Enhanced Microwave Absorption Performance from Magnetic Coupling of Magnetic Nanoparticles Suspended within Hierarchically Tubular Composite

The microwave absorption (MA) performance of carbon materials is severely hindered by their drawbacks of lacking magnetic loss ability and mismatched electromagnetic impedance. In this work, utilizing sustainable biomass kapok as a template, the hierarchically tubular C/Co nanoparticle composite is rationally constructed to acquire the enhanced MA performance for the first time. The fruit‐tree‐like hierarchical structure is composed from a “trunk” of kapok‐derived carbon microtubes, a “branch” of entangled carbon nanotubes, and “fruit” of Co nanoparticles embedded in the nanotubes. Such a hierarchically tubular structure offers the composite: i) a submillimeter‐scale 3D magnetic coupling network and reinforced magnetic loss ability, ii) a hierarchical dielectric carbon network, iii) better matched impedance, confirmed by the off‐axis electron holography and micromagnetic simulation. Accordingly, the as‐prepared hierarchically tubular carbon composite demonstrates impressive MA performance, with a maximum reflection loss of as much as ?52.3 dB and a broad absorption bandwidth of 5.1 GHz. These encouraging achievements light the way to the development of the hierarchical microstructure of magnetic absorbents.     

Calcite Prisms from Mollusk Shells (Atrina Rigida): Swiss‐cheese‐like Organic–Inorganic Single‐crystal Composites

Biogenic single‐crystal composites, such as sea urchin spines and calcitic prisms from mollusk shells, contain organic macromolecules inside of inorganic single‐crystal matrices. The nanoscale internal structure of these materials, however, is poorly understood, especially how the biomacromolecules are distributed within the crystals without significantly disrupting the crystalline lattice. Here, annular dark‐field scanning transmission electron microscopy and electron tomography reveal, in three dimensions, how biomacromolecules are distributed within the calcitic prisms from Atrina rigida shells. Disk‐like nanopatches, whose scattering intensity is consistent with organic inclusions, are observed to be anisotropically arranged within a continuous, single‐crystalline calcite matrix. These nanopatches are preferentially aligned with the (000l) planes of calcite. Along the crystallographic c‐axis, there are alternating organic‐rich and ‐poor regions on a length scale of tens of nanometers, while, in the ab plane, the distribution of nanopatches is more random and uniform. The structural features elucidated in this work have relevance to understanding the structure–property relationships and formation mechanisms of biominerals, as well as to the development of bio‐inspired strategies to extrinsically tune the properties of single‐crystals.     

Uniform Magnetic Chains of Hollow Cobalt Mesospheres from One‐Pot Synthesis and Their Assembly in Solution

Magnetic chains up to 10 μm in length formed of hollow cobalt mesospheres (480–850 nm) with a 60 nm thick shell are synthesized by a new soft‐assembly protocol. The obtained chains show a saturation magnetization of 37.5 emu g^–1, a remnant magnetization of 1.55 emu g^–1, and a coercivity of ca. 66 Oe at 300 K. A possible mechanism for the formation of the chainlike hollow structures is proposed.     

Air‐Operable,High‐Mobility Organic Transistors with Semifluorinated Side Chains and Unsubstituted Naphthalenetetracarboxylic Diimide Cores: High Mobility and Environmental and Bias Stress Stability from the Perfluorooctylpropyl Side Chain

N,N′‐bis(3‐(perfluoroctyl)propyl)‐1,4,5,8‐naphthalenetetracarboxylic acid diimide (8–3‐NTCDI) was newly synthesized, as were related fluorooctylalkyl‐NTCDIs and alkyl‐NTCDIs. The 8–3‐NTCDI‐based organic thin‐film transistor (OTFT) on an octadecyltrimethoxysilane (OTS)‐treated Si/SiO₂ substrate shows apparent electron mobility approaching 0.7 cm² V^‐1s^‐1 in air. The fluorooctylethyl‐NTCDI (8–2‐NTCDI) and fluorooctylbutyl‐NTCDI (8–4‐NTCDI) had significantly inferior properties even though their chemical structures are only slightly different, and nonfluorinated decyl and undecyl NTCDIs did not operate predictably in air. From atomic force microscopy, the 8–3‐NTCDI active layer deposited with the substrate at 120 °C forms a polycrystalline film with grain sizes >4μm. Mobilities were stable in air for one week. After 100 days in air, the average mobility of three OTFTs decreased from 0.62 to 0.12 cm² V^‐1s^‐1, but stabilized thereafter. The threshold voltage (V_T) increased by 15 V in air, but only by 3 V under nitrogen, after one week. On/off ratios were stable in air throughout. We also investigated transistor stability to gate bias stress. The transistor on hexamethlydisilazane (HMDS) is more stable than that on OTS with mobility comparable to amorphous Si TFTs. V_T shifts caused by ON (30 V) and OFF (–20 V) gate bias stress for the HMDS samples for 1 hour were 1.79 V and 1.27 V under N₂, respectively, and relaxation times of 10⁶ and 10⁷ s were obtained using the stretched exponential model. These performances are promising for use in transparent display backplanes.     

Grain boundary segregation in multicrystalline silicon: correlative characterization by EBSD,EBIC, and atom probe tomography

This study aims to better understand the influence of crystallographic structure and impurity decoration on the recombination activity at grain boundaries in multicrystalline silicon. A sample of the upper part of a multicrystalline silicon ingot with intentional addition of iron and copper has been investigated. Correlative electron‐beam‐induced current, electron backscatter diffraction, and atom probe tomography data for different types of grain boundaries are presented. For a symmetric coherent Σ3 twin boundary, with very low recombination activity, no impurities are detected. In case of a non‐coherent (random) high‐angle grain boundary and higher order twins with pronounced recombination activity, carbon and oxygen impurities are observed to decorate the interface. Copper contamination is detected for the boundary with the highest recombination activity in this study, a random high‐angle grain boundary located in the vicinity of a triple junction. The 3D atom probe tomography study presented here is the first direct atomic scale identification and quantification of impurities decorating grain boundaries in multicrystalline silicon. The observed deviations in chemical decoration and induced current could be directly linked with different crystallographic structures of silicon grain boundaries. Hence, the current work establishes a direct correlation between grain boundary structure, atomic scale segregation information, and electrical activity. It can help to identify interface–property relationships for silicon interfaces that enable grain boundary engineering in multicrystalline silicon. Copyright © 2015 John Wiley & Sons, Ltd.     

中脑导水管周围灰质支配桥脑Barrington's核内骶髓投射神经元的电镜双标记研究

本文研究采用电镜双标记技术对大鼠中脑导水管周围灰质神经元投射到桥脑Barrington's核的轴突与该核内投射到骶髓的神经元的胞体和树突之间的突触关系进行了探讨.将生物素标记的葡聚糖胺(BDA)注射于中脑导水管周围灰质用来标记它发出的轴突终末,将辣根过氧化物酶(HRP)注射于脊髓的骶髓部分,用来标记Barrington's核内投射至骶髓的神经元.显色后透射电镜观察发现,BDA标记的轴突终末与HRP标记的胞体和树突间存在直接的突触联系.此结果提示中脑导水管周围灰质在脑桥排尿反射中可能起着重要的作用.     

Ligand-Programmed Consecutive Symmetry Break(s) in Nanoparticle Based Materials Showing Emergent Phenomena: Transitioning from Sixfold to Threefold Symmetry in Anisotropic ZnO Colloids

The central promise of nanoparticle-based materials is that cooperative properties may emerge, when individual quantum dots are positioned on a periodic lattice. Yet, there are only a few papers in the literature reporting such effects. Nevertheless, it is clear that the symmetry of the superlattice is decisive for the desired emergent phenomena. An interesting question is, how the symmetry of the initial monodisperse nanoparticles affects the structure of the colloidal crystal during self-assembly processes. For instance, particles with a hexagonal cross-section demonstrate self-organization, which is very similar to spherical colloids. Likewise, one would also expect that trigonal nanoparticles behave similarly. Unfortunately, it is very hard to obtain monodisperse semiconductor colloids with a trigonal shape, because this requires a symmetry break during morphogenesis of the nanocrystal. While such a symmetry break is known in the literature for structures attached to a solid substrate, herein, colloidal synthesis of trigonal ZnO nanorods is successfully demonstrated, and the mechanism is elucidated via experimental and theoretical methods. 2D-superlattices formed by such particles with trigonal cross-section are compared to hexagonal analogues. It is found that there are distinct differences, which result in important differences in properties such as the formation of voids and also in optical properties.     

Sub‐Micrometer Patterning of Amorphous‐ and β‐Phase in a Crosslinkable Poly(9,9‐dioctylfluorene): Dual‐Wavelength Lasing from a Mixed‐Morphology Device

The metastable β‐phase morphology, inherent to most polyfluorene homo‐polymers, is of interest due to its superior optical and electrical characteristics compared to its amorphous analogue. Here, a polyfluorene with vinyl‐ether‐functionalized aliphatic side‐chains that allow crosslinking is reported. It is demonstrated that the previously induced conformational morphology is preserved in the resulting polyfluorene network, which enables subsequent wet thin‐film processing. Electron‐beam lithography provides a means for sub‐(optical)‐wavelength patterning of the crosslinkable polyfluorene films. As a specific demonstration, optically‐pumped distributed‐feedback (DFB) lasers made from surface‐relief gratings in amorphous and β‐phase polyfluorene are presented. By backfilling gratings of one morphology by the other, devices are demonstrated that exhibit lasing at two wavelengths with a threshold (<1 μJ cm^?2) at least an order of magnitude lower compared with previous data.