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In this paper, a highly efficient dual-band transmitarray antenna using cross and square rings elements is presented for X and Ku bands. The dual-band transmitarray is designed for downlink/uplink frequencies of Ku band satellite communications. The transmitarray element consists of four metal patches and two dielectric substrates. The metal patch is printed on both sides of the substrate. By optimizing the parameters, the transmitarray element can achieve a transmission phase coverage greater than 360° and work independently in both frequency bands. Then, a method to select the size of the element is proposed, so that all the elements in the array can realize the transmission phase of the two frequencies as much as possible. A 201-elements transmitarray antenna is fabricated and measured and the band ratio of the antenna is 1.13. The measured maximum gain at 11.5 GHz is 22.4 dB, corresponding to the aperture efficiency is 52.7%. The measured maximum gain at 13 GHz is 24.2 dB, corresponding to the aperture efficiency is 62.4%. The 1-dB gain bandwidths are 9.7% (10.8-11.9 GHz) at X band and 9% (12.6-13.8 GHz) at Ku band.

During MEMS device fabrication process, the residual stress of thin film caused by thermal expansion coefficient mismatch and lattice mismatch is an important factor that will deteriorate the properties of thin film and bring yield losses to MEMS devices. In this work, a method to release the residual stress by using a folded structure with V‐shaped grooves is proposed. The folded structures with different groove width and groove interval are fabricated and relative Raman frequency shift is adopted to calculate the residual stress. The minimum residual thermal stress of 11.6 MPa can be obtained in the folded structure models by simulation, which is about five times lower than the residual thermal stress of the flat structure. The minimum residual stress of 40 MPa can be obtained in the folded structure by experiment results, which is about 20 times lower than the residual stress of the flat structure. The simulation results and experimental analysis confirms that introducing a folded structure with groove into the design of MEMS device is an effective way to suppress the generation of residual stress, thus enhancing the reliability of MEMS devices.

Selective laser melting (SLM) has been applied to manufacture various alloy components with excellent properties, but its further application is restricted by the intrinsic defects. In this work, the internal defect distributions in samples of three alloys (316L stainless steel, AlSi10Mg and Inconel 718) were investigated respectively, considering the effects of geometrical characteristics of the samples. The defects in the 316L stainless steel sample tend to be formed densely in the central part with large wall thickness, indicating a strong sensitivity to heat accumulation. Contrarily, the Inconel 718 sample shows a higher relative density with homogeneous defect distribution, indicating better formability for the SLM process. For the AlSi10Mg sample, the defect density keeps increasing as the deposition goes on. Typically, the defect density located at sample edges shows an abnormally high level comparing with the inner part, especially in the top sections of AlSi10Mg and Inconel 718 samples. The results are helpful for the geometrical design, the adjustment of building orientation and the further optimization of process parameters in the SLM process.

In this work, we report a method to enlarge the trapezoidal cantilever-based harvester power by using the high-performance Sc0.2Al0.8N/aluminum nitride (AlN) composite film and introducing symmetrical corners to both sides of the beam. Energy harvesters with variable beam structure and piezoelectric film are designed and evaluated by simulations and experiments. The trapezoid with corners (TWCs) cantilever is verified to improve the output power by a factor of five times when compared with the conventional trapezoidal cantilever without corners. The maximum power density of the ScAlN/AlN-based TWC cantilever harvester is about twice that of the AlN-based harvester, reaching 2.054 mW $\cdot \text{g}^{-2}\cdot $ cm−3 at a frequency of 330.25 Hz. The optimization of piezoelectric film and structure can give an inspiration for further improving the performance of cantilever-based energy harvesters.

In the design of composite materials, the properties and failure modes/mechanisms are always of the main concern. In this work, the mechanical properties and failure mechanisms of composite laminates with classical fabric stacking patterns ([(0, 90)]8 and [(0, 90)/(± 45)]4) were systematically investigated through mechanical experiments and FEM (finite element method) numerical simulations. The results show that the tensile modulus and bending modulus of the laminates were reduced by 22.2% and 37% after partially changing the stacking angle to ± 45°, but corresponding elongation and bending displacement were increased by 8.8% and 11.7%, respectively. Bending failure mode changes from complete fracture to partial fracture. Meanwhile, the delamination damage and tow peeling from the matrix increase significantly. FEM simulations on tensile and bending processes of the composites indicate that the ± 45° stacking angle leads to the change of the axial stress direction from SX (0°) to SY (± 45°), which is difficult to be observed from mechanical experiments. The FEM simulation provides a cost effective and efficient way for the structural visual optimization design and failure prediction of the actual composite materials.

Rice husk ash (RHA) is a highly active pozzolanic material produced by rice husk combustion control, and it is widely used as a mineral admixture in the production of high performance concrete. The addition of rice husk ash has a complex effect on cement hydration. Current models do not explain all these complex effects. In this paper, the hydration kinetics model of RHA-cement cementitious system was established by considering the dilution effect, chemical effect and water absorption and release of porous structure of rice husk ash to composite cementitious system. Compared with the experimental results, it is proved that the model can simulate the cementitious system containing RHA-cement well. The hydration process of RHA-cement system can be used to predict the hydration degree of RHA-cement system changing with age.

Under Voigt model, Barsch and Johnson gave the formula of nonliearly elastic constitutive relations for isotropic aggregates of cubic crystallites and orthorhambic aggregates of cubic crystallies, respectively. In this paper, a nonlinear elastic constitutive relation based on Voigt model, which is more general than Barsch's and Johnson's results, is derived for the set of anisotropic cubic grains. The anisotropy of metals is described by the texture coefficient.

This paper presents a ring-shaped Lamb wave resonator based 300 nm-thick Z-cut LiNbO 3 thin film. The proposed structure applied the alternative voltage along both the x and y direction by arranging ring-shaped electrodes, thus exciting the two-dimensional Lamb waves by utilizing both the e 24 and e 15 piezoelectric constants. The measured impedance results show first order asymmetric mode (A 1 ) mode resonance above 6 GHz with effective electromechanical coupling coefficient (K2 eff ) of 8.91%, and third order asymmetric mode (A 3 ) mode resonance above 17 GHz with K2 eff of 1.77%. In the meanwhile, the proposed structure realized a static capacitance (Co) of 0.13 pF within an active region area at 200×200 µm2, which has great potential for 50 Ω impedance match within a miniature size applied in super high frequency, spurious modes free RF front-ends filters.

Due to the increasing demand of higher frequencies for RF front end technologies, mainly for 5G smartphones, there is a need to develop filters for higher frequencies and large bandwidths. One of the promising candidates for satisfying those demands is the recently emerged laterally-excited bulk acoustic wave resonators. In this study, we aim to realize a resonator operating at 6 GHz based on the first-order antisymmetric (A1) mode utilizing Z-cut LiNbO3 thin films and square spiral electrodes.

This paper presents a thin film bulk acoustic resonator (FBAR) with a supporting column structure. The supporting column structure is placed at the vertex of each side of the resonator. The area around the active area of the resonator can be etched to form a trench structure. This structure can reduce the transmission of the lateral acoustic wave to the inactive area and increase the quality factor (Q-factor) of the resonator. Different dimensions of the square supporting column structure are compared in this paper and results show that as the width of the square supporting column increases, the Q-factor of the resonator increases accordingly. Because of the influence of the coupling capacitance at the supporting column, the effective coupling coefficient $(\boldsymbol{K}_{eff}^{2})$ of the resonator gradually decreases as the width of the supporting column increases.

In this paper, we demonstrate a first-order antisymmetric (A1) mode z-cut LiNbO 3 thin film resonator with arc shaped electrode. Arc shaped electrodes are only adopted on the top of the LiNbO 3 thin film piezoelectric material, and the positive and negative voltage is applied alternately to excite A1 mode in the piezoelectric layer. Some parametric finite element simulations are also presented in this paper. We simulated and fabricated the resonators operating at 6 GHz with an electromechanical coupling coefficient ( $K^{2}{_{eff}}$ ) of 17.97% and extracted quality factor (Q) of 975. This achievement provides a potential solution to satisfy the needs of high frequency and large bandwidth.

The cyclopentadithiophene (CPT) unit is a classic building block for constructing organic semiconductor materials with excellent performances. In this work, we designed and synthesized a new acceptor BCPT-4F, incorporating a CPT fused central backbone. BCPT-4F shows a redshift absorption in the near-infrared region compared with CPT based acceptors with an unfused backbone. Importantly, the photovoltaic device based on PBDB-T:BCPT-4F achieved a promising power conversion efficiency (PCE) of 12.43% with a high short circuit current density (Jsc) of 22.96 mA cm−2. Furthermore, based on the above binary device, a ternary device with F-Br as the third component achieved a high PCE of 14.23%, which is presently the highest efficiency for devices with CPT based photovoltaic materials.

Lead toxicity has sparked interest into alternative halide nanomaterials with properties similar to CsPbX3 perovskites. A promising alternative suggested from bulk studies is the family of double p...

Highlighted by the discovery of high-temperature superconductivity, strongly correlated oxides with highly distorted perovskite structures serve as intriguing model systems for pursuing emerging materials physics and testing technological concepts. While 3d correlated oxides with a distorted perovskite structure are not uncommon, their 4d counterparts are unfortunately rare. In this work, we report the tuning of the electrical and optical properties of a quasi-2D perovskite niobate CsBiNb2O7 via hydrogenation. It is observed that hydrogenation induces drastic changes of lattice dynamics, optical transmission, and conductance. It is suggested that changing the orbital occupancy of Nb d orbitals could trigger the on-site Coulomb interaction in the NbO6 octahedron. The observed hydrogen doping-induced electrical plasticity is implemented for simulating neural synaptic activity. Our finding sheds light on the role of hydrogen in 4d transition metal oxides and suggests a new avenue for the design and development of novel electronic phases.

In this paper, we present a new design of laterally-excited bulk wave resonators (XBARs) which contains narrow embedded interdigital electrodes (IDEs). The proposed XBAR has a high electromechanical coupling coefficient $(K_{eff}^{2})$ of 33.51 % and the smooth impedance curve. With the assistance of 149.5° Z-cut lithium niobate (LiNbO3) in XBARs, we obtain a high $K_{ef\int}^{2}$ of 42.54%. We investigate the impact on $K_{eff}^{2}$ and spurious modes of XBARs with different depths of electrodes $T_{e})$ . XBARs with the optimization of embedded electrodes show a great prospect in fabricating broad bandwidth filters.

Microfluidic electroporators integrated with 3D microelectrodes and working with flow-through manner facilitate high throughput transfection and benefit integration of back-end processing module for the electroporated cells. Here we demonstrate for the first time the flow-through electroporation using 3D sidewall microelectrodes made of silver-PDMS (AgPDMS). Such 3D AgPDMS structure, as a result of low-cost and simple casting process, greatly simplifies the fabrication as compared to existing electroporators incorporating 3D electrodes. Meanwhile, it allows flexible control over the height of the electrode with smooth sidewall profile, which in turn projects rather uniform electric field through deep channel. Delivery of the membrane-impermeable dye of propidium iodide achieves efficiency and viability both at ∼80% for Hela cells, and 79% efficiency with 93% viability for A549 cells. We also show the device capability for plasmid DNA transfection on hard-to-transfect Hela cells. Further, we demonstrate intracellular delivery of nanometer-sized quantum dots (QDs). We believe that the innovative device is a useful addition to the microfluidic electroporation toolbox. It holds great potential as a powerful tool for low-cost and high throughput gene transfection as well as engineered nanoparticles delivery for biological applications.

The effects of cement dosage, compaction coefficient, molding method (vertical vibration method and static pressure method), and dry–wet and freeze–thaw cycles on the mechanical strength of cement-improved loess (CIL) were studied to reveal its strength degradation law under dry–wet and freeze–thaw cycles. Results show that when using the vertical vibration molding method, the strength degradation effect of CIL can be improved by increasing the cement dosage and compaction coefficient; however, it is not obvious. Under the action of dry–wet cycle, damages, such as voids and cracks of CIL, develop continuously. Further, the strength deteriorates continuously and does not decrease after more than 15 dry–wet cycles. Therefore, the dry–wet cycle degradation system is selected by considering the most unfavorable conditions. In the process of freeze–thaw alternation, the pores and fissures of CIL develop and evolve continuously and the strength deteriorates continuously under the joint influence of water and low temperature. The strength tends to become stable after more than 12 freeze–thaw cycles. According to the safety principle, the deterioration coefficient of the freeze–thaw cycles is 0.3.

Protein-based nanoparticles have developed rapidly in areas such as drug delivery, biomedical imaging and biocatalysis. Ferritin possesses unique properties that make it attractive as a potential platform for a variety of nanobiotechnological applications. Here we synthesized magnetoferritin (P-MHFn) nanoparticles for the first time by using the human H chain of ferritin that was expressed by Pichia pastoris (P-HFn). Western blot results showed that recombinant P-HFn was successfully expressed after methanol induction. Transmission electron microscopy (TEM) showed the spherical cage-like shape and monodispersion of P-HFn. The synthesized magnetoferritin (P-MHFn) retained the properties of magnetoferritin nanoparticles synthesized using HFn expressed by E. coli (E-MHFn): superparamagnetism under ambient conditions and peroxidase-like activity. It is stable under a wider range of pH values (from 5.0 to 11.0), likely due to post-translational modifications such as N-glycosylation on P-HFn. In vivo near-infrared fluorescence imaging experiments revealed that P-MHFn nanoparticles can accumulate in tumors, which suggests that P-MHFn could be used in tumor imaging and therapy. An acute toxicity study of P-MHFn in Sprague Dawley rats showed no abnormalities at a dose up to 20 mg Fe Kg-1 body weight. Therefore, this study shed light on the development of magnetoferritin nanoparticles using therapeutic HFn expressed by Pichia pastoris for biomedical applications.

Phonon coupling to organic molecule dynamics yields giant isotope effects on transport properties., Lead halide perovskites are strong candidates for high-performance low-cost photovoltaics, light emission, and detection applications. A hot-phonon bottleneck effect significantly extends the cooling time of hot charge carriers, which thermalize through carrier–optic phonon scattering, followed by optic phonon decay to acoustic phonons and finally thermal conduction. To understand these processes, we adjust the lattice dynamics independently of electronics by changing isotopes. We show that doubling the mass of hydrogen in methylammonium lead iodide by replacing protons with deuterons causes a large 20 to 50% softening of the longitudinal acoustic phonons near zone boundaries, reduces thermal conductivity by ~50%, and slows carrier relaxation kinetics. Phonon softening is attributed to anticrossing with the slowed libration modes of the deuterated molecules and the reduced thermal conductivity to lowered phonon velocities. Our results reveal how tuning the organic molecule dynamics enables control of phonons important to thermal conductivity and the hot-phonon bottleneck.

With the rapid commercialization of fifth generation (5G) technology in the world, the market demand for radio frequency (RF) filters continues to grow. Acoustic wave technology has been attracting great attention as one of the effective solutions for achieving high-performance RF filter operations while offering low cost and small device size. Compared with surface acoustic wave (SAW) resonators, bulk acoustic wave (BAW) resonators have more potential in fabricating high- quality RF filters because of their lower insertion loss and better selectivity in the middle and high frequency bands above 2.5 GHz. Here, we provide a comprehensive review about BAW resonator researches, including materials, structure designs, and characteristics. The basic principles and details of recently proposed BAW resonators are carefully investigated. The materials of poly-crystalline aluminum nitride (AlN), single crystal AlN, doped AlN, and electrode are also analyzed and compared. Common approaches to enhance the performance of BAW resonators, suppression of spurious mode, low temperature sensitivity, and tuning ability are introduced with discussions and suggestions for further improvement. Finally, by looking into the challenges of high frequency, wide bandwidth, miniaturization, and high power level, we provide clues to specific materials, structure designs, and RF integration technologies for BAW resonators.

Two types of high temperature superconducting (HTS) linear synchronous motors (LSMs), which could be potentially used as the traction system of high speed railway were demonstrated in this work. One has a stator made of traditional ferromagnetic yoke and three-phase copper windings and the other has a coreless type stator. Different from the permanent magnet motor, the mover of the HTS LSM was made by HTS coils, which can provide high-intensity magnetic field. The HTS coils were electrically connected in series and powered by DC currents to behave as permanent magnets. To comprehensively study the developed HTS LSMs, finite-element models were established to predict its performance in terms of normal force and thrust force. To validate the simulation model, we designed and fabricated a three-dimensional force-measuring system, which could be used to measure the thrust and normal force of the HTS LSMs under different conditions. This work provides some basic knowledge for the study of the HTS LSM with coreless stator.

Adding an additive is one of the effective strategies to fine-tune active layer morphology and improve performance of organic solar cells. In this work, a binary additive 1,8-diiodooctane (DIO) and 2,6-dimethoxynaphthalene (DMON) to optimize the morphology of PBDB-T:TTC8-O1-4F-based devices is reported. With the binary additive, a power conversion efficiency (PCE) of 13.22% was achieved, which is higher than those of devices using DIO (12.05%) or DMON (11.19%) individually. Comparison studies demonstrate that DIO can induce the acceptor TTC8-O1-4F to form ordered packing, while DMON can inhibit excessive aggregation of the donor and acceptor. With the synergistic effect of these two additives, the PBDB-T:TTC8-O1-4F blend film with DIO and DMON exhibits a suitable phase separation and crystallite size, leading to a high short-circuit current density (Jsc) of 23.04 mA·cm-2 and a fill factor of 0.703 and thus improved PCE.

The residual stress of the corrugated diaphragm seriously affects the yield, service life and reliability of the cavity type MEMS device. Therefore, this paper studies the reduction of residual stress by optimizing the structural parameters of the corrugated diaphragm applied to MEMS devices. The test results are in agreement with the simulation results, indicating that the residual stress of the corrugated diaphragm has a positive linear relationship with the thickness of the diaphragm and the interval of the V-shaped grooves, and has a quadratic function relationship with the width of the v-groove. The simulation predicts that when the thickness of the corrugated diaphragm and the interval of the V-shaped groove are the smallest, and the width of the V-shaped groove is close to 9.67 μm, the residual stress of the corrugated film has a minimum, which are consistent with the test results. The results serve as a guide and reference for cavity type MEMS device design.

To minimize the size and weight of a vehicle-mounted accelerator-driven D-T neutron source and protect workers from unnecessary irradiation after the equipment shutdown, a method to optimize radiation shielding material aiming at compactness, lightweight, and low activation for the fast neutrons was developed. The method employed genetic algorithm, combining MCNP and ORIGEN codes. A series of composite shielding material samples were obtained by the method step by step. The volume and weight needed to build a shield (assumed as a coaxial tapered cylinder) were adopted to compare the performance of the materials visually and conveniently. The results showed that the optimized materials have excellent performance in comparison with the conventional materials. The “MCNP6-ACT” method and the “rigorous two steps” (R2S) method were used to verify the activation grade of the shield irradiated by D-T neutrons. The types of radionuclide, the energy spectrum of corresponding decay gamma source, and the variation in decay gamma dose rate were also computed.

In this work, we experimentally investigated the dynamic responses of stacked coated conductor tapes that were levitated over an Nd-Fe-B magnet guideway. The experiments were carried out on a recently designed test rig that can simultaneously measure the acceleration and levitation force during a vibration process. We applied three typical excitations, viz., unloading, free fall, and pulsed excitation. The attenuation coefficient and damping ratio of such stack-based maglev system were analyzed by means of free vibration attenuation method. Last, the dynamic response of mechanical components of the stack-based maglev on pulsed excitation was visualized clearly. Results obtained by this study tell us that the damping ratio is relative to the intensity of external disturbance, which means a weak excitation will cause a small damping ratio and a longer convergence time; however, a larger damping ratio and a faster convergence of vibration will be presented when a stronger stimulation is imposed on. This phenomenon could be contributed by the metal components of the stack, and is promising in practical application, particularly, in construction of HTS maglev where a large damping ratio is required.

Plasmonics has attracted tremendous interests for its ability to confine light into subwavelength dimensions, creating novel devices with unprecedented functionalities. New plasmonic materials are actively being searched, especially those with tunable plasmons and low loss in the visible–ultraviolet range. Such plasmons commonly occur in metals, but many metals have high plasmonic loss in the optical range, a main issue in current plasmonic research. Here, we discover an anomalous form of tunable correlated plasmons in a Mott-like insulating oxide from the Sr1−xNb1−yO3+δ family. These correlated plasmons have multiple plasmon frequencies and low loss in the visible–ultraviolet range. Supported by theoretical calculations, these plasmons arise from the nanometre-spaced confinement of extra oxygen planes that enhances the unscreened Coulomb interactions among charges. The correlated plasmons are tunable: they diminish as extra oxygen plane density or film thickness decreases. Our results open a path for plasmonics research in previously untapped insulating and strongly-correlated materials., Conventional plasmons in metals often suffer from high plasmonic loss in the optical range. Here, the authors report a distinct form of tunable correlated plasmons in Mott-like insulating Sr1−x NbO3+δ films, with multiple plasmon frequencies and low loss in the visible-ultraviolet range.

Phase transitions in halide perovskites triggered by external stimuli generate significantly different material properties, providing a great opportunity for broad applications. Here, we demonstrate an In-based, charge-ordered (In + /In 3+ ) inorganic halide perovskite with the composition of Cs 2 In(I)In(III)Cl 6 in which a pressure-driven semiconductor-to-metal phase transition exists. The single crystals, synthesized via a solid-state reaction method, crystallize in a distorted perovskite structure with space group I 4/ m with a = 17.2604(12) Å, c = 11.0113(16) Å if both the strong reflections and superstructures are considered. The supercell was further confirmed by rotation electron diffraction measurement. The pressure-induced semiconductor-to-metal phase transition was demonstrated by high-pressure Raman and absorbance spectroscopies and was consistent with theoretical modeling. This type of charge-ordered inorganic halide perovskite with a pressure-induced semiconductor-to-metal phase transition may inspire a range of potential applications.

Double perovskite halides are a class of materials with diverse chemistries that are amenable to solution-based synthesis routes, and display a range of properties for a variety of potential applications. Starting from a consideration of the octahedral and tolerance factors of ∼2000 candidate double perovskite compounds, we compute structural, electronic, and transport properties of ∼1000 using first-principles calculations based on density-functional-theory methods. The computational results have been assembled in a database that is accessible through the Materials Project online. As one potential application, double perovskites are candidates in the search for lead-free halide photovoltaic absorbers. We present the application of our database to aid the discovery of new double perovskite halide photovoltaic materials, by combining the results with optical absorption and phonon stability calculations. From three distinct classes of chemistries, 11 compounds were identified as promising solar absorbers and the complex chemical trends for band gap within each of these are analyzed, to provide guidelines for the use of substitutional alloying as a means of further tuning the electronic structure. Other possible applications of the database are also discussed. NRF (Natl Research Foundation, S’pore) Accepted version

The work aimed to calculate the radiation biological shielding performance of particle reinforced metal matrix composite (PRMMCs) using more reasonable model instead of conventional Uniform Filling Model, also attempted to provide a basis for the radiation shielding optimal design of such materials. Firstly, RSA (Random Sequential Adsorption) Model and GRM (Grid Random Model) were established based on MATLAB and Monte Carlo Particle transport program MCNP, and then advantages and disadvantages of them were compared. Later, the influences of metal matrix type, particle (B4C) content, particle shape and particle shape parameters on the biological shielding performance of materials were calculated under different energy neutrons and different thickness shield using random models. Finally, the optimal aspect ratio of regular hexahedral B4C was calculated by Genetic Algorithm combined with MATLAB and MCNP. It indicated that GRM could be applied to radiation shielding calculation of PRMMCs.

Optimizing the shielding material via intelligent optimization algorithms has become a tendency in recent years. This study investigated the calculation modes used in the optimization. Two modes are presented in this study. Mode A optimizes the shield with a variable thickness, the result optimized is exactly the desired result. It is suitable for the application that only need material with small thickness (less than several mean free paths), such as compact systems or mobile devices. Mode B optimizes the shield with a fixed thickness, the optimized result is just an intermediate solution, and the final result needs to be extrapolated. It could be applied to optimize the material whose thickness needed is comparatively larger. Several materials were optimized using the two modes, and comparisons among the materials were made. It is found that, the material properties optimized by the two modes are basically the same, and the thickness should be set at about 10 mean free paths of neutrons in those materials when the mode B is adopted.

Black phosphorus (BP), a new two-dimensional (2D) material, has been deeply developed for extensive applications in electronics and optoelectronics due to its similar physical structure to graphene and thickness dependent direct band gap. Here, we demonstrated a submicrosecond passive Q-switching Er-doped fiber laser with BP as saturable absorber (SA). The BP saturable absorber was fabricated by mechanical exfoliation method. By taking full advantage of the ultrafast relaxation time of BP-SA and careful design of compact ring cavity, we obtained stable Q-switching pulses output with a shortest duration as narrow as 742 ns. With increasing the pump power, the pulse repetition rate accreted gradually almost linearly from 9.78 to 61.25 kHz, and the pulse duration declined rapidly at lower pump power regime and retained approximate stationary at higher pump power regime from 3.05 to 0.742 μs. The experimental results indicate that BP-SA can be an effective SA for nanosecond Q-switching pulse generation.

By using optical heterodyne technique, we demonstrated the stable emission of sub-terahertz wave with the frequency ranging from 88 GHz to 101 GHz, which can operate as microwave source for nonlinear response measurement system. Mutual frequency beating of two well-separated sideband signals at a 0.1 THz photo-detector (PD) allows for the generation of sub-terahertz signal. Based on this approach, we have achieved the radiation of 0.1 THz wave with power up to 4 mW. By transmittance measurement, two-dimensional nanomaterial topological insulator (TI: Bi2Te3) shows saturable absorption behaviors with normalized modulation depth of 47% at 0.1 THz. Our results show that optical heterodyne technique could be developed as an effective microwave source generation for nonlinear measurement at sub-terahertz, even terahertz band.

Microelectromechanical (MEMS) piezoelectric accelerometers are diversely used in consumer electronics and handheld devices due to their low power consumption as well as simple reading circuit and good dynamic performance. In this paper, a tri-axial piezoelectric accelerometer with folded beams is presented. The four beam suspensions are located at two sides of the mass aligned with edges of the mass, and the thickness of the beams is the same as the thickness of the mass block. In order to realize the multi-axis detection, a total of 16 sensing elements are distributed at the end of the folded beams. The structural deformations, stress distribution, and output characteristics due to the acceleration in x-, y-, and z-axis directions are theoretically analyzed and simulated. The proposed accelerometer is fabricated by MEMS processes to form Mo/AlN/ScAlN/Mo piezoelectric stacks as the sensing layer. Experiments show that the charge sensitivity along the x-, y-, and z-axes could reach up to ~1.07 pC/g, ~0.66 pC/g, and ~3.35 pC/g. The new structure can provide inspiration for the design of tri-axial piezoelectric accelerometers with great sensitivity and linearity.

Bulk acoustic wave (BAW) filters have been extensively used in consumer products for mobile communication systems due to their high performance and a standard CMOS compatible integration process. However, a traditional BAW filter generally presents only one frequency transmission band; hence, it cannot meet the demands of multi-mode wireless communication systems. In this work, we propose a radio frequency dual-band filter based on a dual-mode film bulk acoustic resonator (FBAR). The dual-mode FBAR consists of molybdenum electrodes and an aluminum nitride film with a c axis tilt angle, which leads to the coexistence of the longitudinal mode and the shear mode in the resonator. The influence of the tilt angle on the resonant frequency and electromechanical coupling coefficient of the dual-mode FBAR is investigated. Subsequently, the behaviors of the dual-mode FBAR have been emulated by a modified Butterworth–Van Dyke model with two motional branches, which is further used to design and optimize the dual-band filter. The dual-mode FBAR-based filters connected in a ladder configuration present two dual passbands of 43 MHz and 105 MHz, respectively. The developed filters with dual passbands can give an inspiration to the design of BAW devices in modern wireless communications.

An acceptor-donor-acceptor (A-D-A) type small molecule acceptor ITOT-4Cl incorporating a dithienopyran (DTP) fused backbone, has been designed and synthesized. With the strong electron-donating capability of the backbone D unit, ITOT-4Cl shows a narrow band gap of 1.28 eV, and has an efficient absorption in near-infrared region up to 968 nm. The photovoltaic devices based on PBDB-T:ITOT-4Cl give a power conversion efficiency (PCE) of 12.50%, with a high short circuit current density (Jsc) of 22.89 mA cm−2. With F–Br as the third component, the ternary organic solar cells device shows an enhanced PCE of 14.29% with an improved Jsc of 24.40 mA cm−2, which is among the best results for oxygen heterocycle fused nonfullerene acceptor based devices.

A thieno[3,2-b]thiophene-functionalized porphyrin molecule (DEP-TT) with the ethynylene bridges between the diketopyrrolopyrrole and porphyrin units has been designed and synthesized as the donor material. DEP-TT exhibits a broad absorption wavelength in the visible region with the onset absorption to 898 nm of the film and a low optical band gap of 1.38 eV. IDT-C8, as the acceptor material has a relatively strong absorption spectrum ranging from 500 to 750 nm in the solid film, which exactly fills the absorption trough of DEP-TT. The power conversion efficiency (PCE) of all small molecule increased from 0.64% (Jsc = 2.61 mA cm−2, Voc = 0.82 V, and FF = 0.30) to 5.14% (Jsc = 11.15 mA cm−2, Voc = 0.71 V, and FF = 0.65) after solvent vapor annealing. The PCE of 5.14% provided valuable recommendation based on porphyrin all small molecule system, since few work has involved in this field.

Pnictide superconductors will be very promising for applications if wires with high critical current density $J_{c}$ can allow reel-to-reel large-scale fabrication at low costs. To understand the mechanism(s) that limited $J_{c}$ in flat-rolled $\hbox{Sr}_{0.6}\hbox{K}_{0.4}\hbox{Fe}_{2}\hbox{As}_{2}$ (Sr122) tapes, microstructure analysis has been considered the most direct and efficient way. Here, we report on high-resolution microstructure imaging and analysis on Fe-sheathed flat-rolled Sr122 tapes, which have a $J_{c}$ as high as $2.3\times 10^{4}\ \hbox{A/cm}^{2}$ at 10 T and 4.2 K. The overlapping nature of the Sr122 plates was clearly observed. Transmission electron microscopy/scanning transmission electron microscopy analysis showed that, besides the cracks formed during the fabrication process, the $\hbox{SrO}_{2}$ phase and cavities caused by the inhomogeneously dispersed Sr and K are the other important factors suppressing $J_{c}$ . The wetting phase FeAs at the grain boundaries can be partially substituted by Sn in Sn-added samples. Our findings provide insights that pave the way to further enhance the critical current of the rolled 122 tapes up to the practical level.

This paper presents a modified Lame-mode resonator (MLMR) with a high, effective electromechanical coupling coefficient ( K e f f 2 ). With trapezoidal grooves introduced by etching the superficial piezoelectric material between interdigitated electrodes (IDTs), the MLMR can remarkably improve K e f f 2, eliminate spurious modes, and reduce the internal stress of piezoelectric material. The Lame mode resonator (LMR) with four different electrode configurations is investigated by using finite element method simulation first; then, the impact of the groove's vertical ( h ) and horizontal ( θ ) size on K e f f 2 and spurious modes of MLMRs is theoretically analyzed and optimized. It is noted that all the modified structures can improve K e f f 2 except the IDT-Ground structure. This work demonstrates a simulated K e f f 2 as high as 10.47% in the modified IDT-Floating structure, and 10.73% in the modified IDT-IDT structure, which is the highest ever reported in S0 mode AlN LMR. The MLMR shows great prospect for fabricating broad bandwidth filters.

Wide bandgap two-dimensional semiconductors are of paramount importance for developing van der Waals heterostructure electronics. This work reports the use of layer and strain engineering to introduce the feasibility of two-dimensional hexagonal (h)-AlN to fill the scientific and application gap. We show that such one- to five-layer h-AlN has an indirect bandgap, tunable from 2.9 eV for a monolayer to ∼3.5 eV for multilayer structures, along with isotropic effective masses and carrier mobilities between zigzag and armchair directions. With an increase in the layer number to bulk AlN, the bandgap will experience a transition from an indirect gap to direct gap. Surprisingly, high room-temperature mobilities of electrons and holes (of the order of 1000 cm2 V−1 s−1) in a relaxed monolayer h-AlN system and widely adjustable effective masses and carrier mobilities in a different layer h-AlN are observed. In the presence of strain engineering, the bandgap decreases obviously with an increase in tensile strain; meanwhile, the isotropy and value of effective mass or carrier mobility in monolayer h-AlN can also be modulated effectively; the hole mobilities in the armchair direction, especially, will be enhanced dramatically. With a tunable bandgap, high carrier mobilities, and modifiable isotropy, our results indicate that few-layer h-AlN has potential applications in future mechano-electronic devices.

Semiconductor compounds are widely used for photocatalytic hydrogen production applications, where photogenerated electron–hole pairs are exploited to induce catalysis. Recently, powders of a metallic oxide (Sr1−xNbO3, 0.03, Metallic oxide SrNbO3 has been identified as an efficient hydrogen evolution photocatalyst. Here, Venkatesan and co-workers show that its visible light absorption stems from plasmon resonance, thanks to its large carrier density (despite a large 4.1 eV bandgap), as opposed to from an interband transition.

In this study we report the existence of novel ultraviolet (UV) and blue emission in rare-earth based perovskite NdGaO3 (NGO) and the systematic quench of the NGO photoluminescence (PL) by Ce doping. Study of room temperature PL was performed in both single-crystal and polycrystalline NGO (substrates and pellets) respectively. Several NGO pellets were prepared with varying Ce concentration and their room temperature PL was studied using 325 nm laser. It was found that the PL intensity shows a systematic quench with increasing Ce concentration. XPS measurements indicated that nearly 50% of Ce atoms are in the 4+ state. The PL quench was attributed to the novel concept of super hydrogenic dopant (SHD)”, where each Ce4+ ion contributes an electron which forms a super hydrogenic atom with an enhanced Bohr radius, due to the large dielectric constant of the host. Based on the critical Ce concentration for complete quenching this SHD radius was estimated to be within a range of 0.85 nm and 1.15 nm whereas the predicted theoretical value of SHD radius for NdGaO3 is ~1.01 nm.

Three half-turn (Type A) and four half-turn (Type B) hexagonal wire mesh panels were used for tensile tests with and without one center-cut wire mesh panel. The panel opening was 120 by 150 mm. The test loadings were applied either parallel (in longitudinal direction) or perpendicular (in transverse direction) to the twist wire sections. The study results indicated that the ultimate tensile strength for Type A and hexagonal wire mesh panels without any cut loading in longitudinal or transverse direction were similar. However, the four half-turn hexagonal wire panels showed better tensile resistance after one wire broke at the panel center for both loadings either in longitudinal or in transverse condition. This implied that the presence of broken wires within the four half-turn hexagonal wire mesh showed slight influence on the panel’s tensile strength. In general, the tensile strengths for the test conditions for loading in longitudinal direction were about double of those loading in transverse direction. In conclusion, four half-turn (Type A) hexagonal wire mesh is a better structural pattern than a three half-turn (Type B) hexagonal wire mesh for slope stability and river bank protection applications.

Nanosized Li4Ti5O12 powders are synthesized by a polymerization-based method using titanium butoxide and lithium nitrate as precursors and furfuryl alcohol as a polymerizable solvent. The prepared samples are characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and Braunauer-Emmett-Teller (BET) analysis. The electrochemical performances of these Li4Ti5O12 powders are also studied. The effect of different surfactants including citric acid, polyvinylpyrrolidone, and cetyltrimethyl ammonium bromide on the structure and properties is also investigated. It is found that pure spinel phase of Li4Ti5O12 is obtained at an annealing temperature of 700 i?½C or higher. The use of surfactants can improve the powder morphology of nanosized particles with less agglomeration. With suitable annealing temperature and the addition of surfactant, Li4Ti5O12 powders with high BET surface area and favorable electrochemical performance can be obtained.

The adsorption of a piece of graphene nanoribbon on Ni surfaces, edges, and steps along the zigzag edge are studied with first principle calculations. The absolute value of the adsorption energy per contacting point on the (1 0 0) surface is higher than that on the (1 1 1) surface. The edge effects on the graphene adsorption on one side of various edges can be ignored because the cohesive energies and the bond lengths do not change too much on edges compared with that on the bare surfaces. The vertical edge adsorption is not as strong as the one side edge adsorption. For the step adsorption, extra Ni C bonds form at the interface, the absolute values of the adsorption energies on steps increase and the C C bond lengths near interfaces are longer than that on the surfaces and edges. For carbon nanotube (CNT) or graphene growth on Ni nanoparticles, steps are at the outside portions of the particles between different facets. Since stronger adsorption and longer C C bond length near the interface, especially on the steps, may benefit the CNT growth, it can help us understand the relationship between the diameter of CNTs and the size of the Ni particles.

A variety of ZnSe nanostructures, including the single-, bi- and tri-crystal nanobelts, are successfully fabricated through the thermal evaporation method and comprehensively investigated by a combination of various transmission electron microscopy (TEM) techniques. All nanostructures are of metastable wurtzite phase and the bi- and tri-crystal nanobelts are both mediated by the {013} twinning, with the single crystal nanobelts as building blocks. Benefiting from the commonly observed morphological evolutions, not only the crystallographic relations for different variants in an individual bi- or tri-crystal nanobelt, but also the intrinsic connections between different morphologies are fully understood by selected area electron diffraction, convergent beam electron diffraction and high-resolution TEM techniques, which reveals that the accompanying formation of tri-crystal nanobelt, the {013} relationship, though maintained still, is not as strict as that in a bi-crystal nanobelt and holds a ∼0.75° deviation for a case study; the angles between adjacent twinning variants/planes are compressed from ∼125.0° in bi-crystal nanobelts to ∼120°, and finally form an asymmetric twinning plane distributions. The study helps deepen the understanding of tri-crystal and related complex semiconductor nanostructures.

The family of solution-processed tin-based perovskites is demonstrated as a new and superior near-infrared gain medium. Due to the large electron–hole bimolecular recombination associated with tin and the reduced trap density with SnF2 treatment, these lead-free “green” perovskites yield stable coherent light emission extending to ≈1 μm at strikingly low thresholds. NRF (Natl Research Foundation, S’pore) ASTAR (Agency for Sci., Tech. and Research, S’pore) MOE (Min. of Education, S’pore) Accepted version