A novel method for large area graphene transfer on the polymer optical fiber

We develop two simple methods-the dip coat stamping and lift-off methods-to transfer large area, high quality graphene films onto the top and side faces of the polymer optical fiber. The graphene films can be synthesized using chemical vapor deposition method on large Cu foils. After synthesis, the graphene films are characterized by scanning electron microscopy, atomic force microscopy and Raman spectroscopy. The polymer optical fiber probe with the transferred graphene film can be used as a chemical sensor for the detection of various organic aerosols.     

背栅单层石墨烯场效应晶体管的构建及可靠性研究

采用低压化学气相沉积法(LPCVD)制备了高质量的单层石墨烯薄膜,通过湿法转移将所制备的单层石墨烯无损覆盖到两条平行粘贴在SiO2/Si衬底上的热释放胶带表面,胶带间距约500μm,进而对试样进行加热和切割,获得与SiO2/Si衬底紧密结合的石墨烯条带(约10 000μm×500μm),最后采用掩膜法在石墨烯条带上蒸镀金电极,构建成背栅石墨烯场效应晶体管。该方法简单易行,电学性能测试结果表明,石墨烯与金电极具有良好的欧姆接触,室温下,石墨烯的空穴迁移率约为735cm2/(V·s),且表现出了石墨烯所特有的双极性特征。背栅石墨烯场效应晶体管转移特性曲线表现出了滞回行为,且随着施加栅压的增大,滞回行为越来越显著,展示出高的性能可靠性。     

A facile method for fabrication of moisture-sensitive porous membrane with on-off function

In the present work, a facile method is presented for fabrication of moisture sensitive porous polyurethane (PU) membranes with on-off function. A kind of supramolecular hydrogel precursor, never used as pore filling agent before, was firstly formed by the inclusion complexation of PEG diacrylate (PEGDA) with α-cyclodextrin (α-CD) and subsequently in-situ UV photo-cross-linked in pores of the PU membranes. The moisture sensitive property of the supramolecular hydrogels was related to the amount of α-CD added as well as the environmental relative humidity. Especially, the controlled on-off function of the hydrogel-containing porous PU membrane was confirmed from the results of microscopic observation.     

A facile one-step synthesis of TiO2/graphene composites for photodegradation of methyl orange

TiO₂/graphene composite photocatalysts have been prepared by a simple liquid phase deposition method using titanium tetrafluoride and electron beam (EB) irradiation-pretreated graphene as the raw materials. The products were characterized by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and thermogravimetric analysis. The effects of varying the synthesis parameters such as graphene content, concentration of titanium tetrafluoride solution and irradiation dose were investigated. It was found that the preparation conditions had a significant effect on the structure and properties of the final products. The irradiated graphene was covered with petal-like anatase TiO₂ nanoparticles, which were more uniform and smaller in size than those in products synthesized without EB irradiation-pretreated graphene. The photocatalytic activities of the products were evaluated using the photocatalytic degradation of methyl orange as a probe reaction. The results showed that the products synthesized using EB irradiation-pretreated graphene exhibited higher photocatalytic activities than those using graphene without EB irradiation pretreatment.      

大面积碳纳米管薄膜的低温制备与表征

采用研制的大体积射频等离子体红外加热化学气相沉积设备,在600℃的低温下,在5cm×5cm大的Ni片上生长出碳纳米管薄膜。扫描电镜(SEM)和透射电镜(TEM)观察显示,碳纳米管薄膜具有很好的均匀性,管径大约为70～90nm。随机地对样品的3个不同区域进行了场发射特性的测试,结果表明这种薄膜具有良好的场发射特性及一致性。开启电场约为2.4V/μm,在电场为6.6V/μm时的发射电流密度达到1635μA/cm2。实验结果表明在低温条件下,大面积生长场发射用碳纳米管薄膜是可行的。     

Movement of Dirac points and band gaps in graphyne under rotating strain

The introduction of lattice anisotropy causes Dirac cones to shift in response to the applied strain,leaving a pseudogap at the original Dirac points.Here,a group-theory analysis is combined with first-principles calculations to reveal the movement characteristics of Dirac points and band gaps in various graphynes under rotating uniaxial and shear strains.Graphene,where linear effects dominate,is different from a-,β-,and y-graphynes,which generate strong nonlinear responses due to their bendable acetylenic linkages.However,the linear components of the electronic response,which are essential in determining material performance such as intrinsic carrier mobility due to electron-phonon coupling,can be readily separated,and are well described by a unified theory.The movement of the Dirac points in a-graphyne is circular under a rotating strain,and the pseudogap opening is isotropic with a magnitude of only 2％ that in graphene.In comparison,the movement in β-graphyne is elliptical and the center is displaced from the origin.For y-graphyne,three branches of gaps change with the applied strains with a sine/cosine dependence on the strain angle.The developed methodology is useful in determining the electronic response to various strains of Dirac materials and two-dimensional semiconductors.     

A facile method for preparing 3D graphene/Ag aerogel via gamma-ray irradiation

In this article, we report a simple method to fabricate graphene and Ag nanoparticles (NPs) composite aerogel (GA/Ag). The GO and Ag ions were in situ reduced by gamma-ray irradiation and went through self-assembly three-dimensional (3D) honeycomb-like porous composite aerogel in the presence of isopropanol. Measurements using XRD, XPS, SEM, TEM revealed that the GO and Ag ions can efficiently reduction into rGO and Ag NPs. In addition, Ag NPs were homogeneously attached to the graphene nanosheets of the honeycomb-like porous structure and had a typical diameter of 30–70 nm. Thus the gamma-ray irradiation-induced synthesis is an efficient method for preparing 3D GA/Ag composite.     

Influence of growth parameters on the fabrication of high-quality colloidal crystals via a controlled evaporation self-assembly method

A controlled evaporation self-assembly method with multiple controllable parameters was used to synthesize high-quality colloidal crystals. The environmental parameters, such as the relative humidity, evaporation temperature and pressure, were studied for the quality controls of colloidal crystals during the formation. In the experimental results, we show how these parameters influence the quality of colloidal crystals significantly. Moreover, it is found that, under the case of the relative humidity of 70%, evaporation temperature of 35 °C and pressure of 6.0 kPa, the fabricating high-quality colloidal crystals is optimal from aqueous solution of monodisperse polystyrene spheres with a diameter of 260 nm in a short time (less than 10 h). Highest possible crystal quality may be obtained after the natural drying in the vacuum chamber.     

A facile method for morphological control of MgZnO nanostructures on GaAs substrates and their optical properties

This research reports on morphological changes depending on the growth temperature in MgZnO nanostructures grown on GaAs substrates by metalorganic chemical vapor deposition as well as the investigation of their optical properties. As the growth temperature increased, the morphology of the MgZnO nanostructure changed from one-dimensional nanowires (480 degrees C) to pseudo-two-dimensional nanowalls (500 degrees C) to pyramid-shaped structures (520 degrees C). Among these structures, the nanowalls exhibited the best optical properties due to the large active surface area and high crystalline quality.     

Synthesis of large area, homogeneous, single layer graphene films by annealing amorphous carbon on Co and Ni

The synthesis of large area, homogenous, single layer graphene on cobalt (Co) and nickel (Ni) is reported. The process involves vacuum annealing of sputtered amorphous carbon (a-C) deposited on Co/sapphire or Ni/sapphire substrates. The improved crystallinity of the metal film, assisted by the sapphire substrate, proves to be the key to the quality of as-grown graphene film. The crystallinity of the Co and Ni metal films was improved by sputtering the metal at elevated temperature as was verified by X-ray diffraction (XRD). After sputtering of a-C and annealing, large area, single layer graphene that occupies almost the entire area of the substrate was produced. With this method, 100 mm²-area single layer graphene can be synthesized and is limited only by the substrate and vacuum chamber size. The homogeneity of the graphene film is not dependent on the cooling rate, in contrast to syntheses using polycrystalline metal films and conventional chemical vapor deposition (CVD) growth. Our facile method of producing single layer graphene on Co and Ni metal films should lead to large scale graphene-based applications.     

A facile approach to fabricate few-layer chemically modified and reduced graphene oxide sheets: Combination of stitching,reduction and functionaliztion

A facile strategy for the preparation of few-layer chemically stitched and reduced graphene oxide (FL-CMRG) in water using various linear diaminoalkanes with the general formula H₂N(CH₂)_nNH₂ (n = 4, 6, 8) is proposed, and the resulting FL-CMRG was characterized by means of AFM, TEM, XPS, UV-vis, TGA and XRD. Interlayer spacing between bridged FL-CMRG sheets can reach 1.038 nm when the size of the intercalant to (n = 6) H₂N (CH₂)₆ NH₂. A mechanism for forming the FL-CMRG via removal of epoxide and hydroxyl groups from GO and stitching of the GO sheets by various linear diaminoalkanes in water solution has been proposed.     

A novel proposal for all-optical compact and fast XOR/XNOR gate based on photonic crystal

In this paper, we aim to design an all-optical device, which can perform XOR and XNOR functions in a single structure. The proposed structure will be realized by cascading two nonlinear resonant rings. The functionality of the proposed structure is based on controlling the optical behaviour of optical rings via optical intensity. The final structure has one bias and two input control ports, along with two output ports. One port acts as an XOR and the other acts as an XNOR gate. The maximum delay times for the XOR and XNOR gates are 1.5 and 2.5?ps, respectively. Therefore, the working bit rates for the XOR and XNOR gates are 666 and 400?Gbit/s, respectively.     

一种在硅材料表面组装金纳米颗粒的新方法

以氯金酸、L-半胱氨酸为反应试剂,利用内电流和金硫自组装效应,在硅材料表面组装了较为均一的金纳米颗粒,并利用荧光分析与硅纳米线场效应晶体管对该方法进行了相关验证.结果表明:经氢氟酸处理后的硅材料,在氯金酸和L_半胱氨酸混合溶液中反应3 min可在硅表面得到较为均匀、稳定的金纳米颗粒层,其中,氯金酸浓度为0.5mmol/L,氯金酸和L-半耽氨酸浓度比为3∶1.荧光分析表明该方法组装的金颗粒表面已氨基功能化,使得金纳米颗粒修饰的硅材料在应用于生物检测时可直接醛基化修饰蛋白,简化了实验操作,同时,该方法可以在硅纳米线场效应晶体管中特异性组装金纳米颗粒,有力地支持了相关器件在疾病检测方面的应用.     

Reactive particle beam based deposition process of nano-crystalline silicon thin film at low temperature for the flexible AM-OLED backplane

A novel deposition process for depositing nano-crystalline silicon (nc-Si) thin films at low temperature was developed using reactive particle beam assisted chemical vapor deposition (RPB-CVD) for applications to the thin film transistor (TFT) backplane of flexible active matrix-OLEDs with plastic substrates. During the formation of nc-Si thin films by the RPB-CVD process with a silicon reflector electrode at low temperatures or room temperature, energetic particles could induce the formation of a crystalline phase in polymorphous Si thin films without additional substrate heating. The effects of the incident RPB energy controlled by the reflector bias were confirmed by Raman spectroscopy. The dark conductivity of polymorphous Si thin films increased with increasing reflector bias, whereas the ratio of photo and dark conductivity decreased monotonically. The optical band gap of the Si thin films also could be changed from amorphous to nano-crystalline by controlling the reflector bias. The first results of a primitive nc-Si TFT by RPB-CVD at room temperature demonstrate the technical potential of RPB-based processes as flexible TFT backplanes.     

A facile solution-immersion process for the fabrication of superhydrophobic surfaces with high water adhesion

The present work reports a simple and effective way to produce copper compound films on zinc substrate via solution-immersion process. The surfaces were characterized by field-emission scanning electron microscopy, Fourier transform IR, X-ray photoelectron spectrum and X-ray powder diffraction. The wettability of the surfaces is also investigated. The as-prepared superhydrophobic surfaces exhibit high adhesion to water and scratches on the surfaces could be repaired by immersing the damaged samples into the solution again.     

A novel wet-spinning method of manufacturing continuous bio-inspired composites based on graphene oxide and sodium alginate

Nacre is a lightweight, strong, stiff, and tough material, which makes it a mimicking object for material design. Many attempts to mimic nacre by various methods resulted in the synthesis of artificial nacre with excellent properties. However, the fabrication procedure was very laborious and time-consuming due to the sequential steps, and only limited-sized materials could be obtained. Hence, a novel design enabling scalable production of high-performance artificial nacre with uniform layered structures is urgently needed. We developed a novel wet-spinning assembly technique to rapidly manufacture continuous nacremimic graphene oxide (GO, brick)-sodium alginate (SA, mortar) films and fibers with excellent mechanical properties. At high concentrations, the GO-SA mixtures spontaneously produced liquid crystals (LCs) due to the template effect of GO, and continuous, 6 m long nacre-like GO-SA films were wet-spun from the obtained GO-SA liquid crystalline (LC) dope with a speed of up to 1.5 m/min. The assembled macroscopic GO-SA composites inherited the alignment of the GO sheets from the LC phase, and their mechanical properties were investigated by a joint experimental-computational study. The tensile tests revealed that the maximum strength (σ) and Young’s modulus (E) of the obtained films reached 239.6 MPa and 22.4 GPa, while the maximum values of σ and E for the fibers were 784.9 MPa and 58 GPa, respectively. The described wet-spinning assembly method is applicable for a large-scale and fast production of high-performance continuous artificial nacre.

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Reduction of threshold voltage fluctuation for organic field effect transistors by increase of insulator capacitance

Fluctuation of threshold voltages for top contact organic field effect transistors with pentacene active layers were successfully reduced by increase of gate insulator capacitance. Average fluctuation of threshold voltages of devices with 1000-nm-SiO₂-insulator was approximately 4 V, however it became only 0.5 V when the SiO₂ thickness was reduced to 100 nm. Since a vast number of transistors with constant threshold voltage are needed for application to displays, increase of capacitance would be a useful method for improving the reliability of OFETs.     

A facile method for fabrication of highly ordered hollow Ag/TiO2 nanostructure and its photocatalytic activity

This letter reports a facile and efficient strategy for the designed preparation of highly ordered hollow Ag/TiO₂ nanostructure. Different from previous reports, the presently proposed method conveniently combines the long-range ordering porosity and the property of Ag nanoparticles by a general colloidal crystal-templating technique. The sample was characterized by SEM and XRD. The results show that such hollow nanostructured material is composed of anatase TiO₂ and metal Ag. The as-prepared sample shows a good photocatalytic activity for photodegradation of methyl orange compared with the reference samples, which was attributed to its long-range ordering porosity and the addition of Ag nanoparticles.     

A multiple reflection model for the investigation of infrared transmission of a graphene/substrate system

We develop a multiple reflection model (MRM) for the examination of infrared transmission properties of a graphene/substrate system. The incident angle and the multiple reflection beams in the substrate with finite thickness are taken into consideration. The model can be applied to predict the optical responses of graphene/substrate systems or to extract the real part of the optical conductance of graphene from the experimental measurement. As an example, we calculate the relative transmittance of graphene/quartz and graphene/sapphire systems by using MRM and provide an experimental verification in the near-infrared range. The measured results show good agreement with the calculated ones. Our method can be easily extended to accurately and non-invasively identify the layer numbers of other 2D materials, and assess the quality of them.