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

氦纳米液滴是非常小的液氦液滴，直径为人类头发的1/1000~1/100,000。它们非常冷，温度低至0.38K。当分子和原子遇到氦液滴时，它们会被捕获，在大多数情况下，它们会迁移到氦液滴的内部。氦液滴是超流体，氦原子和掺杂剂之间的结合通常很弱。因此，当一个以上的原子或分子被拾取时，就会形成分子团簇。当更多的掺杂剂逐个分子或逐个原子地加入到氦滴中，并依次加入不同的材料时，就会形成核壳纳米颗粒(纳米洋葱)。核壳纳米粒子可以具有奇特的性质，这取决于其大小和组成。氦滴的独特性质使其成为制造纳米粒子的理想材料，因为它们允许生长几乎任何组合材料。然而，并不是所有的东西都进入氦滴的内部。对于高自旋的金属原子，例如Na和K，它们将存在于氦纳米液滴的表面，并将阻碍使用氦滴的相当大的纳米颗粒的生长。因此，在这项研究中将引入种子技术来克服这一主要困难，以形成具有高自旋金属的纳米颗粒。将合成一系列核-壳和核-多壳纳米粒子，这些纳米粒子在材料科学、生物医学、成像和存储设备中具有潜在的应用前景。

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.