Novel nanoscience in superfluid helium droplets: from nanoparticles to nanowires

Superfluid helium droplets have emerged as a new route for the fabrication of nanomaterials. They are large clusters of helium that allow molecules/atoms to be added and subsequently aggregate, providing a confined environment for growing nanometer-sized entities with exotic properties. For droplets composed of less than 107 helium atoms, small particles with diameters no more than 10 nm can be grown. In larger helium droplets quantized vortices play an important role, leading to the aggregation of dopants along the vortex lines and the formation of one-dimensional nanostructures. Combined with other properties of helium droplets, namely the chemical inertness, the very low temperature and the ultrahigh cooling rate, and the ease by which core-shell structures can be formed, many new types of nanomaterials that are difficult to make with conventional “hot” synthesis methods are now possible. Here we present a review focusing on the fundamental properties of helium droplets and address, in particular, their potential for the fabrication of novel nanomaterials. The latter will be illustrated using selected results, with a bias towards work originating from our laboratory.