铜基底预处理对CVD法生长石墨烯薄膜的影响

化学气相沉积法是制备大尺寸、高质量石墨烯的有效方法, 其中金属催化剂的性能直接关系到所制备的石墨烯材料的品质, 因此需对金属催化剂进行表面预处理。本文研究了不同的预处理工艺对常用的铜基底催化剂表面状态的影响, 提出了钝化膏酸洗和电化学抛光协同处理的有效方法, 并对电化学抛光工艺参数(抛光电压、时间)以及铜基底退火工艺(退火温度、时间)等进行了系统研究。研究表明: 电化学抛光电压过高、抛光时间过长容易导致过度抛光, 合适的抛光电压和抛光时间分别为8 V和8 min。退火温度和时间对铜催化剂表面晶粒形态影响较大, 经1000 ℃退火处理30 min后, 铜箔表面晶粒尺寸更大, 分布更均匀。此外, 对CVD法生长制备的石墨烯样品进行表征, 电镜图片和拉曼光谱显示, 获得的石墨烯薄膜的层数较少, 且结构缺陷较少。     

化学气相沉积制备大面积高质量石墨烯的研究进展

石墨烯是由单层碳原子紧密堆积形成的一种碳质新材料,具有优良的电学、光学、热学及力学等性质。在众多的石墨烯制备方法中,化学气相沉积(Chemical vapor deposition,CVD)最有可能实现大面积、高质量石墨烯的可控制备。综述了CVD方法制备大面积、高质量石墨烯的影响因素,包括衬底、碳源及生长条件(气体流量、生长温度、等离子体功率、生长压强、沉积时间、冷却速率等)。最后展望了CVD方法制备石墨烯的发展方向。     

铜基底化学气相沉积石墨烯的研究现状与展望

采用粉末包埋法在中国低活性铁素体马氏体钢（RAFM）基底上制备了低活性渗铝层,利用扫描电镜（SEM）和能谱分析（EDS）对渗铝层的形貌和成分进行了分析。结果表明：低活性渗铝层表面铝含量（原子分数）约40％,主要由厚度为15-20μm的FeAl、Fe3-Al及α-Fe（Al）相组成,该渗铝层表面易发生烧结。为避免表面烧结...     

Graphene Coating of Silicon Nanoparticles with CO2‐Enhanced Chemical Vapor Deposition

Understanding the growth of graphene over Si species is becoming ever more important as the huge potential for the combination of these two materials becomes more apparent, not only for device fabrication but also in energy applications, particularly in Li‐ion batteries. Thus, the drive for the direct fabrication of graphene over Si is crucial because indirect approaches, by their very nature, require processing steps that, in general, contaminate, damage, and are costly. In this work, the direct chemical vapor deposition growth of few‐layer graphene over Si nanoparticles is systematically explored through experiment and theory with the use of a reducer, H₂ or the use of a mild oxidant, CO₂ combined with CH₄. Unlike the case of CH₄, with the use of CO₂ as a mild oxidant in the reaction, the graphene layers form neatly over the surface and encapsulate the Si particles. SiC formation is also prevented. These structures show exceptionally good electrochemical performance as high capacity anodes for lithium‐ion batteries. Density functional theory studies show the presence of CO₂ not only prevents SiC formation but helps enhance the catalytic activity of the particles by maintaining an SiO_x surface. In addition, CO₂ can enhance graphitization.     

Predictive Synthesis of Freeform Carbon Nanotube Microarchitectures by Strain‐Engineered Chemical Vapor Deposition

High‐throughput fabrication of microstructured surfaces with multi‐directional, re‐entrant, or otherwise curved features is becoming increasingly important for applications such as phase change heat transfer, adhesive gripping, and control of electromagnetic waves. Toward this goal, curved microstructures of aligned carbon nanotubes (CNTs) can be fabricated by engineered variation of the CNT growth rate within each microstructure, for example by patterning of the CNT growth catalyst partially upon a layer which retards the CNT growth rate. This study develops a finite‐element simulation framework for predictive synthesis of complex CNT microarchitectures by this strain‐engineered growth process. The simulation is informed by parametric measurements of the CNT growth kinetics, and the anisotropic mechanical properties of the CNTs, and predicts the shape of CNT microstructures with impressive fidelity. Moreover, the simulation calculates the internal stress distribution that results from extreme deformation of the CNT structures during growth, and shows that delamination of the interface between the differentially growing segments occurs at a critical shear stress. Guided by these insights, experiments are performed to study the time‐ and geometry‐depended stress development, and it is demonstrated that corrugating the interface between the segments of each microstructure mitigates the interface failure. This study presents a methodology for 3D microstructure design based on “pixels” that prescribe directionality to the resulting microstructure, and show that this framework enables the predictive synthesis of more complex architectures including twisted and truss‐like forms.     

固态碳源温度对CVD法生长石墨烯薄膜影响的研究

以聚苯乙烯为固态碳源,抛光铜箔为衬底,通过改变固态碳源的温度探索了固态碳源温度对双温区化学气相沉积法生长石墨烯的影响。样品采用拉曼散射光谱、紫外-可见分光光度计和扫描电子显微镜进行了表征。结果表明,固态碳源温度的变化直接影响了气相碳源浓度,通过控制固态碳源温度,可以控制所得石墨烯的层数。固态碳源动态变温生长能够在生长的起始阶段降低石墨烯形核密度,同时打破晶粒长大时氢气刻蚀速率与石墨烯生长速率的动态平衡,可以有效地提升石墨烯的覆盖率。最终在衬底温度为1000℃条件下使用固态碳源动态变温制备了I2D/IG达到2.91,透过率为97.6%的高质量单层石墨烯薄膜。     

绝缘衬底对CVD生长石墨烯的影响研究进展

石墨烯自从2004年问世之后,由于独特的结构和优异的性能很快便成为了碳素家族的明星而引起了各界的关注.石墨烯独特的电学性能使其有望替代硅成为下一代半导体工业的主角.然而要实现石墨烯电子器件的构建,必须先解决在绝缘或半导体衬底上直接制备石墨烯的难题.综述了近几年不同绝缘衬底对化学气相沉积法制备石墨烯所产生的影响,分析比较了不同绝缘衬底的优缺点,并展望了石墨烯的发展及应用前景.     

Multilayer Stacked Low‐Temperature‐Reduced Graphene Oxide Films: Preparation,Characterization, and Application in Polymer Memory Devices

Highly reduced graphene oxide (rGO) films are fabricated by combining reduction with smeared hydrazine at low temperature (e.g., 100 °C) and the multilayer stacking technique. The prepared rGO film, which has a lower sheet resistance (≈160–500 Ω sq⁻¹) and higher conductivity (26 S cm⁻¹) as compared to other rGO films obtained by commonly used chemical reduction methods, is fully characterized. The effective reduction can be attributed to the large “effective reduction depth” in the GO films (1.46 µm) and the high C1s/O1s ratio (8.04). By using the above approach, rGO films with a tunable thickness and sheet resistance are achieved. The obtained rGO films are used as electrodes in polymer memory devices, in a configuration of rGO/poly(3‐hexylthiophene) (P3HT):phenyl‐C61‐butyric acid methyl ester (PCBM)/Al, which exhibit an excellent write‐once‐read‐many‐times effect and a high ON/OFF current ratio of 10⁶.     

Laser‐Assisted Lattice Recovery of Graphene by Carbon Nanodot Incorporation

Producing highly oriented graphene is a major challenge that constrains graphene from fulfilling its full potential in technological applications. The exciting properties of graphene are impeded in practical bulk materials due to lattice imperfections that hinder charge mobility. A simple method to improve the structural integrity of graphene by utilizing laser irradiation on a composite of carbon nanodots (CNDs) and 3D graphene is presented. The CNDs attach themselves to defect sites in the graphene sheets and, upon laser‐assisted reduction, patch defects in the carbon lattice. Spectroscopic experiments reveal graphitic structural recovery of up to 43% and electrical conductivity four times larger than the original graphene. The composites are tested as electrodes in electrochemical capacitors and demonstrate extremely fast RC time constant as low as 0.57 ms. Due to their low defect concentrations, the reduced graphene oxide‐carbon nanodot (rGO‐CND) composites frequency response is sufficiently fast to operate as AC line filters, potentially replacing today's electrolytic capacitors. Using this methodology, demonstrated is a novel line filter with one of the fastest capacitive responses ever reported, and an aerial capacitance of 68.8 mF cm^?2. This result emphasizes the decisive role of structural integrity for optimizing graphene in electronic applications.     

预置镍化学气相沉积法制备定向碳纳米管(英文)

采用化学气相沉积法(CVD),在溅射了镍薄膜的硅基底上制备了定向碳纳米管薄膜。对镍薄膜的氨气预处理过程及其机理进行了研究。结果发现预处理后的岛状区域随着薄膜厚度的增加而增加,纳米粒子区域的变化则与之相反。对5nm的镍薄膜进行预处理能获得细化和均匀分布的纳米粒子,有利于定向碳纳米管的生长。碳纳米管的生长过程及其细微结构与温度有很大关系。碳源的分解、碳原子在催化剂内部的扩散以及催化剂粒子的团聚三者之间的竞争决定了碳纳米管的生长情况。本文分析了碳纳米管的顶部生长模式及该模式下催化剂粒子的形态变化。