Abstract-Active Terahertz Shielding and Absorption Based on Graphene Foam Modulated by Electric and Optical Field Excitation

Shi‐Tong Xu, Fei Fan, Jierong Cheng,  Honghui Chen, Wenle Ma, Yi Huang, Shengjiang Chang,

https://onlinelibrary.wiley.com/doi/abs/10.1002/adom.201900555

Ultralight materials for broadband terahertz (THz) shielding and absorption are promising in practical THz applications. Here, active THz shielding and absorption properties of 3D graphene foam (GF) controlled by both laser pumping and biased electric field are investigated. The GF can be tuned from OFF‐shielding state to ON‐shielding state when the external field excitations are applied, and 10 dB shielding bandwidth expands from 0 to a broad band of 0.2–1.6 THz. Further researches show that the GF always keeps very low THz reflection either with or without external fields, but its absorption characteristics can be remarkably controlled from 13% to 95.4% at 0.3 THz by the power of the external excitations, and its specific average terahertz absorption performance increases from 3.9 × 103 to 1.95 × 104 dB cm3 g−1. This modulation mechanism reveals that the carrier density in GF increases one order of magnitude from 2.6 × 1014 cm−3 to 3.15 × 1015 cm−3. Finally, the tunable THz shielding and absorption characteristics of this GF device are demonstrated by THz transmission imaging, which shows its great potential applications in active THz imaging, radar, and electromagnetic compatibility.

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-Ultra-Broadband Wide-Angle Terahertz Absorption Properties of 3D Graphene Foam

Zhen Ge, Ying Zhou, Yang Yang, Peishuang Xiao, Jiajie Liang, Tengfei Zhang, Qian Shi, Guanghao Li, Yongsheng Chen,

http://onlinelibrary.wiley.com/doi/10.1002/adfm.201704363/abstract

As a next generation of detection technology, terahertz technology is very promising. In this work, a highly efficient terahertz wave absorber based on 3D graphene foam (3DG) is first reported. Excellent terahertz absorption property at frequency ranging from 0.1 to 1.2 THz is obtained owing to faint surface reflection and enormous internal absorption. By precise control of the constant properties for 3DG, the reflection loss (RL) value of 19 dB is acquired and the qualified frequency bandwidth (with RL value over 10 dB) covers 95% of the entire measured bandwidth at normal incidence, which far surpasses most reported materials. More importantly, the terahertz absorption performance of 3DG enhances obviously with increasing the incidence while majority of materials become invalid at oblique incidence, instead. At the incidence of 45°, the maximum RL value increases 50% from 19 to 28.6 dB and the qualified frequency bandwidth covers 100% of the measured bandwidth. After considering all core indicators involving density, qualified bandwidth, and RL values, the specific average terahertz absorption (SATA) property is investigated. The SATA value of 3DG is over 3000 times higher than those of other materials in open literatures.