  From the laboratory to real-world applications, synthesis of two dimensional
(2D) materials requires modular techniques to control morphology, structure,
chemistry, and the plethora of exciting properties arising from these nanoscale
materials. In this review, we explore one of the many available synthesis
techniques; the extremely versatile two-step conversion (2SC) method. The 2SC
technique relies on deposition of a metal or metal oxide film, followed by
reaction with a chalcogen vapor at an elevated temperature, converting the
precursor film to a crystalline transition metal dichalcogenide (TMD). Herein,
we consider the variables at each step of the 2SC process including the impact
of the precursor film material and deposition technique, the influence of gas
composition and temperature during conversion, as well as other factors
controlling high quality 2D TMD synthesis. We feature the specific advantages
to the 2SC approach including deposition on diverse substrates, low temperature
processing, orientation control, and heterostructure synthesis, among others.
Finally, emergent opportunities that take advantage of the 2SC approach are
discussed to include next generation electronics, sensing, and optoelectronic
devices as well as catalysis for energy-related applications; spotlighting the
great potential of the 2SC technique.
