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Two terahertz metamaterials were joined by a conductivity variable VO

Wet chemical methods have demonstrated their unparalleled success to control the size and size distribution of colloidal nanoparticles. In a wet chemical nanoparticle synthesis, precursor reaction, nucleation and growth will occur, not subsequently but often concurrently. The three processes can thus strongly affect each other during the nucleation. Here mathematical models were used to simulate the rate of the concurrently occurring precursor reaction, nucleation and growth. For both the ‘hot-injection’ and ‘heat-up’ methods, the simulation has clearly revealed how the batch nanoparticle products be determined by the interplay of the three processes. The simulation shows that the competition between nucleation and growth determine the size, size distribution, and concentration of batch colloidal nanoparticles, where the dominance between the two can be varied by synthetic conditions. By comprehensively considering the interplay, the nanoparticle synthesis in solution can be much better understood, which benefits the fine design of the synthesis to make desired batch nanoparticles.

The rapid development of power semiconductor devices is helping to realize a low-carbon society and provide a better life for everyone. Power semiconductors not only are used in many large-scale industrial control fields such as power transmission and control in power grids, rail transit traction systems, and defense weapons and equipment, but also play a vital role in daily equipment such as home appliances, medical electronics, and electronic communications; all devices such as power steering in cars, battery chargers, cell phones, and microwave ovens utilize power electronics. This research mainly focuses on the high-voltage LDMOS device model and its implementation. Based on the in-depth study of the structure and physical mechanism of high-voltage LDMOS devices, with the help of BSIM4 core model, which is now very mature and widely used in industry, the drift region of high-voltage LDMOS is mainly modeled, and the drift region of LDMOS is modeled as a variable resistance controlled by voltage. Finally, Verilog-A language and neural network method are used to establish a compact model of LDMOS. The improved model is applied to LDMOS and can better fit the output characteristics with self-heating effect.

In recent years, solar desalination and water evaporation/purification with various artificial architectures have drawn significant attention. Herein, we introduce a rational design structure for efficient solar water evaporation and purification, focusing on the balance between water transportation and thermal insulation. Natural wood after a simple flame treatment on the surface was utilized as the solar absorber, with a high solar absorbance (∼90 %), good hydrophilicity, and excellent heat localization abilities. Besides, a thermal insulator (polystyrene foam) was used to further reduce the thermal loss, and the optimized ratio between the water path and thermal insulator was obtained. A set of floating foam-flamed-wood (F-F-wood) devices were fabricated with a high evaporation rate of 3.92 kg m−2 h−1, exhibiting photothermal purification abilities from seawater and wastewater containing organic dyes and heavy metals. This study sheds light on the rational design of scalable and low-cost devices for solar water evaporation and purification.

The study of surface magnetic anisotropy of magnetic films is beneficial to understanding the behaviors of films at high frequencies and further promoting their high-frequency magnetic applications. We investigated the out-of-plane ferromagnetic resonance (FMR) and surface spin wave modes in 40-nm Ni80Fe20 (NiFe) films deposited on ripple-patterned sapphire substrate with periodicity and a flat sapphire substrate by broad-band FMR technique. When measuring the FMR of the film on ripple-patterned substrate, the in-plane angle (𝜑 H of the external applied magnetic field was along the direction of the ripples (𝜑 H = 90°) and perpendicular to the ripple direction (𝜑 H = 0°) respectively. The spin-wave resonance spectra consisting of up to two surface spin wave (SSW) modes were observed as the external magnetic field polar angle θH varied from “in-plane configuration” (θH = 90° ) to “out-of-plane configuration” (θH = 0°). As the decrease of θH , the two surface spin excitations disappeared in sequence and further only FMR mode was observed in the region θH which was smaller than the “critical angle” θc . The θc of 𝜑 H = 90° is found to be different from that for 𝜑 H = 0°. The dependences of field shift vs. out-of-plane angles θH for each SSW mode were analyzed by the surface inhomogeneity model. From the model, the surface anisotropy constants Ks of films were obtained. The results show that the values of surface anisotropy constants for the two SSW modes are different. Compared with the film sputtered on flat sapphire substrate, after introducing ripple-patterned substrate, the variation of Ks is only on the order of 0.01 erg/cm2 for the film of this thickness.

MXene-based materials are considered to be promising candidates for electrodes in energy storage field owing to their features of two-dimensional layered structure, good conductivity, and chemical stability. Carbon-coated Fe3O4 nanoparticles (C@Fe3O4 NPs)-decorated Ti3C2 MXene composites were synthesized via a facile method for the first time. The prepared C@Fe3O4 NPs/Ti3C2 MXene composite was characterized by various techniques (XRD, SEM, TEM, TGA, and XPS), and the results showed that C@Fe3O4 NPs (diameter: 60 nm, layer thickness: 10 nm) were homogeneously distributed on the surfaces of Ti3C2 MXene interlayers while the accordion-like structure maintained. It is noted that the specific surface areas dramatically increased from 7.8 m2/g to 37.0 m2/g after introducing the nanoparticles. The C@Fe3O4 NPs/Ti3C2 MXene products exhibited a specific capacity of 231.5 mAh g−1 after 200 cycles under 100 mA/g when serving as anode materials for Li-ion batteries, which was markedly higher than that of pure Ti3C2 MXene (107.8 mAh g−1). This study presents and investigates a novel kind of MXene-based composite, which has the potential as electrode materials for energy storage.

Graphene/silicon hybrid diodes have been proven efficient for broad-band terahertz (THz) modulation with electrical and optical stimuli. However, the optimal protocol to apply optical and electrical stimuli has not been well-determined to obtain the best performance. Here, band theory of the hybrid diode has been used to analyze the underlying modulation mechanism and to help determine the optimal modulation protocol. Monolayer gold nanoparticles (AuNPs) were coated on the graphene/silicon hybrid diode to enhance the modulation performance. Both high modulation depth (∼93%) and modulation rate (∼4.6 kHz) were obtained with the AuNP-coated hybrid diode using the proper modulation method. To explore the underlying mechanism for a graphene/silicon hybrid diode THz modulator, this work could throw light on other material systems for THz modulation.

In this study, intrinsic dielectric properties of monoclinic A0.5Zr0.5NbO4 ceramics (A = Mn, Zn, Mg, Co, Ni) with wolframite structure were investigated by chemical bond theory, infrared and terahertz spectroscopy. According to bond theory, Zr–O bonds and A-O bonds with larger bond susceptibility values provide majority contributions to relative permittivity; while Nb–O bonds dominate the structural stability and oxygen polyhedron distortion. Intrinsic dielectric properties calculated via far-infrared reflectivity spectroscopy are close to experimental properties, which indicates that most of dielectric contributions come from absorptions of structural phonon oscillation and infrared modes of dielectric response in A0.5Zr0.5NbO4 ceramics vary with A-site ions. Furthermore, intrinsic properties estimated by terahertz time domain spectra also testify the effectiveness of theoretical dielectric properties.

Traditional charge-based device development is approaching the limit of Moores law, thus, there is a desperate need for new information processing principles or architectures. Replacing traditional charge-based devices with non-charge-based devices for information processing shows promise. Spin waves, which are generated from the collective precession of electron spins, are thought to be an important information carrier for the transmission and processing of information in a beyond-Moore era. Spin-wave logic gates possess incomparable advantages over traditional logic devices in energy consumption, device scale, application frequency, and logical operation, among other factors. This article explains the operating principles of spin-wave logic gates based on a Mach-Zehnder interferometer structure, and then analyzes the realization theory of key spin-wave logic gate elements at a device level. Recent advances in these key elements are also reviewed systematically. Lastly, future prospects of spin-wave logic gates are discussed.

Metamaterials have shown great potential for modulation on the amplitude, phase and polarization of the terahertz wave. Here vacancies were introduced into the metamaterial arrays to tune the mutual interaction between the constituent resonators, which could heavily affect the electromagnetic response of the whole metamaterial arrays. We show that the introduced vacancies in the metamaterial arrays can effectively affect the resonance mode of the metamaterial arrays. Based upon the vacancy mediated coupling, a silicon-metal hybrid metamaterial arrays were designed to achieve active modulation of propagating terahertz waves.

With the advent of the post-Moore era, researches on beyond-Complementary Metal Oxide Semiconductor (CMOS) approaches have been attracted more and more attention. Magnonics, or spin wave is one of the most promising technology beyond CMOS, which magnons-quanta for spin waves-process the information analogous to electronic charges in electronics. Information transmission by spin waves, which uses the frequency, amplitude and (or) phase to encode information, has a great many of advantages such as extremely low energy loss and wide-band frequency. Moreover, using the nonlinear characteristics of spin waves for information transmission can increase the extra degree of freedom of information. This review provides a tutorial overview over the effects of spin wave propagation and recent research progress in uniform spin wave waveguide. The propagation characteristics of spin waves in uniform waveguides and some special propagation phenomena such as spin wave beam splitting and self-focusing are described by combining experimental phenomena and theoretical formulas. Furthermore, we summarize methods for modulating propagation of spin wave in uniform waveguide, and comment on the advantages and limitations of these methods. The review may promote the development of information transmission technology based on spin waves.

We present a tool for batch generation of input scripts and multi-type Fourier analysis from simulation results for the micromagnetic software MuMax3. The introduction of graphical user interface and parameter-sweeping functionality strongly speed up the input scripts creation and accelerate model optimization processes consequently. Three types of important Fourier analysis methods are provided for the acquisition of the quantitative frequency compositions, the spin-wave dispersion curve and the spatial distribution of spin-wave powers at different frequencies, respectively. Since the Fourier analysis is accelerated by parallel computations, the time cost is reduced to an acceptable level even in the presentation of tens of gigabytes data. With the MuMax3 and our proposal, a complete micromagnetic simulating tool chain from scripts generation to post analysis has been developed. Program summary Program title: MuFA (Multi-type Fourier Analyzer) Program Files doi: http://dx.doi.org/10.17632/x6j2f3fvsx.1 Licensing provisions: GNU GPL v3 Programming language: Python3 External routines: Numpy and Matplotlib modules for Python3 Nature of problem: Magnetization dynamic problems in ferromagnetic elements can be investigated with micromagnetic simulations using MuMax3. However, on one hand, practical modeling processes require a great number of tests with different parameters such as geometry size, which is a heavily time-consuming and error-prone work. On the other hand, a whole set of post Fourier analysis tool for the simulation output data is still missing. Moreover, due to tens of gigabytes data can be generated after a single simulation, the analysis time cost can be greater than the simulation time itself up to several times. Solution method: The first part of MuFA is a graphical user interface (GUI) tool for the batch generation of input scripts for MuMax3. Numerous input scripts with different geometry size and excitation parameters from each other can be generated at once. The second part of MuFA provides three kinds of important Fourier analysis approaches: frequency components analysis, spatial distribution analysis of spin-wave (SW) powers at different frequencies and the drawing of SW dispersion curve. The file-reading part, which is the most time-consuming part, is accelerated by multiprocessing technique. Therefore, the total time cost is greatly reduced.

Nanostructure modified semiconductors show enormous potential for the optical terahertz (THz) spatial modulation due to their enhanced modulation depth along with their inherent broad bandwidth, small insertion loss, and fast modulation speed. As a result, it is necessary to explore the mechanism of the performance enhancement by the interface modification. Here, the self-assembled monolayer of gold nanorods and nanoparticles was coated on silicon to enhance the optical modulation depth of THz wave. Comparison experiment and the finite-difference time-domain simulation have been performed between the self-assembled monolayer of gold nanorods and nanoparticles to understand the mechanism for improving the light modulation of THz wave. We found that the modulation depth and the speed of THz wave were mainly determined by the light resonance frequency of gold nanoparticles/nanorods and the area with enhanced light intensity on silicon surface. Our results provide a guide for the light-controlled THz modulator based on the nanostructure modified semiconductor.

In this paper, we demonstrate a trilayer hybrid terahertz (THz) modulator made by combining a p-type silicon (p-Si) substrate, TiO2 interlayer, and single-layer graphene. The interface between Si and TiO2 introduced a built-in electric field, which drove the photoelectrons from Si to TiO2, and then the electrons injected into the graphene layer, causing the Fermi level of graphene to shift into a higher conduction band. The conductivity of graphene would increase, resulting in the decrease of transmitted terahertz wave. And the terahertz transmission modulation was realized. We observed a broadband modulation of the terahertz transmission in the frequency range from 0.3 to 1.7 THz and a large modulation depth of 88% with proper optical excitation. The results show that the graphene/TiO2/p-Si hybrid nanostructures exhibit great potential for terahertz broadband applications, such as terahertz imaging and communication.

Ternary CdSe quantum dots (QDs)/graphene/TiO2 nanosheet composite photocatalysts were synthesized through precipitation by using hydrothermally prepared layered TiO2 nanosheets/graphene sheets as supporting matrix and CdSe QDs solution as precursor. During synthesis, anatase TiO2 nanosheets with exposed (0 0 1) facets were tightly grown on the surface of graphene sheets with face-to-face orientation, and CdSe QDs with an average size of 3.0 nm were uniformly and closely attached to the layered TiO2/graphene sheets through a molecular linker mercaptopropionic acid. The genuine structure and constituents of the prepared ternary CdSe QDs/graphene/TiO2 composites provide their great adsorptive capacity for aromatic dye on graphene, extended visible-light absorption range by CdSe QDs, and efficient charge separation by using TiO2 nanosheets as an electron mediator. Hence, CdSe QDs/graphene/TiO2 composites show high visible light photocatalytic activity and stability for the degradation of methylene blue in aqueous solutions. Moreover, ternary CdSe QDs/graphene/TiO2 composites show high photocatalytic antibacterial activity against Escherichia coli (E. coli) under visible light irradiation by generating active species, such as holes, O2−, and OH. The proposed photocatalytic mechanism and some reactive active species were further confirmed by experiments on transient photocurrent responses, through the addition of the scavenger, and through the detection of OH radicals.

Diffusional growth in solution is the most efficient method to grow monodisperse colloidal nanoparticles. Instead of calculating for a single nanoparticle, here the growth of an ensemble of nanoparticles has been numerically simulated by the generalized growth rate of nanoparticles, which has been deduced in our previous work from the very fundamental laws and equations. By doing that, the dynamic interaction among nanoparticles through monomer attachment and detachment can be clearly revealed. The constant and diminishing monomer concentrations have been simulated separately and compared together. The simulations give the growth dynamics of batch nanoparticles across a broad range of conditions, where diffusivity, adsorption, and concentration of monomers play a significant role. The relations between the average radius and time, the variance and time, and the variance and average radius have been obtained for different growth conditions. The average radius–time curve can be well-fitted to E[R] = E[R0] +...

Magnetite (Fe3O4) has been used for thousands of years as one of the important magnetic materials. The rapid developments of thin film technology in the past few decades attract the attention of material scientists on the fabrication of magnetite thin films. In this article, we present an overview of recent progress on Fe3O4 thin films. The widely used preparation methods are surveyed, and the effect of substrates is discussed. Specifically the modified Fe3O4 thin films exhibit excellent electrical and magnetic properties compared with the pure films. It is noteworthy that modified Fe3O4 thin films can be put into two categories: (1) doped films, where foreign metal ions substitute iron ions at A or B sites; and (2) hybrid films, where magnetite phases are mixed with other materials. Notably, Fe3O4 thin films show great potentials in many applications such as sensors and batteries. It is expected that the investigations of Fe3O4 thin films will give us some breakthroughs in materials science and technology.

(Ba0.6Sr0.4)TiO3 (BST) ceramics modified with both Zr and Mn were synthesized via a traditional solid state reaction route. Pure perovskite structure and dense morphology were obtained for all specimens. An enhanced diffuse phase transition (DPT) behavior induced by Mn substitution was detected. We suggest that such enhanced DPT behavior was beneficial for BST practical applications due to the improved dielectric thermal stability while maintaining good dielectric performance. The impact of Mn concentration on the microstructure, dielectric properties, and DPT diffuseness was investigated.

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.

Tuning the magnetic anisotropy of nanoparticle assemblies is critical for their applications such as on-chip magnetic electronic components and electromagnetic wave absorption. In this work, we developed a facile hierarchical self-assembly method to separately control the magnetic shape and magnetocrystalline anistropy of individual nanoparticle assemblies in arrays. Since magnetic nanoparticle assemblies in the array have the same size, shape and alignment, we are able to study the magnetic properties of individual nanoparticle assembly by measuring the whole arrays. The interplay between the two magnetic anisotropies was systematically studied for disk- and bar-shaped nanoparticle assemblies. Maximum magnetic anisotropy was obtained when the easy axis of magnetic nanoparticles was aligned along the long axes of the bar-shaped nanoparticles assemblies.

In this paper, graphene/Bi:YIG(50 nm)/p-Si hybrid nanostructured graphene field effect transistors (GFETs) were fabricated at the first time. A 50 nm Bi-doped Y 3 Fe 5 O 12 (Bi: YIG) garnet film was deposited using a vacuum RF sputtering technique, forming a nanometer thick high-K gate layer. With reduced Coulomb impurity scattering and cavity effect, a significantly improved modulation depth of 15% and modulation speed of 200 kHz have been successfully achieved with the YIG based GFETs. Moreover, since YIG is a magnetic insulator, we characterized and discussed the possibility of magnetic control of these graphene/Bi:YIG/p-Si hybrid structured THz modulators. A 7% enhancement of THz transmittance with applying an in-plane 22 Oe magnetic field has been revealed in the hybrid nanostructure, which provides a new route to realize electrical/magnetic functional modulators. The results show that graphene/Y 3 Fe 5 O 12 /Si hybrid nanostructures with good THz modulation performances have great potential for THz nondestructive evaluation as well as imaging applications.

We present a model for a skyrmion-based spin-torque nano-oscillator (STNO) that consists of dual free layers with Dzyaloshinskii–Moriya interaction and interlayer exchange coupling. Micromagnetic simulation shows that skyrmions in the dual free layers can precess independently by application of a spin-polarized current at the center of the ferromagnetic nanodisk. Compared to single free-layer devices, the dual free-layer structure is expected to enhance the output power of the STNO and reduce the resonance linewidth. We also propose a skyrmion STNO based on voltage-controlled magnetic anisotropy. The skyrmion precession rate is controlled by modulating the perpendicular magnetic anisotropy of the skyrmion precession track. It is possible to increase the frequency of the generated signal by adjusting the precession rate of the skyrmions.

In this paper, germanium–bismuth (Ge1– x Bi x , $x = 0$ –0.32) is grown by low-temperature molecular beam epitaxy. Because Bi is an element belonging to group V, GeBi films show inherent n-type doping properties compared with GeSn ones. Inherent n-type Ge1– x Bi x films with a doping concentration of $2 \times 10^{15}$ – $2 \times 10^{16}$ /cm3 are epitaxially deposited on p-type Si substrates to form p-n junctions. Current–voltage measurements show that the dark current density of the diodes can approach 0.32 A/cm2. The influence of Bi concentration on the infrared (IR) and terahertz (THz) transmittance of the films is investigated. Near-IR (1–2 $\mu \text{m}$ ) and mid/far-IR (2.6–10 $\mu \text{m}$ ) responsivities of the films are 0.65 and 0.032 A/W, respectively. The THz wave transmittance is tuned by ~6%–8% by tailoring the bias voltage. A modulation depth of ~12% is obtained for a Ge0.78Bi0.22/p-Si diode. The dynamic modulation characteristics of n-Ge1– x Bi x /p-Si diodes are further investigated using a 340-GHz carrier. The experimental maximum THz wave modulation speed is up to 2 MHz. The present results demonstrate that n-GeBi/p-Si diodes are promising for both mid/far-IR photodetectors and broadband high-speed THz wave modulators.

We present a reconfigurable nanoscale spin-wave directional coupler based on spin-orbit torque (SOT). By micromagnetic simulations, it is demonstrated that the functionality and operating frequency of proposed device can be dynamically switched by inverting the whole or part of the relative magnetic configuration of the dipolar-coupled waveguides using SOT. Utilizing the effect of sudden change in coupling length, the functionality of power divider can be realized. The proposed reconfigurable spin-wave directional coupler opens a way for two-dimensional planar magnonic integrated circuits.

Ni80Fe20 (NiFe) films have been deposited on self-organized sapphire substrates with periodical surface ripples formed by 2–10 h thermal annealing at 1400°C. By extracting static and dynamic magnetic parameters from magneto-optical Kerr effect (MOKE) loops and ferromagnetic resonance (FMR) spectra, we quantified and analyzed the substrate annealing effects on the induced in-plane uniaxial magnetic anisotropy and ferromagnetic resonance frequency in these films. The study demonstrates that the uniaxial anisotropy of these NiFe films is strongly related to the annealing-time dependent substrate faceting and coarsening mechanisms. The uniaxial anisotropy field H u changes from ~ 170 Oe to ~ 250 Oe , and the maximum value of it is obtained in film on 8-h annealed substrate. The ferromagnetic resonance response and high frequency characteristics of films can be modulated by self-organized substrate is also confirmed. When external magnetic field is parallel to the direction of ripple, the ferromagnetic resonance frequency of films grown on the self-organized substrates is increased by ~ 0.3 − 1 GHz compared with that of reference film on plane substrate. This work would be helpful to design the high frequency properties of spintronic devices and micro-wave magnetic devices by utilizing self-organized substrates.

Optical Hz wave modulator based on semiconductor is broad used in THz imaging area due to convenient to realize. However, for a long time, the laser wavelength influence to the modulation properties is not clear. Germanium and graphene coated germanium upon different laser wavelength (638, 915 and 1550 nm) laser irradiation were investigated to clear the above influence. As a result, the THz wave modulation depth increase with the laser wavelength due to the surface recombination. And the results were proven by discussing the modulation enhancement of graphene coated germanium. In addition, the short wavelength laser would lead to slow modulation rate. As a result, it is a novel method to improve the THz modulation depth and modulation rate by using long wavelength laser.

All optical THz wave modulation based on semiconductor is a convenient modulation method for real application, which is superior with wideband, large modulation depth and low insertion loss. In some scenario, it is required to use infrared light rather than visible light as the excitation signal where germanium is a better candidate than silicon. Here monolayer gold nanorods and graphene was used to modify the surface of germanium to enhance the THz wave modulation depth by the 1550 nm laser irradiation. Higher modulation depth was achieved by surface modification, which achieve the highest modulation depth of ~90% at 3.5 W/cm2. And the modulation rate is higher than 35 kHz.

This paper reports the use of in-situ thermal treatments to modify the properties of GeSn films and their performance in the infrared and Terahertz wave bands. The GeSn films were grown by molecular beam epitaxy under various conditions. X-ray analysis indicated the presence of amorphous phases and oxides in the GeSn films when they were epitaxially grown under low substrate temperature. Raman spectroscopy showed that the Ge Sn characteristic peak moved toward the larger wavenumber of 3.711 cm−1, and the intensity increased by 22.2% for the annealed GeSn (3.28% Sn) film. Moreover, it was determined from the full-wave reflection spectra that the direct band-gap is around 0.843 eV (1.47 μm). In-situ annealing accelerated the diffusion and ion substitution process of Sn atoms in the Ge lattice, which promoted the stability of the GeSn crystal cell and their optical performances in the infrared and terahertz range.

Ultra-thin GeSn films with high Sn contents were epitaxial grown on single silicon substrates with different substrate temperatures by MBE method. It is found that the GeSn film with substrate temperature lower than 450 °C still represents amorphous or partially amorphous, which might lead to a volatile optical properties or I–V curve in infrared and terahertz bands. XRD measurement shows stronger GeSn single crystal peak (400) and narrower full width at half maximum (FWHM) when increase the substrate temperature during the growth. Mid and far infrared (FT-IR) test suggests that the transmission of the GeSn films get improved for about 46% when the substrate temperature increases from 200 to 450 °C. Terahertz transmission of the GeSn samples also improved with a maximum rising rate of 25%/50 °C as the substrate temperature increases. This study of GeSn substrate temperature during the growth demonstrates it is one of the key factors to control the structure stability of the GeSn films and their infrared and terahertz properties.

A facile low-temperature crystallization method was recently developed for the synthesis of anodic TiO2 nanotubes (NTs). This novel method requires less energy and less sophisticated equipment than traditional high-temperature sintering, but the underlying mechanisms have not yet been elucidated. Here, we systematically studied the low-temperature crystallization mechanism of anodic TiO2 NTs by using different solvents and treatment time. For the first time, we notice a dramatic change of the surrounding water and discuss the TiO2 nanocrystals (NCs) byproducts of the low-temperature crystallization process. Accordingly, we propose a dissolution–recrystallization mechanism in which dissolved Ti(OH)62– dehydrates and crystallizes in situ to form anatase NTs as well as anatase NCs. Overall, this work provides a mechanistic insight into this low-temperature crystallization method, which could benefit the optimization and scale-up of industrial TiO2 NT production.

In this paper, a broadband terahertz wave was optically modulated by laser signal using a graphene field effect transistor. The modulation speed and depth were tuned by varying the gate voltage. The modulating laser and gate voltage together can trigger both inter- and intra-band transitions in graphene. The laser light penetrates through graphene into the p-Si substrate forming a thin loss layer at the graphene/p-Si interface, while the gate voltage tuned the intra-band transitions in graphene by changing the carrier density of states and the Fermi level. The change in carrier concentration, density of states, and mobility in the loss layer directly affected the optical conductivity and refractive index, and thus the modulation depth. Modulation depth of the whole device is between 28.5% and 39.3% at modulation frequencies from 100 kHz to 1.0 MHz.

Controllable phase modulation plays a pivotal role in the researches of magnonic logic gates. Here we propose a reconfigurable spin-current controlled magnonic phase shifter based on a ferromagnetic resonator. The proposed phase shifter requires no magnetic bias field during operation. The device is directly configured over the waveguide while keeping the original structure of the waveguide unaffected. Numerical micromagnetic simulations show that the phase shifter could yield either a {\pi}-phase or no shift depending on the magnetization status of the resonator, which can be controlled by a current pulse. Moreover, the phase-shifting operation could be affected by spin current. At different input current density, the device could be either used as a dynamic controlled phase shifter or a spin-wave valve. Finally, a XNOR magnonic logic gate is demonstrated using the proposed phase shifter. Our work can be a beneficial step to enhance the functionality and compatibility of the magnonic logic circuits., Comment: 11 pages, 13 figures

A terahertz spatial modulator is the critical component for active terahertz imaging using compressive sensing. Here small silicon pieces were put in arrays on flexible polymer substrate to fabricate semiconductor terahertz spatial modulators. By doing this, the inter-diffusion of photo-generated charge carriers is prevented for better resolution, and flexibility is achieved. Since the size of silicon is comparable to the wavelength of the terahertz wave, and the dielectric properties of the gap are very different from silicon, the optical modulation of each element is very different from the large silicon. In this Letter, the terahertz wave interaction and optical modulation of the small silicon are systematically studied by time domain spectroscopy. Notably, a strong resonance-like absorption peak was observed in a transmittance spectrum for the small silicon due to the size and edge effect. The spatial modulation of the terahertz wave was also compared between the silicon array and the large silicon samples.

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