We present a tunable reflector based on VO2 thin films in the terahertz frequency range. The reflectance of the reflector
in the terahertz region can be tuned by controlling electrical properties of VO2 thin films. The change of electrical
properties of VO2 originates from an insulator-metal transition of VO2. The experimental results demonstrated the
effectiveness of the tunable reflector in the terahertz region. The tunable reflector of the VO2 thin films is very suitable
for terahertz systems.
Ferromagnetic high-<i>k</i> dielectrics are very promising candidates to replace SiO<sub>2</sub> in silicon based microelectronics industry, and also could simultaneously enable semiconductor spintronic devices that harness polarized electrons. In present work, Fe doped CeO<sub>2</sub> was synthesized by ceramic method and the effects of Fe doping on the structure and properties were characterized by ordinary methods and terahertz-time domain spectrometer (THz-TDS) technique. Our results show that the pure CeO<sub>2</sub> only has a small dielectric constant (ε) of 4, while a small amount of Fe (0.9%) doping into CeO<sub>2</sub> promotes the densification and induces a large ε of 23. From the THz spectroscopy, it is found that for undoped CeO<sub>2</sub> both the power absorption and the index of refraction increase with frequency, while for Fe doped CeO<sub>2</sub> we measure a remarkable transparency together with a flat index curve. The absorption coefficient of Fe doped CeO<sub>2</sub> was less than 0.35 cm<sup>-1</sup> ranging from 0.2 to 1.8 THz, rendering it a potential THz optical material. Our results also illustrate that THz technique is a powerful tool to differentiate the dielectric related electronic characteristics of high <i>k</i> materials.
In this letter, a bi-layer metamaterial composed of SRR layer and split wires layer is proposed, and the anisotropy of THz propagation through this MTM was firstly addressed and the intrinsic physic foundation was preliminarily discussed. The metamaterial consists of SRR layer, polyimide slab, and metal wires layer on GaAs substrate. A strong absorbance of 99.93% is obtained at 0.836 THz when the THz wave propagates in the "positive" directions of the absorber while in the "negative" case this value is only 2.16%. Our results indicate a strong interaction coupling between the SRR layer and the wires layer, which significantly enhanced the value of the power loss in the space between the two metal layers, leading to the perfect absorbance. The wires layer is a wave reflector which reflects most of the THz wave thus induced the absorbance anisotropy of this metamaterial.