Materials and Structures for Stretchable Energy Storage and Conversion Devices

Stretchable energy storage and conversion devices (ESCDs) are attracting intensive attention due to their promising and potential applications in realistic consumer products, ranging from portable electronics, bio‐integrated devices, space satellites, and electric vehicles to buildings with arbitrarily shaped surfaces. Material synthesis and structural design are core in the development of highly stretchable supercapacitors, batteries, and solar cells for practical applications. This review provides a brief summary of research development on the stretchable ESCDs in the past decade, from structural design strategies to novel materials synthesis. The focuses are on the fundamental insights of mechanical characteristics of materials and structures on the performance of the stretchable ESCDs, as well as challenges for their practical applications. Finally, some of the important directions in the areas of material synthesis and structural design facing the stretchable ESCDs are discussed.     

含预埋梁蜂窝夹层结构数值仿真与试验研究

含预埋梁蜂窝夹层结构是在纯蜂窝结构基础上改进得到的全新结构形式,综合了蜂窝结构和桁条铆接结构的优点,但该类结构的载荷分布形式以及失效模式缺乏相关研究。针对上述问题,结合国内在研尺寸最大的含预埋梁铝蜂窝夹层结构,采用层合板加筋方法进行了数值仿真,设计全尺寸物理试验对结构性能进行了试验验证。通过数值仿真和试验对比,验证了层合板加筋方法模拟含预埋梁蜂窝结构的准确性,同时研究了该类结构的载荷分布和失效模式,并为同类结构设计提供了参考依据。     

Multilevel Hierarchically Ordered Artificial Biomineral

Living organisms are known for creating complex organic–inorganic hybrid materials such as bone, teeth, and shells, which possess outstanding functions as compared to their simple mineral forms. This has inspired many attempts to mimic such structures, but has yielded few practical advances. In this study, a multilevel hierarchically ordered artificial biomineral (a composite of hydroxyapatite and gelatine) with favorable nanomechanical properties is reported. A typical optimized HAp/gelatin hybrid material in the perpendicular direction of the HAp c‐axis has a modulus of 25.91 + 1.78 GPa and hardness of 0.90 + 0.10 GPa, which well matches that of human cortical bone (modulus 24.3 + 1.4 GPa, hardness 0.69 + 0.05 GPa). The bottom‐up crystal constructions (from nano‐ to micro‐ to macroscale) of this material are achieved through a hard template approach by the phase transformation from DCP to HAp. The structural biomimetic material shows another way to mimic the complex hierarchical designs of sclerous tissues which have potential value for application in hard tissue engineering.     

Wafer‐Scale Double‐Layer Stacked Au/Al2O3@Au Nanosphere Structure with Tunable Nanospacing for Surface‐Enhanced Raman Scattering

Fabricating perfect plasmonic nanostructures has been a major challenge in surface enhanced Raman scattering (SERS) research. Here, a double‐layer stacked Au/Al₂O₃@Au nanosphere structures is designed on the silicon wafer to bring high density, high intensity “hot spots” effect. A simply reproducible high‐throughput approach is shown to fabricate feasibly this plasmonic nanostructures by rapid thermal annealing (RTA) and atomic layer deposition process (ALD). The double‐layer stacked Au nanospheres construct a three‐dimensional plasmonic nanostructure with tunable nanospacing and high‐density nanojunctions between adjacent Au nanospheres by ultrathin Al₂O₃ isolation layer, producing highly strong plasmonic coupling so that the electromagnetic near‐field is greatly enhanced to obtain a highly uniform increase of SERS with an enhancement factor (EF) of over 10⁷. Both heterogeneous nanosphere group (Au/Al₂O₃@Ag) and pyramid‐shaped arrays structure substrate can help to increase the SERS signals further, with a EF of nearly 10⁹. These wafer‐scale, high density homo/hetero‐metal‐nanosphere arrays with tunable nanojunction between adjacent shell‐isolated nanospheres have significant implications for ultrasensitive Raman detection, molecular electronics, and nanophotonics.     

Structural Defects Control the Energy Level Alignment at Organic/Organic Interfaces

The dependence of the energy level alignment (ELA) on structural defects at an organic/organic heterojunction (OOH) of perfluoropentacene (PFP)‐on‐diindenoperylene (DIP) was investigated using X‐ray scattering and ultraviolet photoelectron spectroscopy. The density of structural defects near the interface between the PFP and DIP layers was varied by changing the growth temperature of the DIP film. A direct relationship was found between the defect density and the ELA at the OOH; the ELA together with the change in the electrostatic potential (quasi‐interface dipole layer) at the OOH varies systematically with the defect density near the interface. This indicates that a key factor affecting the ELA is the electrostatic potential change across the OOH interface, which is produced by electron transfer from DIP occupied gap states to PFP unoccupied gap states. These gap states originate from the defects and are effectively controlled by adjusting the growth conditions of the organic films. As a result, the ELA at OOH interfaces can be controlled by the density of structural defect, which is important for organic devices employing OOHs, such as organic photovoltaic cells.     

On the degree of completeness of cryptographic functions

This paper discusses the degree of completeness of cryptographic functions, which is one of the cryptographic criteria should be considered in the design of stream ciphers. We establish the re- lationships between the degree of completeness and other cryptographic criteria. For resilient Boolean functions, a method to enhance the degree of completeness is proposed, while the nonlinearity and the algebraic degree do not decrease. Moreover, two constructions of resilient functions are provided, which have optimal degree of completeness, high nonlinearity, and high algebraic degree.     

Core–Shell Si/C Nanospheres Embedded in Bubble Sheet‐like Carbon Film with Enhanced Performance as Lithium Ion Battery Anodes

Due to its high theoretical capacity and low lithium insertion voltage plateau, silicon has been considered one of the most promising anodes for high energy and high power density lithium ion batteries (LIBs). However, its rapid capacity degradation, mainly caused by huge volume changes during lithium insertion/extraction processes, remains a significant challenge to its practical application. Engineering Si anodes with abundant free spaces and stabilizing them by incorporating carbon materials has been found to be effective to address the above problems. Using sodium chloride (NaCl) as a template, bubble sheet‐like carbon film supported core–shell Si/C composites are prepared for the first time by a facile magnesium thermal reduction/glucose carbonization process. The capacity retention achieves up to 93.6% (about 1018 mAh g^?1) after 200 cycles at 1 A g^?1. The good performance is attributed to synergistic effects of the conductive carbon film and the hollow structure of the core–shell nanospheres, which provide an ideal conductive matrix and buffer spaces for respectively electron transfer and Si expansion during lithiation process. This unique structure decreases the charge transfer resistance and suppresses the cracking/pulverization of Si, leading to the enhanced cycling performance of bubble sheet‐like composite.