铜衬底上热丝CVD法低温生长石墨烯薄膜的研究

以乙炔作为碳源,抛光铜片作为衬底,采用热丝CVD法低温生长了石墨烯。通过拉曼散射光谱和紫外-可见分光光度计分析了样品的性能。结果表明,灯丝温度的提高有助于乙炔分解为对石墨烯晶粒形核生长比较有利的含碳活性基团。衬底温度的升高增强了铜衬底对石墨烯生长的催化作用。通过调整气体流量中乙炔的比例,可以有效降低石墨烯薄膜的层数。最终在乙炔浓度为2%,衬底温度为450℃的低衬底温度条件下制得了的单层石墨烯纳米晶薄膜。     

低温氧等离子体处理对单层石墨烯微观结构影响的研究

运用低温氧等离子体对化学气相沉积法生长的单层石墨烯进行处理,通过拉曼光谱仪和X射线光电子能谱仪来表征处理前后的变化,重点探讨了低温氧等离子体处理对单层石墨烯微观结构的影响。在拉曼光谱中,处理后的石墨烯出现了明显的D峰和D′峰,同时G峰和2D峰也出现了明显的退化,而G峰峰位右移,2D峰峰位左移。通过X射线光电子能谱表征,表明处理后向石墨烯中引入了较多的官能团。利用原子力显微镜研究了处理前后SiO_2/Si基底上石墨烯的表面形貌,发现低温氧等离子体处理后石墨烯表面高度明显增加,同时褶皱减少。     

低功率CO2激光辐照对多层石墨烯结构的影响

在真空环境下使用不同功率密度的CO2激光对化学气相沉积法(CVD)生长的石墨烯进行辐照,通过研究辐照前后的拉曼光谱变化考察了激光功率密度及辐照时间对多层石墨烯结构的影响。结果表明,当功率密度较低(13W/cm2)时,石墨烯拉曼光谱中的D峰降低,2D峰增强,石墨烯内的掺杂、缺陷减少。随着功率密度的增加,石墨烯的缺陷增多,部分缺陷连接形成晶界,使石墨烯分解为纳米晶。在58 W/cm2的功率密度下,当作用时间为120s时,在石墨烯表面产生非晶碳。研究表明,适当参数的CO2激光辐照能改善石墨烯的内在性能。     

基于蓝宝石基底转移石墨烯的中波红外透过光谱分析

利用常压化学气相沉积(CVD)法制备大面积单层石墨烯,并分别转移一层和三层至蓝宝石基底表面。采用共焦拉曼光谱仪对样片表面多点进行测量,以表征不同位置转移石墨烯的层数、缺陷与连续性。考虑石墨烯在红外波段的自由载流子吸收和泡利阻塞效应,计算得到光电导率随波长变化的曲线。利用傅里叶变换红外光谱仪对石墨烯样品中波红外(3~5?m)透过率进行了测试,结果表明其在中波红外存在明显的泡利阻塞效应。实测的单层石墨烯中波红外相对透过率为98.5%,明显高于可见区域。三层石墨烯的相对透过率也与仿真结果相仿。由此可见,石墨烯将有望弥补ITO在中波红外透明窗口电磁屏蔽应用方面的不足。     

碳原子的再分布对铂上高质量单层石墨烯生长的影响

二维材料石墨烯以其独特的性质显示出在众多领域的应用潜力。化学气相淀积(CVD)作为最有效的生长单层石墨烯的方法得以良好发展。但在CVD方法中,频繁出现的多层石墨烯“点”严重影响单层石墨烯的有效面积,进而限制了石墨烯在很多场景中的应用。本文通过引入一个新的阶段-再分布阶段,使得在分解阶段溶解在铂片中的碳原子重新分布,进而减少了多层石墨烯“点”的数目。单层石墨烯的平均面积增加到16000μm₂,较未引入再分布阶段的单层面积增大了八倍。最后,拉曼光谱仪的测试结果说明了新方法下生长的石墨烯的高质量特征。     

脉冲激光沉积法制备的单层MoS_2薄膜变温光响应研究（英文）

报导了在c-Al_2O_3衬底上用脉冲激光沉积法制备MoS_2薄膜,并测试了其不同温度下的光响应。通过拉曼散射光谱和X射线衍射光谱证明了所制备的二硫化钼为纯2H相。通过X光电子能谱证明了所制备的二硫化钼硫钼原子比为1.92:1,在Mo元素的3d核心能级谱中存在红移和蓝移,说明薄膜中存在氧化和硫缺陷。此外,通过拉曼和光致发光分布图,证明了薄膜具有良好的均一性。在不同层数的二硫化钼样品中,单层二硫化钼样品具有最强的光响应,达到3 m AW~(-1)。单层二硫化钼的变温光响应实验表明,在室温附近,温度升高会提高二硫化钼的光响应强度和响应时间。     

脉冲激光沉积法制备的单层MoS2薄膜变温光响应研究

报导了在c-Al₂O₃衬底上用脉冲激光沉积法制备MoS₂薄膜,并测试了其不同温度下的光响应。通过拉曼散射光谱和X射线衍射光谱证明了所制备的二硫化钼为纯2H相。通过X光电子能谱证明了所制备的二硫化钼硫钼原子比为1.92：1,在Mo元素的3d核心能级谱中存在红移和蓝移,说明薄膜中存在氧化和硫缺陷。此外,通过拉曼和光致发光分布图,证明了薄膜具有良好的均一性。在不同层数的二硫化钼样品中,单层二硫化钼样品具有最强的光响应,达到3 mAW^-1。单层二硫化钼的变温光响应实验表明,在室温附近,温度升高会提高二硫化钼的光响应强度和响应时间。     

PECVD生长垂直石墨烯的场发射特性研究

采用射频等离子体增强化学气相沉积(PECVD)技术,以甲烷为碳源,在金属铜箔上制备了三维垂直石墨烯。通过调节生长参数,进行了七组对比实验,利用扫描电子显微镜,拉曼光谱对垂直石墨烯的形貌、质量以及层数进行了表征,用二级结构的场发射仪器测试了垂直石墨烯的场发射特性,研究了垂直石墨烯的场发射特性与其形貌、质量和密度的关系,并获得了开启电场低至0.29V/μm的场发射特性。研究结果表明,垂直石墨烯是一种良好的场发射材料,未来在真空电子源中具有广阔的应用前景。     

基于广义Whittaker平滑器的拉曼光谱基线校正方法

拉曼光谱的频率、强度及偏振特性表征散射物质的独特性质,是研究物质结构及组成成分的特征光谱,因而得到了广泛应用。但是,基线漂移现象会给拉曼光谱的定量分析带来不利影响。为了校正拉曼光谱基线漂移,提出了一种结合导数谱峰检测与Whittaker平滑器的基线校正算法。利用拉曼二阶导数光谱检测并标定谱峰区域;Whittaker平滑器结合标定信息计算非谱峰区域的拟合曲线,并同时对谱峰区域进行平滑插值,最终得到整个光谱的基线估计。将该算法应用于模拟和实际拉曼光谱进行基线校正,结果表明,算法可以同时实现光谱去噪与基线估计,而主成分分析结果的改善进一步验证了该算法的有效性。     

1维石墨烯光子晶体的电磁吸收特性

为了研究1维石墨烯光子晶体在可见光波段的吸收特性,采用传输矩阵的方法进行了理论分析和数值仿真,得到了1维石墨烯吸收特性与石墨烯层数、缺陷层介质厚度、电磁波模式有关的结果。结果表明,增加石墨烯层数时,对波长为556nm左右的绿光的吸收作用明显增强;缺陷层介质厚度增加时会引起吸收峰的增加;在TE模式下,入射角对石墨烯光子晶体吸收特性影响较小。该研究结果为1维石墨烯光子晶体吸收器的设计提供了理论依据。     

Large-Scale Synthesis of Graphene Films by Joule-Heating-Induced Chemical Vapor Deposition

We report large-area synthesis of few-layer graphene films by chemical vapor deposition (CVD) in a cold-wall reactor. The key feature of this method is that the catalytic metal layers on the SiO₂/Si substrates are self-heated to high growth temperature (900°C to 1000°C) by high-current Joule heating. Synthesis of high-quality graphene films, whose structural and electrical characteristics are comparable to those grown by hot-wall CVD systems, was confirmed by transmission electron microscopy images, Raman spectra, and current–voltage analysis. Optical transmittance spectra of the graphene films allowed us to estimate the number of graphene layers, which revealed that high-temperature exposure of Ni thin layers to a carbon precursor (CH₄) was critical in determining the number of graphene layers. In particular, exposure to CH₄ for 20 s produces very thin graphene films with an optical transmittance of 93%, corresponding to an average layer number of three and a sheet resistance of ~600 Ω/square.     

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。     

Improving Graphene Diffusion Barriers via Stacking Multiple Layers and Grain Size Engineering

It is shown that the performance of graphene diffusion barriers can be enhanced by stacking multiple layers of graphene and increasing grain size. The focus is on large‐area barriers of graphene grown by chemical vapor deposition (CVD) in the context of passivating an underlying Cu substrate from oxidation in air at 200 °C and use imaging Raman spectroscopy as a tool to temporally and spatially map the barrier performance and to guide barrier design. At 200 °C in air, Cu oxidation proceeds in multiple regimes: first slowly via transport through atomic‐scale grain boundary defects inherent to CVD‐graphene and then more rapidly as the graphene itself degrades and new defects are formed. In the initial regime, the graphene passivates better than previously reported. Whereas oxidation through single sheets primarily occurs through grain boundaries, oxidation through multiple sheets is spatially confined to their intersection. Performance further increases with grain‐size. The degradation of the graphene itself at 200 °C ultimately limits high temperature but suggests superior low temperature barrier performance. This study is expected to improve the understanding of mass transport through CVD‐graphene materials and lead to improved large area graphene materials for barrier applications.     

石墨烯上生长GaN纳米线的研究

在常压条件下采用化学气相淀积(CVD)技术在有石墨烯插入层的衬底上生长GaN纳米线,研究了生长温度、石墨烯插入层、催化剂等因素对GaN纳米线的形貌、光学特性以及结构的影响.通过扫描电子显微镜(SEM)、光致发光(PL)谱、拉曼(Raman)谱和透射电子显微镜(TEM)等表征手段对GaN纳米线的形貌、光学特性以及结构进行表征.结果表明,在1 100℃条件下,同时有石墨烯插层和催化剂的衬底表面能够获得低应力单晶GaN纳米线.石墨烯、催化剂对于获得低应力单晶GaN纳米线有重要的作用.     

Synthesis of Doped Porous 3D Graphene Structures by Chemical Vapor Deposition and Its Applications

Graphene doping principally commenced to compensate for its inert nature and create an appropriate bandgap. Doping of 3D graphene has emerged as a topic of interest because of attempts to combine its large available surface area—arising from its interconnected porous architecture—with superior catalytic, structural, chemical, and biocompatible characteristics that can be induced by doping. In light of the latest developments, this review provides an overview of the scalable chemical vapor deposition (CVD)‐based growth of doped 3D graphene materials as well as their applications in various contexts, such as in devices used for energy generation and gas storage and biosensors. In particular, single‐ and multielement doping of 3D graphene by various dopants (such as nitrogen (N), boron (B), sulfur (S) and phosphorous (P)), the doping configurations of the resultant materials, an overview of recent developments in the field of CVD, and the influence of various parameters of CVD on graphene doping and 3D morphologies are focused in this paper. Finally, this report concludes the discussion by mentioning the existing challenges and future opportunities of these developing graphitic materials, intending to inspire the unveiling of more exciting functionalized 3D graphene morphologies and their potential properties, which can hopefully realize many possible applications.     

Homogeneous Optical and Electronic Properties of Graphene Due to the Suppression of Multilayer Patches During CVD on Copper Foils

A synthesis method of strictly monolayer and fully homogeneous graphene across tens of centimeter squares, by chemical vapour deposition onto standard copper foils, is presented. The growth technique involves cyclic injection of a carbon precursor separated by idle times with constant hydrogen exposure. The formation of spurious multilayer patches, which accompanies the standard growth techniques based on continuous exposure to methane, is inhibited here, in a broad range of pressure and gas composition, including in two pressure regimes which are known to yield distinctive grain morphologies (dendritic versus hexagonal). Raman spectra confirm the absence of defects within the graphene films. A mechanism for growth/suppression of the multilayer patches based on the carbon storage at defective regions is proposed. The importance of multilayer suppression is highlighted in a comparative study showing the detrimental effect of patches on the performances of graphene transistors and on the optical transparency of stacked layers. The full‐layer graphene sheets are superiorly homogeneous in terms of their optical and electronic properties, and are thus suited for applications for high‐density integration as well as transparent electrodes with spatially continuous optical absorbance. Graphene transistors fabricated by the pulsed CVD method exhibit room‐temperature mobilities with a mean value of 5000 cm² V^?1 s^?1.     

Large‐Scale Synthesis of Bi‐layer Graphene in Strongly Coupled Stacking Order

Large‐scale synthesis of single‐layer graphene (SLG) by chemical vapor deposition (CVD) has received a lot of attention recently. However, CVD synthesis of AB stacked bi‐layer graphene (BLG) is still challenging. Here, we report synthesis of BLG homogeneously at large scale by thermal CVD. The 2D Raman band of CVD BLG splits into four components, suggesting splitting of electronic bands due to strong interlayer coupling. The splitting of electronic bands in CVD BLG is further evidenced by the study of near infrared absorption and carrier dynamics are probed by transient absorption spectroscopy. UV photoelectron spectroscopy invesigation also indiates CVD BLG possesses different electronic structures to those of CVD SLG. The growth mechanism of BLG is found to be related to catalytic activity of the copper (Cu) surface, which is determined by the purity of Cu foils employed in the CVD process. Our work shows that strongly coupled or even AB stacked BLG can be grown on Cu foils at large scale, which is of particular importance for device applications based on their split electronic bands.     

Demonstration of enhanced the photocatalytic effect with PtSe2 and TiO2 treated large area graphene obtained by CVD method

Here, we report our method on enhancing the photocatalytic effect with PtSe₂ and TiO₂ treated large area graphene (LAG). The LAG was growth on copper foil at a low temperature (500 °C) under atmospheric pressure by chemical vapor deposition (CVD) method. A facile, fast ultrasonic method was then used to successfully synthesize PtSe₂-LAG/TiO₂ nanocomposites. The composites that were obtained were characterized using X-ray diffraction (XRD) spectroscopy, scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) spectroscopy, transmission electron microscopy (TEM), Raman spectroscopic analysis, and X-ray photoelectron spectroscopy (XPS). UV–vis diffuse reflectance spectra (DRS) analyses were also performed, and the catalytic behavior was investigated by the decomposition of methylene blue (MB).The as-prepared LAG with a Raman D band was obtained, and graphene layers can be clearly seen in High-Resolution Transmission Electron Microscopy (HRTEM) images. The degradation performance of the MB solution was determined via UV–vis spectrophotometry. This improved photocatalytic activity is a result of the positive synergetic effect between PtSe₂ and LAG in the heterogeneous photocatalyst. In this study, the LAG behaves as an electron transfer agent, contributor, collector, and source of active adsorption sites. The optical properties were also observed to be affected by the different weight ratios of the LAG in the composites by observing their respective band gaps from diffuse reflectance spectra.     

Electrical conductivity and photoluminescence of diamond films grown by downstream microwave plasma CVD

Electrical conductivity measurements and photoluminescence (PL) were used to study the effects that sample distance from the plasma during growth has on the carrier transport properties of undoped CVD diamond. The films were grown by downstream microwave plasma chemical vapor deposition at distances from 0.5 to 2.0 cm from the edge of plasma glow. Electrical conductivity measurements were performed between room temperature and 1000° C and then complimented with Raman spectroscopy and PL studies in an attempt to gain a better understanding of the CVD growth process and the resulting electrical and optical properties of the diamond films. Room temperature electrical conductivity was found to vary by over 5 orders of magnitude with increasing growth distance from the plasma, while only moderate changes were observed in the luminescence spectra.     

二硫化钼-石墨烯垂直异质结的制备与表征

以采用化学气相沉积法(CVD)生长的单层石墨烯为导电电极、四硫代钼酸铵水溶液为电解质,通过电化学沉积法合成了二硫化钼/石墨烯(MoS2/graphene)垂直异质结。将合成的MoS2/graphene垂直异质结通过CVD在氢气(H2)和氩气(Ar)环境下进行退火处理。利用拉曼光谱、X射线衍射仪(XRD)、扫描电子显微镜(SEM)、原子力显微镜(AFM)系统地分析了样品的物质成分、表面形貌和厚度等。这种简单、环保、低成本的制备大面积MoS2/graphene垂直异质结的方法具有普遍适用性,为其他垂直异质结的制备开辟了新途径。