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The understanding of the interlayer interactions in vertical heterostructures of two-dimensional (2D) transition metal dichalcogenides (TMDCs) is essential to exploit their advanced functions for next-generation optoelectronics and electronics. Here we demonstrate a monolithic stacking of TMDC heterostructures with 2D MoS2 and WS2 layers via in situ physical vapor deposition. We find that the kinetically sputtered atoms are able to overcome the interlayer van der Waals forces between the vertical layers, leading to a substantial number of randomly oriented stacks with various twist angles. Our X-ray photoelectron spectroscopy results reveal a type II heterojunction for 2D WS2/MoS2, showing a band alignment with a conduction band offset of 0.41 eV and a valence band offset of 0.25 eV. In particular, we observed a remarkable interlayer coupling and associated exciton relaxation at the hetero-interface due to the misoriented stacks. By analyzing the band structures and charge densities of the vertical stacks using first-principles calculations, we reveal that the interlayer coupling is a function of the interlayer distance and is relatively insensitive to the angle of misorientation.

Electronic regulation and structural engineering at the atomic level of electrocatalysts is of vital importance to a highly efficient oxygen evolution reaction (OER). Here we report Fe-doped MoS2 (Fe-MoS2) nanosheets in which the Fe dopant influences the synthesis process to simultaneously tune the edge sites and electronic properties of MoS2. Impressively, the Fe-MoS2 nanosheets exhibit greatly improved catalytic activity towards the OER, achieving a current density of 50 mA cm-2 at 290 mV and satisfactory durability in 1.0 M KOH. Transmission electron microscopy analysis confirms that the Fe-MoS2 nanosheets undergo an atomic-scale structural evolution from horizontally aligned planes to vertically aligned planes, maximally exposing their edge sites. Density functional theory calculations reveal that the substitution of Fe at the Mo site in MoS2 has the lowest formation energy, offering a low overpotential of 328 mV for the OER.