Direct transfer of graphene by control of polydimethylsiloxane surface energy

Abstract

In this study, graphene direct transfer patterning was investigated by using plasma surface modification of polydimethylsiloxane (PDMS) with inductively coupled C4F8/O-2/Ar gas mixture plasma. The spin-coated graphene on the PDMS was directly transferred to a polyethylene terephthalate (PET) substrate. Direct transfer characteristics were analyzed using the film's properties such as the contact angle, and sheet resistance, and the degree of adhesion between the PDMS and graphene. Further analysis was performed on results obtained via transmission electron microscopy (TEM), and Raman spectroscopy. As the O-2 gas ratio in the C4F8/O-2/Ar plasma increased, the contact angle at the PDMS surface decreased. This indicates that the PDMS surface changes from hydrophobic to hydrophilic because of the plasma treatment. As-grown graphene films exhibited D, G, and 2Dpeaks in their Raman spectra, and post-annealing was used to reduce or eliminate the D-peak. The direct transfer of graphene from PDMS to the PET substrate occurred at an O-2 gas ratio that was above 50%. TEM and Raman mapping were used for the evaluation of the direct transfer characteristics. The adhesion between the PDMS and the coated graphene was calculated to confirm the direct transfer mechanism. The adhesion decreased as a consequence of the C4F8/O-2/Ar plasma treatment, while the graphene direct transfer characteristics to the PET substrate were, in turn, improved. Therefore, an important indicator of the efficiency of the direct transfer of graphene is the degree of adhesion between the graphene and the PDMS. The touch sensor was fabricated using the directly transferred graphene thin film and an indium fin oxide (ITO) transparent electrode. The mutual capacitance value, which is characteristic of the touch sensor, confirmed the mutual capacitance value similar to that of the existing ITO.