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.