Superfluid helium droplets: from spectroscopy to magnetic nanoparticles

This project applies superfluid helium droplets in two big areas: spectroscopy and nanoparticles formation. Helium droplets, consisted of more than 103 helium atoms, provide a non-friction and very cold (~0.37 K) environment for clusters/nanoparticles growth, which offers unique advantages as a medium in applications of both spectroscopy and nanostructures formation. By sequentially adding NaCl and water molecules, the dissolution process of NaCl in water can be experimentally studied for the first time. This is achieved by recording the infra-red spectra of NaCl(H2O)n (1 ≤ n ≤ 7) complexes in O-H stretching region in combination with ab initio calculations. In particular, two bands have been assigned to dissolution of NaCl in water. The existence of quantum vortices in helium droplets has been firmly evident from spherical Ag nanoparticles formed in a chain. Quantum vortices provide a new route for the formation of one-dimensional nanostructures, which has been exploited in the fabrication of novel nanowires. Finally the pioneering work on the fabrication of both antiferromagnetic and ferromagnetic nanomaterials is reported for the first time, taking Cr and Ni as examples respectively. It is found that we can force ferromagnetic ordering in magnetic materials in superfluid helium. In particular, antiferromagnetic chromium has been discovered to convert to ferromagnetic, and the magnetism of ferromagnetic materials can have hugely enhanced magnetic moments that are close to the theoretical limit. This will have potential for applications in biomedical science, data storage and energy efficient technologies in the longer term.