Synthesis of a Hybrid Nanostructure of ZnO-Decorated MoS₂ by Atomic Layer Deposition

We introduce the synthesis of hybrid nanostructures comprised of ZnO nanocrystals (NCs) decorating nanosheets and nanowires (NWs) of MoS₂ prepared by atomic layer deposition (ALD). The concentration, size, and surface-to-volume ratio of the ZnO NCs can be systematically engineered by controlling both the number of ZnO ALD cycles and the properties of the MoS₂ substrates, which are prepared by sulfurizing ALD MoO₃. Analysis of the chemical composition combined with electron microscopy and synchrotron X-ray techniques as a function of the number of ZnO ALD cycles, together with the results of quantum chemical calculations, help elucidate the ZnO growth mechanism and its dependence on the properties of the MoS₂ substrate. The defect density and grain size of MoS₂ nanosheets are controlled by the sulfurization temperature of ALD MoO₃, and the ZnO NCs in turn nucleate selectively at defect sites on MoS₂ surface and enlarge with increasing ALD cycle numbers. At higher ALD cycle numbers, the coalescence of ZnO NCs contributes to an increase in areal coverage and NC size. Additionally, the geometry of the hybrid structures can be tuned by changing the dimensionality of the MoS₂, by employing vertical NWs of MoS₂ as the substrate for ALD ZnO NCs, which leads to improvement of the relevant surface-to-volume ratio. Such materials are expected to find use in newly expanded applications, especially those such as sensors or photodevices based on a p-n heterojunction which relies on coupling transition-metal dichalcogenides with NCs.