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

Abstract

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.