Design, Simulation And Fabrication Of Vanadium Oxide-Based Metamaterials

Terahertz(THz) wave has low photon energy, high transmission, low loss and other special properties, so it has been widely applied in non-destructive testing, imaging, communications, and other fields. However, due to the lack of materials that can respond to THz wave in nature, up to now, THz wave has not been well developed and utilized. As a kind of new synthetic material, through reasonably designing the unit structure and the shape size or other factors, metamaterials(MMs) can efficiently respond to the desirable frequency electromagnetic wave. Therefore, the emergence of the MMs has brought new opportunities for the THz research. Vanadium oxides(VOx) are excellent infrared sensitive materials. Consequently, we focused on how to apply VOx in MMs, and fabricate MMs by VOx. Moreover, in this dissertation, we also investigated the response control law of MMs, and optimal process for the preparation of VOx by sol-gel, and design and simulation of VOx–based MMs. The main research contents and conclusions are listed as follows:(1) In combination with previous studies, we propose a new method to adjust the THz response of metamaterials. In our approach, an additional metal strip is introduced in the middle dielectric layer of MMs, and thus the THz response of MMs can be modulated through changing the position and the line width of the additional metal strip. The simulation results reveal that the response frequency of MMs is red shifted if the additional metal strip is moved from the bottom continuous metal film to the surface metal ring. Particularly, when the additional metal strip is located in the middle of the dielectric layer, the absorption of the MM reaches maximum(99.98%). The response frequency of the metamaterials is red shifted, and the absorption of the MM is increased if the width of the additional metal strip is gradually enlarged. According to this novel method, the THz response of MMs can be effectively controlled.(2) By optimizing the process conditions for the preparation of VOx thin films by sol-gel method. Thickness of VOx films can be significantly enlarged by repeating the preparation process. Using this method to prepare VOx thin films for MMs can thus improve the absorption of MMs to the incident electromagnetic wave.(3) The THz responses of the VOx–based MMs were simulated. It was found that the absorption of the VOx–based MMs to the incident electromagnetic wave is enhanced with the increase of the thickness of VOx thin films in the MMs. The absorption rate of the MMs to the incident electromagnetic wave is increased from 20.90% to 41.16%, if the dielectric layer of VOx thin film in MMs is increased from 137 nm to 296 nm.(4) Masks for the VOx–based MMs have been successfully prepared by Micro Electro-Mechanical System(MEMS), and thus VOx–based MMs have been successfully fabricated. For the MMs with the dielectric layers that are yielded by once, twice, and third preparation process for VOx thin films, THz time-domain spectroscopy(THz-TDS) measurements indicate that the absorption frequencies of the as-fabricated VOx–based MMs are 0.648 THz, 0.703 THz, 1.11 THz, respectively, which agree well with the simulation results.