Fabrication and characterization of magnetic nanoporous zeolite templated carbon

The effects of heat-treatment and guest adsorption on the structure and electronic/magnetic properties were investigated for zeolite templated carbon (ZTC) by using potassium, bromine, and helium as guest species. ZTC consists of a curved graphene network, which has regularly arranged nanopores with a periodicity of 1.4 nm. X-ray diffraction and Raman spectra reveal that the regular nanopore structure is preserved during vacuum heat-treatment (<380 °C) and potassium adsorption process. On the other hand, bromine adsorption is found to destroy the nanopore structure. Helium atoms adsorbed in the nanospace participate in the energy dissipation of the radical spins in ZTC through collisions with the spins.     

Inter-collisional cutting of multi-walled carbon nanotubes by high-speed agitation

High-speed agitation by a mixing blade has efficiently achieved the cutting of a large diameter (100-150 nm) of multi-walled carbon nanotubes. The cutting process is caused by an inter-collision of the nanotubes with high transfer energy. The collision-induced cutting allows for the shortening of the nanotubes without serious damage of the original graphitic layers due to the cutting effect being limited to the collision points. Furthermore, the operation under ambient atmosphere introduces oxygen-containing functional groups to the cut nanotubes. The estimated length distribution has indicated that high-speed agitation achieves a large cutting effect during a short duration of several minutes.     

One-step synthesis of pure Cu nanowire/carbon nanotube coaxial nanocables with different structures by arc discharge

Pure Cu nanowire/carbon nanotube (Cu@C) coaxial nanocables are one-step fabricated by arc discharge. The microstructure and morphology of the Cu@C nanocables are investigated via X-ray diffraction (XRD), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM). XRD results reveal that the copper carbide nano-crystals were formed in the nanocables and it plays an important role in the growth of the Cu@C nanocables. As-prepared Cu@C nanocables exhibit three different structures, including well-filled Cu@C nanocables, symmetrically trifurcate Cu@C nanocables, and twice capsulated Cu@C nanocables. The fabrication of Cu@C nanocables with different structures offers more opportunities for the development of nanoelectronic devices. The formation mechanisms of Cu@C nanocables with different structures are discussed as well.     

Temperature dependent transport properties of CuInSe2-ZnO heterostructure solar Cell

Experimental study of dc and ac transport properties of CuInSe₂/ZnO heterostructure is presented. The current-voltage (I-V) and frequency dependent capacitance (C-f) characteristics of CuInSe₂/ZnO heterostructure were investigated in the temperature range 160-393 K. The heterostructure showed non-ideal behavior of I-V characteristics with an ideality factor of 3.0 at room temperature. Temperature dependent dc conductivity studies exhibited Arrhenius type behavior and revealed the presence of trap level. The C⁻²-V plot measured at frequency 50 kHz had shown non-linear behavior. An increase in capacitance with temperature was observed. The capacitance-frequency characteristics exhibited a transition between low frequency and the high frequency capacitance. As the temperature was lowered the transition occurred at lower frequencies. The frequency and temperature dependent device capacitance had shown a defect state having activation energy of 108 meV.     

Synthesis of In-doped Ga2O3 zigzag-shaped nanowires and optical properties

In-doped Ga₂O₃ zigzag-shaped nanowires and undoped Ga₂O₃ nanowires have been synthesized on Si substrate by thermal evaporation of mixed powders of Ga, In₂O₃ and graphite at 1000 °C without using any catalyst via a vapor-solid growth mechanism. The morphologies and microstructures of the products were characterized by field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS) and photoluminescence spectroscopy (PL). The nanowires range from 100 nm to several hundreds of nanometers in diameter and several tens of micrometers in length. A broad emission band from 400 to 700 nm is obtained in the PL spectrum of these nanowires at room temperature. There are two blue-emission peaks centering at 450 and 500 nm, which originate from the oxygen vacancies, gallium vacancies and gallium-oxygen vacancy pairs.     

Fabrication and characterization of fullerene/porphyrin bulk heterojunction solar cells

Fullerene/porphyrin bulk heterojunction solar cells were fabricated and, the electronic and optical properties were investigated. Effects of exciton-diffusion blocking layer of perylene derivative on the solar cells between active layer and metal layer were also investigated. Optimized structures with the exciton-diffusion blocking layer improved conversion efficiencies. Energy levels of the molecules were calculated and discussed. Nanostructures of the solar cells were investigated by X-ray and electron diffraction, which indicated formation of fullerene/porphyrin mixed crystals. Electronic structures of the molecules were investigated by molecular orbital calculation, and energy levels of the solar cells were discussed.     

Structures and photovoltaic properties of copper oxides/fullerene solar cells

Copper oxide (CuO_x) thin films were produced by spin-coating and electrodeposition methods, and their microstructures and photovoltaic properties were investigated. Thin film solar cells based on the Cu₂O/C₆₀ and CuO/C₆₀ heterojunction or bulk heterojunction structures were fabricated on F-doped or In-doped SnO₂, which showed photovoltaic activity under air mass 1.5 simulated sunlight conditions. Microstructures of the CuO_x thin films were examined by X-ray diffraction and transmission electron microscopy, which indicated the presence of Cu₂O and CuO nanoparticles. The energy levels of the present solar cells were also discussed.     

Morphology of carbon nanostructures and their electrochemical performance for lithium ion battery

A comparative study has been carried out on anodes made from carbon nanostructures of five different morphologies—single walled, double walled and multiwalled carbon nanotubes (with two different diameters), and carbon nanofibers. The specific area of the samples of these carbon nanostructures has been determined and their structure and morphology have been characterized by microscopy, X-ray diffraction and Raman spectroscopy. Depending on the morphology and the size of the nanostructures in the anode, the reversible capacity obtained ranges from 450 to 600 mAh g⁻¹ and the coulombic efficiency is in the range of 85–98% after 12 cycles. Increasing the surface area, both inside and outside for the tubes of a nano-size, gives rise to increased number of surface sites, which may be intercalated reversibly leading to increased specific charge capacity. Formation of the solid electrolyte interface layer covers a part of these surface sites as well as results in capacity fading, which also increases with increasing surface area. Increased defect sites responsible for elastic scattering in Raman spectra do not appear to have deciding influence on either enhanced capacity or capacity fading. Nano-sized constituent in the electrode appears to improve mechanical characteristics ensuring good mechanical integrity on cycling and high coulombic efficiency.     

Effects of dielectric barrier discharge in air on morphological and electrical properties of graphene nanoplatelets and multi-walled carbon nanotubes

Multi-walled carbon nanotubes (MWCNTs) and graphene nanoplatelets (GNPs) have been functionalized by dielectric barrier discharge (DBD) in air. The extent of functionalization of MWCNTs and GNPs reaches a maximum at the delivered discharge energy of 720 and 240 J mg⁻¹, respectively. Further exposure to plasma leads to reduction of functional groups from the surface of the treated nanomaterials. It has also been demonstrated that DBD plasma does not produce dramatic structural changes in MWCNTs, while flakes of the treated GNPs become thinner and smaller in the lateral size. Conductive thin films, obtained by drop casting a solution of the treated nanomaterials in N-methyl-1-pyrrolidone on poly(methyl methacrylate) substrate, show significantly lower sheet resistance.     

Optical properties of sol-gel fabricated Ni/SiO2 glass nanocomposites

Nickel nanoparticles were grown in silica glass by annealing of the sol-gel prepared silicate matrices doped with nickel nitrate. TEM characterization of Ni/SiO₂ glass proves the formation of isolated spherical nickel nanoparticles with mean sizes 6.7 and 20 nm depending on annealing conditions. The absorption and photoluminescence spectra of Ni/SiO₂ glasses were measured. In the absorption spectra, we observed the band related to the surface plasmon resonance (SPR) in Ni nanoparticles. The broadening of SPR was observed with decrease of Ni nanoparticle size. The width of the surface plasmon band decreases 1.5 times at the lowering of temperature from 293 to 2 K because of strong electron-phonon interaction. The spectra proved the creation of nickel oxide NiO clusters and Ni²⁺ ions in silica glass as well.     

Modification and characterization of (energetic) nanomaterials

Nanomaterials are a topic of increased interest, since they have properties which differ from their macroscopic counterparts. Many applications nowadays take advantage of the new functionalities which natural and manufactured nanoparticles possess. Based on these developments, also the research on energetic nanomaterials is receiving more and more attention. Apart from the synthesis of energetic nanomaterials, another area of interest is the coating of energetic (nano)powders, in order to be able to modify their properties or to add new functionalities to these particles. (Modified) energetic materials find applications in explosives, gun and rocket propellants and pyrotechnic devices. The modified energetic materials are expected to yield enhanced properties, e.g. a lower vulnerability towards shock initiation, enhanced blast, enhanced shelf-life and environmentally friendly replacements of currently used materials.An experimental set-up for the coating of existing powders has been designed and constructed. The experimental technique is based on a special plasma application which, contrary to more general plasmas, can be operated at relatively low temperatures and ambient pressure. This allows the handling of heat-sensitive materials, which would otherwise readily decompose or react at higher temperatures. The facility used for the coating of energetic powders in the lower micron range is based on a fluidized bed reactor in which the powder circulates.In this paper, the experimental technique will be described and experimental results will be shown of CuO powders that have been coated with a very thin, nanoscale deposit of a SiO-containing layer.     

Effect of sulfur additive on density of localized states in nanostructures chalcogenide Se95−xSxZn5 thin films

This paper reports the measurement of space charge limited conduction (SCLC) on the fabricated thin films of Se_95−xS_xZn₅ (0.2≤x≤10) in temperature range 313–353 K for the first time. At high electric fields (E∼10⁴ V/cm), the current could be fitted into the theory of space charge limited conduction, in case of uniform distribution of localized states in mobility gap. The homogeneity and surface morphology of thin films were assessed by scanning electron microscopy. The crystalline nature of the thin films was confirmed by powder XRD and the crystallite size was calculated using Scherer's formula. The crystallite size and density of localized states were found to increase with the increase of sulfur concentration. DC conductivity and activation energy were calculated and found to decrease and increase respectively, with the increase of sulfur concentration.     

Effect of carbon nanotubes on the anode performance of natural graphite for lithium ion batteries

A comparative investigation was carried out on carbon black and multiwalled carbon nanotubes as conductive additives in spherical natural graphite for lithium ion batteries. Scanning electron microscopy images showed that carbon nanotubes interlaced graphite particles in series to form a three-dimensional network. The constant current charge-discharge experiments showed that carbon nanotubes were more effective in improving reversible capacity and cycle stability. The reversible capacity was improved to 366 mAh/g and the cycle stability was improved effectively when carbon nanotubes were used. The research is of potential interest to the application of carbon nanotubes as conductive additives in anode materials for high-power lithium ion batteries.     

“Heat trap”: Light-induced localized heating and thermionic electron emission from carbon nanotube arrays

Light-induced heating of a typical bulk conductor to thermionic electron emission temperatures usually requires high-power lasers. This is because of the efficient dissipation of heat generated at the illuminated spot to the surroundings, since electrical conductors are normally also good thermal conductors. We show that the situation can be drastically different in a carbon nanotube forest and a spot on the surface of the forest can be heated to above 2000 K using a low-power beam of visible light, leading to localized thermionic electron emission. This unique phenomenon may be explained by a rapid drop in thermal conductivity with increase in temperature, leading to a positive feedback that thermally isolates an island on the forest. Applications include thermoelectrics, photocathodes, optical switches, solar cells and even solar displays.     

Impedance spectroscopy of carbon nanotube/solid polymer electrolyte composites

New composite polymer electrolytes (CPE) have been prepared by a solution-casting technique, using polyethylene oxide, lithium hexafluorate (LiPF₆) as the doping salt, ethylene carbonate (EC) as the plasticizer and amorphous carbon nanotubes (αCNTs) as the filler. The crystallinity and ionic conductivity of the CPE are examined. Differential scanning calorimetry shows a decrease in melting temperature and crystallinity upon the addition of LiPF₆, EC and αCNTs to the polymer electrolyte system. The addition of salt increases the conductivity up to 10⁻⁵ S cm⁻¹. The incorporation of EC and αCNTs into the salted polymer shows a significant conductivity increase of 10⁻⁴ and 10⁻³ S cm⁻¹. The complexation process is examined using Fourier transform infrared spectroscopy. The Vogel-Tamman-Fulcher (VTF) plots suggest that the temperature dependence of conductivity is a thermally activated process.     

Fabrication and characterization of ZnTPP:PCBM bulk heterojunction (BHJ) solar cells

Bulk heterojunction (BHJ) solar cells were fabricated based on blended films of a porphyrin derivative 5,10,15,20-Tetraphenyl-21H,23H-porphine zinc (ZnTPP) and a fullerene derivative [6,6]-phenyl-C₆₁ butyric acid methyl ester (PCBM) as the active layer. The ZnTTP:PCBM BHJ solar cells were fabricated by spin-casting of the blended layer. The weight ratios of ZnTPP and PCBM were varied from 1:1 to 0:10. The electronic and optical properties of each cell were investigated. Optical density (OD) of the blended film for each cell was extracted from its reflection and transmission curves. OD and average absorption coefficients of the active materials were used to determine film thicknesses. Absorption spectra of each component material were compared with the spectra of the blended films. Current density–Voltage (J–V) characteristics were recorded under dark as well as under the illumination of AM 1.5G (1 sun) solar spectrum. The BHJ solar cell with ZnTPP:PCBM ratio of 1:9 showed the best performance . The values of RR, V_OC , J_SC , FF and η for these ratios were 106.3, 0.4 V, 1.316 mA/cm², 0.4 and 0.21%, respectively. The cross-section of this device using SEM was also examined.     

Effect of Fe doping on the structural and gas sensing properties of ZnO porous microspheres

Fe-doped ZnO porous microspheres composed of nanosheets were prepared by a simple hydrothermal method combined with post-annealing, and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), Brunauer–Emmett–Teller N₂ adsorption–desorption measurements and photoluminescence (PL) spectra. In this paper we report Fe doping induced modifications in the structural, photoluminescence and gas sensing behavior of ZnO porous microspheres. Our results show that the crystallite size decreases and specific surface area increases with the increase of Fe doping concentration. The PL spectra indicate that the 4 mol% Fe-doped ZnO has higher ratio of donor (V_O and Zn_i) to acceptor (V_Zn) than undoped ZnO. The 4 mol% Fe-doped ZnO sample shows the highest response value to ppb-level n-butanol at 300 °C, and the detected limit of n-butanol is below 10 ppb. In addition, the 4 mol% Fe -doped ZnO sample exhibits good selectivity to n-butanol. The superior sensing properties of the Fe-doped porous ZnO microspheres are contributed to higher donor defects contents combined with larger specific surface area.     

Annealing effect on the morphologies and photoluminescence properties of ZnO nanocombs

In order to examine the annealing effect on morphologies and photoluminescence properties of the as-synthesized ZnO nanocombs, they were annealed in argon and in air at 800 °C for 10 h, respectively. The SEM, TEM, HRTEM, and PL examination results show that the morphologies and photoluminescence properties of ZnO nanocombs annealed in argon are quite different from those of ZnO nanocombs annealed in air. To anneal ZnO nanocombs in air caused the disappearance of combs, the enhancement of ultraviolet emissions, and the disappearance of emissions in the visible spectral region. On the other hand, the combs still existed, and the green emission centering at 500 nm still existed after annealing ZnO nanocombs in argon. The mechanisms for the morphological and photoluminescence evolution of annealed ZnO nanocombs are also proposed.     

Electrical properties of SrBi2(Nb0.5Ta0.5)2O9 ceramics

Aurivillius SrBi₂(Nb_0.5Ta_0.5)₂O₉ (SBNT 50/50) ceramics were prepared using the conventional solid-state reaction method. Scanning electron microscopy was applied to investigate the grain structure. The XRD studies revealed an orthorhombic structure in the SBNT 50/50 with lattice parameters a=5.522 Å, b=5.511 Å and c=25.114 Å. The dielectric properties were determined by impedance spectroscopy measurements. A strong low frequency dielectric dispersion was found to exist in this material. Its occurrence was ascribed to the presence of ionized space charge carriers such as oxygen vacancies. The dielectric relaxation was defined on the basis of an equivalent circuit. The temperature dependence of various electrical properties was determined and discussed. The thermal activation energy for the grain electric conductivity was lower in the high temperature region (T>303.6 °C, E_a−ht=0.47 eV) and higher in the low temperature region (T<303.6 °C, E_a−lt=1.18 eV).     

Preparation, characterization and photocatalytic activity of multi-walled carbon nanotube-supported tungsten trioxide composites

Multi-walled carbon nanotube (MWCNT)-supported tungsten trioxide (WO₃) composite catalysts were prepared by liquid-phase process. WO₃ nanoparticles grew on the inner and outer surface of MWCNTs. Their photocatalytic activities in the degradation of the Rhodamine B Dye were studied. The effects of mass ratio of MWCNTs to WO₃ were discussed. X-ray diffraction, field emission transmission electron microscopy, thermogravimetric-differential thermal analysis and ultraviolet-visible light absorption spectra were carried out to characterize the composite catalysts. The results indicated that the optimum mass ratio of MWCNTs to WO₃ is 5:100.