Graphene transfer methods compared

CVD graphene grows on metal and has to be moved before it is used. Wet transfer holds it in PMMA while the copper is etched away; roll-to-roll does the same with thermal release tape at metre scale; bubbling lifts it off with hydrogen so the metal can be used again; and dry stamping and van der Waals pick-up place single flakes and build hBN-encapsulated stacks.

1. Wet transfer: Spin-coat PMMA on graphene grown on Cu foil, etch away the copper, rinse in water, lift the film onto SiO₂/Si and dissolve the PMMA in acetone (Li et al. 2009; Gao et al. 2012); aqueous ammonium persulfate is one copper etchant (Zhang et al. 2016). 2. Roll-to-roll: Thermal release tape, which holds at room temperature and lets go when heated, carries the graphene through the copper etchant and onto PET: 30-inch films with sheet resistances as low as about 125 Ω/sq at 97.4 % transmittance (Bae et al. 2010; Woo 2019). 3. Bubbling: PMMA/graphene on Pt is made the cathode in 1 M NaOH; hydrogen bubbles at the interface lift the film off and the platinum can be used to grow again (Gao et al. 2012); graphene comes off copper the same way (Wang et al. 2011). 4. Dry stamping: A PDMS stamp on a glass slide, aligned under a microscope with a micromanipulator, is pressed onto the target and peeled off slowly, leaving the flake (Castellanos-Gomez et al. 2014; Frisenda et al. 2018). 5. van der Waals pick-up: A polymer film on a PDMS stamp picks up hBN, the hBN picks up graphene by van der Waals adhesion, and the stack is dropped onto bottom hBN: 22 encapsulated mono-, bi- and trilayer stacks with close to 100 % yield (Wang et al. 2013; Pizzocchero et al. 2016).

Starting materials: CVD graphene on Cu or Pt foil, or exfoliated flakes on SiO₂/Si. Product: Graphene on SiO₂/Si, PET or another target, or encapsulated in hBN.

Li et al., “Large-area synthesis of high-quality and uniform graphene films on copper foils”, Science 2009 (doi:10.1126/science.1171245); Bae et al., “Roll-to-roll production of 30-inch graphene films for transparent electrodes”, Nat. Nanotechnol. 2010 (doi:10.1038/nnano.2010.132); Gao et al., “Repeated growth and bubbling transfer of graphene with millimetre-size single-crystal grains using platinum”, Nat. Commun. 2012 (doi:10.1038/ncomms1702); Castellanos-Gomez et al., “Deterministic transfer of two-dimensional materials by all-dry viscoelastic stamping”, 2D Mater. 2014 (doi:10.1088/2053-1583/1/1/011002); Pizzocchero et al., “The hot pick-up technique for batch assembly of van der Waals heterostructures”, Nat. Commun. 2016 (doi:10.1038/ncomms11894); Li et al., “Transfer of large-area graphene films for high-performance transparent conductive electrodes”, Nano Lett. 2009 (doi:10.1021/nl902623y); Wang et al., “Electrochemical delamination of CVD-grown graphene film: toward the recyclable use of copper catalyst”, ACS Nano 2011 (doi:10.1021/nn203700w); Zhang et al., “Versatile polymer-free graphene transfer method and applications”, ACS Appl. Mater. Interfaces 2016 (doi:10.1021/acsami.6b00681); Frisenda et al., “Recent progress in the assembly of nanodevices and van der Waals heterostructures by deterministic placement of 2D materials”, Chem. Soc. Rev. 2018 (doi:10.1039/c7cs00556c); Wang et al., “One-dimensional electrical contact to a two-dimensional material”, Science 2013 (doi:10.1126/science.1244358); Woo, “Transparent conductive electrodes based on graphene-related materials”, Micromachines 2019 (doi:10.3390/mi10010013).

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