Thanks to optical multilayers, significant technological advancements have been made in optics and photonics. Many structural colors found in nature also consist of multilayers. Some insects and birds have evolved to use air as an optical material. However, manufacturing air‐gap reflectors like those found in nature is difficult. This work introduces a novel, simple approach to fabricating air‐gap Bragg reflectors using a versatile, thin‐film, self‐rolling technique. First, an array of air‐gap spacers in the form of photoresist pillars is patterned on top of a dielectric thin film. Then, during a dry‐etching step, the film self‐rolls forming a microtubular structure. As the microtube advances, the pillars create air gaps between consecutive tube walls, resulting in a multilayered Bragg reflector. Self‐rolled Bragg reflectors (SBRs) with various air‐gap thicknesses exhibit high‐order reflectance modes. High‐reflectivity SBRs with up to eight air‐gap bilayers have been demonstrated . This approach is compatible with other material systems, paving the way for the creation of ultra‐broadband and multi‐narrowband reflectors spanning the ultraviolet to near infrared spectrum. These air‐gap SBRs contribute to the library of miniaturized photonic and magnetoelectronic devices made possible by the thin film self‐rolling technology in recent decades.
Bermúdez-Ureña et al. (Wed,) studied this question.