Scalable Transfer and Production of Graphene for Industrial Applications

Abstract

Emerging electronics including bendable and rollable displays, and flexible sensors come closer to reality by showing the feasibility of industrial-level production of high quality graphene sheets by Chemical Vapor Deposition (CVD). However, transferring on the desired substrate and patterning for graphene device fabrication are still limited. The quality degradation is evitable during transferred on a desired flexible substrate, which is mainly incurred by the chemical damage and residues on removal of the support layer such as PMMA and the thermal damage by the use of a Thermal Release Tape (TRT). As for patterning, existing methods including lithographical methods and plasma etching are costly and hardly scalable as well as require complicated pre-defined masking and wet chemical etching processes. Here we present a roll-to-roll patterning and transfer of graphene sheets capable of residue-free, no chemical treatment, and fast patterning. The graphene sheet attached to a Pressure Sensitive Film (PSF) is continuously patterned by applying pressure selectively with the pre-defined embossed roll. The patterned graphene sheet is adhered to the PSF with very low strength and can be easily transferred to the curved surface or a variety of flexible substrate without the aid of any heating mechanism. Compared to the transfer by the TRT and the PMMA support, the reduction in the occurrence of debris and defects was verified through Raman spectroscopy. In the other hands, exfoliation based methods are useful for the large scale production of graphene platelets and for low-end products, e.g., fillers for polymer composites, electrode materials for battery and supercapacitor, conductive inks and coatings etc. because of its unique combination of very high strength and stiffness, and excellent electrical and thermal conductivities. These applications require huge quantities of graphene in the form of nanosheets, nanoparticles or nanoplatelets at a reasonable cost

however, purity is not the major issue in this case. As a solution, the mechanical exfoliation by the air jet mill is demonstrated, which is very effective and easy to scale up for any industrial application. The proposed method is especially useful for a layered material such as graphite having low interfacial bonding energy between layers so that the layer can be easily exfoliated by the mechanical forces. The raw graphite flakes of average 800 microns in diameter immediately had size reduction to few microns in average diameter within few minutes, which is advantageous considering typical exfoliation method such as ball milling take few tens hours of operation time. During the process, the fragmentation by collision is observed to be more dominant than the exfoliation by shear and normal forces. It is not usually desirable, but small flakes obtained from the air jet mill can enhance the exfoliation efficiency with the help of intercalation agents or further process with minimum amount of chemical promoter. Formation of bonds with undesirable oxygen species kept low up to only few percent even after few successive air jet mill runs, assuming that the defects on the basal plane would not be produced much during the process.