Surface functionalization and atomic layer deposition of metal oxides on MoS2 surfaces

Transition metal dichalcogenides (TMDs), such as MoS₂, have attracted considerable interest in the field of nanoelectronics due to their unique properties. These layered materials possess a hexagonal structure similar to graphene and exhibit semiconducting behavior, making them ideal candidates for channel materials in field-effect transistors (FETs). However, integrating these channel materials into devices requires the fabrication of a high-quality interface between the TMD and a deposited dielectric layer. The sulfur-terminated MoS₂ surface is hydrophobic, and typical films deposited via atomic layer deposition (ALD) often exhibit a high concentration of pinhole-type defects. To improve the compatibility of MoS₂ with ALD processes, we investigated the effect of seeding the surface with HAuCl₄ salts. These chloride-terminated complexes are expected to react with H₂O, resulting in a hydroxyl-terminated surface that is conducive to a well-behaved ALD process. Following surface treatment, ALD titania and alumina films were deposited using tetrakis (dimethylamino) titanium and trimethylaluminum as the metal-organic precursors, with H₂O serving as the oxidizer. Raman spectroscopy confirmed that the surface treatment did not compromise the structural integrity of MoS₂. X-ray photoelectron spectroscopy measurements verified the presence of gold and aluminum on the surface and the successful removal of chlorine during the process. Atomic force microscopy revealed that the HAuCl₄ treatment influenced the titania film nucleation and morphology; however, 6 nm titania films deposited at 100°C and 200°C still exhibited some pinholes.