Study On A Metamaterial Perfect Absorber Fabricated With Nanoimprint Lithography

Metamaterial Perfect Absorbers(MPAs) have successfully interacted in electromagnetic bands across the spectrum from radio frequencies, to microwave, terahertz, across the infrared spectrum and almost to visible wavelengths And a metamaterial absorber is a type of metamaterial intended to efficiently absorb electromagnetic radiation at desired wavelength. It can offer benefits over conventional absorbers such as further miniaturization, wider adaptability, and increased effectiveness. The applications for the metamaterial absorber include solar photovoltaics, spatial light modulators, sensors, infrared camouflage and photodetectors.Most of the MPAs composed of a periodically arranged metallic plate layer, a dielectric medium layer, and a metal reflector layer. Its excellent light absorption properties originating from local surface plasmon resonance(LSPR) in the interface between the metal nanoparticles and dielectric medium.With the excitation of incident light, collective electron charge oscillations in metallic nanoparticles occurs. At the resonance wavelength, the particle’s optical absorption has a maximum and exhibit enhanced near-field amplitude.The absorbance is determined by the size and shape of nanoparticles, as well as the material properties and the thickness of the dielectric medium. Plamonics is a highly active area due to recent advances in nano-fabrication methods, which can precisely controlled shapes, sizes, and spacings of nanostructures. Micro/nano-fabrication technologies are mainly include: ultra violate lithography(UVL), electron beam lithography(EBL), extreme ultra violet lithography(EUVL), laser direct writing(LDW), and nanoimprint lithography(NIL). While UVL has lower resolution, EBL, EUVL, LDW are all expensive and low efficient methods. NIL has its advantage in preparation of nanoscale structures with high throughput, high resolution and low cost.In this work, Ultraviolet Nanoimprint Lithography(UV-NIL) technology is applied to fabricate a metamaterial perfect absorber with UV-NIL technique.The absorber is composed of Au nanodisk-SiO2 dielectric layer-Au thin film. Numerical computations show that the near perfect absorption of light can be achieved at nearinfrared band of 1.2 μm when the thickness of dielectric medium reaches 20 nm. We use PDMS stamp to prepare absorbers with different SiO2 thicknesses and nano-disk sizes. Experimental results show that with decreasing the thickness of SiO2, the absorption maximum shifts to longer wavelengths. And with increasing nano-disk sizes, the absorption maximum shows a red-shift as well. These results are basically in line with our simulation results which demonstrate the NIL is a reliable and accurate nanotechnology for the metamaterial fabrication with low cost and high efficiency.