7 research outputs found
Mechanism of Gold-Assisted Exfoliation of Centimeter-Sized Transition-Metal Dichalcogenide Monolayers
Exfoliation
of large-area monolayers is important for fundamental
research and technological implementation of transition-metal dichalcogenides.
Various techniques have been explored to increase the exfoliation
yield, but little is known about the underlying mechanism at the atomic
level. Here, we demonstrate gold-assisted mechanical exfoliation of
monolayer molybdenum disulfide, up to a centimeter scale. Detailed
spectroscopic, microscopic, and first-principles density functional
theory analyses reveal that strong van der Waals (vdW) interaction
between Au and the topmost MoS<sub>2</sub> layer facilitates the exfoliation
of monolayers. However, the large-area exfoliation promoted by such
strong vdW interaction is only achievable on freshly prepared clean
and smooth Au surfaces, while rough surfaces and surfaces exposed
to air for more than 15 min result in negligible exfoliation yields.
This technique is successfully extended to MoSe<sub>2</sub>, WS<sub>2</sub>, WSe<sub>2</sub>, MoTe<sub>2</sub>, WTe<sub>2</sub>, and
GaSe. In addition, electrochemical characterization reveals intriguing
interactions between monolayer MoS<sub>2</sub> and Au. A subnanometer-thick
MoS<sub>2</sub> monolayer strongly passivates the chemical properties
of the underlying Au, and the Au significantly modulates the electronic
band structure of the MoS<sub>2</sub>, turning it from semiconducting
to metallic. This could find applications in many areas, including
electrochemistry, photovoltaics, and photocatalysis