Broken Myth of Inter-layer Electronic Decoupling at ReS2: Theoretical understanding, experimental corroboration and application

ReS₂ had generated unresolved controversies about its inter-layer electronic coupling, layer-dependent optical response and electronic structure. While earlier studies predict electronically decoupled layers, experimental reports manifest layer dependent optical response and 3D electronic dispersion across the van der Waals gap. Using DFT and TDDFT, we resolved the structural and electronic disputes of ReS₂. The ReS₆ face-shared distorted octahedral chain along b-axis are bridged along a-axis via a couplet of face-shared warped ReS₅ square pyramides. The coordination of S-atoms in ReS₅ controls the inter and intra-layer electronic dispersion, leading to an indirect and direct bandgap in monolayers and bulk respectively. Next, we have grown large-area CVD films of ReS₂. With increasing temperature, it shows a tendency of vertical growth. The TEM micrograph of the films suggests the same crystal structure as per the theoretical outcome. The static and transient optical studies clearly indicates the presence of both excitons. After an optimization of growth temperature, the film with best optical response is demonstrated to have an optoelectronic application having a good responsivity and detectivity.