原位石墨烯包覆金属复合颗粒的制备与表征

分别采用普通化学气相沉积(CVD)和等离子体增强化学气相沉积(PECVD)在镍粉体颗粒上生长石墨烯的方法,制备出原位石墨烯包覆镍复合颗粒。采用扫描电子显微镜、能谱仪及拉曼光谱仪对两种方法制备的原位石墨烯包覆镍复合颗粒表面石墨烯的形态、分布、结晶质量等特征进行较为系统的测试表征。结果表明,普通CVD法制备的石墨烯沿镍颗粒表面面内生长,较为均匀地包覆着镍颗粒,具有较多褶皱,且石墨烯结晶质量高,缺陷少;PECVD法制备的镍颗粒表面的石墨烯片经较小,呈散乱分布,结晶质量不高,含有缺陷较多。     

石墨烯的化学气相沉积法制备及其表征

石墨烯是由sp2杂化的碳原子键合而成的具有六边形蜂窝状晶格结构的二维原子晶体,其具有电学、力学和光学等方面一系列优良性能,使得它在各个领域的应用一直被人们所关注。然而,石墨烯的工业化制备仍然面临着巨大的挑战。本文采用化学气相沉积法(CVD)制备石墨烯,并用拉曼光谱、高分辨率扫描电镜和X射线多晶衍射对其进行了分析和表征。研究结果表明,用CVD法制备石墨烯具有工业化的可能。     

石墨烯的制备及石墨的剥离与团聚力学性能研究

为了研究石墨在机械剥离法制备石墨烯过程中剥离与团聚的力学性能,以天然超细石墨为原料,采用具有高剪切效果的机械剥离法,在无分散剂的去离子水介质中制备层数不超过5的石墨片体积分数为18.5%的石墨烯悬浮液;采用原子力显微镜、扫描电子显微镜和粒度分布测试仪表征被剥离的石墨片,获得被剥离石墨片的整体层数分布,并基于层间相互作用能计算石墨厚度变化过程中的剥离能与团聚能。结果表明:当研磨、剥离6 h时,层数不超过5的石墨片含量最多;石墨片层变化释放的团聚能是消耗的剥离能的4倍;石墨片层的剥离使层间接触面积被释放,导致团聚能被激活并不断增大;石墨层间范德华能是阻碍石墨剥离和导致团聚的主要能量,库仑能的作用十分微弱。     

超声剥离制备石墨烯纳米片及其结构表征

以鳞片石墨为原料,采用插层氧化法制得可膨胀氧化石墨,然后经高温热解获得膨胀石墨,再通过超声剥离得到石墨烯纳米片,采用FTIR、XRD、SEM、TEM和Raman对所得石墨烯纳米片的微观结构进行表征。结果表明,可膨胀氧化石墨在800℃高温热解30 s得到膨胀体积最大的膨胀石墨,由80目和100目鳞片石墨制得的膨胀石墨的最大体积分别为215 mL/g和85 mL/g,且在50℃条件下超声剥离5 h分别得到30~50层和6~20层的石墨烯纳米片。     

石墨烯的化学气相沉积法制备

化学气相沉积(CVD)法是近年来发展起来的制备石墨烯的新方法,具有产物质量高、生长面积大等优点,逐渐成为制备高质量石墨烯的主要方法.通过简要分析石墨烯的几种主要制备方法(胶带剥离法、化学剥离法、SiC外延生长法和CVD方法)的原理和特点,重点从结构控制、质量提高以及大面积生长等方面评述了CVD法制备石墨烯及其转移技术的研究进展,并展望了未来CVD法制备石墨烯的可能发展方向,如大面积单晶石墨烯、石墨烯带和石墨烯宏观体的制备与无损转移等.     

石墨烯纳米片的制备和表征

以鳞片石墨为原料,采用氧化插层和微波膨化制备膨胀石墨,对膨胀石墨进行二次酸化膨胀处理,利用超声剥离法制备石墨烯纳米片,并借助XRD、SEM、RAMAN和AFM等分析其微观结构和形貌。结果表明:微波膨化处理可快速高效得到膨胀石墨;通过对膨胀石墨超声剥离可破坏其原有网络结构并将石墨晶片剥离为大量的石墨薄片;对二次膨胀处理的膨胀石墨进行超声剥离可得到石墨烯纳米片,其中包含大量的3-5层石墨烯。     

化学气相沉积法制备大面积石墨烯及其光谱学表征

化学气相沉积（CVD）法是近年来发展起来的制备石墨烯的新方法。该方法产物具有生长面积大、质量高等优点,逐渐成为制备石墨烯的主要方法。用CVD法在常压下通过全面优化实验参量,以镍箔为基底制备了大面积少数层和单层石墨烯,用拉曼光谱,场发射扫描电子显微镜（SEM）和原子力显微镜（AFM）手段表征,通过分析常压下不同温度、不同载气成分比等实验参数,最终获得制备高质量、大面积、少数层石墨烯的最佳参量,用双共振理论解释少数层和单层石墨烯的拉曼光谱中2D峰强度随石墨烯层数变化而变化的原理。CVD法制备的石墨烯具有面积大、低成本、可测量性强、可用于大批量生产的优点,为工业用途石墨烯的制备提供了有效途径。     

机械剥离法制备石墨烯及其在石墨烯/陶瓷复合材料制备中的应用

扼要介绍了石墨烯特殊的二维结构及因这种结构导致石墨烯所具有的极其优异的电学、光学和力学性质.回顾了石墨烯的研究历史以及微机械剥离法在其中所起到的重要作用,并对主要制备方法进行了简要的介绍.然后,阐述了以机械磨为剥离工具的新型机械剥离法的发展和已取得的成果.最后,对利用机械剥离法制备石墨烯/陶瓷复合材料粉体的探索进行了总结和概括.同时,展望了机械剥离法在制备石墨烯及其复合材料中的应用前景.     

用糖制备高质量石墨烯片的技术

自从石墨烯片采用粗糙的机械方法第一次分离制备出来后，制备方法很快被不断更新。通过化学气相沉积，可能会生长出很大的石墨烯片。但是此技术并不理想，因为化学气相沉积只能生产纯石墨，而且需要很高的温度。Rice大学的一个研究组最近论证了一个生产大面     

Crystallographic etching of few-layer graphene

We demonstrate a method by which few-layer graphene samples can be etched along crystallographic axes by thermally activated metallic nanoparticles. The technique results in long (>1 microm) crystallographic edges etched through to the insulating substrate, making the process potentially useful for atomically precise graphene device fabrication. This advance could enable atomically precise construction of integrated circuits from single graphene sheets with a wide range of technological applications.     

基于乙烯的化学气相沉积法制备少层石墨烯

采用乙烯作为碳源,利用化学气相沉积法(CVD法),在1 000℃条件下在铜箔上制备了少层石墨烯;采用不引入PMMA和PDMS等杂质的直接转移方法将石墨烯薄膜转移到Si/SiO2基底上,对石墨烯薄膜进行了表征。实验研究表明,减小乙烯的进气量可以提高石墨烯的质量;减少反应时间可以降低无定形碳的含量;增加退火时间可以提高Cu表面结晶质量,更加有利于石墨烯的生长。通过优化各项参数,使用乙烯已经可以制备I2D/IG=0.88的少层石墨烯。     

Imaging stacking order in few-layer graphene

Few-layer graphene (FLG) has been predicted to exist in various crystallographic stacking sequences, which can strongly influence the material's electronic properties. We demonstrate an accurate and efficient method to characterize stacking order in FLG using the distinctive features of the Raman 2D-mode. Raman imaging allows us to visualize directly the spatial distribution of Bernal (ABA) and rhombohedral (ABC) stacking in tri- and tetralayer graphene. We find that 15% of exfoliated graphene tri- and tetralayers is composed of micrometer-sized domains of rhombohedral stacking, rather than of usual Bernal stacking. These domains are stable and remain unchanged for temperatures exceeding 800 °C.     

Thermal transport in suspended and supported few-layer graphene

We report thermal conductivity (κ) measurements from 77 to 350 K on both suspended and supported few-layer graphene using a thermal-bridge configuration. The room temperature value of κ is comparable to that of bulk graphite for the largest flake, but reduces significantly for smaller flakes. The presence of a substrate lowers the value of κ, but the effect diminishes for the thermal transport in the top layers away from the substrate. For the suspended sample, the temperature dependence of κ follows a power law with an exponent of 1.4 ± 0.1, suggesting that the flexural phonon modes contribute significantly to the thermal transport of the suspended graphene. The measured values of κ are generally lower than those from theoretical studies. We attribute this deviation to the phonon-boundary scattering at the graphene-contact interfaces, which is shown to significantly reduce the apparent measured thermal conductance of graphene.     

Direct imaging of atomic-scale ripples in few-layer graphene

Graphene has been touted as the prototypical two-dimensional solid of extraordinary stability and strength. However, its very existence relies on out-of-plane ripples as predicted by theory and confirmed by experiments. Evidence of the intrinsic ripples has been reported in the form of broadened diffraction spots in reciprocal space, in which all spatial information is lost. Here we show direct real-space images of the ripples in a few-layer graphene (FLG) membrane resolved at the atomic scale using monochromated aberration-corrected transmission electron microscopy (TEM). The thickness of FLG amplifies the weak local effects of the ripples, resulting in spatially varying TEM contrast that is unique up to inversion symmetry. We compare the characteristic TEM contrast with simulated images based on accurate first-principles calculations of the scattering potential. Our results characterize the ripples in real space and suggest that such features are likely common in ultrathin materials, even in the nanometer-thickness range.     

Spatially resolved Raman spectroscopy of single- and few-layer graphene

We present Raman spectroscopy measurements on single- and few-layer graphene flakes. By using a scanning confocal approach, we collect spectral data with spatial resolution, which allows us to directly compare Raman images with scanning force micrographs. Single-layer graphene can be distinguished from double- and few-layer by the width of the D' line: the single peak for single-layer graphene splits into different peaks for the double-layer. These findings are explained using the double-resonant Raman model based on ab initio calculations of the electronic structure and of the phonon dispersion. We investigate the D line intensity and find no defects within the flake. A finite D line response originating from the edges can be attributed either to defects or to the breakdown of translational symmetry.     

Hydrothermally grown ZnO nanostructures on few-layer graphene sheets

This study describes the hydrothermal growth of ZnO nanostructures on few-layer graphene sheets and their optical and structural properties. The ZnO nanostructures were grown on graphene sheets of a few layers thick (few-layer graphene) without a seed layer. By changing the hydrothermal growth parameters, including temperature, reagent concentration and pH value of the solution, we readily controlled the dimensions, density and morphology of the ZnO nanostructures. More importantly, single-crystalline ZnO nanostructures grew directly on graphene, as determined by transmission electron microscopy. In addition, from the photoluminescence and cathodoluminescence spectra, strong near-band-edge emission was observed without any deep-level emission, indicating that the ZnO nanostructures grown on few-layer graphene were of high optical quality.