Synthetic Metals (v.159, #3-4)
Investigation of electrical properties of nanostructured carbon films derived from block copolymers
by P. Kulkarni; L.A. McCullough; T. Kowalewski; L.M. Porter (pp. 177-181).
Electrical properties of nanostructured carbon (ns-C) films fabricated by pyrolysis of PAN–b–PBA copolymers were investigated. Films having cylindrical morphology and pyrolyzed at 400, 500 and 600°C were investigated. Both carbide forming (Zr, Ti) and non-carbide forming (Cu, Pt) metals spanning a wide range of electron work functions (4.1–5.5eV) formed ohmic contacts to the ns-C films in the as-deposited state. The conductivity of the ns-C films increased roughly three orders of magnitude for every 100°C increase in the pyrolysis temperature. Hall-effect measurements showed that the films pyrolyzed at 600°C were n-type with a majority carrier concentration and mobility of 5.8×1018cm−3 and 0.97cm2/V s, respectively. Current–voltage measurements as a function of temperature ( I– V– T) were performed on films pyrolyzed at 600°C, whereas films pyrolyzed at 400 and 500°C were too resistive for reliable resistivity–temperature and Hall-effect measurements. The resistivity as a function of temperature was analyzed by using the reduced activation energy method and was determined to follow variable-range hopping (VRH) mechanisms at and below room temperature. The data indicates a crossover from Efros–Shklovskii VRH [J. Phys. C 8, (1975) L49] to Mott VRH [J. Non-Cryst. Solids 1, (1968) 1] at temperatures above 100K.
Keywords: Nanostructured carbon films; Variable-range hopping; Conduction mechanism; Porous
A polythiophene derivative with octyloxyl triphenylamine-vinylene conjugated side chain: Synthesis and its applications in field-effect transistor and polymer solar cell
by Yingping Zou; Guangyi Sang; Weiping Wu; Yunqi Liu; Yongfang Li (pp. 182-187).
A new polythiophene derivative with octyloxyl triphenylamine-vinylene (OTPAV) conjugated side chain,OTPAV-PT, was synthesized according to the Stille coupling method, and characterized by1H NMR, elemental analysis, GPC, TGA, UV–vis absorption spectroscopy, photoluminescence spectroscopy, and cyclic voltammetry. The polymer possesses excellent solubility in common organic solvents and good thermal stability with 5% weight loss temperature of 413°C. The weight-average molecular weight ofOTPAV-PT was 1.04×104 with the polydispersity index of 1.45. Polymer solar cell with the configuration of ITO/PEDOT:PSS/OTPAV-PT:PCBM/Al was fabricated, and the power conversion efficiency of the device was 0.21% under the illumination of AM1.5, 100mW/cm2. The field effect hole mobility of the polymer reached 1.6×10−4cm2V−1s−1.
Keywords: Conjugated polymers; Polythiophene derivative; Triphenylamine-vinylene; Polymer solar cell; Field effect transistor
Electrochromism of poly(pyrrole) film on Au nano-brush electrode
by Katsumi Yamada; Koji Seya; Gyosuke Kimura (pp. 188-193).
Au nano-brush membranes were prepared by a modified template method. Poly(pyrrole) (PPy) films were immobilized by an electropolymerization with the product membrane as the working electrode. In contrast to the PPy film on an Au planar electrode, the PPy film on the nano-brush electrode showed a higher electrochemical stability for the continuous cyclic polarization. Based on the measurement of the reflectance using a simple two-electrode device, a fine electrochromic performance including the switching response and repetition stability was obtained from the device with the PPy film on the Au nano-brush electrode.
Keywords: Poly(pyrrole); Au nano-brush electrode; Electropolymerization; Electrochromism; Electric paper display
Organic light-emitting devices (OLED) based on new triphenylamine derivatives
by Chuanyang Xia; Xiaomei Wang; Jian Lin; Wanli Jiang; Yuan Ni; Wei Huang (pp. 194-200).
In this paper, we reported the synthesis of two new triphenylamine derivatives: 1,4-bis[- E-4-( N,N-diphenylamino)styryl]naphthalene (Np-G1) and 2,8-bis[- E-4-( N, N-diphenylamino) styryl]dibenzothiophene (ST-G1) and investigated the electroluminescence characteristics of the three-layer devices with Np-G1 or ST-G1 as emitting layer. The results have shown that introduction electron-acceptor group, naphthalene, into triphenylamine units, Np-G1 with linear geometric conformation can lower its LUMO level obviously and resulting facilitate electron injection and transport for the device. Thus, the three-layer device (ITO/TCTA/Np-G1/BCP /Mg:Ag) improved the electroluminescence properties the best, presenting the brightness of ∼10,000cd/m2 and current efficiency of ∼3.0cd/A. On the other hand, ST-G1 with V-shaped conformation containing dibenzothiophene linked triphenylamine groups cannot effectively decreased its LUMO level. As a result, ST-G1 has little contribution to the carrier recombination within itself.
Keywords: Electroluminescence; Electrochemical behavior; Triphenylamine; Naphthaline; Dibenzothiophene; Geometrical structure
Synthesis of a benzothiadiazole/thiophene-based oligomer for bulk heterojunction photovoltaic cells
by Ji-Cheng Li; Hye-Young Lee; Soo-Hyoung Lee; Kyukwan Zong; Sung-Ho Jin; Youn-Sik Lee (pp. 201-208).
An electron-donor–acceptor-type oligomer, oligo(B–EDOT2–HT3), composed of 2,1,3-benzothiadiazole (B), 3,4-ethylenedioxythiophene (EDOT) and 3-hexylthiophene (HT) units was synthesized via a multi-step procedure. The UV–vis absorption and photoluminescence emission peaks of the material in chloroform were observed at 510 and 660nm, respectively. The lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) levels of the material were estimated as −3.47 and −5.49eV, respectively, corresponding to a band-gap of 1.97eV. Bulk heterojunction photovoltaic cells were fabricated, using oligo(B–EDOT2–HT3) and PCBM, in the device configuration of ITO/PEDOT:PSS:6% glycerol/oligo(B–EDOT2–HT3):PCBM/LiF/Ag. The short-circuit current density, open-circuit voltage and fill factor of the device were estimated to be 1.44mA/cm2, 0.33V and 0.36, respectively, with a 1:4 ratio of oligo(B–EDOT2–HT3) to PCBM, corresponding to an energy conversion efficiency of 0.17% under AM 1.5 illumination. One main reason for the low efficiency of the device was attributed to the low absorptivity of oligo(B–EDOT2–HT3) in the UV–vis spectral range.
Keywords: Thiophene; Benzothiadiazole; Oligomer; Organic photovoltaic cell; Absorptivity
Sulfonated polyaniline–titanium dioxide nanocomposites synthesized by one-pot UV-curable polymerization method
by Mohammad Rezaul Karim; Kwon Taek Lim; Mu Sang Lee; Ketack Kim; Jeong Hyun Yeum (pp. 209-213).
Sulfonated polyaniline–titanium dioxide (SPAni–TiO2) hybrid composites have been synthesized by using a new strategy in one-pot system of UV-cured polymerization method. Aqueous solution of aniline and orthoanilinic acid comonomers, a free-radical oxidant and titania precursor were irradiated by UV rays. Hydrolysis and reprecipitation of the titania precursor in aqueous aniline and orthoanilic acid lead to the formation of titanium dioxide particles which in turn catalyze oxidation of comonomers to sulfonated polyaniline. The resultant SPAni–TiO2 composites were characterized by using different spectroscopy analyses like X-ray diffraction, UV–visible (UV–vis) and infrared spectroscopy. The UV–vis absorption bands revealed that SPAni–TiO2 nanocomposites are optically active and the blue-shifted peaks due to the presence of titania within the SPAni matrix. Scanning electron microscopy and transmission electron microscopy of the nanocomposite showed a uniform size distribution with spherical and granular morphology. Thermogravimetric analysis revealed that the SPAni–TiO2 composites have a good thermal stability than the pristine SPAni.
Keywords: UV-curable polymerization method; Sulfonated polyaniline; Titanium dioxide nanocomposites
Hole-injection properties of annealed polythiophene films to replace PEDOT–PSS in multilayered OLED systems
by Joji Ohshita; Yosuke Tada; Atsutaka Kunai; Yutaka Harima; Yoshihito Kunugi (pp. 214-217).
Hole-injection properties of annealed poly(alkoxy- and alkylthiophene) films in OLEDs were studied. Among them, annealed poly(3,3′-dihexyloxy-2,2′-bithiophene) (aPHOBT) film exhibited good hole-injection properties and a triple-layered OLED with the structure ITO/aPHOBT/PVK/Alq3/Mg–Ag (device I) showed much higher performance than a double-layered device without the aPHOBT layer (device II, ITO/PVK/Alq3/Mg–Ag). Device I was slightly inferior to a device having a PEDOT–PSS layer as the hole injector (device III, ITO/PEDOT– PSS/PVK/Alq3/Mg–Ag) in the low-intermediate region of the applied voltage (6–11V), but gave comparable luminance to III when the applied voltage exceeded 11V.
Keywords: Polythiophene; Hole-injection; OLED; Annealing
Glass-forming carbazolylidene-containing hydrazones as hole-transporting materials
by A. Michaleviciute; J. Ostrauskaite; G. Buika; R. Lygaitis; J.V. Grazulevicius; V. Jankauskas (pp. 218-222).
The synthesis, optical, thermal and photoelectrical properties of carbazole- and phenothiazine-containing hydrazones are reported. The ionization potentials of the films of the hydrazones, measured by the electron photoemission technique, range from 5.20 to 5.60eV. Room temperature time-of-flight hole mobilities in the solid solutions of carbazole phenothiazine and carbazole carbazole hydrazones in bisphenol-Z polycarbonate exceeded 10−5cm2/(Vs) at high applied electric fields.
Keywords: Hydrazone; Carbazole; Phenothiazine; Ionization potential; Hole-drift mobility
Thiophene-based hydrazones as hole-transporting materials
by Asta Michalevičiūtė; Ramūnas Lygaitis; Juozas V. Gražulevičius; Gintaras Buika; Vygintas Jankauskas; Algimantas Undzėnas; Eglė Fataraitė (pp. 223-227).
The synthesis, optical, thermal and photoelectrical properties of thiophene-based hydrazones are reported. The HOMO levels in a solid state of thiophene-based hydrazones measured by the electron photoemission technique are −5.25eV and −5.28eV. Hole-drift mobilities of the solid solutions in bisphenol-Z polycarbonate (PC-Z) of the synthesized hydrazones were studied by the time-of-flight technique. Room temperature hole mobilities in the solid solution of thiophene-2-carbaldehyde N, N-diphenylhydrazone in PC-Z exceeded 10−5cm2/(Vs) at high electric fields.
Keywords: Thiophene; Hydrazones; Ionization potential; Dipole moment; Charge transport
Polymerization of fluorene-based monomers modified with thiavinylidene structure at 9-position and their optical properties
by Koji Takagi; Shinri Sugimoto; Manabu Mitamura; Yasuo Yuki; Shin-ichi Matsuoka; Masato Suzuki (pp. 228-233).
Two iodo-functionalized fluorene-based monomers having a thiavinylidene moiety at 9-position [2,7-diiodo-9-( n-hexylthiavinylidene)fluorene and 2,7-diiodo-9-((2-(2-methoxyethoxy)ethyl)thiavinylidene)fluorene] were synthesized. Suzuki coupling reactions with thienylboronic acids bearing a n-hexyl chain were subsequently conducted to obtain two thiophene-functionalized monomers [2,7-bis(4-hexylthienyl)-9-( n-hexylthiavinylidene)fluorene and 2,7-bis(3-hexylthienyl)-9-( n-hexylthiavinylidene)fluorene]. The dehalogenative polycondensation using Ni(cod)2/cod/bpy system and the oxidation coupling polymerization using FeCl3 gave three homopolymers (HP1,HP2, andHP3). The polymerization under Suzuki coupling condition gave three copolymers (CP1,CP2, andCP3). The number-averaged molecular weights ranged from 2500 to 23,000. The optical properties of polymer were dependent upon the character of arylene unit. Namely,HP1 solely consisting of a 9-( n-hexylthiavinylidene)fluorene segment demonstrated the short absorption maximum wavelength but the large red-shift (13nm) from the solution state to film state.CP3 having a hydrophilic side chain showed the larger red-shift (13nm) as compared withCP2 bearing the similar backbone and a hydrophobic side chain.
Keywords: Fluorene; Thiavinylidene; Optical properties; Stacking
White organic light-emitting diodes based on blue fluorescent bis(2-(2-hydroxyphenyl)benzoxazolate)zinc [Zn(hpb)2] doped with DCM dye
by Virendra Kumar Rai; Ritu Srivastava; M.N. Kamalasanan (pp. 234-237).
Bright white organic light-emitting diodes (WOLEDs) with single active layer has been demonstrated from blue emitting zinc complex bis(2-(2-hydroxyphenyl)benzoxazolate)zinc [Zn(hpb)2] doped with orange luminescent 4-(dicyanomethylene)-2-methyl-6-( p-dimethyl-aminostyryl)-4H-pyran (DCM) dye. White light electroluminescence (EL) spectrum from Zn(hpb)2 has been achieved by adjusting the concentration of DCM dye. WOLED with a structure of ITO/α-NPD/Zn(hpb)2:DCM ( x%)/BCP/Alq3/LiF/Al has been fabricated. The EL spectra covering the whole visible spectra range of 400–700nm, with two peaks at 446 and 555nm has been measured. The device emits white light at 10V with Commission Internationale de I’ Eclairage (CIE) coordinates (0.27, 0.31) and brightness 1083Cd/m2. The maximum current efficiency of the device was 1.23Cd/A at 9.5V and maximum luminance reaches 2210Cd/m2 at 12V.
Keywords: Zinc complex; White OLEDs; Electroluminescence; Luminance; CIE coordinates
Immobilization of DNA on nano-hydroxyapatite and their interaction with carbon nanotubes
by Rizwan Wahab; S.G. Ansari; Young Soon Kim; T.R. Mohanty; I.H. Hwang; Hyung-Shik Shin (pp. 238-245).
Here we present a preliminary study on the interaction of bio-molecules (deoxyribonucleic acid (DNA) and nano-hydroxyapatite (HA)) with multi-wall carbon nanotubes (MWCNTs). Initially, nano-size hydroxyapatite was interacted with functionalized carbon nanotubes (FCNTs, HFCNTs) and then 100 base pair (bp) DNA was immobilized (DHFCNTs). Well-known acid treatment was used to functionalize the MWCNTs. The characteristic vibrational and stretching modes of hydroxyl and carbonyl group were observed at 3401, 1632 and 1708cm−1, validating fucntionalization. The existence of31P and1H signals were measured by the solid state NMR spectroscopy for HA, HFCNTs and DHFCNTs which revealed the chemical interaction between HA powder and FCNTs. Appearance of an N 1 s peak in the photoelectron spectra indicated the covalent attachment. Band deterioration is observed from slab gel-electrophoresis studies. Electrophoretic time study indicated that 20min is required to run the DNA in column.
Keywords: Hydroxyapatite; Bio-molecules; Carbon nanotubes
Bio-based conductive composites: Preparation and properties of polypyrrole (PPy)-coated silk fabrics
by I. Cucchi; A. Boschi; C. Arosio; F. Bertini; G. Freddi; M. Catellani (pp. 246-253).
Silk fabrics were coated with electrically conducting doped polypyrrole (PPy) by in situ oxidative polymerisation from an aqueous solution of pyrrole (Py) at room temperature, by using FeCl3 as catalyst. The amount of polymer deposited on the fabrics increased with increasing the reaction time or the concentration of Py in the reaction system. PPy-coated silk fabrics were characterized by optical microscopy (OM) and scanning electron microscopy (SEM), Fourier transform-infrared (FT-IR) spectroscopy, and thermal analysis (differential scanning calorimetry (DSC), thermogravimetric (TG)). OM and SEM showed that PPy completely coated the surface of individual silk fibres and that the polymerisation process occurred only at the fibre surface and not in the bulk. FT-IR (attenuated total reflectance (ATR) mode) showed a mixed spectral pattern with bands typical of silk and PPy overlapping over the entire wavenumbers range. The intrinsic crystalline structure and the molecular conformation of silk were not affected by the polymerisation. PPy-coated silk fabrics attained a significantly higher thermal stability than untreated ones, owing to the protective effect of the PPy layer against thermal degradation. PPy-coated silk fabrics displayed excellent electrical properties. Current versus voltage curves showed a linear fit, with higher current increments at higher PPy amount. The resistance of PPy-coated silk fabrics decreased exponentially with increasing the reaction time or the concentration of Py in the reaction system. Due to the Joule effect, the temperature of PPy-coated silk fabrics increased as a function of the electrical potential applied and of the amount of PPy. The encouraging results reported in this study open new perspectives for future application of PPy-coated silk fabrics, from interactive and smart textiles to innovative bio-based conductive composites for biomedical end-uses.
Keywords: Conductive polymers; Polypyrrole; Silk
Synthesis and characterization of benzothiazole derivatives for blue electroluminescent devices
by Hui-Ying Fu; Xiao-Yu Sun; Xin-dong Gao; Fei Xiao; Bing-Xian Shao (pp. 254-259).
Two benzothiazole derivatives, 4-(benzo[d]thiazol-2-yl)-N-(4-(benzo[d]thiazol-2-yl)phenyl)-N-phenylbenzenamine (BBPA) and 4-(benzo[d]thiazol-2-yl)-N-(4-(benzo[d]thiazol-2-yl)phenyl)-N-naphthylbenzenamine (BBNA), were synthesized and characterized. Electroluminescent devices with compound BBPA or BBNA as the blue-emitting layer were fabricated. The triple-layer device, in which BBPA acted as the blue-emitter, NPB as the hole-transporting layer and TPBI as the electron-transporting layer (Device 1), showed a current efficiency of 5.24cd/A, a power efficiency of 1.21lm/W and an external quantum efficiency of 2.88% at a driving current density of 20mA/cm2. The double-layer device with BBNA as the emitting layer and electron-transporting layer and NPB as the hole-transporting layer (Device 4) exhibited a maximum brightness of 1430cd/m2 at 13V with the CIE coordinates (0.21, 0.23).
Keywords: PACS; 78.60.Fi; 78.55.KzBenzothiazole; Triarylamine; Organic light-emitting diodes
In-situ electrochemical polymerization of multi-walled carbon nanotube/polyaniline composite films for electrochemical supercapacitors
by Jing Zhang; Ling-Bin Kong; Bin Wang; Yong-Chun Luo; Long Kang (pp. 260-266).
Multi-walled carbon nanotube (MWCNT)/polyaniline (PANI) composite films were prepared by in-situ electrochemical polymerization of an aniline solution containing different MWCNT contents. The supercapacitive behaviors of these films were investigated with cyclic voltammetry (CV), charge–discharge tests, and ac impedance spectroscopy. The results revealed that the MWCNT/PANI films show much higher specific capacitance (SC), better power characteristic, better cyclic stability, and more promising for applications in supercapacitors than a pure PANI film electrode. The highest specific capacitance value of 500Fg−1 was obtained for the MWCNT/PANI composite film containing MWCNT of 0.8wt.%. The improvement mechanisms of the capacitance of the composites are also discussed in detail.
Keywords: Supercapacitors; Multi-walled carbon nanotubes; Polyaniline; Electrochemical polymerization; Specific capacitance
An investigation on the stabilization of special polyacrylonitrile nanofibers as carbon or activated carbon nanofiber precursor
by D. Esrafilzadeh; M. Morshed; H. Tavanai (pp. 267-272).
This paper reports the effect of the conditions of stabilization process on the properties of special polyacrylonitrile nanofibers (SAF) with an average diameter of 467nm. Stabilization constitutes an important pretreatment for the production of either carbon fibers or activated carbon fibers. It was found that the higher the stabilization temperature, the lower the initial induction time and the total reaction time. Extent of reaction increases with both treatment time and temperature of stabilization process. Crystallinity index and crystal size of stabilized nanofibers decreases as a result of stabilization. Special polyacrylonitrile nanofibers containing itaconic acid shows a higher capability for stabilization process. Potassium permanganate as a catalyst leaves a positive effect on the extent of reaction of stabilization. The diameter of nanofibers decreases by about 20% as a result of stabilization at 250°C. Thermally stabilized nanofiber shows a wider exothermic peak with a lower height.
Keywords: Special polyacrylonitrile; Nanofibers; Electrospinning; Stabilization; Extent of reaction
Reversible and efficient photocurrent switching of ultra-long polypyrrole nanowires
by Xiuhua Wang; Mingwang Shao; Guang Shao; Yan Fu; Shaowu Wang (pp. 273-276).
Ultra-long polypyrrole nanowires with an average diameter of 60nm and length up to tens of micrometers were successfully synthesized via chemical oxidation polymerization in an aqueous solution. Cyclic voltammetry curves showed that the conductive polymer nanowires were reversible in electrochemical behavior. And the excellent photosensitivity and photoresponse of polypyrrole nanowires were also investigated, which showed that the photocurrent enhanced by ca. 6 times under irradiation of an incandescence lamp with power density of 2.5mW/cm2. This work might be useful in the fabrication of photosensor and photoswitch microdevices or nanodevices in the future.
Keywords: Polypyrrole; Nanowires; Photocurrent; Cyclic voltammetry
Electrodeposition of polyaniline nanostructures: A lamellar structure
by Haibin Zhang; Jixiao Wang; Zhi Wang; Fengbao Zhang; Shichang Wang (pp. 277-281).
The growth process of polyaniline (PANI) nanofibers during the electrochemical polymerization was investigated in detail. The nano-fibrillar morphology appears to be intrinsic to PANI, and the unique character is attributable to a combined effect of electrophilic substitution reaction mainly taking place at the para-position of aniline or its oligomers and aniline oligomers with one-dimensional (1D) structure. Interestingly, the PANI film formed on the electrode exhibits a lamellar structure with compact two-dimensional (2D), micro-granular, nanorod-shaped, and nano-fibrillar PANI layers from bottom to top. In addition, the possible formation mechanism of the lamellar structure of PANI film is discussed.
Keywords: Electrochemistry; Polyaniline; Nanofiber; Mechanism; Lamellar structure
Supramolecular associations of poly(ketanil)s with sulfonic acid derivatives of benzenetricarboxamide via Brönsted acid–base interactions: Preparation, spectroscopic morphological and thermal investigations
by Agnieszka Iwan; Henryk Janeczek; Bozena Kaczmarczyk; Jan Jurusik; Zbigniew Mazurak; Danuta Sek; Patrice Rannou; Jean-Pierre Bonnet; Adam Pron (pp. 282-291).
Supramolecular aggregations have been obtained via ionic self-assembly of conjugated poly(ketanil)s and sulfonic acid derivatives of benzenetricarboxamides. To achieve this goal a new protonating molecule has been synthesized which is a derivative of 1,3,5-benzenetricarboxamide with sulfonic acid group at each of its ends. 1,3,5-benzenetricarboxamides of C3 symmetry tend to form ordered supramolecular aggregations via π-stacking and this property is retained in their sulfonic acid derivative. Because of their Brönsted acid nature the new molecules can additionally associate conjugated polymers with basic centers such as poly(ketanil)s. Depending on the processing solvent used (MC or DMA) 1,3,5- the sulfonic acid derivative of benzenetricarboxamide and its associations with poly(ketanil)s form aggregations of spherullite-like or feather-like morphologies as evidenced by polarized optical microscopy and atomic force microscopy. The similarity of this supramolecular organization is also corroborated by DSC studies which in both cases show endothermic type transitions of the same origin. The supramolecular acid–base associations are semi-crystalline in nature and exhibit good mechanical properties at room temperature because of a rather low Tg, in the vicinity of 300K. This unusual lowering of Tg by ca. 90K as compared to the case of poly(ketanil)s in their basic form is caused by the plasticizing effect of the protonating agent. Finally polyketanil–1,3,5-benzenetricarboxamide sulfonic acid derivatives show tunable photoluminescence which depends on the solvent andSO3H/CN molar ratio.
Keywords: Polyketimines; Aromatic polyazomethines; Protonation; Photoluminescence
Influence of the counter ion on the properties of poly(o-toluidine) thin films and their Schottky diodes
by A. Elmansouri; A. Outzourhit; A. Lachkar; N. Hadik; A. Abouelaoualim; M.E. Achour; A. Oueriagli; E.L. Ameziane (pp. 292-297).
The influence of various counter ions on the electrochemical, morphological and optical properties of poly(o-toluidine) (POT) thin films and on the electrical properties of POT-based diodes was investigated. The POT thin films were deposited on indium tin oxide (ITO)-coated glass substrates by electrochemical polymerization under cyclic voltammetric conditions from o-toluidine monomer in aqueous solutions of HCl, H2SO4 and HNO3. The deposited films were characterized by cyclic voltammetry, scanning electron microscopy and UV–vis spectrophotometry. It was observed that the current densities and optical absorption spectra are influenced by the counter ions of the electrolyte solutions.On the other hand, ITO/POT/Al devices were fabricated by thermal evaporation of aluminum circular electrodes on the as-deposited POT films. The current–voltage ( C– V) characteristics of these devices are non linear. The diode parameters were calculated from current–voltage ( I– V) characteristics using the modified Shockley equation. The C– V and capacitance–frequency ( C– F) characteristics were also measured. These measurements revealed that the junction electrical parameters depend strongly on the type of supporting electrolytes used in the synthesis of the polymer.
Keywords: Schottky diode; Supporting electrolyte; Poly(o-toluidine); I; –; V; characteristics
Electrochemical polymerization of 9-cyanophenanthrene and characterization of its polymer
by Yu Xie; Fengxing Jiang; Jingkun Xu; Liqiang Zeng; Bin Dong; Changli Fan; Feng Zhao (pp. 298-303).
A novel conducting polymer poly(9-cyanophenanthrene) (P9CP) was synthesized electrochemically by direct anodic oxidation of 9-cyanophenanthrene (9CP) in boron trifluoride diethyl etherate (BFEE). The oxidation onset potential of 9CP in the medium was measured to be 1.6V vs. a saturated calomel electrode (SCE). P9CP films obtained from BFEE showed good electrochemical behavior and good thermal stability with electrical conductivity of 0.13Scm−1 in the doped state. The polymer of P9CP may be an attractive candidate material for organic light-emitting material with blue-green-light-emitting upon irradiation with 365nm UV light. Moreover, the P9CP films on the ITO electrode showed good electrochromic property from dark green to dark yellow, between the doped and dedoped state. FTIR and the quantum chemistry calculation indicated that the 9CP was grown via the coupling of the monomer mainly at the C3, and C12 positions.
Keywords: Conducting polymer; Electrochemical polymerization; 9-Cyanophenanthrene; Boron trifluoride diethyl etherate; Quantum chemistry calculation
Double-stage poly-o-phenylenediamine modification with palladium nanoparticles
by E. Yu. Pisarevskaya; V.I. Zolotarevskiy; L.P. Kazanskiy; E.V. Ovsyannikova; N.M. Alpatova (pp. 304-310).
Accumulation of palladium ions in poly-o-phenylenediamine (PPD) redox polymeric matrix was studied by means of cyclic voltammetry (CVA), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and spectroelectrochemistry. CVA and XPS studies demonstrated nitrogen atoms binding palladium cations upon impregnation of PPD film with palladium chloride solution. Higher residual reduced or partially reduced PPD form of cathodic polymer doping was shown to increase the number of palladium cations in the polymeric matrix. AFM recorded a significant effect produced to the film surface structure by intercalation of both palladium cations and metal formed by reduction of cations.
Keywords: Electroactive polymer; Redox polymer; Poly-o-phenylenediamine (PPD); Loaded polymer; Doping–undoping; AFM; XPS
A hybrid p-Si/poly(1,4-diaminoanthraquinone) photoconductive diode for optical sensor applications
by Fahrettin Yakuphanoglu; B. Filiz Şenkal (pp. 311-314).
We report on the fabrication and characterization of a hybrid Si/poly(1,4-diaminoanthraquinone) photoconductive diode for optical sensor applications. The electrical and photoconductivity properties of the diode have been investigated by dark current–voltage, steady-state and transient photoconductivity measurements. At lower voltages, the current mechanism of the diode is controlled by thermionic emission theory, whereas at higher voltages, the current mechanism is controlled by space charge limited current due to the electrical conductivity of the poly(1,4-diaminoanthraquinone). The ideality factor, barrier height and series resistance values of the diode were found to be 1.72, 0.82eV and 1.15MΩ, respectively. The steady-state photoconductivity mechanism of the diode indicates the presence of continuous distribution of trap levels. The transient photoconductivity results indicate that the photocurrent of the diode was varied from 1.81×10−12 to 8.16×10−7A. This suggests that the photocurrent under the illumination of 3500lx is 4.50×105 times higher than the dark current. It is evaluated that the hybrid Si/poly(1,4-diaminoanthraquinone) device is a photoconductive diode with photovoltaic properties.
Keywords: Inorganic/organic; Photodiode; Organic semiconductor
Optical and electrical characterizations of ZnS nanoparticles embedded in conducting polymer
by Kousik Dutta; Sujit Manna; S.K. De (pp. 315-319).
ZnS nanoparticles of average size (5nm) have been prepared using thioglycerol. Inorganic–organic hybrid nanocomposites have been synthesized by dispersing nanosized ZnS in the conducting polyaniline matrix. The samples have been characterized by X-ray diffraction (XRD), transmission electron microscope (TEM) and scanning electron microscope (SEM) and UV–vis spectrophotometer. The wavelength of optical absorption peak of ZnS nanoparticle increases from 270 to 330nm with the decrease of polyaniline concentration. Studies on direct current (DC) electrical conductivity as a function of temperature suggest that three-dimensional Mott’s hopping process occurs in ZnS–polyaniline nanocomposites. The correlated barrier hopping is confirmed from temperature dependent alternating current (AC) conductivity. The incorporation of ZnS nanoparticles enhances the barrier height.
Keywords: ZnS nanoparticles; Polymer nanocomposites; Optical; Electrical
Unusual spectroscopic properties of PPE/TiO2 composite and its sensor response to TNT
by Changmin Deng; Qingguo He; Jiangong Cheng; Defeng Zhu; Chao He; Tong Lin (pp. 320-324).
A composite from a broad bandgap polymer, poly(phenylene ethylene) (PPE), and nano-sized TiO2 particles was found to be able to sense 2,4,6-trinitrotoluene (TNT) for TNT sensor. Fluorescence quenching induced by charge transfer from PPE to nano-sized TiO2 was observed in toluene solution. At high TiO2 composition, a strong exciplex band occurred at 550nm. Under prolonged light irradiation at 400nm, unusual fluorescence gains took place at 460nm, companied with a very small change in the UV–vis absorbance. After 30min light irradiation, the fluorescence at 460nm reached a maximum, but the peak at 550nm disappeared. This composite showed amplified sensor response to TNT compared to the pristine PPE film, which can be potentially used as sensing material for detecting TNT based explosives.
Keywords: PPE/TiO; 2; composites; TNT sensor; Fluorescence
Balancing the white emission of OLED by a design of fluorescent blue and phosphorescent green/red emitting layer structures
by Young Hoon Lee; Byung-Kwon Ju; Woo Sik Jeon; Jang Hyuk Kwon; O. Ok Park; Jae-Woong Yu; Byung Doo Chin (pp. 325-330).
In this paper, we performed the design on the relative thickness of fluorescent–phosphorescent light emitters and evaluated the corresponding change of spectral characteristics of white organic light emitting diode (WOLED). Use of a 3-nm-thick separator composed of undoped phosphorescent host, which provides the confinement of singlet exciton, yields relatively well-defined broadband white emission. The optimized multilayers in WOLED comprises one of the simplest device structures among the reported fluorescent–phosphorescent hybrid WOLEDs, representing the Commission Internationale de l’Eclairage (CIE) 1931 chromaticity ranging from the nearly pure (0.30, 0.35) to warm white (0.35, 0.40) of 9.0–12.5cd/A (24,000cd/m2 at 12V bias). Although the presented efficiency data is not as high as the reports of others, design principles for a bright and stabilized three-peak-balanced white emission are discussed in detail, which will be beneficial for a step forwards in the development of broadband WOLED.
Keywords: White OLED; Fluorescent and phosphorescent; Broadband emission; Design methods
Pseudocapacitance properties of AC/LiNi1/3Co1/3Mn1/3O2 asymmetric supercapacitor in aqueous electrolyte
by Y. Zhao; Y.Y. Wang; Q.Y. Lai; L.M. Chen; Y.J. Hao; X.Y. Ji (pp. 331-337).
NH2NH2·H2O which was used as controlling agent was applied to prepare the precursor Ni1/3Co1/3Mn1/3(OH)2 in the hydroxide co-precipitation method. The precursor was used to synthesize LiNi1/3Co1/3Mn1/3O2. The samples were characterized by XRD, XPS and SEM. It has been found that sintered sample at 800°C for 16h is considered as the optimal synthetic condition. The LiNi1/3Co1/3Mn1/3O2 was used as positive electrode and the activated carbon as negative electrode of the asymmetric supercapacitor. The electrochemical capacitance performance was tested by cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge/discharge. The results indicate that species of aqueous electrolyte, current density, scan rate and potential limit, etc. have influence on the capacitance property of AC/LiNi1/3Co1/3Mn1/3O2 supercapacitor. The initial discharge specific capacitance of 298Fg−1 was obtained in 1molL−1 Li2SO4 solution within potential range 0–1.4V at the current density of 100mAg−1 and was cut down less than 0.058Fg−1 per cycling period in 1000 cycles. The asymmetric supercapacitor exhibited a good cycling performance.
Keywords: LiNi; 1/3; Co; 1/3; Mn; 1/3; O; 2; Pseudocapacitance; Electrochemical supercapacitor; Activated carbon
Crystalline structure of solution-processed pentacene thin films
by Y. Natsume; T. Minakata; T. Aoyagi (pp. 338-342).
We report on the crystalline structure of solution-processed pentacene thin films, prepared without using any precursors or derivatives. In these films, two types of surface structure were observed: flat domains and rough domains. The flat domains exhibited higher field effect mobilities than the rough domains and were composed of two-dimensional plate-like domains of several hundred micrometers containing large crystallites. The in-plane structures of the solution-processed thin films were analyzed by grazing-incidence X-ray diffraction (GIXD). The in-plane two-dimensional mapping of the GIXD patterns reveals that the solution-processed pentacene thin films have a crystal structure similar to that reported by Campbell et al. [Acta Crystallogr. 15 (1962) 289].
Keywords: Pentacene; Solution process; Field effect transistor; In-plane XRD
Magnetite nanoparticles by organic-phase synthetic route for carbon nanotube growth
by Debmalya Roy; Kanik Ram (pp. 343-346).
In the present study, monodisperse Fe3O4 nanoparticles with diameters ranging from 10nm to 25nm were synthesized using a simple organic-phase synthetic route and these monodispersed nanoparticles were then used as catalyst for seed growth of carbon nanotube. Fe3O4 nanoparticles were reduced to iron nanoparticles assembly by Argon mixed with 5% Hydrogen gas at 400°C and then it was examined by atomic force microscopy (AFM), thermomechanical analysis (TMA) and powder diffraction X-ray spectroscopic techniques. XRD indicates that iron clusters are bcc in nature and AFM image shows that the iron nanoparticles assemblies are 50–65nm in size. To control the agglomeration of iron nanoparticles, nanoporous hybrid support material of Al2O3 and SiO2 was used. However, this matrix also fails to stop the agglomeration of iron nanoparticles mainly due to the inhomogeneous distribution of pore diameters. TMA analysis of iron clusters shows a temperature-dependent morphology, therefore, the CNTs growth temperature critically ascertain the nature and structure of CNTs.
Keywords: Monodisperse magnetite nanoparticles; Morphology of catalyst; Carbon nanotube
Temperature dependence of the electrical and interface states of the Sn/Rhodamine-101/p-Si Schottky structures
by Ş. Karataş; M. Çakar (pp. 347-351).
In this paper, the current–voltage ( I– V) characteristics of Sn/Rhodamine-101/p-Si/Al contacts have been measured at temperatures ranging from 80 to 400K at 30K intervals. The nonpolymeric organic compound Rhodamine-101 (Rh101) film on a p-type Si substrate has been formed by means of the evaporation process and the Sn/Rhodamine-101/Si contacts have been fabricated. The current–voltage characteristics of the diode show rectifying behaviour consistent with a potential barrier formed at the interface. The obtained I– V barrier heights ( Φ b) were in the range of 0.208–0.940eV with ideality factors ( n) of 14.37–2.72. The high values of ideality factor ( n) may be ascribed to decrease the exponentially increase rate in current due to space-charge injection into Rh101 thin film at higher voltage. Temperature dependence of the energy distribution of interface states density profile was determined from the forward bias I– V characteristics. It is shown that organic semiconductor layer (Rhodamine-101) controls electrical charge transport properties of Sn/p-Si Schottky structure by excluding effects.
Keywords: Organic semiconductor/inorganic semiconductor structures; Rectification; Barrier heights; Interface states densities