CARBON 56 (2013) 271– 278 Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/carbon High-quality and efficient transfer of large-area graphene films onto different substrates Xu-Dong Chen a, Zhi-Bo Liu a,*, Chao-Yi Zheng a, Fei Xing a, Xiao-Qing Yan a,b, Yongsheng Chen b, Jian-Guo Tian a a The Key Laboratory of Weak Light Nonlinear Photonics, Ministry of Education, Teda Applied Physics School and School of Physics, Nankai University, Tianjin 300071, China b The Key Laboratory of Functional Polymer Materials and Center for Nanoscale Science & Technology, Institute of Polymer Chemistry, College of Chemistry, Nankai University, Tianjin 300071, China ARTICLE INFO ABSTRACT Article history: We used a two-layer structure consisting of polyethylene terephthalate (PET) and silicone Received 16 October 2012 to transfer graphene grown by chemical vapor deposition onto various rigid and flexible Accepted 8 January 2013 substrates through dispersive adhesion. It only takes a few seconds to transfer graphene Available online 25 January 2013 from PET/silicone to the target substrates at ambient conditions. And the recycling of the PET/silicone decreases the production cost greatly. The transferred graphene films were characterized by optical and atomic force microscopy, Raman spectroscopy, electrical anal- yses, and optical transmittance measurements, and the results show that the graphenes transferred by PET/silicone have a cleaner and more continuous surface, lower doping level, and higher optical transmittance and conductivity than those transferred by thermal release tape. Considering its high efficiency, low cost, large area and high quality, the PET/ silicone transfer method would be particularly useful for graphene’s electronic applications such as field-effect transistors and transparent conducting electrodes. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction devices such as field-effect transistors (FET) and transparent conducting electrodes, it is necessary to transfer graphene Since the first graphene was obtained by mechanical exfolia- onto different substrates with high efficiency, low cost, large tion of highly ordered pyrolytic graphite in 2004 [1], it has area and high quality. been intensively studied due to its extraordinary mechanical, Various methods have been developed to transfer graph- thermal and electrical properties, such as high carrier mobil- ene onto different substrates [3–5,8–17]. Currently, the most ity, superelastic mechanical behavior, and ultraelectrical con- commonly used transfer methods rely on polymethyl- ductivity with high optical transmittance [2–5]. In despite of methacrylate (PMMA) [4,8–11] or thermal release tape (TRT) the high quality of the mechanical exfoliation graphene, it [3,12,16] to support the graphene film and to prevent folding is hard to meet the need for mass fabrication of large-area while the growth substrate is etched. However, both of those uniform graphene. Large-area graphene is typically produced two materials have their own disadvantages. For instance, via epitaxial growth on SiC substrates [6], and chemical vapor PMMA is not suitable for the transfer of large-area graphene deposition (CVD) on metal surface [7]. Considering its low cost films, because it is easy to introduce contamination, cracks and high efficiency, high quality, and large area, CVD-grown and tears during the transfer process [8,10], and requires high graphene is promising for industrial applications. To fabricate handling skills. For TRT, while it can be easily used to transfer * Corresponding author: Fax: +86 22 23499981. E-mail address: [email protected] (Z.-B. Liu). 0008-6223/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.carbon.2013.01.011 272 CARBON 56 (2013) 271– 278 large-area graphene onto rigid and flexible substrates than (PDMS) from Dow Corning (SYLGARDâ 184) was cured at PMMA [3,16], it invariably contaminates the transferred 75 °C for 1 h with a 10:1 base to curing agent mixing ratio. graphene surface with adhesive from TRT [10,16]. The resid- The FeCl3 (Analytical reagent, P99%), hydrochloric acid (Ana- ual adhesive affects seriously the performance of graphene lytical regent, 37%), and Chloroform (Analytical reagent, in optical and electrical applications. It is necessary to devel- P99%) were produced by Jiangtian reagent company. PMMA op a new efficient method for the transfer of graphene with (average Mw 996,000 by GPC, crystalline, Aldrich) were the scale and quality required in the research and industrial bought from the Sigma–Aldrich. applications. The graphene/Cu sample was first flattened between two The adhesion of polymer supports (i.e., PMMA and TRT) to cleaned glass slides and then attached to the PET/silicone film the graphene mainly depends on the viscosity of the polymer with dispersive adhesion. In order to make the PET/silicone film. The residual PMMA or adhesive left on the graphene sur- fully adhere onto the rough substrate with micro-rolling, a face is inevitable. To get a clean surface, we select dispersive pressure of 0.05 MPa was applied on it for 1 h. The underlying adhesion, also known as physisorption, to replace the adhe- Cu foil was etched in FeCl3 solution (1 M) for 1 h. After rinsed sives. The transfer mechanism with dispersive adhesion is with deionized water to remove residual etchant, the PET/sil- discussed in Supplementary Information (SI). Due to the icone/graphene stack was rinsed in 10% HCl (60 °C) for half an reversible process of the dispersive adhesion without using hour to remove residual Fe3+ ions. The sample was rinsed any chemical adhesives, the graphene surface will keep clean with deionized water to remove residual HCl solution and after desorption process. In this paper, we used a two-layer then dried with N2. The PET/silicone/graphene stack was at- structure of polyethylene terephthalate (PET) and silicone, tached to the new substrates such as SiO2/Si wafer and PET PET layer for support and silicone layer for dispersive adhe- film with dispersive adhesion. Lastly, the PET/silicone film sion, to transfer graphene onto arbitrary substrates with high was peeled off and the graphene was transferred to the new efficiency, high quality and large scale. The Attenuated Total substrate successfully. The surfaces of the target materials Reflection Flourier Transformed Infrared (ATR-FTIR) spectrum are pristine without any treatment. of the silicone (see Fig. S1, SI) shows that the silicone contains Si–O–Si and Si–(CH3)2 groups [18]. Due to the low surface ten- 2.2. FET fabrication sion of the silicone, graphene can be released on arbitrary substrates successfully. And owing to the reversible process After the 3-layer graphene films transferred to the SiO2/Si wa- of the dispersive adhesion, the recyclable use of the PET/sili- fer, metal electrodes were deposited on the surface by metal cone can be achieved to reduce the production cost. Now the mask. And then the FETs were annealed at 120 °C for 1 h un- technology for the production of the materials with two-layer der vacuum to remove water and air doping on the graphene. structure has been very mature, such as the screen protector for iPad and iPhone, making it possible for large-area graph- 2.3. Characterization ene transfer in industrial applications. For comparison, we transferred graphene films to rigid and The ATR-FTIR spectrum was recorded on a Nexus 870 FTIR flexible substrates (i.e., SiO2/Si wafer and PET) by TRT and PET/ spectrometer. The surface morphology of transferred graph- silicone, respectively. The transferred graphene films were ene on SiO2/Si wafer was investigated by optical microscopy characterized with optical microscopy, atomic force micros- (Nikon ECLIPSE Ti-U) and AFM (MultiModeTM). Raman spectra copy (AFM), Raman spectrum, electrical analyses and optical were carried out using RENISHAW RM2000 Raman System transmittance measurement. Compared with the TRT meth- equipped with a 514 nm laser source and 50 · objective lens. od, the graphene transferred by PET/silicone had a cleaner To obtain the Raman images, samples were moved with a step and more continuous surface, lower doping level, and higher size of 1 lm and a Raman spectrum was recorded at every optical transmittance and conductivity. Four graphene films point. The region we measured was 20 · 20 lm. The transfer were transferred by a recycled PET/silicone successfully, with characteristic curves were measured by using an Agilent clean and continuous surfaces. We also transferred graphene 34401A Digit Multimeter. The optical transmittance spectros- onto different rigid and flexible substrates with PET/silicone copy measurement was performed using HITACHI U-4100 successfully. Spectrophotometer. The sheet resistance of the graphene was measured using Accent HL5550 Hall Effect Measurement 2. Experimental System. The contact angles were measured with a video con- tact angle system (JC2000C). 2.1. Preparation and transfer of graphene 3. Results and discussion The commercial screen protector used to transfer graphene in this work was Capdase iMAG Screen Protector for iPhone 4/4S. Fig. 1 gives the schematic diagram of the dry transfer of The thicknesses of the PET and silicone layers were about 100 CVD-grown graphene onto arbitrary substrates, such as and 60 lm, respectively. The single-layer and multi-layer SiO2/Si wafer and PET film. There are three essential steps graphene on copper foil we used in the experiments were in the PET/silicone transfer process: 1. adhesion of the PET/ ACS Material Graphene/Cu. The TRT and high n-doped SiO2/ silicone to the graphene/Cu; 2. etching of the Cu layer; 3. Si wafers with 285 nm oxide were bought from the Graphene release of the graphene layer and transfer onto the target sub- Supermarket. A two-component polydimethylsiloxane strate. The main difference between PET/silicone and the CARBON 56 (2013) 271– 278 273 Fig. 1 – Schematic illustration of (a) graphene transfer by PET/silicone and (b) the designed two-layer structure.