地物介电常数测量和分析

详细分析了基于矢量风络分析仪的同轴线探头介电常数测量系统和地物介电常数的测量方法。给出了几种典型地物（沙子、岩石、树木、棉叶）介电常数的测量和分析结果，并在模型进行了比较。本文实测数据可用于地物散射和辐射特性研究。     

Effects of Crystallinity in Spin‐On Pure‐Silica‐Zeolite MFI Low‐Dielectric‐Constant Films

Low‐dielectric‐constant (low‐κ) materials are a critical requirement for future generations of computer microprocessors. As a unique class of porous silicas, pure silica zeolites (PSZs) have been shown to be a promising low‐κ material with excellent mechanical strength (e.g., elastic modulus of 16–18 GPa) due to their crystalline nature. In the present study, we show for the first time that higher crystallinity of spin‐on PSZ MFI films leads to lower κ values and less moisture sensitivity—two critical properties of a porous low‐κ material. We have also advanced the two‐stage synthesis method to produce zeolite nanoparticles with high yield (77 %) and a small diameter (< 80 nm). A κ value of 1.6 is obtained from the silylated highly crystalline PSZ MFI film and the κ value only increases by 12.5 % after exposure to ambient conditions for a period of 24 h.     

Enhanced Initial Permeability and Dielectric Constant in a Double- Percolating Ni0.3Zn0.7Fe1.95O4–Ni– Polymer Composite

A novel, three-phase, double-percolating composite with NiZn-ferrite particles and nickel particles embedded in a poly(vinylidene fluoride) matrix is prepared by a simple hot-pressing method. Large ferrite particles in the composite not only act as a magnetic phase, thus endowing the composite with a high initial permeability, but also present (in a high volume fraction) a discrete (non-percolating) phase, confining polymer and metallic particles into a continuous double-percolating structure of low volume fraction. In particular, a large enhancement in both the initial permeability and the dielectric constant of the three-phase composites is observed, which is due mainly to the addition of a small number of nickel particles that act as both magnetic and percolative metallic phases. The dielectric and magnetic behavior observed in the three-phase composites can be explained by effective-medium and percolation theories.     

All‐Dielectric Programmable Huygens' Metasurfaces

Low‐loss nanostructured dielectric metasurfaces have emerged as a breakthrough platform for ultrathin optics and cutting‐edge photonic applications, including beam shaping, focusing, and holography. However, the static nature of their constituent materials has traditionally limited them to fixed functionalities. Tunable all‐dielectric infrared Huygens' metasurfaces consisting of multi‐layer Ge disk meta‐units with strategically incorporated non‐volatile phase change material Ge₃Sb₂Te₆ are introduced. Switching the phase‐change material between its amorphous and crystalline structural state enables nearly full dynamic light phase control with high transmittance in the mid‐IR spectrum. The metasurface is realized experimentally, showing post‐fabrication tuning of the light phase within a range of 81% of the full 2π phase shift. Additionally, the versatility of the tunable Huygen's metasurfaces is demonstrated by optically programming the spatial light phase distribution of the metasurface with single meta‐unit precision and retrieving high‐resolution phase‐encoded images using hyperspectral measurements. The programmable metasurface concept overcomes the static limitations of previous dielectric metasurfaces, paving the way for “universal” metasurfaces and highly efficient, ultracompact active optical elements like tunable lenses, dynamic holograms, and spatial light modulators.     

基于7600Plus和LD-3测量介电常数的几种方法

文章描述了测摄嗣体介质和液体材料介电常数的集成系统。系统由7600Hus和LD-3构成。多种测量固体样本的介电常数方法，也包括测蟹液体样本介电常数的方法。     

High Electromechanical Response of Ionic Polymer Actuators with Controlled‐Morphology Aligned Carbon Nanotube/Nafion Nanocomposite Electrodes

Recent advances in fabricating controlled‐morphology vertically aligned carbon nanotubes (VA‐CNTs) with ultrahigh volume fraction create unique opportunities for markedly improving the electromechanical performance of ionic polymer conductor network composite (IPCNC) actuators. Continuous paths through inter‐VA‐CNT channels allow fast ion transport, and high electrical conduction of the aligned CNTs in the composite electrodes lead to fast device actuation speed (>10% strain/second). One critical issue in developing advanced actuator materials is how to suppress the strain that does not contribute to the actuation (unwanted strain) thereby reducing actuation efficiency. Here, experiments demonstrate that the VA‐CNTs give an anisotropic elastic response in the composite electrodes, which suppresses the unwanted strain and markedly enhances the actuation strain (>8% strain under 4 V). The results reported here suggest pathways for optimizing the electrode morphology in IPCNCs using ultrahigh volume fraction VA‐CNTs to further enhanced performance.     

The Dielectric Constant of Self‐Assembled Monolayers

Self‐assembled monolayers (SAMs) are fundamental building blocks of molecular electronics and find numerous applications in organic (opto)electronic devices. Their properties are decisively determined by their response to electric fields, which are either applied externally (e.g., when biasing devices) or originate from within the monolayer itself in case it consists of dipolar molecules (which are used to tune charge‐injection barriers). This response is typically described by the dielectric constant of the monolayer. In this work it is explicitly show that there is no “general” dielectric constant that simultaneously applies to both cases. This is first derived on the basis of density‐functional theory (DFT) calculations for substituted biphenyl‐thiol SAMs at varying packing densities. Depolarization effects, which play a crucial role for the dielectric properties of the monolayers, are subsequently analyzed on the basis of packing‐dependent charge rearrangements. Finally, the DFT results are rationalized using an electrostatic model. In this context, the importance of finite‐size effects is highlighted and a connection between the macroscopic dielectric properties and the molecular polarizability is established providing a monolayer equivalent to the Clausius–Mossotti relationship. This allows deriving general trends for the packing‐density dependent dielectric response of monolayers to both external and internal electric fields.     

High Electroactive Material Loading on a Carbon Nanotube@3D Graphene Aerogel for High‐Performance Flexible All‐Solid‐State Asymmetric Supercapacitors

Freestanding carbon‐based hybrids, specifically carbon nanotube@3D graphene (CNTs@3DG) hybrid, are of great interest in electrochemical energy storage. However, the large holes (about 400 µm) in the commonly used 3D graphene foams (3DGF) constitute as high as 90% of the electrode volume, resulting in a very low loading of electroactive materials that is electrically connected to the carbon, which makes it difficult for flexible supercapacitors to achieve high gravimetric and volumetric energy density. Here, a hierarchically porous carbon hybrid is fabricated by growing 1D CNTs on 3D graphene aerogel (CNTs@3DGA) using a facile one‐step chemical vapor deposition process. In this architecture, the 3DGA with ample interconnected micrometer‐sized pores (about 5 µm) dramatically enhances mass loading of electroactive materials comparing with 3DGF. An optimized all‐solid‐state asymmetric supercapacitor (AASC) based on MnO₂@CNTs@3DGA and Ppy@CNTs@3DGA electrodes exhibits high volumetric energy density of 3.85 mW h cm^?3 and superior long‐term cycle stability with 84.6% retention after 20 000 cycles, which are among the best reported for AASCs with both electrodes made of pseudocapacitive electroactive materials.     

Biocompatible Electromechanical Actuators Composed of Silk‐Conducting Polymer Composites

Single‐component, metal‐free, biocompatible, electromechanical actuator devices are fabricated using a composite material composed of silk fibroin and poly(pyrrole) (PPy). Chemical modification techniques are developed to produce free‐standing films with a bilayer‐type structure, with unmodified silk on one side and an interpenetrating network (IPN) of silk and PPy on the other. The IPN formed between the silk and PPy prohibits delamination, resulting in a durable and fully biocompatible device. The electrochemical stability of these materials is investigated through cyclic voltammetry, and redox sensitivity to the presence of different anions is noted. Free‐end bending actuation performance and force generation within silk‐PPy composite films during oxidation and reduction in a biologically relevant environment are investigated in detail. These silk–PPy composites are stable to repeated actuation, and are able to generate forces comparable with natural muscle (>0.1 MPa), making them ideal candidates for interfacing with biological tissues.     

Multiferroic Polymer Laminate Composites Exhibiting High Magnetoelectric Response Induced by Hydrogen‐Bonding Interactions

The coupling of the magnetic, electric, and elastic properties in multiferroics creates new collective phenomena and enables next‐generation device paradigms. In this work, the hydrogen bonding interaction between hydrate salts and ferroelectric polymers is exploited in the development of high‐performance magnetoelectric (ME) polymer laminate composites. The microstructures and crystallite structures of the Al(NO₃)₃·9H₂O doped poly(vinylidene fluoride‐co‐hexafluoropropylene), P(VDF‐HFP), are carefully studied. The effect of hydrogen bonding interaction on the polarization ordering of the ferroelectric polymers is investigated by 2D wide‐angle X‐ray diffraction, polarized Fourier transform infrared spectra, and dielectric spectra at varied frequencies and temperatures. It is found that hydrogen bond not only promotes the formation of the polar crystallite phase but also improves the polarization ordering in the ferroelectric polymer, which subsequently increases the remnant polarization of the polymers as verified in the polarization‐electric field loop measurements. These entail marked improvement in the ME voltage coefficients (α_ME) of the resulting polymer laminate composites based on ferromagnetic Metglas relative to analogous composites. The composite exhibits a state‐of‐the‐art α_ME value of 20 V cm^‐1 Oe under a dc magnetic field of ≈4 Oe and a colossal α_ME of 320 V cm^‐1 Oe at a frequency of 68 kHz.     

Dielectric constant of barium titanate/cyanoethyl ester of polyvinyl alcohol composite in comparison with the existing theoretical models

A unique method has been introduced to measure the dielectric constant of polymer/ceramic composites using an effective medium instead of using the general methods of preparing bulk sintered pellets or films. In this work, a new and a simple method has been applied to measure the dielectric constant of polyvinyl cyanoethylate/barium titanate composites. The results are obtained by dispersing the ceramic powders in the polymer of a relatively low dielectric constant value. The dielectric constant of the composites is measured with varying ceramic volume percentages. The obtained results are compared with the many available theoretical models that are generally in practice to predict the dielectric constant of the composites. Then these results are extrapolated to comprehend the dielectric constant values of ceramic particles as these values form the base for the design of the composite. The precision and simplicity of the method can be exploited for predictions of the properties of nanostructure ferroelectric polymer/ceramic composites.     

Charge Recombination Dynamics in Organic Photovoltaic Systems with Enhanced Dielectric Constant

Increasing the dielectric constant of organic photovoltaic materials to reduce recombination rates has long been pursued, however, material modification often results in the modification of multiple device characteristics, making system comparison difficult. In this study, a fullerene derivative with an increased blend dielectric constant is examined by the addition of a triethylene glycol appendage to the fullerene (TEG‐PCBM). Density functional theory calculations show a small change to the permanent dipole moment between TEG‐PCBM and [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PC₆₀BM) resulting in similar solubility, morphology, and device performance. TEG‐PCBM is blended with donors P3HT and PTB7‐Th and a comparable performance to PC₆₀BM is found. This model system shows the rarely reported characteristic of an increase in the dielectric constant while leaving its other properties unaltered. Looking at light intensity effects on open‐circuit voltage (V_oc), short‐circuit current (J_sc), and fill factor (FF) along with exciton dissociation efficiency, it is observed that when switching to the TEG‐ modified fullerene derivative, geminate recombination is not reduced, and Shockley–Read–Hall recombination is increased. While triethlyene glycol appendages may prove to be ineffective in improving recombination through increased dielectric constant, an approach for studying recombination in future high dielectric systems is provided.     

Novel Film‐Casting Method for High‐Performance Flexible Polymer Electrodes

A new film‐casting method for polymer electrodes is reported, in which thickness‐controlled drop‐casting (TCDC), using polyaniline doped with camphorsulfonic acid (PANI:CSA) is used. By combining the advantages of conventional spin‐casting and drop‐casting methods, and by rigorously controlling the film formation parameters, flexible polymer electrodes with high conductivity and excellent transmittance can be produced. The PANI:CSA electrodes cast by the TCDC method exhibited constant thickness‐independent conductivities of ～600 S cm^?1 down to a film thickness of 0.2 μm, and a high optical transmittance of about 85% at 550 nm. Furthermore, the new casting method significantly reduced the sheet resistance (～90 Ω/square) of the PANI:CSA electrodes compared with the conventional spin‐cast films, enhancing the performance of the devices deposited on plastic substrates. The flexible polymer light‐emitting diode produced a brightness of 6000 cd m^?2, and the flexible polymer solar cell exhibited a power conversion efficiency of 2%, both of which were much higher than those of the devices fabricated by the conventional spin‐casting method.     

高介电常数材料在半导体存储器件中的应用

高介电常数材料是当前微电子行业最热门的研究课题之一。它的应用为解决当前半导体器件尺寸缩小导致的栅氧层厚度极限问题提供了可能性 ,同时利用一些高介电常数材料具有的特殊物理特性 ,可实现具有特殊性能的新型器件。文中主要介绍几类常用的高介电常数材料的特性和制备方法 ,及其在半导体存储器件中的应用和前沿课题     

Generation of Compositional‐Gradient Structures in Biodegradable,Immiscible, Polymer Blends by Intermolecular Hydrogen‐Bonding Interactions

A biodegradable, immiscible poly(butylenes adipate‐co‐butylenes terephthalate) [P(BA‐co‐BT)]/poly(ethylene oxide) (PEO) polymer blend film with compositional gradient in the film‐thickness direction has been successfully prepared in the presence of a low‐molecular‐weight compound 4,4′‐thiodiphenal (TDP), which is used as a miscibility‐enhancing agent. The miscibilities of the P(BA‐co‐BT)/PEO/TDP ternary blend films and the P(BA‐co‐BT)/PEO/TDP gradient film were investigated by differential scanning calorimetry (DSC). The compositional gradient structure of the P(BA‐co‐BT)/PEO/TDP (46/46/8 w/w/w) film has been confirmed by microscopic mapping measurement of Fourier‐transform infrared spectra and dynamic mechanical thermal analysis. We have developed a new strategy for generating gradient‐phase structures in immiscible polymer‐blend systems by homogenization, i.e., adding a third agent that can enhance the miscibility of the two immiscible polymers through simultaneous formation of hydrogen bonds with two component polymers.     

Substantial Recoverable Energy Storage in Percolative Metallic Aluminum‐Polypropylene Nanocomposites

Chemisorption of the activated metallocene polymerization catalyst derived from [rac‐ethylenebisindenyl]zirconium dichlororide (EBIZrCl₂) on the native Al₂O₃ surfaces of metallic aluminum nanoparticles, followed by exposure to propylene, affords 0–3 metal‐isotactic polypropylene nanocomposites. The microstructures of these nanocomposites are characterized by X‐ray diffraction, transmission electron microscopy, scanning electron microscopy, and atomic force microscopy. Electrical measurements show that increasing the concentration of the filler nanoparticles increases the effective permittivity of the nanocomposites to ?_r values as high as 15.4. Because of the high contrast in the complex permittivities and conductivities between the metallic aluminum nanoparticles and the polymeric polypropylene matrix, these composites obey the percolation law for two‐phase composites, reaching maximum permittivities just before the percolation threshold volume fraction, v_f ≈ 0.16. This unique method of in situ polymerization from the surface of metallic Al particles produces a new class of materials that perform as superior pulse‐power capacitors, with low leakage current densities of ≈10^?7–10^?9 A/cm² at an applied field of 10⁵ V/cm, low dielectric loss in the 100 Hz–1 MHz frequency range, and recoverable energy storage as high as 14.4 J/cm³.     

High‐Energy‐Density Dielectric Polymer Nanocomposites with Trilayered Architecture

The development of advanced dielectric materials with high electric energy densities is of crucial importance in modern electronics and electric power systems. Here, a new class of multilayer‐structured polymer nanocomposites with high energy and power densities is presented. The outer layers of the trilayered structure are composed of boron nitride nanosheets dispersed in poly(vinylidene fluoride) (PVDF) matrix to provide high breakdown strength, while PVDF with barium strontium titanate nanowires forms the central layer to offer high dielectric constant of the resulting composites. The influence of the filler contents on the electrical polarization, breakdown strength, and energy density is examined. Simulations are carried out to model the electrical tree formation in the layered nanocomposites and to verify the experimental breakdown results. The trilayered polymer nanocomposite with an optimized filler content displays a discharged energy density of 20.5 J cm^?3 at Weibull breakdown strength of 588 MV m^?1, which is among the highest discharged energy densities reported so far. Moreover, the nanocomposite exhibits a superior power density of 0.91 MW cm^?3, more than nine times that of the commercially available biaxially oriented polypropylene. The findings of this research provide a new design paradigm for high‐performance dielectric polymer nanocomposites.     

Nanoporous Low‐κ Polyimide Films via Poly(amic acid)s with Grafted Poly(ethylene glycol) Side Chains from a Reversible Addition–Fragmentation Chain‐Transfer‐Mediated Process

Thermally‐initiated living radical graft polymerization of poly(ethylene glycol) methyl ether methacrylate (PEGMA) with ozone‐pretreated poly[N,N′‐(1,4‐phenylene)‐3,3′,4,4′‐benzophenonetetra‐carboxylic amic acid] (PAmA) via a reversible addition–fragmentation chain‐transfer (RAFT)‐mediated process was carried out. The chemical compositions and structures of the copolymers were characterized by nuclear magnetic resonance (NMR) spectroscopy, thermogravimetric analysis (TGA), X‐ray photoelectron spectroscopy (XPS), and molecular weight measurements. The “living” character of the grafted PEGMA side chains was ascertained in the subsequent extension of the PEGMA side chains. Nanoporous low‐dielectric‐constant (low‐κ) polyimide (PI) films were prepared by thermal imidization of the PAmA graft copolymers under reduced argon pressure, followed by thermal decomposition of the side chains in air. The nanoporous PI films obtained from the RAFT‐mediated graft copolymers had well‐preserved PI backbones, porosity in the range of 5–17 %, and pore size in the range of 30–50 nm. The pores were smaller and the pore‐size distribution more uniform than those of the corresponding nanoporous PI films obtained via graft copolymers from conventional free‐radical processes. Dielectric constants approaching 2 were obtained for the nanoporous PI films prepared from the RAFT‐mediated graft copolymers.     

Wood‐Inspired 3D‐Printed Helical Composites with Tunable and Enhanced Mechanical Performance

Helical fibers are versatile building blocks used by Nature to improve mechanical performance and to tune local behavior of load‐bearing materials. Helicoidal biocomposites are arranged in multiple layers with different fiber orientations. Such heterogeneity, not matched in synthetic materials, provides biological structures with superior properties. This is the case of the multilayer tube‐like structure of the wood cell wall, where each ply features a compliant matrix reinforced by stiff helicoidal microfibrils. Here, 3D polyjet printing and computer simulations are combined to investigate wood‐inspired helix‐reinforced cylinders. Composites with a main layer containing helicoidal fibers, bordered by inner and outer plies having thinner fibrils are considered. It is shown how the mechanical functionalities of the synthetic structures can be programmed by varying fibers/fibrils orientation and matrix compliance. It is demonstrated that failure resistance can be enhanced by enclosing the main helicoidal layer with a minimum amount of thin fibrils oriented perpendicular to the applied load, as observed in wood. Finite element simulations are used to highlight the critical role of the matrix in load‐transfer mechanisms among stiff elements. These structures have the potential to be assembled into larger systems, leading to graded composites with region‐specific properties optimized for multiple functionalities.     

One‐ and Two‐Dimensionally Structured Polymer Networks in Liquid Crystals for Switchable Diffractive Optical Applications

We have created one‐ and two‐dimensionally structured polymer networks dispersed in a liquid‐crystal solvent using a holographic exposure technique. These structures have potential for electrically switchable, reverse‐mode, polarization selective and non‐selective diffractive optical elements. Using a simple phenomenological model to describe our diffraction measurements in conjunction with microscopic studies, we are able to estimate the structured polymer wall thickness as a function of monomer concentration.