Seed-induced penetration: a new tool for the synthesis of core-shell nanoparticles using superfluid helium droplets

Helium nanodroplets are very small drops of liquid helium, with diameters at 1/1000 ~ 1/100,000 of a human hair. They are extremely cold, with a temperature as low as 0.38 K. When molecules and atoms encounter helium droplets, they will be captured, and in most cases, migrate to the interior of helium droplets. Helium droplets are superfluid, and the bonding between helium atoms and the dopants are often very weak. Therefore, when more than one atom or molecule are picked up, molecular clusters will be formed. When more dopants are added to helium droplets molecule by molecule, or atom by atom, and different materials are added in sequence, core-shell nanoparticles (the nano-onions ), will be formed. Core-shell nanoparticles can have exotic properties depending on the size and compositions. The unique properties of helium droplets make it ideal for fabrication of nanoparticles because they allow almost any combination materials to be grown.However, not everything goes to the interior of helium droplets. For high-spin metal atoms, e.g., Na and K, they will reside on the surface of helium nanodroplets and will hinder the growth of sizeable nanoparticles using helium droplets. A seeding technique will be therefore introduced in this research to overcome this major difficulty for the formation of nanoparticles with high-spin metals. A number of core-shell and core-multiple shell nanoparticles will be synthesized which have potential for a number of applicatoins in material science, biomedical science, imaging and strorage devices.

This is a ground-breaking research programme for the fabrication of novel core-shell nanoparticles using superfluid helium droplets. An innovative technique will be developed and applied to tackle major problems occurring in the synthesis of magnetic nanoparticles involving high-spin metals initially located on the surface of helium droplets. With this technique helium droplets will become uniquely powerful and versatile nano-reactors for the fabrication of core-shell nanoparticles, allowing almost a combination of any desired materials. Small metal clusters of a few metal atoms to large core and multi-shell magnetic nanoparticles (CMS-MNPs) of thousand metal atoms will be synthesized and investigated, from which the evolution of magnetism, and the size and composition-dependence of magnetic properties will all be investigated, hence will generate precious information for the understanding of nano-scale material science, theoretical modelling on magnetism and the design of functional nanoparticles in the future. The CMS-MNPs to be synthesized will possess unique magnetic properties, and will have the potential for a wide range of niche applications, such as MRI imaging, tumour hyperthermia therapy, digital storage devices, etc. The impact of this proposal to fundamental material science and nanotechnology is straight. From the point of view of physical chemistry, a new route to produce sizeable high-spin metal clusters inside helium droplets will be established by this research, and this will stimulate the investigation of metal clusters and their applications, for example, on nano-catalysis. Beyond the scientific impact, this research will also have the potential for positive societal impact because the unique CMS-MNPs could have the potential for technological innovation in biomedical and life science, which might contribute to the better quality of life for human being in the future. PUBLICATIONS AND PROFESSIONAL DISSEMINATION: through publication of our work in the high impact scientific literature. Given that the research project is original and innovative for both fundamental science and applied nanotechnology, it will be credible to seek publication in high-impact journals such as PRL, Nature Materials, Nano Letters, Science and Nature. Equally, the work will be presented at a wide range of conferences above and beyond specialist meetings. COMMUNICATIONS AND ENGAGEMENT: the unique capability and wide-range possibilities brought forward by this research will lend itself to a far wider audience within the international research community and this will be pursued in several meanss including: (i) a schools outreach programme, including a specific lecture and the production of articles for education journals; (ii) high quality web-based supporting materials, including a video resource that shows a movie on how to form nano-onions . Other source of publicity will be pursued, e.g., through press releases. EXPLOITATION: Some part of this research can be patentable, and this will be in contact with EBDO of the University of Leicester. In addition, industrial partners will be sought to commercialize the unique CMS-MNPs, such as imaging, tumor hyperthermia, etc, starting at 42nd month of the project. TRAINING IMPACT: Two young researchers would be trained in this project, one at the PDRA level and the other at PhD level. A wide range of trainings are involved in this project, e.g., design and operation of advanced instrumentation (such as UHV systems, helium droplet source, electronics and mass spectrometer, microscopes, etc.), characterization of core-shell structures and their magnetic properties. This will equip both the PDRA and the PhD student with skills that will be attractive to a variety of potential employers. They will be also required to contribute to impact-related activities, including public outreach, thereby providing a further layer of skills and expertise that would add to their employability.