Ultrahigh electrical conductivity in solution-sheared polymeric transparent films

With consumer electronics transitioning toward flexible products, there is a growing need for high-performance, mechanically robust, and inexpensive transparent conductors (TCs) for optoelectronic device integration. Herein, we report the scalable fabrication of highly conductive poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) thin films via solution shearing. Specific control over deposition conditions allows for tunable phase separation and preferential PEDOT backbone alignment, resulting in record-high electrical conductivities of 4,600 ± 100 S/cm while maintaining high optical transparency. High-performance solution-sheared TC PEDOT:PSS films were used as patterned electrodes in capacitive touch sensors and organic photovoltaics to demonstrate practical viability in optoelectronic applications.Conductive films of high optical transparency are required in a myriad of applications, including electromagnetic shielding, antistatic layers, lighting displays, touch sensors, and as electrodes for photovoltaics (1, 2). As flexible, lightweight displays for televisions and portable consumer electronics become closer to reality, emerging transparent conductors (TCs) need to be mechanically robust (3). An ideal TC, therefore, should have a sheet resistance <100 Ω/□, transmissivity greater than 0.90, and be inherently flexible, all while remaining inexpensive to process on a mass scale (4).Indium tin oxide (ITO) is the most widely used TC material due to the combination of low sheet resistance and high transparency when grown on a variety of substrates. Although common to use, ITO is an expensive material due to the requirement for vacuum deposition and a number of postprocessing steps (5). For example, in organic photovoltaic (OPV) modules ITO was estimated to represent 24% of the module cost (6). However, alternative transparent conductor materials, such as poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) are estimated to comprise only ∼1% of an OPV module cost. Additionally, ITO is not compatible with flexible applications, because small applied strains of as little as 4.5% lead to an order of magnitude increase in the resistance (7).In recent years there have been a number of emerging TC materials studied in the literature ranging from metal nanowires (Au, Ag, Cu) (8–11), conducting carbon allotropes (graphene, carbon nanotubes) (12–15), conducting polymers (16, 17), and other hybrid approaches (18). Recent attempts using metal nanotroughs by Wu et al. have resulted in superior optoelectronic properties with a sheet resistance of 2 Ω/□ at 90% transmission (19). The use of metal mesoscale grids further enhanced the properties of metal nanowires electrodes to a sheet resistance of 0.36 Ω/□ at 92% transmission (20). Although metal nanowires combine low resistance and high transparency, they have inferior flexibility and stretchability compared with polymer-based TCs (3).PEDOT:PSS consists of insoluble PEDOT that is charge stabilized by PSS (Fig. 1A), which affords good solubility in aqueous formulations. Within these solutions, PEDOT:PSS forms micelles where hydrophilic PSS is in contact with water and hydrophobic PEDOT is located in the micelle core (21). Upon spin-coating from solution, the micelles are deposited as a film and can have conductivities on the order of ∼1 S/cm (22). Subsequent annealing, treatment with cosolvents, and postprocessing steps can increase the conductivity of films to over 3,000 S/cm (23, 24). High-performing spin-cast PEDOT:PSS TCs have reached a sheet resistance of 46 Ω/□ at 90% transmission (25, 26). Furthermore, it is compatible with flexible electronics as films can withstand over 90% applied strain without electrical breakdown (7).Open in a separate windowFig. 1.Schematic of solution shearing process. (A) Chemical structure of PEDOT:PSS. (B) Schematic of the solution shearing design and (C) patterning PEDOT:PSS via selective patterning of solvent wetting and dewetting regions.There is a wide variety of solution processing techniques used to deposit uniform, low-roughness films (27). Spin-casting is a popular laboratory-scale deposition technique due to its simplicity and ability to deposit high-quality films with a variety of materials. However, it is a batch process that is difficult to implement on a continuous mass production scale. Furthermore, it is difficult to use elevated substrate temperatures during spin-coating, a parameter that may play a role in the final film characteristics. Contrarily, scalable fabrication through solution shearing allows for tunable deposition conditions which enable enhanced kinetic control resulting in large impacts on the electrical performance of organic electronics (28–30).In this work we use solution shearing to fabricate high-performance TC PEDOT:PSS films (Fig. 1B). Tunable control of PEDOT backbone orientation, local ordering, and phase separation is demonstrated via precise control of the deposition parameters. Record-high PEDOT:PSS conductivities of 4,600 ± 100 S/cm are obtained and reach a sheet resistance of 17 ± 1 Ω/□ at 97.2 ± 0.4% transmission. A patterning method (Fig. 1C) is also developed which enables the use of high-conductivity transparent conductive films in capacitive pressure sensors and OPV devices.     

Overview of Electricity Transmission Conductors: Challenges and Remedies

Electricity transmission is an essential intermediary linking power generation and distribution. Voltage drops or total blackouts have always characterized the transmission and distribution of electricity in the sub-Saharan Africa and some Asian dwellers. This has been attributed partly to faulty, defective or dilapidated transmission conductors/networks. The aim of this study is to identify the causes of those defects in the transmission conductors and proffer possible remedies to them. Studies have shown that the current production techniques of transmission conductors (TCs) generate defective products, and that the materials used have their own challenges too. This work, therefore, reviewed all the production techniques and materials used in the development of TCs. It was observed that pultrusion, extrusion, hot-rolling, and stir-casting were the techniques used in the production of transmission conductors. Defects such as shrinkage, pores, impurities, and warps were identified in those techniques and some recommendations to ameliorate the defects of those techniques were presented. Spark plasma sintering is recommended as the most promising solid- state production techniques that should be adopted in fabricating transmission conductors, though it is yet to be developed for producing long-span products. In addition, advanced TCs materials such as Al-CNTs, Al-Nb, Al-Ti, and Al-B2 were presented as better alternatives to the existing TCs materials. By producing TCs with the recommended techniques and materials, the electricity availability will be enhanced; and this will lead to sustainable industrial growth and economic stability in the third world countries and the entire world.     

心脏电活动正问题仿真研究进展

近年来随着心脏疾病越来越为人们所重视，用心脏仿真模型研究各种心脏疾病的应用新研究成为热点；与此同时，在仿真理论方面也向着更加真实地反映复杂的人体环境和更加简单易操作两方面发展，研究者们发表了很多新的研究成果。从源、容积导体及算法等方面综述了心脏仿真建模理论的最新发展。     

Induced Current Bio-impedance Technique for Monitoring Bone Mineral Density—A Simulation Model

In this study, the feasibility of using induced current bio-impedance technique as a method to determine and monitor bone mineral density (BMD) was theoretically evaluated using computerized simulation model. A 2D polar coordinates numerical solver was developed using the Finite Volume Method (FVM) in order to simulate the developed potentials over an axial CT cross section of a human thigh. Varying femur BMD were simulated by varying femur relative permittivity values. At the chosen excitation current of 1 ampere at a frequency of 20 kHz, the real component of the surface potential was found to be more sensitive to BMD variation than the imaginary component (3.9 compared with 0.174 ). The correlation between varying femur permittivities and the real component of the developed surface potential was found to be quadratic and influenced by the coil geometry and the measuring point location. Measurement sensitivity was improved either by taking the measuring point closer to the femur location or by minimizing the distance between the excitation coil and the femur. These results provide the basic principle that may enable a future use of bio-impedance technique for bone density evaluation and monitoring.     

铁路机车乘务员心理健康状况Meta分析

目的了解我国铁路机车乘务员整体心理健康状况,为评价及干预铁路机车乘务员心理健康提供科学依据。方法计算机检索中国期刊全文数据库,收集国内近10年有关铁路机车乘务员心理健康状况研究的文献,对符合纳入条件的文献进行Meta分析,以全国男性常模及2006年全国三省区正常男性人群为对照,采用RevMan4.2软件进行数据统计分析。结果符合纳入标准的文献计11篇,总样本量共计4 681人。统计结果显示,铁路机车乘务员除人际关系一项与全国男性常模比较差异无统计学意义外(Z=1.31,P>0.05),其他各项因子得分均高于全国男性常模及我国三省区正常男性人群,且差异有统计学意义(P<0.01)。结论铁路机车乘务员心理健康状况总体水平较差,考虑机车乘务员职业的特殊性,其SCL-90常模有待建立。     

Densification of a NASICON-Type LATP Electrolyte Sheet by a Cold-Sintering Process

A NASICON-type Li_1.3Al_0.3Ti_1.7(PO₄)₃ (LATP) electrolyte sheet for all-solid-state batteries was fabricated by a cold sintering process (CSP). The microstructure of the LATP sheet was controlled to improve the wettability which is an essential factor in CSP. The porous sheets of LATP were prepared by calcination the green sheets to remove the organic components and form the porous structure. By the CSP using the porous sheets, the densification of grain boundary was observed and further densified with increasing reaction time. The total conductivity of the prepared LATP sheet was improved from 3.0 × 10⁻⁶ S/cm to 3.0 × 10⁻⁴ S/cm due to the formation of necks between the particles at the grain boundary.     

喷雾(冰冻)干燥法制备钠、锂快离子导体

对两种性能较好的快离子导体Na_3Zr_2Si_2P_3O_(12)(Nasicon)和Li_(1.8)Ti_(1.2)·Cr_(0.8)P_3O_(12)用喷雾干燥法和冰冻干燥法制备粉料和陶瓷烧结,并对样品进行了X射线衍射分析,形貌和显微结构观察以及阻抗谱测量等。实验结果表明:两种方法制备的粉料具有颗粒细,均匀性好,合成温度低等优点。在300℃时,两种样品的电阻半分别为10.05 Ω.cm和94.8 Ω.cm。激活能分别为0.25 eV和0.27ev。     

心阻抗血流图模型中电阻的计算方法

本文是我们建立一种心阻抗血流图技术新理论的系列研究之一，是正式论文的简要快讯。本文旨在判明常用电阻公式是否适用于心阻抗血流图模型。本文研究了套在园柱形均匀导体侧表面一对接到恒流源上的供电电极在此园柱体内产生的电势、电流以及套在园柱体侧表面另一对测量电极测得的电阻；最后将所得电阻公式与常用电阻公式作了对比。     

Systematics in Bi-2201, -2212 and -2223 superconductors studied by positron annihilation radiation measurements

Positron lifetimes in Bi₂Sr₂Ca_(n−1)Cu_nO_(2n+4+δ) or Bi-22(n−1)n superconducting compounds for n=1, 2 and 3 have been determined from positron annihilation lifetime (PAL) spectroscopy of associated γ-radiations. Bulk lifetime is shown to increase systematically with increase of n, the number of CuO₂-layers in the Bi-22(n−1)n compound. Positron annihilation probing of structural units of this perovskite-like crystal system has thus been demonstrated.