Versatile Multilayer Metamaterial Nanoparticles with Tailored Optical Constants for Force and Torque Transduction

Overview & Synopsis

The ability to apply force and torque directly to micro-and nanoscale particles without contact in optical traps has generated wide range of applications in scientific research and engineering. However, most of the particles for such optical manipulations are comprised of a single material that is chosen from the library of naturally available materials. Hence, the design and performance of the particles have been severely constrained by the narrow range of the given set of physical and chemical properties. Here, we overcome these limitations by implementing the concept of dielectric multilayer metamaterial based on the effective medium theory. It allows to obtain a designed combination of refractive index and birefringence suitable for each specific need, by choosing different consisting materials and changing the relative composition ratio of them. Aiming for being highly birefringent yet easily trap-pable and chemically stable, we have designed and fabricated highly uniform Nb 2 O 5 /SiO 2-multilayered and square cuboid-shaped nanoparticles. The resulting maximum birefringence is similar to that of calcite CaCO 3 crystal while the refractive index can be as low as that of other common dielectric probes such as silica and polystyrene. These desired properties are successfully demonstrated by tight 3D-trapping and generation of ∼16 nN·nm torque and ∼5 kHz rotation frequency at a ∼100 mW single-beam optical trap in water. This extension to the library of optically trappable materials beyond the existing ones paves the way for further improvements and opportunities in advanced optical manipulation systems.