(739e) Low-Temperature Transfer-Free Synthesis of Large-Area Unfolding Graphene Films By Electrospray On Super-Hydrophilic Glass

Low-temperature transfer-free synthesis of large-area unfolding graphene films by electrospray on super-hydrophilic glass

Li-Ju Wang, Lei Li, Xilian Ouyang, Hongyan He, Yun Wu, Jianfeng Yu, L. James L Lee*

Nanoscale Science and Engineering Center for Affordable Nanoengineering of Polymeric Biomedical Devices, the Ohio State University,

Columbus, Ohio 43210, United States

Abstract

Graphene as a new material is widely studied in optoelectronics, energy storage, composites and biomedical applications because graphene possesses a unique combination of extraordinary electrical, optical, thermal and mechanical properties and high specific surface area. However the synthesis of large area graphene film is a challenge work and greatly limiting the application of graphene. The most commonly used synthesis method of graphene films is via chemical vapor deposition (CVD) at elevated temperature (~1,000 ˚C) on polycrystalline metal surfaces and later transferred from metal support to desirable substrates. The high growth temperature imposes limitation on the choice of substrates and results in the sequential transfer process. During the transfer process, wrinkled or rippled graphene frequently forms cracks or tears.

Solution-based synthesis of graphene film, such as filtration method, is an alternative way used to overcome the high-temperature limitation and to avoid the transfer process. However, the soft sheet-like graphene tend to compress and aggregate together because of strong van der waals attraction. Once the graphene dispersions are dried, the sheet-like graphene not only aggregate to form coffee-ring but also forming three-dimensional (3D) crumpled ball-like structure. Therefore, fabrication of large-area thin graphene films is still a big challenge due to preventing aggregation (coffee ring) and making uniform unfolding films in a scalable and inexpensive method.

      In this study, we present an effective and scalable transfer-free synthesis of large-area unfolding graphene thin films by electrospraying graphene sheets directly on the super-hydrophilic heated glass at relatively lower temperature (100-150˚C).  When the graphene nanosheets were directly electrospray bombarded onto the super-hydrophilic and preheated glass, the strong shear force unfolded the crumpled graphene and the fast water evaporating simultaneously applies capillary forces to spread and pin graphene sheets on glass surface. This fabrication method was able to avoid aggregation (coffee-ring) and to make the uniformly graphene film. Efficiently, for the large-area (4.4cm×4.4cm) graphene film deposition, only 1ml graphene solution (~0.4 mg/ml) is required to fabricate transparent glass with 80% transparency and ~2kΩ/sq resistance. This low-temperature transfer-free approach enables us to fabricate large-area unfolding graphene coatings with few amount of solution and this method has great potential for large scale and low cost applications.