Growth of centimeter scale Nb_1−xW_xSe₂ monolayer film by promoter assisted liquid phase chemical vapor deposition

Two-dimensional (2D) transition-metal dichalcogenide materials (TMDs) alloys have a wide range of applications in the field of optoelectronics due to their capacity to achieve wide modulation of the band gap with fully tunable compositions. However, it is still a challenge for growing alloys with uniform components and large lateral size due to the random distribution of the crystal nucleus locations. Here, we applied a simple but effective promoter assisted liquid phase chemical vapor deposition (CVD) method, in which the quantity ratio of promoter to metal precursor can be controlled precisely, leading to tiny amounts of transition metal oxide precursors deposition onto the substrates in a highly uniform and reproducible manner, which can effectively control the uniform distribution of element components and nucleation sites. By this method, a series of monolayer Nb_1−xW_xSe₂ alloy films with fully tunable compositions and centimeter scale have been successfully synthesized on sapphire substrates. This controllable approach opens a new way to produce large area and uniform 2D alloy film, which has the potential for the construction of optoelectronic devices with tailored spectral responses.