Metal sulphides with a lamellar structure will form nano-tubes, and these are currently employed in medical devices, as fibres with extremely high tensile strength, in hydrogen storage, for rechargeable batteries, in catalysis, and in nanotechnological applications. However, high temperatures are required for the planar structures to be induced to bend to form cylinders, and these unstable intermediate products must be trapped. This is nearly impossible in the case of tin disulphide, as the nanotube collapses already at significantly lower temperatures.
According to a report published in the journal Angewandte Chemie, the researchers, led by Wolfgang Tremel, have implemented an alternative method for the production of tin disulphide nanotubes which uses the vapour-liquid-solid (VLS) process, a technique more commonly used to produce semicon-ductor nanowires. Bismuth powder is combined with tin disulphide nanoflakes, and the mixture is heated in a tube furnace under an argon gas flow. The product of the reaction is deposited at the cooler end. Nanodroplets of bismuth are formed in the furnace, and these act as local collection points for tin. In this manner, the reaction partners accumulate in the metal droplets, providing the raw material from which nanotubes can be grown.
"In this process, the metal droplets are retained in the form of spheres at the end of the tubes, while the nanotubes grow out of them like hairs from follicles,” says Tremel. “And thanks to the catalytic effect provided by the metal droplets, it is possible to grow nanotubes even at relatively low temperatures."
Using the new technique, the team has been able to produce perfect nanotubes with diameters in a range of 30- 40nm and lengths of 100- 500nm consisting of several layers of SnS2.
