Ultrabroadband Optical Superchirality in a 3D Stacked-Patch Plasmonic Metamaterial Designed by Two-Step Glancing Angle Deposition

• Published in: Advanced functional materials Vol. 26; no. 43; pp. 7807 - 7816
• Main Authors: Hou, Yidong, Leung, Ho Ming, Chan, Che Ting, Du, Jinglei, Chan, Helen Lai-Wai, Lei, Dang Yuan
• Format: Journal Article
• Language: English
• Published: Blackwell Publishing Ltd 15.11.2016
• Subjects: Arrays; chiral metamaterials; circular dichroism; Circularity; Deposition; Dichroism; Disorders; glancing angle deposition; Handedness; Metamaterials; plasmonic nanostructures; Plasmonics; polarization rotation
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.201602800

Low‐cost and large‐scale fabrication of 3D chiral metamaterials is highly desired for potential applications such as nanophotonics devices and chiral biosensors. One of the promising fabrication methods is to use glancing angle deposition (GLAD) of metal on self‐assembled dielectric microsphere array. However, structural handedness varies locally due to long‐range disorder of the array and therefore large‐scale realization of the same handedness is impossible. Here, using symmetry considerations a two‐step GLAD process is proposed to eliminate this longstanding problem. In the proposed scheme, the unavoidable long‐range disorder gives rise to microscale domains of the same handedness but of slightly different structural geometries and ultimately contributes to a broad‐band response. Experimentally, a record‐breaking superchiral response of circular dichroism signal of ≈11° is demonstrated and an average polarization rotation angle of 27° in the visible region on ≈1 cm2 sample is observed. Computer‐aided geometric reconstruction with experimental parameters unambiguously reveal the presence of strong structural anisotropy and chirality in the prepared stacked‐patch plasmonic chiral metamaterial; microscopic spectral analyses combined with full‐wave electromagnetic simulations coherently provide deeper insights into the measured circular dichroism and optical activity. The observed chiroptical response can also be flexibly controlled by adjusting the deposition parameters for various potential applications. A 3D stacked‐patch plasmonic metamaterial is fabricated and it shows a circular dichroism signal of ≈11° and an average polarization rotation angle of 27° in a wide spectral range from 480 to 750 nm. This giant ultrabroadband chiroptical response results from a constructively weighted average of local chiralities and concurrent elimination of the racemic mixture in the sample.