Abstract-Annealing temperature dependent terahertz-thermal-electrical conversion characteristics of three-dimensional microporous graphene

Meng Chen, Yingxin Wang, Jianguo Wen, Honghui Chen, Wenle Ma, Fei Fan, Yi Huang, and Ziran Zhao

https://pubs.acs.org/doi/10.1021/acsami.8b20095


Three-dimensional microporous graphene (3DMG), possesses ultrahigh photon absorptivity and excellent photothermal conversion ability, and shows great potential in energy storage and photodetection, especially for the not well-explored terahertz (THz) frequency range. Here, we report on the characterization of THz-thermal-electrical conversion properties of 3DMG with different annealing treatments. We observe distinct behavior of bolometric and photothermoelectric responses varying with annealing temperature. Resistance-temperature characteristics and thermoelectric power measurements reveal that marked charge carrier reversal occurs in 3DMG as the annealing temperature changes between 600 and 800 °C, which can be well explained by Fermi-level tuning associated with oxygen functional group evolution. Benefiting from the large specific surface area of 3DMG, it has an extraordinary capability of reaching thermal equilibrium quickly and exhibits a fast photothermal conversion with a time constant of 23 ms. In addition, 3DMG can serve as an ideal absorber to improve the sensitivity of THz detectors and we demonstrate that the responsivity of a carbon nanotube device could be enhanced by 12 times through 3DMG. Our work provides new insight into the physical characteristics of carrier transport and THz-thermal-electrical conversion in 3DMG controlled by annealing temperature and opens an avenue for the development of highly efficient graphene-based THz devices.

Abstract-Terahertz wave modulation enhanced by laser processed PVA film on Si substrate

Weimin Liu, Fei Fan, Shitong Xu, Meng Chen, Xianghui Wang, Shengjiang Chang,

https://www.nature.com/articles/s41598-018-26778-7

An optically pumped ultrasensitive broadband terahertz (THz) wave modulator based on polyvinyl alcohol (PVA) film on Si wafer was demonstrated in this work. The THz time domain spectroscopy experiments confirm that the PVA/Si can drastically enhance the photo-induced THz wave modulation on the Si surface, especially when the PVA film is heated by a high-power laser. A modulation depth of 72% can be achieved only under 0.55 W/cm2 modulated laser power, which is superior significantly to the bare Si. The numerical simulations indicate that the laser processed PVA (LP-PVA) film increases the photo-generated carrier concentration on the Si surface in two orders of magnitude higher than that of bare Si. Moreover, the modulation mechanism and the dynamic process of laser heating on the PVA/Si have been discussed. This highly efficient THz modulation mechanism and its simple fabrication method have great application potentials in THz modulators.

Abstract-Nanoparticles doped film sensing based on terahertz metamaterials

Weimin Liu, . Author links open the author workspace.Fei Fan, . Author links open the author workspace.Shengjiang Chang, Jiaqing Hou, . Author links open the author workspace.Meng Chen, . Author links open the author workspace.Xianghui  Wang, Jinjun Bai, 

http://www.sciencedirect.com/science/article/pii/S0030401817306739?via%3Dihub


. Author links open the author workspace.FeiFan
A nanoparticles concentration sensor based on doped film and terahertz (THz) metamaterial has been proposed. By coating the nanoparticles doped polyvinyl alcohol (PVA) film on the surface of THz metamaterial, the effects of nanoparticle concentration on the metamaterial resonances are investigated through experiments and numerical simulations. Results show that resonant frequency of the metamaterial linearly decreases with the increment of doping concentration. Furthermore, numerical simulations illustrate that the redshift of resonance results from the changes of refractive index of the doped film. The concentration sensitivity of this sensor is 3.12 GHz/0.1%, and the refractive index sensitivity reaches 53.33 GHz/RIU. This work provides a non-contact, nondestructive and sensitive method for the detection of nanoparticles concentration and brings out a new application on THz film metamaterial sensing.

Abstract-Terahertz artificial birefringence and tunable phase shifter based on dielectric metasurface with compound lattice

Yun-Yun Ji, Fei Fan, Meng Chen, Lei Yang, and Sheng-Jiang Chang

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-10-11405

A dielectric metasurface with line-square compound lattice structure has been fabricated and demonstrated in the terahertz (THz) regime by the THz time-domain spectroscopy and numerical simulation. A polarization dependent electromagnetically induced transparency (EIT) effect is achieved in this metasurface due to the mode coupling and interference between the resonance modes in line and square subunits of the metasurface. Accompany with the EIT effect, a large artificial birefringence effect between two orthogonal polarization states is also observed in this compound metasurface, of which birefringence is over 0.6. Furthermore, the liquid crystals are filled on the surface of this dielectric metasurface to fabricate an electrically tunable THz LC phase shifter. The experimental results show that its tunable phase shift under the biased electric field reaches 0.33π, 1.8 times higher than the bare silicon, which confirms the enhancement role of THz microstructure on the LC phase shift in the THz regime. The large birefringence phase shift of this compound metasurface and its LC tunable phase shifter will be of great significance for potential applications in THz polarization and phase devices.

© 2017 Optical Society of America

• Meng Chen
• , Fei Fan
• , Shi-Tong Xu
•  & Sheng-Jiang Chang

http://www.nature.com/articles/srep38562

Subwavelength dielectric gratings are widely applied in the phase and polarization manipulation of light. However, the dispersion of the normal dielectric gratings is not flat while their birefringences are not enough in the THz regime. In this paper, we have fabricated two all-dielectric gratings with gradient grids in the THz regime, of which artificial birefringence is much larger than that of the equal-grid dielectric grating demonstrated by both experiments and simulations. The transmission and dispersion characteristics are also improved since the gradient grids break the periodicity of grating lattices as a chirp feature. From 0.6–1.4 THz, a broadband birefringence reaches 0.35 with a low dispersion and good linearity of phase shift, and the maximum phase shift is 1.4π. Furthermore, these gradient gratings are applied as half-wave plates and realize a linear polarization conversion with a conversion rate over 99%, also much higher than the equal-grid gratings. These gradient gratings show great advantages compared to the periodic gratings and provide a new way in the designing of artificial birefringence material.