Extrinsic Corrugation‐Assisted Mechanical Exfoliation of Monolayer Graphene

Abstract

Figure 1 . a) The optical microscopy (OM) image of ≈ 100 nm thick graphite fl akes on silicon substrate after thermal annealing at 350 ° C for 2 h. b) The OM image of the same position after the reverse exfoliation [∗] S. Pang , Dr. H. N. Tsao , Dr. Y. Hernandez , Dr. X. Feng , Prof. K. Mullen Max Planck Institute for Polymer Research Ackermannweg 10, D-55128 Mainz (Germany) E-mail: feng@mpip-mainz.mpg.de; muellen@mpip-mainz.mpg.de J. M. Englert , Prof. A. Hirsch Zentralinstitut fur Neue Materialien und Prozesstechnik Dr.-Mack Str. 81 D-90762 Furth (Germany) Since the reports of the fi rst isolation and observation of the exceptional electronic, mechanical, and chemical properties, single layer graphene has attracted intense interest from both academic and industrial communities. [ 1–3 ] While the mechanical exfoliation method led to many exciting discoveries, several promising approaches have been reported for the preparation of monolayer graphene including solution exfoliation of graphite, [ 4 , 5 ] epitaxial growth from SiC, [ 6 , 7 ] reduction of graphene oxide, [ 8–10 ] and chemical vapor deposition (CVD) on metal surfaces. [ 11–13 ] Up to now, the CVD growth method seems to be the most promising technique for the production of large-scale few layer graphene fi lms. [ 13 , 14 ] However, this surface-mediated process requires very high temperatures, and tedious additional steps involving etching and transfer, thus rendering the production of graphene-based electronic devices diffi cult. Ultra-large monolayer graphene [ 15–17 ] and patterned graphene structures [ 18–22 ] constitute two important aspects for graphene fabrication technology. A simple way to directly “print” a high-quality graphene monolayer on insulating substrates from a graphite stamp would be particularly appealing for electronic applications. Covalent immobilization [ 23 , 24 ] and electrostatic forces [ 18 , 25 ] have been devised for the modifi cation of mechanical exfoliation, with the aim to improve the yield of monolayer graphene or to achieve patterned graphene structures. Despite the success in deposition of graphene patterns over a large area, these procedures suffer from a low monolayer yield ( < 10%). [ 18 , 19 , 26 ] Here, we describe an extrinsic corrugationassisted mechanical exfoliation (ECAME) for synthesizing monolayer graphene on substrates. This strategy involves a simple thermal treatment of deposited graphite on a silicon wafer in association with a wafer processing tape peeling process. This work reveals that underlayer graphene sheets can corrugate following the rough SiO 2 surface when the thick graphite fl ake is thermally annealed. Such a surface-mediated extrinsic corrugation process thus serves as the key driving force for exfoliation leading to more than 60% high-quality monolayer graphene. This protocol can be further employed to fabricate graphene patterns on the surface, a technique that may be explored for graphene-based electronic device fabrication.