Effect of chemical treatment on electrical conductivity, infrared absorption, and Raman spectra of single-walled carbon nanotubes

We investigate the magnitude and temperature dependence of electrical conductivity, the optical and infrared absorption, and the Raman spectra of single-walled carbon nanotube (SWNT) bucky-paper after chemical treatment and determine the correlations between the changes in these properties. Ionic-acceptor doping of the SWNT bucky-paper (with SOCl(2), iodine, H(2)SO(3), etc.) causes an increase of electrical conductivity that correlates with an increase of the absorbance in the far-IR region and an increase in the frequency of Raman spectral lines. Conversely, treatment with other molecules (e.g., aniline, PyPhF(5), PhCH(2)Br, etc.) leads to a decrease in both conductivity and far-IR absorption. The temperature dependence of the conductivity gives a good indication of the presence of metallic charge carriers and is in agreement with the model of interrupted metallic conduction.     

ZrOCl2掺杂的磷硅酸盐凝胶的机械化学合成

纯磷硅酸盐干凝胶在潮湿环境下存放会使磷酸从中析出,导致其质子电导率显著下降。为此,人们通常采用化学改性处理的方式以解决其化学耐久性差的问题。利用ZrOCl2.8H2O通过溶胶凝胶法对磷硅酸盐进行掺杂,我们发现掺杂量为0.97%时,所得凝胶的质子电导率最高。基于此,本文利用高能球磨技术研究了磷硅酸盐凝胶的ZrOCl2掺杂。研究结果表明:机械研磨能够提高原料混合物的质子电导率,当研磨时间为10 h时,所得材料的质子电导率最大,σ130=2.4 S·m-1。这一数值与利用溶胶-凝胶法制备的同样化学成分的样品相同。但前者的质子传导激活能高于后者,造成这一差别的主要原因是两者内部的组织结构存在一定差别。31P NMR(Nuclear Magnetic Resonance核磁共振)谱测试结果表明:机械研磨处理的样品(尤其MM10 h)化学耐久性较好。     

Ab initio study of NH3 and H2O adsorption on pristine and Na-doped MgO nanotubes

We have investigated, on the basis of density functional theory calculations, the structural and electronic properties of chemical modification of pristine and Na-doped MgONTs with NH₃ and H₂O molecules. We found that the NH₃ and H₂O molecules can be barrierlessly adsorbed on the Mg atom of the tube sidewall along with a charge transfer from the adsorbate to MgONT. The adsorption is chemical in nature with adsorption energies about ?22.3 and ?21.5 kcal/mol for H₂O and NH₃, respectively. The calculated density of state (DOS) shows that the chemical modification of MgONTs with these molecules can be generally classified as certain type of “harmless modification.” In other words, the electronic properties of the MgONT are little changed by the adsorption processes. The substitution of an Mg atom in the tube surface with an Na atom results in a semi-insulator to p-type semiconductor transition based on DOS analysis. It was also found that the doping process reduces the adsorption energies and the electronic properties of Na-doped MgONT is slightly more sensitive toward NH₃ and H₂O molecules, compared with the pristine one.     

Amphoteric doping of carbon nanotubes by encapsulation of organic molecules: electronic properties and quantum conductance

In order to investigate and optimize the electronic transport processes in carbon nanotubes doped with organic molecules, we have performed large-scale quantum electronic structure calculations coupled with a Green's function formulation for determining the quantum conductance. Our approach is based on an original scheme where quantum chemistry calculations on finite systems are recast to infinite, non-periodic (i.e., open) systems, therefore mimicking actual working devices. Results from these calculations clearly suggest that the electronic structure of a carbon nanotube can be easily manipulated by encapsulating appropriate organic molecules. Charge transfer processes induced by encapsulated organic molecules lead to efficient n- and p-type doping of the carbon nanotube. Even though a molecule can induce p and n doping, it is shown to have a minor effect on the transport properties of the nanotube as compared to a pristine tube. This type of doping therefore preserves the intrinsic properties of the pristine tube as a ballistic conductor. In addition, the efficient process of charge transfer between the organic molecules and the nanotube is shown to substantially reduce the susceptibility of the pi electrons of the nanotube to modification by oxygen while maintaining stable doping (i.e., no dedoping) at room temperature.     

硅氧烷交联的咪唑基团功能化聚苯醚/聚四氟乙烯耐高温质子交换膜

以聚苯醚(PPO)为基体材料, 通过溴甲基化及咪唑基团功能化, 与聚四氟乙烯(PTFE)复合、 硅氧烷基团水解交联及磷酸掺杂, 制备了兼具高磷酸掺杂含量、 高质子电导率和良好机械性能的高温质子交换膜材料. 以甲基咪唑(MeIm)和咪唑基硅氧烷化合物(SiIm)为功能化试剂(其中咪唑基团提供了磷酸作用位点, 同时SiIm中的硅氧烷基团水解后得到Si—O—Si交联网络结构), 提高了膜材料的机械稳定性. 与PTFE的复合进一步增强了膜材料的机械强度. 结果表明, 复合膜具有较高的电导率和一定的机械强度. 当磷酸掺杂质量分数为242.5%时, PPO-50%SiIm-50%MeIm/PTFE复合膜在160 ℃不加湿条件下的电导率为0.09 S/cm, 室温下的断裂拉伸强度为3.6 MPa.     

Facet-dependent and au nanocrystal-enhanced electrical and photocatalytic properties of Au-Cu2O core-shell heterostructures

We report highly facet-dependent electrical properties of Cu(2)O nanocubes and octahedra and significant enhancement of gold nanocrystal cores to the electrical conductivity of Au-Cu(2)O core-shell octahedra. Cu(2)O nanocubes and octahedra and Au-Cu(2)O core-shell cubes and octahedra were synthesized by following our reported facile procedures at room temperature. Two oxide-free tungsten probes attached to a nanomanipulator installed inside a scanning electron microscope made contacts to a single Cu(2)O nanocrystal for the I-V measurements. Pristine Cu(2)O octahedra bounded by {111} facets are 1100 times more conductive than pristine Cu(2)O cubes enclosed by {100} faces, which are barely conductive. Core-shell cubes are only slightly more conductive than pristine cubes. A 10,000-fold increase in conductivity over a cube has been recorded for an octahedron. Remarkably, core-shell octahedra are far more conductive than pristine octahedra. The same facet-dependent electrical behavior can still be observed on a single nanocrystal exposing both {111} and {100} facets. This new fundamental property may be observable in other semiconductor nanocrystals. We also have shown that both core-shell cubes and octahedra outperform pristine cubes and octahedra in the photodegradation of methyl orange. Efficient photoinduced charge separation is attributed to this enhanced photocatalytic activity. Interestingly, facet-selective etching occurred over the {100} corners of some octahedra and core-shell octahedra during photocatalysis. The successful preparation of Au-Cu(2)O core-shell heterostructures with precise shape control has offered opportunities to discover new and exciting physical and chemical properties of nanocrystals.     

Ion implantation doping and electrical properties of high-temperature ladder polymers

We report the first ion implantation doping studies on high-temperature ladder polymers and show that insulting films of the benzimidazobenzophenanthroline-type ladder polymer (BBL) can be doped by boron, argon, and krypton implantation to conductivities as high as 224 S/cm at a dose of 4.0 × 10¹⁶/cm² while retaining the excellent mechanical properties of the pristine films. Effects of dose (ions/cm²) and beam current density (microamps/cm²) on electrical conductivity at fixed ion energies are reported. The temperature dependence of the conductivity indicates that the implanted ladder polymer films are semiconductors. Spatially selective implantation, creating regions of conducting lines in an insulating matrix, which suggests microelectronic device applications of the ladder polymers, is demonstrated.     

Electronic properties of the linear ladder polymer,poly[4-(3-pyridyl),8-methyl,2,3–6,7-quinolino] (PPMQ)

Electronic paramagnetic resonance (EPR) and conductivity of pristine and iodine-doped PPMQ were studied. The pristine polymer EPR signal exhibited a Lorentzian line shape. Unpaired spin density measurements indicated that the spin concentrations of the undoped polymer lie in the range of one spin per 150–190 repeat units at room temperature. The peak-to-peak width doubled, the line shape became asymmetric and the spin concentration in the polymer increased slightly after doping with iodine. EPR saturation experiments show that the spin lattice relaxation time T₁ is sensitive to trace impurity. Considerable reduction of T₁ after doping with iodine shows strong coupling between the spin system and N-iodonium nucleus. Conductivity increases up to 5 orders of magnitude by iodine doping; at room temperature, the best value found was 0.017 S/cm. The activation energy for conductance after doping is about half that of pristine polymer.     

LaCo(1-x)Ni(x)O(3) with Improved Electrical Conductivity

To determine the applicability of LaCo(1-x)Ni(x)O(3) in a conductive material for electrical wiring, the dependence of the electronic transport property on the Ni content is investigated via Hall effect measurements, Rietveld analyses, and band-structure calculations. Ni doping (50 mol %) into the Co sites realizes a high electrical conductivity of 1.9 × 10(3) S/cm, which is an unexpectedly high value for a LaCo(1-x)Ni(x)O(3) system, at room temperature due to the high carrier concentration of 2.2 × 10(22) cm(-3) and the small effective mass of 0.1 m(e). In addition, the high electrical conductivity is maintained from room temperature to 900 °C; that is, the temperature coefficient of the conductivity is smaller than that of standard metals. Thus, the results indicate that LaCo(0.5)Ni(0.5)O(3) is suitable as a conductive material for electrical wiring at high temperatures in air.     

Preparation of electrically conducting cellulose fibres utilizing polyelectrolyte multilayers of poly(3,4-ethylenedioxythiophene):poly(styrene sulphonate) and poly(allyl amine)

The primary goal with this work is to create electrically conductive cellulose fibres, this has been done to explore possible new applications for fibre based material. This research uses various methods to create polyelectrolyte multilayers (PEMs) on bleached softwood fibres and on SiO₂ model surfaces, by sequentially treating these materials with poly(3,4-ethylenedioxythiophene):poly(styrene sulphonate) (PEDOT:PSS) and poly(allyl amine) (PAH). Paper sheets were then produced from the PEM-modified pulp and evaluated in terms of tensile strength, adsorbed amount of polymer, and electrical conductivity. To evaluate the influence of fibre charge on the measured paper properties, pulps of two different initial fibre charge densities were prepared via carboxymethylation. Because of the bluish colour of PEDOT:PSS, the build-up of PEM could be easily followed, since the fibres grew increasingly darker blue throughout the modification sequence. The conductivity of the fibre network increased by 2−3 orders of magnitude when the pulp of a higher fibre charge density was used. This suggests that it is more important to create a fibrous network with a high fibre-fibre joint strength and a large total joined area in the sheet rather than to maximize the adsorbed amount of PEDOT:PSS. A difference in conductivity could also be noted depending on the polyelectrolyte adsorbed in the outer layer, PAH lowered the conductivity compared to PEDOT:PSS. Evaluating the mechanical properties revealed that the use of PEDOT:PSS reduces the tensile strength of the paper. When five double layers had been adsorbed onto the carboxymethylated sample in which PEDOT:PSS formed the outer layer, calculations indicated a 25% decrease in tensile strength compared to that of reference material without PEMs. ESEM studies indicate that PEM treatment produces a significantly changed and somewhat smoother fibre surface.     

Dielectric properties and surface morphology of swift heavy ion beam irradiated polycarbonate films

Swift heavy ion beam irradiation induces modification in the dielectric properties and surface morphologies of polycarbonate (PC) films. The PC films were irradiated by 55 MeV energy of C⁵⁺ beam at various ions fluences ranging from 1 × 10¹¹ to 1 × 10¹³ ions cm^?2. The dielectric properties (i.e., dielectric constant, dielectric loss, and AC conductivity) and surface morphologies of pristine and SHI beam irradiated PC films were investigated by dielectric measurements, atomic force microscopy (AFM), and optical microscopy. The dielectric measurements show that the dielectric constant, dielectric loss, and AC conductivity increase with ion fluences and temperature, however, the dielectric constant and AC conductivity decrease while dielectric loss increases with frequency. AFM shows the increase in average roughness values with ion fluences. The change of color in PC films has been observed from colorless to yellowish and then dark brown with increases of ion fluence by using optical microscopy.     

ZrOCl2掺杂对磷硅酸盐凝胶质子导电性能的影响

采用溶胶-凝胶技术研究了ZrOCl₂·8H₂O掺杂对磷硅酸盐凝胶质子导电性能的影响. 结果表明, 掺杂ZrOCl₂·8H₂O能提高磷硅酸盐凝胶的质子电导率, 并且掺杂质量分数为0.97%时质子电导率达到最大值(σ₁₃₀=2.38 S/m). 掺杂样品在相对湿度为40%条件下放置30 d后, 未发生H₃PO₄渗出现象, 其质子传导性能基本不变. 核磁共振谱结果表明, 掺杂ZrOCl₂减少了磷硅酸盐凝胶结构中自由磷酸的形成, 提高了与四面体之间的化学结合力.     

Fabrication and optimization of proton conductive polybenzimidazole electrospun nanofiber membranes

Phosphoric acid (PA)–doped polybenzimidazole (PBI) proton exchange membranes have received attention because of their good mechanical properties, moderate gas permeability, and superior proton conductivity under high temperature operation. Among PBI‐based film membranes, nanofibrous membranes withstand to higher strain because of strongly oriented polymer chains while exhibiting higher specific surface area with increased number of proton‐conducting sites. In this study, PBI electrospun nanofibers were produced and doped with PA to operate as high temperature proton exchange membrane, while changes in proton conductivity and morphologies were monitored. Proton conductive PBI nanofiber membranes by using the process parameters of 15 kV and 100 μL/h at 15 wt% PBI/dimethylacetamide polymer concentration were prepared by varying PA doping time as 24, 48, 72, and 96 hours. The morphological changes associated with PA doping addressed that acid doping significantly caused swelling and 2‐fold increase in mean fiber diameter. Tensile strength of the membranes is found to be increased by doping level, whereas the strain at break (15%) decreased because of the brittle nature of H‐bond network. 72 hour doped PBI membranes demonstrated highest proton conductivity whereas the decrease on conductivity for 96‐hour doped PBI membranes, which could be attributed to the morphological changes due to H‐bond network and acid leaking, was noted. Overall, the results suggested that of 72‐hour doped PBI membranes with proton conductivity of 123 mS/cm could be a potential candidate for proton exchange membrane fuel cell.     

Preparation and characterization of LiNi0.8Co0.2O2/PANI microcomposite electrode materials under assisted ultrasonic irradiation

A preparation method for a new electrode material based on the LiNi_0.8Co_0.2O₂/polyaniline (PANI) composite is reported. This material is prepared by in situ polymerization of aniline in the presence of LiNi_0.8Co_0.2O₂ assisted by ultrasonic irradiation. The materials are characterized by XRD, TG-DTA, FTIR, XPS, SEM-EDX, AFM, nitrogen adsorption (BET surface area) and electrical conductivity measurements. PANI in the emeraldine salt form interacts with metal-oxide particles to assure good connectivity. The dc electrical conductivity measurements at room temperature indicate that conductivity values are one order of magnitude higher in the composite than in the oxide alone. This behavior determines better reversibility for Li-insertion in charge-discharge cycles compared to the pristine mixed oxide when used as electrode of lithium batteries.     

聚并苯的链间作用对其导电能力的影响

采用量子化学晶体轨道ＣＮＤＯ／ ２ 方法,在考虑聚并苯链间作用的基础上对聚并苯双链模型的电子结构进行计算和讨论．结果表明：聚并苯链处于不同相对位置的链间作用对聚并苯的电荷分布规律及能带结构均有一定影响,位置不同,影响不同．从聚并苯的能带结构可以得出：聚并苯是有较小能隙、良好本征导电性能的半导体材料,考虑链间作用,对能带结构特征未有大的改变,能隙等值略有修正,导电能力有所加强．利用此模型讨论,更接近于晶体的真实结构,对进行聚并苯导电材料的性能改进将有一定帮助．     

聚吡咯/多壁碳纳米管及其聚氨酯导电复合材料的制备和性能

以羧基化多壁碳纳米管(MWCNTs)做模版剂,采用化学氧化法将吡咯(Py)在羧基化MWCNTs表面聚合制备PPy/MWCNTs导电材料,将其添加到溶剂型聚氨酯(PU)溶液中制备了PPy/MWCNTs/PU导电复合材料,研究了Py用量对PPy/MWCNTs及其PU复合材料性能的影响.研究表明,随Py用量的增加,PPy/MWCNTs的长度不变,管径增大,sp~2和sp~3杂化C含量先提高后减少,N的掺杂梯度降低,PPy/MWCNTs的导电率高于羧基化MWCNTs和PPy.当Py用量为羧基化MWCNTs的20%时,其导电率最大.PPy/MWCNTs中N元素的掺杂程度及其管径变化是引起PPy/MWCNTs/PU复合材料的性能不同的主要原因.增加Py用量,MWCNTs中亲水的羧基因对PPy掺杂而消耗,相同导电材料用量时纳米导电粒子数目相对减少,PPy/MWCNTs/PU复合材料的耐水性能提高,定向应力、储能模量和玻璃化温度降低,导电率先增加后减小.当Py用量为羧基化MWCNTs的15%时,导电率最大.     

Effect of synthesis temperature and doping level on conductivity and structure of poly(3-methyl thiophene)

Poly(3-methyl thiophene) was synthesized by oxidative chemical polymerization technique using ferric chloride as the dopant in an inert atmosphere. Samples of different doping levels were prepared and analyzed by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy, and direct current (DC) conductivity measurement at room temperature (300 K). Synthesis of the polymer was confirmed by FTIR studies. FTIR spectra showed a shift in the heterocyclic bands in the region of 700-1200 cm(-1) with a decrease in synthesis temperature. It was evident from the scanning electron micrographs that the surface structure of the polymer became denser with an increase in doping level. The measured DC conductivity increased initially up to the doping level of 0.8 M and then this increase tended to slow down. Samples having a doping level of 0.4 M were synthesized at 300, 280, and 270 K while maintaining the other synthesis parameters. The conductivity and yield were found to increase as the temperature of the polymerization decreased.     

Unusual enhancement in electrical conductivity of tin oxide thin films with zinc doping

Electrical conductivity of SnO(2)-based oxides is of great importance for their application as transparent conducting oxides (TCO) and gas sensors. In this paper, for the first time, an unusual enhancement in electrical conductivity was observed for SnO(2) films upon zinc doping. Films with Zn/(Zn + Sn) reaching 0.48 were grown by pulsed spray-evaporation chemical vapor deposition. X-Ray diffraction (XRD) shows that pure and zinc-doped SnO(2) films grow in the tetragonal rutile-type structure. Within the low doping concentration range, Zn leads to a significant decrease of the crystallite size and electrical resistivity. Increasing Zn doping concentration above Zn/(Zn + Sn) = 0.12 leads to an XRD-amorphous film with electrical resistivity below 0.015 ? cm at room temperature. Optical measurements show transparencies above 80% in the visible spectral range for all films, and doping was shown to be efficient for the band gap tuning.     

Structures and Electromagnetic Properties of Boron Nitride Nanoribbons Doped with Transition Metals

Inspired by the recent discovery of the Ti-doped BN nanocages, here we report the design of novel boron nitride (BN) nanoribbons (BNNRs) doped with fourth-row transition metals (Sc−Cu) and the prediction of their structural and electromagnetic properties. First-principles calculations and ab initio molecular dynamics simulations show that Ti-doped BNNR possesses both thermodynamic and kinetic stability at high temperatures for synthesis of BN materials. Metal doping may make the nonmagnetic pristine BNNR ferromagnetic or antiferromagnetic, depending on the metal. The doping with all considered metals reduces substantially the band gap of pristine BNNR. For example, Sc-doped BNNR is ferromagnetic with an indirect band gap of 1.18 eV, while V-doped nanoribbon is antiferromagnetic with a direct gap of 2.50 eV. Remarkably, the carrier mobility in both materials is significantly enhanced compared to the pristine BNNR. Our findings suggest that doping with different metals may endow BNNRs with versatile electronic and magnetic properties.     

Regeneration of a Conjugated sp2 Graphene System through Selective Defunctionalization of Epoxides by Using a Proven Synthetic Chemistry Mechanism

Graphene is a promising material capable of driving technological advancement. It is, however, a challenge to obtain pristine graphene in large quantities given the limitation of current synthetic methods. Among the numerous methods available, the chemical approach provides an optimistic outlook and has garnered much interest within the graphene community as a potential alternative. One of the most crucial steps of the chemical approach is the chemical reduction of graphene oxide as this dictates the final quality of the graphene sheets. In recent years, much of the focus has shifted to the usage of established reducing agents or oxygen removal reagents, frequently applied in organic chemistry, onto a graphene oxide platform. Herein, the selective removal of epoxide groups and subsequent regeneration of disrupted conjugated sp² system is highlighted, based on the synergistic effect of indium and indium(I) chloride. The morphological, structural, and electrical properties of the resulting graphene were fully characterized with X‐ray photoelectron, Fourier transform IR, solid‐state ¹³C NMR, and Raman spectroscopy; thermogravimetric analysis; scanning electron microscopy; and conductivity measurements. The as‐prepared graphene showed a tenfold increase in conductivity against conventional graphene treated with hydrazine reducing agent and demonstrated a high dispersion stability in ethanol. Moreover, the selective defunctionalization of the epoxide groups provides opportunities for potential tailoring of graphene properties for prospective applications.