Layer‐Controlled and Wafer‐Scale Synthesis of Uniform and High‐Quality Graphene Films on a Polycrystalline Nickel Catalyst

Chemical vapor deposition (CVD) provides a synthesis route for large‐area and high‐quality graphene films. However, layer‐controlled synthesis remains a great challenge on polycrystalline metallic films. Here, a facile and viable synthesis of layer‐controlled and high‐quality graphene films on wafer‐scale Ni surface by the sequentially separated steps of gas carburization, hydrogen exposure, and segregation is developed. The layer numbers of graphene films with large domain sizes are controlled precisely at ambient pressure by modulating the simplified CVD process conditions and hydrogen exposure. The hydrogen exposure assisted with a Ni catalyst plays a critical role in promoting the preferential segregation through removing the carbon layers on the Ni surface and reducing carbon content in the Ni. Excellent electrical and transparent conductive performance, with a room‐temperature mobility of ≈3000 cm² V^?1 s^?1 and a sheet resistance as low as ≈100 Ω per square at ≈90% transmittance, of the twisted few‐layer grapheme films grown on the Ni catalyst is demonstrated.     

FeCl3‐Based Few‐Layer Graphene Intercalation Compounds: Single Linear Dispersion Electronic Band Structure and Strong Charge Transfer Doping

Graphene has attracted much attention since its first discovery in 2004. Various approaches have been proposed to control its physical and electronic properties. Here, it is reported that graphene‐based intercalation is an efficient method to modify the electronic properties of few‐layer graphene (FLG). FeCl₃ intercalated FLGs are successfully prepared by the two‐zone vapor transport method. This is the first report on full intercalation for graphene samples. The features of the Raman G peak of such FLG intercalation compounds (FLGIC) are in good agreement with their full intercalation structures. The FLGICs present single Lorentzian 2D peaks, similar to that of single‐layer graphene, indicating the loss of electronic coupling between adjacent graphene layers. First principle calculations further reveal that the band structure of FLGIC is similar to single‐layer graphene but with a strong doping effect due to the charge transfer from graphene to FeCl₃. The successful fabrication of FLGIC opens a new way to modify properties of FLG for fundamental studies and future applications.     

铁基合金激光熔覆层的摩擦学特性

为评估激光熔覆技术修复塑料模具的磨损性能,采用铁基合金粉末在40Cr钢基体表面进行激光熔覆。激光熔覆层为上试样,GCr15钢球为下试样,利用HT-500磨损试验机进行摩擦磨损试验,研究在干摩擦、润滑条件下,激光熔覆层及其配副的摩擦学特性。利用表面形貌仪测量磨痕的深度和宽度,理论计算磨损率。研究结果表明,在干摩擦条件下,随载荷的增加,激光熔覆层及其配副的摩擦系数先降低后增加,当载荷为300 g时摩擦系数最小;随载荷的继续增加,摩擦系数逐渐增大。在相同载荷与润滑条件下,激光熔覆层及其配副的摩擦系数、磨损率、磨痕宽度均小于干摩擦条件下的值;随着磨损时间的增加,摩擦系数在磨损后期略有上升,磨损深度、磨损体积、磨损率逐渐增大。     

Flexible and Transparent Graphene Electrode Architecture with Selective Defect Decoration for Organic Light‐Emitting Diodes

Graphene produced by chemical vapor deposition (CVD) has attracted great interest as a transparent conducting material, due to its extraordinary characteristics such as flexibility, optical transparency, and high conductivity, especially in next‐generation displays. Graphene‐based novel electrodes have the potential to satisfy the important factors for high‐performance flexible organic light‐emitting diodes (OLEDs) in terms of sheet resistance, transmittance, work function, and surface roughness. In this study, flexible and transparent graphene electrode architecture is proposed by adopting a selective defect healing technique for CVD‐grown graphene, which results in several benefits that produce high‐performance devices with excellent stabilities. The proposed architecture, which has a multi‐layer graphene structure treated by a layer‐by‐layer healing process, exhibits significant improvement in sheet resistance with high optical transparency. For improving the charge transport property and mechanical robustness, various defect sites of the CVD‐grown graphene are successfully decorated with gold nanoparticles through a simple electroplating (EP) method. Further, a graphene‐based OLED device that integrates the proposed electrode architecture on flexible substrates is demonstrated. Therefore, this architecture provides a new strategy to fabricate graphene electrode in OLEDs, extending graphene's immense potential as an advanced conductor toward high‐performance, flexible, and transparent displays.     

Photoquantum Hall Effect and Light‐Induced Charge Transfer at the Interface of Graphene/InSe Heterostructures

The transfer of electronic charge across the interface of two van der Waals crystals can underpin the operation of a new class of functional devices. Among van der Waals semiconductors, an exciting and rapidly growing development involves the “post‐transition” metal chalcogenide InSe. Here, field effect phototransistors are reported where single layer graphene is capped with n‐type InSe. These device structures combine the photosensitivity of InSe with the unique electrical properties of graphene. It is shown that the light‐induced transfer of charge between InSe and graphene offers an effective method to increase or decrease the carrier density in graphene, causing a change in its resistance that is gate‐controllable and only weakly dependent on temperature. The charge transfer at the InSe/graphene interface is probed by Hall effect and photoconductivity measurmentes and it is demonstrated that light can induce a sign reversal of the quantum Hall voltage and photovoltaic effects in the graphene layer. These findings demonstrate the potential of light‐induced charge transfer in gate‐tunable InSe/graphene phototransistors for optoelectronics and quantum metrology.     

Graphene Versus Carbon Nanotubes in Electronic Devices

Advances in semiconductor device during last few decades enable us to improve the electronic device performance by minimizing the device dimension. However, further development of these systems encounters scientific and technological limits and forces us to explore better alternatives. Low‐dimensional carbon allotropes such as carbon nanotube and graphene exhibit superior electronic, optoelectronic, and mechanical properties compared to the conventional semiconductors. This Feature Article reviews the recent progresses of carbon nanotubes and graphene researches and compares their electronic properties and electric device performances. A particular focus is the comparison of the characteristics in transparent conducting films (transparency and sheet resistance) and field‐effect transistors (FETs) (device types, ambipolarity, mobility, doping strategy, FET‐performance, logic and memory operations). Finally, the performance of devices that combine graphene and carbon nanotubes is also highlighted.     

Robust Fabrication of Nonstick,Noncorrosive, Conductive Graphene‐Coated Liquid Metal Droplets for Droplet‐Based,Floating Electrodes

Nontoxic liquid metals (conductive materials in a liquid state at room temperature) are an emerging class of materials for applications ranging from soft electronics and robotics to medical therapy and energy devices. Their sticky and corrosive properties, however, are becoming more of a critical concern for circuits and devices containing other metals as these are easily destroyed or contaminated by the liquid metals. Herein, a feasible method for fabricating highly conductive graphene‐coated liquid metal (GLM) droplets is reported and their application as nonstick, noncorrosive, movable, soft contacts for electrical circuits is demonstrated. The as‐prepared GLM droplets consist of a liquid‐phase soft core of liquid metal and a slippery outer layer of graphene sheets. These structures address the issue of simultaneous control of the wettability and conductivity of a soft electronic contact by combining extraordinary properties, i.e., nonstick, noncorrosive, yet exhibiting high electronic conductivity while in contact with metal substrates, e.g., Au, Cu, Ag, and Ni. As proof‐of‐concept, the as‐prepared GLM droplets are demonstrated as floating electrodes for movable, recyclable electronic soft contacts in electrical circuits.     

激光冲击20CrNiMo钢表面微造型摩擦学性能研究

为了探索激光冲击20CrNiMo钢表面微造型摩擦学性能,从表层微观结构和表面宏观形貌两个角度,研究了激光冲击强化的方法对20CrNiMo钢表面摩擦磨损性能的影响。采用激光以不同搭接率搭接冲击20CrNiMo钢,用透射电子显微镜观察激光搭接冲击20CrNiMo钢试样表层微观组织结构,取得了试样表层晶粒状态的照片;采用CETR UMT摩擦磨损试验机对其进行摩擦磨损试验,取得了试样表面摩擦系数和磨损量的数据。结果表明,激光冲击强化作用可以导致20CrNiMo钢试样表层晶粒细化,在磨损过程中,晶粒细化层明显抑制表面疲劳磨损的产生,从而提高其耐磨性能;激光冲击搭接率越高,金属材料表面的摩擦磨损性能越好。     

Engineering of Graphene Layer Orientation to Attain High Rate Capability and Anisotropic Properties in Li‐Ion Battery Electrodes

Novel carbon films with different graphene layer orientations are investigated as electrode materials for Li‐ion batteries. It is demonstrated that engineering the crystallographic orientation with graphene layers oriented perpendicular to the surface substantially alters stress evolution during Li insertion. With this crystallographic orientation the intercalating/de‐intercalating Li‐ions also have direct access to the graphene interlayer spaces, resulting in higher capacity at faster electrochemical cycling, compared to carbon films with graphene layers parallel to the film surface. Electrodes with perpendicular alignment are prepared by supramolecular synthesis using either spin coating or bar coating of chromonic liquid crystal precursors into precursor organic films followed by in situ carbonization. These materials are compared with in situ stress measurements during lithiation/delithiation cycles, and the bar‐coated films exhibit a highly anisotropic stress which is consistent with long‐range alignment of the graphene layers. In contrast, the in‐plane stresses in the spin‐coated films are isotropic, which is consistent with the presence of randomly oriented domains (still with graphene layers oriented perpendicular to the surface). Overall, the use of thin film graphitic materials with controlled crystallographic orientations provides a valuable platform for investigating the impact of graphene structure on the properties of Li‐ion battery electrode materials.     

Graphene‐Based Nanomaterials: Synthesis,Properties, and Optical and Optoelectronic Applications

Graphene, a two‐dimensional, single‐atom‐thick carbon crystal arranged in a honeycomb lattice, shows extraordinary electronic, mechanical, thermal, optical, and optoelectronic properties, and has great potential in next‐generation electronics, optics, and optoelectronics. Graphene and graphene‐based nanomaterials have witnessed a very fast development of both fundamental and practical aspects in optics and optoelectronics since 2008. In this Feature Article, the synthesis techniques and main electronic and optical properties of graphene‐based nanomaterials are introduced with a comprehensive view. Recent progress of graphene‐based nanomaterials in optical and optoelectronic applications is then reviewed, including transparent conductive electrodes, photodetectors and phototransistors, photovoltaics and light emitting devices, saturable absorbers for ultrafast lasers, and biological and photocatalytic applications. In the final section, perspectives are given and future challenges in optical and optoelectronic applications of graphene‐based nanomaterials are addressed.     

激光熔覆镍基金属陶瓷涂层的组织性能研究

运用 5kWCO2 连续激光器在 16Mn钢表面激光熔覆镍基B4 C金属陶瓷层 (NB4 C)和镍基SiC金属陶瓷层(NSiC) ,研究了两种激光熔覆层的组织、结构、显微硬度及滑动磨损特性 ,并用激光熔覆镍基合金层 (Ni6 0 )进行了滑动磨损对比试验。结果表明 ,熔覆合金层显微组织由枝晶固溶体及其间细密的共晶组织组成 ,NB4 C熔覆层主要组成相为γ Ni,γ (Ni,Fe) ,(Cr,Fe) 7C3,CrB ,Ni3B ,Fe2 B ,Fe2 3(C ,B) 6 和B4 C等 ,NSiC熔覆层主要组成相为γ Ni,γ (Fe,Ni) ,(Cr,Fe) 7C3,Cr2 3C6 和 (Cr ,Si) 3Ni3Si等。三种激光熔覆层的显微硬度及耐滑动磨损性能由高到低的顺序为 :NB4 C→NSiC→Ni6 0。     

Fatigue‐Resistant Bioinspired Graphene‐Based Nanocomposites

Graphene is an attractive building block for constructing functional materials of flexible electronic devices, due to its extraordinary mechanical and electrical properties. Up to now, large amounts of high‐performance graphene‐based nanocomposites are fabricated. However, the fatigue behavior of graphene‐based nanocomposites, a key parameter for flexible electronic devices, is rarely investigated. According to the fatigue mechanisms of thermosetting polymer composites, the fatigue resistance of graphene‐based nanocomposites can be significantly improved by effectively restricting the crack growth. Natural nacre demonstrates unique multisuppression of crack propagation, which is attributed to its sophisticated interfacial architecture over multiple length scales, resulting in remarkable fracture toughness. The crack suppression mechanisms corresponding to different interfacial design strategies within bioinspired graphene‐based nanocomposites (BGBNs) are summarized in this feature article. The static mechanical properties, electrical conductivity, and fatigue resistance of these BGBNs are compared and discussed. The synergistic effect from various interfacial interactions and building blocks is highlighted to serve as the guidance for constructing novel fatigue‐resistant BGBNs. The promising applications of fatigue‐resistant BGBNs in flexible electronic devices are reviewed, and several challenges and corresponding solutions are proposed. The perspective of fatigue‐resistant BGBNs for fundamental research and commercial application is depicted.     

Facile Doping and Work‐Function Modification of Few‐Layer Graphene Using Molecular Oxidants and Reductants

Doping of graphene is a viable route toward enhancing its electrical conductivity and modulating its work function for a wide range of technological applications. In this work, the authors demonstrate facile, solution‐based, noncovalent surface doping of few‐layer graphene (FLG) using a series of molecular metal‐organic and organic species of varying n‐ and p‐type doping strengths. In doing so, the authors tune the electronic, optical, and transport properties of FLG. The authors modulate the work function of graphene over a range of 2.4 eV (from 2.9 to 5.3 eV)—unprecedented for solution‐based doping—via surface electron transfer. A substantial improvement of the conductivity of FLG is attributed to increasing carrier density, slightly offset by a minor reduction of mobility via Coulomb scattering. The mobility of single layer graphene has been reported to decrease significantly more via similar surface doping than FLG, which has the ability to screen buried layers. The dopant dosage influences the properties of FLG and reveals an optimal window of dopant coverage for the best transport properties, wherein dopant molecules aggregate into small and isolated clusters on the surface of FLG. This study shows how soluble molecular dopants can easily and effectively tune the work function and improve the optoelectronic properties of graphene.     

Microtribological and Nanomechanical Properties of Switchable Y‐Shaped Amphiphilic Polymer Brushes

We have characterized the morphology and nanomechanical properties of surface‐grafted nanoscale layers consisting of Y‐shaped binary molecules with one polystyrene (PS) arm and one poly(acrylic acid) (PAA) arm. We examined these amphiphilic brushes in fluids (in‐situ visualization), and measured their microtribological characteristics as a function of chemical composition. Atomic force microscopy (AFM)‐based nanomechanical testing has shown that nanoscale reorganization greatly influences the adhesion and elastic properties of the nanoscale brush layer. In water, a bimodal distribution of the elastic modulus, arising from the mixed chemical composition of the topmost layer, is observed. In contrast, the top layer is completely dominated by PS in toluene. As a result of this reorganization, the Y‐shaped‐brush layer exhibits a dramatic variation in the friction and wear properties after exposure to different solvents. Unexpectedly, the tribological properties are enhanced for the hydrophilic and polar, PAA‐dominated, surface, which shows a lower friction coefficient and higher wear stability, despite higher adhesion and heterogeneous surface composition. We suggest that this unusual behavior is caused by the combination of the presence of a thicker water layer on the PAA‐enriched surface that acts as a boundary lubricant and the glassy state of the PAA chains.     

Nonvolatile Charge Injection Memory Based on Black Phosphorous 2D Nanosheets for Charge Trapping and Active Channel Layers

2D van der Waals atomic crystal materials have great potential for use in future nanoscale electronic and optoelectronic applications owing to their unique properties such as a tunable energy band gap according to their thickness or number of layers. Recently, black phosphorous (BP) has attracted significant interest because it is a single‐component material like graphene and has high mobility, a direct band gap, and exhibits ambipolar transition behavior. This study reports on a charge injection memory field‐effect transistor on a glass substrate, where few‐layer BPs act as the active channel and charge trapping layers, and Al₂O₃ films grown by atomic layer deposition act as the tunneling and blocking layers. Because of the ambipolar properties of BP nanosheets, both electrons and holes are involved in the charge trapping process, resulting in bilateral threshold voltage shifts with a large memory window of 22 V. Finally, a memory circuit of a resistive‐load inverter is implemented that converts analog signals (current) to digital signals (voltage). Such a memory inverter also shows a clear memory window and distinct memory on/off switching characteristics.     

Nanotribology and nanomechanics of MEMS/NEMS and BioMEMS/BioNEMS materials and devices

The micro/nanoelectromechanical systems (MEMS/NEMS) need to be designed to perform expected functions typically in millisecond to picosecond range. Expected life of the devices for high speed contacts can vary from few hundred thousand to many billions of cycles, e.g., over a hundred billion cycles for digital micromirror devices (DMDs), which puts serious requirements on materials. For BioMEMS/BioNEMS, adhesion between biological molecular layers and the substrate, and friction and wear of biological layers may be important. There is a need for development of a fundamental understanding of adhesion, friction/stiction, wear, and the role of surface contamination, and environment. Most mechanical properties are known to be scale dependent. Therefore, the properties of nanoscale structures need to be measured. MEMS/NEMS materials need to exhibit good mechanical and tribological properties on the micro/nanoscale. There is a need to develop lubricants and identify lubrication methods that are suitable for MEMS/NEMS. Methods need to be developed to enhance adhesion between biomolecules and the device substrate. Component-level studies are required to provide a better understanding of the tribological phenomena occurring in MEMS/NEMS. The emergence of micro/nanotribology and atomic force microscopy-based techniques has provided researchers a viable approach to address these problems. This paper presents a review of micro/nanoscale adhesion, friction, and wear studies of materials and lubrication studies for MEMS/NEMS and BioMEMS/BioNEMS, and component-level studies of stiction phenomena in MEMS/NEMS devices.     

AISI 8620合金钢激光冲击强化层摩擦学特性

采用高能量激光束对AISI 8620合金钢表面进行冲击强化,利用CETR UMT-2摩擦磨损试验机对激光冲击试样表面进行磨损试验,并用扫描电子显微镜观察磨痕表面的形貌,研究激光冲击强化技术对AISI 8620合金钢耐磨损性能的影响。结果表明,激光冲击在AISI 8620合金钢表层形成残余压应力层,虽然残余压应力会降低氧化磨损和粘着磨损的抗性,但是会增加疲劳磨损的抗性,使AISI 8620合金钢试样的耐磨性提高1倍,多次冲击耐磨性能会更好。随着载荷的增加,激光冲击的AISI 8620合金钢试样的平均摩擦系数呈现先缓慢减小后缓慢增加的趋势。     

X‐Ray Spectroscopic Investigation of Chlorinated Graphene: Surface Structure and Electronic Effects

Chemical doping of graphene represents a powerful means of tailoring its electronic properties. Synchrotron‐based X‐ray spectroscopy offers an effective route to investigate the surface electronic and chemical states of functionalizing dopants. In this work, a suite of X‐ray techniques is used, including near edge X‐ray absorption fine structure spectroscopy, X‐ray photoemission spectroscopy, and photoemission threshold measurements, to systematically study plasma‐based chlorinated graphene on different substrates, with special focus on its dopant concentration, surface binding energy, bonding configuration, and work function shift. Detailed spectroscopic evidence of C–Cl bond formation at the surface of single layer graphene and correlation of the magnitude of p‐type doping with the surface coverage of adsorbed chlorine is demonstrated for the first time. It is shown that the chlorination process is a highly nonintrusive doping technology, which can effectively produce strongly p‐doped graphene with the 2D nature and long‐range periodicity of the electronic structure of graphene intact. The measurements also reveal that the interaction between graphene and chlorine atoms shows strong substrate effects in terms of both surface coverage and work function shift.     

Thermally Controlled,Patterned Graphene Transfer Printing for Transparent and Wearable Electronic/Optoelectronic System

Graphene has been highlighted as a platform material in transparent electronics and optoelectronics, including flexible and stretchable ones, due to its unique properties such as optical transparency, mechanical softness, ultrathin thickness, and high carrier mobility. Despite huge research efforts for graphene‐based electronic/optoelectronic devices, there are remaining challenges in terms of their seamless integration, such as the high‐quality contact formation, precise alignment of micrometer‐scale patterns, and control of interfacial‐adhesion/local‐resistance. Here, a thermally controlled transfer printing technique that allows multiple patterned‐graphene transfers at desired locations is presented. Using the thermal‐expansion mismatch between the viscoelastic sacrificial layer and the elastic stamp, a “heating and cooling” process precisely positions patterned graphene layers on various substrates, including graphene prepatterns, hydrophilic surfaces, and superhydrophobic surfaces, with high transfer yields. A detailed theoretical analysis of underlying physics/mechanics of this approach is also described. The proposed transfer printing successfully integrates graphene‐based stretchable sensors, actuators, light‐emitting diodes, and other electronics in one platform, paving the way toward transparent and wearable multifunctional electronic systems.     

激光熔覆Ni35+11%wc熔覆层的组织及耐腐蚀研究

镍基合金熔覆层的耐腐蚀、耐磨性、硬度,是45钢零件表面技术改性的理想熔覆层。为节约45钢的成本,增加45钢零件使用寿命,研究了激光熔覆Ni35+11%wc熔覆层的组织及耐腐蚀性。采用Xrd、维氏硬度计,磨损实验,电化学腐蚀方式研究熔覆层的组织和性能。结果表明:熔覆层的主相为Fe2Ni7Si20、NiSi,与基体冶金结合良好。熔覆层的硬度值均在730 HV左右,自腐蚀电位是-0.833 V,自腐蚀电流密度是 0.981 A/m2,熔覆层tafel曲线正向偏移耐腐蚀性有所提高,熔覆层的磨擦系数低于基体。