Organic–inorganic hybrid three-dimensional (3D) perovskite materials have emerged as potential candidates for terahertz (THz) modulators. In this study, the metasurface of electromagnetically induced transparency resonance was integrated with 3D perovskite to achieve a high-efficiency dynamic THz modulator. The integration was achieved by modulating the intrinsic optoelectronic properties of perovskite with three wavelengths of optical pump and external voltage excitation. The maximum modulation depth was 466.8 %, with a pump flux of 11.5 mW/cm2 and excitation at 532 nm. The Dirac-like semimetal-Fermi energy band model was proposed to explain the dynamic transitions of free carriers in perovskites and reveal the internal mechanism of the dynamic modulation. In addition, we verified our proposed theoretical model by simulation and theoretical fitting, and calculated the conductivity and number of free carriers of perovskite under different excitations. The system thoroughly explains the observed differences under three wavelengths of optical pump excitation. The active control of THz waves based on Dirac semimetal materials with optical and electrical inputs could have many potential applications that have been proposed by few studies.
The property of Si-doped ZnSnO (SiZTO) thin film, thin-film transistor (TFT), and associated CMOS inverter has been optimized by Si doping. Under positive voltage and light negative voltage bias stresses, the SiZTO TFT shows a smaller threshold voltage shift (1.5 and 2.2 V, respectively) than that of the ZTO TFT (4.0 and 4.9 V, respectively). The ${C}$ – ${V}$ hysteresis has reduced from 3.5 V of ZTO TFT to 0.9 V of SiZTO TFT. A good electrical property and stability of SiZTO TFT ensure the construction of high-performance CMOS inverter constructed by SiZTO and solution processed semiconductor single-walled carbon nanotube (CNT) TFT. Moreover, by Si doping, the SiZTO-based CMOS inverter has shown a smaller hysteresis of about 0.17 V and a larger voltage gain of about 44.7 than that of undoped ZTO-based CMOS inverter (voltage gain $\sim $ 37.5 and hysteresis $\sim $ 0.31 V). The enhanced stability of SiZTO TFT and CMOS inverter is attributed to the suppression of oxygen vacancy by Si doping. This work provides an efficient strategy to improve the electrical and stability of ZTO/CNTs CMOS inverter and opens a new opportunity for use in wearable electronics and logic circuits.
In this study, a unique 0-D/2-D Ti3C2 structure was assembled by salt-etching Ti3C2 nanodots out of their parent 2-D Ti3C2 nanosheets. The strong quantum confinement in finite-sized nanodots and concomitant nanodents endowed this structure with a gradient bandgap. UV–Vis diffuse reflectance spectrum revealed the bandgap energies of the coated nanodots and inner nanosheets were 2.82 and 2.40 eV, respectively. Accordingly, the 0-D/2-D Ti3C2 was fairly sensitive to sunlight and could efficiently degrade MB, MeB and RhB dyes in contaminated water under solar illumination. Photocatalytic experiments evidenced that less dye adsorption would induce higher removal ratio of the dye. Moreover, cyclic removal experiments showed the photodegradation efficiency of 0-D/2-D Ti3C2 could still exceed 60% after the fifth cycle for MB, MeB and RhB dyes.
This paper aims to study the effect of the secondary lateral stopper on the compressed stability of the couplers in order to improve the running safety of the heavy-haul locomotives. The influence mechanism of the secondary lateral stopper on the compressed stability of the couplers is theoretically analyzed. To verify the effect of the secondary lateral stopper, both the simulation and the field braking tests are conducted. The multi-body dynamic model consists of two eight-axle locomotives, one dummy of freight vehicle and four detailed connected couplers. The field braking tests are conducted on the tangent line using three eight-axle locomotives. The results indicate that decreasing the free clearance and increasing the stiffness of the secondary lateral stopper both have a positive effect. However, when the free clearance decreases from 20 mm to 10 mm, there is no remarkable decrease in the yaw angles of the coupler and the car body, and the maximum lateral force of the wheelset is still out of the standard in the simulation. When the stiffness of the secondary lateral stopper increases by five times, the yaw angles of the coupler and the car body are reduced significantly and the running safety of the locomotives is also enhanced.
Although terahertz metasurface-enabled biosensors focus on current research, reports of multidimensional ultra-sensitive detection in the terahertz (THz) regime are rare. Here, we present a novel flexible THz biosensor that consists of electromagnetic-induced transparency-like metasurfaces and patterned graphene, which is used for the multidimensional ultra-sensitive detection of plant protein. Based on changes in frequencies and amplitude, the proposed biosensor could detect plant protein molecules with a 42.3 pg/ml limit. The internal mechanism can be explained by the positive impact of plant proteins on the dielectric environment. As plant protein concentration increases and covalent bonding of the patterned graphene strengthens, the Fermi level of graphene moves to the Dirac point, and the conductivity of graphene correspondingly decreases. As a result, we observed marked enhancement of the transmission amplitude and all frequency point shifts. We also show results for fitting the coupled harmonic oscillator model and theoretical analysis of the changes of graphene Fermi level to explain the sensing mechanism. In addition, we successfully achieved biological-assisted optical modulation amplification under laser excitation. This work may provide a new strategy for applying terahertz metasurfaces in the field of biosensing.
This paper aims to investigate the vibration characteristics and frequency domain of heavy haul locomotives at operation speed of 70 km/h based on the field test. A 10000t freight trains that included double HX-type heavy haul locomotives and 105 C80-type freight wagons, was used to conduct an on-track field tests. Test results indicate that suspension systems of locomotives can effectively attenuate high-frequency vibration induced by wheel-rail interface excited by the track irregularity. Axle box vibration energy distributes in a wide frequency range which includes both low-frequency and high-frequency vibrations, while the vibrations of bogie frame and car body mainly concentrated on low-frequency ranges. Forced vibrations induced by sleepers (32.1 Hz) can be transmitted from axle box to bogie frame and car body, and contribute to significant vibration energy, especially for bogie frame. Besides, although vibration energy induced by wheel perimeter (5.0 Hz) is a small proportion of both axle box and bogie frame vibration, it has a significant effect on car body vibration. According to UIC-518, test locomotives have an excellent hunting stability at operation speed of 70 km/h .
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