Formation Of Single-layer Graphene Research Articles

Studying the Formation of Single-Layer Graphene on the Surface of SiC

Regions of single-layer- and bilayer graphene on the surface of thermally processed 4H-SiC substrates are studied using Kelvin probe force microscopy and Raman spectroscopy. We establish experimentally the key parameters of the adopted graphene growth technique which enables the fraction of bilayer graphene to be reduced to a minimum, while samples with a fraction of single-layer graphene as high as 95% are obtained.

Re-nucleation and Etching of Graphene During the Cooling Stage of Chemical Vapor Deposition

Graphene growth on copper foil via chemical vapor deposition (CVD) is extensively used because the low carbon solubility of Cu leads to uniform, single-layer graphene formation. However, re-nucleation and etching, which dramatically weaken the quality of graphene, occur in some cooling conditions. CVD graphene growth on Cu is influenced by the cooling stage. In this work, the role of cooling in CVD graphene domain growth on Cu foil was studied, and the effects of cooling rate and atmosphere on the growth of graphene during the cooling stage were investigated. The re-nucleation and etching of graphene domains were observed in some cooling processes. These phenomena occur due to the processes related with the varying cooling rate and hydrogen (H2) and methane (CH4) concentrations in the reactor.

Formation of graphene on the surface of copper under the conditions of chemical deposition from the gas phase

This work is devoted to experimental studies of the effect of synthesis conditions on formation of single-layer graphene on the copper surface. Under the conditions of formation and growth of single-layer graphene, it is shown that characteristic times of graphite nuclei formation are about 1 min and times of primary layer growth are about 0.5 min. The subsequent layers form in 10 min. It is shown that hydrogen concentration at the initial stage of synthesis affects the growth rate of the second layer significantly.

Synthesis of single-layer graphene in benzene–oxygen flame at low pressure

ABSTRACTThe results of investigations on synthesis of single-layer graphene on nickel substrate in the flame of premixed benzene–oxygen mixture at the pressure of 45 Torr with and without application of electric potential direct current of positive and negative polarity are presented. It is stated that at low pressure in benzene–oxygen flame, single-layer graphene is synthesized with minimum defects ID/IG = 0.27. The temperature of substrate 900°C and exposure time 0.5–1 min are sufficient for synthesis of single-layer graphene. It is shown that application of electric potential to the substrate influences synthesis of graphene in the flame. It is stated that at negative and positive potentials on a nickel substrate, formation of single-layer graphene is observed, at the value of negative potential U = −2V on a nickel substrate, one can observe formation of defectless single-layer graphene (ID/IG ≈ 0).

Stable aqueous dispersion of polymer functionalized graphene sheets from electrochemical exfoliation for anticorrosion application

A green approach of achieving stable aqueous dispersion of graphene by noncovalent functionalization using hydrolyzed styrene-maleic anhydride copolymer has been successfully accomplished. The alkaline solution of hydrolyzed styrene-maleic anhydride copolymer was used as the electrolyte during the electrochemical exfoliation of graphite and simultaneously functionalized the exfoliated graphene sheets. The formation of single-layer graphene was confirmed by X-ray diffraction, atomic force microscopy, and transmission electron microscopy analyses. Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and thermogravimetric analyses confirm the existence of hydrolyzed styrene-maleic anhydride copolymer on the surface of graphene via noncovalent interaction. The results of electrochemical measurements performed in 3.5 wt% NaCl solution indicated that the addition of well-dispersed hydrolyzed styrene-maleic anhydride copolymer functionalized graphene (SMA-graphene) into waterborne organic silicone resin system remarkably improved anticorrosion performance compared with pure waterborne organic silicone resin coating. This significantly enhanced corrosion protection is mainly due to the longer and circuitous diffusion pathway of the corrosive medium derived from highly dispersed SMA-graphene sheets in the composite coating.

Electrical transport properties of polycrystalline CVD graphene on SiO2/Si substrate

Abstract Transport behavior of single layer graphene (SLG) grown by chemical vapor deposition technique on copper foil and transferred to SiO 2 /Si substrate has been studied by measuring the dc conductivity and Hall mobility in the temperature range 2–460 K. The samples of size 1 × 1 cm 2 have been found to be polycrystalline in nature. Raman spectrum has been studied at various locations of the sample and the formation of SLG has been confirmed. From dc conductivity and mobility measurements it has been concluded that the one dimensional grain boundary defects are mainly responsible for the deterioration of mobility and conductivity of charge carriers in the polycrystalline samples.

Graphene growth on h-BN by molecular beam epitaxy

The growth of single layer graphene nanometer size domains by solid carbon source molecular beam epitaxy on hexagonal boron nitride (h-BN) flakes is demonstrated. Formation of single-layer graphene is clearly apparent in Raman spectra which display sharp optical phonon bands. Atomic-force microscope images and Raman maps reveal that the graphene grown depends on the surface morphology of the h-BN substrates. The growth is governed by the high mobility of the carbon atoms on the h-BN surface, in a manner that is consistent with van der Waals epitaxy. The successful growth of graphene layers depends on the substrate temperature, but is independent of the incident flux of carbon atoms.

Electrochemically exfoliated graphene using 9-anthracene carboxylic acid for supercapacitor application

A green approach for the electrochemical exfoliation of graphite to graphene is reported. After the exfoliation of graphite, the 9-anthracene carboxylate ion (ACA), which was used as an electrolyte, was adsorbed on the surface of graphene through noncovalent interaction. X-ray diffraction analysis confirms the exfoliation of graphite to graphene. Atomic force microscopy and transmission electron microscopy analyses show the formation of single layer graphene. Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and Raman spectroscopy confirm the noncovalent attachment of ACA on the surface of graphene. The 9-anthracene carboxylic acid modified graphene (ACEG) shows good electrochemical performance with a high specific capacitance of 577 F g−1 in 1 M H2SO4. The ACEG electrode shows 83.4% retention in specific capacitance after 1000 charge–discharge cycles. A high coulombic efficiency of 102% is also observed indicating its suitability as energy storage electrode materials.

Graphene growth and stability at nickel surfaces

The formation of single-layer graphene by exposure of a Ni(111) surface to ethylene at low pressure has been investigated. Two different growth regimes were found. At temperatures between 480 and 650 °C, graphene grows on a pure Ni(111) surface in the absence of a carbide. Below 480 °C, graphene growth competes with the formation of a surface Ni2C carbide. This Ni2C phase suppresses the nucleation of graphene. Destabilization of the surface carbide by the addition of Cu to the surface layer facilitates the nucleation and growth of graphene at temperatures below 480 °C. In addition to the growth of graphene on Ni substrates, the interaction between graphene and Ni was also studied. This was done both experimentally by Ni deposition on Ni-supported graphene and by density functional theory calculation of the work of adhesion between graphene and Ni. For graphene sandwiched between two Ni-layers, the work of adhesion between graphene and the Ni substrate was found to be four times as large as that for the Ni-supported graphene without a top layer. This stronger interaction may cause the destruction of graphene that is shown experimentally to occur at ∼200 °C when Ni is deposited on top of Ni-supported graphene. The destruction of graphene allows the Ni deposits to merge with the substrate Ni. After the completion of this process, the graphene sheet is re-formed on top of the Ni substrate, leaving no Ni at the surface.

A highly practical route for large-area, single layer graphene from liquid carbon sources such as benzene and methanol

Through a detailed systematic study, we determined the parameters critical for high-quality, single-layer graphene formation and developed a straightforward synthesis that requires no explosive hydrogen or methane gas flow. The synthesis is further simplified by using only a liquid carbon source such as methanol. Of over a dozen liquid carbon sources studied, methanol is found to be unique in that it acts as both a carbon/hydrogen source and an inhibitor to amorphous carbon growth. No deposition of amorphous carbon was observed, regardless of vapor pressure, unlike methane and other hydrocarbons. Finally, we describe a protocol to control graphene growth to a single side or selected location on the copper substrate, which is required for most device applications. Using our novel methods, we have prepared high-quality, single-layer graphene samples at the inch scale that have been thoroughly characterized with Raman spectroscopy, optical transmittance, scanning electron microscopy and sheet resistance measurements. Our method is safe, simple, and economical and will be of value to both fundamental researchers and nanodevice engineers.