Role of graphene in improving catalytic behaviors of AuNPs/MoS2/Gr/Ni-F structure in hydrogen evolution reaction

The efficient production of hydrogen through electrocatalytic decomposition of water has broad prospects in modern energy equipment. However, the catalytic efficiency and durability of hydrogen evolution catalyst are still very deficient, which need to be further explored. Here in this work, we prove that introducing a graphene layer (Gr) between the molybdenum disulfide and nickel foam (Ni-F) substrate can greatly improve the catalytic performance of the hybrid. Owing to the excitation of local surface plasmon resonance (LSPR) of gold nanoparticles (NPs), the electrocatalytic hydrogen releasing activity of the MoS₂/Gr/Ni-F heterostructure is greatly improved. This results in a significant increase in the current density of AuNPs/MoS₂/Gr/Ni-F composite material under light irradiation and in the dark at 0.2 V (versus reversible hydrogen electrode (RHE)), which is much better than in MoS₂/Gr/Ni-F composite materials. The enhancement of hydrogen release can be attributed to the injection of hot electrons into MoS₂/Gr/Ni-F by AuNPs, which will improve the electron density of MoS₂/Gr/Ni-F, promote the reduction of H₂O, and further reduce the activation energy of the electrocatalyst hydrogen evolution reaction (HER). We also prove that the introduction of graphene can improve its stability in acidic catalytic environments. This work provides a new way of designing efficient water splitting system.     

In situ,facile synthesis of La<Subscript>0.8</Subscript>Sr<Subscript>0.2</Subscript>MnO<Subscript>3</Subscript>/nitrogen-doped graphene: a high-performance catalyst for rechargeable Li-O<Subscript>2</Subscript> batteries

We have successfully devised a simple method to synthesize La_0.8Sr_0.2MnO₃ with nitrogen-doped graphene composites (LSM/NrGO) and investigated their catalytic performance in the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Interestingly, the LSM/NrGO composites demonstrate outstanding catalytic performance in ORR, including high limiting current density and superior onset potential, compared to bare LSM nanocrystals or nitrogen-doped graphene, showing a performance close to that of commercial Pt/C. Moreover, Li-O₂ batteries assembled based on the LSM/NrGO catalysts exhibited brilliant performance, especially during long-term cycling, where the terminal discharge voltage still exceeded 2.31 V after 360 cycles. The excellent catalytic performance is mainly attributed to the large specific surface area (152.24 m² g^?1) of the materials, which provides many catalytic active sites, and the mesoporous structure (2 to 50 nm), which can facilitate the penetration of oxygen molecules into the surface of the nanoparticles and mass transfer.     

Edge effect and interface confinement modulated strain distribution and interface adhesion energy in graphene/Si system

In order to clarify the edge and interface effect on the adhesion energy between graphene(Gr)and its substrate,a theoretical model is proposed to study the interaction and strain distribution of Gr/Si system in terms of continuum medium mechanics and nanothermodynamics.We find that the interface separation and adhesion energy are determined by the thickness of Gr and substrate.The disturbed interaction and redistributed strain in the Gr/Si system induced by the effect of surface and interface can make the interface adhesion energy decrease with increasing thickness of Gr and diminishing thickness of Si.Moreover,our results show that the smaller area of Gr is more likely to adhere to the substrate since the edge effect improves the active energy and strain energy.Our predictions can be expected to be a guide for designing high performance of Grbased electronic devices.     

类石墨烯复杂晶胞光子晶体中的确定性界面态

拓扑绝缘体是当前凝聚态物理领域研究的热点问题.利用石墨烯材料的特殊能带特性来实现拓扑输运特性在设计下一代电子和能谷电子器件方面具有较广泛的应用前景.基于光子与电子的类比,利用光子拓扑材料实现了确定性界面态;构建了具有C_(6v)。对称性的类似石墨烯结构的的光子晶体复杂晶格;通过多种方式降低晶格对称性来获得具有C_(3v),C_3,C_(2v)和C_2对称的晶体,从而打破能谷简并实现全光子带隙结构;将体拓扑性质不同的两种光子晶体摆放在一起,在此具有反转体能带性质的界面上,实现了具有单向传输特性的拓扑确定性界面态的传输.利用光子晶体结构的容易加工性,可以简便地调控拓扑界面态控制光的传播,可为未来光拓扑绝缘体的研究提供良好的平台.     

Graphene/silicon photoelectrode with high and stable photoelectrochemical response in aqueous solution

The graphene (Gr)/Si electrodes were fabricated by electrophoresis method and then following an annealing process. The p-Si surface was found to be covered completely with successive and transparent Gr sheets, and thus the impairment of aqueous solution on the photoelectrochemical capability of silicon could be avoided. This annealing process was a key process for improving the adhesion of Gr/Si interface. After annealing at 400 °C, the Gr/Si electrodes displayed high photoresponse ability and high stability in aqueous solution. The carriers transfer between Gr and Si is discussed on the basis of the semiconductor energy band theory. The results demonstrated that the Gr/Si electrodes would be a promising candidate as solar energy materials using in aqueous solution.     

Preparation of Co<Subscript>3</Subscript>O<Subscript>4</Subscript> hollow microsphere/graphene/carbon nanotube flexible film as a binder-free anode material for lithium-ion batteries

A flexible Co₃O₄ hollow microsphere/graphene/carbon nanotube hybrid film is successfully prepared through a facile filtration strategy and a subsequent thermally treated process. The composition, morphology, and structure of the as-prepared film are characterized by X-ray diffraction, X-ray photoelectron spectrometer, scanning electron microscopy, and transmission electron microscopy. Based on the morphology characterizations on the hybrid film, the Co₃O₄ hollow microspheres are uniformly and closely attached on three-dimensional (3D) graphene/carbon nanotubes (GR/CNTs) network, which decreases the agglomeration of Co₃O₄ microspheres effectively. In this hybrid film, the 3D GR/CNT network which enhances conductance as well as prevents aggregation is a benefit to help Co₃O₄ to exert its lithium storage capabilities sufficiently. When used as a binder-free anode material for lithium-ion batteries, the hybrid film delivers excellent electrochemical properties involving reversible capacity (863 mAh g^?1 at a current density of 100 mA g^?1) and rate performance (185 mAh g^?1 at a current density of 1600 mA g^?1).     

Hydrothermal synthesis of graphene oxide/multiwalled carbon nanotube/Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> ternary nanocomposite for removal of Cu (II) and methylene blue

In this work, highly activated graphene oxide/multiwalled carbon nanotube/Fe₃O₄ ternary nanocomposite adsorbent was prepared from a simple hydrothermal route by using ferrous sulfate as precursor. For this purpose, the graphene oxide/multiwalled carbon nanotube architectures were formed through the π-π attractions between them, followed by attaching Fe₃O₄ nanoparticles onto their surface. The structure and composition of as-prepared ternary nanocomposite were characterized by XRD, FTIR, XPS, SEM, TEM, Raman, TGA, and BET. It was found that the resultant porous graphene oxide/multiwalled carbon nanotube/Fe₃O₄ ternary nanocomposite with large surface area could effectively prevent the π-π stacking interactions between graphene oxide nanosheets and greatly improve sorption sites on the surfaces. Thus, owing to the unique ternary nanocomposite architecture and synergistic effect among various components, as-prepared ternary nanocomposite exhibited high separation efficiency when they were used to remove the Cu (II) and methylene blue from aqueous solutions. Furthermore, the adsorption isotherms of ternary nanocomposite structures for Cu (II) and methylene blue removal fitted the Langmuir isotherm model. This work demonstrated that the graphene oxide/multiwalled carbon nanotube/Fe₃O₄ ternary nanocomposite was promising as an efficient adsorbent for heavy metal ions and organic dye removal from wastewater in low concentration.     

Effect of graphene/ZnO hybrid transparent electrode on characteristics of GaN light-emitting diodes

In order to reduce the Schottky barrier height and sheet resistance between graphene(Gr) and the p-GaN layers in GaN-based light-emitting diodes(LEDs), conductive transparent thin films with large work function are required to be inserted between Gr and p-GaN layers. In the present work, three kinds of transparent conductive oxide(TCO) zinc oxide(ZnO) films, Al-, Ga-, and In-doped ZnO(AZO, GZO, and IZO), are introduced as a bridge layer between Gr and p-GaN,respectively. The influence of different combinations of Gr/ZnO hybrid transparent conducting layers(TCLs) on the optical and thermal characteristics of the GaN-LED was investigated by the finite element method through COMSOL software. It is found that both the TCL transmittance and the surface temperature of the LED chip reduce with the increase in Gr and ZnO thickness. In order to get the transmittance of the Gr/ZnO hybrid TCL higher than 80%, the appropriate combination of Gr/ZnO compound electrode should be a single layer of Gr with ZnO no thicker than 400 nm(1 L Gr/400-nm ZnO),2 L Gr/300-nm ZnO, 3 L Gr/200-nm ZnO, or 4 L Gr/100-nm ZnO. The LEDs with hybrid TCLs consisting of 1 L Gr/300-nm AZO, 2 L Gr/300-nm GZO, and 2 L Gr/300-nm IZO have good performance, among which the one with 1 L Gr/300-nm GZO has the best thermal property. Typically, the temperature of LEDs with 1 L Gr/300-nm GZO hybrid TCLs will drop by about 7 K compared with that of the LEDs with a TCL without ZnO film.     

Flower-like MoS<Subscript>2</Subscript> supported on three-dimensional graphene aerogels as high-performance anode materials for sodium-ion batteries

Flower-like MoS₂ supported on three-dimensional graphene aerogel (MoS₂/GA) composite has been prepared by a facile hydrothermal method followed by subsequent heat-treatment process. Each of MoS₂ microflowers is surrounded by the three-dimensional graphene nanosheets. The MoS₂/GA composite is applied as an anode material of sodium-ion batteries (SIBs) and it exhibits high initial discharge/charge capacities of 562.7 and 460 mAh g^?1 at a current density of 0.1 A g^?1 and good cycling performance (348.6 mAh g^?1 after 30 cycles at 0.1 A g^?1). The good Na⁺ storage properties of the MoS₂/GA composite could be attributed to the unique structure which flower-like MoS₂ are homogeneously and tightly decorated on the surface of three-dimensional graphene aerogel. Our results demonstrate that as-prepared MoS₂/GA composite has a great potential prospect as anodes for SIBs.     

Fabrication of three‐dimensional photonic crystals in quantum‐dot‐based materials

Controlling spontaneous emission (SE) is of fundamental importance to a diverse range of photonic applications including but not limited to quantum optics, low power displays, solar energy harvesting and optical communications. Characterized by photonic bandgap (PBG) property, three‐dimensional (3D) photonic crystals (PCs) have emerged as a promising synthetic material, which can manipulate photons in much the same way as a semiconductor does to electrons. Emission tunable nanocrystal quantum dots (QDs) are ideal point sources to be embedded into 3D PCs towards active devices. The challenge however lies in the combination of QDs with 3D PCs without degradation of their emission properties. Polymer materials stand out for this purpose due to their flexibility of incorporating active materials. Combining the versatile multi‐photon 3D micro‐fabrication techniques, active 3D PCs have been fabricated in polymer‐QD composites with demonstrated control of SE from QDs. With this milestone novel miniaturized photonic devices can thus be envisaged.     

AA-stacked borophene-graphene bilayer as an anode material for alkali-metal ion batteries with a superhigh capacity

As the lightest two-dimensional material, monolayer borophene exhibits great potential as electrode materials, but it suffers from stability issues in the free-standing form. Here, the striped-borophene and graphene bilayer (sB/Gr) is found to be a high-performance anode material for rechargeable alkali-metal ion batteries. The first-principles results show that all the three alkali-metal atoms, Li, Na, and K, can be strongly adsorbed on sB/Gr with ultra-low diffusion barriers than that on pristine borophene/graphene, indicating good charge-discharge rates. Remarkably, high storage capacities are proposed for LIBs (1880 mA·h/g), NIBs (1648 mA·h/g), and KIBs (470 mA·h/g) with relatively small lattice change rate (<2.9%) in the process of alkali-metal atoms intercalations. These intriguing features of sB/Gr make it an excellent choice for batteries.     

Development of monodispersed MnCO<Subscript>3</Subscript>/graphene nanosheet composite as anode for lithium-ion battery by hydrothermal synthesis

A unique monodispersed MnCO₃/graphene nanosheet composite is synthesized by a simple one-step hydrothermal method and used as anode of lithium-ion battery. X-ray diffraction patterns show the typical rhombohedral structure of MnCO₃. A transmission electron micrograph reveals that MnCO₃ is evenly distributed on the graphene nanosheet surface with a uniform diameter of 100 nm. Electrochemical performance results show that the specific discharge capacities of MnCO₃/graphene nanosheet composite remain above 1015.9 mAh g^?1 at a rate of 0.2 C after 85 cycles in the potential window of 0.01–2.0 V and even at a high rate of 1.0 C this parameter remains at 683.5 mAh g^?1 after 100 cycles. Thus, the composite also exhibits favorable rate performance. The excellent reversible capacities are attributed to the highly dispersed and large nanosheet structure of the composite, which may not only facilitate the fast transport of Li⁺ ions between the electrode and electrolyte but also provide enough surfaces to accommodate extra Li⁺ ions that contribute to partial interfacial storage capacities. Additionally, graphene nanosheet can effectively improve electrical conductivity of the composite. Therefore, MnCO₃/graphene nanosheet composite can be a great potential anode material for lithium-ion batteries.     

Superior dielectric properties and bandgap modulation in hydrothermally grown Gr/MgO nanocomposite

MgO nanoparticles (NPs) and Gr/MgO nanocomposite (NC) have been synthesized by hydrothermal route. X-ray diffraction (XRD) analysis confirmed the crystalline cubic phase of MgO and Gr/MgO NC. Raman spectroscopy was used to study the defects in the NCs. Electron microscopy study display spherical NPs of MgO on graphene sheets. UV-visible spectroscopy shows a red shift in the absorption band and a significant reduction in the bandgap for Gr/MgO NC. The improvements in dielectric properties of NC can be ascribed to interfacial polarization between rGO and MgO. The rGO in the NCs supports the electron transfer and improves the electrical conductivity.     

Simulation on effect of metal/graphene hybrid transparent electrode on characteristics of GaN light emitting diodes

In order to decrease the Schottky barrier height and sheet resistance between graphene(Gr) and the p-GaN layers in GaN-based light-emitting diodes(LEDs), some transparent thin films with good conductivity and large work function are essential to insert into Gr and p-GaN layers. In this work, the ultra-thin films of four metals(silver(Ag), golden(Au), nickel(Ni), platinum(Pt)) are explored to introduce as a bridge layer into Gr and p-GaN, respectively. The effect of a different combination of Gr/metal transparent conductive layers(TCLs) on the electrical, optical, and thermal characteristics of LED was investigated by the finite element methods. It is found that both the TCLs transmittance and the surface temperature of the LED chip reduces with the increase of the metal thickness, and the transmittance decreases to about 80% with the metal thickness increasing to 2 nm. The surface temperature distribution, operation voltage, and optical output power of the LED chips with different metal/Gr combination were calculated and analyzed. Based on the electrical, optical, and thermal performance of LEDs, it is found that 1.5-nm Ag or Ni or Pt, but 1-nm Au combined with 3 layered(L) Gr is the optimal Gr/metal hybrid transparent and current spreading electrode for ultra-violet(UV) or near-UV LEDs.     

Preparation and electrochemical properties of LiFePO<Subscript>4</Subscript>/graphene composites from tailoring graphene oxides

LiFePO₄/graphene composites have been prepared by using tailoring graphene oxide (GO) nanosheets as precursors. The structure and electrochemical properties of the composites were investigated by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), Raman microscopy, and a variety of electrochemical testing techniques. The decrease in graphene size reduces the contact resistance between activated materials, and enhances the lithium-ion transport in LiFePO₄/graphene composites. With low weight fractions of small-size graphene sheets, the composites show better electrochemical performance than those with large size graphene sheets.     

Switching and memory effects in composite films of semiconducting polymers with particles of graphene and graphene oxide

The effects of switching were investigated in composite films based on multifunctional polymers. i.e., derivatives of carbazole (PVK) and fluorene (PFD), as well as based on particles of graphene (Gr) and graphene oxide (GO). The concentration of Gr and GO particles in the PVK(PFD) matrix was varied in the range of 2–3 wt %, which corresponded to the percolation threshold in these systems. The atomic composition of the composite films PVK: GO was examined using X-ray photoelectron spectroscopy. It was found that the effect of switching in structures of the form Al/PVK(PFD): GO(Gr)/ITO/PET manifests itself in a sharp change of the electrical resistance of the composite film from a low-conducting state to a relatively high-conducting state when applying a bias to Al-ITO electrodes of ∼0.1–0.3 V (E ∼ 3–5 × 10⁴ V/cm), which is below the threshold switching voltages for similar composites. The mechanism of resistance switching, which is associated with the processes of capture and accumulation of charge carriers by Gr (GO) particles introduced into the matrices of the high-molecular-weight (PVK) and relatively low-molecular-weight (PFD) polymers, was discussed.

     

Ring resonator of surface modes based on photonic crystals

We design a compact ring resonator of surface modes based on photonic crystals (PCs). The structure is formed by sandwiching a surface mode ring waveguide (SMRW) into two parallel surface mode waveguide (SMW) based on two dimensional (2D) PCs. The SMRW is created on the surface of a circular photonic crystal (CPC) structure, where the wave propagates with high transmission efficiency. As a fundamental mode is introduced in the input SMW, at certain frequencies, the SMRW modes are enhanced because of resonance and the light-waves are coupled to the output SMW. It is demonstrated by the simulation results that the surface mode ring resonator has a low radiation loss with a very small size because of the good wave-guiding of surface mode based on PCs, and can be used in the future wavelength division multiplex (WDM) optics communication systems.     

Interface injection-limited carrier-transport properties of Alq<Subscript>3</Subscript>

We have studied the carrier-transport properties of the amorphous organic material tris (8-hydroxyquinoline) aluminium (Alq₃) for Al and LiF/Al cathodes at room temperature. The investigation was made by the current–voltage characteristic measurements for different Alq₃ film thicknesses. It is found that the current–voltage characteristic has a linear dependence on the thickness of the Alq₃ film. The current density increases by several orders for a LiF/Al cathode over that of Al at a given bias voltage. The carrier-injection processes at the metal/organic contact dominate the current–voltage characteristics. The carrier injection seems to be limited by the charge hopping of interfacial molecular sites. PACS 73.50.Gr; 73.40.-c; 73.61.Ph; 78.45.+h; 42.70.Jk     

Casimir friction force between a SiO<Subscript>2</Subscript> probe and a graphene-coated SiO<Subscript>2</Subscript> substrate

The possibility of mechanical detection of Casimir friction with the use of a noncontact atomic force microscope is discussed. A SiO₂ probe tip located above a graphene-coated SiO₂ substrate is subjected to the frictional force caused by a fluctuating electromagnetic field produced by a current in graphene. This frictional force will create the bend of a cantilever, which can be measured by a modern noncontact atomic force microscope. Both the quantum and thermal contributions to the Casimir frictional force can be measured using this experimental setup. This result can also be used to mechanically detect Casimir friction in micro- and nanoelectromechanical systems.     

Growth of FePO<Subscript>4</Subscript> nanoparticles on graphene oxide sheets for synthesis of LiFePO<Subscript>4</Subscript>/graphene

FePO₄·xH₂O/graphene oxide (FePO₄·xH₂O/GO) composites were prepared by a facile chemical precipitation method. Using the as-prepared FePO₄·xH₂O/GO and LiOH·H₂O as precursors and followed by carbothermal reduction, LiFePO₄/graphene composites were obtained. Scanning electron microscope (SEM) images indicated that the graphene had very good dispersity and uniformly attached to the LiFePO₄ particles. The conductive framework of graphene improved the electrochemical properties of the composites. The composites deliver high initial discharge capacity of 163.4 mAh g^?1 as well as outstanding rate performance.