Mechanism of conduction in TTF and TMTSF organic conductors from a study of their vibrational spectra

The charge transfer complexes of organic donors TTF and TMTSF have been prepared and studied with infrared spectroscopy. The nature of transition has been studied by analyzing features of absorption. TTF-TCNQ was found to be a Peierls semiconductor and not metallic. This shows that the mean field transition temperature is operative in TTF-TCNQ. TMTSF-TCNQ and TMTSF-DDQ showed lesser band gap than that of TTF-TCNQ. TTF-DDQ and TTF-I₂ also showed very small band gap and were more conducting than TTF-TCNQ. The band gaps could be assigned to either the Peierls gap or the pinning gap of charge density waves.     

Numerical study of the current conduction in single-layer organic light-emitting devices

A numerical model for the current conduction in single-layer organic light-emitting devices is established under the basis of trapped charge-limited conduction with an exponential trap distribution. The dependences of the current density on the operation voltage, the thickness of the organic layer, and the trap properties are numerically studied. The current density decreases nearly exponentially with the thickness of the organic layer and the relative trap depth (l), and it is inversely proportional to the lth power of the total trap density. The results from simulations for the current–voltage characteristics agree very well with those from experiments. PACS 78.60.Fi; 75.40.Mg; 73.21.Ac     

Direct laser interference ablating nanostructures on organic crystals

Two-beam interference ablation of 1,4-Bis(4-methylstyryl)benzene organic crystal by short laser pulses (10 ns, 355 nm) is presented. The influence of laser fluence, interference period, and pulse number on the morphology have been studied. The morphology is closely associated with the molecular interactions in the crystals, and it could be well controlled by adjusting the laser fluence and pulses number. Through interference ablating the crystals with high fluence pulses, and then treated with low fluence laser pulses, grating structures with smooth surface could be fabricated without any additional process.     

Nanoporous ZnO nanostructures for photocatalytic degradation of organic pollutants

ZnO porous bamboo-leave-like nanorods and nanoporous networks were prepared by thermal conversion from Zn₂CO₃(OH)₂?H₂O bamboo-leave-like nanorods, Zn(OH)₂ nanoparticle networks and Zn(OH)₂ long nanostrand networks, respectively. Among them, the ZnO nanoporous networks prepared from Zn(OH)₂ nanostrands had the highest surface area of 78.57 m²/g and presented the best photocatalytic decomposition of organics. The morphologies of the Zn(OH)₂ nanostructures significantly depended on the solvent used for the precursors of aminoethanol and Zn(NO₃)₂ and then determined the corresponding structures and properties of the final ZnO nanostructures. The ethanol/water mixture solvent dramatically increased the stability of Zn(OH)₂ nanostrands. This is very beneficial for the collection and application of Zn(OH)₂ nanostrands.     

Efficient catalytic effect of CuO nanostructures on the degradation of organic dyes

An efficient catalytic effect of petals and flowers like CuO nanostructures (NSs) on the degradation of two organic dyes, methylene blue (MB) and rhodamine B (RB) were investigated. The highest degradation of 95% in CuO petals and 72% in flowers for MB is observed in 24 h. For RB, the degradation was 85% and 80% in petals and flowers, respectively for 5 h. It was observed that CuO petals appeared to be more active than flowers for degradation of both dyes associated to high specific surface area. The petals and flower like CuO NSs were synthesized using the chemical bath method at 90 °C. The grown CuO NSs were characterized using scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), and X-ray diffraction (XRD).     

One-dimensional organic nanostructures: A novel approach based on the selective adsorption of organic molecules on silicon nanowires

Scanning tunneling microscopy (STM) is used to investigate the formation of one-dimensional organic nanostructures by chemisorption of specific molecules on silicon nanowires. STM data demonstrate that depending on the molecular functional groups, the molecules adsorb either randomly on the substrate or preferentially on the nanowires. In the latter case, chemisorption of suitable organic molecules on the nanowires leads to a well-defined one-dimensional aggregation and changes the metallic character of the nanowires to a semi-conducting one.     

苝四甲酸二酐有机单晶纳米结构的制备及形成机理的研究

在分子束外延(MBE)系统中, 利用物理气相沉积(PVD)的方法在阳极氧化铝(AAO)模板上制备了有机 染料分子苝四甲酸二酐(PTCDA)的不同纳米结构; 并使用扫描电子显微镜(SEM)、透射电子显微镜(TEM)、 高分辨透射电子显微镜(HRTEM)以及选区电子衍射(SAED)技术进行了系统的研究. 结果发现, 当衬底温度(T_s)为330 ℃时得到的是纳米丝、针、带以及棒; T_s为280 ℃, 230 ℃, 180 ℃时得到的主要是纳米棒, 并且纳米棒的长度随T_s的降低而变短; T_s为50 ℃时只能得到连续的PTCDA薄膜. HRTEM以及SAED结果证实了纳米针与棒为单晶. 依据SEM结果, 提出纳米结构的生成主要受T_s以及衬底表面曲率的影响.     

Mechanism of dc conduction in polyaniline doped with sulfuric acid

A temperature variation of dc conductivity in the range 77–300 K has been carried out in order to explore the mechanism of charge transport in polyaniline (PAN) doped with sulfuric acid. The variable range hopping (VRH) exponent changes as the transition of the PAN lattice takes place in a narrow pH range thereby indicating that the charge transport is crucially composition dependent. A decrease in activation energy has been observed as the doping level is increased. Spin concentration of charge carriers determined by electron spin resonance spectroscopy has also been found to depend on the doping level of the specimen. Polarons and bipolarons formed during the doping process are the charge carriers in this system. The temperature dependence of dc conductivity and activation energy data are indicative of existence of both VRH and mixed conduction for various doping levels in these samples.     

Universal crossover from band to hopping conduction in molecular organic semiconductors

The charge transport in a variety of herringbone-stacked organic molecular semiconductors is investigated in the temperature range from 10 to 550 K. A crossover from coherent bandlike charge transport with mobilities up to several thousand cm (2)/V s at low temperature to an incoherent hopping motion at high temperatures is observed. This is attributed to the localization of the charge carrier due to increased electron-phonon interaction and, finally, the formation of a lattice polaron.     

Transition from gas-kinetic to minimal metal-type conductivity in a supercritical fluid of metal vapor

We have proposed a peculiar model of the plasma of dense metal vapors, containing atoms embedded into the electron jelly, as well as free (thermally ionized) electrons and ions. The main feature of the model is the presence of the electron jelly existing at any density of the atomic component. The number of electrons in the jelly increases under compression. The process of its formation can be called the “cold” ionization, or pressure ionization. The composition of the gas–plasma mixture, including the concentration of atoms and electrons in the jelly, as well as the concentration of free thermally ionized electrons and ions, has been calculated. The conductivity of dense vapors is determined by the sum of the conductivities of thermal electrons (which is calculated using the Frost formula) and jelly electrons (which is calculated by the Regel–Ioffe formula for the minimal metal-type conductivity). The concentration of thermal electrons decreases and the concentration of jelly electrons increases upon compression of the vapor. Accordingly, the conductivity varies from the conductivity of thermal electrons to the conductivity of jelly electrons, continuously passing through the minimum. The calculated values of the conductivity of supercritical metal vapors are in satisfactory agreement with experimental results.     

非周期微纳结构增强有机发光二极管光耦合输出的研究进展

有机发光二极管（OLED）具有功耗低、重量轻、色域宽、响应时间快及对比度高等优点,在全彩平板显示和固态照明等领域均显现出巨大的应用潜力,受到人们的广泛关注.然而,较低的光输出效率使得器件的外量子效率远低于内量子效率,这严重制约了OLED器件的发展和应用.因此如何提高OLED器件的光耦合输出效率已成为备受关注的研究课题.本文主要介绍了采用非周期微纳结构提高OLED器件光耦合输出效率的最新研究进展,对随机微纳透镜结构、光散射介质层、聚合物多孔散射薄膜、随机凹凸波纹结构及随机褶皱结构等多种对器件亮度分布和光谱稳定性无明显影响的光耦合输出技术进行了总结和讨论.最后,对提高OLED器件光耦合输出研究做了总结和展望.     

Characterization of hybrid organic and inorganic functionalised membranes for proton conduction

Titanium zirconium phosphate and organic polymer hybrid (poly-vinyl alcohol, (3-glycidoxypropyl)-trimethoxysilane and ethylene glycol) based membranes were investigated for their potential application as proton conductors. The hybrid materials were characterized by XRD, FTIR, SEM, TGA and impedance spectroscopy analysis. It was found that embedding of functionalised inorganic particles (TiZrP) into composite polymer matrix allowed for some crystallinity formation, and cross-linking of hydroxyl groups during annealing or reactions within the organic and inorganic phases during synthesis. A complex structure was formed, as many FTIR peaks were masked by more defined peaks assigned to P–O–R bonds. The high concentration of phosphorus in the TiZrP (1:1:9 molar ratio) samples resulted in more hydrophilic particles. This was further reflected in the hybrid membranes as the water losses increased from 13 to 25 wt.% as a function of the TiZrP content changing from 10 to 50 wt.% in the final hybrid membrane, respectively. As a result, proton conductivity increased by two to three orders of magnitude from blank (organic phase only) membranes (2.61 × 10^− 5 S cm^− 1) to TiZrP hybrid membrane (2.41 × 10^− 2 S cm^− 1) at 20 °C. Proton conduction changed as a function of temperature and the Ti1Zr1P9 particles content, mainly attributed to the membrane ability to retain water, thus complying with the Grotthus mechanism.     

Mechanism of the dc conduction in undoped and Sr doped ammonium zinc chloride crystal

The dc conductivity of ammonium zinc chloride (AZC) crystal as functions of temperature, electric field intensity and Sr²⁺-doping concentration has been studied. Anomalous changes at the transition points connecting the antiferroelectric (AF), commensurate (C), incommensurate (IC) and normal (N) phases have been detected. The broadening of the peak anomaly at the C-IC phase transition suggested an important role for impurities assisting creation and annihilation of discommensuration (DC). Considerable shifts of the transition temperatures after doping with different Sr²⁺ concentrations were noticed. Electric conduction in AZC continuously increased with increasing Sr²⁺-concentration. Parameters extracted from the current density-electric field intensity relationship according to the usual Richardson-Schottky (R-S) emission equation were found inconsistent with corresponding experimental values. The results have been treated using the modified R-S equation for dielectrics with small electronic mean-free path. The Pool-Frenkel (P-F) conduction mechanism was also considered and the possibility of conduction by either of R-S or P-F was discussed.     

Thermal effect on the dielectric function and small polaron hopping conduction in organic molecular crystals

A Green function formalism is applied to study the dielectric function spectra and the small polaron hopping conduction in organic molecular crystals. In the calculations, the electron-phonon interaction is considered within the Hartree-Fock approximation, and the temperature effect is taken into account. Our theoretical approach is based on the polar electron-phonon interaction (Fröhlich type) to characterize the non-degenerate polaron gas, with the assumption of the electronic hopping between the first-neighbor.     

Hall effect and conduction anisotropy in the organic conductor (TMTSF)2PF6

Both the Hall effect and the ab(')-plane conduction anisotropy are directly addressing the unconventional normal phase properties of the Bechgaard salt (TMTSF)2PF6. We found that the dramatic reduction of the carrier density deduced from recent optical data is not reflected in an enhanced Hall resistance. The pressure and temperature dependence of the b(')-direction resistivity reveal isotropic relaxation time and do not require explanations beyond the Fermi liquid theory. Our results allow a coherent-diffusive transition in the interchain carrier propagation, however the possible crossover to Luttinger liquid behavior is placed at an energy scale above room temperature.     

Numerical investigations on the current conduction in bilayer organic light—emitting devices with ohmic injection of charge carriers

A numerical model for bilayer organic light-emitting diodes (OLEDs) has been developed on the basis of trappedcharge limited conduction. The dependences of the current density on the operation voltage, the thickness andtrap properties of the hole transport layer (HTL) and emission layer (EML) in bilayer OLEDs of the structure an-ode/HTL/EML/cathode have been numerically investigated. It has been found that, for given values of reduced trapdepth, total trap density, and carrier mobility of HTL and EML, there exists an optimum thickness ratio of HTL tothe sum of HTL and EML, by which a maximal current density, and hence maximal quantum efficiency and luminance,can be achieved. The current density decreases quickly with the mean trap density, and decreases nearly exponentiallywith the mean reduced trap depth.     

Mechanism of dc conduction in ferric chloride doped poly(3-methyl thiophene)

Poly(3-methyl thiophene) has been synthesized by chemical oxidation method in an inert atmosphere using ferric chloride as a dopant. The doping level varies from 0.1 to 2.0 M. The dc conductivity has been measured in the temperature range 20–300 K. The observed dc conductivity data has been analyzed in the light of existing theoretical models. Different Mott’s parameters such as characteristic temperature (T₀), density of states at Fermi level [N(E_F)], average hopping energy (W) and the average hopping distance (R) have been evaluated that agree well with the values reported earlier for the other conjugated polymers. A detailed analysis of the mechanism of charge transport in this system has been reported.     

Mechanism of sonochemical excitation in the reactions of lead tetraacetate with some organic substrates

Strikingly contrasting positive and negative sonochemical effects were observed in the reactions of lead tetraacetate with styrene and 2-octanol, respectively. The decomposition of lead tetraacetate itself in the absence of a substrate is not accelerated by ultrasound. These results are consistent with the idea that the radical chain reaction of lead tetraacetate and styrene involves the bimolecular initiation step of the two species; under ultrasonic irradiation, styrene is excited in the gas phase of the cavity. The efficiency of the sonochemical excitation must be decisively different between the gas phase and the liquid shell of the cavity. The importance of the boiling point of a substrate involved in the radical initiation step is proposed as a hypothetical guideline in homogeneous sonochemistry.