This document summarizes the mechanism of graphene growth by chemical vapor deposition (CVD) on transition metals. It discusses how CVD uses transition metal catalysts like copper and nickel, which adsorb hydrocarbon gases and enable the growth of graphene through surface processes. The growth kinetics differ between copper and nickel, with graphene expanding across copper's surface but segregating on nickel. Effective separation and reuse of the metal catalysts is key to making graphene production cost-effective at large scales.

1. Mechanism of graphene growth by chemical
vapour deposition on transition metals
S.N.Ramachandra
15MT60R10
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.

2. 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

3. 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)

4. Properties of graphene
• High electronic and thermal conductivity
• Good thermal stability
• Excellent mechanical strength
• Extremely very thin
• High charge carrier mobility
• High optical transparency

5. Synthesis of monolayer or few layer
graphene by different routes
• Mechanical Exfoliation
• Epitaxial growth of graphene from SiC
• Chemical Vapour Deposition(CVD)

6. 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)

7. 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

8. 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

9. 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.

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

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

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

14. 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.

15. 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.

16. 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.