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CHAPTER 4

4. Synthesis of graphene from methane, acetonitrile, xylene and

ethanol

4.1 Introduction

In this chapter, the synthesis of graphene from three different carbon precursors include gases

(methane, ethylene), liquid (ethanol, methanol) and solid (PMMA and polystyrene) using

CVD method is reported. Srivastava et al.[89] demonstrated the substrate-selective growth of

centimetre size (∼3.5 cm x1.5 cm), uniform and continuous single and few-layer graphene

films employing vacuum-assisted chemical vapor deposition on polycrystalline Cu foils using

liquid hexane as the carbon precursor and it exhibits better FET properties as compared to

exfoliated graphene. Guermoune et al. reported the synthesis of the graphene from methanol,

ethanol and propanol using CVD at 850°C. Low-purity carbon sources were used to grow

high purity, large area graphene films. Many researchers reported the growth of graphene

from solid carbon sources included PMMA [90], silicon carbide [91],amorphous carbon [92]

and highly oriented pyrolytic graphite (HOPG) [93] The solid precursors have large and

complex molecular structures. Synthesis of graphene from these precursors involves

complicated chemical reactions and processes.

Zhancheng Li et al. reported synthesis of graphene from liquid benzene precursor at low

temperature (300°C) compared to conventional high temperature. The benzene ring

resembles the basic unit of graphene. In contrast to the large molecules such as PMMA or

polystyrene, benzene molecules just need to dehydrogenate and connect to each other to form

the graphene structure. The activation energy of benzene dehydrogenation on Cu [111] is

(1.47 eV), which is lower than conventional carbon precursor [methane 1.77 eV]. Hence,

growing high-quality graphene using benzene as the carbon precursor might require lower

temperatures as compared using gas precursors such as methane, and acetylene [94].

Thus, there is value in further investigating the synthesis of high quality graphene (including

single layer) from new liquid organic precursors. This is also significant since graphene

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synthesis becomes possible without the use of expensive high purity gaseous hydrocarbons

(methane, acetylene and ethylene) [95, 96].

The modulation of electronic/electrical properties of graphene is highly important for the

development of electronic devices. Theoretical studies have revealed that substitutional

doping can alter the Fermi level and induce the metal-to-semiconductor transition in

graphene. Elements such as nitrogen and boron are ideal candidates as dopants in graphene.

Nitrogen-doped graphene (NG) has been successfully developed by direct synthesis and post

treatments. The promising applications of N-doped graphene in electronic devices, oxygen

reduction reaction, biosensing, and energy storage devices have attracted great attention [97].

Graphene synthesis using organic liquid precursors is feasible since most organic compounds

and their derivatives readily vaporize below 200°C. Doping of graphene with different

elements can be conducted by using organic precursors containing those elements. E.g.

Nitrogen and boron containing compounds such as pyridine and triethylborane for N-doped

and B-doped graphene respectively[89]. The liquid precursors can be more easily stored and

handled as compared to hydrocarbon gases. The use of inductive heating in the synthesis of

carbon nanotubes and graphene by CCVD can significantly reduce the energy consumption

and overall reaction time [64, 98]. This can lead to significant reduction in price, even while

maintaining the quality (purity and crystallinity) of carbon nanotubes and graphene.

In this chapter, we report the synthesis of large area (1 cm2 x 4 cm2), continuous graphene

films using atmospheric pressure radio frequency chemical vapor deposition (RF-CVD). The

catalyst used was polycrystalline copper foil, which is shown to have advantage of allowing

the synthesis of single to few layer graphene[60] at a reasonable cost. The different

precursors used were methane, xylene, ethanol and acetonitrile at temperatures ranging from

700–1000°C (Table 4-1).

4.2 Experimental method The two major steps involved in the synthesis of graphene are as follows

• Pre-treatment of the copper foils

• Growth of graphene on copper by CVD [method]

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4.2.1 Pretreatment of copper foil The catalyst used for graphene synthesis is copper.

Figure 4-1: Copper foils (Alfa Aesar 25μ thick) substrates for the synthesis of graphene.

The copper foil is cut with a flange and a hole in the centre to the dimension [1×1cm2] shown

in Figure 4–1 and Figure 4–2 shows the flange helps in holding the foil without causing

damage to the surface of copper while transferring and it is maintained as a reference for

positioning the foil. Also, for viewing the sample in optical microscopy the punched hole acts

as a reference point.

Figure 4-2: Schematic of the copper foil with dimension in mm The foil is placed between two glass slides to make it wrinkle free. The foil is taken from the

glass slide and it is rinsed in iso propyl alcohol (IPA) and acetone for 10 seconds respectively

to decrease the surface of organic impurities. Then the foil is dipped in acetic acid at 35°C for

10 min to remove if any oxide layer was formed and it is weighed. Before weighing, the

traces of acetic acid are cleaned using lint-free tissue paper. The cleaned copper foil is placed

in the graphite boat immediately, to avoid further formation of oxide layer, according to the

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arrangement shown in Figure 4-3 to study the deposition gradient. The graphite susceptor is

then carefully placed in the quartz tube. A summary of the procedure is shown in Figure 4-4

 

Figure 4-3: Arrangements of copper foils

Figure 4-4: Pretreatment steps in synthesis of graphene.

4.2.2 Graphene growth in CVD

A pressure gauge is placed in between the flow control rotameter and quartz tube as shown in

Figure 4-5. Argon gas is introduced into the one end of quartz tube and the other end of the

quartz tube is closed. So the pressure in the tube builds up and it will be indicated in pressure

gauge. After this process, the argon flow is stopped and a leak test is performed using soap

solution at every joint to identify any leakage and this process is repeated till the system is

leak proof.

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Figure 4-5: Pressure gauge for leak test If the pressure remains stable then the CVD system is considered to be leak proof and the

quartz tube is purged using argon gas with a flow rate of 600 mL/min for 20 minutes. Figure

4-6 shows the removal of oxygen and the increase in the concentration of Ar as a function of

time. These curves were obtained from a simple model considering the flow of argon and air

in the quartz tube as a plug flow (with no axial or radial counter-diffusion). It is clear from

the figure that after about 10 min, the level of oxygen becomes low enough to be undetected.

Yet the purging time for all experiments is kept at 20 min as a factor of safety before

introducing the hydrocarbon precursor. This is to prevent possible ignition or explosion of the

hydrocarbon gas in the presence of oxygen, as well as possible defects that might arise in the

graphene during its synthesis.

Table 4-1: Reaction condition of graphene synthesis Precursor Flow rate Temperature (°C) Reaction Time (min)

Methane 15 mL/min 1000 15

Acetonitrile 1 mL/hr 1000 15

Ethanol 2 mL/ min 1000 15

Xylene 1 mL/hr 1000-700 15

The temperature is then increased to 1000°C and the argon flow rate is reduced to 200

mL/min. Once the temperature reaches 1000°C, H2 at 100mL/min is introduced for 30min to

reduce the copper oxide layer from the copper foil. Then carbon precursors are introduced

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according to Table 4-1. The samples are then cooled down to room temperature in Ar

atmosphere.

Figure 4-6: Purging time chart

4.2 2 Transfer of Graphene The fabrication of samples and devices using other types of substrates is relevant for

fundamental studies or the optimization of graphene’s performance. The identification of

graphene sheets, down to one layer in thickness, with optical microscopy is possible via

colour contrast caused by the light interference effect on the SiO2 which is modulated by the

graphene layer. This makes the preparation of graphene samples and devices not only

possible but also efficient. However, the observation of a clear colour contrast requires Si

substrates with a specific SiO2 thickness (280-300nm), thus limiting the fabrication of

graphene devices to these substrates. Therefore, it is necessary to develop transfer methods

which can integrate graphene sheets with a wider variety of substrate materials [PMMA]

while also allowing an efficient identification of the graphene.

The graphene films synthesized from the Cu foils were removed by etching in an aqueous

solution of ferrous nitrate. The etching time was found to be a function of the etchant

concentration, the area, and thickness of the Cu foils. Typically, a 1 cm2 by 25-μm thick Cu

foil can be dissolved by a 0.05 g/ml ferrous nitrate solution overnight. For a 2 cm2and 25-μm

thick Cu foil, the optimized concentration of iron nitrate used was 0.083g/ml. The blank

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experiment of copper etching in ferrous nitrate is shown in Figure 4-7 and the graphene

grown on copper is etched in ferrous nitrate as shown in Figure 4-8.

We used two methods to transfer the graphene from the Cu foils: (1) The copper film is

dissolved, a substrate is brought into contact with the graphene film and it is ‘pulled’ from the

solution, (2) the surface of the graphene-on-Cu is coated with poly-methyl methacrylate

(PMMA) and the Cu is dissolved in the PMMA-graphene which is lifted from the solution.

The first method is simple, but the graphene films experiences more tear damage. The

graphene films are easily transferred with the second method to other desired substrates such

as SiO2/Si, with significantly fewer holes or cracks (<5% of the film area).

Figure 4-7: Etching of copper (without graphene) by ferrous nitrate

Figure 4-8: Etching of graphene grown copper by ferrous nitrate

Figure: 4-9: Steps involved in the transfer of graphene

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The overall steps involved in the transfer of graphene are listed below and shown in Figure

4-8 and depicted in Figure: 4-9

Remove the graphite boat out of the quartz tube slowly.

Use tweezers to gently remove the copper foil with graphene on a glass slide as shown

in Figure: 4-9a

Use a micropipette to drop coat a known amount PMMA solution in acetone

(0.0467g/mL) so that it just covers the surface of graphene as shown in Figure: 4-9 b

Carefully place the glass slide containing PMMA-coated graphene in the oven at

180˚C for 1 min to dry the PMMA coating.

Immediately remove the glass slide from the oven and place the PMMA/

graphene/copper foil onto the ferrous nitrate solution using tweezers so that it floats as

shown in Figure: 4-9c

After the completion of etching the PMMA/graphene film will remain floating on

nitrate solution where as the copper foil may or may not completely dissolve but it

will detach from the PMMA/graphene film as shown in Figure: 4-9d.

Gently scoop the PMMA/graphene from the iron nitrate solution using the required

substrate like silicon wafer or Cu grid coated with Formvar™ or glass slide

Depending on the convenience for further characterization as shown in Figure: 4-9d e

Figure 4-10: Steps in the transfer of graphene.  

 

 

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4.2.3 Characterization High-resolution scanning electron microscopy (HRSEM) observations of the nanoparticles

were performed with a HRSEM Hitachi S4800 with EDX at an acceleration voltage of 5.0 kV

(This SEM instrument was used in Chapter 6, 7 & 8). Raman spectra were obtained with a

WITec Alpha 300 Confocal Raman system equipped with a Nd:YAG laser (532 nm) as the

excitation source (for used methane, acetonitrile and xlyene). X-ray photoelectron

spectroscopy (XPS) utilizing a PHOIBOS 100 analyser with an Al Ka radiation (1486.6 eV)

as an excitation source.

4.3 Results and Discussions

4.3.1 Synthesis of graphene from methane and acetonitrile The second-order Raman spectrum (2D band) of graphene is quite sensitive in determining

the number of layers of graphene [99]. The graphene layers were estimated from the FWHM

of the 2D band and the intensity ratio of the 2D and G band (I2D/IG). According to literature,

FWHM values of the 2D band < 32 cm-1 indicate single layer graphene, 33–55 cm-1 indicate

bilayer graphene and >70 cm-1 indicate few layer-graphene. Also, when the ratio of intensity

of the G and 2D bands (IG/I2D ratio) is less 0.5, then it is an indication of single-layer

graphene. Similarly, an IG/I2D ratio ~ 1 indicates bilayer and IG/I2D ratio >1.5 indicates few-

layer graphene [100, 101, 102]. The IG/ID ratio indicates the crystalline nature of graphene

and a higher value indicates a better quality material with low defects [103, 104]. The

presence of disorder in the crystalline lattice is indicated by the D band, which arises from the

A1g mode breathing vibrations of six-membered sp2 carbon rings [105].

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Table 4-2: Raman features of graphene and N-doped graphene Sample Reaction

Temperature

°C

G- Band

cm-1

D- Band

cm-1

2D– band

cm-1

2D- FWHM

cm-1*

IG/ID

cm-1*

I2D/IG

cm-1*

Methane 1000 1575 1354 2713 90±2.12 2.42±0.166 0.536±0.014

Acetonitrile 1000 1593 1337 2649 95±15.55 0.82±0.038 0.64±0.057

* Standard deviation value

Figure 4-11 indicates the Raman spectra of the graphene obtained from methane at 1000°C.

We observed peak positions at 1354, 1575 and 2713 cm-1 for D, G and 2D bands

respectively. The 2D band is the second order of the D band and its shape as well as its

position is used to identify a single layer sheet of graphene. The ratio of I2D/IG value was

0.536 ± 0.014 and 2D band FWHM value was 90±2.12 cm-1. These results indicate the

presence of good quality few-layer graphene (IG/ID was 2.42±0.166) [94, 96]. Figure 4-12 (a-

b) show SEM images of graphene in which different layers of graphene with wrinkles and

folds can be seen clearly. Figure 4-12(c) shows graphene sheets and multilayer graphitic

flakes along with nanoparticulate impurities, presumably from the catalyst (Cu) and etchant

(Fe (NO3)2[106]. Figure 4-12(d) shows an HRTEM image of graphene, in which few layer to

multilayer graphene is clearly visible (5–10 layers).

Figure 4-13 indicates the Raman spectrum of N-doped graphene, with IG/ID value of

0.82±0.038. This value is indicative of higher defect concentration, which is expected

because of the doping of nitrogen in graphene leading to a more pronounced D band. In

comparison, the IG/ID of graphene from methane was 2.42±0.166 indicating fewer defects.

Further, the Raman spectrum of N-doped graphene also shows a pronounced D’ peak, which

is absent in the graphene synthesized from methane. Since nitrogen atoms on graphene lattice

positions act as defects, the appearance of a D’ peak in the Raman spectrum can be related to

an incorporation of nitrogen [107].

The Figure 4-14 (a-b) indicates X-ray photoelectron spectroscopy of the N- doped graphene,

which is synthesized from acetonitrile at 1000°C.Figure 4-14 (a) indicates the main peak at

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284.6eV corresponds to the graphite-like sp2 C, indicating that most of the carbon atoms are

arranged in honeycomb lattice. The small peaks (Figure 4-14a) at 285.09 and 286.06eV can

be attributed to C-N bonding. (Figure 4-14b) N1s line scan of NG sample, which confirms

the presence of substitutional (400.6eV) and pyridine-like (399.41eV) nitrogen dopants[97].

The morphology analysis of N-doped graphene is shown in Figure 4-15 (a-b). Figure 4-15(a)

shows a large area graphene layer and its one edge was folded. Figure 4-15 (b) shows

graphene sheets with a darker region possibly corresponding to multi or few layers of

graphene.

Figure 4-11: Raman Spectrum of graphene from methane carbon precursor

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Figure 4-12: (a-b) SEM, (c-d) TEM image of graphene from methane

Figure 4-13: Raman Spectrum of graphene from acetonitrile carbon precursor

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Figure 4-14: XPS spectra of N-doped graphene from acetonitrile at 1000°C

Figure 4-15: TEM images of N-doped graphene from Acetonitrile at 1000°C (a-b)

4.3.2 Synthesis of graphene from xylene at different temperature (700–1000°C) Graphene was synthesized using xylene precursor in the temperature range 700–1000°C.

From the Raman analysis, the formation of single to double layer graphene at lower

temperature, and multilayer graphene at higher temperature was observed [108]. Figure 4-16

(a-d) shows the Raman features of graphene synthesized from xylene at 700-1000°C. For

graphene obtained from xylene, with an increase in synthesis temperature from 700 to

1000°C, there was an increase in the FWHM of the 2D band from 53±2.5 to 100±5.1 cm-1.

These results reveal the presence of double-layer graphene at 700°C. As the reaction

temperature increases, few-layer graphene is formed, and the 2D peak position shifts to

higher wave number. Among the samples the highest IG/ID ratio of 2.14±0.25 was obtained at

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800°C, while for other samples, the ratio was in the range of 1.31 1.41. This indicates the

presence of graphene with the best sp2-hybridized graphitic nature at 800°C.

a b

dc

Figure 4-16: Raman Analysis of graphene from xylene at 700 -1000°C

Table 4 3: Raman features of graphene synthesized from xylene at 700 – 800°C

Sample

Reaction Temperature

°C

G- Band

cm-1

D- Band

cm-1

2D – band

cm-1

2D- FWHM

cm-1

IG/ID

cm-1

I2D/IG

cm-1

1 700 1586 1326 2653 53±2.5 1.41±0.21 0.63±0.03

2 800 1561 1332 2661 65±3.1 2.14±0.25 0.92±0.05

3 900 1582 1330 2661 96±4.5 1.37±0.17 0.59±0.02

4 1000 1582 1330 2663 100±5.1 1.31 ±0.15 0.21±0.02

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Figure 4-17: SEM (a) and TEM (b-c) images of the graphene from xylene at 700°C

Figure 4-18: SEM (a, c) and TEM (b, d) images of the graphene from xylene at 800°C and 900°C

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Figure 4-19: SEM (a) and TEM (b) images of the graphene from xylene at 1000°C

The morphology analysis of the graphene samples synthesized at 700°C, 800°C, 900°C and

1000°C are obtained by SEM and TEM analysis shows in Figure 4-17 to Figure 4-19. These

results indicate a very transparent single to few layer graphene obtained from growth

temperature at 700 and 800°C.

Figure 4-17(c) shows presence of 1–3 layers of graphene sheet (700°C). Figure 4-18 (a-b)

SEM (a) and TEM (b) images of graphene from 800°C, Figure 4-18(b) indicates more

wrinkles and folded graphene sheets with less transparent as compared to graphene

synthesized at 700°C. However, Figure 4-18 (c) and Figure 4-19 (a) shows the less

transparent and more wrinkles with light dark colour graphene sheet [synthesized at 900 and

1000°C]. The same result also observed from TEM [Figure 4-18 (d) and Figure 4-19 (b)]

analysis, higher temperatures leads to the formation of fast decomposition of carbon

precursor and carbon solubility which leads to the formation of multilayer graphene.

4.3.2.1 Mechanism of graphene formation using xylene

Here reported, graphite boat with length 90mm and it is connected to K-type thermocouple,

RF-induction coil is used as a heating element. Induction heating leads to the heating of the

graphite boat surface alone. As a result, the xylene decomposes, leaving carbon deposits on a

small area since the boat length is 90mm. The decomposition of the xylene molecules is

uniform due to this induction heating process.

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Shevel'kova et al has investigated the pyrolysis of p-xylene at temperatures of 830°-1000°C

with different hydrocarbon partial pressures (argon/p-xylene=10:1, 20:1, 30:1). The

pyrolysed product contained following free radicals namely (aromatic hydrocarbon),

naphthalene, methylnaphthalene, biphenyl, diphenylmethane, diphenylethane, phenanthrene,

methyl- and dimethylphenanthrene, anthracene, methyl- and dimethylanthracene, di-p-

xylene, and dimethylstilbene. Methane and ethylene molecules were obtained from pyrolysis

of xylene at higher temperature. The formations of methane and ethylene molecule increased

at higher temperatures (830-1000°C) from 22 to 25.0 mol % and 0.1 to 1.7 mol%

respectively. At higher temperatures, ring opening of xylene molecules is favored, which

leads to the formation of non-aromatic compounds [109]. Further, the pyrolysis of the xylene

also shows 5.3 mole % of toluene as a byproduct at lower temperature (830°C, andargon:

xylene = 10:1).

Based on the above discussion, it could be concluded that at lower temperatures, aromatic

free radicals are present in significant concentrations, which deposit on copper surface. They

further undergo surface diffusion on copper until they are stabilized by London dispersive

forces and then cyclization of aromatic radical occurs by dehydrogenation. Finally, graphene

is formed on copper foil. The temperature, for the decomposition of xylene is at 1000°C,

results produced more number of free radicals with aromatic and non-aromatic compounds.

So most of the carbon radicals are deposited on copper foil, which leads to the formation of

multilayer graphene sheet.

4.3.3 Synthesis of graphene from ethanol Raman characterization was carried out on a JobinYvon Horiba LABRAM-HR 800

instrument with a laser source of 488nm (E= 2.53ev) and optical lens with optical

magnification is 50x, a spot size of 0.59μm, a single monochromator and a Peltier cooled

charge-coupled device. Raman mapping images show the typical Raman spectra of graphene

films at selected locations, the graphene films grown from ethanol as carbon precursor. All

the CVD graphene samples are etched from copper foil using ferric nitrate solution and then

transfer to silicon wafer. Raman mapping was performed over an area of 20 x 16 μm on each

sample, with each map consisting of 30 points of measurement Figure 4-20 shows the Raman

mapping of 2D band features (a) FWHM (b) intensity (c) peak position of the 2D band. The

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Figure 4-20 (a) 2D FWHM mapping (a) where size of the mapping with 30 points of the

Raman measurement on 20 x16 μm area of graphene film. The 2D FWHM maps we see that

most of the sample area had values 68–73 cm-1 (red color region), corresponding to few layer

graphene. The yellow colour region has 74-75 cm-1 and green color region is above 76 cm-1

which indicates the presence of multilayer graphene. Figure 4-20 (c) mapping of the 2D peak

position shows that the peak position at various points on the sample lie in the range of 2716

to 2720 cm-1. The peak position of the 2D band shifting towards a higher wave number is

indicative of the presence of few layers to multilayer graphene. Figure 4-20 (b) shows the

intensity of the 2D band, which lies between 3000-5500 a.u (red to green colour) and a higher

intensity is generally indicative of a better quality of graphene.

Figure 4-21(a) shows the I2D/IG ratio of 2D and G bands, which is related to number of the

layer of graphene, where the ratio ranges between 0.55-0.80 indicating few to multilayer

graphene as also inferred from the FWHM of 2D band. Figure 4-22(a, b &c) shows the

mapping of the D band features, FWHM of the D band 44±0.8 cm-1 due to presence of the

structural defects and Figure 4-22 (b) shows the intensity of the D band, red colored area

indicates the less defect compared to green colored (more defect due the graphene transferred

from copper foil to silicon wafer). The quality of the graphene sheet measured by FWHM and

the intensity of G band. Figure 4-23 (a) indicates the FWHM of the G-band with 38-44 cm-1.

A sharp G band indicates good quality of graphene sheet (lower values of FWHM of G

band). The G band intensity map revealed that most of the sample area has higher intensity

shown in yellow to green color region in Figure 4-23 (b). The G-peak position shifted 1581-

1584 cm-1, which indicates the change of the electronic properties of graphene due to the

presence of oxygen atoms. The graphene layer quality and crystallinity are determined by

intensity ratio of the G band and D band, Figure 4-21 (b) shows the mapping of IG/ID ratio,

the ratio is 0.90 -1.10 with 20×16µM (Raman mapping area). The results show most of the

area having good quality graphene sheet (light yellow to dark green colour) and few areas D

band intensity higher compared to G band intensity.

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Figure 4-20: Raman mapping of 2D-band features of graphene synthesized from ethanol at 1000°C. (a) FWHM, (b) Intensity and (c) Peak position of the 2D-band

Figure 4-21: Raman mapping of features of graphene synthesized from ethanol at 1000°C (a) Intensity ratio of 2D/G and (b) intensity ratio of G/D

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Figure 4-22: Raman mapping of D-band features of graphene synthesized from ethanol at

1000°C. (a) FWHM, (b) Intensity and (c) Peak position of the D-band.

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Figure 4-23: Raman mapping of G-band features of graphene synthesized from ethanol at

1000°C. (a) FWHM, (b) Intensity and (c) Peak position of the G-band

s Figure 4-24: TEM images of graphene from ethanol precursor

Figure 4-24 (a-b) shows the TEM image of graphene samples, which is obtained from ethanol

carbon precursor at 1000°C. Figure 4-24 (b) shows high resolution TEM image, where

observed 5-10 layer of graphene and Figure 4-24 (a) shows lager area graphene folded with

wrinkles. These results are well supported for micro Raman mapping (No. of the graphene

layers).

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4.4 Conclusions

We have synthesized graphene and N-doped graphene from different carbon precursors at

different temperatures (700–1000°C) on copper foil using atmospheric RF-CVD method.

Raman analysis indicates that few layer graphenes are obtained from methane and acetonitrile

precursor at 1000°C. The quality of the graphene as measursed by the intensity ratio of IG/ID,

for the few-layer graphene sheets obtained from methane [IG/ID is 2.42] was better as

compared to N-doped graphene [IG/ID is 0.82] due to presence of nitrogen atoms in the latter.

This was also confirmed with XPS results. Graphene was also synthesized from aromatic

carbon precursor (xylene) for the growth of graphene in the temperature range 700-1000°C

using CVD. The results indicate that an increase in the synthesis temperature favors the

formation few layer graphene sheets, while lower temperatures are more favorable for the

synthesis of single layer graphene. Graphene was also synthesized from ethanol precursor on

copper foil at 1000C and the Raman features (FWHM, peak intensity, and peak position of

the G, D, and 2D bands as well as the IG/ID and I2D/IG ratios) were mapped.