  Two-dimensional (2D) transition metal dichalcogenides (TMDCs) have attracted
much interest and shown promise in many applications. However, it is
challenging to obtain uniform TMDCs with clean surfaces, because of the
difficulties in controlling the way the reactants are supplied to the reaction
in the current chemical vapor deposition (CVD) growth process. Here, we report
a new growth approach called dissolution-precipitation (DP) growth, where the
metal sources are sealed inside glass substrates to control their feeding to
the reaction. Noteworthy, the diffusion of metal source inside glass to its
surface provides a uniform metal source on the glass surface, and restricts the
TMDC growth to only a surface reaction while eliminates unwanted gas-phase
reaction. This feature gives rise to highly-uniform monolayer TMDCs with a
clean surface on centimeter-scale substrates. The DP growth works well for a
large variety of TMDCs and their alloys, providing a solid foundation for the
controlled growth of clean TMDCs by the fine control of the metal source.
