Three Dimensional Chiral Metamaterial Nanospirals in the Visible Range by Vertically Compensated Focused Ion Beam Induced-Deposition

Fabrication and characterization of chiral metallic nanospirals for application as metamaterials in the visible and near infrared range are described. The structures consist of platinum helicoidal three-dimensional nanostructures realized by focused ion beam induced-deposition, where the interaction with incident light can be controlled as a function of light circular polarization state and spectral region, showing a circular dichroism across a wide range of optical wavelengths. An accurate size control and nanometer resolution on the fabrication of the chiral structures are achieved by exploring substrate surface charge effects on substrates with different electrical properties and by studying and implementing an accurate scanning procedure for the nanostructure growth that allows compensation of the proximity and charge effects. Optical measurements carried out on the nanospiral arrays using a high spatial resolution setup show a transmittance difference of the right- and left-circular polarized light near to 40%.