Reliable Exfoliation of Large-Area High-Quality Flakes of Graphene and Other Two-Dimensional Materials.
Mechanical exfoliation has been a key enabler of the exploration of the properties of two-dimensional materials, such as graphene, by providing routine access to high-quality material. The original exfoliation method, which remained largely unchanged during the past decade, provides relatively small flakes with moderate yield. Here, we report a modified approach for exfoliating thin monolayer and few-layer flakes from layered crystals. Our method introduces two process steps that enhance and homogenize the adhesion force between the outermost sheet in contact with a substrate: Prior to exfoliation, ambient adsorbates are effectively removed from the substrate by oxygen plasma cleaning, and an additional heat treatment maximizes the uniform contact area at the interface between the source crystal and the substrate. For graphene exfoliation, these simple process steps increased the yield and the area of the transferred flakes by more than 50 times compared to the established exfoliation methods. Raman and AFM characterization shows that the graphene flakes are of similar high quality as those obtained in previous reports. Graphene field-effect devices were fabricated and measured with back-gating and solution top-gating, yielding mobilities of ∼4000 and 12,000 cm(2)/(V s), respectively, and thus demonstrating excellent electrical properties. Experiments with other layered crystals, e.g., a bismuth strontium calcium copper oxide (BSCCO) superconductor, show enhancements in exfoliation yield and flake area similar to those for graphene, suggesting that our modified exfoliation method provides an effective way for producing large area, high-quality flakes of a wide range of 2D materials.
Center for Functional Nanomaterials, Brookhaven National Laboratory , Upton, New York 11973, United States.
Yuan
Y
Huang
Department of Mechanical & Materials Engineering, University of Nebraska-Lincoln , Lincoln, Nebraska 68588, United States.
Eli
E
Sutter
Department of Applied Physics and Applied Mathematics, Columbia University , New York, New York 10027, United States.
Norman N
NN
Shi
Electrical Engineering and Computer Science, Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States.
Jiabao
J
Zheng
Institute of Physics, Chinese Academy of Sciences , P.O. Box 603, Beijing 100190, China.
Tianzhong
T
Yang
Electrical Engineering and Computer Science, Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States.
Dirk
D
Englund
Institute of Physics, Chinese Academy of Sciences , P.O. Box 603, Beijing 100190, China.
Hong-Jun
HJ
Gao
Department of Electrical & Computer Engineering, University of Nebraska-Lincoln , Lincoln, Nebraska 68588, United States.
Peter
P
Sutter
2D materials; exfoliation; graphene; processing; van der Waals force