Optical analysis of grain size in graphene on copper revealed by wet chemical oxidation (original) (raw)
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Nature Materials, 2011
The strong interest in graphene has motivated the scalable production of high-quality graphene and graphene devices. As the large-scale graphene films synthesized so far are typically polycrystalline, it is important to characterize and control grain boundaries, generally believed to degrade graphene quality. Here we study single-crystal graphene grains synthesized by ambient chemical vapour deposition on polycrystalline Cu, and show how individual boundaries between coalescing grains affect graphene’s electronic properties. The graphene grains show no definite epitaxial relationship with the Cu substrate, and can cross Cu grain boundaries. The edges of these grains are found to be predominantly parallel to zigzag directions. We show that grain boundaries give a significant Raman ‘D’ peak, impede electrical transport, and induce prominent weak localization indicative of intervalley scattering in graphene. Finally, we demonstrate an approach using pre-patterned growth seeds to control graphene nucleation, opening a route towards scalable fabrication of single-crystal graphene devices without grain boundaries.
Direct observation of grain boundaries in chemical vapor deposited graphene
Carbon, 2017
Graphene has received great attention owing to its superior physical properties, making graphene suitable for multiple applications. Numerous graphene growth techniques have been developed in the past decade to provide scalable high quality graphene. Among these techniques, chemical vapor deposition (CVD) on catalytic metal films holds great promises for a large-scale graphene growth. Even though extensive efforts have been devoted to synthesize high quality graphene, formation of defects. In particular, grain boundaries (GBs) have a dominant effect on properties, motivating extensive efforts to tune the CVD growth process to minimize GB. Rapid imaging of GBs will significantly aid in studies of CVD graphene grain structure. Here we report a straightforward technique to optically observe GBs in CVD-grown graphene via optical microscopy, allowing rapid assessment of graphene quality as well as the number of layers. The local oxidation of copper through the damaged GBs induces an optically discernable color change in the underlying copper due to different extend of oxidation between the two copper regions under grains and GBs. Our observation technique for GBs of graphene paves a path for understanding fundamental mechanisms of graphene growth and efficient quality evaluation of largescale graphene sheet for mass production.
Synthesis of Graphene via Chemical Vapour Deposition on Copper Substrates with Different Thicknesses
ANADOLU UNIVERSITY JOURNAL OF SCIENCE AND TECHNOLOGY A - Applied Sciences and Engineering, 2017
The quality of the graphene grown on the top and subside of copper substrate with different thicknesses was investigated. Graphenes were grown on the 9, 25, 150 and 250 μm thickness copper substrates with Low-Pressure CVD by using CH4 process gas. Copper substrates were examined through XRD/XRF analysis. Graphenes that are grown on the surface of the copper substrate were characterized by Raman spectrometer. The results show that the grain size calculated from XRD data is decreasing as the thickness increases except for 25 μm thick copper. Besides the micro-strain in the structure is increasing according to the thickness of substrate. Raman spectroscopy results show that the graphene grown on the top surface of the 9 μm thick substrate is purely single-layer. The other samples consist of not only single-layer graphene but also few-layer graphene domains. When we look at I2D/IG ratios for samples on the top surface of coppers, the graphene doping decreases together with increasing thickness of substrate. At the same time, graphenes on the copper subsurface have blueshift and higher FWMH values. It reveals there is a close relation between the graphene and the copper subsurface. The graphene grown on the top side of the 150 μm copper has the typical attribute of suspended single-layer graphene with the redshift of a narrow 2D peak and I2D/IG ≈ 4. In this study, the best sample is obtained on the top surface of the 150 μm thick copper substrate. The large single-layer graphene is depend on microstrain rather than grain orientation.
The role of copper pretreatment on the morphology of graphene grown by chemical vapor deposition
Microelectronic Engineering, 2015
The effect of pretreatment of copper on the ensuing morphology and surface coverage of graphene grown using chemical vapor deposition (CVD) has been investigated. Specifically, graphene grown on electropolished copper (EP-Cu) was analyzed with respect to its surface morphology, surface roughness and thickness, and compared with graphene grown on as cold-rolled acetic acid cleaned copper (AA-Cu). Results show an improvement in the quality of graphene obtained using EP-Cu over AA-Cu. Additionally, electrochemical polarization studies were performed on annealed and graphene coated EP-Cu in acidic solutions. The results indicate that corrosion inhibition of EP-Cu is possible through the use of graphene films.
Investigation of CVD graphene topography and surface electrical properties
Surface Topography: Metrology and Properties, 2016
Combining scanning probe microscopy techniques to characterise samples of graphene, a self-supporting single atomic layer hexagonal lattice of carbon atoms, provides far more information than a single technique can. Here we focus on graphene grown by chemical vapour deposition (CVD), grown by passing carbon containing gas over heated copper, which catalyses single atomic layer growth of graphene on its surface. To be useful for applications the graphene must be transferred onto other substrates. Following transfer it is important to characterise the CVD graphene. We combine atomic force microscopy (AFM) and scanning Kelvin probe microscopy (SKPM) to reveal several properties of the transferred film. AFM alone provides topographic information, showing 'wrinkles' where the transfer provided incomplete substrate attachment. Combined with SKPM which measures the surface potential (SP), indicating regions with different graphene layer numbers, local defects and impurities can also be observed in the SP scan. Finally, Raman spectroscopy can confirm the structural properties of the graphene films, such as the number of layers and level of disorder, by observing the peaks present. We report example data on a number of CVD samples from different sources.
Single-crystal Grains and Grain Boundaries in Graphene Grown by Chemical Vapor Deposition
2010
The strong interest in graphene has motivated the scalable production of high quality graphene and graphene devices. Since large-scale graphene films synthesized to date are typically polycrystalline, it is important to characterize and control grain boundaries, generally believed to degrade graphene quality. Here we study single-crystal graphene grains synthesized by ambient CVD on polycrystalline Cu, and show how individual boundaries between coalescing grains affect graphene's electronic properties. The graphene grains show no definite epitaxial relationship with the Cu substrate, and can cross Cu grain boundaries. The edges of these grains are found to be predominantly parallel to zigzag directions. We show that grain boundaries give a significant Raman "D" peak, impede electrical transport, and induce prominent weak localization indicative of intervalley scattering in graphene. Finally, we demonstrate an approach using pre-patterned growth seeds to control graphene nucleation, opening a route towards scalable fabrication of single-crystal graphene devices without grain boundaries.
Advances in Science and Technology, 2014
Chemical Vapor Deposition (CVD) is generally utilized for producing large area, good quality graphene films on suitable substrates. Copper (Cu) substrate is used mainly as a substrate and catalyst during graphene synthesis process by CVD technique. The purpose of the present work is to investigate the evolution of Cu surface morphology after graphene growth and its influence on grown graphene quality. In this study, graphene was grown using methane as the carbon source at temperature of 1040 o C for 5 minutes. Scanning electron microscopy (SEM), Optical Microscopy (OM) and atomic force microscopy (AFM) were utilized to analyze the change of Cu surface morphology after graphene synthesis. Raman spectroscopy was used to characterize the characteristics of grown graphene. SEM and AFM results showed that copper substrate surface morphology was modified after annealing and graphene growth associated with formation of large size Cu particles located basically on the surface terraces, resulting in deposition of multilayer, very small graphene domains aligned linearly along rolling marks direction.
Substrate grain size and orientation of Cu and Cu–Ni foils used for the growth of graphene films
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 2012
Graphene growth on Cu foils by catalytic decomposition of methane forms predominantly single-layer graphene films due to the low solubility of carbon in Cu. On the other hand, graphene growth on Cu–Ni foils can result in the controlled growth of few-layer graphene films because of the higher solubility of carbon in Ni. One of the key issues for the use of graphene grown by chemical vapor deposition for device applications is the influence of defects on the transport properties of the graphene. For instance, growth on metal foil substrates is expected to result in multidomain graphene growth because of the presence of grains within the foil that exhibit a variety of surface terminations. Therefore, the size and orientation of the grains within the metal foil should influence the defect density of the graphene. For this reason, we have studied the effect of total anneal time and temperature on the orientation and size of grains within Cu foils and Cu–Ni alloy foils with a nominal conc...