Nano-and microsized chiral materials are receiving significant attention because of their unique characteristics, which include chiroptical activities and enantioselective interactions with living materials. However, the realization of chiral morphologies in such small-scale materials has been an issue because of the complicated fabrication methods and limited material selection. In this study, a facile and reproducible method is developed for fabricating 3D chiral microwrinkles with twisted shapes by asymmetric and biaxial buckling. Soft polydimethylsiloxane (PDMS) substrates are asymmetrically stretched with angled biaxial strains and exposed to UV/ozone to prepare hard silica layers on top of the PDMS substrates to induce microwrinkles. The chiral shapes are controlled by changing the angle (θ) between the two strain axes and the UV/ozone exposure times (t 1 , t 2 ) in each stage of buckling. The 3D chiral microwrinkles are shaped like "fusilli pasta" and occupy an area of 1.5 cm × 1.5 cm. The patterned area can be easily scaled, and no innate chiral biomaterial is necessary. This method could be widely extended to the fabrication of diverse types of chiral materials for advanced optical and bio-applications.

Artificial chiral materials at the nano- and microscales have unique optical properties, known as optical activities, that correspond to preferential interactions with circularly polarized light. Unlike the chiroptical responses of biomaterials, nano- and microscale materials with artificial chirality can present intense and tunable chiroptical responses in a broad range of frequencies from the ultraviolet to terahertz regimes. These particular properties of artificial chiral materials have been highlighted because of their potential use in photoelectronic and biomedical applications. The precise fabrication and manipulation of such small-scale materials are among the most important factors affecting their applicability; however, improvements remain necessary. From this perspective, we provide an overview of this field with introductions to types of artificial chiral materials, major parameters in the determination of chiroptical properties, fabrication methods that focus on mechanical-instability-induced buckling methods, and inclined-angle deposition methods. We also present application areas and outlooks.

Chiral-structured nanoscale materials exhibit chiroptical properties with preferential absorptions of circularly polarized light. The distinctive optical responses of chiral materials have great potential for advanced optical and biomedical applications. However, the fabrication of three-dimensional structures with mirrored nanoscale geometry is still challenging. This study introduces chiral plasmonic nanopatterns in wavy shapes based on the unidirectional alignment of block copolymer thin films and their tilted transfer, combined with buckling processes. The cylindrical nanodomains of polystyrene-block-poly­(2-vinylpyridine) thin films were unidirectionally aligned over a large area by the shear-rolling process. The aligned block copolymer thin films were transferred onto uniaxially prestrained polydimethylsiloxane films at certain angles relative to the stretching directions. The strain was then released to induce buckling. The aligned nanopatterns across the axis of the formed microwrinkles were selectively infiltrated with gold ions. After reduction by plasma treatment, chiral plasmonic nanowave patterns were fabricated with the presence of mirror-reflected circular dichroism spectra. This fabrication method does not require any lithography processing or innately chiral biomaterials, which can be advantageous over other conventional fabrication methods for artificial nanoscale chiral materials.

In article number 1808979, Bongjun Yeom and co‐workers fabricate “fusilli”‐shaped 3D chiral microwrinkles by asymmetric stretching of the flexible polydimethylsiloxane substrates at the macroscale. The handedness and shapes are finely controlled based on the optimization of the biaxial strain angle, UV/ozone exposure times, and sequences in two buckling stages.

Chiral metamaterials comprise a promising platform for advanced optoelectronic and biomedical applications. However, conventional fabrication via lithography is limited by its complexity and high cost. Herein, the lithography-free fabrication of terahertz chiral metamaterials and their enhancement for sensing the chirality of biocrystal enantiomers is presented. Chiral Au microstrip patterns (CHAMs) in a saw-tooth shape are fabricated by combining two-step buckling processes and glancing-angle deposition. Non-superimposable geometric chirality is achieved by controlling the tilt angle between the asymmetric and biaxial strain axes and the selective area deposition of the Au layers by using the shadow effect. The manufactured chiral metamaterials show mirror-shaped terahertz circular dichroism (TCD) signals in the range of 0.2-2.5 THz. Coupling of the induced electric and magnetic dipoles to the chiral-shaped Au surfaces results in effective optical chirality enhancement. Finite-difference time-domain computational simulations reveal the homogeneous distribution of optical chirality with an absolute maximum of 2.24 in the near field. Summing the TCD signals for enantiomeric cystine biocrystals onto the chiral metamaterials shows an ≈7-fold amplification in magnitude. This enhancement can be attributed to the synergistic effects of superchiral field enhancement and the electromagnetic resonance between the CHAMs and biocrystals.