The chiral coating on an achiral nanostructure by the secondary effect in focused ion beam induced deposition.

Optical metamaterials are widely used in electromagnetic wave modulation due to their sub-wavelength feature sizes. In this paper, a method to plate an achiral nanopillar array with chiral coating by the secondary effect in focused ion beam induced deposition is proposed. Guided by the pattern defined in a bitmap with variable residence time, the beam scan strategy suppresses the interaction between adjacent nanostructures. A uniform chiral coating is formed on the target nanostructure without affecting the adjacent nanostructure, under carefully selected beam parameters and the rotation angle of the sample stage. Energy dispersive x-ray spectroscopy results show that the chiral film has high purity metal, which enables the generation of localized surface plasmon resonances and causes the circular dichroism (CD) under circularly polarized light illumination. Finally, the tailorable CD spectrum of the coated array is verified by the finite difference time domain method.