Growth of graphene layers on HOPG via exposure to methyl radicals

Wellmann, Ralf; Böttcher, Artur; Kappes, Manfred M.; Köhl, Ulrich; Niehus, Horst

doi:10.1016/s0039-6028(03)00928-2

Cited by 30 publications

(35 citation statements)

References 23 publications

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“…Table 7 shows the degrees of hybridization (m) and altitudes (h) of the C atoms of the PAH involved in bonding. As for perylene [1], we find equilibrium structures with h % 40 pm and m % 0.2 for bonding to inner carbons ( [9], [10], [15], [16]). As for [1], bonding is more difficult to a C atom inside the zigzag edge ( [16]).…”

Section: Geometrymentioning

confidence: 84%

“…This fact seems to support the idea that a methyl radical migrates easily on graphene, and seems to confirm the proposal of Wellmann et al that the growth of the graphene sheet on the HOPG surface occurs after migration of methyl radicals over long distances. [9] We base this reasoning not only on thermodynamic data (relative energies of minima) but also on kinetics, since transition-state energies, which link the different minima, decrease when the size of the model molecule increases. Thus, migration is expected to be rather easy on infinite systems such as graphene sheets.…”

Section: Isomermentioning

confidence: 99%

“…[9] Their work showed that the interaction of methyl radicals with hot HOPG leads to a substantial carbon deposition only if the surface is treated before exposure. That treatment consists of generating microscopic defects by bombarding the surface with fullerenes with high kinetic energy.…”

Section: Introductionmentioning

confidence: 99%

“…We show that the energetically most favourable positions of the two methyl groups are at the outer edge of the PAH, which suggests a growing process for the graphene layers around the defects of the surface, as observed experimentally. [9] 2. Computational Details…”

Section: Introductionmentioning

confidence: 99%

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Density Functional Study of Methyl Chemisorption on Polycyclic Aromatic Hydrocarbons

2006

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The reactions of methyl radicals with large (up to C(96)H(24)) polycyclic aromatic hydrocarbons (PAHs) are studied by density functional calculations to shed light on the experimentally observed deposition of carbon on highly oriented pyrolytic graphite (HOPG), which occurs when hot HOPG (decorated by nanometre-sized defects) is exposed to methyl radicals. The equilibrium structures of the reaction products, together with transition structures for PAHs up to the size of phenanthroperylene, are determined using the density functionals B3LYP, TPSSh, BP86 and TPSS. The structures are analysed by computing the pi orbital axis vector (POAV) and the altitude of the reactive carbon above the molecular plane of the PAH. The strongest C-CH(3) bonds are found at the edges of the PAHs, where the s character of the C orbital involved in the bond is roughly 25 % (sp(3) hybrid orbital). Carbon atoms inside the PAH form bonds with the methyl radical through atomic orbitals with about 16 % s character in the POAV analysis. These bonds are much weaker than those at the edges of the PAH, while the reactive carbon has moved about 40 pm above the molecular plane. At the edges, the PAH carbon atoms do not leave the molecular plane to this extent. The computed barrier heights and geometrical parameters of the transition structures are in agreement with Hammond's postulate, and the relative energies of all of the equilibrium structures can be rationalized by Hückel molecular orbital (HMO) theory.

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Section: Geometrymentioning

confidence: 84%

Section: Isomermentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Density Functional Study of Methyl Chemisorption on Polycyclic Aromatic Hydrocarbons

2006

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“…Similar to acetylene, methyl radical is also produced significantly during pyrolysis and oxidation of most aliphatic and alkylaromatic hydrocarbons. On the basis of the substantial growth of a graphene layer by methyl radicals, Wellmann et al [15] suggested that the influence of methyl radicals might also be significant in soot formation. From a literature review of the reactions of methyl radical with aromatic species and PAHs, it is found that studies have been generally limited to the reaction of methyl radical with toluene.…”

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confidence: 99%

Role of methyl radicals in the growth of PAHs

Shukla

Miyoshi

Koshi

2010

J. Am. Soc. Mass Spectrom.

103

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The role of methyl radicals in the networking of sp 2 carbons has been explored through kinetic analysis of mass spectra of the gas-phase products of the pyrolysis of toluene and toluene/acetone mixtures. Pyrolytic reactions were performed in a flow tube reactor at temperatures of 1140 -1320 K and a constant total pressure of 10.38 Torr with a residence time of 0.585 s. On addition of acetone, methyl substituted products and their derivatives were enhanced. Mass peaks were observed in several sequences at an interval of 14 mass units; these ions correspond to methyl substituted products formed as a result of hydrogen abstraction (ϪH) followed by methyl radical addition (ϩCH 3 ). Each major peak was usually preceded by a peak at two mass units lower, which was likely produced through dehydrogenation/dehydrocyclization (ϪH 2 ) of methyl substituted products. Detected species include a large number of alkyl, cyclotetrafused (CT), cyclopentafused (CP) mono-, di-, and polycyclic aromatic hydrocarbons (PAHs) along with primary PAHs. The analysis showed that MAC (methyl addition/cyclization) has a unique capacity to induce the sequential growth of hexagonal networks of sp 2 carbons from all fusing sites [1] of a PAH. Moreover, MAC was found capable of answering an important question in PAH growth, which is expansion of the CT ¡ CP ¡ hexagonal network for which other reported mechanisms are inefficient. (J Am Soc Mass Spectrom 2010, 21, 534 -544)

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Regulating Surficial Catalysis Mechanism of Copper Metal by Manipulating Reactive Intermediate for Growth of Homogenous Bernal‐Stacked Bilayer Graphene

Yang

Yan

et al. 2017

Adv Materials Inter

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Large scale and homogenous bernal‐stacked bilayer (AB‐stacked) graphene is a promising 2D functional material due to its distinct electronic properties. As motivated by some evidence, the continuous carbon radicals (e.g., ·CH3) can greatly contribute to the nucleation and growth of second layer graphene film; thus, overcoming the self‐limited catalysis regime of metallic Cu surface by conventional chemical vapor deposition. Herein, a two‐step reaction system is designed to facilitate more continuously supplying reactive intermediate for the second layer growth of graphene. With this strategy, monolayer and AB‐stacked bilayer graphene films can be controllably grown by simply tuning the confined amount of predeposited amorphous carbon (α‐C) under atmospheric pressure rather than low pressure or vacuum. This approach opens a straightforward way to grow 2D materials by managing the surficially catalytic kinetics in the two separated reaction units.

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Growth of graphene layers on HOPG via exposure to methyl radicals

Cited by 30 publications

References 23 publications

Density Functional Study of Methyl Chemisorption on Polycyclic Aromatic Hydrocarbons

Density Functional Study of Methyl Chemisorption on Polycyclic Aromatic Hydrocarbons

Role of methyl radicals in the growth of PAHs

Regulating Surficial Catalysis Mechanism of Copper Metal by Manipulating Reactive Intermediate for Growth of Homogenous Bernal‐Stacked Bilayer Graphene

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