- Nano Express
- Open Access
Synthesis of flake-like graphene from nickel-coated polyacrylonitrile polymer
© Kwon et al.; licensee Springer. 2014
- Received: 5 September 2014
- Accepted: 11 October 2014
- Published: 18 November 2014
Graphene can be synthesized from polyacrylonitrile (PAN) polymer through pyrolysis. A metal catalyst such as nickel (Ni) is required for the conversion of the polymer to graphene. The metal catalysts can be placed either atop or underneath the polymer precursor. We observed that spatially non-uniform and disconnected graphene was fabricated when PAN film coated with a Ni layer was pyrolyzed, resulting in flake-like graphene. Formation of the flake-like graphene is attributed to the dewetting of the Ni layer coated on the PAN film. Dewetting phenomenon can be reduced by decreasing the pyrolysis temperature, and hence, more uniform graphene could be prepared. The effects of Ni coating thickness and the pyrolysis temperature on the fabricated graphene have been experimentally analyzed.
- Graphene flake
Ever since the discovery of graphene , research on graphene, a flat monolayer of carbon atoms arranged in a two-dimensional (2D) honeycomb lattice , has progressed rapidly. Due to the relatively simple and cheap procedures to obtain high-quality graphene  and its outstanding properties such as high electron mobility at room temperature , high intrinsic mechanical strength , high thermal conductivity , and complete impermeability to gas , graphene can be exploited in a variety of fields like electronics, photonics, energy generation and storage, sensor, and bio applications . So far, many methods to obtain graphene have been developed, including mechanical cleavage of graphite , chemical exfoliation [8–10], epitaxial growth [11, 12], chemical vapor deposition (CVD) [13–16], and solid-phase method [17–23].
The solid-phase method employs transition metals such as Ni and Cu as a catalyst to form graphene from solid-state carbon sources such as polymer, SiC, small molecule, and self-assembled monolayer. Particularly, in the method using polymer as a precursor of graphene, various polymers like polyacrylonitrile (PAN), polystyrene, and polymethylmethacrylate were used, and the polymer placed either atop or underneath metal catalysts were pyrolyzed in a reductive gas to form graphene [20–23]. When graphene is synthesized from a polymer precursor on a metal catalyst, an additional process to transfer the synthesized graphene on an insulator such as SiO2 is required for the application to electronic device [14, 24]. This transfer procedure can result in the degradation of the synthesized graphene. The opposite case where polymer precursor is underneath a metal catalyst can solve this problem; however, few results have been reported on this case [22, 23].
Here, we present systematic experimental results to synthesize graphene on a SiO2/Si substrate from PAN coated with a Ni film through pyrolysis. The Ni coating layer tends to be aggregated to form particulates due to dewetting  at a high pyrolysis temperature, and hence, the synthesized graphene was not generally continuous. The effects of the Ni film and pyrolysis temperature on the quality of graphene were investigated. As a consequence, continuously connected graphene could be prepared by reducing the pyrolysis temperature.
Polyacrylonitrile (PAN, Sigma-Aldrich, St. Louis, MO, USA, Mw =150,000) (0.5 wt.%) dissolved in N,N-Dimethylformamide (DMF, Showa Chemical, Tokyo, Japan) was spin-coated on 1 × 1 cm2 SiO2 (300 nm thickness)/Si wafers. Subsequently, a Ni layer was coated on the spin-coated PAN/SiO2/Si substrates with a magnetron sputtering system. The sputtering rate was approximately 10 nm/min, and the thickness of the Ni layer was changed by the sputtering time. The Ni-coated PAN/SiO2/Si samples were pyrolyzed in a high-vacuum furnace; the vacuum level in the furnace was roughly 10-5 Torr.
During the pyrolysis process, the samples were gradually annealed with a heating rate of 8°C/min to a maximum temperature and then were quickly cooled down by moving the heating zone of the furnace to the opposite side. The maximum temperature was changed from 1,050°C to 700°C (Since we exploited a high-vacuum furnace made of quartz for pyrolysis, the maximum temperature has to be limited up to 1,100°C. Besides, although the melting point of nickel is approximately 1,450°C at 1 atm., a very thin nickel thickness (up to 200 nm) is easily agglomerated in the vacuum atmosphere. So the temperature of 1,050°C was selected as the maximum temperature. In the case of the minimum temperature range, the temperature where graphene is formed and the agglomeration of the nickel layer is suppressed was selected as the minimum temperature. Therefore, the temperature ranged from 1,050°C to 700°C was selected for the pyrolysis).
Evaluation of FWHM 2D , I (D) / I (G) , and I (G) / I (2D) for the Ni-coated PAN/SiO 2 /Si films after pyrolysis and subsequent nickel removal
We have demonstrated that spatially non-uniform and flake-like graphene is synthesized when Ni-coated PAN film is pyrolyzed at a high temperature. Such non-uniform graphene is produced due to the dewetting of the Ni layer coated on the PAN film. Dewetting phenomenon can be reduced by increasing the Ni thickness and/or by decreasing the pyrolysis temperature. However, as the pyrolysis temperature is decreased, graphene with lower quality is synthesized. Therefore, it is important to optimize both the Ni thickness and the pyrolysis temperature considering the necessary quality of the synthesized graphene and required spatial uniformity for certain applications. In addition, non-uniform and flake-like graphene is not so good for the application to electronic devices; however, such flake-like graphene might be useful for certain applications of graphene (e.g., gas sensor and energy storage [32, 33]) if the flake size can be controlled through future studies.
This work was supported by a National Research Foundation of Korea (NRF) grant funded by the Korea government (MEST) (no. 2012-0009523).
- Novoselov S, Geim AK, Morozov SV, Jiang D, Zhang Y, Dubonos SV, Grigorieva IV, Firsov AA: Electric field effect in atomically thin carbon films. Science 2004, 306: 666–669. 10.1126/science.1102896View ArticleGoogle Scholar
- Geim AK, Novoselov KS: The rise of graphene. Nature Mater 2007, 6: 183–191. 10.1038/nmat1849View ArticleGoogle Scholar
- Novoselov KS, Fal’ko VI, Colombo L, Gellert PR, Schwab MG, Kim K: A roadmap for graphene. Nature 2012, 490: 192–200. 10.1038/nature11458View ArticleGoogle Scholar
- Mayorov AS, Gorbachev RV, Morozov SV, Britnell L, Jalil R, Ponomarenko LA, Blake P, Novoselov KS, Watanabe K, Taniguchi T, Geim AK: Micrometer-scale ballistic transport in encapsulated graphene at room temperature. Nano Lett 2011, 11: 2396–2399. 10.1021/nl200758bView ArticleGoogle Scholar
- Lee C, Wei XD, Kysar JW, Hone J: Measurement of the elastic properties and intrinsic strength of monolayer graphene. Science 2008, 321: 385–388. 10.1126/science.1157996View ArticleGoogle Scholar
- Balandin AA: Thermal properties of graphene and nanostructured carbon materials. Nature Mater 2011, 10: 569–581. 10.1038/nmat3064View ArticleGoogle Scholar
- Bunch JS, Verbridge SS, Alden JS, van der Zande AM, Parpia JM, Craighead HG, McEuen PL: Impermeable atomic membranes from graphene sheets. Nano Lett 2008, 8: 2458–2462. 10.1021/nl801457bView ArticleGoogle Scholar
- Stankovich S, Dikin DA, Dommett GHB, Kohlhaas KM, Zimney EJ, Stach EA, Piner RD, Nguyen ST, Ruoff RS: Graphene-based composite materials. Nature 2006, 442: 282–286. 10.1038/nature04969View ArticleGoogle Scholar
- Eda G, Fanchini G, Chhowalla M: Large-area ultrathin films of reduced graphene oxide as a transparent and flexible electronic material. Nature Nanotech 2008, 3: 270–274. 10.1038/nnano.2008.83View ArticleGoogle Scholar
- Hernandez Y, Nicolosi V, Lotya M, Blighe FM, Sun Z, De S, McGovern IT, Holland B, Byrne M, Gun’ko YK, Boland JJ, Niraj P, Duesberg G, Krishnamurthy S, Goodhue R, Hutchison J, Scardaci V, Ferrari AC, Coleman JN: High-yield production of graphene by liquid-phase exfoliation of graphite. Nature Nanotech 2008, 3: 563–568. 10.1038/nnano.2008.215View ArticleGoogle Scholar
- Berger C, Song Z, Li X, Wu X, Brown N, Naud C, Mayou D, Li T, Hass J, Marchenkov AN, Conrad EH, First PN, de Heer WA: Electronic confinement and coherence in patterned epitaxial graphene. Science 2006, 312: 1191–1196. 10.1126/science.1125925View ArticleGoogle Scholar
- de Heer WA, Berger C, Wu X, First PN, Conrad EH, Li X, Li T, Sprinkle M, Hass J, Sadowski ML, Potemski M, Martinez G: Epitaxial graphene. Solid State Commun 2007, 143: 92–100. 10.1016/j.ssc.2007.04.023View ArticleGoogle Scholar
- Reina A, Jia X, Ho J, Nezich D, Son H, Bulovic V, Dresselhaus MS, Kong J: Large area, few-layer graphene films on arbitrary substrates by chemical vapor deposition. Nano Lett 2009, 9(1):30–35. 10.1021/nl801827vView ArticleGoogle Scholar
- Kim KS, Zhao Y, Jang H, Lee SY, Kim JM, Kim KS, Ahn JH, Kim P, Choi JY, Hong BH: Large-scale pattern growth of graphene films for stretchable transparent electrodes. Nature 2009, 457: 706–710. 10.1038/nature07719View ArticleGoogle Scholar
- Wei D, Liu Y, Wang Y, Zhang H, Huang L, Yu G: Synthesis of N-doped graphene by chemical vapor deposition and its electric properties. Nano Lett 2009, 9(5):1752–1758. 10.1021/nl803279tView ArticleGoogle Scholar
- Li X, Cai W, An J, Kim S, Nah J, Yang D, Piner R, Velamakanni A, Jung I, Tutuc E, Banerjee SK, Colombo L, Ruoff RS: Large-area synthesis of high-quality and uniform graphene films on copper foils. Science 2009, 324: 1312–1314. 10.1126/science.1171245View ArticleGoogle Scholar
- Juang ZY, Wu CY, Lo CW, Chen WY, Huang CF, Hwang JC, Chen FR, Leou KC, Tsai CH: Synthesis of graphene on silicon carbide substrates at low temperature. Carbon 2009, 47: 2026–2031. 10.1016/j.carbon.2009.03.051View ArticleGoogle Scholar
- Hofrichter J, Szafranek BN, Otto M, Echtermeyer TJ, Baus M, Majerus A, Geringer V, Ramsteiner M, Kurz H: Synthesis of graphene on silicon dioxide by a solid carbon source. Nano Lett 2010, 10: 36–42. 10.1021/nl902558xView ArticleGoogle Scholar
- Shin HJ, Choi WM, Yoon SM, Han GH, Woo YS, Kim ES, Chae SJ, Li XS, Benayad A, Loc DD, Gunes F, Lee YH, Choi JY: Transfer-free growth of few-layer graphene by self-assembled monolayers. Adv Mater 2011, 23: 4392–4397. 10.1002/adma.201102526View ArticleGoogle Scholar
- Sun Z, Yan Z, Yao J, Beitler E, Zhu Y, Tour JM: Growth of graphene from solid carbon sources. Nature 2010, 468: 549–552. 10.1038/nature09579View ArticleGoogle Scholar
- Gao H, Guo L, Wang L, Wang Y: Synthesis of nitrogen-doped graphene from polyacrylonitrile. Mater Lett 2013, 109: 182–185.View ArticleGoogle Scholar
- Byun SJ, Lim H, Shin GY, Han TH, Oh SH, Ahn JH, Choi HC, Lee TW: Graphenes converted from polymers. J Phys Chem Lett 2011, 2: 493–497. 10.1021/jz200001gView ArticleGoogle Scholar
- Yan Z, Peng Z, Sun Z, Yao J, Zhu Y, Liu Z, Ajayan PM, Tour JM: Growth of bilayer graphene on insulating substrates. ACS Nano 2011, 5(10):8187–8192. 10.1021/nn202829yView ArticleGoogle Scholar
- Lee Y, Bae S, Jang H, Jang S, Zhu SE, Sim SH, Song YI, Hong BH, Ahn JH: Wafer-scale synthesis and transfer of graphene films. Nano Lett 2010, 10: 490–493. 10.1021/nl903272nView ArticleGoogle Scholar
- Thompson CV: Solid-state dewetting of thin films. Annu Rev Mater Res 2012, 42: 399–434. 10.1146/annurev-matsci-070511-155048View ArticleGoogle Scholar
- Joh HI, Lee S, Kim TW, Han TH, Hwang SY, Hahn JR: Synthesis and properties of an atomically thin carbon nanosheet similar to graphene and its promising use as an organic thin film transistor. Carbon 2013, 55: 299–304.View ArticleGoogle Scholar
- Ferrari AC, Robertson J: Interpretation of Raman spectra of disordered and amorphous carbon. Phys Rev B 2000, 61(20):14095–14107. 10.1103/PhysRevB.61.14095View ArticleGoogle Scholar
- Ferrari AC, Meyer JC, Scardaci V, Casiraghi C, Lazzeri M, Mauri F, Piscanec S, Jiang D, Novoselov KS, Roth S, Geim AK: Raman spectrum of graphene and graphene layers. Phys Rev Lett 2006, 97: 187401–187404.View ArticleGoogle Scholar
- Ferrari AC: Raman spectroscopy of graphene and graphite: disorder, electron–phonon coupling, doping and nonadiabatic effects. Solid State Commun 2007, 143: 47–57. 10.1016/j.ssc.2007.03.052View ArticleGoogle Scholar
- Mattevi C, Kim H, Chhowalla M: A review of chemical vapour deposition of graphene on copper. J Mater Chem 2011, 21: 3324–3334. 10.1039/c0jm02126aView ArticleGoogle Scholar
- Seah CM, Chai SP, Mohamed AR: Mechanisms of graphene growth by chemical vapour deposition on transition metals. Carbon 2014, 70: 1–21.View ArticleGoogle Scholar
- Omidvar A, Mohajeri A: Edge-functionalized graphene nanoflakes as selective gas sensors. Sens Actuat B 2014, 202: 622–630.View ArticleGoogle Scholar
- Low CTJ, Walsh FC, Chakrabarti MH, Hashim MA, Hussain MA: Electrochemical approaches to the production of graphene flakes and their potential applications. Carbon 2013, 54: 1–21.View ArticleGoogle Scholar
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