Electrowetting on paper for electronic paper display

The use of paper as a material for various device applications (such as microfluidics and energy storage) is very attractive given its flexibility, versatility, and low cost. Here we demonstrate that electrowetting (EW) devices can be readily fabricated on paper substrates. Several categories of paper have been investigated for this purpose, with the surface coating, roughness, thickness, and water uptake, among the most important properties. The critical parameter for EW devices is the water contact angle (CA) change with applied voltage. EW devices on paper exhibit characteristics very close to those of conventional EW devices on glass substrates. This includes a large CA change in oil ambient (90-95°), negligible hysteresis (～2°), and fast switching times of ～20 ms. These results indicate the promise of low-cost paper-based EW devices for video rate flexible e-paper on paper.     

“Electro‐Typing” on a Carbon‐Nanoparticles‐Filled Polymeric Film using Conducting Atomic Force Microscopy

Next‐generation electrical nanoimprinting of a polymeric data sheet based on charge trapping phenomena is reported here. Carbon nanoparticles (CNPs) (waste carbon product) are deployed into a polymeric matrix (polyaniline) (PANI) as a charge trapping layer. The data are recorded on the CNPs‐filled polyaniline device layer by “electro‐typing” under a voltage pulse (V_ET, from ±1 to ±7 V), which is applied to the device layer through a localized charge‐injection method. The core idea of this device is to make an electrical image through the charge trapping mechanism, which can be “read” further by the subsequent electrical mapping. The density of stored charges at the carbon–polyaniline layer, near the metal/polymer interface, is found to depend on the voltage amplitude, i.e., the number of injected charge carriers. The relaxation of the stored charges is studied by different probe voltages and for different devices, depending on the percolation of the CNPs into the PANI. The polymeric data sheet retains the recorded data for more than 6 h, which can be refreshed or erased at will. Also, a write–read–erase–read cycle is performed for the smallest “bit” of stored information through a single contact between the probe and the device layer.     

A fundamental study on electrowetting by traditional and multifunctional ionic liquids: possible use in electrowetting on dielectric-based microfluidic applications

Water or aqueous electrolytes are the dominant components in electrowetting on dielectric (EWOD)-based microfluidic devices. Low thermal stability, evaporation, and a propensity to facilitate corrosion of the metal parts of integrated circuits or electronics are drawbacks of aqueous solutions. The alternative use of ionic liquids (ILs) as electrowetting agents in EWOD-based applications or devices could overcome these limitations. Efficient EWOD devices could be developed using task-specific ILs. In this regard, a fundamental study on the electrowetting properties of ILs is essential. Therefore electrowetting properties of 19 different ionic liquids, including mono-, di-, and tricationic, plus mono- and dianionic ILs were examined. All tested ILs showed electrowetting of various magnitudes on an amorphous flouropolymer layer. The effects of IL structure, functionality, and charge density on the electrowetting properties were studied. The enhanced stability of ILs in electrowetting on dielectric at higher voltages was studied in comparison with water. Deviations from classical electrowetting theory were confirmed. The physical properties of ILs and their electrowetting properties were tabulated. These data can be used as references to engineer task-specific electrowetting agents (ILs) for future electrowetting-based applications.     

The design of a multi‐speed PSK modem

Abstract

Charge‐temperature, modified from bias‐temperature, technique is presented for the investigation of the interface properties of Al‐SiO₂‐Si (P) MOS capacitors. By using this technique, the change of interface trap states was found to be related to the treatment of charge‐temperature agin gand consequently the distribution of the mobile charges inside the oxide. An equivalent equation is expressed for the evaluation of interface trap states from the measured C‐V data. In addition, a two‐region model describing the distributions of the mobile charges of the capacitor after various charge‐temperature agings is proposed for the experimental observations. And the fitting results indicate that the effective Debye length due to interface trap states is about 20 Å.     

MEASUREMENT AND CONTROL OF ELECTROSTATIC CHARGES ON PULVERIZED COAL IN A PNEUMATIC PIPELINE∗

Abstract

Pulverized coal particles flowing in a pneumatic pipeline are naturally charged to a detectable level due to collisions with pipe walls. Systematic charge measurements of Anthracite (AN) coals, Medium Volatile Bituminous (MVB) coals and Lignite A (LIGA) coals in a grounded copper pipe have been made with an upgraded charge measuring system. The net particle charges were found to be positive, although both negative and positive charges were detected in all experiments. Effects of air humidity and conveying velocity on particle charges were examined. The mean particle charge was found in the order of 10^?12 Coulomb and the charge-to-mass ratio in the order of 10^?5 C/kg. Charge elimination techniques by strict humidity control and by introducing neutralizing charge carriers, such as minus 1 μm activated charcoal fines, ammonia, and piezoelectric ionized gas were explored. Effective reduction of 70 % to 85 % of particle charges was achieved. A charge neutralization mechanism was proposed to interpretate the measured results.     

Realization of High Performance AR‐coatings with Dust‐ and Water‐Repellent Properties

Hydrophobic coatings enable the manufacture of easy‐to‐clean surfaces having dust‐ and water‐repellent properties. In this work, a hydrophobic coating is deposited as a top layer on an antireflective (AR) multilayer system to produce low reflectance optical surfaces at a normal incident angle in the visible spectrum with dust‐ and water‐repellent properties for applications in precision optics. It is shown that the hydrophobic coating can be considered, from an optical point of view, as two adjacent thin layers having specific thicknesses and densities. In fact, the hydrophobic layer is one monolayer comprising molecular chains with anchoring groups responsible for the chemical bond with the substrate material and functional groups responsible for the water‐ and oil‐repellent properties. Their optical constants are determined and included in the final coating design. High performance AR coatings having an average reflectance of 0.14% at 7° incident angle in the 400‐680nm spectral range together with a pleasing purplered reflex color are produced. Coated lenses exhibit an excellent abrasion resistance, environmental stability, resistance to cleaning agents, homogeneity and water repellence with contact angles against water higher than 110°.     

Direct Probing of Polarization Charge at Nanoscale Level

Ferroelectric materials possess spontaneous polarization that can be used for multiple applications. Owing to a long‐term development of reducing the sizes of devices, the preparation of ferroelectric materials and devices is entering the nanometer‐scale regime. Accordingly, to evaluate the ferroelectricity, there is a need to investigate the polarization charge at the nanoscale. Nonetheless, it is generally accepted that the detection of polarization charges using a conventional conductive atomic force microscopy (CAFM) without a top electrode is not feasible because the nanometer‐scale radius of an atomic force microscopy (AFM) tip yields a very low signal‐to‐noise ratio. However, the detection is unrelated to the radius of an AFM tip and, in fact, a matter of the switched area. In this work, the direct probing of the polarization charge at the nanoscale is demonstrated using the positive‐up‐negative‐down method based on the conventional CAFM approach without additional corrections or circuits to reduce the parasitic capacitance. The polarization charge densities of 73.7 and 119.0 µC cm^?2 are successfully probed in ferroelectric nanocapacitors and thin films, respectively. The obtained results show the feasibility of the evaluation of polarization charge at the nanoscale and provide a new guideline for evaluating the ferroelectricity at the nanoscale.     

Polarization at metal–biomolecular interfaces in solution

Metal surfaces in contact with water, surfactants and biopolymers experience attractive polarization owing to induced charges. This fundamental physical interaction complements stronger epitaxial and covalent surface interactions and remains difficult to measure experimentally. We present a first step to quantify polarization on even gold (Au) surfaces in contact with water and with aqueous solutions of peptides of different charge state (A3 and Flg-Na3) by molecular dynamics simulation in all-atomic resolution and a posteriori computation of the image potential. Attractive polarization scales with the magnitude of atomic charges and with the length of multi-poles in the aqueous phase such as the distance between cationic and anionic groups. The polarization energy per surface area is similar on aqueous Au {1 1 1} and Au {1 0 0} interfaces of approximately −50 mJ m⁻² and decreases to −70 mJ m⁻² in the presence of charged peptides. In molecular terms, the polarization energy corresponds to −2.3 and −0.1 kJ mol⁻¹ for water in the first and second molecular layers on the metal surface, and to between −40 and 0 kJ mol⁻¹ for individual amino acids in the peptides depending on the charge state, multi-pole length and proximity to the surface. The net contribution of polarization to peptide adsorption on the metal surface is determined by the balance between polarization by the peptide and loss of polarization by replaced surface-bound water. On metal surfaces with significant epitaxial attraction of peptides such as Au {1 1 1}, polarization contributes only 10–20% to total adsorption related to similar polarity of water and of amino acids. On metal surfaces with weak epitaxial attraction of peptides such as Au {1 0 0}, polarization is a major contribution to adsorption, especially for charged peptides (−80 kJ mol⁻¹ for peptide Flg-Na₃). A remaining water interlayer between the metal surface and the peptide then reduces losses in polarization energy by replaced surface-bound water. Computed polarization energies are sensitive to the precise location of the image plane (within tenths of Angstroms near the jellium edge). The computational method can be extended to complex nanometre and micrometer-size surface topologies.     

Electrowetting‐Mediated Transport to Produce Electrochemical Transistor Action in Nanopore Electrode Arrays

Understanding water behavior in confined volumes is important in applications ranging from water purification to healthcare devices. Especially relevant are wetting and dewetting phenomena which can be switched by external stimuli, such as light and electric fields. Here, these behaviors are exploited for electrochemical processing by voltage‐directed ion transport in nanochannels contained within nanopore arrays in which each nanopore presents three electrodes. The top and middle electrodes (TE and ME) are in direct contact with the nanopore volume, but the bottom electrode (BE) is buried beneath a 70 nm silicon nitride (SiN_x) insulating layer. Electrochemical transistor operation is realized when small, defect‐mediated channels are opened in the SiN_x. These defect channels exhibit voltage‐driven wetting that mediates the mass transport of redox species to/from the BE. When BE is held at a potential maintaining the defect channels in the wetted state, setting the potential of ME at either positive or negative overpotential results in strong electrochemical rectification with rectification factors up to 440. By directing the voltage‐induced electrowetting of defect channels, these three‐electrode nanopore structures can achieve precise gating and ion/molecule separation, and, as such, may be useful for applications such as water purification and drug delivery.     

Highly efficient liquid droplet manipulation via human-motion-induced direct charge injection

The current electrowetting mechanisms show a low efficiency, although manipulating liquid droplets is essential to biological and chemical fields. Herein, we propose a highly efficient droplet manipulating method using direct charge injection (DCI) via human motion induced triboelectricity. A triboelectric nanogenerator (TENG) is used to provide both the charges and strong electric fields to drive the movement of liquid droplets. Using this method, the charge quantity and average velocity of the droplet (10 μL) reach 0.25 nC and 255 mm s⁻¹, respectively, over 6 times higher than those of traditional methods (0.03 nC and 43.2 mm s⁻¹). Alternative charge injection was demonstrated to enable both reciprocating and jumping motions of the droplet. Finally, we also successfully devised and demonstrated a platform with versatile system-level functions including droplets transportation, positioning, merging, and cleaning. This work advances the current droplet manipulation field via introducing a compelling approach using human-motion-induced direct charge injection.     

High‐Performance Polymers Sandwiched with Chemical Vapor Deposited Hexagonal Boron Nitrides as Scalable High‐Temperature Dielectric Materials

Polymer dielectrics are the preferred materials of choice for power electronics and pulsed power applications. However, their relatively low operating temperatures significantly limit their uses in harsh‐environment energy storage devices, e.g., automobile and aerospace power systems. Herein, hexagonal boron nitride (h ‐BN) films are prepared from chemical vapor deposition (CVD) and readily transferred onto polyetherimide (PEI) films. Greatly improved performance in terms of discharged energy density and charge–discharge efficiency is achieved in the PEI sandwiched with CVD‐grown h ‐BN films at elevated temperatures when compared to neat PEI films and other high‐temperature polymer and nanocomposite dielectrics. Notably, the h ‐BN‐coated PEI films are capable of operating with >90% charge–discharge efficiencies and delivering high energy densities, i.e., 1.2 J cm^?3, even at a temperature close to the glass transition temperature of polymer (i.e., 217 °C) where pristine PEI almost fails. Outstanding cyclability and dielectric stability over a straight 55 000 charge–discharge cycles are demonstrated in the h ‐BN‐coated PEI at high temperatures. The work demonstrates a general and scalable pathway to enable the high‐temperature capacitive energy applications of a wide range of engineering polymers and also offers an efficient method for the synthesis and transfer of 2D nanomaterials at the scale demanded for applications.     

Electron Transfer in Nanoscale Contact Electrification: Effect of Temperature in the Metal–Dielectric Case

The phenomenon of contact electrification (CE) has been known for thousands of years, but the nature of the charge carriers and their transfer mechanisms are still under debate. Here, the CE and triboelectric charging process are studied for a metal–dielectric case at different thermal conditions by using atomic force microscopy and Kelvin probe force microscopy. The charge transfer process at the nanoscale is found to follow the modified thermionic‐emission model. In particular, the focus here is on the effect of a temperature difference between two contacting materials on the CE. It is revealed that hotter solids tend to receive positive triboelectric charges, while cooler solids tend to be negatively charged, which suggests that the temperature‐difference‐induced charge transfer can be attributed to the thermionic‐emission effect, in which the electrons are thermally excited and transfer from a hotter surface to a cooler one. Further, a thermionic‐emission band‐structure model is proposed to describe the electron transfer between two solids at different temperatures. The findings also suggest that CE can occur between two identical materials owing to the existence of a local temperature difference arising from the nanoscale rubbing of surfaces with different curvatures/roughness.     

Charge Trapping-Based Electricity Generator (CTEG): An Ultrarobust and High Efficiency Nanogenerator for Energy Harvesting from Water Droplets

Strategies toward harvesting energy from water movements are proposed in recent years. Reverse electrowetting allows high efficiency energy generation, but requires external electric field. Triboelectric nanogenerators, as passive energy harvesting devices, are limited by the unstable and low density of tribo-charges. Here, a charge trapping-based electricity generator (CTEG) is proposed for passive energy harvesting from water droplets with high efficiency. The hydrophobic fluoropolymer films utilized in CTEG are pre-charged by a homogeneous electrowetting-assisted charge injection (h-EWCI) method, allowing an ultrahigh negative charge density of 1.8 mC m⁻². By utilizing a dedicated designed circuit to connect the bottom electrode and top electrode of a Pt wire, instantaneous currents beyond 2 mA, power density above 160 W m⁻², and energy harvesting efficiency over 11% are achieved from continuously falling water droplets. CTEG devices show excellent robustness for energy harvesting from water drops, without appreciable degradation for intermittent testing during 100 days. These results exceed previously reported values by far. The approach is not only applicable for energy harvesting from water droplets or wave-like oscillatory fluid motion, but also opens up avenues toward other applications requiring passive electric responses, such as diverse sensors and wearable devices.     

Penetration behaviour of individual hydrophilic particle at a gas–liquid interface

The penetration behaviour of a hydrophilic particle impacting on a gas–liquid interface was studied both experimentally and mathematically. The aim of this study was to determine the critical impact velocity below which a falling hydrophilic particle would remain on a horizontal liquid surface. A model to predict the critical velocity has been developed based on energy balance of both the particle and liquid volume in the vicinity of the impact zone. The model also includes the effect of hydrophobicitiy (contact angle) of the particle as well as the change in potential energy of the impacted liquid. Experiments were performed using spherical glass beads of diameter 0.97–1.66 mm, and using liquids with varying density (1000–1182 kg/m³), viscosity (1.002–4.796 mPa s) and surface tension (50.31–87.42 mN/m). High speed video camera was used to obtain the particle impact velocity, cavity profile and velocity of the three-phase contact line (TPCL) at the critical conditions. The TPCL line velocity and cavity profile were used as inputs for the model. The fitted advancing contact angle was employed in the model. It was found that the model was in good agreement with the experimental observations, and the fitted advancing contact angle agreed with the combined molecular-hydrodynamic model well.     

海南省嘉积大桥拆除爆破

对长达388m的海南省嘉积大桥的粗大钢筋混凝土桥墩实施爆破时,要使桥梁倒塌充分又不落入深水中是该工程的关键。通过采取综合技术措施,对直径达2.5m的重型布筋椭圆形桥墩实施了彻底的爆破,使河滩漫流区及浅水区的桥梁向一侧倾倒;爆后深水区桥梁整体垂直下落降低高度,落在桥墩承台上,避免了主梁折断及悬吊梁错位坠入水中,方便二次机械破碎及清碴。由于爆破方案和爆破参数设计合理、安全防护措施得当,大桥爆破取得圆满成功,为同类工程提供理论依据和经验参考。     

厚壁不等壁厚水池的水压爆破

介绍了厚壁、不等壁厚水池的水压爆破拆除。论述了采用水压爆破技术拆除这类水池时的药量计算、药包布置、入水深度,以及偏炸、起爆方法、爆破安全技术等,并对爆破效果进行了分析,可供同类工程参考。     

Charge‐Accumulation Effect in Transition Metal Dichalcogenide Heterobilayers

Charge transfer in transition‐metal‐dichalcogenides (TMDs) heterostructures is a prerequisite for the formation of interlayer excitons, which hold great promise for optoelectronics and valleytronics. Charge accumulation accompanied by a charge‐transfer process can introduce considerable effect on interlayer exciton‐based applications; nevertheless, this aspect has been rarely studied up to date. This work demonstrates how the charge accumulation affects the light emission of interlayer excitons in van der Waals heterobilayers (HBs) consisting of monolayer WSe₂ and WS₂. As excitation power increases, the photoluminescence intensity of interlayer excitons increases more rapidly than that of intralayer excitons. The phenomenon can be explained by charge‐accumulation effect, which not only increases the recombination probability of interlayer excitons but also saturates the charge‐transfer process. This scenario is further confirmed by a careful examination of trion binding energy of WS₂, which nonlinearly increases with the increase of the excitation power before reaching a maximum of about 75 meV. These investigations provide a better understanding of interlayer excitons and trions in HBs, which may provoke further explorations of excitonic physics as well as TMDs‐based devices.     

A Highly Emissive Surface Layer in Mixed‐Halide Multication Perovskites

Mixed‐halide lead perovskites have attracted significant attention in the field of photovoltaics and other optoelectronic applications due to their promising bandgap tunability and device performance. Here, the changes in photoluminescence and photoconductance of solution‐processed triple‐cation mixed‐halide (Cs_0.06MA_0.15FA_0.79)Pb(Br_0.4I_0.6)₃ perovskite films (MA: methylammonium, FA: formamidinium) are studied under solar‐equivalent illumination. It is found that the illumination leads to localized surface sites of iodide‐rich perovskite intermixed with passivating PbI₂ material. Time‐ and spectrally resolved photoluminescence measurements reveal that photoexcited charges efficiently transfer to the passivated iodide‐rich perovskite surface layer, leading to high local carrier densities on these sites. The carriers on this surface layer therefore recombine with a high radiative efficiency, with the photoluminescence quantum efficiency of the film under solar excitation densities increasing from 3% to over 45%. At higher excitation densities, nonradiative Auger recombination starts to dominate due to the extremely high concentration of charges on the surface layer. This work reveals new insight into phase segregation of mixed‐halide mixed‐cation perovskites, as well as routes to highly luminescent films by controlling charge density and transfer in novel device structures.     

Electrostatic electrochemistry at insulators

The identity of charges generated by contact electrification on dielectrics has remained unknown for centuries and the precise determination of the charge density is also a long-standing challenge. Here, electrostatic charges on Teflon (polytetrafluoroethylene) produced by rubbing with Lucite (polymethylmethacrylate) were directly identified as electrons rather than ions by electrochemical (redox) experiments with charged Teflon used as a single electrode in solution causing various chemical reactions: pH increases; hydrogen formation; metal deposition; Fe(CN)(6)(3-) reduction; and chemiluminescence in the system of Teflon(-)/Ru(bpy)(3)(2+)/S(2)O(8)(2-) (analogous to electrogenerated chemiluminescence). Moreover, copper deposition could be amplified by depositing Pd first in a predetermined pattern, followed by electroless deposition to produce Cu lines. This process could be potentially important for microelectronic and other applications because Teflon has desirable properties including a low dielectric constant and good thermal stability. Charge density was determined using Faraday's law and the significance of electron transfer processes on charged polymers and potentially other insulators have been demonstrated.     

Imaging the charge distribution within a single molecule

Scanning tunnelling microscopy and atomic force microscopy can be used to study the electronic and structural properties of surfaces, as well as molecules and nanostructures adsorbed on surfaces, with atomic precision, but they cannot directly probe the distribution of charge in these systems. However, another form of scanning probe microscopy, Kelvin probe force microscopy, can be used to measure the local contact potential difference between the scanning probe tip and the surface, a quantity that is closely related to the charge distribution on the surface. Here, we use a combination of scanning tunnelling microscopy, atomic force microscopy and Kelvin probe force microscopy to examine naphthalocyanine molecules (which have been used as molecular switches) on a thin insulating layer of NaCl on Cu(111). We show that Kelvin probe force microscopy can map the local contact potential difference of this system with submolecular resolution, and we use density functional theory calculations to verify that these maps reflect the intramolecular distribution of charge. This approach could help to provide fundamental insights into single-molecule switching and bond formation, processes that are usually accompanied by the redistribution of charge within or between molecules.