Synthesis Of Monolayer Graphene On Polycrystalline Nickel And Nickel-Copper Bimetallic Catalyst And Study Toward The Reuse Of Nickel Catalyst
Graphene is a layer of sp2 hybridized carbon atoms with a thickness of only one atom, which exposed most of its atoms to the surrounding medium. Since the discovery of graphene in 2004, it has become the main subject of research around the world. The attractiveness of graphene is mainly attribute...
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| Format: | Thesis |
| Language: | English |
| Published: |
2016
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| Subjects: | |
| Online Access: | http://eprints.usm.my/46996/1/Synthesis%20Of%20Monolayer%20Graphene%20On%20Polycrystalline%20Nickel%20And%20Nickel-Copper%20Bimetallic%20Catalyst%20And%20Study%20Toward%20The%20Reuse%20Of%20Nickel%20Catalyst.pdf |
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| Summary: | Graphene is a layer of sp2 hybridized carbon atoms with a thickness of only
one atom, which exposed most of its atoms to the surrounding medium. Since the
discovery of graphene in 2004, it has become the main subject of research around the
world. The attractiveness of graphene is mainly attributed to its remarkable
mechanical, optical, thermal and electrical properties, enabling graphene to be
potentially used in various applications. To date, CVD is the promising method to
produce wafer-scale graphene, because it allows an easier separation of graphene
from the catalytic substrate. With the assist of fast cooling, monolayer graphene was
grown directly on polycrystalline Ni foil under atmospheric pressure CVD with
temperature of 850 ºC, methane partial pressure of 0.2 atm and reaction duration of 5
min. However, monolayer graphene could not be formed on Cu under the chosen
CVD conditions. Fast cooling after CVD allowed the quenching of the activity of the
catalyst and limiting diffusion of dissolved carbon to the surface of Ni, which later
facilitate the formation of predominantly wafer scale monolayer graphene. To further
improve the uniformity of monolayer graphene, a facile technique was applied to
grow monolayer graphene simultaneously on both polycrystalline Ni and Cu foils
using a Ni-Cu bilayer catalyst at temperature of 950 ºC, methane partial pressure of
0.2 atm and reaction duration of 5 min. High uniformity and quality of the crystalline
structure of the grown graphene was evidenced by Raman spectroscopy mapping and
High Resolution Transmission Electron Microscope. The straightforward bimetallic
catalytic system allows the control of carbon diffusion to the interface of Ni and Cu.
In particular, carbon accessibility is reduced at the inner Ni surface, and Cu behaves
as a carbon barrier. The growth mechanism of monolayer graphene was facilitated by
carbon diffusion through the bulk and Ni grain boundary, the driving force coming
from concentration gradient between carbon-rich surface to carbon-lacked surface.
The grain boundaries were shown to play a crucial role in carbon control during the
growth stage. Facilitated by the applied fast cooling, the quenching process reduced
the amount of carbon atoms segregated, only the carbon atoms situated near the
surface had enough time to segregate and form graphene. Meanwhile, diffusion of
carbon atoms at the middle of the Ni foil was highly inhibited; forming Ni3C. Ni3C is
known to offer good protection against corrosion. The presence of Ni3C combined
with the use of iron nitrate (0.5mol/L) as soft etchant for graphene separation, the Ni
foil could be reused again up to 6 cycles without causing a huge deviation on the
quality and the uniformity of bilayer graphene. Ni3C is indeed able to limit the
etching effect of the Ni foil. This work has successfully demonstrated a simple and
novel route to synthesize monolayer graphene with high quality. |
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