Deposition of levitated charged nanoparticles on a substrate using an electrostatic lens

摘要

A charged nanoparticle that is confined and cooled in an ion trap can, in principle, be expelled from the trap and directed onto a substrate with high positional accuracy using an electrostatic lens. This deposition technique could provide a complement to studies of trapped nanoscale objects by allowing examination of the object outside the trap. It may also be used to assemble new types of structures (for example, by depositing a 2D material onto a reactive surface in high vacuum). In our system, a charged nanoparticle held in a quadrupole electric field trap is released from the trap and directed toward a removable indium tin oxide (ITO) coated substrate in ultrahigh vacuum (UHV), using an Einzel lens to focus the particle's trajectory. We have worked with a variety of materials: graphene nanoplatelets around 1 micron in diameter, as well as three-dimensional nanoparticles (including gold, silver, tin, silica, polystyrene, and graphite) with diameters of 200-800 nm. We have consistently detected particles striking the substrate by means of a charge sensor connected to the conductive substrate coating. Some particles, but not others, are observed to stick to the substrate; we are currently working to increase the chance of adhesion for metal nanoparticles by raising their temperature before deposition. We have had some success in locating the deposited particles using a camera positioned above the substrate; efforts to improve the imaging method are ongoing.