环境温度变化压电智能骨料信号稳定性试验研究

研究了压电智能骨料在环境温度变化时的信号稳定性问题,并明确其变化规律及分析原因,为基于压电智能骨料的混凝土结构健康监测奠定基础。将预先埋设压电智能骨料的小尺寸素混凝土梁置入恒温试验箱中,改变箱内温度并记录不同温度下的压电智能骨料信号能量值,利用试验数据拟合出信号能量值与温度之间的关系。试验结果表明,压电智能骨料信号幅值受温度影响变化明显且表现出明显的非线性变化规律及符合压电材料机电耦合系数随温度变化的规律,其原因是由于压电陶瓷材料本身弹性常数随温度变化,并在宏观上体现为机电耦合系数的变化。     

Elastic Energy Storage Enables Rapid and Programmable Actuation in Soft Machines

Storage of elastic energy is key to increasing the efficiency, speed, and power output of many biological systems. This paper describes a simple design strategy for the rapid fabrication of prestressed soft actuators (PSAs), exploiting elastic energy storage to enhance the capabilities of soft robots. The elastic energy that PSAs store in their prestressed elastomeric layer enables the fabrication of grippers capable of zero‐power holding up to 100 times their weight and perching upside down from angles of up to 116°. The direction and magnitude of the force used to prestress the elastomeric layer can be controlled not only to define the final shape of the PSA but also to program its actuation sequence. Additionally, the release of the elastic energy stored by PSAs causes their high‐speed recovery (≈50 ms), which significantly improves the actuation rates of soft pneumatic actuators, especially after motions requiring large deformations. Moreover, judicious prestressing of PSAs can also create bistable soft robotic systems, which use their stored elastic energy as a source of power amplification for rapid movements. These strategies serve as a basis for a new class of entirely soft robots capable of recreating bioinspired high‐powered and high‐speed motions using stored elastic energy.     

Effects of Ca and Mn Additions on the Microstructure and Dielectric Properties of (Bi<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>)TiO<Subscript>3</Subscript> Ceramics

Dielectric ceramics based on the solid solution (1 − x)Bi_0.5Na_0.5TiO₃ (BNT)-xCaTiO₃ (CT) were synthesized by the conventional solid-state route. BNT with various contents of CT formed a complete solid solution and exhibited a rhombohedral structure. CT in this solid solution with BNT was observed to decrease the dielectric constant at higher temperatures and raise the dielectric constant at lower temperatures. On the other hand, decreased ferroelectricity was observed with increasing CT concentration, resulting in a downward shift of the depolarization temperature and a decrease of the dissipation factor. With the addition of Mn²⁺ to 0.86BNT-0.14CT, the temperature characteristics of capacitance were improved (−55°C to 250°C, ΔC/C _25°C ≤ ±15%). By doping with 1.5 wt.% Mn²⁺, the dielectric constant at room temperature reached over 900, with a dielectric loss of less than 1%.     

Room-Temperature Symmetric Giant Positive and Negative Electrocaloric Effect in PbMg0.5W0.5O3 Antiferroelectric Ceramic

As an emerging solid-state refrigeration technology with zero-emission and high energy conversion efficiency, there is a compelling need for ferroelectric materials with giant electrocaloric effects (ECEs) at room temperature suitable for refrigeration applications. The complex perovskite antiferroelectric (AFE), PbMg_0.5W_0.5O₃, containing non-equivalent B-site ions with a symmetric giant positive and negative ECE near room temperature is presented. At the Curie temperature of 36 °C, the first-order AFE–paraelectric phase transition gives rise to a large enthalpy change of 3.92 J g⁻¹, more than four times that of BaTiO₃. This leads to a significant ECE under the influence of an electric field. The direct electrocaloric characterization shows that the adiabatic temperature change, ΔT, exhibits symmetric peaks with a giant positive maximum of 1.79 K (ΔS = 1.68 J kg⁻¹ K⁻¹) at 36 °C and a negative maximum of −2.02 K (ΔS = −1.93 J kg⁻¹ K⁻¹) at 34 °C. The ultrahigh magnitude of ΔT near room temperature makes PbMg_0.5W_0.5O₃ a superior electrocaloric material far beyond traditional PbZrO₃-based AFEs. The coexistence of symmetric giant positive and negative ΔT to further improve cooling efficiency is expected. In addition, the good reversibility and negligible leakage current should pave the way for practical applications.     

Storage moduli,loss moduli and damping factor of GaAs and Ga1−xMnxAs thin films using DMA 2980

The spin injector part of spintronic FET and diodes suffers from fatigue due to rising heat on the depletion layer. In this study the stiffness of Ga_1−xMn_xAs spin injector in terms of storage modulus with respect to a varying temperature, 45 °C≤T≤70 °C was determined. It was observed that the storage modulus for MDLs (Manganese Doping Levels) of 0%, 1% and 10% decreased with increase in temperature while that with MDLs of 20% and 50% increase with increase in temperature. MDLs of 20% and 50% appear not to allow for damping but MDLs ≤20% allow damping at temperature range of 45 °C≤T≤70 °C. The magnitude of storage moduli of GaAs is smaller than that for ferromagnetic Ga_1−xMn_xAs systems. The loss moduli for GaAs were found to reduce with increase in temperature. Its magnitude of reducing gradient is smaller than Ga_1−xMn_xAs systems. The two temperature extremes show a general reduction in loss moduli for different MDLs at the study temperature range. From damping factor analysis, damping factors for ferromagnetic Ga_1−xMn_xAs was found to increase with decrease in MDLs contrary to GaAs which recorded the largest damping factor at 45 °C≤T≤70 °C. Hence, MDL of 20% shows little damping followed by 50% while MDL of 0% has the most damping in an increasing trend with temperature.     

Barnacle Cement Proteins-Inspired Tough Hydrogels with Robust,Long-Lasting,and Repeatable Underwater Adhesion

The development of adhesives that can achieve robust and repeatable adhesion to various surfaces underwater is promising; however, this remains a major challenge primarily because the surface hydration layer weakens the interfacial molecular interactions. Herein, a strategy is proposed to develop tough hydrogels that are robust, reusable, and long-lasting for underwater adhesion. Hydrogels from cationic and aromatic monomers with an aromatic-rich composition inspired by the amino acid residuals in barnacle cement proteins are synthesized. The hydrogels are mechanically strong and tough (elastic modulus 0.35 MPa, fracture stress 1.0 MPa, and fracture strain 720%), owing to the interchain π–π and cation–π interactions. In water, the hydrogels firmly adhere to diverse surfaces through interfacial electrostatic and hydrophobic interactions (adhesion strength of 180 kPa), which allows for instant adhesion and reversibility (50 times). Moreover, the hydrogel shows long-lasting adhesion in water for months (100 days). Novel adhesive hydrogels may be useful in many applications, including underwater transfer, water-based devices, underwater repair, and underwater soft robots.     

Whisker mitigation measures for Sn-plated Cu for different stress tests

The effectiveness of the widely-used whisker mitigation measures for Sn-plated Cu base material (annealing at 150 °C for 1 h or a Ni interlayer) were investigated after temperature cycling and after storage at room temperature. It was found that these measures prevent whisker growth during isothermal storage, but not during temperature cycling. These mitigation measures do apparently not reduce the compressive stress that builds up during temperature cycling due to different coefficients of thermal expansion of Sn and Cu. A change of the Sn microstructure to globular grains is proposed and investigated as potential whisker mitigation measure for temperature cycling.     

Evaluation of the mechanical properties of a ternary Sn-20In-2.8Ag solder

The Sn-20In-2.8Ag solder alloy is a potential lead-free solder for replacing the traditional Sn-Pb solders. In this study, the mechanical properties of the bulk material are reported by tensile test at various strain rates and temperatures. The Sn-20In-2.8Ag solder possessed a solidus and liquidus between 170.8°C and 195.5°C. The ultimate tensile strength (UTS) and elongation were 59.3 MPa and 50.2% at a strain rate of 10⁻³ s⁻¹ at room temperature. Moreover, the UTS of this alloy decreased, but its elongation increased, with increasing testing temperature. Stress exponents of Sn-20In-2.8Ag alloy varied from 6.5 at room temperature to 4 at 100°C, and the activation energy for creep was 51.0 kJ/mol at the higher temperature range from 50°C to 100°C. The typical intergranular creep fracture mode was observed in Sn-20In-2.8Ag solder during tensile creep deformation.     

Tailoring Pressure Sensitive Adhesives with H6XDI-PEG Diacrylate for Strong Adhesive Strength and Rapid Strain Recovery

The development of flexible electronic technology has led to convenient devices, including foldable displays, wearable, e-skin, and medical devices, increasing the need for flexible adhesives that can quickly recover their shape while connecting the components of the device. Conventional pressure sensitive adhesives (PSAs) can improve recoverability via crosslinking, but often have poor adhesive strength. In this study, new types of urethane-based crosslinkers are synthesized using m-xylylene diisocyanate (XDI) or 1,3-bis(isocyanatomethyl)cyclohexane (H₆XDI) as a hard segment, and poly(ethylene glycol) (PEG) group as a soft segment. The PSA with the synthesized H₆XDI-PEG diacrylate (HPD) demonstrates a significantly improved recoverability compared to XDI-PEG diacrylate and a conventional crosslinker 1,6-hexanediol diacrylate (HDDA) while maintaining high adhesion strength (≈25.5 N 25 mm⁻¹). The excellent recovery property of the PSA crosslinked with HPD is further confirmed by 100k folding tests and 10k multi-directional stretching tests exhibiting high folding and stretching stability. PSA with HPD also shows high optical transmittance (> 90%) even after 20% straining, suggesting its applicability in fields that simultaneously require high flexibility, recoverability, and optical clarity such as foldable displays.     

Elevated temperature nitrogen implants in 6H-SiC

Elevated temperature (700°C) N ion implantations were performed into 6H-SiC in the energy range of 50 keV-4 MeV. By analyzing the as-implanted depth distributions, the range statistics of the N⁺ in 6H-SiC have been established over this energy range. Annealing at 1500 and 1600°C for 15 min resulted in Rutherford backscattering spectrometry scattering yields at the virgin crystal level, indicating a good recovery of the crystalline quality of the material without any redistribution of the dopant. A maximum electron concentration of 2 × 10¹⁹ cm⁻³, at room temperature, has been measured even for high-dose implants. The p-n junction diodes made by N ion implantation into a p-type substrate have a forward turn-on voltage of 2.2 V, an ideality factor of 1.90, and a reverse breakdown voltage of 125 V with nA range leakage current for -10 V bias at room temperature. By probing many devices on the same substrate we found uniform forward and reverse characteristics across the crystal.     

On-chip Diamond MEMS Magnetic Sensing through Multifunctionalized Magnetostrictive Thin Film

Electrically integrable, high-sensitivity, and high-reliability magnetic sensors are not yet realized at high temperatures (500 °C). In this study, an integrated on-chip single-crystal diamond (SCD) micro-electromechanical system (MEMS) magnetic transducer is demonstrated by coupling SCD with a large magnetostrictive FeGa film. The FeGa film is multifunctionalized to actuate the resonator, self-sense the external magnetic field, and electrically readout the resonance signal. The on-chip SCD MEMS transducer shows a high sensitivity of 3.2 Hz mT⁻¹ from room temperature to 500 °C and a low noise level of 9.45 nT Hz^−1/2 up to 300 °C. The minimum fluctuation of the resonance frequency is 1.9 × 10⁻⁶ at room temperature and 2.3 × 10⁻⁶ at 300 °C. An SCD MEMS resonator array with parallel electric readout is subsequently achieved, thus providing a basis for the development of magnetic image sensors. The present study facilitates the development of highly integrated on-chip MEMS resonator transducers with high performance and high thermal stability.     

Band gap engineered resistor for mitigating linear energy transfer sensitivities in scaled submiron CMOS technology SRAM cells

Use of cross-coupling latch resistors is a prime method of mitigating single event upsets (SEU). Scaling has dramatically reduced ability of using this technique because of the large area needed as well as high temperature coefficient of resistance (TCR) of lightly doped polysilicon resistors. We present results of a study of the electrical properties of Al_1?xIn_xN films resistor which offers distinct advantage over polysilicon resistors. The films were grown on silicon nitride by magnetron sputter deposition at room temperature. Sheet resistance in the range of 8–10 kΩ/□ was reproducibly grown. The resistor film is thermally stable with TCR of less than minus 0.09%/°C for temperature range of minus 55 °C to +125 °C.     

High-Dose Phosphorus-Implanted 4H-SiC: Microwave and Conventional Post-Implantation Annealing at Temperatures ≥1700°C

Semi-insulating 4H-SiC ⟨0001⟩ wafers have been phosphorus ion implanted at 500°C to obtain phosphorus box depth profiles with dopant concentration from 5 × 10¹⁹ cm⁻³ to 8 × 10²⁰ cm⁻³. These samples have been annealed by microwave and conventional inductively heated systems in the temperature range 1700°C to 2050°C. Resistivity, Hall electron density, and Hall mobility of the phosphorus-implanted and annealed 4H-SiC layers have been measured in the temperature range from room temperature to 450°C. The high-resolution x-ray diffraction and rocking curve of both virgin and processed 4H-SiC samples have been analyzed to obtain the sample crystal quality up to about 3 μm depth from the wafer surface. For both increasing implanted phosphorus concentration and increasing post-implantation annealing temperature the implanted material resistivity decreases to an asymptotic value of about 1.5 × 10⁻³ Ω cm. Increasing the implanted phosphorus concentration and post-implantation annealing temperature beyond 4 × 10²⁰ cm⁻³ and 2000°C, respectively, does not bring any apparent benefit with respect to the minimum obtainable resistivity. Sheet resistance and sheet electron density increase with increasing measurement temperature. Electron density saturates at 1.5 × 10²⁰ cm⁻³ for implanted phosphorus plateau values ≥4 × 10²⁰ cm⁻³, irrespective of the post-implantation annealing method. Implantation produces an increase of the lattice parameter in the bulk 4H-SiC underneath the phosphorus-implanted layer. Microwave and conventional annealing produce a further increase of the lattice parameter in such a depth region and an equivalent recovered lattice in the phosphorus-implanted layers.     

Multiple Surface Optimizations for a Highly Durable LiCoO2 beyond 4.6 V

Recently, lots of researches have focused on enhancing the structure stability of LiCoO₂ (LCO) at a cutoff voltage of 4.6 V (vs Li/Li⁺) at room temperature. However, the high temperature (≥45 °C) performances are more significant for practical applications. Herein, the mechanism of unsatisfactory structure stability of LCO at 45 °C via comparing a commercial LCO (C-LCO) and a surface optimized LCO (O-LCO) is revealed first. The deteriorated structure stability of LCO at 45 °C is mainly due to two aspects: i) the promoted bulk Li⁺ ion diffusion kinetics at 45 °C leads to a higher state of charge for the charged LCO, which triggers more side reactions; ii) the more prominent surface structure collapse at 45 °C blocks the Li⁺ ion transport channels. Surface optimizations, including the anions (F⁻ and PO₄³⁻) and cations (Al³⁺) surface modulation and a subsurface spinel reinforcement, are comprehensively applied to alleviate the side reaction and structure collapse issues of O-LCO, leading to a high reversible discharge capacity of 238 mAh g⁻¹, as well as an obviously enhanced cycle and floating stability at 45 °C and beyond 4.6 V. A new insight is provided here for developing more advanced and practical high-voltage LCO.     

Broadband Dielectric Characterization of a Silicone Elastomer

The dielectric properties of an electronics grade silicone elastomer have been investigated in the frequency intervals 0.1 Hz to 1 MHz at −150°C to 100°C and from 7 GHz to 18 GHz at room temperature. The measurements were performed with a dielectric spectrometer for the low frequency range and with a waveguide setup for the high frequency range. The results are discussed in terms of performance and usability of the material in electronic packaging. Minor direct current (dc) conduction has been observed at high temperatures and is probably related to low levels (ppm) of ionic impurities.     

Porous Proton Exchange Membrane with High Stability and Low Hydrogen Permeability Realized by Dense Double Skin Layers Constructed with Amino tris (methylene phosphonic acid)

Porous proton exchange membranes (PEMs) with abundant porous structures show enhanced phosphoric acid (PA) doping levels and proton transport capability. However, the high PA loss rate and serious hydrogen cross-over lead to poor membrane stability. Enhancing the stability of PA-doped porous PEMs is therefore crucial for obtaining high-performance proton exchange membrane fuel cells. Herein, a porous polybenzimidazole membrane with dense double skin layers is reported using amino tris (methylene phosphonic acid) (ATMP) constructed. This membrane effectively alleviates hydrogen permeation and PA loss in a water/anhydrous environment and exhibits enhanced stability. Surprisingly, as an organic proton conductor, ATMP has strong hydrogen bonding with PA, leading to the formation of more continuous proton transport channels. Due to the dense double skin layers protection and the synergistic mass transfer of ATMP and PA, the porous membrane shows excellent proton conductivity (0.112 S cm⁻¹) and a H₂-O₂ fuel cell peak power density of 0.98 W cm⁻² at 160 °C. Moreover, it presents excellent fuel cell stability, with a voltage decay rate of only 5.46 µV h⁻¹. In addition, the porous membrane surpasses the traditional working temperature range, operating in the range of 80–220 °C. This study provides new insight into developing high-performance porous PEMs.     

Bioinspired Dynamic Camouflage in Programmable Thermochromic-Patterned Photonic Films for Sophisticated Anti-Counterfeiting

Although the encrypted anti-counterfeiting technology based on infiltration-controlled photonic crystals has attracted widespread attention, the information has only hidden and display states. The more diverse and complex encryption effect requires a continuous and programmable color transformation. Inspired by the dynamic camouflage in chameleons and cephalopods, a programmable thermochromic patterned photonic film is developed for encrypted anti-counterfeiting, which is constructed by infiltrating thermoresponsive poly(oligo ethylene glycol acrylate) copolymers in SiO₂-coated ZnS photonic crystals. The responsive temperature range is determined by the lower critical solution temperature of filled copolymers, which is tunable by controlling the ratios of different monomers in copolymerization. Based on this, the responsive range is adjusted to 5–55 °C and decoding temperature is set at 20 °C. The pattern is hidden either when the water temperature is >55 °C or <5 °C. Only when the water temperature accurately matches the decoding temperature (20 °C), do the different areas display the preset colors, resulting in the complete pattern being revealed. The design of this programmable thermochromic patterned photonic film indicates a new direction for the encrypted anti-counterfeiting technology, which can carry more abundant information and encrypt them more complex and sophisticated.     

Oligothiophenes in organic thin film transistors – Morphology,stability and temperature operation

We have investigated a series of oligothiophenes in organic thin film transistors (TFTs), with special emphasis on their thin film morphology related to device performance and application requirements. The transistor performance was studied for devices fabricated at different substrate temperatures during semiconductor deposition (ranging from room temperature to 120 °C). A significant dependence of thin film morphology on the substrate temperature was observed, whereas the charge carrier mobility in devices occurs almost unaffected. We have tested the long-term stability of 78 transistor devices (shelf-life in ambient conditions) over a period up to 100 days. Only a small degradation in mobility by less than one order of magnitude was observed. Investigations at elevated temperatures during TFT operation (room temperature to 105 °C) show that devices with α,α′-hexylsexithiophene (Hex-6T-Hex) degrade in their charge carrier mobility by a factor of 8, but completely recover to their initial value of 0.7 cm²/Vs after a short period of storage at room temperature in ambient conditions.     

Effects of substrate temperature on the degradation of RF sputtered NiO properties

Nickel oxide (NiO) film was grown on Si (100) substrate through RF sputtering of NiO target in Ar plasma at various temperatures ranging from room temperature (RT) to 300 °C. The structural study revealed (200) oriented NiO diffraction peak at RT and at 100 °C, however, by increasing the substrate temperature to 200 °C, intensity of (200) NiO diffraction peak was decreased. At higher temperature (300 °C), crystalline quality of NiO was significantly degraded and the film was decomposed into Ni. The EDS results confirmed an increase of Ni atomic percentage with increase of the substrate temperature. The surface morphology of NiO film at RT and at 100 °C displayed cubical like grains that were changed into elongated grains with further increase of the substrate temperature. The UV–vis reflectance measurements of NiO revealed a small decrease in its band gap by increasing the substrate temperature to 200 °C.     

Dielectric properties of low loss Ba<Subscript>6−3x</Subscript>Nd<Subscript>8+2x</Subscript>Ti<Subscript>18</Subscript>O<Subscript>54</Subscript> thin films prepared by pulsed laser deposition for microwave applications

Ba_6−3xNd_8+2xTi₁₈O₅₄ with x=0.25 (BNT-0.25, or simply, BNT) dielectric thin films with a thickness of 320 nm have been prepared on Pt-coated silicon substrates by pulsed laser deposition (PLD) at the substrate temperature of 650°C in 20 Pa oxygen ambient. X-ray analysis showed that the as-deposited films are amorphous and the films remain amorphous after a postannealing at 750°C for 30 min. The dielectric constant of the BNT films has been determined to be about 80 with a low loss tan δ of about 0.006 at 1 MHz. The capacitance-voltage (C-V), capacitance-frequency, and capacitance-temperature characteristics of a BNT capacitor with Pt top electrode were measured. A low leakage-current density of 4×10⁻⁶ A/cm² at 6 V was measured, and a preliminary discussion of the leakage-current mechanism is also given. It is proposed that amorphous BNT-0.25 thin films will be a potential dielectric material for microwave applications.