Achieving sub-seconds growth of monolayer WSe2 crystals with time-resolved capturing of growth dynamics

Controlled and time-resolved growth of atomically thin monolayer transition-metal dichalcogenides (TMDCs) has long been demanded in the emerging field of two-dimensional (2D) materials. However, due to the complex precursor vaporization, mixing, and chemistry as well as random nucleation and ultra-long growth times in the common synthesis techniques such as CVD, understandings the growth kinetics and crystal evolution has been elusive. To address these challenges, here we introduce the laser-assisted synthesis technique (LAST), where a continuous wave CO2 laser is used for the time-resolved vaporization of bulk stoichiometric TMDC powders in a tube furnace under the growth substrate. This technique enables us to study growth dynamics down to a few milliseconds (10ms) along with the record highest growth rate (60μm/s) on a non-epitaxial substrate such as Si/SiO2 ever reported for TMDC mono- and few-layer single crystals.