Mechanism of graphene growth by chemical vapour deposition on transition metals

S.N.Ramachandra15MT60R10

Reference:-Choon-Ming Seah , Siang-Piao Chai , Abdul Rahman M. (2014), “Mechanism of graphene growth by chemical vapour deposition on transition metals”, Carbon,Vol 70,pp 1-21.

Contents• Introduction• Properties of graphene• Synthesis of monolayer or few layer graphene • Chemical vapour deposition(CVD)• Use of catalysts in CVD• Graphene growth mechanism on Cu and Ni

substrates• Future prospects• Summary

Introduction

What is graphene? • 2-dimensional hexagonal lattice of carbon.

•SP2 hybridized carbon

atoms.

•Each carbon atom bounds to

its 3 neighbors.Fig 1.1 structure of graphene (from web)

Properties of graphene

• High electronic and thermal conductivity• Good thermal stability• Excellent mechanical strength• Extremely very thin• High charge carrier mobility• High optical transparency

Synthesis of monolayer or few layer graphene by different routes

• Mechanical Exfoliation

• Epitaxial growth of graphene from SiC

• Chemical Vapour Deposition(CVD)

Chemical Vapour Deposition(CVD)• Deposition of a solid on a heated surface from a chemical

reaction in the vapour phase.

Fig 1.2 CVD Schematic diagram of the process (From Handbook of CVD)

Chemical Vapour Deposition

• Diffusion of reactants through boundary layer• Adsorption of reactants on substrate• Chemical reaction takes place• Desorption of the by products from the surface• Diffusion out of byproducts through boundarylayer

Use of catalysts in CVD• Transition metals have partially-filled d-orbitals that enable them to

adsorb and interact with the hydrocarbons that are used as the carbon sources

• Different metals each have their own unique mechanism for growing graphene

• Use of Ru, Ir, Ni, or Co lead to a segregation growth procedure, and the graphene expand with carpet growth mode

• For Cu catalyst, the formation of graphene can be explained by the surface growth model

Graphene growth mechanism on Cu and Ni substrates

Fig 1.3. Growth kinetics in CVD graphene on different catalyst: Case of CH4 on Ni and Cu.

Fig 1.4 Graphene formation on single crystal Ni(111) surface and polycrystalline Ni surface

Fig 1.5 Optical image of graphene/ Ni (111) surface and Poly crystalline Ni Surface after the CVD process.

Fig. 1.6 – SEM images for graphene with (a) a hexagonal shape (b) a four-lobed flower shape and (c) a dendrite shape

Future prospects• The use of expensive metals such as Ru, Ir, Pt, and Pd for the synthesis

of graphene is not practical.• Those metals are relatively inert, which makes the separation of

graphene from the catalyst substrate difficult.

• Reuse of the catalyst substrate is the most crucial step to reducing the production cost and facilitating large-area graphene production

• The direct peel-off method using thermal release tape for graphene separation always causes mechanical damage to the graphen

• Another challenge is to grow large-area single-crystal graphene most ideal graphene is a flat single crystal with no defects, which will be uniformly reactive.

Summary• Graphene is an innovative material that possesses various desirable

properties, and CVD appears to be the most promising route for accomplishing large-area graphene synthesis.

• Among all the metals that have been studied for graphene formation, Ni and Cu are the two transition metals with the potential for synthesising large-area graphene with ease.

• Effective separation and reuse of the catalysts would be the key obstacle for the mass production of graphene at low cost.

• The rapid pace of graphene research ensures that a more practical graphene synthesis and transfer method will be discovered.

Summary(continued)

• Studies are required to achieve controllable synthesis, which includes the ability to tailor and fabricate the size and the number of layer of graphene.

• This can only be achieved if the graphene growth mechanism, kinetics, and rate-limiting step are revealed and new classes of catalysts and processing conditions are discovered.

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