Inherently Selective and Anisotropic Ruthenium Deposition on the Basal Plane of Single-Layer Transition Metal Dichalcogenide Crystals

Abstract

Area-selective deposition (ASD) provides promise to facilitate the fabrication of nano-electronic devices with 2D transition metal dichalcogenide channels. This paper explores Ru ASD by chemical vapor deposition (CVD) on a Si/SiO2 substrate that is partly covered by triangular single-layer WS2 crystals. Opposite to most chemically driven deposition techniques, this Ru deposition is inherently selective, with the WS2 basal plane being more active than the WS2 crystals edges. Continuous Ru layers form on the basal plane of the WS2 crystals with less than 2% selectivity loss on the SiO2 surface. Ru deposition initiates near the WS2 crystal edges and expands over the WS2 basal plane with a lateral growth rate that is more than 10 times larger than the vertical growth rate. The anisotropic growth is attributed to diffusion-mediated aggregation of Ru adspecies on the WS2 basal plane. Moreover, experimental observations are consistent with theoretical predictions for self-confined deposition on the WS2 crystals, while there is no physical barrier to prevent lateral overgrowth. The obtained insights are relevant for a wide range of applications that rely on chemically driven deposition on 2D materials, and promote further research on precise nanopattern replication by self-confined growth without relying on physical barriers.