Implantation of Gallium into Layered Tungstene Disulfide Nanostructures is Facilitated by Hydrogenation

In this work, experimental results and theoretical simulations for the implantation of Ga into WS₂ nanoparticles exposed to focused Ga⁺ ion beams (FIB) with various doses are reported.<br/>Multiwall WS₂ and MoS₂ nanotubes and polyhedral fullerene-like nanoparticles were discovered in the earlier 1990s. An efficient synthesis method for the scaled-up production of high purity inorganic fullerene WS₂ nanoparticles was later developed, which allows to produce tens of kilograms per day. Additional efforts resulted in renewed synthesis of highly crystalline WS₂ and MoS₂ nanotubes in pure phase and scalable fashion. The availability of these nanomaterials led to investigation of their properties, and stimulated numerous applications in photoelectronics and nano-optics, tribology, and hydrogen storage.<br/>Implantation of atoms into solid materials provides a way to modify their properties. Doping of layered MoS₂ and WS₂ nanoparticles with alkali metal atoms, Re, Nb, and possibly other elements is a promising technique to change the electronic (semiconductor to metal), magnetic (diamagnetic to paramagnetic), and optical properties, the surface characteristics, and the mechanical and chemical behavior of these materials. The modified materials could be used in nanotechnology applications, catalysts and sensors, as well as in tribology and lubrication. However, the implantation processes often have a damaging effect on the materials structure.<br/>Bombarding WS₂ multilayered nanoparticles and nanotubes with FIB of Ga⁺ ions at high doses, larger than 10¹⁶cm⁻², indeed leads to drastic structural changes and melting of the material. At lower doses, when the damage was negligible or significantly smaller, the amount of implanted Ga was very small. A substantial increase in the amount of implanted Ga, and not appreciable structural damage, were observed in nanoparticles previously hydrogenated by a radio-frequency activated hydrogen plasma.<br/>Density functional theory calculations reveal that the implantation of Ga in the spaces between adjacent layers of pristine WS₂ nanoparticles is difficult due to the presence of activation barriers. In contrast, in hydrogenated WS₂ the hydrogen molecules are able to intercalate in between adjacent layers of the WS₂ nanoparticles, giving rise to the expansion of the interlayer distances, that in practice leads to the vanishing of the activation barrier for Ga implantation. This facilitates the implantation of Ga atoms in the irradiation experiments.