Catalytic graphitization of PAN-based carbon fibers with electrodeposited Ni-Fe alloy

Ni-Fe alloy was electrodeposited on the surface of polyacrylonitrile （PAN）-based carbon fibers, and catalytic graphitization effect of the heat-treated carbon fibers was investigated by X-ray diffractometry and Raman spectra. It is found that Ni-Fe alloy exhibits significant catalytic effect on the graphitization of the carbon fibers at low temperatures. The degree of graphitization of the carbon fibers coated with Ni-Fe alloy （57.91% Fe, mass fraction） reaches 69.0% through heat treatment at 1 250 °C. However, the degree of graphitization of the carbon fibers without Ni-Fe alloy is only 30.1% after being heat-treated at 2 800 °C. The catalytic effect of Ni-Fe alloy on graphitization of carbon fibers is better than that of Ni or Fe at the same temperature, indicating that Ni and Fe elements have synergic catalytic function. Furthermore, Fe content in the Ni-Fe alloy also influences catalytic effect. The catalytic graphitization of Ni-Fe alloy follows the dissolution-precipitation mechanism.

Preparation and mechanical properties of carbon/carbon composites with high textured pyrolytic carbon matrix

Short carbon fiber felts with an initial porosity of 89.5% were deposited by isobaric, isothermal chemical vapor infiltration using natural gas as carbon source. The bulk density of the deposited carbon/carbon （C/C） composites was 1.89 g/cm3 after depositing for 150 h. The microstructure and mechanical properties of the C/C composites were studied by polarized light microscopy, X-ray diffraction, scanning electron microscopy and three-point bending test. The results reveal that high textured pyrolytic carbon is deposited as the matrix of the composites, whose crystalline thickness and graphitization degree highly increase after heat treatment. A distinct decrease of the flexural strength and modulus accompanied by the increase of the toughness of the C/C composites is found to be correlated with the structural changes in the composites during the heat treatment process.

Flexible free-standing graphene-like film electrode for supercapacitors by electrophoretic deposition and electrochemical reduction

Electrophoretic deposition in conjunction with electrochemical reduction was used to make flexible free-standing graphene-like films. Firstly, graphene oxide （GO） film was deposited on graphite substrate by electrophoretic deposition method, and then reduced by subsequent electrochemical reduction of GO to obtain reduced GO （ERGO） film with high electrochemical performance. The morphology, structure and electrochemical performance of the prepared graphene-like film were confirmed by SEM, XRD and FT-IR. These unique materials were found to provide high specific capacitance and good cycling stability. The high specific capacitance of 254 F/g was obtained from cyclic voltammetry measurement at a scan rate of 10 mV/s. When the current density increased to 83.3 A/g, the specific capacitance values still remained 132 F/g. Meanwhile, the high powder density of 39.1 kW/kg was measured at energy density of 11.8 W-h/kg in 1 mol/L H2SO4 solution. Furthermore, at a constant scan rate of 50 mV/s, 97.02% of its capacitance was retained for 1000 cycles. These promising results were attributed to the unique assembly structure of graphene film and low contact resistance, which indicated their potential application to electrochemical capacitors.

Layer Dependence of Graphene for Oxidation Resistance of Cu Surface

We studied the oxidation resistance of graphene-coated Cu surface and its layer dependence by directly growing monolayer graphene with different multilayer structures coexisted, di- minishing the influence induced by residue and transfer technology. It is found that the Cu surface coated with the monolayer graphene demonstrate tremendous difference in oxidation pattern and oxidation rate, compared to that coated with the bilayer graphene, which is considered to be originated from the strain-induced linear oxidation channel in monolayer graphene and the intersection of easily-oxidized directions in each layer of bilayer graphene, respectively. We reveal that the defects on the graphene basal plane but not the boundaries are the main oxidation channel for Cu surface under graphene protection. Our finding indicates that compared to putting forth efforts to improve the quality of monolayer graphene by reducing defects, depositing multilayer graphene directly on metal is a simple and effective way to enhance the oxidation resistance of graphene-coated metals.

Preparation of BiPO4/graphene photoelectrode and its photoelectrocatalyitic performance

In this work, a two-step electrodeposition method was employed to prepare BiPO4 nanorod/reduced graphene oxide/FTO composite electrodes(BiPO4/r GO/FTO). The BiPO4/r GO/FTO composite electrode showed the higher photoelectrocatalytic(PEC) activity for the removal of methyl orange than pure BiPO4, which was 2.8 times higher than that of BiPO4/FTO electrode. The effects of working voltage and BiPO4 deposition time on the degradation efficiency of methyl orange were investigated. The optimum BiPO4 deposition time was 45 min and the optimum working voltage was 1.2 V. The trapping experiments showed that hydroxyl radicals(·OH) and superoxide radicals(·O2-) were the major reactive species in PEC degradation process. The BiPO4/r GO/FTO composite electrode showed the high stability and its methyl orange removal efficiency remained unchanged after four testing cycles. The reasons for the enhanced PEC efficiency of the BiPO4/r GO/FTO composite electrode was ascribed to the broad visible-light absorption range, the rapid transmission of photogenerated charges, and the mixed BiPO4 phase by the introduction of r GO in the composite electrode films.

Hybrid functional IrO_2-TiO_2 thin film resistor prepared by atomic layer deposition for thermal inkjet printheads

IrO2-TiO2 thin films were prepared by atomic layer deposition using Ir（EtCp）（COD） and titanium isopropoxide （TTIP）. The resistivity of IrO2-TiO2 thin films can be easily controlled from 1 500 to 356.7 μΩ·cm by the IrO2 intermixing ratio from 0.55 to 0.78 in the IrO2-TiO2 thin films. The low temperature coefficient of resistance（TCR） values can be obtained by adopting IrO2-TiO2 composite thin films. Moreover, the change in the resistivity of IrO2-TiO2 thin films was below 10% even after O2 annealing process at 600 ℃. The step stress test results show that IrO2-TiO2 films have better characteristics than conventional TaN08 heater resistor. Therefore, IrO2-TiO2 composite thin films can be used as a heater resistor material in thermal inkjet printhead.

One-step electrodeposition to fabricate robust superhydrophobic silver/graphene coatings with excellent stability

A facile method was proposed to prepare stretchable silver-based composite coatings with excellent conductivity and stability for flexible electronics.Silver coating was firstly deposited on thermoplastic polyurethane(TPU)elastomer rubber surface via two-component spraying technique,then the superhydrophobic surface was obtained by one-step electrodeposition of cerium compounds(CeM)and graphene nanosheets(GNS)to produce Ag/CeM/GNS composite coatings.The obtained Ag/CeM/GNS composite coatings maintained high conductivity after experiencing bending cycles and stretching cycles.Furthermore,the as-prepared Ag/CeM/GNS composite coatings showed excellent self-cleaning and anti-fouling properties,and the corrosion resistance has improved significantly compared to the original Ag coating.In addition,the Ag/CeM/GNS composite coatings could drive the circuit normally in the states of tensile,bending and twisting deformation,showing excellent mechanical stability and applicability.As a result,it is believed that the prepared Ag/CeM/GNS composite coatings with excellent conductivity and stability have promising applications for flexible electronics in harsh conditions.

In-situ preparation of TiO_(2)/N-doped graphene hollow sphere photocatalyst with enhanced photocatalytic CO_(2) reduction performance

Photocatalytic CO_(2)conversion efficiency is hampered by the rapid recombination of photogenerated charge carriers.It is effective to suppress the recombination by constructing cocatalysts on photocatalysts with high-quality interfacial contact.Herein,we develop a novel strategy to in-situ grow ultrathin/V-doped graphene(NG)layer on TiO_(2) hollow spheres(HS) with large area and intimate interfacial contact via a chemical vapor deposition(CVD).The optimized TiO^(2)/NG HS nanocomposite achieves total CO_(2)conversion rates(the sum yield of CO,CH_(3)OH and CH_(4))of 18.11μmol·g^(-1)h^(-1),which is about 4.6 times higher than blank T1O_(2)HS.Experimental results demonstrate that intimate interfacial contact and abundant pyridinic N sites can effectively facilitate photogenerated charge carrier separation and transport,realizing enhanced photocatalytic CO_(2)reduction performance.In addition,this work provides an effective strategy for in-situ construction of graphene-based photocatalysts for highly efficient photocatalytic CO_(2)conversion.

Low Temperature Plasma CVD Grown Graphene by Microwave Surface-Wave Plasma CVD Using Camphor Precursor

Hydrocarbon precursor such as methane has been widely used to grow graphene films and the methods of growing quality graphene films are dominated by thermal CVD （chemical vapor deposition） system. Graphene films grown by plasma process are generally highly defective which in turns degrade the quality of the films. Here, using a green precursor, camphor we demonstrate a simple and economical method to get high-quality graphene film on copper substrate by micro wave surface-wave plasma CVD at relatively low temperature 550℃. Graphene film grown using camphor shows superior quality than that of the film grown using methane. Results revealed that camphor precursor is a good alternative to hydrocarbon precursors for graphene research.

长沟流月去无声——风华绝代张爱玲

无声逝去的是月，寂然行走的是她。经历伤痛，享受甜蜜，攀上顶峰，沉入谷底。她的人生大起大落，沉沉浮浮。她写就了《传奇》，她也成为了传奇。

Flexible all-solid-state micro-supercapacitor based on Ni fiber electrode coated with MnO_2 and reduced graphene oxide via electrochemical deposition

Flexible and micro-sized energy conversion/storage components are extremely demanding in portable and multifunctional electronic devices, especially those small,flexible, roll-up and even wearable ones. Here in this paper, a two-step electrochemical deposition method has been developed to coat Ni fibers with reduced graphene oxide and MnO2 subsequently, giving rise to Ni@reduced-graphene-oxide@MnO2 sheath-core flexible electrode with a high areal specific capacitance of 119.4 mF cm^-2 at a current density of 0.5 mA cm^-2 in 1 mol L^-1 Na2SO4 electrolyte. Using polyvinyl alcohol（PVA）-LiCl as a solid state electrolyte, two Ni@reduced-grapheneoxide@Mn02 flexible electrodes were assembled into a freestanding, lightweight, symmetrical fiber-shaped micro-supercapacitor device with a maximum areal capacitance of26.9 mF cm^-2. A high power density of 0.1 W cm^-3 could be obtained when the energy density was as high as0.27 mW h cm^-3. Moreover, the resulting micro-supercapacitor device also demonstrated good flexibility and high cyclic stability. The present work provides a simple, facile and low-cost method for the fabrication of flexible, lightweight and wearable energy conversion/storage micro-devices with a high-performance.

Oxide-on-graphene field effect bio-ready sensors

Electrical detection schemes using nanoscale devices offer fast and label-free alternatives to biosensing techniques based on chemical and optical interactions. Here we report on the design, fabrication, and operation of oxide-on-graphene ion-sensitive field effect sensor arrays using large-area graphene sheets synthesized by chemical vapor deposition. In this scheme, HfO2 and SiO2 thin films are deposited atop the graphene sheet and play the dual role of the sensing interface, as well as the passivation layer protecting the channel and electrodes underneath from direct contact with the electrolyte. We further demonstrate the functionalization of the SiO2 surface with 3-aminopropyltrimethoxysilane （APTMS）. The oxide-on-graphene sensors operate in solution with high stability and a high average mobility of 5,000 cm2/（V＇s）. As a proof of principle, we demonstrate pH sensing using the bare or the APTMS-functionalized SiO2 as the sensing surface. The measured sensitivities, 46 mV/pH and 43 mV/pH, respectively, agree well with existing studies. We further show that by applying the solution gate voltage in pulse, the hysteresis in the transfer curve of the graphene transducer can be eliminated, greatly improving the ionic potential resolution of the sensor. These experiments demonstrate the potential of oxide-on-graphene ion-sensitive field effect sensors in on-chip, label-free and real-time biosensing applications.

Insight into the rapid growth of graphene single crystals on liquid metal via chemical vapor deposition

Previous reports about the growth of large graphene single crystals on polycrystalline metal substrates usually adopted the strategy of suppressing the nucleation by lowering the concentration of the feedstock, which greatly limited the rate of the nucleation and the sequent growth. The emerging liquid metal catalyst possesses the characteristic of quasi-atomically smooth surface with high diffusion rate. In principle, it should be a naturally ideal platform for the lowdensity nucleation and the fast growth of graphene. However,the rapid growth of large graphene single crystals on liquid metals has not received the due attention. In this paper, we firstly purposed the insight into the rapid growth of large graphene single crystals on liquid metals. We obtained the millimeter-size graphene single crystals on liquid Cu. The rich free-electrons in liquid Cu accelerate the nucleation, and the isotropic smooth surface greatly suppresses the nucleation.Moreover, the fast mass-transfer of carbon atoms due to the excellent fluidity of liquid Cu promotes the fast growth with a rate up to 79 μm s^-1. We hope the research on the growth speed of graphene on liquid Cu can enrich the recognition of the growth behavior of two-dimensional(2 D) materials on the liquid metal. We also believe that the liquid metal strategy for the rapid growth of graphene can be extended to various 2 D materials and thus promote their future applications in the photonics and electronics.

Large-area nanopatterned graphene for ultrasensitive gas sensing

Chemical vapor deposited （CVD） graphene is nanopatterned using a spherical block copolymer etch mask. The use of spherical rather than cylindrical block copolymers allows homogeneous patterning of cm-scale areas without any substrate surface treatment. Raman spectroscopy was used to study the con- trolled generation of point defects in the graphene lattice with increasing etching time, confirming that alongside the nanomesh patterning, the nanopatterned CVD graphene presents a high defect density between the mesh holes. The nanopatterned samples showed sensitivities for NO2 of more than one order of magnitude higher than for non-patterned graphene. NO2 concentrations as low as 300 ppt were detected with an ultimate detection limit of tens of ppt. This is the smallest value reported so far for non-UV illuminated graphene chemiresistive NO2 gas sensors. The dramatic improvement in the gas sensitivity is believed to be due to the high adsorption site density, thanks to the combination of edge sites and point defect sites. This work opens the possibility of large area fabrication of nanopatterned graphene with extremely high densities of adsorption sites for sensing applications.

Synthesis of Large-Area, Few-Layer Graphene on Iron Foil by Chemical Vapor Deposition

We demonstrate a simple and controllable way to synthesize large-area, few-layer graphene on iron substrates by an optimized chemical vapor deposition （CVD） method using a mixture of methane and hydrogen. Based on an analysis of the Fe-C phase diagram, a suitable procedure for the successful synthesis of graphene on Fe surfaces was designed. An appropriate temperature and cooling process were found to be very important in the synthesis of highly crystalline few-layer graphene. Graphene-based field-effect transistor （FET） devices were fabricated using the resulting few-layer graphene, and showed good quality with extracted mobilities of 300-1150 cm2/（V.s）.

High densities of magnetic nanoparticles supported on graphene fabricated by atomic layer deposition and their use as efficient synergistic microwave absorbers

An atomic layer deposition （ALD） method has been employed to synthesize Fe3O4/graphene and Ni/graphene composites. The structure and microwave absorbing properties of the as-prepared composites are investigated. The surfaces of graphene are densely covered by Fe3O4 or Ni nanoparticles with a narrow size distribution, and the magnetic nanoparticles are well distributed on each graphene sheet without significant conglomeration or large vacancies. The coated graphene materials exhibit remarkably improved electromagnetic （EM） absorption properties compared to the pristine graphene. The optimal reflection loss （RL） reaches -46.4 dB at 15.6 GHz with a thickness of only 1.4 mm for the Fe3O4/graphene composites obtained by applying 100 cycles of Fe2O3 deposition followed by a hydrogen reduction. The enhanced absorption ability arises from the effective impedance matching, multiple interfacial polarization and increased magnetic loss from the added magnetic constituents. Moreover, compared with other recently reported materials, the composites have a lower filling ratio and smaller coating thickness resulting in significantly increased EM absorption properties. This demonstrates that nanoscale surface modification of magnetic particles on graphene by ALD is a very promising way to design lightweight and high-efficiency microwave absorbers.

Realization of low contact resistance close to theoretical limit in graphene transistors

Realizing low contact resistance between graphene and metal electrodes remains a well-known challenge for building high-performance graphene devices. In this work, we attempt to reduce the contact resistance in graphene transistors and further explore the resistance limit between graphene and metal contacts. The Pd/graphene contact resistance at room temperature is reduced below the 100 Ω·μm level both on mechanically exfoliated and chemical-vapor-deposition graphene by adopting high-purity palladium and high-quality graphene and controlling the fabrication process to not contaminate the interface. After excluding the parasitic series resistances from the measurement system and electrodes, the retrieved contact resistance is shown to be systematically and statistically less than 100 Ω·μm, with a minimum value of 69 Ω·μm, which is very close to the theoretical limit. Furthermore, the contact resistance shows no clear dependence on temperature in the range of 77-300 K; this is attributed to the saturation of carrier injection efficiency between graphene and Pd owing to the high quality of the graphene samples used, which have a sufficiently long carrier mean-free-path.

Anomalous moire pattern of graphene investigated by scanning tunneling microscopy： Evidence of graphene growth on oxidized Cu（111）

The growth of graphene on oriented （111） copper films has been achieved by atmospheric pressure chemical vapor deposition. The structural properties of as-produced graphene have been investigated by scanning tunneling microscopy. Anomalous moir6 superstructures composed of well-defined linear periodic modulations have been observed. We report here on comprehensive and detailed studies of these particular moir6 patterns present in the graphene topography revealing that, in certain conditions, the growth can occur on the oxygen-induced reconstructed copper surface and not directly on the oriented （111） copper film as expected.

Kinetics of defect formation in chemically vapor deposited （CVD） graphene during laser irradiation： The case of Raman investigation

The effect of laser irradiation on chemically vapor deposited （CVD） graphene was studied by analyzing the temporal evolution of Raman spectra acquired under various illumination conditions. The spectra showed that the normalized intensity of the defect-related peak increases with the square root of the exposure time and varies almost linearly with the laser power density. Furthermore, the hardness of graphene to radiation damage depends on its intrinsic structural quality. The results suggest that, contrary to the common belief, micro-Raman spectroscopy cannot be considered a noninvasive tool for the characterization of graphene. The experimental observations are compatible with a model that we derived from the interpretative approach of the Staebler-Wronski effect in hydrogenated amorphous silicon; this approach assumes that the recombination of photoexcited carriers induces the breaking of weak C-C bonds.

High-quality bilayer graphene grown on softened copper foils by atmospheric pressure chemical vapor deposition

Bilayer graphene(BLG)shows great application prospect and potential in next-generation electronics because of its unique electrical and mechanical properties.However,the scalable synthesis of large-area high-quality BLG films is still a great challenge,despite the maturity of chemical vapor deposition(CVD)technique.In this study,we report a robust method to grow BLGs on flat,softened Cu foils by atmospheric pressure CVD.A moderate amount of residual oxygen accelerates the growth of BLG domains while suppressing the formation of multilayers.Raising the nucleation density at low hydrogen pressure efficiently increases the film continuity.Based on the optimized CVD process,the growth of graphene films on 4×4 cm^2 Cu foils with an average BLG coverage of 76%is achieved.The morphology and structure characterizations demonstrate a high quality of the BLG.Dual gate field-effect transistors are investigated based on AB-stacked BLG,with a tunable bandgap and high carrier mobility of up to 6790 cm2 V^−1 s^−1 at room temperature.