A New Route for the Fabrication of Nanoparticles in Superfluid Helium

This project intends to establish a new route for the fabrication of nanoparticles using superfluid helium droplets as the growth medium, which offers a high degree of control over the growth of nanoparticles, allowing tailoring to specific applications. Starting from the characterization of the UHV superfluid helium droplet source, we progressively add more and more dopants to the droplets, leading to the formation of small clusters composed of a few molecules and/or metal atoms, and large nanoparticles composed of >104 atoms. The helium droplet source and small clusters are characterized using mass spectrometry while nanoparticles are investigated by transmission electron microscope imaging. By sequential doping we have obtained binary clusters, unlocking the possibility of producing heterogeneous clusters of any two or more materials. In addition, we have fabricated core-shell nanoparticles, and have provided microscopy images that clearly show core-shell structure for nanoparticles fabricated by this route for the first time. Finally, in this project we have obtained the first direct evidence for the presence of quantized vortices in nanoscale superfluid helium, which are then utilized as templates for the growth of nanowires. This opens up new a landscape of helium nanodroplet technology and new possibilities for nanoscience and nanotechnology.