High-Efficiency Alignment of 3D Biotemplated Helices via Rotating Magnetic Field for Terahertz Chiral Metamaterials

A high-efficiency strategy is proposed to fabricate helix terahertz metamaterials through the large-area alignment of 3D microhelices. The Spirulina were used as biotemplates to massively produce 3D magnetic helices by way of nickel electroless deposition. It is noteworthy that the helix angle alpha, instead of the aspect ratio, determines their magnetizing properties, quite distinct from other magnetic particles. The tight helix (alpha > approximate to 55 degrees) can be magnetized along the short axis, and the loose helix (alpha < approximate to 55 degrees) along the long axis. Based on this magnetization property, the rotating magnetic field (100 mT, 1 Hz) is introduced to efficiently align the tight helices and control their long axis perpendicular to the rotating plane. This is the first time that the mass alignment of complex 3D microhelices is achieved via a rotating magnetic field, and the programmable alignment of helix-units, i.e., vertical, horizontal, or hybrid orientation can also be developed. Moreover, the as-prepared materials with vertical helices exhibit remarkable chirality, and those with horizontal helices show polarization conversion about 20%. These helix metamaterials could be adopted in creating functional photonic devices in THz frequency regime, and the magnetic alignment may open up future possibilities for high-efficiency fabrication of metamaterials for practical engineering applications.