Mechanical exfoliation has been a preferred method for obtaining various two-dimensional (2D) materials due to its ability to produce high-quality thin flakes. However, traditional exfoliation techniques often yield flakes of limited size and low yield. Herein, we present a systematic approach to improve mechanical exfoliation by using vacuum treatment to enhance the van der Waals forces between the substrate and the 2D material. This method comprises oxygen plasma cleaning followed by vacuum treatment, effectively removing organic adsorbates from the substrate and maximizing contact between the outermost layer of 2D material and the substrate. This vacuum-assisted exfoliation approach substantially enhances both the yield and flake size of graphene, resulting in single-layer graphene (SLG) flakes approximately eighty times larger than those achieved through conventional methods. The quality of the exfoliated SLG was assessed using Raman spectroscopy and atomic force microscopy (AFM), which confirmed that it is highly similar to that obtained from conventional exfoliation. Furthermore, the exfoliated SLG flakes were encapsulated between hexagonal boron nitride (hBN) layers and fabricated into SLG field-effect transistors (FETs). These devices exhibited high-performance characteristics, yielding a field-effect mobility (μ) of approximately 110,000 cm2∕V ⋅ s at room condition, demonstrating the effectiveness of the vacuum-assisted exfoliation method in producing high-quality, large-area graphene suitable for advanced electronic applications.

Vacuum-assisted exfoliation method for large-area, high-quality graphene flakes in nanodevice applications
    Abstract
    1 Introduction
    2 Experimental details
    3 Results and discussion
        3.1 Optical microscopic analysis
        3.2 Raman spectroscopic analysis
        3.3 AFM analysis
        3.4 Mechanism of the vacuum method
    4 Electronic transport properties
    5 Conclusions
    Acknowledgements 
    References

• Minwook Kim(Department of Nanotechnology and Advanced Materials Engineering and HMC, Sejong University, Seoul 05006, South Korea)
• Sunil Kumar(Department of Nanotechnology and Advanced Materials Engineering and HMC, Sejong University, Seoul 05006, South Korea) Corresponding author
• Sohee Lee(Department of Nanotechnology and Advanced Materials Engineering and HMC, Sejong University, Seoul 05006, South Korea)
• Muhammad Suleman(Department of Nanotechnology and Advanced Materials Engineering and HMC, Sejong University, Seoul 05006, South Korea)
• Yongho Seo(Department of Nanotechnology and Advanced Materials Engineering and HMC, Sejong University, Seoul 05006, South Korea)
• Van Huy Nguyen(Department of Nanotechnology and Advanced Materials Engineering and HMC, Sejong University, Seoul 05006, South Korea, National Graphene Institute, University of Manchester, Manchester M13 9PL, UK)
• Zhigang Jiang(School of Physics, Georgia Institute of Technology, Atlanta, GA 30332, USA)
• Takashi Taniguchi(National Institute for Materials Science, Ibaraki 305‑0044, Japan)
• Kenji Watanabe(National Institute for Materials Science, Ibaraki 305‑0044, Japan)