Chiral Plasmonic Nanowaves by Tilted Assembly of Unidirectionally Aligned Block Copolymers with Buckling-Induced Microwrinkles

Abstract

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.

Lithography‐Free Fabrication of Terahertz Chiral Metamaterials and Their Chirality Enhancement for Enantiomer Sensing

“…Details of the experimental parameters, such as the strain for biaxial stretching, the stretching angle (𝛼), the UV-ozone exposure time, the thickness of the PDMS substrate, and the release speed for the mechanical strain were precisely controlled to obtain reproducible chiral-shaped patterns (please see the details for each parameter in the Experimental Section). [20,22] As we confirmed the completed CHAM patterns with OM, CHAMs showed consistent chiral shapes with variations in the periodicity less than 5% for CHAM devices from five different batches (Figure S2, Supporting Information). In both the LH and RH samples, the first set of microwrinkles had wavelength 𝜆 1 = 30.2 ± 1.4 μm and amplitude A 1 = 1.2 ± 0.1 μm (the left panel in Figure 2b) while the second set of microwrinkles had wavelength 𝜆 2 = 72.7 ± 3.5 μm and amplitude A 2 = 5.6 ± 0.5 μm (the right panel in Figure 2b).…”

“…We previously reported the tilted-angle transfer of directionally aligned block copolymer 2D nanopatterns to form buckled microwrinkles. [20] In particular, twisted or asymmetric buckling of the rotating direction can be introduced to prepare chiral-shaped wrinkled micropatterns with the aid of deformable substrates. [21,22] However, only a few approaches using mechanical instability-based self-assembly processes for the fabrication of chiral metamaterials have so far been reported.…”

“…The two-step buckling process with asymmetric biaxial strains, which does not require biomaterials or lithography, was adapted from our previous research. [20][21][22] Structural chirality was controllable via the macroscale manipulation of the tilt angle between the biaxial strain regions. The manufactured chiral metamaterials showed terahertz CD (TCD) signals with maximum CD values of 14°in the range of 0.2-2.5 THz, which were simulated via finite-difference time-domain (FDTD) computational simulation.…”

Chiral Inorganic Nanostructures from Achiral Platforms: A Universal Synthesis Route via Supramolecular Self-Assembly

“…An anisotropy factor of −8.6 ×10 −4 at 522 nm was obtained from our BCP/Au NP hybrid, which is relatively high compared to chiral Au nanostructures synthesized using chiral BCP templates and enantiomer additives (Table S3). 20,21,67 The anisotropy factor of the BCP/Ag NP hybrid was −8.0 × 10 −4 at 520 nm, which was also larger than that of the chiral Ag NPs grown using chiral polymeric templates. 30,31 The chiral BCP/PdO and BCP/TiO 2 NP hybrids showed anisotropy factors of −1.2 × 10 −4 and −1.0 × 10 −4 at 286 and 360 nm, respectively.…”

Tunable Chiral Plasmonic Activities Enabled via Stimuli Responsive Micro‐Origami

“…gold nanospheres/nanorods, AuNSs/AuNRs) based on chiral templates (such as DNA, [2,[29][30][31] cellulose nanocrystals, [32] chirality fibers [33] ), amino acid-based ligand, [34,35] and nanofabrication rendered layered thin film. [36][37][38][39] Following this strategy, diverse chiral morphologies, like helix, [2] pyramids, [40] and propellers, [41] can be obtained. However, the magnitude of ellipticity is usually quite weak with a CD value of several to tens of millidegree and a g-factor ≈10 −5 -10 −3 .…”