Study On The Planar Chiral Metamaterials Fabricated By Nanoimprint Lithography

Nanoimprint lithography becomes a hot focus of novel lithography technologies of next generation due to its advantages of low cost, high yield and fidelity of large area pattern transfer. Due to its novel structure, planar chiral metamaterials exhibit polarization rotation effect and possess greater polarization rotation capability than conventional birefringent crystal. Also, in some cases that planar chiral metamaterial shows very large polarization azimuth rotation, it exhibits negative refractive index. Therefore, planar chiral metamaterials are regarded to be a useful device used in the antenna and invisible materials and attracts intensive research. This thesis utilizes nanoimprint lithography to fabricate both metallic and dielectric planar chiral metamaterials and investigates the impact of imprint parameters on the processing and performance of planar chiral metamaterials theoretically and experimentally.Firstly, utilizing FDTD solutions, the mechanism of the planar chiral metallic metamaterials of complementary structure is analyzed. The simulation results of the planar chiral metallic metamaterials of complementary structure indicate that resonance peaks can shift, enhance and decrease by varying the distance between the two metal layers of the structure. While the magnetic resonance peaks disappear, intensify or shift due to the distance change of the two metal layers, the resonance peaks resulted by electrical resonance in one layer does not vary. Employing the imprint lithography, we successfully fabricate the planar chiral metamaterials with rosette pattern in 600nm period and verify the simulation result that the magnetic resonance peaks will change with the different distances between two metal layers. We also show that planar chiral metamaterial with complementary structure of 600nm period rosette pattern in the optical range possesses the polarization rotation capability of 6×104°/mm and 10°-15°of polarization azimuth rotation.This thesis also investigates the possibility of applying ZnO as a material for the dielectric optical components like planar chiral metamaterial and grating structure. The patterned growth technology for ZnO nanostructure by the combination of nanoimprint lithography and hydrothermal method are realized. The patterns are transferred to SU-8 resist by nanoimprint lithography and form the SU-8 trenches to limit the growth of ZnO nanorods. We successfully synthesize discrete ZnO nanorods of rosette pattern and grating pattern by HMTA and zinc nitrate. For application in the planar chiral metamaterial, we synthesize the continuous ZnO nanostructure by the solution consisting of DMAB and zinc nitrate. The thesis further discusses the key points of patterned ZnO nanorods growth, and suggests that the control of synthesis time is the most important key point for the precisely patterned growth of ZnO nanostructure. The oxygen reactive etching during the processing is found out to be an effective way to improve the photoluminescence of ZnO nanorods. The processing originated by the thesis owns the advantages of simple processing steps, low cost and high fidelity contrasted to other patterned ZnO growth technologies. At last, the extinction ratio of ZnO grating is measured.