Sapphire substrate enabled ultraflat gold tape for reliable mechanical exfoliation of monolayer MoS2

Monolayer MoS 2 has attracted extensive interest since its unique photoelectrical properties. Large-scale and high-quality preparation is the first step for its fundamental research and practical application, which has drawn huge attention. Recently, gold-assisted exfoliation method has emerged as a thrilling technique to obtain high-quality MoS 2 monolayer. Note that surface roughness and flatness are key factors in enhancing strong adhesive force between gold film and MoS 2 . We developed an ultraflat gold tape (∼7 nm thick) based on sapphire substrate, whose upper surface was directly used to exfoliate MoS 2 monolayer by taking advantage of the ultra-smooth and rigid surface of sapphire. Besides, we developed low-temperature annealing recipes, achieving excellent reproducibility (∼100 %). Finally, a polymer-assisted transfer method was proposed to transfer MoS 2 monolayer from the gold tape to arbitrary substrate, e. g. Si/SiO 2 substrate. Atomic force microscopy (AFM), Raman, photoluminescence (PL) measurements, and electrical characterization of exfoliated MoS 2 collectively provide convincing evidence for its monolayer and high-quality characteristics. The exploration of this work will improve the reliability and reproducibility of gold-assisted exfoliation of monolayer MoS 2 and other 2D materials , which benefits the application of two-dimensional (2D) materials and developments in the field of optoelectronics .