Sensitization effect in conducting polyaniline by rhodamine 6G

Rhodamine 6G (R6G), an n-type dye, has been employed at small concentrations (0–15 mM/monomer) for sensitizing conducting polyaniline (PANI) in solid-state photocells with the configuration Au/PANI/SPE+R6G/ITO. It is observed that a p–n junction is formed at the PANI/dye interface. The photosensitivity factor (S) is observed to be maximum at a dye concentration of 6.3 mM/monomer. The variation of the dark (I_d) and light (I_l) current with respect to the dye concentration in the linear portion of the current–voltage (I–V) characteristic reveals that light current goes through a maximum whereas dark current remains more or less constant. Thus, it is the variation of the light current (I_l) that is more important and is one of the reasons for maximum photosensitivity at a certain dye concentration. The mechanism of the dye-sensitization process is explained on the basis of the energy band diagram of the materials forming the photocell. The observed photosensitivity is due to the lowering of the potential barrier in the presence of light at the PANI/dye interface.     

Conduction studies in anthraquinone derivatives. VI

Contrary to the results of the early 1960s, it has been found that the anthraquinone (AQ) and its derivatives can be made photoconductive (I _ph/I_D 10³) by substituting suitable donors in the periphery of the benzenoid rings. The conductivity of the AQ derivatives, generally speaking, are not as good as those of the charge transfer kind. The darkcurrent in the case of AQ derivatives ranges from 10^–14–10^–12 for 9,10-AQ to 10^–10–10^–8 for 1,4,5,8-tetra amino AQ. The AQs are n-type semiconductors with electrons being the majority charge carriers. In the present article, we describe the charge carrier generation and transport processes in three di-substituted AQ derivatives whose spectral properties have been well studied. The magnetic field effect has been observed for the first time in these compounds.     

Non-exponential photocurrent growth and decay in Safranine-T dye doped solid state polymer photoelectrochemical cell

In the present communication photoconductivity has been studied in Safranine-T dye doped solid state polymer photoelectrochemical cell (PEC). The cell contains a blend made of Safranine-T dispersed in polyvinyl alcohol (PVA), polyethylene oxide (PEO) complexed with ammonium perchlorate (NH₄ClO₄), ethylene carbonate (EC) and propylene carbonate (PC). A thin layer of this blend is sandwiched between two ITO coated glass plate electrodes. The photoresponse is observed in our system illuminated by a tungsten lamp in presence of an external bias voltage. Photocurrent changes with the applied bias voltage and the typical change is about 1.68 A for a device area of 0.64 cm² at a bias voltage of 1.5 V and at an incident intensity of about 40 mW/cm² which indicates a sensitivity of $0.66 × 10^–4 A/W. In the present work the dark current–voltage (I-V) characteristic and the variation of the photocurrent with time have been investigated. At low operating voltage the I-V characteristic is ohmic while at high bias voltage an exponential distribution of trap centers gives a good fit to the dark I-V characteristic. The experimental results show a non-exponential growth and decay of photocurrent with rich structure which may indicate a dispersive transport in such disordered amorphous systems. The dispersive transport model has been applied to explain qualitatively the experimental findings of this non-exponential photocurrent behaviour. The experimental data are fitted with a power law function as I _ph (t) t for photocurrent growth and I _ph (t) t ^– for decay where I _ph (t) is photocurrent and and are some constants at a particular bias voltage. The observed slow response speed of the device may be due to slow diffusion of ions as well as the immobilization of charge carriers at deep traps. The present investigation will be helpful to understand the performance of the device and the charge transport mechanism in dye doped solid state polymer electrolyte cell.     

Rapid electroplating of photocatalytically highly active TiO2-Zn nanocomposite films on steel

Nanocomposite films consisting of TiO₂ and Zn with thickness of 10–15 m (TiO₂-Zn) have been electrodeposited on steel plates by rapid plating from a ZnSO₄-based bath (I _d > 10 A dm^–2). Upon addition of NH₄NO₃ to the bath (<0.3 g L^–1), the uptake of TiO₂ in the film significantly increased. Glow discharge optical emission spectrometry clarified that TiO₂ particles were incorporated throughout the film and the loaded amount increased near the surface. The first-order rate constant (k/h^–1) for gas-phase CH₃CHO oxidation was employed as an indicator of the photocatalytic activity. The k value for the TiO₂-Zn film prepared at I _d = 12 A dm^–2 (0.20 h^–1) was comparable to that for the sample from a ZnCl₂-based bath at I _d = 4 A dm^–2 (0.27 h^–1). X-ray diffraction measurements indicated that a TiO₂-ZnO nanocomposite layer was generated on the surface by the heat treatment in air at 673 K for 6 h. Consequently, the photocatalytic activity was further improved (k = 0.29 h^–1); this effect was explained in terms of the synergy of TiO₂ and ZnO in photocatalysis.     

Sorption of 131I? and 131IO3? from Aqueous Solutions on Porous Inorganic Sorbents Modified with d-Element Ammoniates at 25°C

Sorption of ¹³¹I⁻ and ¹³¹IO ₃ ⁻ from aqueous solutions on porous inorganic sorbents modified with d elements is studied at 25°C. The sorbents modified with Ag, Zn, Ni, Cu, and Co ammoniates are characterized by low distribution coefficients of ¹³¹I⁻ and ¹³¹IO ₃ ⁻ (K _d <150 ml g⁻¹ at V/m = 1000). Calcination of the sorbents modified with Ag, Cu, and Zn ammoniates at a temperature above 250°C affects the chemical state of the metals in the sorbent matrix, which is accompanied by slight increase in K _d of ¹³¹I⁻ and ¹³¹IO ₃ ⁻ as compared to as-prepared samples. With the γ-Al₂O₃-based sorbents modified with Ni or Cu, K _d of ¹³¹I⁻ and ¹³¹IO ₃ ⁻ is well comparable with that for the Ag-modified sorbents based on MSKG silica gel.__________Translated from Radiokhimiya, Vol. 47, No. 3, 2005, pp. 265–268.Original Russian Text Copyright © 2005 by Kulyukhin, Mizina, Krasavina, Rumer, Konovalova, Tanashchuk, Bogachev.     

Optical and electrical properties of electrodeposited silver based thin films

The electrodeposited superionic conductor Ag₆I₄WO₄ was doped with various concentrations of [CrO₄]^2– to form the quarternary compound Ag₆I₄WO_4(1–xCrO_4(x). The doping level,x, was varied from 0 to 0.6 and the optimum compound was used for further analysis. X-ray diffraction (XRD) analysis indicated major peaks occurring atd values of 3.75,2.29,1.96 and 3.96 in the order of decreasing intensity. The energy dispersive analysis of X-rays (EDAX) technique verified quantitatively the ratio of the components in the solid electrolyte. From the fringes seen in the interference pattern of the transmission spectrum, the refractive index and thickness of the film was calculated. The absorption spectrum indicated the characteristic chromate peak at 310 nm when the dopant was present. An open circuit voltage (OCV) of 670 mV was observed for the fabricated cells with optimum performance at a doping level ofx=0.1, where the best discharge characteristics were observed. The subsequent conductivity was calculated to be of the order 10^–3–1 cm^–1 from the Cole-Cole plot.     

X-ray Photoelectron Spectra of La0.8 – x Ce x Sr0.2MnO3

La_{0.8 – x} Ce _x Sr_0.2MnO₃ (x= 0–0.3) mixed-conducting manganites are studied by x-ray photoelectron spectroscopy. The effect of A-site Ce substitution on the surface composition of the samples, charge states of the constituent cations, and bonding configuration is analyzed. The binding energies of the constituent elements are determined. The spectral shapes of the O 1s, La 4d, La 3d, Sr 3d, Mn 2p, Ce 4d, and Ce 3d peaks are examined as a function of Ce content.     

An experimental study concerning the electrical and the thermal characteristics of stabilized arcs

Results are shown of an experimental study concerning the electric field intensity and the useful power of a plasma jet as well as the electron and the atom-ion gas temperature in an argon arc under atmospheric pressure.Notation l _a length of arc - E electric field intensity in the arc column - d diameter of arc channel - d₀ unit diameter - H enthalpy - I _a arc current - Re Reynolds number - T_e electron temperature - T atom-ion gas temperature Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 22, No. 6, pp. 1089–1095, June, 1972.     

Magnetic Specific Heat of Heavily p-Type Doped (Zn,Mn)Te:P

The magnetic contribution to the specific heat of bulk crystals of Zn_1–x Mn _x Te ( x = 0.03) heavily (up to 10¹⁹ cm^–3) p-type doped with P is studied over the temperature range 0.5–15 K and magnetic field range 0–3 T. The magnetic specific heat observed at zero magnetic field indicates that a substantial part of the magnetic ions has the degeneracy of their magnetic ground state lifted by d–d and p–d exchange interactions. The effect increases for doped and annealed samples with higher concentration of conducting holes. We have also carried out a theoretical analysis that takes into account the contributions due to small magnetic clusters, single magnetic ions in crystal field of distorted crystal lattice, and low energy excitations of the p–d exchange-coupled system of local moments and carriers.     

Angular dependence of transport current near critical at fields to 4 T in metalorganic thin films

Values of the transport current have been obtained as a function of angle of the magnetic field to the plane of the thin film YBa₂Cu₃O_7–d (YBCO) prepared by metalorganic deposition. Current flowed in thea, b planes at various angles to the applied magnetic fields to 4.2 T. Films with thicknesses near 350 nm were studied. For these thin films andHc a secondary maximum is observed whenJ _c> 1 MA/cm₂. NearHa, b a large increase inI _c is observed, and the sharpness, field dependence, and field directional dependence is discussed. The response to currents aboveI _c is determined and the fit to a power lawVI _n shows a strong correlation betweenI _c andn.     

Performance characteristics of a plasma-type sputter ion source

A low-power, plasma-type sputter source for the production of positive ions of non-volatile elements has been constructed and tested. Argon and copper were employed as support gas and sample material, respectively. The source output was measured as a function of the discharge current, the axial magnetic field, the sputter voltage, the spacing between the sputter sample and the source exit, the diameter of the sputter sample, and the argon pressure. It was found that the Cu⁺ current, I_Cu, increases with increasing discharge current i_d as I_Cu ∝ i_dⁿ, where n 2. I_Cu increases with decreasing sample-to-exit spacing s. For not too small spacings, I_Cu ∝ s⁻². Cu⁺ currents of up to 6 μA were produced at a total power consumption of less than 60 W. The simultaneous prese nce of an intense Ar⁺ component in the beam causes space charge expansion which becomes significant at low energies and large ratios of the drift length to the beam-size defining apertures. Loss of target current may also be caused by neutralization of ions in charge-transfer collisions outside of the source.     

Fabrication and properties of an anisotropic PZT/polymer 0–3 composite

Anisotropic 0–3 PZT platelet/polymer composites were prepared by a route involving the tape casting and sintering of PZT sheets and the subsequent alignment of platelets in a polymer matrix by either calendering or tape casting; both techniques induced a strong alignment of the platelets. At 60 vol 1/2 loading, measured d ₃₃- and d _h-values of ~ 30 pC N^–1 and ~ 100 pC N^–1, respectively, were obtained; the calculated g _h-value was 83 mV mN^–1. A strong relaxation effect observed is considered most likely to be dependent on the characteristics of the polymer phase.     

Vortex-induced rectification in type II superconductors

We report a large rectification effect in superconducting films in a parallel magnetic field. This rectification effect is manifested in two features in current-voltage characteristics: The critical current, I_c,is found to differ by as much as 40% for negative and positive currents, and beyond I_c,the magnitude of the voltage is different for positive and negative currents, ¦V(+I)¦ ¦V(–I)¦.Furthermore, the critical current difference ¦I_c+¦ – ¦I_c–¦shows complicated behavior, changing sign as temperature and magnetic field are varied. We discuss a model based on the Bean-Livingston surface barrier and inhomogeneous bulk pinning that accounts for all observed behavior.     

Mass-Spectrometric Study of the Kinetics of Ionic and Molecular Sublimation of Sodium Chloride Single Crystals

A mass-spectrometric method is used to study the kinetics of ionic and molecular sublimation of sodium chloride single crystals. The positive ions Na⁺, Na₂ ⁺, and Na₂Cl⁺ were identified in the mass spectrum in the temperature range 820–970 K. Up to 970 K no emission of negative ions was observed. The temperature dependence of thermal ion currents, lnI _i – (1/T), exhibits a maximum and a minimum successively with increasing temperature. These features are identified with a change in the electrical properties of the surface. It is inferred that in the intrinsic temperature range the sign of the surface charge in NaCl is negative and thus the Gibbs free energy of formation of cation vacancies is greater than that of anion vacancies. In the electron impact ionization mass spectrum of molecular fluxes vaporized from an open crystal surface, Na⁺, NaCl⁺, and Na₂Cl⁺ ions originating from NaCl and Na₂Cl₂ precursors are detected in the temperature range 779–982 K. The dimer-to-monomer ratio is found to be of the same order of magnitude in the cases of equilibrium and free-surface vaporization. However, the dependence on temperature of this ratio is different in these two cases. Mechanisms which account for this observation are discussed in light of the terrace–ledge–kink and surface charge models.     

Study of the effect of trap levels on steady-state dark I–V characteristics in Safranine-T-based solid-state thin film photoelectrochemical cell

In this work we describe the steady-state current–voltage (I–V) characteristic of solid-state photoelectrochemical cells (PEC). The cell contains a blend made of Safranine-T dye dispersed in polyvinyl alcohol (PVA), polyethylene oxide (PEO) complexed with ammonium perchlorate (NH₄ClO₄), ethylene carbonate (EC) and propylene carbonate (PC). A thin film (20 m) of this blend is sandwiched between two transparent indium-tin-oxide (ITO)-coated glass plates, which act as the two contact electrodes. Addition of ion salt in the active materials alters the device characteristics in a significant way. In the present work we have concentrated on the steady-state dark I–V characteristics of the device. The trap-assisted charge carrier transport model is used to satisfactorily describe the I–V characteristics. The experimental results are explained by the transport of carriers having traps with exponential distribution. The characteristic temperature of the traps and trap energy level have been estimated to be 1164 K and 0.1 eV, respectively, within the experimental limit. The present experimental data will be helpful to understand the steady-state operation of a photoelectrochemical cell.     

Phase Relations in the NiFe2O4–NiCr2O4–CuCr2O4System

The phase relations in the NiFe₂O₄–NiCr₂O₄–CuCr₂O₄system were investigated experimentally and theoretically. X-ray diffraction data were used to construct the phase diagram of the system and elucidate the structural mechanisms of the transitions from the cubic spinel structure to the tetragonal (I42d, c/a< 1 and I4₁/amd, c/a> 1) and orthorhombic (Fdd2) structures.     

Phase Behaviors of Binary Hard-Sphere Mixtures Using Simple Analytical Equations of State

Recently, we have proposed a unified analytical equation of state (EOS) for solid–liquid–vapor states of matter, and have examined the thermodynamic properties of argon, carbon dioxide, and methane, as well as binary mixtures of methane and carbon dioxide. Also it has been demonstrated that the EOS can be applied for the solid–fluid transition of hard spheres, by eliminating the attractive part of the EOS. The present work is an extension of the earlier calculations for identical hard spheres, and here we examine the phase behavior of binary hard-sphere mixtures. The hard-sphere EOS employed in this study is

Photoelectrochemical solar (PES) cells with Cd1−xPbxSe polycrystalline thin film electrodes

An electrochemical solar cell behavior of a mixed type n-Cd_1–x Pb _x Se (0x0.5) thin film electrode is presented in this paper. A series of the electrodes were prepared for the values of x in the above range and the electrochemical cells of the configuration n-Cd_1–x Pb _x Se/K₄Fe(CN)₆/C were fabricated. The current–voltage and capacitance–voltage characteristics of the as-fabricated cells in dark were examined to understand nature of the charge transfer process across the electrode/electrolyte interface. These cells were then illuminated with a light of 20 mW cm^–2 intensity and the power output curves were obtained and analyzed. Both open circuit voltage (V_oc) and short circuit current (I_sc) found boosted enhancing the power conversion efficiency (%) from 0.065% to 0.28% at x=0.1. The flat band potentials (V_fb) were also determined for these cells and it is found to attain a maximum value at x=0.1. The other cell parameters were estimated and showed improvement in the overall performance of a cell. Attempts were made to explain the observed results through modified electrode properties.     

Stress transfer in single-fibre composites: effect of adhesion,elastic modulus of fibre and matrix,and polymer chain mobility

The stress transfer in single-fibre composites is studied experimentally by determining the critical fibre length to diameter ratio,I _c/d, in carbon fibre-epoxy resin or poly (ethylene vinyl acetate) systems. Our results and a great number of others available in the literature are compared with the predictions given, on the one hand, by the analytical approach by Cox and, on the other hand, by the theoretical study using finite element technique by Termonia. First, the influence of the fibre-matrix adhesion is analysed and it is observed, in agreement with Termonia, thatI _c/d strongly decreases when the bonding efficiency between the two components is increased. Secondly, assuming a perfect fibre-matrix adhesion, it is shown that the critical fibre aspect ratio is proportional to the square root of the ratio of fibre to matrix elastic modulus, as predicted by Cox. However, two linear relationships are established: the first corresponds to the thermosetting and thermoplastic matrices, while the second corresponds to the elastomeric matrices. The difference between these two kinds of materials is attributed to the great difference in polymer chain mobility as shown by a study of the temperature dependence ofI _c/d, particularly in the glass transition temperature zone of the matrices. However, in the case of elastomeric materials, the existence of an interphase layer between the fibre and the matrix, having an elastic modulus close to that of the elastomer in its glassy state, can also explain this particular behaviour.     

Phonon-limited mean free path in the Sondheimer oscillation of aluminum

The phonon-limited part of the electron mean free path l _Hp ,in aluminum has been investigated by the Sondheimer size effect for a magnetic field along the three principal crystallographic orientations in the temperature range 1.8–12 K. It is found that l _Hp decreases with temperature approximately as T ^–3 and varies from 1.4 × 10^–3 to 1.3 × 10^–2 cm, with the orbits responsible for the oscillations at 20 K. The results are in agreement with a calculation based on the 4-OPW Fermi surface model and the anisotropic electron-phonon scattering time given by Leung et al.Work supported in part by a Grant-in Aid for Scientific Research from the Ministry of Education.