In this work heterostructures based on hydrogenated microcrystalline diamond thin films with attached MoS2 nanosheets were formed by a single-zone Mo annealing at atmospheric pressure. By varying the input parameters, MoS2 sheets were controllably synthesized in a vertical or horizontal orientation with respect to the diamond grain facets, which leads to a pronounced impact on the electronic and optoelectronic properties of the heterostructures. Comprehensive characterization shows the influence of the MoS2 orientation and thickness on the work function, surface potential, spatially and spectrally resolved photovoltage, and charge transfer kinetics in heterostructures. The aligned growth of MoS2 nanosheets and their properties are elucidated by molecular mechanics and time-dependent DFT calculations, which explain the mechanism of the assembly and the related optoelectronic effects in a straightforward way. The major orientation switching point occurs precisely at 11 nm of the MoS2 thickness/length. The highest photoresponse of 350 meV and favorable charge transfer are observed for the vertical MoS2 arrangement on diamond, yet without a covalent bond. The results and theoretical model hint at broader implications beyond the MoS2-diamond system.
