复杂电磁环境下装甲部队通信干扰与抗干扰探析

石墨烯优异的电学、光学和力学性能掀起了多领域的研究热潮,其制备方法也成为重点研究方向。机械剪切剥离法成本低,操作简单,且不会破坏石墨烯本征特性等特性,备受研究者关注。文中介绍了石墨烯的性质和剥离机理,并阐述了机械剥离法中低能纯剪法、三辊磨剥法和球磨法,比较了各方法的特点及面临的问题。由于球磨法是目前最有望大规模制造石墨烯的方法,故文中优化了球磨工艺,提出了一种磨盘式结构球磨机。该球磨机有效避免了磨球之间的撞击力,保护石墨晶格免于破环,提高了剪切效率。     

电化学剥离制备石墨烯及其光电特性研究进展

石墨烯是一种新型的二维纳米碳材料,具有优良的物理、化学和机械性能,在储能器件、电子器件以及复合材料等诸多领域有广阔的应用前景。石墨烯的产业化生产一直是现在国际上材料科学研究的热点。在石墨烯的诸多制备方法中,电化学剥离方法具有快速高效、绿色环保等特点,有望实现产业化。首先综述了最近国内外电化学剥离法制备石墨烯和类石墨烯材料(BN和MoS2)的研究进展,并对其反应机理进行了探讨,然后简单介绍了石墨烯在光电子器件领域的研究现状和应用,最后对石墨烯前景进行了展望。     

石墨烯的制备与应用研究进展

综述了石墨烯的分类、重要的制备方法包括化学气相沉积法、电弧放电法和剥离法等,以及其在电子器件、电容器、场发射、复合材料和储能等领域应用的研究进展。探讨了石墨烯真正走向应用领域需要解决的问题。最后评述了石墨烯纳米材料研究的发展趋势和应用前景。     

石墨烯的制备及研究现状

阐述了石墨烯的制备方法如机械剥离法、氧化石墨还原法、加热SiC法和化学气相沉积法等,分析了各种制备方法的优缺点。论述了石墨烯在纳米电子器件、取代硅芯片、制造最快的碳晶体管、减少噪声和潜在的储氢材料领域等方面的应用,同时简要分析了石墨烯的结构对其性质的影响,展望了其未来的发展前景。     

氧化程度对热剥离石墨烯电化学性能的影响

采用改进Hummers法,在不同KMnO4用量下制得了不同氧化程度的系列氧化石墨,并以其为前驱体在N2中经400℃热还原制备了石墨烯。利用XRD、FT-IR、Raman光谱与SEM表征了所得石墨烯的结构、官能团及表面形貌,通过循环伏安和恒流充放电测试研究了氧化石墨的氧化程度对石墨烯电化学性能的影响。结果表明,当KMnO4用量较低(1.0 g)时,前驱体氧化程度较低,不能被剥离;当KMnO4用量较高(≥1.0 g)时,前驱体氧化程度增高,可实现剥离制备石墨烯。随着前驱体氧化程度增加,所制石墨烯堆叠层数与sp2平均尺寸逐渐减小,含氧官能团与缺陷逐渐增多,比容量逐渐增大。     

石墨烯/Si晶体管的研究进展

石墨烯具有很多优异的力学、电学和结构特性,可用于制备高速、低功耗的半导体电子器件和集成电路芯片。简要介绍了三种石墨烯/Si的制备方法,即剥离法、外延法、剪切和选择转移印刷法,其中外延生长的石墨烯被认为是最终实现碳集成电路的唯一途径。并给出了采用上述方法制备的石墨烯/Si晶体管的电阻、磁阻、载流子迁移和输运特性以及量子霍尔效应(QHE)等电学特性。发现石墨烯/Si晶体管最高频率达155GHz,在室温下具有异常的量子霍尔效应和分数量子霍尔效应。其电荷载流子浓度在电子和空穴之间连续变化,可高达1013 cm-2,迁移率可达2×105 cm2/(V.s)。     

超级电容器用石墨烯纳米片的制备及性能

通过在低温、常压条件下热剥离氧化石墨(GO)前驱体制备了石墨烯纳米片,然后用其制成了超级电容器。利用XRD、FT-IR、SEM和TEM对所制石墨烯纳米片的物相组成和形貌进行了分析,另外,采用循环伏安、恒流充放电和交流阻抗谱技术对所制超级电容器的超级电容性能进行了研究。结果表明:GO在200℃、常压下即可被有效热剥离;所制超级电容器在6 mol/L KOH体系中的最大比电容约为276 F/g。     

多肽聚合物对氧化石墨烯材料稳定性的研究

为进一步提高氧化石墨烯在水溶剂中的稳定性,文中采用多肽聚合物对氧化石墨烯进行表面改性。傅里叶红外变换光谱和热重分析表明,两者可以通过非共价键的方式进行复合。然后,用紫外可见光吸收光谱法测定分散液浓度,表征氧化石墨烯分散液的稳定情况,并探索多肽聚合物修饰氧化石墨烯时的最佳添加量,在此基础上又探索了多肽聚合物对氧化石墨烯在水溶剂中长期稳定性的影响。实验结果表明,在氧化石墨烯浓度为1 mg/mL的条件下,当加入的多肽聚合物与氧化石墨烯的质量比为3:100时,可以有效避免氧化石墨烯片层的再次团聚,经多肽聚合物修饰过的氧化石墨烯在水溶剂中表现出良好的稳定性,且经过8周静止后也没有明显的沉淀产生。     

碳化硅衬底外延石墨烯

通过高温热解法和化学气相沉积(CVD)法在SiC(0001)衬底外延石墨烯。采用光学显微镜、原子力显微镜、扫描电子显微镜、喇曼光谱、X射线光电子能谱和霍尔测试系统对样品进行表征,并对比了两种不同生长方法对石墨烯材料的影响以及不同的成核机理。结果表明,高温热解法制备的石墨烯材料有明显的台阶形貌,台阶区域平坦均匀,褶皱少,晶体质量取决于SiC衬底表面原子层,电学特性受衬底影响大,迁移率较低。CVD法制备的石墨烯材料整体均匀,褶皱较多,晶体质量更好。该方法制备的石墨烯薄膜悬浮在SiC衬底表面,与衬底之间为范德华力连接,电学特性受衬底影响小,迁移率较高。     

无结场效应管——新兴的后CMOS器件研究进展(续)北大核心CSCD

EEACC:2500目前,在衬底上形成石墨烯的主要方法有:(1)石墨晶体表面剥离/转移方法。采用胶带从石墨晶体表面剥离一层石墨烯并转移到衬底上[107]。(2)化学气相沉积/转移方法。大约在800~1 000°C温度下,将石墨烯生长在金属催化剂膜上,然后剥离转移到别的衬底上[123]。(3)SiC表面分解方法。在1 200~1     

The Exfoliation of Graphene in Liquids by Electrochemical,Chemical, and Sonication‐Assisted Techniques: A Nanoscale Study

The different exfoliation routes of graphite to produce graphene by sonication in solvent, chemical oxidation and electrochemical oxidation are compared. The exfoliation process and roughening of a flat graphite substrate is directly visualized at the nanoscale by scanning probe and electron microscopy. The etching damage in graphite and the properties of the exfoliated sheets are compared by Raman spectroscopy and X‐ray diffraction analysis. The results show the trade‐off between exfoliation speed and preservation of graphene quality. A key step to achieve efficient exfoliation is to couple gas production and mechanical exfoliation on a macroscale with non‐covalent exfoliation and preservation of graphene properties on a molecular scale.     

High-Conductivity–Dispersibility Graphene Made by Catalytic Exfoliation of Graphite for Lithium-Ion Battery

Despite the progress made on the production of graphene using liquid-phase exfoliation methods, the fabrication of graphene with both high conductivity and dispersibility remains challenging. Through catalytic exfoliation of graphite, an effective synthesis method for graphene with large lateral size (≈10 µm), high conductivity (926 S cm^–1), and excellent water solubility (≈10 mg mL^–1) is reported herein. Such graphene can be used broadly for applications such as lithium ion batteries, where both high conductivity and dispersibility are required. As an example, the synthesis of graphene and lithium-iron-phosphate composites is demonstrated, which leads to electrodes with dramatically improved cycling stability and rate performance. Adaption of such material leads to electrodes with volumetric energy density as high as 658.7 and 287.6 W h L^–1 under 0.5 and 20 C, respectively, which is significantly higher than that of commercial LiFePO₄ (394.7 and 13.5 W h L^–1 at 0.5 and 20 C, respectively). This work provides a new method of making high-conductivity–dispersibility graphene for various applications.     

Kitchen Chemistry 101: Multigram Production of High Quality Biographene in a Blender with Edible Proteins

A high yielding aqueous phase exfoliation of graphite to high quality graphene using edible proteins and kitchen chemistry is reported here. Bovine serum albumin (BSA), β‐lactoglobulin, ovalbumin, lysozyme, and hemoglobin are used to exfoliate graphite and the exfoliation efficiency depended on the sign and magnitude of the protein charge. BSA showed maximum exfoliation rate, facilitated graphite exfoliation in water, at room temperature, by turbulence/shear force generated in a kitchen blender at exfoliation efficiencies exceeding 4 mg mL^?1 h^?1. Raman spectroscopy and transmission electron microscopy indicated 3–5 layer, defect‐free graphene of 0.5 μm size. Graphene dispersions loaded on a cellulose paper (650 μg cm^?2) showed the film conductivity of 32 000 S m^?1, which is much higher than graphene/polymer composites. Our method yielded ≈7 mg mL^?1, BSA‐coated graphene with controllable surface charge, which is stable under wide ranges of pH (3.0–11) and temperature (5.0–50 °C), and in fetal bovine serum, for more than two months.These findings may lead to the large scale production of graphene for biological applications.     

Simultaneous Electrochemical Dual‐Electrode Exfoliation of Graphite toward Scalable Production of High‐Quality Graphene

Developing scalable methods to produce large quantities of high‐quality and solution‐processable graphene is essential to bridge the gap between laboratory study and commercial applications. Here an efficient electrochemical dual‐electrode exfoliation approach is developed, which combines simultaneous anodic and cathodic exfoliation of graphite. Newly designed sandwich‐structured graphite electrodes which are wrapped in a confined space with porous metal mesh serve as both electrodes, enabling a sufficient ionic intercalation. Mechanism studies reveal that the combination of electrochemical intercalation with subsequent thermal decomposition results in drastic expansion of graphite toward high‐efficiency production of graphene with high quality. By precisely controlling the intercalation chemistry, the two‐step approach leads to graphene with outstanding yields (85% and 48% for cathode and anode, respectively) comprising few‐layer graphene (1–3 layers, >70%), ultralow defects (I_D/I_G < 0.08), and high production rate (exceeding 25 g h^?1). Moreover, its excellent electrical conductivity (>3 × 10⁴ S m^?1) and great solution dispersibility in N‐methyl pyrrolidone (10 mg mL^?1) enable the fabrication of highly conductive (11 Ω sq^?1) and flexible graphene films by inkjet printing. This simple and efficient exfoliation approach will facilitate the development of large‐scale production of high‐quality graphene and holds great promise for its wide application.     

Spontaneous Formation of Liquid Crystals in Ultralarge Graphene Oxide Dispersions

A novel process is developed to synthesize graphene oxide sheets with an ultralarge size based on a solution‐phase method involving pre‐exfoliation of graphite flakes. Spontaneous formation of lyotropic nematic liquid crystals is identified upon the addition of the ultralarge graphene oxide sheets in water above a critical concentration of about 0.1 wt%. It is the lowest filler content ever reported for the formation of liquid crystals from any colloid, arising mainly from the ultrahigh aspect ratio of the graphene oxide sheets of over 30 000. It is proposed that the self‐assembled brick‐like graphene oxide nanostructure can be applied in many areas, such as energy‐storage devices and nanocomposites with a high degree of orientation.     

Modification of Chemically Exfoliated Graphene to Produce Efficient Piezoresistive Polystyrene–Graphene Composites

We report the chemical exfoliation of grapheneoxide from graphite and its subsequent reduction to graphene nanosheets (GN) to obtain highly conducting composites of graphene sheets in a polymer matrix. The effect of using graphite nanoparticles or flakes as precursors, and different drying methods, was investigated to obtain multilayer graphene sheets of atomically controlled thickness, which was essential to optimizing their dispersion in a polystyrene (PS) polymer matrix. In situ emulsion polymerization of the styrene monomer in the presence of GN was performed to obtain thin composite films with highly uniform dispersion and fewer graphene layers when GN were obtained from graphite flakes then freeze drying. The highest electrical conductivity of PS–GN composites was ~0.01 S/m for a graphene filling fraction of 2%. The piezoresistance of the PS–GN composites was evaluated and used in pressure sensor arrays with pressure field imaging capability.     

Two-dimensional air-stable CrSe2 nanosheets with thickness-tunable magnetism

Since Geim et al.firstly separated graphene from graph-ite by mechanical exfoliation method in 2004,the research of two-dimensional (2D) van der Waals (vdW) layered materials has begun[1].Compared with three-dimensional materials,2D vdW layered materials exposing the most atoms to exterior are more sensitive to external control and have the great po-tential applications in electronic,optoelectronic and electro-chemical area[2].     

Synthesis of Graphene Sheets and Characterization of Poly(3-hexylthiophene):Graphene Blends

Graphite is a bulk-layered material that can be separated into sheets which exhibit folds and pleat-like structures. Graphene sheets are easily obtained via an exfoliation process using graphite in organic solvent. Spin-coated graphene:poly(3-hexylthiophene) (P3HT) blend films are characterized by absorption and photoluminescence spectroscopy measurements. Doping of 2.5% graphene into P3HT induces better light absorption and photoluminescence quenching in the blend film. This finding indicates that graphene is a potential alternative material in various applications such as an acceptor material in organic solar cells.