Dark DC conductivity and spectroscopy of clean and gas doped thin films of organic semiconductors

The dark DC conductivity of thin films of phthalocyanine (I), meso-tetra(p-methylphenyl)porphin (II), meso-tetraphenylporphin (III), hemiporphyrazine (IV), dihydrodibenzo [b,i][1,4,8,11] tetra-azacyclotetradecine (V) and three derivatives of V have been studied in vacuo and in the presence of a wide range of gases. The only gases to produce marked increases in the conductivity were electron acceptors; however, IV was unaffected even by these. The interactions of I, II, III and V and its derivatives with $\text{NO}{}_2\text{N}{}_2\text{O}{}_4$ (NOX) were of particular interest and were studied by conductivity measurements, UV/VIS and IR transmission spectroscopy and IR reflectance spectroscopy. The material most sensitive to NOX and other electron acceptors was I; however, V has a favourable combination of sensitivity coupled with reversibility at room temperature. The Interactions of NOX with I, II and HI are complex, and there is spectroscopic evidence for the generation of NO₂ and the organic radical cations.     

有机固体薄膜的交流电导

本文讨论了有机固体薄膜交流电导的频率依赖性,指出在较高频率下,电导正比于频率两次方的依赖性,是由于电极接触电阻和薄膜电容所引致的假象。作者建议了一种外加串联电阻法来求取电极接触电阻值,从而使电导和电容的频率依赖性实验数据得到改正。提出了表征有机固体薄膜交流电导特性的三个参数,即在极低频下的直流电导率σ_d.c.值、在较高频区σ(f)∝fⁿ中的n值和在lgσ-lgf图上高频区直线与σ_d.c.水平线的交点f_x。对聚乙烯咔唑( 关键词：     

The Relationship of Nitrate Reductase Activity to Uptake and Assimilation of Atmospheric 15NO2-Nitrogen in Needles of Norway Spruce (Picea abies [L.] Karst.)

Abstract

Using ¹⁵NO₂, relations between nitrate reductase activity and stomatal conductance, ¹⁵N-uptake and ¹⁵N-glutamate were studied in the two youngest needles flushes of potted Norway spruce (Picea abies [L.] Karst.). There were linear correlations between the stomatal conductance and the ¹⁵N-uptake and between the ¹⁵N-uptake and nitrate reductase (E.C. 1.6.6.1/1.6.6.2) activity. The ¹⁵N labelling of free glutamate shows the assimilation of NO₂ from the atmosphere in addition to the nitrogen from the soil. The portion of glutamate originating from ¹⁵NO₂ was linearly related to nitrate reductase activity in spring experiments. This indicates that this enzyme activity reflected the rate of NO₂-assimilation.     

Potentiometric sensor for sulfur oxides using NASICON as a solid electrolyte

The ac conductivity of NASICON is higher by two orders of magnitude than that of Na₂SO₄ at 1000 K. The dc polarization measurement reveals that NASICON shows sodium ion conduction even at the temperature of about 1200 K, and that the electronic transference number is of the order of 10^?5. The SO₂-O₂-SO₃ concentration cell using NASICON electrolyte gives essentially the same electromotive force as in the cell using Na₂SO₄ electrolyte because a thin layer of Na₂SO₄ if formed on NASICON at the electrodes. The high sinterability of NASICON offers a dense electrolyte without permeation of gases. The SO_x sensor using NASICON electrolyte exhibits good response and excellent selectivity against CO₂ and NO₂.     

Synthesis, characterization, DNA binding and cleavage studies of mixed-ligand Cu(II) complexes of 2,6-bis(benzimidazol-2-yl)pyridine

Four novel copper(II) complexes of the composition [CuLX] where L = 2,6-bis(benzimidazole-2yl)pyridine, X = dipyridophenazine (L₁), 1,10-phenanthroline (L₂), hydroxyproline (L₃) and 2,6-pyridine dicarboxylic acid (L₄) were synthesized and characterized by using elemental analysis, FT-IR, UV–vis, ESI-MS, molar conductance and magnetic susceptibility measurements. The complexes [CuLL₁](NO₃)₂ [1], [CuLL₂](NO₃)₂ [2], [CuLL₃](NO₃) [3] and [CuLL₄] (NO₃) [4] are stable at room temperature. In DMSO the complexes [1] and [2] are 1:2 electrolytes, [3] and [4] are 1:1 electrolytes. Based on elemental and spectral studies five coordinated geometry is assigned to all the four complexes. The interaction of four copper ion complexes with calf thymus DNA were carried out by UV–vis titrations, fluorescence spectroscopy, thermal melting and viscosity measurements .The binding constant (K_b) of the above four metal complexes were determined as 5.43 × 10⁴ M_,⁻¹ 2.56 × 10⁴ M⁻¹, 1.21 × 10⁴ M⁻¹ and 1.57 × 10⁴ M⁻¹ respectively. Quenching studies of the four complexes indicates that these complexes strongly bind to DNA, out of all complex 1 is binding more strongly. Viscosity measurements indicate the binding mode of complexes with CT DNA by intercalation through groove. Thermal melting studies also support intercalative binding. The nuclease activity of the above metal complexes shows that 1, 2 and 3 complexes cleave DNA through redox chemistry.     

Binding of rare earth metal complexes with an ofloxacin derivative to bovine serum albumin and its effect on the conformation of protein

The water-soluble Pr (Ⅲ) and Nd (Ⅲ) complexes with an ofloxacin derivative have been prepared and characterized. The single-crystal X-ray diffraction showed that the Pr (III) and Nd (III) complexes have the similar molecular structure. Under physiological pH condition, the effects of [PrL(NO₃)₂(CH₃OH)](NO₃) and [NdL(NO₃)₂(CH₃OH)](NO₃) on bovine serum albumin (BSA) were examined using fluorescence spectroscopy in combination with UV-vis absorbance and circular dichroism (CD) spectra. The result reveals that the quenching mechanism of fluorescence of BSA by two complexes is a static quenching process and the number of binding sites is about 1 for both. The thermodynamic parameters (ΔH=−14.52 kJ mol⁻¹, ΔS=56.54 J mol⁻¹ K⁻¹ for [PrL(NO₃)₂(CH₃OH)](NO₃) and ΔH=−24.63 kJ mol⁻¹, ΔS=22.07 J mol⁻¹ K⁻¹ for [NdL(NO₃)₂(CH₃OH)](NO₃)) indicate that hydrophobic and electrostatic interactions are the main binding force in the complexes-BSA system. The binding average distance between complexes and BSA was obtained on the basis of Förster's theory. In addition, it was proved by the CD spectra that the BSA secondary structure was changed in the presence of complexes in an aqueous solution.     

Adsorption-induced conductance changes of thin Pt films and PtPd/TiO2 gas sensors

Chemisorption of H₂ and O₂ and resulting changes in electrical conductance of a typical gas sensing material, PtPd/TiO₂, and thin Pt films on glass are studied and compared. The activation energy of conduction increases as Pt film thickness decreases. Chemisorption of H₂ on thin Pt films causes an increase in conductance and activation energy of conduction. O₂ chemisorption results in a decrease in conductance and increase in activation energy of conduction. Alteration in the number of charge carriers and reduction in charge carrier mobility are the mechanisms proposed for the observed changes. Compared to thin Pt films, relatively large changes in electrical conductance are observed upon chemisorption of gases on TiO₂ supported PtPd. The role of the oxide substrate in the observed chemical interaction and electronic response is discussed. The electronic changes upon adsorption/desorption of gases are reversible for thin Pt films but only partially reversible for TiO₂ supported PtPd.     

Measuring the solubility of benzoic acid in room temperature ionic liquids using chronoamperometric techniques

The electrochemical reduction of benzoic acid (BZA) has been studied at platinum micro‐electrodes (10 and 2 µm diameters) in acetonitrile (MeCN) and six room temperature ionic liquids (RTILs): [C₂mim][NTf₂], [C₄mim][NTf₂], [C₄mpyrr][NTf₂], [C₄mim][BF₄], [C₄mim][NO₃] and [C₄mim][PF₆] (where [C_nmim]⁺ = 1‐alkyl‐3‐methylimidazolium, [NTf₂]^? = bis(trifluoromethylsulphonyl)imide, [C₄mpyrr]⁺ = N‐butyl‐N‐methylpyrrolidinium, [BF₄]^? = tetrafluoroborate, [NO₃]^? = nitrate and [PF₆]^? = hexafluorophosphate). Based on the theoretical fitting to experimental chronoamperometric transients in [C₄mpyrr][NTf₂] and MeCN at several concentrations and on different size electrodes, it is suggested that a fast chemical step preceeds the electron transfer step in a CE mechanism (given below) in both RTILs and MeCN, leading to the appearance of a simple one‐electron transfer mechanism. The six RTIL solvents and MeCN were saturated with BZA, and potential‐step chronoamperometry revealed diffusion coefficients of 170, 4.6, 3.2, 2.7, 1.8, 0.26 and 0.96 × 10^?11 m² s^?1 and solubilities of 850, 75, 78, 74, 220, 2850 and 48 mM in MeCN and the six ionic liquids, respectively, at 298 K. The high solubility of BZA in [C₄mim][NO₃] may suggest a strong interaction of the dissolved proton with the nitrate anion. Although there are relatively few literature reports of solubilities of organic solutes in RTILs at present, these results suggest the need for further studies on the solubilities of organic species (particularly acids) in RTILs, because of the contrasting interaction of dissolved species with the RTIL ions. Chronoamperometry is suggested as a convenient methodology for this purpose. Copyright © 2008 John Wiley & Sons, Ltd.     

Influence of self-assembly monolayers on the characteristics of copper phthalacyanine thin film transistor

Self-assembly monolayers (SAMs) of octadecyltrichlorosilane (OTS) on a silicon dioxide substrate were formed in solution, or by vacuum vapor methods, and characterized by Fourier transform infrared (FTIR) spectroscopy. We found that the OTS SAMs on SiO₂ substrates greatly affect the order and connectivity of evaporated copper phthalocyanine (CuPc) thin films, as confirmed by an atomic force microscopy (AFM) and X-ray diffraction analysis. The performance of the organic CuPc thin film transistor comprising OTS SAMs interposed between a gate dielectric and an organic semiconductor layer could be effectively enhanced as a result of improvements in the quality both of the organic/dielectric interface and the evaporated CuPc thin films. The deposition of an OTS SAM leads to a mobility of 1.48×10^-3 cm²/Vs, 1–2 orders higher than that of bare silicon dioxide. PACS 73.61.Ph; 85.30.Tv; 78.66.Tr     

Preparation of Nd-doped BiFeO3 films and their electrical properties

The Nd-doped BiFeO₃ thin films were prepared on SnO₂(FTO) substrates spin-coated by the sol–gel method using Nd(NO₃)₃·6H₂O, Fe(NO₃)₃·9H₂O and Bi(NO₃)₃·5H₂O as raw materials. The microstructure and electric properties of the BiFeO₃ thin films were characterized and tested. The results indicate that the diffraction peak of the Nd-doped BiFeO₃ films is shifted towards right as the doping amounts are increased. The structure is transformed from the rhombohedral to pseudotetragonal phase. The crystal grain is changed from an elliptical to irregular polyhedron. Structure transition occurring in the Bi_0.85Nd_0.15FeO₃ films gives rise to the largest Pr of 64 μC/cm². The leakage conductance of the Nd doped thin films is reduced. The dielectric constant and dielectric loss of Bi_0.85Nd_0.15FeO₃ thin film at 10 kHz are 190 and 0.017 respectively.     

Coadsorption of NO and other small gases (H2 and CO) on polycrystalline rhodium surface

The coadsorption of NO and other small gases (H₂ and CO) on a polycrystalline Rh filament has been studied by thermal desorption mass spectroscopy, using ¹⁵NO. The sample was exposed to a mixture of nitric oxide and other gases with various concentrations of ¹⁵NO at room temperature. It is indicated that NO, CO and H₂ coadsorbs on the rhodium surface, and NO desorbs as N₂ and O₂. NO is adsorbed mainly in the dissociation at lower coverage and molecular adsorption becomes dominant at higher coverage. But the amount of desorbed O₂ was very small. The chemisorption of CO is affected by the chemisorbed NO. Thermal desorption of hydrogen is detected when the value of P_15NO/P_CO is very small. The hydrogen adsorbed on the rhodium surface is replaced by NO with a longer exposure time.     

Stereochemical studies of oligomers XXIX. Reinvestigation of the structure of N-m-tolyl phthalimide

C₁₅H₁₁NO₂, Mr 237.3, monoclinic, space groupC _c, a=8.539(2),b=19.865(4),c=7.599(2)?,β=111.44(2)°,V=1199.8 ?³,Z=4,D _c=1.31 gcm⁻³,λ(CuKα)=1.5418 ?,μ=6.74cm⁻¹,F(000)=496, room temperature. The structure was solved by direct methods with SHELX-86 and refined down to agreement valueR=0.046 for 1117 reflections above 2σ(I). The angle between the plane of the phthalimide group, which shows a little bent [1.2(2)°] between its two rings, and the tolyl group is 56.1(1)°. The packing of the molecules is stabilized by van der Waal’s forces only. Part XXVIII: Bocelli and Rizzoli (1990)     

Structural,optical and electrical properties of europium picrate tetraethylene glycol complex as emissive material for OLED

A new europium complex [Eu(Pic)₂(H₂O)(EO4)](Pic)·0.75H₂O was synthesized and used as the emission material for the single layer device structure of ITO/EO4–Eu–Pic/Al, using a spin-coating technique. Study on the optical properties of the [Eu(Pic)₂(H₂O)(EO4)](Pic)·0.75H₂O complex where EO4=tetraethylene glycol and Pic=picrate anion, had to be undertaken before being applicable to the study of an organic light emitting diode (OLED). The electrical property of an OLED using current–voltage (I–V) measurement was also studied. In complex, the Eu(III) ion was coordinated with the EO4 ligand as a pentadentate mode, one water molecule, and with two Pic anions as bidentate and monodentate modes, forming a nine-coordination number. The photoluminescence (PL) spectra of the crystalline complex in the solid state and its thin film showed a hypersensitive peak at 613.5–614.9 nm that assigned to the ⁵D₀→⁷F₂ transition. A narrow band emission from the thin film EO4–Eu–Pic was obtained. The typical semiconductor I–V curve of device ITO/EO4–Eu–Pic/Al showed the threshold and turn on voltages at 1.08 and 4.6 V, respectively. The energy transfer process from the ligand to the Eu(III) ion was discussed by investigating the excitation and PL characteristics. Effect of the picrate anion on the device performance was also studied.     

Structural and electrical properties of the α-form of metal-free phthalocyanine (α-H2Pc) semiconducting thin films

An X-ray structural study of thermally evaporated metal-free phthalocyanine thin films with various film thicknesses was performed. All samples studied had polycrystalline structure and the unit cell was found to be of the α-form. Variation of the deposition rate from 0.5 to 1 nm s⁻¹ had little effect on the structure. The films exhibit preferential orientation at low thickness; however, at higher thickness they become less orientated as additional peaks appear in the spectrum. The increase in the intensity of the first significant low angle peak with increasing thickness is attributed to the increased volume of the crystal probed during the X-ray exposure.The current density–voltage (J–V) characteristics of α-H₂Pc films sandwiched between two aluminum electrodes showed ohmic behavior at low voltages and space–charge-limited conduction (SCLC) at higher voltages. For comparison, similar measurements of the current density as a function of voltage were performed on zinc phthalocyanine, ZnPc, thin films using aluminum electrodes. The J–V characteristics showed ohmic behavior at low voltages followed by SCLC dominated by an exponential trap distribution at higher voltages. Consequently, in both H₂Pc and ZnPc films, aluminum electrodes act as if they are ohmic contacts. The implied provision of ohmic contacts using aluminum in this case is attributed to the formation of a thin Al₂O₃ layer during the deposition process.     

Surface study of fine MgFe2O4 ferrite powder prepared by chemical methods

To study surface behaviors, MgFe₂O₄ ferrite materials having different grain sizes were synthesized by two different chemical methods, i.e., a polymerization method and a reverse coprecipitation method. The single phase of the cubic MgFe₂O₄ was confirmed by the X-ray diffraction method for both the precursors decomposed at 600-1000 °C except for a very small peak of Fe₂O₃ was detected for the samples calcined at 600 and 700 °C by the polymerization method. The crystal size and particle size increased with an increase in the sintering temperature using both methods. The conductance of the MgFe₂O₄ decreased when the atmosphere was changed from ambient air to air containing 10.0 ppm NO₂. The conductance change, C = G(air)/G(10 ppm NO₂), was reduced with an increase in the operating temperature. For the polymerization method, the maximum C-value was ca. 40 at 300 °C for the samples sintered at 900 °C. However, the samples sintered at 1000 °C showed a low conductance change in the 10 ppm NO₂ gas, because the ratio of the O₂ gas adsorption sites on the particle surface is smaller than those of the samples having a high C-value. The low Mg content on the surface affects the low ratio of the gas adsorption sites. For the reverse coprecipitation method, the particle size was smaller than that of the polymerization method. Although a stable conductance was obtained for the sample sintered at 900 and 1000 °C, its conductance change was less than that of the polymerization method.     

A study of the uptake of NO3 on film coatings of natural sea salt

A comparative analysis of the uptake NO₃ on natural sea salt (NSS) and Dead Sea salt (DSS) is performed using a coated-insert flow reactor coupled to an electron impact ionization mass spectrometer for detecting gas-phase reactants and products. The uptake coefficients are determined by measuring both reactant consumption and gaseous products formation at various concentrations of NO₃, from 8 · 10¹² to 4 · 10¹³ cm^?3, and water vapor, from 8 · 10¹² to 1.6 · 10¹⁵ cm^?3. It has been established that the uptake on a fresh coating is time-dependent, with the uptake coefficient exponentially varying with time, γ(t) = γ _a exp(?t/τ) + γ _s , from an initial value to a steady-state value, both of which depends on the type of salt and the concentration of the gaseous reactant but do not depend on [H₂O] in this range of water vapor concentrations. The dependence of the coefficient of steady-state uptake of the gaseous reactant is determined as 1/γ _s = a + b[NO₃]. It is shown that the main primary products of the NO₃ uptake on NSS are HCl and Cl _ad formed with branching ratios of 1 : 1 and 1 : 2 in the initial and steady-state uptake stages, respectively. For the uptake of NO₃ on DSS, the primary products are HCl and Br, formed in proportions of 1 : 0.1 and 1 : 0.006 for the respective uptake stages. Chemical reactions leading to the formation of these products are proposed.     

Anisotropic giant magnetoresistance originating from the π-d interaction in a molecule

We synthesized TPP[Fe^III(Pc)(CN)₂]₂, PTMA_x[Fe^III(Pc)(CN)₂]·y(MeCN), and PXX [Fe^III(Pc)(CN)₂], a new series of charge-transfer salts containing the axially-substituted phthalocyanine (Pc), [Fe^III(Pc)(CN)₂]⁻. In this molecular unit, the π conduction electron derived from the Pc-ring coexists with the d electron which is a potential source of a local magnetic moment. Therefore various phenomena associated with the interplay between local magnetic moments and conduction electrons are expected. We observed the giant negative magnetoresistance (GNMR) in all the three salts. The GNMR is highly anisotropic for the magnetic-field direction, and reflects the g-tensor anisotropy of the local magnetic moment in the [Fe^III(Pc)(CN)₂]⁻ unit. This indicates that the GNMR in these salts originates from the strong π-d interaction in the [Fe^III(Pc)(CN)₂]⁻ unit.     

Organic thin films based on a dicyanovinyl-quaterthiophene: Influence of electrode configuration on third-order nonlinear optical properties measured by electroabsorption spectroscopy

Electroabsorption (EA) studies at room temperature on organic thin films based on a dicyanovinyl-quaterthiophene 4T-V(CN)₂ are reported. An electric field modulation is applied to the samples for two different electrode geometries, i.e. sandwich and coplanar versus the organic layer. Changes in optical absorption coefficient of 4T-V(CN)₂ based thin films are measured and analyzed to determine the character of the optical transition in the visible range (400-800 nm). Depending on the experimental electrode configuration, magnitude of electroabsorption responses are different, possibly due to different distribution of the externally applied electric field. The results indicate a higher resolution of EA response for the sandwich electrode configuration and confirm the charge transfer exciton character of 4T-V(CN)₂ in contrast to the unsubstituted quaterthiophene 4T. Finally, a third-order nonlinear susceptibility χ⁽³⁾ (−ω; ω, 0, 0) of 16 × 10⁻¹² e.s.u. is obtained.     

Application of photocatalytic technology for NO<Subscript>x</Subscript> removal

Materials that contain a photocatalyst have a semi-permanent capacity for removing harmful gases from the ambient air. It is the purpose of this study to investigate the photocatalytic activity of commercial paints containing TiO₂ nanoparticles towards NO and NO₂. Experiments were carried out in a stainless steel (30 m^-3) walk-in type environmental chamber (Indoortron), under “real world setting” conditions of temperature, relative humidity, irradiation and pollutant concentrations. Two types of nanoparticle TiO₂-containing paints were tested for their depolluting properties: a mineral silicate paint and a water-based styrene acrylic paint. The results showed a significant effect of TiO₂-materials in reducing NO_x. It was found that up to 74% of NO and 27% of NO₂ were photo-catalytically degraded by the mineral silicate paint, while degradation percentage using the styrene acrylic paint reached 91% and 71% for NO and NO₂, respectively. The photo-catalytic rate of NO on the mineral and styrene acrylic paint was calculated to 0.11 μg m^-2 s and 0.18 μg m^-2 s, respectively, indicating higher photocatalytic performance of the organic based material. The effect of relative humidity (RH) was also investigated. An increase of RH from 20% to 50% inhibited the NO_x photocatalysis on the surface of the samples. PACS 81.16.Hc; 81.65.Mq; 82.33.Tb; 82.50.Hp; 82.65.+r     

Structure and luminescence studies of tris(nitrato-O,O′)bis(2,2′-bipyridyl-N,N′)dysprosium(III) complex

The title compound, [Dy(NO₃)₃(bipy)₂], is isostructural with the La, Pr, Nd, Eu and Lu analogues where bipy=2, 2′-bipyridyl. The Dy complex was crystallized in orthorhombic with space group Pbcn. The Dy(III) ion was coordinated with the two bipy ligands and three nitrate anions giving a ten coordination number. Measurements of the molar conductance in ethanol and water solutions indicate that the complex is non-electrolyte. A comparative study of the emission of [Dy(NO₃)₃(bipy)₂] complex with those of the adduct mixture of bipy and Dy at a 1:1 ratio, has been investigated. In the solid state, photoluminescence (PL) spectrum of the complex had sharp emission bands corresponding to the ⁴F_9/2→⁶H_15/2 (476.5 and 482 nm), ⁴F_9/2→⁶H_13/2(572.6 and 573.8 nm), ⁴F_9/2→⁶H_11/2 (661.6 nm) and ⁴H_3/2→⁶H_15/2 (961.0 nm) transitions. The hypersensitive peak of the complex has the yellow emission stronger than the blue emission in the solid state as well as in the solution. The complex has a good thermal stability due to the role of π-π interactions stacking.