Tunable WS₂ Nanotubes from Ga-Ion Seeding

Two-dimensional layered materials have attracted a lot of attention following the discovery of graphene and the demonstration of its remarkable properties. This renewed interest resulted in the discovery of numerous new 2D layered materials, including 2D materials of the transition metal dichalcogenide (TMD) family. A key feature of these materials is that the reduction of the number of layers is accompanied by the modification of the local electrical and optical properties. Furthermore, it has also been shown that this tunability is not restricted to two-dimensional nanosheets, but is also present within the one-dimensional configuration. In this context, TMD-based one-dimensional nanotubes benefit from unique properties that strongly depend on their chirality, diameter, and number of walls. The ability to control these parameters, and thus tune the properties of the nanotubes, is an essential requirement to deploy TMD nanotubes for realistic application, yet achieving such tunability at the nanofabrication level remains a challenge. Here we report on an approach by means of which WS₂ nanotubes of uniform diameter were fabricated and the investigation of their local electronic properties. We find that by implanting gallium ions in a tungsten film and subsequent annealing, highly uniform tungsten oxide nanowires could be fabricated. The sulfurization of these nanowires results in multiwall, close-ended WS₂ nanotubes with similar diameters. These WS₂ nanotubes are then characterised by using advanced transmission electron microscopy techniques, including high resolution electron energy loss spectroscopy. Our results demonstrate how the proposed gallium-assisted synthesis method provides an efficient way of controlling the morphology of WS₂ nanotubes, and thus tuning the electronic properties of these one-dimensional TMD structures, paving the way for the use of WS₂ nanotubes in nanotechnology applications.