Chiral metamaterials have attracted much attention ever since it was predicted that negative refraction can be achieved by large chirality. In fact, chiral metamaterials also have other interesting properties, such as giant optical activity and circular dichroism, which may find applications in opto-electronics. However, it is still challenging to fabricate large area and qualified chiral metamaterials at visible range due to material losses and technique limitations. In this thesis, we report a new method to fabricate 3D visible range chiral metamaterials. The focus of this work is on chiral pattern design, fabrication, and chirality characterization. In addition, simulations are conducted to verify the experimental results.

Based on the technique of glancing angle deposition (...[ Read more ]

Chiral metamaterials have attracted much attention ever since it was predicted that negative refraction can be achieved by large chirality. In fact, chiral metamaterials also have other interesting properties, such as giant optical activity and circular dichroism, which may find applications in opto-electronics. However, it is still challenging to fabricate large area and qualified chiral metamaterials at visible range due to material losses and technique limitations. In this thesis, we report a new method to fabricate 3D visible range chiral metamaterials. The focus of this work is on chiral pattern design, fabrication, and chirality characterization. In addition, simulations are conducted to verify the experimental results.

Based on the technique of glancing angle deposition (GLAD), our method is called shadowing vapor deposition (SVD). This method is simple and has a potential for mass production of metallic chiral structures. Using this method, firstly, chiral metamaterials of Ag/PMMA square columnar arrays are fabricated by just one-time ~ 60° shadowing vapor deposition, which show tunable transmission difference for circularly, left- (LCP) and right- (RCP) handed, polarized light with largest value 0.3 and circular dichroism 1.3 at ~ 690 nm. Simulation results also show good agreement with the experimental results.

Secondly, L-shaped Ag/PMMA columnar arrays are fabricated by 45° Ag shadowing vapor deposition. The L-shaped structure shows good 3D chirality with forward and backward transmittances coincidence with each other. The transmission difference between LCP and RCP can approach 0.36 at 737 nm even for transmittance as high as 70%. The transmittance difference is induced by selective absorption and scattering of LCP and RCP in specific frequencies. The large 3D chirality makes this structure the most promising candidate to realize negative refractive index in the visible range. The high transmittance increases the potential to be used in optical-electric devices.

Thirdly, Z-shaped hole Ag arrays are designed and fabricated by two opposite direction 45° shadowing vapor deposition. The optical activity of the sample with two opposite direction deposition is obviously larger than that of just one-time Ag deposition. The sample shows significant response to both circularly and linearly polarized light with large asymmetry transmission. Especially for linearly polarized light, optical transmittance difference can be up to 0.5 or even larger with a linear dichroism as high as 1.8. The Z-shaped hole Ag arrays have the potential to be used as broadband polarizer in the visible range.

To conclude we have shown that the shadowing vapor deposition is a simple and effective method for fabricating chiral metamaterials. It has a great potential for mass production of metallic-dielectric chiral metamaterials in the visible range. This method could become popular in fabricating nano-structures with designated EM properties in the future.