Dual-band terahertz all-silicon metasurface with giant chirality for frequency-undifferentiated near-field imaging.

Chiral metasurfaces are widely used in imaging and biosensing due to their powerful light field control capabilities. Most of the work is devoted to achieving the goals of chirality enhancement and tunability, but lacks consideration of design complexity, loss, cost, and multi-band operation. In order to alleviate this situation, we propose a pair of dual-frequency giant chiral structures based on all-silicon, which can achieve excellent and opposite spin-selective transmission around 1.09 THz and 1.65 THz. The giant chirality derives from the in-plane electric and magnetic dipole moments excited in different degrees. Theoretically, the maximum circular dichroism at the two frequencies are both as high as 0.34, and the coverage bandwidths of the two giant chirality are 85.5 GHz and 41.4 GHz, respectively. The experimental results are in good agreement with the simulation results. Based on the dual-band giant chiral patterns, the terahertz near-field imaging of different Chinese character images is demonstrated at two frequencies. The frequency-undifferentiated characteristics, good intensity contrast and three-dimensional imaging information are shown by the results. This work provides new ideas for the design of terahertz devices with simple structure and multi-functions, which are expected to be applied in the field of terahertz imaging or multi-channel communication.

Transition-Metal-Ion (Fe, Co, Cr, Mn, Etc.) Doping of TiO2 Nanotubes: A General Approach.

Transition-metal (TM)-ion-doped TiO2 materials are of great importance for photocatalysis- and photoelectrochemical (PEC)-related applications. We introduced a facile, low-cost, and scalable doping method of TM ions (Cr, Co, Cu, Fe, Mn, etc.) into TiO2 nanotubes (NTs), while maintaining their high-ordered tubular structures (with ∼120 nm outside diameter). Both crystallization and doping processes were simultaneously accomplished in aqueous solution at a temperature as low as ∼90 °C, and the fastest doping process could be accomplished in 30 min for Fe doping. Besides, the surface areas of the doped TiO2 NTs were increased to 129.0 m2/g, and their absorption ranges could be expanded from 380 to >500 nm. This study shed light on a facile method for doping TM ions that is extendable to other semiconductors in the field of PEC water splitting and could improve their efficiencies as well.

Magnetite/Iron Foil as an Effective and Nonfiltration Catalyst for Heterogeneous Fenton-like Reactions under Neutral Conditions.

A magnetite/iron foil (MIF) composite was synthesized as a heterogeneous Fenton-like catalyst. The MIF catalyst effectively degraded Rhodamine B under neutral conditions (degradation efficiency = 86%), avoiding the procedure of pH adjustment. The MIF catalyst could be conveniently recycled without filtration, and the advantages of the stability and reusability of a MIF catalyst made it promising in practical wastewater treatment.

Revisiting Person Re-Identification by Camera Selection.

Person re-identification (Re-ID) is a fundamental task in visual surveillance. Given a query image of the target person, conventional Re-ID focuses on the pairwise similarities between the candidate images and the query. However, conventional Re-ID does not evaluate the consistency of the retrieval results of whether the most similar images ranked in each place contain the same person, which is risky in some applications such as missing out a place where the patient passed will hinder the epidemiological investigation. In this work, we investigate a more challenging task: consistently and successfully retrieving the target person in all camera views. We define the task as continuous person Re-ID and propose a corresponding evaluation metric termed overall Rank-K accuracy. Different from the conventional Re-ID, any incorrect retrieval under an individual camera view that raises an inconsistency will fail the continuous Re-ID. Consequently, the defective cameras, in which the images are hard to be automatically associated with the images from other views, strongly degrade the performance of continuous person Re-ID. Since the camera deployment is crucial for continuous tracking across camera views, we rethink person Re-ID from the perspective of camera deployment and assess the quality of a camera network by performing continuous Re-ID. Moreover, we propose to automatically detect the defective cameras that greatly hamper the continuous Re-ID. Because brute-force search is costly when the camera network becomes complicated, we explicitly model the visual relations as well as the spatial relations among cameras and develop a relational deep Q-network to select the properly deployed cameras and the un-selected cameras are regarded as the defective cameras. Since most existing datasets do not provide topology information about the camera network, they are unsuitable for investigating the importance of spatial relations on camera selection. Thus, we collect a new dataset including 20 cameras with topology information. Compared with randomly removing cameras, the experimental results show that our method can effectively detect the defective cameras so that people could take further operations on these cameras in practice (https://www.isee-ai.cn/∼yixing/MCCPD.html).

Zn2+-Enhanced Lithium Magnesium Molybdate Ultralow Temperature Cofired Ceramics for Terahertz Wavefront Modulation Applications.

High efficiency, high frequency, low error, and low latency of wavefront modulation are challenges that must be addressed simultaneously in 5G/6G communication systems. In order to cope with these challenges, novel Li2Mg2-xZnxMo3O12 (x = 0.00-0.08) ceramics are prepared by a solid-state reaction method. The microwave dielectric properties (εr = 8.7, Q × f = 61,312 GHz, τf = -59.1 ppm/°C) and terahertz transmission properties (εr1 = 8.3, tanδ1 = 0.00908, Tamplitude = 0.673, Δphase = 27.65°) of this ceramic (x = 0.06, 625 °C) are effectively enhanced by Zn2+. The chemical compatibility between this ceramic and the Al electrode is demonstrated. The reflection amplitude of this ceramic combined with the Al electrode at 0.5 THz is revealed, and the error between simulation and experiment is only 0.06. A terahertz reflective device for wavefront modulation is designed and demonstrated by using this ceramic and Al electrode. This device can deflect the wavefront of cross-polarized waves and has a certain isolation effect on co-polarized waves. This work accelerates the development of dielectric ceramics and ultralow temperature cofired ceramics technology in the terahertz field.

Splitting phenomenon of ferromagnetic resonance spectra in NiFe films deposited on periodically rippled sapphire substrates.

The splitting phenomenon of ferromagnetic resonance (FMR) spectra of Ni80Fe20 (NiFe) films deposited on periodically rippled sapphire substrates is studied experimentally and with the help of micromagnetic simulation. The analyses show that the splitting of FMR spectra is related to the periodic ripple topography of films. When the applied magnetic field is perpendicular to the ripple direction, the effective field of periodically rippled films becomes inhomogeneous. The splitting of ferromagnetic resonance spectra originates from localized FMR peaks corresponding to different regions with different effective field intensities in the rippled structure. Furthermore, the relative intensity and position between the split mode and the main FMR mode can be changed by designing ripple topography. This work would help understand the splitting phenomenon of FMR spectra for these NiFe films deposited on the periodically rippled sapphire substrates.

Simulation and Optimization of CNTs Cold Cathode Emission Grid Structure.

Carbon nanotubes (CNTs) show significant advantages in the development of cold cathode X-ray tubes due to their excellent field emission performance; however, there are still some problems, such as short lifetime and the low emission current of large-area CNTs. In this paper, a front-grid carbon nanotube array model was established, and the electric field intensity near the tip of the CNTs' electric field enhancement factor was analytically calculated. A simulation model of a CNT three-dimensional field emission electron gun was established by using computer simulation technology (CST). The effects of grid wire diameter, grid aperture shape, and the distribution of grid projection on the cathode surface on the cathode current, anode current, and electron transmission efficiency were analyzed. The aperture ratio was used to evaluate the grid performance, and the simulation results show that the ideal aperture ratio should be between 65% and 85%. A grid structure combining a coarse grid and a fine grid was designed, which can make the electric field intensity around the grid evenly distributed, and effectively increased the cathode emission current by 24.2% compared with the structure without the fine grid. The effect of grid aperture ratio on the electron transmission efficiency was tested. The simulation results and optimized structure can provide a reference for the grid design of cold cathode emission X-ray tubes.

[Raman spectrum study of 3.3'-diethylthiatri carbocyanine iodide].

3.3'-Diethylthiatricarbocyanine iodide (DTTC) dye is an important infrared Raman probe molecule, and has received great attention in the past decades due to their potential applications in Raman imaging, single cell detection, and tumor marker. In the present work, ordinary Raman, surface enhanced Raman scattering (SERS), and theoretical Raman spectra were given to estimate the Raman spectrum of DTTC suspension. More specifically, the original gold nanospheres (60-nm diameter) and gold nanorods (NRs) were encoded with DTTC and stabilized with a layer of thiol-polyethylene glycol (PEG) as Raman reporter, and SERS data were obtained from the samples. Density functional theory (DFT) calculation was applied to calculate the optimized Raman spectra of DTTC water solvent on a B3LYP/6-31G level. Subsequently, the obtained experimental spectra from the DTTC were carefully compared with the theoretically calculated spectra. From the spectra comparation, good agreements were obtained between the theoretical and experimental results. This work will facilitate the development of ultrasensitive SERS probes for advanced biomedical applications.

Electrochemical studies of prothioconazole as a novel corrosion inhibitor for copper in acidic solutions.

Prothioconazole is a fungicide that has a wide number of applications in agriculture, and it can ensure the safety of crops, users, and the environment. Prothioconazole, as a suppressor of copper dissolution in 0.5 M H2SO4 solution, has been evaluated using electrochemical experiments, weight loss tests, quantum chemical calculations, and scanning electron microscopy (SEM). The electrochemical test results showed that prothioconazole was an excellent inhibitor, and the anticorrosion ability increased with the inhibitor concentration. The interaction of prothioconazole with copper is a spontaneous adsorption process accompanied by typical chemisorption. The number of water molecules (X) displaced by one prothioconazole molecule was obtained using diverse substitutional adsorption models based on electrochemical impedance spectroscopy (EIS) data. In addition, the Fukui functions indicate that the triazole and benzene rings and the -C[double bond, length as m-dash]S atoms were the main active sites for the adsorption process.

Electrochemical Investigation of Tetrazolium Violet as a Novel Copper Corrosion Inhibitor in an Acid Environment.

Tetrazolium violet (TZV) is an important pharmaceutical intermediate for the preparation of various medicines, taking into account microbiological studies and TZV as a new inhibitor of heterocyclic compound. The corrosion inhibiting action of TZV for copper in 0.5 M H2SO4 solutions was assessed by potentiodynamic polarization and electrochemical impedance spectroscopy. The corroded copper surfaces were evaluated by scanning electron microscopy. Thereafter, the thermodynamics of TZV adsorption onto copper was computed and evaluated. As a result, the target TZV compound shows great corrosion inhibition performance to protect copper in sulfuric acid. Thermodynamic test results reveal that the Langmuir, Dhar-Flory-Huggins, and Bockris-Swinkels isotherm models provide a better description for the adsorption process of TZV on the metal surface. The calculated values of ΔG ads 0 indicate a spontaneous adsorption process of TZV on the copper surface accompanied by two kinds of interactions, physical adsorption and chemisorption.

Transmission line model and fields analysis of metamaterial absorber in the terahertz band.

Metamaterial (MM) absorber is a novel device to provide near-unity absorption to electromagnetic wave, which is especially important in the terahertz (THz) band. However, the principal physics of MM absorber is still far from being understood. In this work, a transmission line (TL) model for MM absorber was proposed, and with this model the S-parameters, energy consumption, and the power loss density of the absorber were calculated. By this TL model, the asymmetric phenomenon of THz absorption in MM absorber is unambiguously demonstrated, and it clarifies that strong absorption of this absorber under studied is mainly related to the LC resonance of the split-ring-resonator structure. The distribution of power loss density in the absorber indicates that the electromagnetic wave is firstly concentrated into some specific locations of the absorber and then be strongly consumed. This feature as electromagnetic wave trapper renders MM absorber a potential energy converter. Based on TL model, some design strategies to widen the absorption band were also proposed for the purposes to extend its application areas.

Spectroscopic investigations of a novel tricyanofuran dye for nonlinear optics.

A novel tricyanofuran dye was synthesized and the dye-in-polymer films were fabricated by spin-coating process. The spectroscopic properties of the dye in the solutions and polymer films were investigated by the absorption spectra and fluorescence emission spectra. It is found that the absorption and fluorescence maxima are largely red-shifted along with the increase of the solvent polarity. And the low values of fluorescence quantum yield in higher polarity solvents suggest the presence of twisted intramolecular charge transfer states of the dye. Moreover, the second order polarizability value of the novel dye was estimated based on the quantum-mechanical two-level model.

A Facile Method for Loading CeO2 Nanoparticles on Anodic TiO2 Nanotube Arrays.

In this paper, a facile method was proposed to load CeO2 nanoparticles (NPs) on anodic TiO2 nanotube (NT) arrays, which leads to a formation of CeO2/TiO2 heterojunctions. Highly ordered anatase phase TiO2 NT arrays were fabricated by using anodic oxidation method, then these individual TiO2 NTs were used as tiny "nano-containers" to load a small amount of Ce(NO3)3 solutions. The loaded anodic TiO2 NTs were baked and heated to a high temperature of 450 °C, under which the Ce(NO3)3 would be thermally decomposed inside those nano-containers. After the thermal decomposition of Ce(NO3)3, cubic crystal CeO2 NPs were obtained and successfully loaded into the anodic TiO2 NT arrays. The prepared CeO2/TiO2 heterojunction structures were characterized by a variety of analytical technologies, including XRD, SEM, and Raman spectra. This study provides a facile approach to prepare CeO2/TiO2 films, which could be very useful for environmental and energy-related areas.

Preparation of ZnO@TiO2 nanotubes heterostructured film by thermal decomposition and their photocatalytic performances.

TiO2 nanotubes (NTs) arrays prepared by anodic oxidation were modified with ZnO particles and their morphology and photocatalytic properties were investigated. A simple thermal decomposition process was involved in the modification method. Zinc acetate solution was filled into the TiO2 NTs arrays, and ZnO@TiO2 heterojunction films were formed after the thermal treatment. The morphology and catalytic properties of the heterojunction films could be manipulated by the concentration of zinc acetate solution. Compared to TiO2 NTs arrays, the ZnO@TiO2 heterojunction films with an optimized concentration of zinc acetate showed enhanced catalytic performances. Their photocatalytic activities were discussed with respect to the formation of ZnO@TiO2 heterojunctions and enforced charge separation. This study demonstrates a simple method to prepare ZnO nanoparticles@TiO2 NT heterojunction films, which is promising for other environmental and energy related applications.

Low Temperature-Derived 3D Hexagonal Crystalline Fe3O4 Nanoplates for Water Purification.

Fe3O4 nanoplates were fabricated by an anodic oxidation process and a subsequent water assisted crystallization process at low temperature, which was found to be very efficient and environmentally friendly. The as-prepared Fe3O4 nanoplates have hexagonal outlines with a thickness of about 20 nm. Tremendous grooves were distributed on the entire surfaces of the nanoplates, making the two-dimension nanoplates have a unique 3D morphology. Transmission electron microscopy results confirmed that the single-crystalline nature of the nanoplates was well maintained. Owing to the unique structures and porous morphologies, the as-prepared 3D nanoplates show excellent ability for absorbing solar energy and absorbing organic pollutants, which can be utilized for cleaning up water. Moreover, the Fe3O4 nanoplates show good magnetic properties that enable them to be easily collected and recycled. We believe this study will inspire the application of Fe3O4 nanoplates with 3D structures in energy and environmental areas.

Rod-shaped polyaniline-barium ferrite nanocomposite: preparation, characterization and properties.

Rod-shaped polyaniline (PANI)-barium ferrite nanocomposite was synthesized by in situ polymerization of aniline in the presence of BaFe(12)O(19) nanoparticles with diameters of 60-80 nm. The structure, morphology and properties of the nanocomposite were measured using powder x-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy and vibrating sample magnetometry. Different ferrite/PANI ratios were selected in order to study magnetic and conductive properties. The results indicated that there were some interactions between PANI chains and ferrite particles. The saturation magnetization and the coercivity varied with the ferrite content. The conductivity at room temperature decreased from 43.35 to 6.9 × 10(-2) S cm(-1) when the ferrite content changed from 0 to 50 wt%. The composite has excellent electromagnetic parameters which indicates potential application in high performance adsorbing materials in broadband and high frequency ranges. The polymerization mechanism and interactions in the nanocomposites were also studied.