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-Reduction degree regulated room-temperature terahertz direct detection based on fully suspended and low-temperature thermally reduced graphene oxides

Yang Cao, Yajing Zhao, Yingxin Wang, Yue Zhang, Jianguo Wen, Ziran Zhao, Lianqing Zhu,

https://www.sciencedirect.com/science/article/pii/S0008622318311540#!

A series of fully-suspended reduced graphene oxide (RGO) room-temperature THz detectors were fabricated based on low-temperature (from 100 to 350 °C) thermally-reduced free-standing graphene oxide (GO) thin films. The suspended configuration results in a four-fold increase in responsivity and at least one order of magnitude increase in response speed compared to the substrate-supported detector. More importantly, the responsivity can be adjusted over a wide range from 10−2–102 mA W−1 and simultaneously the response speed can be adjusted on the order of tens of milliseconds by only tuning the reduction temperature of GO namely the reduction degree of GO. The regulation mechanism was revealed at the molecular level, i. e., the content of C=O functional group and the O/C ratio inside RGO, which are vary with the reduction degree of GO, are closely related to THz absorbance and electrical conductivity of RGO thin films, respectively. The experimental results demonstrated that the as high as possible content of C=O functional group and simultaneously a moderate O/C ratio can achieve optimal synergy between the THz absorption and electrical conductivity of the RGO thin films, thereby achieving an optimal THz detection performance.

Abstract-Ultrabroadband photosensitivity from visible to terahertz at room temperature

Dong Wu, Yongchang Ma, Yingying Niu, Qiaomei Liu, Tao Dong, Sijie Zhang, Jiasen Niu, Huibin Zhou, Jian Wei,Yingxin Wang, Ziran Zhao,  Nanlin Wang,

http://advances.sciencemag.org/content/4/8/eaao3057

Charge density wave (CDW) is one of the most fundamental quantum phenomena in solids. Different from ordinary metals in which only single-particle excitations exist, CDW also has collective excitations and can carry electric current in a collective fashion. Manipulating this collective condensation for applications has long been a goal in the condensed matter and materials community. We show that the CDW system of 1T-TaS2 is highly sensitive to light directly from visible down to terahertz, with current responsivities on the order of ~1 AW−1 at room temperature. Our findings open a new avenue for realizing uncooled, ultrabroadband, and sensitive photoelectronics continuously down to the terahertz spectral range.

Abstract-Uncooled EuSbTe3 photodetector highly sensitive from ultraviolet to terahertz frequencies

Biao Wang, Dong Wu, Hai Zhu, Huibin Zhou, Jian Wei, Nan Lin Wang, Jiasen Niu, Ping Zheng, Yingxin Wang, Yingying Niu, Yu Quan Su, Ziran Zhao

http://iopscience.iop.org/article/10.1088/2053-1583/aa939c/pdf

Light probe from Uv to THz is critical in photoelectronics and has great applications ranging from imaging, communication to medicine. However, the room temperature ultrabroadband photodetection across visible down to far-infrared is still challenging. The challenging arises mainly from the lack of suitable photoactive materials. Because that conventional semiconductors, such as silicon, have their photosensitive properties cut off by the bandgap and are transparent to spectrum at long-wavelength infrared side. Comparatively, the dielectrics with very narrow band-gap but maintain the semiconductor-like electrical conduction would have priorities for ultrabroadband photodetection. Here we report on EuSbTe3 is highly sensitive from ultraviolet directly to terahertz (THz) at room temperature. High photoresponsivities 1 ~ 8 A W-1 reached in our prototype EuSbTe3 detectors with low noise equivalent power (NEP) recorded, for instances ~ 150 pW  Hz-1/2 (at λ = 532 nm) and ~0.6 nW  Hz-1/2 (at λ = 118.8 µm) respectively. Our results demonstrate a promising system with direct photosensitivity extending well into THz regime at room temperature, shed new light on exploring more sophisticated multi-band photoelectronics

Abstract-Terahertz photodetector based on double-walled carbon nanotube macrobundle–metal contacts

Yingxin Wang, Xiangquan Deng, Guowei Zhang, Jinquan Wei, Jia-Lin Zhu, Zhiqiang Chen, Ziran Zhao, and Jia-Lin Sun
https://www.osapublishing.org/oe/abstract.cfm?uri=oe-23-10-13348

We report on the characterization of a terahertz (THz) photodetector with an extremely simple structure consisting of only a macroscopic bundle of double-walled carbon nanotubes (DWCNTs) suspended between two metal electrodes. Polarization-sensitive, broadband, and significant photoresponse occurring at the DWCNT–metal contacts under THz illumination are observed with room-temperature photocurrent and photovoltage responsivities up to ∼16 mA/W and ∼0.2 V/W at 2.52 THz, respectively. Scanning photocurrent measurements provide evidence that the photothermoelectric mechanism dominates the detector response. The simple geometry and compact nature of our device make it suitable for integration and show promising applications for THz detection.

© 2015 Optical Society of America

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Abstract-Compressive sensing for direct millimeter-wave holographic imaging

Compressive sensing for direct millimeter-wave holographic imaging Lingbo Qiao, Yingxin Wang, Zongjun Shen, Ziran Zhao, and Zhiqiang Chen  »View Author Affiliations

http://www.opticsinfobase.org/ao/abstract.cfm?uri=ao-54-11-3280

Applied Optics, Vol. 54, Issue 11, pp. 3280-3289 (2015)
http://dx.doi.org/10.1364/AO.54.003280

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Direct millimeter-wave (MMW) holographic imaging, which provides both the amplitude and phase information by using the heterodyne mixing technique, is considered a powerful tool for personnel security surveillance. However, MWW imaging systems usually suffer from the problem of high cost or relatively long data acquisition periods for array or single-pixel systems. In this paper, compressive sensing (CS), which aims at sparse sampling, is extended to direct MMW holographic imaging for reducing the number of antenna units or the data acquisition time. First, following the scalar diffraction theory, an exact derivation of the direct MMW holographic reconstruction is presented. Then, CS reconstruction strategies for complex-valued MMW images are introduced based on the derived reconstruction formula. To pursue the applicability for near-field MMW imaging and more complicated imaging targets, three sparsity bases, including total variance, wavelet, and curvelet, are evaluated for the CS reconstruction of MMW images. We also discuss different sampling patterns for single-pixel, linear array and two-dimensional array MMW imaging systems. Both simulations and experiments demonstrate the feasibility of recovering MMW images from measurements at 1/2 or even 1/4 of the Nyquist rate.

© 2015 Optical Society of America

Abstract-Calibration of a thermal detector for pulse energy measurement of terahertz radiation

Yingxin Wang, Ziran Zhao, Zhiqiang Chen, and Kejun Kang
http://www.opticsinfobase.org/ol/abstract.cfm?uri=ol-37-21-4395

We present a calibration method for measuring the terahertz pulse energy through a conventional thermal power detector. Short terahertz pulses were generated by mechanically modulating a continuous wave source with a chopper containing a narrow slot and detected by a Golay cell. We use a calibrated calorimeter to monitor the total source power so we can know the terahertz pulse energy in advance. The Golay detector response to rectangular pulses is theoretically analyzed and the peak amplitude of its output signal is found to be the relevant parameter to determine the pulse energy. We accomplish absolute calibration for the pulse responsivity of the Golay cell by examining the linear correlation between the output signal and the incident energy.