原位聚合导电高分子包混对硬碳性能的影响

采用原位聚合方法对硬碳材料进行了导电聚合物包混,并测试了导电聚合物包混硬碳材料的电化学性能.利用扫描电镜,拉曼光谱,电导率仪及恒电流法研究了导电聚合物包混的硬碳材料的结构以及充放电特性.研究发现,聚苯胺、聚吡咯和聚噻吩等均能通过原位聚合包混在硬碳表面.其中,采用噻吩在硬碳表面原位聚合增强了硬碳材料的导电性.经聚噻吩包混的硬碳首次充电容量达到了385mAh g-1以上,高于未包混的硬碳(320mAh g-1).循环20周以后聚噻吩包混硬碳的容量仍保持在325 mAh g-1以上,而未包混硬碳的容量则降低到290 mAh g-1以下.     

Electrochemical performance of fixed-charge polymer films prepared on electrodes by plasma polymerization

Plasma-polymerized films were prepared from a 1:1 mixture of allylamine vapour and NH₃ on glassy carbon electrodes. The amine groups in the matrix were protonated at pH 2, producing a fixed-charge membrane. Electrochemical experiments were performed with these coated electrodes. Cyclic voltammograms showed that the redox system Fe(CN)₆^3-/Fe(CN)₆^4- was partitioned strongly into the films because of chemical interactions with the matrix.     

Electrochemical polymerization of aniline investigated using on-line electrochemistry/electrospray mass spectrometry

A thin-layer electrochemical flow cell coupled on-line with electrospray mass spectrometry (EC/ES-MS) was used to investigate the soluble products from the controlled-potential anodic polymerization of aniline in H(2)O and H(2)O/CH(3)OH (1/1 v/v) with ammonium acetate and acetic acid or ammonium hydroxide as electrolytes (pH 4, 6.5, or 9). At a working electrode (glassy carbon) potential of 1.0 V versus Ag/AgCl, singly protonated aniline oligomers containing as many as 10 aniline units (10-mer) were observed in the ES mass spectra when the polymerization in H(2)O/CH(3)OH at pH 4 was carried out. The abundance of the higher n-mers decreased at higher solution pH and in 100% H(2)O at pH 4. Most of the oligomers were observed in more than one redox state ranging from fully oxidized (all imine nitrogens) to fully reduced (all amine nitrogens). The number of different redox states observed for the n-mers increased with increasing n. The structures of the reduced (m/z 185) and oxidized (m/z 183) aniline dimer ions (head-to-tail, tail-to-tail, or head-to-head) produced from the polymerization of aniline at pH 4, 6.5, and 9 in H(2)O/CH(3)OH were revealed to vary as a function of pH by comparison of their tandem mass spectrometry product ion spectra with the product ion spectra of the dimer standards. EC/ES-MS potential scan experiments, in which the working electrode current and major n-mer ions for n = 2, 3, and 4 were monitored as a function of electrode potential, were used to probe the growth mechanism to higher aniline oligomers. Under the conditions used, the controlled-current electrolytic process inherent to the operation of the ES ion source did not significantly influence the formation or nature of the oligomers observed. Beyond the current application, the results presented here serve to demonstrate the utility of EC/ES-MS as a tool in identifying the initial products of electropolymerization and in studying the products of electrode reactions in general.     

Preparation of a ZnS shell on CdSe quantum dots using a single-molecular ZnS precursor

A simple synthetic route to the preparation of a thin ZnS shell on CdSe quantum dot cores from the air-stable, single-molecular precursor zinc diethyldithiocarbamate, Zn(S(2)CNEt(2))(2), in the three-component solvent system octadec-1-ene/oleylamine/tri-n-octylphosphine (ODE/OLA/TOP) is presented. The one-pot synthesis proceeds through heating of the solution of CdSe cores and the amount of crystalline Zn(S(2)CNEt(2))(2) corresponding to a shell thickness of two monolayers of ZnS to 110-120 °C for 1-2 h. The role of the surfactants OLA and TOP and the significance of the temperature and the amount of Zn(S(2)CNEt(2))(2) have been investigated with optical absorption and luminescence spectroscopy. We show that the presence of both OLA and TOP is crucial for the low-temperature growth and that the amount of precursor corresponding to two monolayers of ZnS results in the highest quality of core/shell CdSe/ZnS quantum dots.     

Electrochemical growth of poly(3-dodecylthiophene) into porous silicon: a nanocomposite with tubes or wires?

A derivative of polythiophiene: poly(3-dodecylthiophene) (PT 12) has been used to fill electrochemically a porous silicon matrix. The composite, obtained by this way, should have a high third order nonlinear optical coefficient and good mechanical properties. SEM and TEM micrographs were taken after matrix dissolution in NaOH. Columns of polymer with the matrix pore shape show up like fingers. In consideration of the homogeneous filling profile of PT 12 measured by EDX and XPS and the low amount of polymer, we are probably dealing with tubes instead of wires.     

Electrochemical performance of conducting polymer and its nanocomposites prepared by chemical vapor phase polymerization method

In this work, conducting polymers poly(3,4-ethylenedioxythiophene) (PEDOT), PEDOT/carbon nanotubes (CNTs), and PEDOT/reduced graphene oxide (RGO) were prepared via an in situ chemical vapor phase polymerization (VPP) process. Experiment results showed that PEDOT and PEDOT nanocomposites were uniformly constructed in oxidant and oxidant nanocomposite films through a modifying template effect. The VPP PEDOT and its nanocomposites were built on aluminium film as supercapaitor electrode materials and electrochemical capacitive properties were investigated by using cycle voltammetry and charge/discharge techniques. The VPP PEDOT exhibited a specific capacitance of 92 F/g at a current density of 0.2 A/g. The VPP PEDOT composites consisting of CNTs and RGO displayed specific capacitances of 137 and 156 F/g, respectively, at the same current density. For VPP nanocomposites, more than 80 % of initial capacitance was retained after 1,000 charge/discharge cycles, suggesting a good cycling stability for electrochemical electrode materials. The good capacitive performance of the conducting polymer nanocomposites are contributed to the synergic effect of the two components.     

Electrochemical polymerization of 9-phenylcarbazole in mixed electrolytes of boron trifluoride diethyl etherate and sulfuric acid

Poly(9-phenylcarbazole) (P9PC) films were synthesized electrochemically by direct anodic oxidation of 9-phenylcarbazole in boron trifluoride diethyletherate (BFEE) containing additional 2% sulfuric acid (by volume). The oxidation potential onset of 9-phenylcarbazole in this medium was measured to be 0.9 V vs. SCE, which was much lower than that in acetonitrile containing 0.1 mol L⁻¹ Bu₄NBF₄ (1.1 V vs. SCE). P9PC films obtained from this medium showed good electrochemical behavior and good thermal stability with an electrical conductivity of 0.09 S cm⁻¹. The structure and morphology of the polymer were investigated by UV–visible spectroscopy, infrared spectroscopy, and scanning electron microscopy (SEM), respectively. The results of quantum chemistry calculations of 9-phenylcarbazole monomer indicated that the polymerization mainly occurred at C₃ and C₆ positions. Fluorescent spectral studies indicated that P9PC was a blue-light emitter.     

Bottom-gated epitaxial graphene

High-quality epitaxial graphene on silicon carbide (SiC) is today available in wafer size. Similar to exfoliated graphene, its charge carriers are governed by the Dirac-Weyl Hamiltonian and it shows excellent mobilities. For many experiments with graphene, in particular for surface science, a bottom gate is desirable. Commonly, exfoliated graphene flakes are placed on an oxidized silicon wafer that readily provides a bottom gate. However, this cannot be applied to epitaxial graphene as the SiC provides the source material out of which graphene grows. Here, we present a reliable scheme for the fabrication of bottom-gated epitaxial graphene devices, which is based on nitrogen (N) implantation into a SiC wafer and subsequent graphene growth. We demonstrate working devices in a broad temperature range from 6 to 300 K. Two gating regimes can be addressed, which opens a wide engineering space for tailored devices by controlling the doping of the gate structure.     

Electrochemical polymerization of benzene in the presence of Ag+, Pb2+ and Cu+ ions

Poly(p-phenylene) (PPP) films were synthesized by using benzene and fluorosulphonic acid (FSO₃H) as a strong acid containing Ag⁺, Pb²⁺ and Cu⁺ ions in methylene chloride (CH₂Cl₂) solution. Addition of Ag⁺ or Pb²⁺ ions into the polymerization medium improved the PPP films formation, but Cu⁺ ion did not have an effect on polymerization. PPP films were characterized by cyclic voltammetry, IR and TGA. Dry conductivities were measured by using four probe technique. Received: 18 September 2000 / Reviewed and accepted: 20 September 2000     

Modeling of epitaxial graphene functionalization

A new model for graphene epitaxially grown on silicon carbide is proposed. Density functional theory modeling of epitaxial graphene functionalization by hydrogen, fluorine, methyl and phenyl groups has been performed, with hydrogen and fluorine showing a high probability of cluster formation in high adatom concentration. It has also been shown that the clusterization of fluorine adatoms provides midgap states in formation, due to significant flat distortion of graphene. The functionalization of epitaxial graphene using larger species (methyl and phenyl groups) renders cluster formation impossible, due to the steric effect, and results in uniform coverage with the energy gap opening.     

Preparation of epitaxial galliumnitride II

Single crystal GaN has been grown on sapphire from the vapour phase containing NH₃ and either Ga(C₂H₅)₂Cl or GaCl₃. Zn-doping could be achieved with diethylzinc. Both CL uv-intensities and carrier concentrations are dependent upon the deposition temperature. GaN:Zn shows a very intense blue peak at 2.85 ± 0.02eV. With sufficient Zn-doping in-structures can be grown showing blue electroluminescence. GaN was subjected to nitrogen pressures ?500 bar at 1020°C. The effects on the electrical and optical properties were studied.     

The geometry of sintering wires

The geometries of various sintering wire compacts are determined for both surface- and bulk-transport controlled processes. The results indicate very little difference in the geometries during the initial stage of sintering. However, significant differences become apparent when the latter stage of sintering is approached. Under the action of a bulk-transport mechanism, compact shrinkage is expected. The present calculations of shrinkage versus neck size are compared favourably with previously published data. As a result, the relation between shrinkage and neck size is modified. Finally, the specific surface area variation with neck growth is determined for both forms of mass transport, indicating this may be an alternative measure of sintering progression.     

Cold-drawn pearlitic steel wires

Cold-drawn pearlitic steel wires have attracted considerable interest because of their excellent combination of strength and ductility. The physical interpretation of these properties has been a subject of repeated controversial discussions in the literature. Unquestioned is the fact that during the process of cold drawing, cementite is partially dissolved, while the ferrite is obviously enriched in carbon. The debate is related to the questions why cementite is decomposed and where the carbon is accommodated. It is the aim of this work to review the relevant literature and to conciliate the controversies. Special attention is paid to the microstructural evolution during progressive cold-drawing, which eventually attains nanometer-scale in two dimensions and is essential for the evolution of the mechanical as well as electrical properties. This is all the more important as recent developments in atom probe tomography allowed to study the chemical composition on the atomic scale. A further important aspect is the path of recovery and recrystallization, accompanied by softening, during post-draw annealing. A consolidated view indicates that carbon-defect interactions play a major role in all aspects of the wire properties.     

Electrochemical polymerization of an aniline-terminated self-assembled monolayer on indium tin oxide electrodes and its effect on polyaniline electrodeposition

Indium tin oxide (ITO) transparent electrodes were surface modified by a self-assembled monolayer of N-phenyl-γ-aminopropyl-trimethoxysilane (PAPTS). Cyclic voltammetry of the PAPTS monolayer in aniline-free aqueous electrolyte showed the typical shape of a surface-confined monomer, due to the oxidation of the aniline moieties. This process resulted in a two-dimensional polyaniline film with uniform thickness of 1.3 nm, as measured by atomic force microscopy. X-ray photoelectron and UV–visible spectroscopic techniques confirm the formation of a conjugated polymer film. The influence of the surface modification of ITO electrodes on polyaniline electrochemical deposition was also studied. The initial oxidation rate of aniline increased in the PAPTS-modified ITO electrodes, although the overall film formation rate was lower than that of unmodified ITO electrodes. The morphology of the electrodeposited polyaniline films on PAPTS-modified and unmodified ITO electrodes was studied by atomic force microscopy. Films of smaller grain were grown in the PAPTS-modified ITO as compared to films grown on unmodified ITO. A blocking effect due to the propyl spacer is proposed to explain the reduced electron transfer in PAPTS-modified electrodes.     

Production of Fe-P-C amorphous wires by in-rotating-water spinning method and mechanical properties of the wires

Continuous amorphous wires with high strength and good ductility have been produced in the Fe-P-C alloy system by the in-rotating-water spinning technique; however, no amorphous wires are formed, using the same technique, in the Fe-P-B, Fe-P-Si and Fe-B-C systems. The Fe-P-C amorphous wires have a circular cross-section, smooth peripheral surface, and diameters in the range of about 80 to 230m. Their tensile strength, _f, and Vickers hardness,H _v, increase with increasing phosphorus and/or carbon content and reach 3000 MPa and 895 DPN for Fe₇₅P₁₀C₁₅. Fracture elongation, _f, including elastic elongation is about 2.8%. Cold-drawing to an appropriate reduction in area causes an increase in _f and _f of about 3.7 and 79%, respectively. This increase is interpreted to result from an interaction between crossing deformation bands introduced by cold-drawing and the increase in the uniformity of shape for the drawn wires. Further, the undrawn and drawn amorphous wires are so ductile that no cracks are observed even after a sharp bending test. Thus, the Fe-P-C amorphous wires are attractive for fine-gauge high-strength materials both because of the uniform shape of the wires and because of their superior mechanical qualities.