Ultrafast growth of submillimeter-scale single-crystal MoSe₂ by pre-alloying CVD

The synthesis of large-scale monolayer single-crystal MX₂ (M = Mo, W; X = S, Se), a typical transition metal dichalcogenide (TMD), is the premise for their future applications. Compared with insulating substrates such as SiO₂ and sapphire, Au is more favourable for the fast growth of TMDs by chemical vapor deposition (CVD). Recently, large-scale single-crystal WX₂ was successfully grown and transferred on Au. In sharp contrast, the growth and transfer for monolayer MoX₂ is still very challenging, because Au has a higher solubility of Mo and stronger interaction with MoX₂ than WX₂. Compared with the most studied MoS₂, MoSe₂ is superior in many aspects because of the narrower band gap and tunable excitonic charging effects. However, the synthesis of large-scale single-crystal MoSe₂ on Au has not been reported so far. Here, a pre-alloying CVD method was developed to solve the problems for the growth and non-destructive transfer of MoX₂. It has realized the ultrafast growth (30 s) of submillimeter-scale (560 μm) single-crystal MoSe₂ for the first time. As-grown samples are strictly monolayers with good optical and electrical properties, which can be easily transferred without sacrificing Au foils by the electrochemical bubbling method. It was found that pre-alloying not only passivates the energetically active sites on Au but also weakens the interaction between Au and MoSe₂, which is responsible for the ultrafast growth and easy transfer of MoSe₂. This method is also universal for the fast growth and non-destructive transfer of other 2D TMDs.