The functionalized graphene (GNS
PF6) was fabricated by simple and fast method of electrolysis with potassium hexafluorophosphate solution as electrolyte under the static potential of 15
V. The ...characterization results of transmission electron microscopy, atom force microscopy, X-ray photoelectron spectroscopy, X-ray powder diffraction, Raman spectroscopy and thermogravimetric analysis indicate that graphite rod was completely exfoliated to graphene layer containing 30
wt.% PF
6ˉ with the average thickness ca. 1.0
nm. Our sample of GNS
PF6 was developed for the removal of Pb(II) or Cd(II) ions from water, and the determined adsorption capacities are 406.6
mg/g (pH
=
5.1) for Pb(II) and 73.42
mg/g (pH
=
6.2) for Cd(II), which is much higher than that by our previous sample of GNS
C8P and carbon nanotube. The adsorption processes reach equilibrium in just 40
min and the adsorption isotherms are described well by Langmuir and Freundlich classical isotherms models.
Ni–Ce/SiO2 catalysts were prepared by calcination under Ar, CO2, O2 and H2 ambience, and applied in CO2 reforming of methane for synthesis gas production. BET, XRD, XPS, TPR, SEM, TEM and TPH ...techniques were employed to characterize the fresh and used catalysts. Highly dispersed nickel oxides bearing stronger interaction with SiO2 prevented the metal sintering. The formation of reactive carbon species on Ni–Ce/SiO2 catalyst calcined under Ar ambience effectively promoted the carbon elimination and kept the catalyst more stable. Nevertheless, the oxygen storage capacity of CeO2 might partly lose on Ni–Ce/SiO2 calcined under H2 ambience. As a result, the inhibition of carbon elimination and the deposition of inert carbon were responsible for its partial deactivation.
Ni–Ce/SiO2 catalyst calcined under Ar ambience exhibited higher metal dispersion and stronger metal–support interaction. Moreover, the formation of reactive carbonaceous species effectively improved the carbon elimination, keeping the catalyst more stable. Display omitted
► Ni–Ce/SiO2 catalyst calcined under Ar ambience exhibited good stability. ► Highly dispersed NiO bearing strong interaction with SiO2 inhibited the sintering. ► The formation of reactive carbonaceous species facilitated the carbon elimination. ► The loss of oxygen storage capacity of CeO2 led to the deactivation of Ni–Ce–H2.
A novel recessed gate graded AlGaN high-electron-mobility transistor (RGGA HEMT) for high-sensitivity terahertz (THz) detectors is reported, which exhibits significant potential for high-sensitivity ...THz detectors, and consequently. The simulation results indicate the exceptional field-effect factor of the proposed RGGA HEMT, which is largely attributed to the three-dimensional electron gas generated by the graded AlGaN barrier layer and the subsequent enhancement of channel conductance. The responsivity and noise equivalent power reach 58mA/W and 43pW/Hz respectively at 227GHz by utilizing a technical computer-aided design platform. As compared to conventional structure GaN HEMT experimental data, the current responsivity is improved by 2.64 times, and the NEP is reduced by 43.4%. The unprecedented improvement in detection performance renders the RGGA HEMT a highly promising approach for future THz real-time single-pixel imaging applications at room temperature.
•The study innovatively introduces a recessed gate and three-dimensional electron gas into this type of detector for the first time.•This structure not only significantly improves the field-effect factor of the detectors but also reduces the channel resistance.•The method demonstrates a degree of universality, making it potentially extendable to transistor detectors composed of other material types.•It would be a promising approach to achieve terahertz imaging at room temperature and broad-spectrum detection of chemicals, owing to its outstanding responsivity and noise equivalent power (NEP).
Terahertz (THz) radar imaging has gained great interests in various applications due to its capability of deep penetration in some specific contents such as plastic and non-conductive materials ...without water. However, the image quality would be highly degraded by the scattering of the rough surfaces, which remains a challenge in the area. Here, we propose a confocal terahertz synthetic aperture radar (SAR) to alleviate the scattering issues with both improved signal-to-noise ratio (SNR) and resolution. Inspired by the confocal non-line-of-sight imaging in visible wavelength, a convex lens is added into the conventional SAR system to localize the effect of scattering within each spatial sampling point by the confocal configuration. Then, the random phase aberration caused by scattering could be corrected through a simple shift in temporal domain. The performance of the proposed method under different roughness occlusions is evaluated through experiments. All the results demonstrate great enhancements in both resolution and SNR over the conventional methods.
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•The high-sensitivity terahertz spectrometer for detecting trace gas and quantitation.•Superior spectral specificity was demonstrated by comparing with the JPL database.•Limit of ...detection of terahertz heterodyne spectrometer for CH3CN is obtained.•Quantitation method based on collision broadening for trace gas is proposed.
Quantitative analysis of trace gases is an important research field in analytical chemistry. The terahertz electronic spectrometer is one of the most powerful tools for detecting trace gas. Here, a terahertz spectrometer based on frequency multiplier chain and heterodyne detection was presented. The rotational spectra of acetonitrile (CH3CN) gas were measured in the 290–370 GHz frequency band with 100 kHz spectral resolution. The spectrometer demonstrated excellent spectral specificity and the extrapolated limit of detection for CH3CN gas of 1.4 ppm. Furthermore, a novel quantification method of trace gas was proposed based on broadening mechanisms. The CH3CN self- and nitrogen (N2)- collisional broadening coefficients were obtained experimentally for verifying the method. The CH3CN concentration of the validation group was calculated, and the relative error was 0.1%. The error analysis of the different number of measurements of the method was carried out. The method could provide a new perspective for trace gas quantitative analysis.
A method-of-moments (MoMs) approach is proposed for the modal analysis of two-dimensional (2-D) all-metal leaky-wave structures periodic along one direction. The electric-field integral equations ...(EFIEs) for both TM and TE polarizations are formulated in the unit cell (UC) by employing a rapidly convergent Ewald representation for the relevant 2-D periodic Green's function. The integral equations are discretized using triangular subsectional basis functions and a Galerkin testing scheme. Effective modal dispersive analyses are developed for a variety of leaky-wave structures. Real proper (bound) modes, as well as complex proper (backward leaky) and improper (forward leaky) modes, are investigated. The proposed method allows for the accurate design and tuning of asymmetric UCs required to suppress the open stopband (OSB), which cannot be easily carried out by means of full-wave simulations with commercial software. Validations are provided through alternative methods and in all cases the presented formulation shows high accuracy and versatility.
As an essential passive component in modern wireless communication systems, the design of high-frequency filters has become increasingly crucial. To achieve the target behavior specifications, ...traditional design methods are constrained by designers’ expertise or reliant on repetitive frequency sweeps using commercial software. Such processes suffer from low efficiency, limited applicability, and high computational costs. Artificial neural network-based modeling has become an important tool for designing devices. To realize accurate and fast electromagnetic modeling and design of passive components, this work proposes an inverse model integrating transfer functions and one-dimensional multi-channel convolutional neural networks (TF-1DMC-CNN). This model introduces transfer functions to ensure precise representation of electromagnetic responses while addressing the challenge of input dimensionality in wideband modeling. Input dimensions are reduced from 161 to 20 and 221 to 20 for two examples. The 1DMC-CNN processes distinct TF coefficients in each channel and extracts features in parallel. The geometrical parameters can be directly predicted in a single feedforward pass through the trained inverse model without needing iterative optimization. Compared to other inverse neural networks, the proposed model achieves the smallest testing errors. It obtains better model accuracy with fewer training samples, reducing data generation time. Compared to the traditional EM optimization method, this approach reduces CPU time for optimizations, enabling predictions of geometric structures that meet different design indexes. For multi-objective optimization, the proposed model predicts the structure within 0.16 seconds.
Controllable conversion between propagating light waves and surface waves (SWs) has recently attracted significant research interests. This paper demonstrates, via numerical simulation, for the first ...time all-dielectric SW converters that possess a tunable and directional SW conversion efficiency. The SW converters contain multiple metagratings of Si pillars embedded in a deformable substrate. In the analysis, an infinitely large, bi-periodic metagrating under the illumination of linearly polarized light is considered first. The SW conversion efficiency of this metagrating can be modulated between 4.3% and 51.0% for incident light frequency at 0.8 THz by stretching the deformable substrate along the direction of SW propagation. Subsequently, two SW converters under circularly polarized light illumination are analyzed, where a similar level of efficiency modulation is retained in finite-sized metagratings. In these converters, only the metagrating channels along the stretch direction have a strong SW conversion efficiency, which can reach 40.4% after normalization against the effective grating area. The directivity, a parameter defined here to reveal the energy contrast among the output channels, reaches 38.6 in one of the converters. Due to its high tunability, high directivity and compact size, the SW converters may be used as tunable optical sensors and light couplers in the THz regime.
All-dielectric, phase-gradient metasurfaces manipulate light via a judiciously designed planar distribution of high and low refractive indices. In the established design approaches, the high-index ...elements play a dominant role, while the electromagnetic field existing between these elements is routinely viewed as either an incidental by-product or detrimental crosstalk. Here we propose an alternative approach that concentrates on exploring the low-index materials for wavefront shaping. In our Si metasurface, the low-index air gap between adjacent Si fins is judiciously tuned, while the high-index Si fins only have a single size across the whole metasurface. These gap modes provide the full 2π phase coverage, as well as high and relatively uniform transmission, at the deep-subwavelength scale. These characteristics are ideal for mapping a steep phase gradient, consequently suitable for high-efficiency and large-angle wavefront bending. This light manipulation capability is exemplified with numerical simulation in PW-SW (freely propagating wave to surface wave) conversion, where the wavefront is deflected by an angle of 90°. In the gap-mode meta-converters, the average unit size can be only 1/60 of free-space wavelength, an order of magnitude smaller than that of conventional all-dielectric metasurfaces. Their conversion efficiency can reach 68%, the highest value reported for any all-dielectric gradient metasurface THz converter.
Dielectric materials, commonly used in conventional terahertz devices, are applied in all-dielectric metasurfaces for many functional applications in recent years. Various measurement systems, ...including time-domain spectrometer (TDS), vector network analyzer (VNA) and Fourier transform infrared (FTIR) spectrometer, have been used to analyze the dielectric properties of common materials in terahertz region. However, only the influence of thickness or Fabry-Perot (FP) term on transmittance under a specified incident angle was considered. In this paper, the influences of refractive index, absorption coefficient and thickness on the extrema and fluctuation period of transmittance spectra are systematically analyzed for the first time. Moreover, the transmittance spectra of four plates, which are two different thicknesses of each TPX and HDPE material, were measured by 3 THz systems. These three systems are frequency multiplication chain (FMC), VNA and TDS which are corresponding to direct and coherent detection methods by electronic, and optical coherent detection method. For each plate, the transmittance spectra measured by three systems have been compared, which can obtain the average error of each system. These measurement results are in good agreement with the theoretical calculation values. The electronic coherent detection technique shows half of the test error compared with the other two techniques. The criteria for dielectrics selection proposed in this paper can provide some guidance for the selection of suitable material and thickness of high transmittance windows and the substrate of dielectric metasurfaces.
•The selection criteria guide dielectrics selection under three different applications in terahertz region.•The electronic coherent detection technique possesses smaller test errors.•The influences of refractive index, absorption coefficient and thickness on the transmittance spectra are analyzed.
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