Myonghoo Hwang1,Bongjun Yeom1
Hanyang University1
Myonghoo Hwang1,Bongjun Yeom1
Hanyang University1
Chiral metamaterials can interact differently with circularly polarized lights, that is determined by their mirror-symmetric structures in three-dimension. Fabrications of the chiral structures in nano and microscales were mostly accomplished by advanced lithography techniques and wet chemical synthesis methods with bio derivatives containing innate molecular chirality. These previous fabrication methods limit wide applications of chiral metamaterials because of high cost in mass production and narrow windows for material selections. Herein, we suggest a facile and general fabrication method based on step-wise buckling processes with biaxial and asymmetric strains for twisted wrinkled patterns in chiral geometry. Soft polydimethylsiloxane substrates were utilized to be biaxially stretched in asymmetric directions. Then, the PDMS surfaces were oxidized by ozone treatment or oxygen plasma to produce hard oxide layers with different moduli from the substrates. By removing in-plane strains in stepwise manner with additional surface treatments, fusilli pasta-shaped twisted wrinkle patterns were produced on top of the substrates. Based on asymmetric angle, degree of strains and the surface treatments, the mirror-symmetric geometries of the twisted wrinkle patterns were controlled, which further utilized for fabrications of various 3D chiral metamaterials. Layer-by-Layer assembly methods for depositions of plasmonic nanoparticles and selective areal depositions over the pattern surfaces were introduced. Optical activity in wide ranges of optical frequencies from visible to THz were realized based on these chiral twisted metapatterns. It is noted that preparations of these materials do not necessitate any lithography or bio-additives, which will be advantageous for facile fabrications of chiral structures for various applications, such as advanced optoelectronic devices, bio sensors and pharmaceutical applications.