- Nano Express
- Open Access
The deviation of growth model for transparent conductive graphene
© Chan et al.; licensee Springer. 2014
Received: 1 September 2014
Accepted: 11 October 2014
Published: 20 October 2014
An approximate growth model was employed to predict the time required to grow a graphene film by chemical vapor deposition (CVD). Monolayer graphene films were synthesized on Cu foil at various hydrogen flow rates from 10 to 50 sccm. The sheet resistance of the graphene film was 310Ω/□ and the optical transmittance was 97.7%. The Raman intensity ratio of the G-peak to the 2D peak of the graphene film was as high as ~4 when the hydrogen flow rate was 30 sccm. The fitting curve obtained by the deviation equation of growth model closely matches the data. We believe that under the same conditions and with the same setup, the presented growth model can help manufacturers and academics to predict graphene growth time more accurately.
Graphene, comprising two-dimensional monolayer of sp2-bonded carbon atoms, has attracted substantial attention for use in transparent conductive electrodes (TCE), owing to its chemical stability and high optical transmittance from the ultraviolet to the infrared regions. Graphene as a TCE has a wide range of applications, including in solar cells, solid-state lighting, and detectors, owing to not only its higher optical transmittance but also its more favorable conductance[1–4] than those of traditional transparent conductive electrodes, such as indium tin oxide (ITO) and zinc oxide (ZnO). (Additionally, Furthermore, or Moreover), ITO is an expensive material, and it is unstable in chemical solution and cannot be utilized in a hydrogen-containing environment. ZnO-based thin film has also attracted interest for use in TCEs owing to its low cost, non-toxicity, and abundant constituent elements. However, the properties of ZnO-based thin films are not uniform or stable. The several ways to produce graphene include mechanical exfoliation, graphene oxide (GO), and chemical vapor deposition (CVD). Mechanical exfoliation can yield high-quality graphene from graphite but this method produces graphene over a small area of the order of only a few tens of micrometers. Graphene oxide can be formed by oxidizing graphite flakes; this method can produce large quantities of graphene whose electrical properties are, however, affected by the functional groups and various defects in the graphene. Nevertheless, CVD is a promising method for growing high-quality graphene over a large area using Cu foils. Li et al. were the first to grow graphene over a large area of the order of square centimeters on Cu foil by CVD using methane, and this method has become a standard approach to forming graphene films in recent years. Four-layered graphene exhibits a sheet resistance of about 350Ω/□, which represents a large step toward lower sheet resistance and a large increase in the range of graphene applications. Additionally, various methods have been proposed to optimize the properties of CVD graphene[10–14]. This work develops a simply derived graphene growth model to predict the growth time with various hydrogen flow rates.
Graphene films were grown by chemical vapor deposition (APCVD) on 25-μm-thick Cu foils (99.8%, Alfa-Aesar, item no. 13382) in a 3-in. quartz tube furnace under atmospheric pressure. Beforehand, electrochemical polishing (50% H3PO4 in deionized water of 100 mL) was utilized to smooth out the foil, and a voltage from 2 to 4 V was applied until the Cu foil glowed. Thereafter, the Cu foil was rinsed in a large amount of deionized water with sonication and then blow-dried with nitrogen gas. The Cu foil was placed in the reaction chamber, the Ar and H2 (1,000 and 2 sccm, respectively) gases were introduced into the chamber during temperature ramp-up. The Cu foil was annealed at 1,070°C for an hour. Then, 0.3 sccm of methane (purity, 99.99%) was used as a source of carbon to grow the graphene. The H2 flow rate was varied from 10 to 50 sccm prior to observation of the morphology of the graphene domains and the nucleation density. Following the growth process, the as-grown graphene/Cu foil was removed from the heating zone for rapid cooling. Polymethyl methacrylate (PMMA) was spin-coated on the as-grown graphene/Cu foil as a supporting layer to prevent any cracking during the transfer process. The graphene grew on both sides of the Cu foil. The graphene at the back of the foil was removed by floating on nitride acid solution (30% in deionized water) for 10 s. The Cu foil was etched away overnight using an ammonium persulfate solution (0.1 M) and then rinsed three times in deionized water. The PMMA/graphene was placed on the substrate, and the PMMA was then dissolved in hot acetone bath for 24 h. The residual PMMA was removed by annealing in air at 200°C for an hour and reduced to pristine graphene using an H2/Ar (7/20 sccm) mixture. The morphology and the nucleation density of the graphene domain were measured by scanning electron microscopy (SEM); The surface profile of Cu foils were measured by atomic force microscopy (AFM); the sheet resistance was measured using a four-probe stage; the Raman shift of the graphene was measured by Raman spectroscopy using a laser with a wavelength of 532 nm, the laser power at the focused spot was 2 mW, and the numerical aperture value was 0.75 on the sample with an area of 1 μm2.
Results and discussion
An approximate growth model of the synthesis of graphene by APCVD was developed. When the hydrogen flow rate was 30 sccm, the transmittance as a function of wavelength for single-layer graphene reached its maximum of 97.7% at λ =550 nm. The 2D/G ratio and the FWHM indicated that the graphene comprised a single layer of high quality. The lowest obtained sheet resistance of a single layer of graphene was about 310Ω/□. The results of the experiments closely matched the fitting curve. We believe that, under the same conditions and with the same experimental setup, the proposed growth model can help manufacturers and academics predict the growth time of graphene more accurately.
The authors would like to thank the National Science Council of the Republic of China, Taiwan, for financially supporting this research under contract nos. NSC 102-2633-E-008-001, NSC 103-2623-E-008-001-ET, and MOST 103-2221-E-008-101-MY2.
- Wang X, Zhi LJ, Mullen K: Transparent, conductive graphene electrodes for dye-sensitized solar cells. Nano Lett 2008, 8: 323–327. 10.1021/nl072838rView ArticleGoogle Scholar
- Kim YS, Joo K, Jerng SK, Lee JH, Moon D, Kim J, Yoon E, Chun SH: Direct integration of polycrystalline graphene into light emitting diodes by plasma-assisted metal-catalyst-free synthesis. ACS Nano 2014, 8: 2230–2236. 10.1021/nn405477fView ArticleGoogle Scholar
- Chitara B, Krupanidhi SB, Rao CNR: Solution processed reduced graphene oxide ultraviolet detector. Appl Phys Lett 2011, 99: 3.View ArticleGoogle Scholar
- Geim AK, Novoselov KS: The rise of graphene. Nat Mater 2007, 6: 183–191. 10.1038/nmat1849View ArticleGoogle Scholar
- Wu CC, Wu CI, Sturm JC, Kahn A: Surface modification of indium tin oxide by plasma treatment: an effective method to improve the efficiency, brightness, and reliability of organic light emitting devices. Appl Phys Lett 1997, 70: 1348–1350. 10.1063/1.118575View ArticleGoogle Scholar
- Kim KH, Park KC, Ma DY: Structural, electrical and optical properties of aluminum doped zinc oxide films prepared by radio frequency magnetron sputtering. J Appl Phys 1997, 81: 7764–7772. 10.1063/1.365556View ArticleGoogle Scholar
- Dreyer DR, Park S, Bielawski CW, Ruoff RS: The chemistry of graphene oxide. Chem Soc Rev 2010, 39: 228–240. 10.1039/b917103gView ArticleGoogle Scholar
- Li XS, Cai WW, An JH, Kim S, Nah J, Yang DX, 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
- Li XS, Zhu YW, Cai WW, Borysiak M, Han BY, Chen D, Piner RD, Colombo L, Ruoff RS: Transfer of large-area graphene films for high-performance transparent conductive electrodes. Nano Lett 2009, 9: 4359–4363. 10.1021/nl902623yView ArticleGoogle Scholar
- Hao YF, Bharathi MS, Wang L, Liu YY, Chen H, Nie S, Wang XH, Chou H, Tan C, Fallahazad B, Ramanarayan H, Magnuson CW, Tutuc E, Yakobson BI, McCarty KF, Zhang YW, Kim P, Hone J, Colombo L, Ruoff RS: The role of surface oxygen in the growth of large single-crystal graphene on copper. Science 2013, 342: 720–723. 10.1126/science.1243879View ArticleGoogle Scholar
- Kang J, Hwang S, Kim JH, Kim MH, Ryu J, Seo SJ, Hong BH, Kim MK, Choi JB: Efficient transfer of large-area graphene films onto rigid substrates by hot pressing. ACS Nano 2012, 6: 5360–5365. 10.1021/nn301207dView ArticleGoogle Scholar
- Zhang J, Hu PA, Wang XN, Wang ZL, Liu DQ, Yang B, Cao WW: CVD growth of large area and uniform graphene on tilted copper foil for high performance flexible transparent conductive film. J Mater Chem 2012, 22: 18283–18290. 10.1039/c2jm33881eView ArticleGoogle Scholar
- Vlassiouk I, Regmi M, Fulvio PF, Dai S, Datskos P, Eres G, Smirnov S: Role of hydrogen in chemical vapor deposition growth of large single-crystal graphene. ACS Nano 2011, 5: 6069–6076. 10.1021/nn201978yView ArticleGoogle Scholar
- Li XS, Magnuson CW, Venugopal A, Tromp RM, Hannon JB, Vogel EM, Colombo L, Ruoff RS: Large-area graphene single crystals grown by low-pressure chemical vapor deposition of methane on copper. J Am Chem Soc 2011, 133: 2816–2819. 10.1021/ja109793sView ArticleGoogle Scholar
- Nair RR, Blake P, Grigorenko AN, Novoselov KS, Booth TJ, Stauber T, Peres NMR, Geim AK: Fine structure constant defines visual transparency of graphene. Science 2008, 320: 1308–1308. 10.1126/science.1156965View ArticleGoogle Scholar
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