Formation of nano-sized Y2O3 dispersoids in mechanically alloyed Ni-(Cr, Y2O3, Y) alloys during heat-treatments

In the present work, the evolution of nanoparticles during annealing and hot-consolidation in mechanically alloyed Ni-22Cr-1.5Y, Ni-22Cr-1.5Y2O3 and Ni-3% Y2O3 was examined. The high-energy ball-milling of elemental powders resulted in the complete dissolution of the constituent Cr, Y, or Y2O3, forming a Ni-based solid solution. During the subsequent annealing, however, oxide particles precipitated from the solid solution. In the case of mechanically alloyed Ni-22Cr-1.5Y2O3, over-grown Cr2O3 precipitated at a temperature as low as above approximately 500 degrees C and ternary YCrO3 particles precipitated at 1100 degrees C. In the case of mechanically alloyed Ni-22Cr-1.5Y, on the other hand, the binary Y2O3 phase precipitated at 1100 degrees C during spark plasma sintering. The presence of Cr in the alloy composition facilitated the formation of Cr2O3 or YCrO3, and the precipitated oxides were highly prone to grain growth during hot-consolidation, sometimes reaching several micrometers. In Cr-exempt Ni-3%Y or Ni-3% Y2O3, however, the growth of nanodispersoids was restrained even at temperatures as high as 1000 degrees C and the resulting dispersoid was only nano-sized Y2O3.     

Synthesis and characterization of novel p-type alkyl bithiophene end-capped anthracene and naphthalene derivatives for organic thin-film transistors

New semiconductors having naphthalene and anthracene cores with hexylated bithiophene side units, 2,6-bis(5'-hexylbithiophen-2'-yl)naphthalene (HBT-NA) and 2,6-bis(5'-hexylbithiophen-2'-yl)anthracene (HBT-AN), were synthesized. HBT-AN and HBT-NA were characterized using FT-IR, 1H-NMR, Mass spectrum and elemental analysis. HBT-AN and HBT-NA showed well ordered crystalline with high thermal stabilities as evidenced by 5% weight loss at 447 degrees C for HBT-AN and 434 degrees C for HBT-NA. The closed packed structures between adjacent molecules were observed by studying UV-visible and photoluminescence (PL) in solution and film. The HOMO energy levels of HBT-NA and HBT-AN were found to be 5.47 eV and 5.42 eV, respectively. HBT-NA exhibits hole mobility of 8.4 x 10(-2) cm2Ns and on/off ratio of 5.6 x 10(5). HBT-AN shows 5.2 x 10(-2) cm2Ns and on/off ratio of 1.0 x 10(5).     

An unconventional route to high-efficiency dye-sensitized solar cells via embedding graphitic thin films into TiO2 nanoparticle photoanode

Graphitic thin films embedded with highly dispersed titanium dioxide (TiO(2)) nanoparticles were incorporated for the first time into the conventional dye-sensitized solar cells (DSSCs), resulting in a remarkably improved cell efficiency due to its superior electron conductivity. Massively ordered arrays of TiO(2) dots embedded in carbon matrix were fabricated via UV-stabilization of polystyrene-block-poly(4-vinylpyridine) films containing TiO(2) precursors followed by direct carbonization. For dye-sensitized TiO(2) based solar cells containing carbon/TiO(2) thin layers at both sides of pristine TiO(2) layer, an increase of 62.3% [corrected] in overall power conversion efficiency was achieved compared with neat TiO(2)-based DSSCs. Such a remarkably improved cell efficiency was ascribed to the superior electron conductivity and extended electron lifetime elucidated by cyclic voltammetry and impedance spectroscopy.     

Structure and electrochemical applications of boron-doped graphitized carbon nanofibers

Boron-doped graphitized carbon nanofibers (CNFs) were prepared by optimizing CNFs preparation, surface treatment, graphitization and boron-added graphitization. The interlayer spacing (d???) of the boron-doped graphitized CNFs reached 3.356 ?, similar to that of single-crystal graphite. Special platelet CNFs (PCNFs), for which d??? is less than 3.400 ?, were selected for further heat treatment. The first heat treatment of PCNFs at 2800?°C yielded a d??? between 3.357 and 3.365 ?. Successive nitric acid treatment and a second heat treatment with boric acid reduced d??? to 3.356 ?. The resulting boron-doped PCNFs exhibited a high discharge capacity of 338 mAh g?1 between 0 and 0.5 V versus Li/Li? and 368 mAh g?1 between 0 and 1.5 V versus Li/Li?. The first-cycle Coulombic efficiency was also enhanced to 71-80%. Such capacity is comparable to that of natural graphite under the same charge/discharge conditions. The boron-doped PCNFs also exhibited improved rate performance with twice the capacity of boron-doped natural graphite at a discharge rate of 5 C.     

Stable cycling of double-walled silicon nanotube battery anodes through solid-electrolyte interphase control

Although the performance of lithium ion-batteries continues to improve, their energy density and cycle life remain insufficient for applications in consumer electronics, transport and large-scale renewable energy storage. Silicon has a large charge storage capacity and this makes it an attractive anode material, but pulverization during cycling and an unstable solid-electrolyte interphase has limited the cycle life of silicon anodes to hundreds of cycles. Here, we show that anodes consisting of an active silicon nanotube surrounded by an ion-permeable silicon oxide shell can cycle over 6,000 times in half cells while retaining more than 85% of their initial capacity. The outer surface of the silicon nanotube is prevented from expansion by the oxide shell, and the expanding inner surface is not exposed to the electrolyte, resulting in a stable solid-electrolyte interphase. Batteries containing these double-walled silicon nanotube anodes exhibit charge capacities approximately eight times larger than conventional carbon anodes and charging rates of up to 20C (a rate of 1C corresponds to complete charge or discharge in one hour).     

Effect of hydrogen plasma passivation on performance of HIT solar cells

We studied the performance improvement of HIT solar cells by optimizing H₂ plasma exposure and deposition of thin a-S:H layer on c-Si. With increasing H₂ treatment time, the V_OC increases until 80 s and then decreases, indicating the optimum time is 80 s. It is found that the cell performance is almost the same with and without a thin a-Si:H layer when 80 s plasma is treated on the c-Si before i-layer deposition. The conversion efficiency of 14.04% was achieved at the substrate temperature of 160 °C.     

Intense blue-emitting Ca₂PO₄Cl:Eu²⁺ phosphor for near-ultraviolet converting white light-emitting diodes

A blue phosphor Ca2PO4Cl:Eu2+(CAP:Eu2+) was synthesized by solid state reaction.The Ca2PO4Cl:Eu2+ exhibited high quantum efficiency and excellent thermal stability.The luminescent intensity of Ca2PO4Cl:Eu2+ was found to be 128% under excitation at 380 nm,149% under 400 nm,and 247% under 420 nm as high as that of BaMgAl10O17:Eu2+.The optimal doping concentration was observed to 11 mol.% of CAP:Eu2+.The energy transfer between Eu2+ ions in CAP were occurred via electric multipolar interaction,and the critical transfer distance was estimated to be 1.26 nm.A mixture of blue-emitting Ca2PO4Cl:Eu2+,green-emitting(Ba,Sr)2SiO4:Eu2+ and red-emitting CaAlSiN3:Eu2+ phosphors were selected in conjunction with 400 nm chip to fabricate white LED devices.The average color-rendering index Ra and correlated color temperature(Tc) of the white LEDs were found to be 93.4 and 4590 K,respectively.The results indicated that it was a promising candidate as a blue-emitting phosphor for the near-UV white light-emitting diodes.     

Photocatalytic performance of nanocrystalline Bi5Ti3FeO15 layered perovskite under visible light

Nanocrystalline Bi5Ti3FeO15 layered perovskite exhibiting Aurivillius phase was synthesized by polymerized complex (PC) method and investigated for its physico-chemical as well as optical properties. The crystallization of Bi5Ti3FeO15 synthesized by PC method was found to occur in the temperature range of 800-1050 degress C, whereas the single crystalline Bi5Ti3FeO15 formed at 1030 degrees C by solid state reaction (SSR) method. The observation of highly pure phase and such lower crystallization temperature in Bi5Ti3FeO15 prepared by PC method, is in total contrast to that observed in Bi5Ti3FeO15 prepared by the conventional solid-state reaction (SSR) method. The band gap of nanocrystalline Bi5Ti3FeO15 determined from UV-Vis diffusion reflectance spectrometer was 2.38 eV (525 nm). The photocatalytic activity of Pt/Bi5Ti3FeO15 prepared by PC method was investigated with the photodecomposition of isopropyl alcohol (IPA) and hydrogen production from water-methanol mixed solution under visible light (lambda > or = 420 nm). The respective activities for PC sample were higher than that of Pt/Bi5Ti3FeO15 prepared by SSR as well as Pt/TiO(2-x)N(x).     

Electrospinning of polystyrene/dicyanopyrazine-linked porphyrin nanofibers

We have fabricated fluorescing polystyrene/dicyanopyrazine-linked porphyrin (PS/4-TDCPP) nanofibers using the electrospinning technique. UV-vis spectroscopy shows a strong Soret band and two relatively weak Q bands from the PS/4-TDCPP films and fibers, and reveals that the 4-TDCPP molecules are homogeneously dispersed in the films and fibers. Scanning electron microscopy (SEM) reveals the effect of solvent and collecting distance on the morphology of the electro-spun PS/4-TDCPP fibers. Fibers spun from a 50% dimethlyformamide (DMF), 50% methylethylketone (MEK) solution have ultra-fine structures with an average diameter of 300 nm. In the case of fibers from pure DMF and DMF:MEK (1:3) solutions, beads are formed along the length of the fibers. Variation of the collecting distance from 20 to 30 cm does not induce significant differences in the morphology of the electro-spun PS/4-TDCPP fibers. However, at a collecting distance of 15 cm, many beads are formed along the fibers. Acid-sensing capability of the PS/4-TDCPP fibers is demonstrated by fluorescence microscopy.     

Self-sensing of carbon fiber/carbon nanofiber–epoxy composites with two different nanofiber aspect ratios investigated by electrical resistance and wettability measurements

Electro-micromechanical techniques, wettability test, and acoustic emission (AE) were use to compare self-sensing and stress-transferring effects in single carbon fiber embedded in carbon nanofiber (CNF)–epoxy composites with two different aspect ratios. Electrical resistivity and standard deviation were used as indirect measures of comparative dispersion degree of CNF. The dispersion was observed to decrease with increasing CNF content due to an increase in the electrical contacts. Composites with higher aspect ratio exhibited better self-sensing than lower aspect ratio case. This was attributed to differences in dispersion, orientation, coagulation of CNF with different aspect ratios. The opposite effect was observed for apparent Young’s modulus, which was larger for composites with lower aspect ratio. This is probably related to better stress transfer linked to orientation effects. Work of adhesion consistently followed same trend as apparent Young’s modulus. Single carbon fiber pull-out tests and AE provided additional information on the effects of aspect ratio.