Effect of Sulfur Evaporation Rate on Screw Dislocation Driven Growth of MoS2 with High Atomic Step Density

We report the sulfur evaporation rate controlled screw dislocation driven growth of two-dimensional MoS2 that contains unprecedented atomic step density. Screw dislocation assisted growth of atomic thin MoS2 on amorphous SiO2 or a crystalline and conducting Si substrate paves the way to form spiral morphology of two-dimensional materials without the need for single crystalline miscut substrates to initiate the line defects. The unique spiral morphology promoted by screw dislocation is typically observed at a high nucleation rate induced by an abrupt increase in sulfur concentration. Screw dislocation assisted spiral MoS2 growth leads to a high step density with an fold increase in the total edge length. Statistical analysis from detailed atomic force microscope phase imaging of flat and spiral MoS2 flakes reveals the linear increase in total edge length from similar to 470 nm to similar to 2325 nm with respect to variation in the number of steps available at the spiral structure in the range of 2-8. High resolution transmission electron microscopy imaging reveals the local atomic structure of the ledge that separates the individual layers in spiral MoS2 structure and aids the development of growth mechanism. The optimized spiral growth of MoS2 provides countless active sites for hydrogen energy generation applications. Hydrogen evolution performance of as-grown MoS2 on p-type Si substrates decorated with high ledge density provides active adsorption sites leading to hydrogen evolution at a lower potential with a higher current density. The developed strategy of increasing the sulfur evaporation rate to induce a spike in the nucleation rate promotes screw dislocation driven growth of MoS2 with spiral morphology. Such sulfur evaporation rate controlled spiral growth is important for surface engineering of two-dimensional materials to harvest the benefits of active edge sites for hydrogen evolution, catalyst, and sensor applications.