Effects of polymerization media on the nanoscale conductivity and current-voltage characteristics of chemically synthesized polyaniline films

A current sensing atomic force microscope (CS-AFM) was used to probe the conducting homogeneity and band structures of fully doped polyaniline (PANI) films prepared from in situ chemical polymerization/deposition of aniline on indium tin oxide in various inorganic acids. The charge transport properties of PANI films depend on the film thickness as well as polymerization medium. Fluctuations in conductivity are observed on all acid-doped PANI films and the conducting homogeneity was dependent on the film thickness: the conductivity of thick film is more uniform. The current-voltage (I-V) characteristics of all thick (>200 nm) films displayed a metal-like behavior and conductivity as high as 40 S/cm was detected in high conducting regions of film thicker than 400 nm. Whereas thin (<120 nm) films revealed insulating, semiconducting, and semimetal conducting, wide distribution in conductivity and interband distances (estimated from the I-V ordI/dV-V curves) was found. The interband distances is 0-1.35, 0-1.0, and 0-0.78 eV for thin PANI film prepared from HCl(aq), HClO(4)(aq), and H2SO4(aq), respectively. PANI film (260 nm) prepared from H2SO4(aq) revealed fiberlike morphology, and compared to PANI films prepared from HCl(aq) and HClO4(aq) with similar thickness, it has higher average nanoscale conductivity but lower bulk conductivity. This result could be direct evidence which supports that the bulk conductivity of PANI depended on the carriers hopping between the conducting domains.     

Gradient doping of conducting polymer films by means of bipolar electrochemistry

In this paper, we report a novel electrochemical doping method for conducting polymer films based on bipolar electrochemistry. The electrochemical doping of conducting polymers such as poly(3-methylthiophene) (PMT), poly(3,4-ethylenedioxythiophene) (PEDOT), and poly(aniline) (PANI) on a bipolar electrode having a potential gradient on its surface successfully created gradually doped materials. In the case of PEDOT film, the color change at the anodic side was also observed to be gradually transparent. PANI film treated by the bipolar doping gave a multicolored gradation across the film. The results of UV-vis and energy dispersive X-ray analyses for the doped films supported the distribution of dopants in the polymer films reflecting the potential gradient on the bipolar electrode. Furthermore, the reversibility of the bipolar doping of the PMT film was demonstrated by a spectroelectrochemical investigation.     

高导电聚苯胺薄膜的制备及其电磁屏蔽性能的研究

随着电器制品、电子器件的商用、军事用和科学应用的迅速增长 ,产生了亟待解决的电磁干扰 (也称作电磁环境污染 )问题 ,电磁干扰屏蔽日益受到关注 .本文从聚苯胺掺杂工艺角度出发 ,通过改变掺杂剂用量和溶剂种类 ,制备出高导电的聚苯胺薄膜 ,并对其电磁屏蔽特性进行了初步的测试与理论分析 ,将屏蔽效能的实测结果与理论计算值进行了比较     

Structural,optical and photoelectron spectroscopic studies of nano/micro ZnO:Cd rods synthesized via sol-gel route

Thin films of cadmium doped zinc oxide rod like microstructure have been synthesized by a very simple sol-gel dip coating technique. Sols were prepared from hydrated zinc oxide precursor and 2-methoxyethanol solvent with monoethanolamine as a sol stabilizer. XRD pattern confirmed the hexagonal wurtzite structure of the deposited ZnO films. Surface morphologies of the films have been studied by a scanning electron microscope and an atomic force microscope, which confirmed that the films are composed of densely packed randomly oriented nano/submicron rods with diameter in the range 300–400 nm having various lengths. We proposed a possible growth mechanism for this rodlike structure. X-ray photoelectron spectroscopic study was used to determine the binding energies and the Zn 2p3/2, Cd 3d5 and O 1s peaks in the XPS spectra were located at 1021.08 eV, 404.6 eV and 529.8 eV respectively, which confirmed the Cd doping in ZnO. Cadmium content in the film was estimated both from energy dispersive X-ray analysis and XPS measurement. Band gap energy determined from optical transmittance spectra systematically varied from 3.28 eV to 3.15 eV for 0% to 5.6% of Cd doping. Urbach parameter determined from the band tail of the transmittance spectra showed that it increased with doping percentage and this parameter for a fixed cadmium doping level decreased with increase of temperature.     

Synthesis and characterization of polyaniline/silicon dioxide composites and preparation of conductive films

The focus of this study was to synthesize the inherently conductive polymer polyaniline using an optimized process to prepare polyaniline/silicon dioxide (PANI/SiO₂) composites by in situ polymerization and ex situ solution mixing. PANI and PANI/SiO₂ composite films were prepared by drop‐by‐drop and spin coating methods. The electrical conductivities of HCl doped PANI film and PANI/SiO₂ composite films were measured according to the standard four‐point‐probe technique. The composite films exhibited an increase in electrical conductivity over neat PANI. PANI and PANI/SiO₂ composites were also investigated by spectroscopic methods including UV‐Vis, FT‐IR, and Photoluminescence. UV‐Vis and FT‐IR studies showed that SiO₂ particles affect the quinoid units along the polymer backbone and indicate strong interactions between the SiO₂ particles and the quinoidal sites of PANI (doping effect). The photoluminescence properties of PANI and PANI/SiO₂ composites were studied and the PANI/SiO₂ composites showed increased intensity as compared to neat PANI. The increase of conductivity of PANI/SiO₂ composite may be partially due to the doping or impurity effect of SiO₂ where the silicon dioxides compete with chloride ions. The morphology of particles and films were examined by a scanning electron microscope (SEM). SEM measurements indicated that the SiO₂ were well dispersed and isolated in composite films. Copyright © 2009 John Wiley & Sons, Ltd.     

聚苯胺纳米点阵列的制备和库仑台阶现象

本文制备了PANI纳米点阵列, 利用导电原子力显微镜(C-AFM)表征了其形貌和导电性能, 在室温下观察到PANI纳米点的库仑台阶(Coulomb staircase)现象, 并利用库仑阻塞效应的理论进行了初步的分析.     

显微共焦拉曼光谱研究电化学合成聚苯胺膜

显微共焦拉曼技术被用来研究电化学合成的聚苯胺（PANI）膜. 研究结果表明：在不同的激发光聚焦深度，聚苯胺膜的拉曼光谱有明显变化.从而反映出聚苯胺膜的掺杂程度在膜生长过程中随膜厚度的增长而增加. 并由X射线电子能谱（XPS）和紫外吸收光谱（UV）分析证实.     

Preparation of polyaniline conductive composites with diene‐rubber or polyphenylacetylene

We describe the preparation of polyaniline (PANI‐EB) by aniline oxidation with KIO₃ and the purification of the resulting dedoped polymer by an acetone extraction step to eliminate undesired by‐products from polyaniline, which could generate some safety concerns in the application and use of PANI. Excellent homogeneous and electrically conducting composite films can be prepared from chloroform solutions of purified PANI doped with camphorsulfonic acid in presence of cis‐1,4‐polybutadiene as the film‐forming agent. These films have been characterized by FT‐IR and UV‐VIS‐NIR spectroscopy. A method to synthesisze PANI directly doped with dodecylbenzenesulfonic acid (DBSA) is also reported. DBSA‐doped‐PANI was then used to prepare composites with polyphenylacetylene (PPA) by growing homogeneous films from chloroform solution. These films were conductive and were studied by FT‐IR and UV‐VIS‐NIR spectroscopy. In view of the application of these composites as gas sensors or in “electronic noses”, a short discussion is presented about the criteria used in the selection of the chemical nature of the host polymer where doped PANI is included to confer electrical conductivity. The interaction between the molecules to be detected and the polymeric sensing surface is discussed in terms of physisorption, chemisorption and charge‐transfer‐complex formation. Copyright © 2001 John Wiley & Sons, Ltd.     

Phenol assisted deaggregation of polyaniline chains: simple route to high quality polyaniline film

High conducting polyaniline films were readily prepared by in situ chemical oxidative polymerization/deposition of aniline in the presence of a very small amount of organic additive such as phenol. The conductivity of a thin ( approximately 150 nm) polyaniline film synthesized in the presence of 0.01 wt % of phenol ( r-PANI) is an order of magnitude higher (as well as better conducting homogeneity) than that of a film (PANI) obtained from the conventional method without an additive. r-PANI also has better adhesion and electrochemical stability/reversibility, more transparency in the visible-light region, and faster/easier doping/dedoping response compared to PANI. The function of phenol molecule is to avoid the formation of the inter- and/or intrachain hydrogen bonding during the growth of the polyaniline chains. The deaggregation/reducing intrachain hydrogen bonding of polyaniline chains by phenol molecules was revealed with IR, SAXS, and SEM data. All these data supported that phenol does assist the deaggregation of polyaniline chains during the growth of polymer chains or nanorods.     

Contribution of conformational change of polymer structure to electrochemomechanical deformation based on polyaniline

The pH dependencies of electrochemomechanical deformation (ECMD) including the cyclic voltammetry and the expansion ratio in conducting polymers, polyaniline (PANI), and poly(o-methoxyaniline) film were studied to elucidate the mechanisms. It was found that the ECMD is governed by the conformational change of polymer structure as well as the insertion of bulky ions in the manner of comparable magnitude. Expansion ratios >20% in the ECMD were demonstrated for the thickness direction of PANI film. The results suggest that the magnitude of ECMD can be improved by choosing the preparation method of films.     

Synthesis,characterization and enhanced electrical properties of CTAB-directed polyaniline nanoparticles

Inverse microemulsion system of cetyltrimethylammonium bromide (CTAB) molecules is utilized for virtually monodispersed and controlled growth of HCl polyaniline (PANI) nanoparticles at room temperature (ca. 300 K). The templated electroconductive polymer reveals lamellar crystalline structure under X-ray diffraction signifying marked sub-chain alignment of the polymerized nanoparticles. The nanostructured polymer has spherically symmetric morphology in a size range of 2.0 nm to 6.0 nm under electron microscope examination. Gel permeation chromatography gives polydispersity index of 1.02 for nanostructured polymer in agreement with the size monodispersity transpired by electron microscopy. The d.c. electrical conductivity σ _dc of PANI at room temperature is 10.11 S/cm whereas the variation of conductivity with temperature in the range 227–303 K reveals that the conducting mechanism can be considered as three-dimensional variable-range-hopping (3D-VRH). UV-Vis spectrum indicates two broad absorption bands due to polaron formation that contributes to enhanced electrical conductivity of the polymer. The fundamental absorption edge in the polymer is formed by direct allowed transitions to the extent that the optical band gap value was found to be 2.35 eV. The crystalline nanostructure and homogeneous doping attained in the cationic template of amphiphile are argued as contributing factors to the enhanced conductivity of the polymer.     

Direct electrochemical nanopatterning of polycarbazole monomer and precursor polymer films: ambient formation of thermally stable conducting nanopatterns

The direct nanopatterning of polycarbazole on ultrathin films of a "precursor polymer" and monomer under ambient conditions is reported. In contrast to previous reports on electrochemical dip-pen nanolithography using monomer ink or electrolyte-saturated films in electrostatic nanolithography, these features were directly patterned on spin-cast films of carbazole monomer and poly(vinylcarbazole) (PVK) under room temperature and humidity conditions. Using a voltage-biased atomic force microscope (AFM) tip, electric-field-induced polymerization and cross-linking occurred with nanopatterning in these films. Different parameters, including writing speed and bias voltages, were studied to demonstrate line width and patterning geometry control. The conducting property (current-voltage (I-V) curves) of these nanopatterns was also investigated using a conducting-AFM (C-AFM) setup, and the thermal stability of the patterns was evaluated by annealing the polymer/monomer film above the glass transition (T(g)) temperature of the precursor polymer. To the best of our knowledge, this is the first report in which thermally stable conducting nanopatterns were drawn directly on monomer or polymer film substrates using an electrochemical nanolithography technique under ambient conditions.     

Electrical transport properties of an organic semiconductor on polyaniline doped by boric acid

The electrical conductivity, thermoelectric power, and dielectric properties of polyaniline doped by boric acid (PANI‐B) have been investigated. The room temperature electrical conductivity of PANI‐B was found to be 1.02 × 10^?4 S cm^?1. The thermoelectric power factor for the polymer was found to be 0.64 µW m^?1 K^?2. The optical band gap of the PANI‐B was determined by optical absorption method, and the PANI‐B has a direct optical band gap of 3.71 eV. The alternating charge transport mechanism of the polymer is based on the correlated barrier hopping (CBH) model. The imaginary part of the dielectric modulus for the PANI‐B suggests a temperature dependent dielectric relaxation mechanism. Electrical conductivity and thermoelectric power results indicate that the PANI‐B is an organic semiconductor with thermally activated conduction mechanism. Copyright © 2008 John Wiley & Sons, Ltd.     

Optical properties of nanostructure boron doped NiO thin films

Boron doped NiO films were prepared by sol–gel method. The effects of B content on the morphological and optical properties of NiO films were studied with atomic force microscopy, and optical characterization method. The average transmittance at the visible region is reached to 75 % for lower doped films (0.1 and 0.2 % B), whereas, the recorded average value of transmittance was about 62 % for doped film with 1 % B throughout the region. The optical energy gap value for pure NiO film was found to be 3.73 eV. These values were affected by B doping with non-monotonic variation and reached to 3.64 eV for 0.1 % B doped NiO. Also, the refractive index dispersion and dielectric constants of the NiO films were studied throughout the investigated range of wavelengths. The obtained results indicate that the optical parameters of the NiO film are controlled with boron doping.     

TiO_2聚苯胺复合膜的光电化学

利用电化学方法制备了TiO2 聚苯胺 (PANI)复合膜 .该膜具有比TiO2 或PANI膜更宽的吸收谱区 ,并且不同于利用聚苯胺光敏化的TiO2 膜 ,表现为两者复合材料膜的性质 .扫描电镜图表明 ,TiO2 微粒不完全覆盖着PANI膜 .根据TiO2 微粒光电流谱带的阈值能可得复盖在部分氧化态聚苯胺膜上的TiO2 微粒的禁带宽度为 3.0eV .部分氧化态聚苯胺膜的光电流谱遵循Fowler定律 ( 1/2 ～hυ成线性 ) .通过Fowler图得出部分氧化态聚苯胺的绝缘母体禁带宽度为 3.33eV ,并证实该绝缘母体为还原态聚苯胺 .从Mott Schottky图得到在 0 .0 5mol/LK3Fe(CN) 6 /K4 Fe(CN) 6 溶液中 (pH =8.52 )部分氧化态聚苯胺的平带电位为 0 .13V ,掺杂浓度为 5.3× 10 18cm- 3;TiO2 PANI复合膜的平带电位为 - 0 .6 5V ,掺杂浓度为 9.1× 10 19cm- 3.解释了TiO2 PANI复合膜的光电化学过程并描绘出其能带图 .利用TiO2 PANI复合膜能够有效地光降解苯酚溶液 .     

Electrically conducting plastic films from polyethylene terephthalate for optoelectronic applications

Iodine doping of polyethylene terephthalate (PET) has been made to develop intrinsically conducting plastic films. The doped material is investigated in terms of structure and morphology, electrical and optical characteristics. Considerable decrease in the value of the degree of crystallinity is observed on doping the samples. Further there are discernible shifts found in the energy gap and band edge towards lower energies on doping with iodine. The refractive index of the complex films is also found to increase.     

Polyaniline-coated carbon particles and their electrode behavior in organic carbonate electrolyte

In an attempt to increase the interface stability of carbon used in Li-ion batteries, a thin conducting polyaniline (PANI) film was fabricated on the surface of carbon by in situ chemical polymerization. The chemical and electrochemical properties of the composite material were characterized using X-ray diffraction, Raman spectroscopy, scanning electron microscope, cyclic voltammetry, and electrochemical impedance spectroscopy. It was confirmed that the PANI film has an obvious effect on the morphology and the electrochemical performance of carbon. The results could be attributed to the electronic and electrochemical activity of the conducting PANI films.     

Phosphoric acid diesters protonated polyaniline: Preparation,spectroscopic properties,and processability

Aliphatic and aromatic diesters of phosphoric acid were tested as dopants improving pro-cessability of polyaniline (PANI) in its doped (conducting) state. It has been found that both aromatic and aliphatic diesters effectively protonate polyaniline, inducing at the same time its solubility. The protonated state has been confirmed by three independent spec-troscopic methods (FTIR, Raman, and UV-vis-NIR). Both aromatic and aliphatic diesters of phosphoric acid plasticize polyaniline which, in turn, allows for the preparation of highly conducting films of PANI or highly conducting blends of PANI with classical nonconducting polymers by thermal processing. © 1995 John Wiley & Sons, Inc.     

Investigations on silver/polyaniline electrodes for electrochemical supercapacitors

Polyaniline (PANI) and silver doped polyaniline (Ag/PANI) thin films were deposited on stainless steel substrates by a dip coating technique. To study the effect of doping concentration of Ag on the specific capacitance of PANI the concentration of Ag was varied from 0.3 to 1.2 weight percent. Fourier transform-infrared and Fourier transform-Raman spectroscopy, and energy dispersion X-ray techniques were used for the phase identification and determination of the doping content in the PANI films, respectively. The surface morphology of the films was examined by Field Emission Scanning Electron Microscopy, which revealed a nanofiber like structure for PANI and nanofibers with bright spots of Ag particles for the Ag/PANI films. There was decrease in the room temperature electrical resistivity of the Ag/PANI films of the order of 10(2) with increasing Ag concentration. The supercapacitive behavior of the electrodes was tested in a three electrode system using 1.0 M H(2)SO(4) electrolyte. The specific capacitance increased from 285 F g(-1) (for PANI) to 512 F g(-1) for Ag/PANI at 0.9 weight percent doping of Ag, owing to the synergic effect of PANI and silver nanoparticles. This work demonstrates a simple strategy of improving the specific capacitance of polymer electrodes and may also be easily adopted for other dopants.     

Novel electrical properties of nanoscale thin films of a semiconducting polymer: quantitative current-sensing AFM analysis

Thin films (20-150 nm thickness) of poly(o-anthranilic acid) with various doping levels were prepared on silicon substrates with deposited indium tin oxide, and their topography and current-voltage (I-V) characteristics were quantitatively investigated using current-sensing atomic force microscopy with a platinum-coated tip. The films were found to have a surface morphology like that of orange peel, with a periodic modulation and a surface roughness. The films exhibited nonuniform current flows and I-V characteristics that depended on the doping level as well as on the film thickness. Films with a high doping level were found to exhibit Zener diode switching behavior, whereas the films with a very low doping level (or that were dedoped) exhibited no current flow at all, and so are insulators. Interestingly, self-doped films (which are at an intermediate doping level) were found to have a novel electrical bistability, i.e., a switching characteristic like that of Schottky diodes, and increasingly insulating characteristics as the film thickness was increased. The films with thickness < or =62 nm, which exhibited this novel and stable electrical bistability, can potentially be used in the fabrication of high-density, stable, high-performance digital nonvolatile memory devices based only on transistors. The measured current images and I-V characteristics indicate that the electrical switching and bistability of the films are governed by local filament formation and charge traps.