Mesoporous carbon nanofiber network derived from agarose for supercapacitor electrode

Great efforts have been devoted on searching for sustainable and earth-abundant precursors to prepare activated carbon suitable for supercapacitor electrode applications. In this paper, we demonstrated the preparation of mesoporous carbon nanofiber network (~?10 nm in diameter of the nanofibers) from agarose precursors. With the aid of zinc acetate, the nanofiber network structure existing in natural agarose gel can be well retained after the carbonization process and the yielded mesoporous carbon nanofiber networks have high surface area and large pore volume without further activation. Supercapacitor electrodes were made from such mesoporous carbon nanofiber networks and specific capacitance of 157 F g^?1 can be achieved with the optimized zinc acetate concentration and carbonization temperature.     

Diffraction properties of binary graphene sheet arrays

We theoretically and numerically investigate the diffraction properties of surface plasmon polariton(SPP) in binary graphene sheet arrays. The single SPP band splits into two minibands by alternatively arranging the graphene waveguides with two different chemical potentials. Numerical simulations show that SPP beams in the array split into two different paths due to the different diffraction relation.     

Plasma oxidation and stabilization of electrospun polyacrylonitrile nanofiber for carbon nanofiber formation

The effect of plasma treatment on the stabilization of copolymer P(AN-MA) containing 6.1 mol% methyl acrylate (MA) prepared by an electrospinning technique has been investigated at various oxygen contents (10 %, 20 % and 30 %) and different exposure times. The morphology and chemical structural evolution of electrospun and oxidized nanofibers were studied using field–emission scanning electron microscopy (FE-SEM), Fourier transform infrared (FT-IR) spectroscopy and differential scanning calorimetry (DSC). FT-IR analysis indicated that the treated nanofibers were effectively oxidized under different contents of oxygen and prolonged plasma exposure times by increasing the peak intensities of polar groups at 1730 and 3400 cm^?1 corresponding to C=O stretching band and OH stretching vibration mode, respectively. Additionally, a reduction in the extent of the cyclization reaction is observed with further increase in exposure times and contents of oxygen, which implies lower conversion of C≡N bands into C=N ones in the copolymer chain. According to the FE-SEM studies, the surfaces of the treated nanofibers were completely etched after 15 min of treatment due to the existence of strong ion bombardment and a reduction in the average fiber diameters was observed.     

Diffraction engineering in arrays of photonic crystal waveguides

Light propagation in uniform arrays of photonic crystal waveguides is studied. We demonstrate that, in stark contrast to the case of conventional waveguide arrays, diffraction can be tailored both in magnitude and sign by varying only the spacing between adjacent waveguides. Diffraction management in ultracompact arrays of straight photonic crystal waveguides is demonstrated by solving Maxwell's equations through the time-domain finite-element method.     

Nanomechanics of individual carbon nanotubes from pyrolytically grown arrays

The bending modulus of individual carbon nanotubes from aligned arrays grown by pyrolysis was measured by in situ electromechanical resonance in transmission electron microscopy (TEM). The bending modulus of nanotubes with point defects was approximately 30 GPa and that of nanotubes with volume defect was 2-3 GPa. The time-decay constant of nanotube resonance in a vacuum of 10(-4) Torr was approximately 85 micros. A femtogram nanobalance was demonstrated based on nanotube resonance; it has the potential for measuring the mass of chain-structured large molecules. The in situ TEM provides a powerful approach towards nanomechanics of fiberlike nanomaterials with well-characterized defect structures.     

Electron emission from arrays of carbon nanotubes/fibres

The overall aim of this work is to produce arrays of field emitting microguns, based on carbon nanotubes, which can be utilised in the manufacture of large area field emitting displays, parallel e-beam lithography systems and electron sources for high frequency amplifiers. This paper will describe the work carried out to produce patterned arrays of aligned multiwall carbon nanotubes (MWCNTs) using a dc plasma technique and a Ni catalyst. We will discuss how the density of the carbon nanotube/fibres can be varied by reducing the deposition yield through nickel interaction with a diffusion layer or by direct lithographic patterning of the Ni catalyst to precisely define the position of each nanotube/fibre. Details of the field emission behaviour of the different arrays of MWCNTS will also be presented.     

Synthesis of crystalline SiC nanofiber through the pyrolysis of polycarbomethylsilane coated platelet carbon nanofiber

SiC nanofiber with high crystallinity was synthesized through the pyrolysis of polycarbomethylsilane (PS) coated platelet carbon nanofiber (PCNF) over 700 °C and burning PCNF under the oxidative atmosphere. The as-prepared β-SiC nanofiber exhibited a diameter less than 100 nm and a medium surface area of 50 m²/g. The crystallinity of silicon carbide (SiC) nanofiber increases with increasing heat-treatment temperature, showing the formation of high crystalline SiC nanofiber at 1400 °C. PCNF can be used as a unique template to govern the shape, crystallinity and morphology of SiC.     

镜像势对碳纳米管阵列场发射特性的影响

采用多尺度量子化学方法模拟了碳纳米管阵列的场发射特性.碳纳米管镜像势的作用可以等效地用原子尺寸的理想金属球的镜像势来代替.模拟计算结果表明,考虑了镜像势作用后的碳纳米管阵列发射电流密度比没有考虑镜像势的结果增大了约6倍. 关键词： 镜像势 碳纳米管 场致发射     

Diffraction integral for misaligned systems and interference effects of optical arrays

Summary In the present paper, a diffraction integral formula for a misaligned optical system is derived. The interference effects of opticalelement arrays are studied by means of such a formula. The possibility of eliminating interference fringes is discussed. The conclusion is that the interference fringes could be eliminated when the αβγδ condition for arrays is satisfied. The synthetical aberration is simultaneously eliminated. However, in this case, the synthetical image coincides with the individual images. For some special application, the synthetical image does not coincide with the individual images and the αβγδ condition is not fulfilled. But the interference fringes may disappear in some special cases.

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Riassunto La formula di Collins, che esprime il cammino ottico fra un punto del piano oggetto e un punto del piano immagine nel caso di un sistema ottico centrato, è generalizzata al caso di un sistema ottico disallineato. La formula cosí ottenuta è applicata allo studio del fenomeno d’interferenza che ha luogo nel piano della cosiddetta ?immagine sintetica? fra i vari fasci emergenti da una cortina di elementi ottici. Si discutono infine le condizioni in cui non si hanno frange d’interferenza sull’immagine sintetica.

     

碳纳米管阵列水渗透性质的研究

碳纳米管阵列组成的碳纳米管分子膜在生物学分子器件等方面有重要应用. 本文利用分子动力学方法计算研究水分子对(11, 11)碳纳米管阵列的渗透过程. 结果发现, 只有当阵列间隙面积大于57.91 Ų时, 水分子才能进入阵列间隙中, 并揭示了碳管内部、阵列间隙内水分子结构随相邻碳管间距变化的演化趋势以及管内外水分子电偶极矩的分布特性.     

阵列碳纳米管的石墨化程度

采用化学气相沉积法制备了阵列碳纳米管薄膜,对阵列碳纳米管的石墨化程度进行了系统研究。利用扫描电子显微镜(SEM)、拉曼光谱(Raman)对样品形貌以及结构进行了表征。探讨了不同实验参数对阵列碳纳米管石墨化程度影响的机理。结果发现,在一定催化剂浓度范围内,催化剂浓度过低时,阵列碳纳米管的石墨化程度较差,而随着催化剂浓度的增加,阵列碳纳米管的石墨化程度逐渐变好;生长石墨化程度较好的阵列碳纳米管需要合适的进液速度,进液速度过低或过高都会使得碳纳米管的石墨化程度变差;此外,生长石墨化程度较好的阵列碳纳米管也需要合适的生长温度,生长温度过低或过高都会使得碳纳米管的石墨化程度变差。     

阵列碳纳米管的石墨化程度

采用化学气相沉积法制备了阵列碳纳米管薄膜,对阵列碳纳米管的石墨化程度进行了系统研究。利用扫描电子显微镜(SEM)、拉曼光谱(Raman)对样品形貌以及结构进行了表征。探讨了不同实验参数对阵列碳纳米管石墨化程度影响的机理。结果发现,在一定催化剂浓度范围内,催化剂浓度过低时,阵列碳纳米管的石墨化程度较差,而随着催化剂浓度的增加,阵列碳纳米管的石墨化程度逐渐变好;生长石墨化程度较好的阵列碳纳米管需要合适的进液速度,进液速度过低或过高都会使得碳纳米管的石墨化程度变差;此外,生长石墨化程度较好的阵列碳纳米管也需要合适的生长温度,生长温度过低或过高都会使得碳纳米管的石墨化程度变差。     

Diffraction of partially coherent X‐rays in clessidra prism arrays

When small triangular prisms are arranged in arrays which have an overall appearance like an hourglass (in Italian: clessidra) they can focus X‐rays owing to a combined action of diffraction and refraction. From the optical point of view these objects can be regarded as a Fresnel variant of concave transmission lenses. Consequently they can provide larger apertures than purely refractive lenses. However, one has to recognize that clessidra lenses will strongly diffract as the lens structure is periodic in the direction perpendicular to the incident beam. In experiments the diffraction is reduced because it is difficult to illuminate the large apertures with a full spatially coherent wavefront. So the illumination is at best partially coherent. In order to interpret available experimental data for this condition, diffraction theory has been applied appropriately to the clessidra structure, taking into account the limited spatial coherence. The agreement between the theoretical simulations and experimental data is very good, keeping the lens properties at their projected values and allowing for only two free model parameters. The first is the lateral spatial coherence; the second is a lens defect, a rounding of all edges and tips in the structure. Both values obtained from the simulations have been found to be in agreement with expectations.     

Dielectric spectroscopy of melt-extruded polypropylene and as-grown carbon nanofiber composites

The European Physical Journal E - The phenomenon of a precursor spreading in front of an advancing droplet is still not fully understood. We recently used a driven lattice-gas model to study the...     

Fabrication and structural characterization of electro-spun polybenzimidazol-derived carbon nanofiber by graphitization

Here we fabricate high-purity carbon sheets consisting of 250 nm nanofibers through the fibre formation of poly (benzimidazol) by electro-spinning and subsequent heat treatment up to 3000 °C without the stabilization process (the most time-consuming step). The non-graphitic character of these nanofibers is due to: (1) the low graphitization-ability of the polymer itself, (2) the limited graphitization of the size effect (small diameter) (3) the existence of internal pores formed during the electrospinning process.     

Li2MnSiO4/carbon nanofiber cathodes for Li-ion batteries

Pure single-phase Li₂MnSiO₄ nanoparticle-embedded carbon nanofibers have been prepared for the first time via a simple sol-gel and electrospinning technique. They exhibit an improved electrochemical performance over conventional carbon-coated Li₂MnSiO₄ nanoparticle electrodes, including a high discharge capacity of ～200 mAh g^?1, at a C/20 rate, with the retention of 77 % over 20 cycles and a 1.6-fold higher discharge capacity at a 1 C rate.