Designer nanostructures for visible light

Most nanostructures are chemically synthesized, but they tend to be highly symmetrical and achiral. A recent advance in physical vapor deposition, known as Glancing Angle Deposition, permits the growth of chiral thin films and chiral nanocolloids. The optical properties of plasmonic nanohelices that can be produced on wafer scale samples, offer very strong polarization dependence, i.e. the circular optical activity can be precisely tailored by the shape of the nanohelices from the UV to the IR. This is useful to obtain meta-materials which can be programmed to have an index of refraction that can change from n ~ +1.1 down to n ~ –0.2, depending on the ellipticity of the incident light.

Using magnetic metals, thin films with both large natural and magnetic optical activity can be obtained that permit the detection of magneto-chiral dichroism in absorption for visible light through arrays of ferromagnetic nanohelices at room conditions, with perturbing magnetic fields < 10^–1 T.