基于混合表面等离子体弯曲波导的紧凑型宽带偏振分束转换器的设计研究

设计了一种宽带的基于混合表面等离子体弯曲波导的偏振分束转换器, 使用有限元法计算硅波导、混合表面等离子体波导的模场分布和有效折射率, 为器件建模仿真分析提供了依据. 使用时域有限差分法优化器件结构, 以获得最佳的性能参数. 由于混合表面等离子体波导的双折射增强, 设计获得的偏振分束转换器具有超小尺寸和宽带的工作特性. 仿真结果表明 在1550nm的中心波长处消光比大于23dB, 插入损耗小于0.8dB; 在80nm的带宽上, 横磁偏振光转换为横电偏振光的偏振转换效率大于95％.     

A new formulation for fictitious mass of viscous dynamic relaxation method

Abstract

In this article, a new relationship is proposed for the fictitious mass of viscous dynamic relaxation (DR) method. First, incremental equations are derived for DR steps. Using transformed Gershgörin theory, a new relationship is achieved for fictitious mass of viscous DR by formulating modified time step ratio. This procedure presents a new algorithm for the viscous DR method. To evaluate the numerical efficiency of the proposed method, some 2D and 3D truss and frame structures are analyzed with elastic linear and geometrically nonlinear behaviors. Results show that by using the proposed algorithm for fictitious mass, the convergence rate of the viscous DR method is improved so that the proposed algorithm presents the structural response with lower iterations in comparison with other common DR techniques.

Communicated by Joerg Fehr.     

Advances in stable and flexible perovskite solar cells

Roll-to-roll (R2R) production is an innovative approach and is fast becoming a very popular industrial method for high throughput and mass production of solar cells. Replacement of costly indium tin oxide (ITO), which conventionally has served as the transparent electrode would be a great approach for roll to roll production of flexible cost effective solar cells. Indium tin oxide (ITO) and fluorine-doped tin oxide (FTO) are brittle and ultimately limit the device flexibility. Perovskite solar cells (PSCs) have been the centre of photovoltaic research community during the recent years owing to its exceptional performance and economical prices. The best reported PSCs fabricated by employing mesoporous TiO₂ layers require elevated temperatures in the range of 400–500 °C which limits its applications to solely glass substrates. In such a scenario developing flexible PSCs technology can be considered a suitable and exciting arena from the application point of view, them being flexible, lightweight, portable, and easy to integrate over both small, large and curved surfaces.     

Y掺杂WS2二维材料的第一性原理研究

WS₂由于其优异的物理和光电性质引起了广泛关注。本研究基于第一性原理计算方法,探索了本征单层WS₂及不同浓度W原子替位钇(Y)掺杂WS₂的电子结构和光学特性。结果表明本征单层WS₂为带隙1.814 eV的直接带隙半导体。进行4%浓度(原子数分数)的Y原子掺杂后,带隙减小为1.508 eV,依旧保持着直接带隙的特性,随着Y掺杂浓度的不断增大,掺杂WS₂带隙进一步减小,当浓度达到25%时,能带结构转变为0.658 eV的间接带隙,WS₂表现出磁性。适量浓度的掺杂可以提高材料的导电性能,且掺杂浓度增大时,体系依旧保持着透明性并且在红外光和可见光区对光子的吸收能力、材料的介电性能都有着显著提高。本文为WS₂二维材料相关光电器件的研究提供了理论依据。     

基于吸收互补有机半导体本体复合薄膜的高性能柔性光突触晶体管

采用光吸收互补的聚(3-己基噻吩)(P3HT)和引达省并二噻吩-苯并噻二唑共聚物(PIDT-BT), 通过溶液法制备了两者的本体复合异质结构有机半导体薄膜, 并研究了薄膜的表面结构和光电性质. 将PIDT-BT:P3HT复合薄膜作为一类新型光敏沟道层, 与聚电解质介电材料相结合, 制备了高性能柔性低电压光突触晶体管. 考察了不同光刺激条件对光突触晶体管性能的影响及半导体机制, 发现PIDT-BT:P3HT器件具有明显光突触特性, 并且相较于单纯PIDT-BT或P3HT器件具有更高响应的兴奋性突触后电流. 基于PIDT-BT:P3HT薄膜的光突触器件, 在绿红双色光刺激下的响应大于两种单色光分别刺激的响应之和, 表明附加光刺激可调控器件的记忆效率. 该研究为发展高性能光响应半导体薄膜及柔性低功耗光突触器件提供了新策略.     

Rational design of thermoelastic damping in microresonators with phase-lagging heat conduction law

The design of thermoelastic damping (TED) affected by the phase-lagging non-Fourier heat conduction effects becomes significant but challenging for enlarging the quality factor of widely-used microresonators operating in extreme situations, including ultra-high excitation frequency and ultra-low working temperature. However, there does not exist a rational method for designing the TED in the framework of non-Fourier heat conduction law. This work, therefore, proposes a design framework to achieve low thermoelastic dissipation of microresonators governed by the phase-lagging heat conduction law. The equation of motion and the heat conduction equation for phase-lagging TED microresonators are derived first, and then the non-Fourier TED design problem is proposed. A topology optimization-based rational design method is used to resolve the design problem. What is more, a two-dimensional (2D) plain-strain-based finite element method (FEM) is developed as a solver for the topology optimization process. Based on the suggested rational design technique, numerical instances with various phase lags are investigated. The results show that the proposed design method can remarkably reduce the dissipation of microresonators by tailoring their substructures.     

Graphene Nanoribbons from Tetraphenylethene‐Based Polymeric Precursor: Chemical Synthesis and Application in Thin‐Film Field‐Effect Transistor

Graphene nanoribbons (GNRs) with a non‐zero bandgap are regarded as a promising candidate for the fabrication of electronic devices. In this study, large‐scale solution synthesis of narrow GNRs was firstly achieved by the intramolecular cyclodehydrogenation of kinked tetraphenylethene (TPE) polymer precursors prepared by A₂B₂‐type Suzuki‐Miyaura polymerization. After the cyclization reaction, the nanoribbons have a better conjugation than the twisted polymer precursor, resulting in obvious red shift in UV/vis absorption and photoluminescence (PL) spectra. The efficient formation of conjugated nanoribbons was also investigated by Raman, FTIR spectroscopy, and microscopic studies. Furthermore, such structurally well‐defined GNRs have been successfully developed for top‐gated field‐effect transistor (FET) by directly solution processing. The AFM images show that the prepared‐GNRs thin films form crystalline fibrillar intercalating networks, which can effectively facilitate the charge transport. These FET devices with ion‐gel gate dielectrics exhibit low‐voltage operation (<5 V) with excellent mobility up to 0.41 cm²·V^?1·s^?1 and an on‐off ratio of 3×10⁴, thus opening up new opportunities for flexible GNRs‐based electronic devices.     

不同孪晶界密度银纳米线拉伸形变行为的分子动力学模拟

采用分子动力学方法模拟了不同孪晶界密度银纳米线的拉伸形变行为, 分析了孪晶界密度对多晶银纳米线屈服强度、弹性模量和塑性变形机理的影响. 在弹性形变区域, 孪晶界的存在对杨氏模量变化的作用不明显. 在塑性形变阶段, 首先从表面边缘开始产生位错成核, 然后延伸并受阻于孪晶界. 在进一步拉伸载荷作用下, 孪晶界将作为位错源产生新的位错. 模拟结果表明, 银纳米线的强度与孪晶界和晶粒的尺寸有关. 孪晶界密度较小(即晶粒的长径比大于1)时, 此纳米线的屈服应力比单晶纳米线还要小, 只有当孪晶界密度较大时(即晶粒的长径比小于1), 孪晶界使得纳米线得到强化. 综合分析了孪晶界和晶粒尺寸对银纳米线的影响, 为构建高强度金属纳米线打下基础. 最后讨论了温度和拉伸速度对孪晶纳米线屈服应力所产生的影响, 随着温度的升高, 孪晶纳米线与单晶纳米线的屈服应力差先升高后趋于稳定; 当拉伸速度逐渐增大, 孪晶纳米线与单晶纳米线的屈服应力差先稳定后增大.     

Realizing both High Energy and High Power Densities by Twisting Three Carbon‐Nanotube‐Based Hybrid Fibers

Energy storage devices, such as lithium‐ion batteries and supercapacitors, are required for the modern electronics. However, the intrinsic characteristics of low power densities in batteries and low energy densities in supercapacitors have limited their applications. How to simultaneously realize high energy and power densities in one device remains a challenge. Herein a fiber‐shaped hybrid energy‐storage device (FESD) formed by twisting three carbon nanotube hybrid fibers demonstrates both high energy and power densities. For the FESD, the energy density (50 mWh cm^?3 or 90 Wh kg^?1) many times higher than for other forms of supercapacitors and approximately 3 times that of thin‐film batteries; the power density (1 W cm^?3 or 5970 W kg^?1) is approximately 140 times of thin‐film lithium‐ion battery. The FESD is flexible, weaveable and wearable, which offers promising advantages in the modern electronics.