Theoretical insight into the mechanism for spontaneous vertical growth in ReS₂

While vertical growth can be observed in some transition metal dichalcogenides (TMDs) under special conditions, vertical growth of rhenium disulfide (ReS₂) is unique in that it is thermodynamically favorable over horizontal growth regardless of substrate. In this study, we use density functional theory (DFT) to shed light on the mechanism that initiates vertical growth in ReS₂ to explain its substrate-independence. We propose that ReS₂ growth has two stages. First, ReS₂ grows parallel to the substrate, in a manner similar to that of conventional TMDs. However, as a growing ReS₂ flake reaches a critical diameter, spontaneous vertical growth is nucleated at points near the flake’s center. At these sites, an additional Re atom binds to a cluster of “pinched” Re atoms, leaving an under-coordinated S atom protruding out of the ReS₂ plane. This S atom is “reactive” and readily binds to free Re and S atoms, initiating growth in a direction perpendicular to the ReS₂ surface. The resulting vertical ReS₂ arrays possess high surface-to-volume ratios and can therefore accommodate a broad range of applications including surface enhanced Raman spectroscopy, field emission, and solar-based disinfection of bacteria.