Electrostatic deposition of graphene

physica status solidi (b), 2012

We report Raman analysis of few-layer graphene (FLG) transferred on flat and patterned substrate structures. These different surface structures created by patterning an area of a Si-substrate produce differences in the interaction between FLG and the substrate surface. The topography measurement performed by scanning tunneling potentiometry shows that the FLG on the patterned substrate was deformed periodically with 3-4 nm depth variation. Raman spectroscopy reveals that two important features related to the G-and 2D-modes in graphitic structures show different sensitivity to the interaction with the substrate for single-layer graphene (SLG), FLG, and graphite. Whereas SLG and FLG placed on the patterned substrate demonstrate a strong shift of both 2D-and G-peaks to lower frequencies with respect to the flat part, the multilayer graphene in a graphite flake shows almost no difference between patterned and non-patterned substrates. We identified the origin of the observed changes in the Raman spectra of SLG and FLG as effects created by the underlying substrate. Especially, substrate induced periodic strain and surface interaction were taken into account to interpret the results.

Nanomaterials, 2021

To achieve high-quality chemical vapor deposition of monolayer graphene electrodes (CVD-MG), appropriate characterization at each fabrication step is essential. In this article, (1) Raman spectroscopy/microscopy are employed to unravel the contact effect between the CVD-MG and Cu foil in suspended/supported formation. (2) The Surface-Enhanced Raman spectroscopy (SERS) system is described, unveiling the presence of a z-directional radial breathing-like mode (RBLM) around 150 cm−1, which matches the Raman shift of the radial breathing mode (RBM) from single-walled carbon nanotubes (SWCNTs) around 150 cm−1. This result indicates the CVD-MG located between the Au NPs and Au film is not flat but comprises heterogeneous protrusions of some domains along the z-axis. Consequently, the degree of carrier mobility can be influenced, as the protruding domains result in lower carrier mobility due to flexural phonon–electron scattering. A strongly enhanced G-peak domain, ascribed to the presence ...

Understanding surface structure of graphene is important for its integration into composite materials. Here, we have used synchrotron X-ray reflectivity (XRR) to study the structure of commercially available graphene samples (prepared via chemical vapor deposition, and marketed as graphene monolayers) on SiO 2 /Si at different temperatures. X-ray photoelectron spectroscopy, photoemission electron microscopy and atomic force microscopy (AFM) were employed to evaluate the composition and morphology of the graphene layer. Our results indicate that the samples we characterized consisted of 3e4 layers of graphene, which should thus be more accurately described as few layer graphene (FLG). Furthermore, a "contaminant" layer, comprising polymethylmethacrylate and graphene multilayers, was found present atop FLG. We also report tentative results on the effect of temperature on the graphene sample thickness. At 25 C, the FLG thickness from XRR measurements was 13.0 ± 1.0 Å, in agreement with that obtained from AFM (13.9 ± 0.7 Å). Upon heating to 60 C, the FLG thickness expanded to 13.8 Å, which further increased to 14.3 Å upon cooling to 25 C. We attribute this temperature dependent thickness to the outof-plane rippling of graphene as previously reported. These unprecedented results on the FLG surface structure are valuable to its potential bioanalytical applications.

Applied Physics Letters, 2010

Method to prepare suspended multilayer graphene ͑MLG͒ flakes and to form highly conductive ͑contact resistivity of ϳ0.1 k⍀ m 2 ͒ and tight mechanical connection between MLG and metal electrodes is described. MLG flakes prepared from natural graphite were precisely deposited over tungsten electrodes using dielectrophoresis, followed by high-temperature thermal annealing in high-vacuum. Considerable strain induced in the suspended part of flakes was revealed by Raman imaging.

Advanced Materials, 2011

Surface Science, 2003

The interaction of methyl radicals with hot HOPG (highly oriented pyrolytic graphite) surfaces under single-collision conditions has been studied by scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). Methyl radicals were generated by thermal decomposition of azomethane N 2 (CH 3) 2. Significant carbon deposition under elevated surface temperature conditions was observed if substrates were used which had been decorated by nanometer sized defects prior to methyl radical exposure. Graphene layers as well as protrusions were observed to be formed depending on the defect. No carbon deposition was observed for surface temperature below 800°C. Largest sticking probabilities of up to 10 À6 were observed for HOPG (highly oriented pyrolytic graphite) surfaces prestructured with hexagonal nanometer sized etch pits. Here, the initially resulting mono-atomic layers are pinned by the hole periphery and exhibit a densely packed hexagonal atomic structure corresponding to the graphite basal plane. For surfaces held at 1000°C, the lateral growth rate of a graphene layer around a single hole can exceed 230 A A 2 /s at a CH Å 3 flux of 3 • 10 17 molecules/cm 2 s. The deposition kinetics switches from 2D to 3D growth prior to completion of the first graphene layer. A growth mechanism based on CH Å 3 decomposition and hydrogen desorption is proposed.

Chemical Physics Letters, 2013

We examined the number of layers in graphene using Raman microscopy and investigated the interlayer interactions by understanding the layer stacking through the E ⁄ (low) mode measured in Raman spectroscopy designed for low-frequency observation. The number of layers in Raman image was determined from the G/2D intensity ratio, and the interlayer stacking for 2, 3 and 4 layers was understood from the positions of the E ⁄ (low) mode. While most part of sample showed AB stacking, a small area showed random stacking of layers. Low-frequency Raman spectroscopy revealed that such sample area was consisted of weakly interacted random stacking of graphene layers.

Nanoscale, 2013

We present a multi-technique characterisation of graphene grown by chemical vapour deposition (CVD) and thereafter transferred to and suspended on a grid for transmission electron microscopy (TEM). The properties of the electronic band structure are investigated by angle-resolved photoelectron spectromicroscopy, while the structural and crystalline properties are studied by TEM and Raman spectroscopy. We demonstrate that the suspended graphene membrane locally shows electronic properties comparable with those of samples prepared by micromechanical cleaving of graphite.

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.

physica status solidi (c), 2010