Polyacrylonitrile/vapor grown carbon nanofiber composite films

Polyacrylonitrile (PAN)/vapor grown carbon nanofiber (VGCNF) composite films were processed from N, N-dimethylformamide (DMF) at various nanofiber loadings: 5, 10, 20, 40, 60, 80, and 90 wt%. Tensile, dynamic mechanical, electrical, structural, and morphological properties of these composite films were studied. Enhancement in tensile properties was observed in composites with nanofiber loading up to 40 wt%. The storage modulus of PAN increased upon incorporation of nanofiber particularly above the glass transition temperature. The tan δ peak broadens and shifts to higher temperatures with the addition of VGCNF. The activation energy for PAN molecular motion was higher than that in the control PAN film. The electrical conductivity of composite films increased with increasing nanofiber loading and exhibited a percolation at 3.1 vol%. Scanning electron microscopy (SEM) indicated PAN coated nanofibers in the composite film.     

Novel approach to the fabrication of Au/silica core-shell nanostructures based on nanosecond laser irradiation of thin Au films on Si

We demonstrate the possibility of producing Au/SiO(2) core-shell nanoparticles by nanosecond laser irradiation of thin (5 and 20 nm) Au films on Si. The Au/Si eutectic reaction and dewetting process caused by the fast melting and solidification dynamics induced by the nanosecond laser irradiations are investigated as the origin of the formation of core-shell nanoparticles. Using several microscopic techniques (Rutherford backscattering spectrometry, scanning electron microscopy, atomic force microscopy, transmission electron microscopy, and energy filtered transmission electron microscopy) the formation and evolution of the core-shell structures are investigated as a function of the laser fluence in the 500-1500 mJ cm(-2) range for both film thicknesses. In particular, the mean height and diameter and surface density evolution of the core-shell structures are quantified and correlated to the laser fluence and Au film thickness.     

Thin film deposition on plastic substrates using silicon nanoparticles and laser nanoforming

Reduced melting temperature of nanoparticles is utilized to deposit thin polycrystalline silicon (c-Si) films on plastic substrates by using a laser beam without damaging the substrate. An aqueous dispersion of 5 nm silicon nanoparticles was used as precursor. A Nd:YAG (1064 nm wavelength) laser operating in continuous wave (CW) mode was used for thin film formation. Polycrystalline Si films were deposited on flexible as well as rigid plastic substrates in both air and argon ambients. The films were analyzed by optical microscopy for film formation, scanning electron microscopy (SEM) for microstructural features, energy dispersive spectroscopy (EDS) for impurities, X-ray photoelectron spectroscopy (XPS) for composition and bond information of the recrystallized film and Raman spectroscopy for estimating shift from amorphous to more crystalline phase. Raman spectroscopy showed a shift from amorphous to more crystalline phases with increasing both the laser power and irradiation time during laser recrystallization step.     

Preparation of silver nanoparticles dispersed in polyacrylonitrile nanofiber film spun by electrospinning

Ag nanoparticles dispersed in polyacrylonitrile (PAN) nanofiber film spun by electrospinning were in situ prepared by reduction of silver ions in N₂H₅OH aqueous solution. The Ag/PAN nanocomposite film was characterized by UV absorption spectroscopy, transmission electron microscopy (TEM) and surface-enhanced Raman scattering (SERS) spectroscopy. UV spectrum and TEM image show that silver nanoparticles with average diameter of 10 nm were obtained and dispersed homogeneously in PAN nanofibers. SERS spectrum indicates that the structure of PAN has been changed after Ag nanoparticles are dispersed in PAN.     

Facile fabrication and photocatalytic application of Ag nanoparticles-TiO2 nanofiber composites

A novel chemical method has been developed for the fabrication of Ag nanoparticles-coated TiO2 nanofiber composites. The method involves dispersion of TiO2 nanofibers in silver salt solution under ultrasonication, followed by addition of sodium citrate as a reducing agent. The Ag-coated TiO2 composites were characterized by high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) and X-ray photoelectron microscopy (XPS). Furthermore, the photocatalytic performance was evaluated by the photocatalytic degradation of methyl orange under UV-light irradiation. It was found that the heterogeneous Ag-TiO2 composite showed a higher activity than the pure TiO2 nanofiber; the enhanced activity can be attributed to the excellent distribution and interaction of Ag nanoparticles with the TiO2 nanofiber support. A plausible mechanism for the formation of the Ag-coated TiO2 composite and reasons for the enhancement of photocatalytic activity are also discussed.     

Preparation of fluoride-containing gelatin nanofiber scaffold

A novel material, fluoride-containing gelatin nanofiber scaffold, was prepared by electrospinning process successfully. Scanning electron microscopy (SEM) image showed that the morphology of nanofibers was uniform and smooth, and the average diameter was about 200 nm. An even distribution in the fiber matrix of some nanoparticles which is about 20 nm was also observed in transmission electron microscopy (TEM) images. X-ray diffraction (XRD) demonstrated that the nanoparticles dispersed in the gelatin fiber matrix were CaF₂ crystals. This scaffold was crosslinked with glutaraldehyde (GTA) vapor at room temperature for 4 days in order to improve the water-resistant ability. After soaking in Dulbecco's Modified Eagle's Medium (DMEM) solution (37 °C) for 4 weeks the crosslinked scaffold still maintained a good appearance and morphology. All the properties of this novel material show a good potential to be a bone tissue engineering scaffold.     

Novel surfactant-stabilized graphene-polyaniline composite nanofiber for supercapacitor applications

In this work, we present a new synthesis method for surfactant stabilized graphene (SSG) combined with polyaniline nanofiber (PANI-Nf) and apply the composite material as supercapacitor (SC) electrodes by screen-printing technique. Surfactant stabilized graphene polyaniline nanofiber composite (PANI-SSG) was synthesized by electrolytic exfoliation of graphite and subsequent interfacial polymerization. Firstly, graphite was electrolytically exfoliated in an electrolyte containing anionic surfactant. Next, ammonium peroxydisulfate initiator and hydrochloric acid were added to the graphene dispersion to form the aqueous phase for interfacial polymerization of polyaniline nanofiber. This dispersion was then added to the water-insoluble solvent phase containing aniline monomer. The polymerization only occurred at the interface of the two immiscible phases leading to polyaniline nanofiber decorated graphene structures. Characterizations by scanning electron microscopy, transmission electron microscopy, atomic force microscopy and Raman spectroscopy suggested nanocomposite formation with intermolecular π-π bonding of graphene with polyaniline nanofibers. Pastes of the materials were screen printed on stainless steel current collectors and tested for SC performance by cyclic voltammetry (CV) and galvanostatic charge–discharge (GCD) measurements with 2 M H₂SO₄ electrolyte using a home-built two-electrode test-cell. CV results showed redox peaks of polyaniline with wide cyclic loop, indicating large pseudocapacitance of the nanocomposite. From GCD measurement, a high specific capacitance of 690 Fg⁻¹ at 1 Ag⁻¹ was achieved. Therefore, PANI-SSG nano-composite prepared by electrolytic exfoliation and interfacial polymerization is a promising candidate for SC applications.     

表面改性及原位还原法制备聚酰亚胺/镍纳米复合薄膜

通过对均苯四甲酸二酐-4,4’-二胺基二苯醚(PMDA-4,4’-ODA)型聚酰亚胺(PI)成品薄膜的表层水解处理、并在硫酸镍水溶液中实施离子交换以及随后的乙二醇热还原的方法,制备了聚酰亚胺/镍纳米复合薄膜。通过X射线衍射仪(XRD)、傅立叶变换红外光谱仪(FT-IR),透射电子显微镜(TEM)等方法研究了复合薄膜结构的变化,结果表明,经乙二醇热还原后,水解后的聚酰亚胺表层又重新形成亚胺环结构,并在其内部形成了均匀分散的具有面心立方晶型(FCC)的金属镍粒子,直径约为100 nm~200 nm。     

Characterization of polyacrylonitrile based carbon nanofiber mats via electron beam processing

The aim of this study was to evaluate the ability of electron beam irradiation to drive stabilization reactions within PAN nanofiber mats to obtain carbon nanofiber mats. PAN nanofiber mats with fiber diameters of 300-400 nm were prepared via an electrospinning method. Electrospun PAN nanofiber mats were stabilized by electron beam irradiation with various doses up to 5,000 kGy. Using the irradiation-stabilized PAN nanofiber mats, carbon nanofibers were obtained by pyrolysis in a tube furnace for 1 h at 1,000 degrees C under an N2 atmosphere. FT-IR analysis indicated that the transformation of C[triple bond]N groups to C==N groups was accelerated by electron beam stabilization. The thermal behavior of the PAN nanofiber mats was studied using DSC and TGA. DSC thermograms showed that the peak temperatures of the exothermic reactions were found to decrease with increasing electron beam irradiation doses. Irradiation-stabilized PAN nanofiber mats were not observed to dramatically decrease in weight between 290 degrees C and 320 degrees C, an observation presumed to be related to cyclization. The char yields of PAN were found to increase with increasing irradiation doses.     

Pulsed laser dewetting of nickel catalyst for carbon nanofiber growth

We present a pulsed laser dewetting technique that produces single nickel catalyst particles from lithographically patterned disks for subsequent carbon nanofiber growth through plasma enhanced chemical vapor deposition. Unlike the case for standard heat treated Ni catalyst disks, for which multiple nickel particles and consequently multiple carbon nanofibers (CNFs) are observed, single vertically aligned CNFs could be obtained from the laser dewetted catalyst. Different laser dewetting parameters were tested in this study, such as the laser energy density and the laser processing time measured by the total number of laser pulses. Various nickel disk radii and thicknesses were attempted and the resultant number of carbon nanofibers was found to be a function of the initial disk dimension and the number of laser pulses.     

Growth and characterization of GaAs nanowires on carbon nanotube composite films: toward flexible nanodevices

Poly(ethylene imine) functionalized carbon nanotube thin films, prepared using the vacuum filtration method, were decorated with Au nanoparticles by in situ reduction of HAuCl4 under mild conditions. These Au nanoparticles were subsequently employed for the growth of GaAs nanowires (NWs) by the vapor-liquid-solid process in a gas source molecular beam epitaxy system. The process resulted in the dense growth of GaAs NWs across the entire surface of the single-walled nanotube (SWNT) films. The NWs, which were orientated in a variety of angles with respect to the SWNT films, ranged in diameter between 20 to 200 nm, with heights up to 2.5 microm. Transmission electron microscopy analysis of the NW-SWNT interface indicated that NW growth was initiated upon the surface of the nanotube composite films. Photoluminescence characterization of a single NW specimen showed high optical quality. Rectifying asymmetric current-voltage behavior was observed from contacted NW ensembles and attributed to the core-shell pn-junction within the NWs. Potential applications of such novel hybrid architectures include flexible solar cells, displays, and sensors.     

聚氨酯/碳纳米纤维复合材料的结构和抗凝血性能

分别采用溶液共混和熔融共混的方法制备出聚氯酯／碳纳米纤维复合材料，研究了碳纳米纤维对聚氯酯的热行为和表面微观化学组成的影响，并观察和测定了血小板在复合材料表面的粘附以及血液中血红蛋白浓度、纤维蛋白原浓度的变化，分析了碳纳米纤维对聚氯酯血液相容性的影响．结果表明，引入碳纳米纤维后，聚氯酯复合材料的表面氧含量有不同程度的提高，玻璃化转变温度及熔融温度都发生了改变；血小板在复合材料表面的粘附受到明显的抑制；经血泵循环4h后，在与聚氯酯复合材料表面接触的血液中，血红蛋白和纤维蛋白原浓度的变化相对减小；复合材料的血液相容性提高．     

Diamond-like carbon,a barrier coating for polymers used in packaging applications

Water and oxygen permeability measurements on two polymers, poly(ethylene terephthalate) and polypropylene, are presented as a function of diamond-like carbon coating thickness. Results show that reliable and reproducible coatings can be achieved on poly(ethylene terephthalate) such that levels of permeability are about 1 cc/m²/day for oxygen and 1.5 g/m²/day for water vapour, comparable to the levels for silicon oxides and aluminium coatings used in the packaging industry. The advantages conferred by diamond-like carbon over aluminium is primarily that of retaining optical transparency in the thickness of films used in this work (20 nm). The advantages of diamond-like carbon over silicon oxides is related to its intrinsic flexibility. Other advantages over other barrier films (e.g. polyvinylidine chloride) and coating technologies is the ability to recycle the used product. The permeability of diamond-like carbon-coated polypropylene to oxygen is in the range of 200 cc/m²/day, again comparable to results obtained with the other coatings. The optimum film thickness for poly(ethylene terephthalate) to minimize permeability was 20 nm. Atomic force microscopy revealed agglomerated structures (possibly graphitic) with the underlying substrate appearing smoother than the starting material. In comparison, polypropylene exhibited increased surface roughness under the same coating conditions.     

Preparation and catalytic activity of Pt/C materials via microwave irradiation

Microwave heating was employed to prepare highly dispersed Pt/C catalyst. Uniform platinum nanoparticles with average diameter of about 3.0-5.0 nm dispersed on carbon materials (XC-72) were synthesized using a domestic microwave oven. Synthesized Pt/C materials were characterized by X-ray diffraction and transmission electron microscopy. The particle size and size distribution of Pt nanoparticles greatly depend on microwave irradiation duration, where the heating temperature rises rapidly as the process proceeds. Cyclic voltammetry demonstrates that Pt/C catalysts derived from microwave irradiation for 90 s exhibits higher catalytic activity than a commercial Pt/C catalyst (E-Tek) at room temperature. The improvement in electrocatalytic activity of synthesized Pt/C materials is attributed to uniformity of particle size, well dispersion and high surface area, which is obtained around 175 °C and irradiation for 90 s.     

Synthesis and magnetic properties of nickel nanoparticles in magnesium fluoride matrix

A new composite material, comprising a diamagnetic matrix (magnesium fluoride) containing metal nanoparticles (nickel), has been synthesized in a high-vacuum laser-based universal cluster ablation system. The structure and magnetic properties of the composite were studied by transmission electron microscopy (TEM) and ferromagnetic resonance (FMR). According to TEM data, the nickel nanoparticles have a spherical shape and their dimensions are described by a narrow distribution function with an average value of 3.2 nm. An analysis of the FMR spectra reveals strong interaction between nickel nanoparticles in the composite, which accounts for an out-of-plane magnetic anisotropy and suggests the formation of granular magnetic films.     

炭纸上原位生长CNF/CP复合体的氧气电催化反应性能

利用催化气相化学沉积(Catalytic chemical vapor deposition,CCVD)法在炭纸上原位生长得到CNF/CP复合体,并对这种复合体的物理化学性能和氧气电催化还原反应(Oxygen reduction reaction,ORR)性能进行了研究.结果表明:纳米炭纤维较为均匀地分散在炭纸上,其中纳米炭纤维具有窄的直径分布.所制CNF/CP复合体具有较大的比表面积和独特的中孔结构;相对于炭纸,CNF/CP复合体的端面碳原子和基面碳原子比例较高.另外,CNF/CP还具有较高的ORR反应活性,其ORR为2电子反应过程,原因可以归结于纳米炭纤维独特的微结构.同时,CNF/CP也具有较高的交换电流密度和较正的平衡电压.     

DEPOSITION OF DIAMOND-LIKE AND OTHER SPECIAL COATINGS BY PULSED LASER ABLATION AND THEIR POST-SYNTHESIS PROCESSING

Use of pulsed laser ablation technique for deposition of diamond-like and other special coatings is discussed here at length, establishing the correlation between the process parameters and the film quality. Process parameters dealt with sufficient detail are the laser wavelength, laser pulse width and energy density, nature of ambient and the corresponding partial pressure, substrate temperature and the electric field, if any, applied during deposition. The optimum parameter space for deposition of films having high performance features are identified in the case of diamond-like films and films of cubic boron nitride, titanium nitride and tungsten carbide. In this context, results on the characterization of the films deposited under different conditions are discussed. These include data obtained by Raman spectroscopy, IR spectroscopy, X-ray diffraction, ellipsometry, UV-VIS transmission, scanning electron microscopy. The post-synthesis of the laser deposited films using ion and laser beams from I he standpoint of enhancing their quality or etching of dielectric features therein are also discussed.     

Ferromagnetic composite coatings on carbon fibers

Alumina- and titania-based composite coatings containing ferromagnetic nanoparticles have been produced on UKN-5000P carbon fibers by an in situ organo-inorganic hybrid sol-gel process using appropriate aqueous metal chloride solutions containing Fe(III) and Co(II). The morphology, phase composition, and elemental composition of the coatings have been studied by high-resolution electron microscopy, X-ray diffraction, and energy-dispersive X-ray microanalysis. The results demonstrate that the oxide coatings containing ferromagnetic nanoparticles are uniform in thickness along and across the fibers and adhere well to the fiber surface. The coatings range in thickness from 100 to 500 nm. In all of the systems studied, the coatings produced on carbon fibers differ in phase composition from powders prepared from identical hydrosols.     

Two-step electrochemical synthesis of Au nanoparticles decorated polyaniline nanofiber

The present work reports the electrochemical synthesis of H₂SO₄-doped polyaniline nanofibers (PANINFs) on conducting ITO substrate. The subsequent dissociation of HAuCl₄ in an acidic solution of HNO₃ and deposition of Au particles was carried out by using cyclic voltammetery (CV) to form Au particles decorated PANINFs (Au–PANINFs) composite film. Electrical conductivity of the Au particles decorated PANINFs has been measured by a two-probe method. Scanning electron microscopy (SEM) investigations of PANINFs and Au–PANINFs samples revealed good porous and fibrous structure with identical distribution of gold nanoparticles coupled with the surface of PANINFs. The average diameter of the PANINFs ranges from 184 nm to 210 nm. X-ray diffraction (XRD) and EDAX spectra also supported the formation of Au particles on the surface of PANINFs. The structural analysis was carried out by Raman spectroscopic technique. A possible mechanism for the formation of Au–PANINFs composite has been proposed.     

Nanosecond UV laser graphitization and delamination of thin tetrahedral amorphous carbon films with different sp/sp content

We have produced hydrogen-free tetrahedral amorphous carbon films with different densities and Young's modulus by coating silicon with a filtered vacuum arc under different angles. The films were modified with a pulsed laser (wavelength 355 nm) into sp² rich amorphous carbon and nano crystalline carbon films. The graphitization threshold of the films depends on the film thickness as well as on the carbon density. Simulations of the optical absorption of the different carbon films permitted to confirm the experimental results. On the other side, the delamination threshold of carbon films increases with the film thickness and was found to be controlled by thermal properties of the film. The thin film graphitization and delamination is investigated by optical microscopy, atomic force microscopy, scanning electron microscopy and Raman spectroscopy.