, Huan-Wen Wang, and Shun-Qing ShenMagnetoresistance in many samples of Dirac semimetals and topological insulators displays nonmonotonic behavior over a wide range of magnetic fields. Here a formula of magnetoconductivity is presented for massless and massive Dirac fermions in Dirac materials due to quantum interference of Dirac fer…[Phys. Rev. Lett. 122, 246601] Published Wed Jun 19, 2019

Published in: "Physical Review Letters".

Effect of resonant impurity scattering of carriers on the Drude-peak broadening in uniaxially strained graphene

2019-06-19T15:32:18+00:00June 19th, 2019|Categories: Publications|Tags: |

Author(s): V. O. Shubnyi, Y. V. Skrypnyk, S. G. Sharapov, and V. M. LoktevAn explanation is proposed for the recently observed in optical spectra of monolayer graphene giant increase in the Drude-peak width under applied uniaxial strain. We argue that the underlying mechanism of this increase can be based on resonant scattering of carriers from inevitably present impuriti…[Phys. Rev. B 99, 235421] Published Wed Jun 19, 2019

Published in: "Physical Review B".

Superior Hydrogen Evolution Reaction Performance in 2H‐MoS2 to that of 1T Phase

2019-06-19T08:48:52+00:00June 19th, 2019|Categories: Publications|Tags: , |

The significant influence of the Fermi level on the thermodynamic limitation of electrocatalysis performance is demonstrated. In particular, with the Fermi level position approaching the conduction band, the 2H‐MoS2 can achieve a better hydrogen evolution reaction activity (74 mV at 10 mA cm−2 in 0.5 mol L−1 H2SO4) than 1T‐MoS2. Abstract In the hydrogen evolution reaction (HER), energy‐level matching is a prerequisite for excellent electrocatalytic activity. Conventional strategies such as chemical doping and the incorporation of defects underscore the complicated process of controlling the doping species and the defect concentration, which obstructs the understanding of the function of band structure in HER catalysis. Accordingly, 2H‐MoS2 and 1T‐MoS2 are used to create electrocatalytic nanodevices to address the function of band structure in HER catalysis. Interestingly, it is found that the 2H‐MoS2 with modulated Fermi level under the application of a vertical electric field exhibits excellent electrocatalytic activity (as evidenced by an overpotential of 74 mV at 10 mA cm−2 and a Tafel slope of 99 mV per decade), which is superior to 1T‐MoS2. This unexpected excellent HER performance is ascribed to the fact that electrons are injected into the conduction band under the condition of back‐gate voltage, which leads to the increased Fermi level of 2H‐MoS2 and a shorter Debye screen length. Hence, the required energy to drive electrons from the electrocatalyst surface to reactant will decrease, which activates the 2H‐MoS2 thermodynamically.

Published in: "Small".

A Facile and Effective Method for Patching Sulfur Vacancies of WS2 via Nitrogen Plasma Treatment

2019-06-19T08:48:49+00:00June 19th, 2019|Categories: Publications|Tags: |

There are formidable challenges to essentially improve carrier scattering during the transmission of devices and distinct contact barrier between metal and semiconductors, which are caused by inevitable vacancies in transition metal dichalcogenides. To address these issues, a facile and effective defect patching approach is developed via nitrogen plasma doping, and the effective vacancies patching events are confirmed by a high‐resolution spherical aberration correction transmission electron microscopy. Abstract Although transition metal dichalcogenides (TMDs) are attractive for the next‐generation nanoelectronic era due to their unique optoelectronic and electronic properties, carrier scattering during the transmission of electronic devices, and the distinct contact barrier between the metal and the semiconductors, which is caused by inevitable defects in TMDs, remain formidable challenges. To address these issues, a facile, effective, and universal patching defect approach that uses a nitrogen plasma doping protocol is developed, via which the intrinsic vacancies are repaired effectively. To reveal sulfur vacancies and the nature of the nitrogen doping effects, a high‐resolution spherical aberration corrected scanning transmission electron microscopy is used, which confirms the N atoms doping in sulfur vacancies. In this study, a typical TMD material, namely tungsten disulfide, is employed to fabricate field‐effect transistors (FETs) as a preliminary paradigm to demonstrate the patching defects method. This doping method endows FETs with high electrical performance and excellent contact interface properties. As a result, an electron mobility of up to 184.2 cm2 V−1 s−1 and a threshold voltage of as low as 3.8 V are realized. This study provides a valuable approach

Published in: "Small".

Fully Integrated Microscale Quasi‐2D Crystalline Molecular Field‐Effect Transistors

2019-06-19T08:43:08+00:00June 19th, 2019|Categories: Publications|

Monolithic integration of microscale organic field‐effect transistors (micro‐OFETs) could determine future low‐cost integrated circuits and large‐area displays. In this work, by mastering the local growth of molecular semiconductors on pre‐defined terraces and developing nondestructive photolithographic processes, micro‐OFETs based on single‐crystal quasi‐2D molecular layers tens of square micrometers in size are created, delivering high mobilities up to 34.6 cm2 V−1 s−1. Abstract Monolithic integration of microscale organic field‐effect transistors (micro‐OFETs) is the only and inevitable path toward low‐cost large‐area electronics and displays. However, to date, such an ultimate technology has not yet evolved due to challenges in positioning and patterning highly crystalline microscale molecular layers as well as in developing micrometer scale integration schemes. In this work, by mastering the local growth of molecular semiconductors on pre‐defined terraces, single‐crystal quasi‐2D molecular layers tens of square micrometers in size are created in dense periodic arrays on a Si substrate. Nondestructive photolithographic processes are developed to pattern micro‐OFETs with mobilities up to 34.6 cm2 V−1 s−1. This work demonstrates the feasibility to integrate arrays of short‐channel micro‐OFETs into electronic circuitry by highly parallel and size scalable fabrication technologies.

Published in: "Advanced Functional Materials".

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