Two-step conversion of metal and metal oxide precursor films to 2D transition metal dichalcogenides and heterostructures

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.