The Impact of Reaction Parameters on Graphene-like Material Synthesized Using Chemical Vapour Deposition

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ScienceDirect Procedia Engineering 184 (2017) 460 – 468

Advances in Material & Processing Technologies Conference

The Impact of Reaction Parameters on Graphene-like Material Synthesized using Chemical Vapour Deposition H. Cheun Lee1, Wei-Wen Liu1,*, Siang-Piao Chai2, Abdul Rahman Mohamed3, C.H.Voon1, U.Hashim1, M. K. Md Arshad1, P.Y.P Adelyn1, A.R.N. Huda1, S.M. Kahar1, N.M.S Hidayah1, Chin Wei Lai4, Cheng-Seong Khe5 1

Institue of Nanoelectronic Engineering, Universiti Malayisa Perlis, 01000 Kangar, Perlis, Malaysia. School of Engineering, Monash Univeristy, Jalan Lagoon Selatan, Bandar Sunway, 46150, Selangor, Malayisa. 3 School of Chemical Engineering, Engieering Campus, Universiti Sains Malaysia, 14300 Nibong Tebal Seberang Perai Selatan, P. Pinang, Malaysia. 4 Nanotechnology and Catalysis Research Center (NANOCAT), Institute of Graduate Studies, Universiti Malaya, 50603 Kuala Lumpur, Malaysia. 5 Department of Fundamental and Applied Sciences, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, 31750 Tronoh Perak, Malaysia. 2

Abstract The remarkable properties of graphene have directly accelerated the graphene research. Due to its unique and remarkable characteristics, graphene can be potentially used in various applications. Chemical Vapour Deposition (CVD) has been identified as a promising and important method for preparation and production of graphene due to its good film uniformity and large scale production. Herein, we demonstrated that reaction parameters including the reaction duration and reaction temperature could affect the quality, quantity and morphology of synthesized samples. Energy Dispersive X-ray (EDX) results indicated that the carbon content on the graphene-like samples increased with the increasing reaction duration. Scanning electron microscopy (SEM) images showed that thicker carbon clusters were grown when a longer reaction time was used. X-ray diffraction (XRD) pattern indicted carbon existed in the samples synthesized. The comparison between different reaction parameters can assist in selecting the optimum growth parameters of graphene-like samples. © 2017 The Authors. Published by Elsevier Ltd. © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license Peer-review under responsibility of the organizing committee of the Advances in Material & Processing Technologies (http://creativecommons.org/licenses/by-nc-nd/4.0/). Conference. Peer review under responsibility of the organizing committee of the Advances in Materials & Processing Technologies Conference Keywords: Graphene; Chemical Vapour Deposition; Electron Microscopy; Carbon; X-Ray Diffraction

1877-7058 © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license

(http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer review under responsibility of the organizing committee of the Advances in Materials & Processing Technologies Conference

doi:10.1016/j.proeng.2017.04.117

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1. Introduction Graphene is a two-dimensional crystallite that is composed of a flat sheet of carbon atoms that are arranged in a honeycomb lattice. It displays a single atom thick sheet of sp2-bonded carbon atoms that are configured in a hexagonal manner [1]. Therefore, graphene is the basic building block of other carbon allotropes. It has received a lot of attention from the world due to its remarkable electrical, mechanical, optical and thermal properties [2]. Due to its fascinating properties, graphene can be potentially applied in a vast variety of applications across different types of fields from medicine studies to electronics sensors and even optoelectronics. For that reason, graphene has surged after the discovery of graphene in year 2004 by Andre Geim and Kostya Novoselov [3]. Graphene can be synthesized by a number of methods including mechanical exfoliation [4], chemical synthesis [5], epitaxial growth on silicon carbide (SiC) [6], and chemical vapour deposition (CVD) [7]. Some other techniques such as unzipping carbon nanotubes need to be explored more extensively in order to be able to produce graphene. Among these methods, the most popular and promising method to synthesize graphene is CVD because of its scalability and productivity. In the graphene synthesis by CVD process, graphene is deposited onto a variety of different metal catalyst substrates such as nickel (Ni), palladium (Pd), ruthenium (Ru) or copper (Cu). Hydrocarbon gas species are supplied into the CVD furnace and decomposed into carbon radicals and form graphene layers. As a result, manipulating the reaction parameters, like reaction duration and reaction temperature is crucial in the CVD synthesis process. It is because by controlling these reaction parameters can directly control the amount of carbon to be deposited on the substrate. In this paper, graphene-like samples were synthesized on copper foil substrate and the effect of varying the stated reaction parameters were studied. Nomenclature CVD CH4 N2

Chemical Vapour Deposition methane nitrogen

2. Experimental 2.1. Sample Preparation Samples were synthesized on 25 µm thick copper foil (99.8% purity, Alfa Aesar Company). The as-received copper foil was cut into a size of 4.5cm × 3cm and flattened using a ruler. The copper foil was then rinsed with DI water to remove organic impurities and contaminants. After DI water rinsing treatment, the copper foil was dried completely and put into a quartz boat of same size. The copper foil in the quartz boat was loaded into the thermal CVD furnace which was supplied by two different precursor gases: methane (CH4) and nitrogen (N2). CH4 gas acts as a carbon containing precursor gas whereas N 2 acts as a carrier gas. After the copper foil was loaded into the CVD frunace, the N2 flow was switched on while the temperature of CVD furnace was ramped up. This nitrogen flow can help to purge out the unwanted gases in the CVD furnace chamber. Once the desired temperature was achieved, the temperature was maintained for 5 minutes to stabilize the temperature and for the copper foil to be annealed. Then, the methane gas was turned on at a desired flow rate for a desired duration. The methane flow and the heater of the CVD furnace were switched off once the desired duration was ended. However, the N 2 flow was kept on during the ramping down of the CVD furnace to room temperature in order to prevent the oxidation of the samples. There are two reaction parameters to be investigated in this experiment, they are reaction duration and reaction temperature. In the reaction duration experiment, reaction temperature and methane flow rate were kept at 1000°C and 130mlpm while the reaction duration was controlled at 5, 60, 300, and 900seconds (Table 1). In the second part of the experiment, the reaction temperature was increased from 700°C to 1050°C whereas reaction duration and methane flow rate were fixed at 5 seconds and 130mlpm (Table 2).

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Table 1: Different reaction durations are varied Temperature (degree Celsius)

Methane flow rates (milliliter per minutes)

Duration (seconds)

1000

130

5

1000

130

60

1000

130

300

1000

130

900

Temperature (°C)

Methane flow rates (milliliter per minutes)

Duration (seconds)

700

130

5

800

130

5

900

130

5

1050

130

5

Table 2: Different reaction temperatures are varied

2.2. Sample Characterization After the graphene-like samples were synthesized, the surface morphologies of the samples were characterized by using scanning electron microscope (SEM; JEOL JSM-6010LV) at the magnification of 20kX with an accelerating voltage of 20kV. On the other hand, the carbon samples were characterized by energy dispersive X-ray spectroscopy (EDX) for its quantification analysis. X-ray diffraction Siemens Diffractometer Model D-5000 using Cu Kα radiation (λ = 0.14406nm) source in Ө/2Ө mode was used to obtain the X-ray diffraction (XRD) pattern of the graphene samples. XRD measurements were made with a fast duration at a scan rate of 5°/min at the scanning range from 10° to 90°. 3. Results and Discussion 3.1 Effect of reaction times The comparison of surface morphologies and elemental composition between centers of grains and grain boundaries of the samples synthesized using different reaction times by CVD were observed by SEM as shown in Figure 1. It is observed that carbon atoms agglomerated at certain spots on the samples. These agglomerations of carbon clusters were seen along the lines which are expected to be the grain boundaries of the copper substrate. Moreover, the agglomeration became bigger when the reaction time was increased (Figure 1). When reaction time exceeded 5 minutes, thick piles of carbon clusters were observed at grain boundaries. In addition, the elemental composition of the graphene samples was analyzed using EDX and the corresponding EDX spectrum for each reaction time was inserted. The EDX spectra illustrate that three elements were detected within the graphene samples: carbon, oxygen and copper. The presence of oxygen was due to the low vacuum condition in the EDX chamber. The extremely high intensity peak at 0.93keV (the first peak from the left) represents the Cu substrate. The carbon and oxygen peaks were observed at 0.278 keV and 0.525 keV, respectively. It is evident that the overall carbon content on the samples increased with increasing reaction time (Figure 1 and 2). Furthermore, the size of carbon clusters increased with the increasing of reaction duration from 5 seconds to 900 seconds. This can be explained by the fact that more and more carbon atoms were deposited from the decomposition of methane gas when the reaction time was increased.

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Figure 1: SEM images of carbon content for different reaction times of (a) 5 sec, (b) 60 sec, (c) 300 sec, (d) 900 sec

Figure 2: Comparison of carbon weight percentage on different reaction times.

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Figure 3: (a) SEM image of sample synthesized by using reaction duration of 5 seconds, methane flow rate of 130mlpm and reaction temperature of 1000°C. (b) XRD spectra for reaction duration of 5 seconds

In Figure 3(a), the amount of carbon agglomerated along the copper grain boundaries were much higher than that of grains and happened to all samples. According to the literature review, copper has a low carbon solubility of 0.084 at. % at around 1084°C in which carbon atoms are expected to adsorb on the surface without dissolution of carbon atoms into the bulk copper substrate [7], [8]. However, in contrast to this, the carbon atoms are expected to dissolve into the bulk copper substrate and diffuse out along the copper grain boundaries at high methane flow rate. Therefore, to support the hypothesis that carbon atoms might accumulated along the copper grain boundaries, two different areas: grains and grain boundaries were examined using EDX as shown in Figure 3(a) and the results show that carbon content was higher at grain boundaries than that of grains (Figure 2). Furthermore, the size of carbon clusters increased with the increasing of reaction duration from 5 seconds to 900 seconds. However, the carbon content along the copper grain boundaries and grains across the different reaction durations were not consistent. We speculate it is due to the inhomogeneous deposition of carbon atoms on the copper foil substrate which might be caused by the uneven flow of methane gas in the CVD furnace. In Figure 3(b), the XRD spectra of the graphene sample synthesized using a process duration of 5 seconds is shown. The extremely high peak of 2Ө=50.43° is attributed to the copper foil substrate of having an orientation of (100). This copper peak exists in all samples of different reaction durations as shown in Figure 4. This is in good agreement with the literature [9]. As shown in the Figure 3(b), we can see that the copper foil substrate appeared in oxide form which might be oxidized due to the presence of small quantity of oxygen when insufficient purging of nitrogen gas during the CVD growth process. In addition, the heating process in the CVD furnace could induced the formation of CuO from Cu2O [11]. Thus, cupric oxide (CuO) was found to be the dominant copper oxide species than cuprous oxide (Cu2O) [10]. It is known that graphene could exhibit a sharp crystal diffraction peak at 2Ө=26.5° which is corresponding to (002) plane with an interlayer spacing of 3.35Å [12]. However, the diffraction peak was not distinctly seen in Figure 3(b) and Figure 4. Therefore, Raman spectroscopy is needed to identify the D, G and 2D peaks which should appear in all samples.

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Figure 4: XRD patterns of the samples prepared from the reaction duration of 5 seconds, 60 seconds, 5 minutes and 15 minutes.

3.2 Effect of different reaction temperatures

Figure 5: SEM images of carbon content for different reaction temperature of (a) 700°C, (b) 800°C, (c) 900°C, and (d) 1050°C.

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Figure 6: Comparison of carbon weight percentage on different reaction temperature.

The second part of the experiment is about the effect of different reaction temperatures on surface morphologies and elemental composition of samples as shown in Figure 5. It is observed that at low temperature of 700°C, very low amount of carbon was deposited onto the copper foil (Figure 5a). When the temperature was increased, more carbon was deposited onto the copper foil as shown in the SEM images (Figure 5). From 700°C and 800°C, the agglomeration of carbon atoms was seen to cover the entire surface of copper foil where grains and its boundaries were underneath. When high reaction temperature such as 900°C and 1050°C were used, the carbon atoms appeared to be agglomerated in larger sizes. In Figure 6, the overall carbon content within the samples increased with increasing reaction temperatures. This indicates that more carbon atoms were deposited onto the copper foil. Based on the literature review, methane decomposed at a temperature of above 900°C [13]. Thus, we believe that the reaction temperature has higher influences as compared to the reaction durations on the amount of deposited carbon. Similar to the study reaction duration in part 3.1, carbon atoms are expected to precipitate along the grain boundaries and agglomerate on the surface of the copper foil. Therefore, by using EDX, it shows that carbon content along the grain boundaries was found higher than that of the grains in all reaction temperatures as shown in Figure 6. Furthermore, the difference in the carbon contents along the grain boundaries and the grains were getting significant as the reaction temperature was increased. In Figure 7, the similar XRD patterns to Figure 4 was observed. The diffraction peak at 2Ө=50.43° represents the copper foil substrate of (200) crystal orientation [14]. On the hand, the diffraction peaks of cuprous oxide and cupric oxide can be found in all of the samples. However, the carbon peak of (002) crystal orientation at 2Ө=26.5° are too low to be observed.

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Figure 7: XRD patterns of the samples prepared using the reaction temperature of 700°C, 800°C, 900°C, and 1050°C

4. Conclusion We reported the synthesis of graphene-like samples which affected by reaction times and temperatures. We found that reaction temperature has the most significant influences on the amount of deposited carbon content. At the lowest temperature of 700°C, carbon clusters were observed at the whole surface of copper foil and the sizes of carbon clusters were increased with reaction temperature. Besides, the accumulation of carbon was started at grain boundaries at lowest reaction time whereas thicker carbon clusters covered whole surface of copper foil at longer reaction durations. This signifies that copper substrate, a low carbon solubility material, the carbon atoms could undergo segregation and precipitation in copper foil along the grain boundaries like high carbon solubility material when extremely high carbon precursor was supplied. References [1] J. C. Meyer, a K. Geim, M. I. Katsnelson, K. S. Novoselov, T. J. Booth, and S. Roth, “The structure of suspended graphene sheets.,” Nature, vol. 446, no. 7131, pp. 60–3, Mar. 2007. [2] W. Choi, I. Lahiri, R. Seelaboyina, and Y. S. Kang, “Synthesis of Graphene and Its Applications: A Review,” Crit. Rev. Solid State Mater. Sci., vol. 35, no. 1, pp. 52–71, Feb. 2010. [3] T. H. E. Royal, S. Academy, and O. F. Sciences, “compiled by the Class for Physics of the Royal Swedish Academy of Sciences Graphene,” R. Swedish Acad. Sci., vol. 50005, no. October, pp. 0–10, 2010. [4] K. S. Novoselov, A. K. Geim, S. V Morozov, D. Jiang, Y. Zhang, S. V Dubonos, I. V Grigorieva, a a Firsov, a. a. F. K.S. Novoselov1, A.K. Geim1, S.V. Morozov2, D. Jiang1, Y. Zhang1, S.V. Dubonos2, I.V.Grigorieva1, and K. Using, “Electric Field Effect in Atomically Thin Carbon Films,” Science (80-. )., vol. 306, no. 5696, pp. 666–669, 2004. [5] S. Park and R. S. Ruoff, “Chemical methods for the production of graphenes.,” Nat. Nanotechnol., vol. 4, no. 4, pp. 217–24, Apr. 2009.

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