Synthesis Of Large Area Graphene And Graphene Flake Via Chemical Vapor Deposition Using Copper Catalyst And Methane
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Date
2018-05-01
Authors
Mohd Zuhan, Mohd Khairul Nizam
Journal Title
Journal ISSN
Volume Title
Publisher
Universiti Sains Malaysia
Abstract
Graphene is a two-dimensional material arranged in hexagonal honeycomb
structures and is a single layer of graphite. Several fascinating properties of graphene
such as a very conductive and highly transparent material is expected to contribute
significantly towards the advancement of electronics, solar cell, composites, and
medical sector. In this study, atmospheric chemical vapour deposition (APCVD) was
used as synthesis method. Methane was used as carbon feedstock, nitrogen as a carrier
gas and hydrogen as reducing agent for two types of graphene synthesis which is large
area graphene (lateral size >1 cm2) and graphene flakes (lateral size <1 µm2) with Cu
was used as a catalyst. The study is also focusing on solving the tendency of
polycrystalline large area graphene from breaking into small fragments during the
transfer process via wet etching by reducing the surface tension of graphene/water
interface using n-heptane as support and avoiding polymer contamination on the
graphene. The proposed method is easier and more environmentally friendly as the
practice reduce the use copious amount of organic solvent to remove the polymer layer
as the process often creates plentiful of chemical waste. N-heptane as support material
for wet etching process is easier to conduct, generated less waste and does not cause
significant contamination on the graphene and can be reused for another graphene
transfer and create less toxic waste as compared by using polymer support. In addition,
a wet etching method requires the use of an etchant and the process produce wastes
contain metal that generally disposed of in single-use. The practice limits the use of
the metal substrate and harmful to the environmentally. Hence, recovery of the metal
from the waste as a precursor to a new form of catalyst for graphene flake synthesis is
suggested. The study utilised 30 sccm and 50 sccm of CH4 gases flow-rate with
reaction time were set for 30 min and 60 min with growth temperature was set at 950 °C for large area graphene synthesis. Nine metal foils were used in three zones
locations inside the horizontal tubular furnace. Furthermore, the effect of H2 flow rate
on graphene crystallinity which was set at 0, 25, 50, 75, 100, 125 and 150 sccm was
also studied. Subsequently, graphene transfer from Cu foil onto Si/SiO2 was performed
using 0.1 mol ammonium persulfate solution as an etching solution and n-heptane as
supporting layer. Next, the etched Cu foil was recovered and reused by heat treatment
temperature of 800 °C for 3 hours to obtain CuO for graphene flakes synthesis. Two
formulations of 10% MgO with 90% CuO and 1% MgO with 99% CuO were dispersed
in ethanol and was kept overnight in an oven at 60 °C before undergoing calcination
process at 950 °C to produce CuO/MgO that was used for graphene flake synthesis.
The graphene flakes synthesis was conducted at 950 °C for 60 min with 10 sccm of
CH4. Thermogravimetric analysis (TGA), X-Ray Diffraction (XRD), X-ray
Fluorescence (XRF), optical imaging, Raman spectroscopy (single point and
mapping), high-resolution transmission electron microscopy (HRTEM), Field
emission scanning electron microscopy (FESEM), and X-Ray Photoelectron
Spectroscopy (XPS) were used to evaluate the properties of the synthesized graphene
and CuO/MgO. The result shows large area graphene and graphene flakes were
successfully synthesized using Cu foil and recovered Cu, the positions of the Cu shows
the different quality of graphene and the hydrogen flow rates shows the quality of the
graphene is affected by the hydrogen flow rates with positive effect on graphene
formation at 50 to 100 sccm and negative effect when no (0 sccm), inadequate (25
sccm) or excessive (>125 sccm) hydrogen flow rates were supplied. The locations of
the catalyst at zone 1 and zone 2 of the horizontal furnace show good graphitic
structure formation while at zone 3 amorphous carbon formation is more dominant. N-heptane is found as a useful material for large area graphene transfer that reduces
contamination on graphene surface. Cu from etching solution waste can be reused for
CuO formation and graphene flakes synthesis using a similar method for synthesis of
large area graphene. In conclusion, the catalyst locations in the horizontal CVD and
hydrogen flow rates play an important factor in graphene formation. The transfer
method using the n-heptane as support layer assisting in graphene transfer process that
reduces contamination and damage to graphene structure. Also, the graphene flakes
have been successfully synthesized using the CuO / MgO catalyst obtained from
recovered Cu.