2, Department of Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Institute, Troy, New York, United States
4, Department of Mechanical, Aerospace and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States
5, Department of Chemical, Biological and Pharmaceutical Engineering, New Jersey Institute of Technology, Troy, New York, United States
3, Department of Material Science and Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States
Rhenium disulfide (ReS2) differs fundamentally from other group VI transition metal dichalcogenides (TMDs) due to its low structural symmetry, which results in its optical and electrical anisotropy. Although vertical growth is observed in some TMDs under special growth conditions, vertical growth in ReS2 is very different in that it is highly spontaneous and substrate independent. In this study, the mechanism that underpins the thermodynamically favorable vertical growth mode of ReS2 is uncovered. It is found that the governing mechanism for ReS2 growth involves two distinct stages. In the first stage, ReS2 grows parallel to the growth substrate, consistent with conventional TMD growth. However, subsequent vertical growth is nucleated at points on the lattice where Re atoms are “pinched” together. At such sites, an additional Re atom binds with the cluster of pinched Re atoms, leaving an undercoordinated S atom protruding out of the ReS2 plane. This undercoordinated S is “reactive” and binds to free Re and S atoms, initiating growth in a direction perpendicular to the ReS2 surface. The utility of such vertical ReS2 arrays in applications where high surface to volume ratio and electric field enhancement are essential, such as surface enhanced Raman spectroscopy and solar based disinfection of bacteria is demonstrated.
 Gao et al. Nano Letters, 16, 3780 ( 2016).
 Q. Zhang et al. Adv. Mater., 28, 2616 (2016)