Theoretical and experimental study of photocurrent action spectrum of ITO/sexithiophene/Al structure

We have studied photovoltaic cells using sexithiophene in (ITO/6T/Al) structure, and we have measured the action spectrum obtained by illumination through the aluminum side which is compared to the measured absorption spectrum. Two models were used to interpret this experiment: the Ghosh model using the carriers diffusion property in the bulk, and the kinetic model describing the dynamic behavior of the charge carriers in the device. The confrontation of these models with the experimental spectra allows us to reach the diffusion length of electron–hole pair L=2×10⁻⁶ cm. We also give the mobility of carriers (μ_n≈1.5×10⁻⁴ cm²/V s, and μ_p≈1.5×10⁻⁵ cm²/V s) and their diffusion coefficients (D_n≈4×10⁻⁶ cm²/s, and D_p≈4×10⁻⁷ cm²/s).     

Thermal expansion of the W5Si3 and T2 phases of the W–Si–B system investigated by high-temperature X-ray diffraction

The coefficients of thermal expansion (CTE) of the W₅Si₃ and T₂ phases of the W–Si–B system were determined using high-temperature X-ray diffraction in the 298–1273 K temperature interval. Alloys with nominal compositions 62.5W37.5Si (at%) and 58W21Si21B (at%) were prepared from high-purity materials through arc melting followed by heat treatment at 2073 K for 12 h under argon atmosphere. The highly different thermal expansion coefficients of W₅Si₃ along the a (5.0 × 10⁻⁶ K⁻¹) and c (16.3 × 10⁻⁶ K⁻¹) axes lead to a high thermal expansion anisotropy (α_c/α_a ≅ 3.3). On the other hand, the T₂-phase exhibits similar thermal expansion coefficients along the a (6.9 × 10⁻⁶ K⁻¹) and c (7.6 × 10⁻⁶ K⁻¹) axes, indicating a behavior close to isotropic (α_c/α_a ≅ 1.1).     

Synthesis,crystal structure and electrical conductivity of [bmim][Ni(dmit)2]3 (bmim = 1-butyl-3-methylimidazolium,dmit = 1,3-dithiol-2-thione-4,5-dithiolate)

A new complex [bmim][Ni(dmit)₂]₃ has been prepared, and its crystal structure and electrical conductivity where determined and measured. Crystallographic parameters for C₂₆H₁₅N₂S₃₀Ni₃: triclinic system; space group: P-1; a=12.760(3), b=19.441(4), c=11.670(2) Å; α=102.00(3), β=117.10(3), γ=95.06(3)°; Z=2, R=0.0579 (I>2σ(I)). The conductivity of this salt at room temperature is 1.7×10⁻² S cm⁻¹ and it shows semiconduction in the temperature range of 110–290 K.     

Laser doping of chromium as a double acceptor in silicon carbide with reduced crystalline damage and nearly all dopants in activated state

Chromium, a p-type dopant, has been incorporated into silicon carbide by laser doping. Secondary ion mass spectrometric data revealed enhanced solid solubility (2.29 × 10¹⁹ cm⁻³ in 6H–SiC and 1.42 × 19¹⁹ cm⁻³ in 4H–SiC), exceeding the equilibrium limit (3 × 10¹⁷ cm⁻³ in 6H–SiC above 2500 °C). The roughness, surface chemistry and crystalline integrity of the doped sample were examined by optical interferometry, energy dispersive X-ray spectrometry and transmission electron microscopy, respectively, and showed no crystalline disorder due to laser heating. Deep-level transient spectroscopy confirmed Cr as a deep-level acceptor with activation energies E_v + 0.80 eV in 4H–SiC and E_v + 0.45 eV in 6H–SiC. The Hall effect measurements showed that the hole concentration (1.942 × 10¹⁹ cm⁻³) is almost twice the average Cr concentration (1 × 10¹⁹ cm⁻³), confirming that almost all of the Cr atoms were completely activated to the double acceptor state by the laser-doping process without requiring any additional annealing step.     

Alkyl chain length dependence of the field-effect carrier mobility in regioregular poly(3-alkylthiophene)s

The field-effect mobility of holes in regioregular poly(3-alkylthiophene)s was determined for a series of 5 alkyl chain lengths from C₄ (n-butyl) to C₁₂ (n-dodecyl). Contrary to a previous report, a non-monotonic dependence of field-effect mobility on alkyl chain length was found. The average hole mobility varied from 1.2 × 10⁻³ cm²/Vs in poly(3-butylthiophene) and 1 × 10⁻² cm²/Vs in poly(3-hexylthiophene) to 2.4 × 10⁻⁵ cm²/Vs for poly(3-dodecylthiophene). We believe that the hexyl side chain is optimum for charge transport because of better self-organization in poly(3-hexylthiophene) compared to other polymers in the series. The present results provide an important structure–carrier mobility relationship for the regioregular poly(3-alkylthiophene)s which are of wide interest for thin film transistors and photovoltaic cells.     

ZnO ultraviolet photodiodes with Pd contact electrodes

ZnO epitaxial films were grown on sapphire (0 0 0 1) substrates by using RF plasma-assisted molecular beam epitaxy (MBE). Metal–semiconductor–metal (MSM) ZnO photodiodes with palladium contact electrodes were then fabricated. With an incident wavelength of 370 nm and an applied bias of 1 V, it was found that maximum responsivity of the Pd/ZnO/Pd MSM photodetectors was 0.051 A W⁻¹, which corresponds to a quantum efficiency of 11.4%. Furthermore, it was found that the time constant of our photodiodes was 24 ms with a three-order decay exponential function. For a given bandwidth of 100 Hz and an applied bias of 1 V, we found that noise equivalent power and corresponding detectivity D¹ were 1.13 × 10⁻¹² W and 6.25 × 10¹¹ cm Hz^0.5 W⁻¹, respectively.     

Analysis of electrochemical impedance of polypyrrole|sulfate and polypyrrole|perchlorate films

PPy|SO₄ and PPy|ClO₄ films have been synthesized and investigated in K₂SO₄, ZnSO₄ and NaClO₄ aqueous solutions by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and electron probe microanalysis (EPMA) methods. On the basis of obtained data and calculated impedance parameters as the potential functions, the role of different processes (diffusion of ions, double-layer charging, adsorption and charge transfer) in oxidized, partially reduced and reduced PPy films is estimated. The lowest pseudocapacitance values (from n × 10⁻⁶ to n × 10⁻⁴ μF cm⁻² for 1 μm film), independent of solution concentration, were established for PPy|SO₄ in ZnSO₄. This phenomenon is related with strongly aggravated film reduction process in the solution of double-charged cations. In the case of PPy|ClO₄ in NaClO₄ and PPy|SO₄ in K₂SO₄,where the mono-charged cations participate in redox process, the capacitance values are in the range from: n × 10⁻³ to n × 10⁻² μF cm⁻² and even somewhat higher for PPy|ClO₄ system at oxidized state. The calculated effective diffusion coefficients of ions D remain inside the range from n × 10⁻¹² to n × 10⁻¹⁴ cm² s⁻¹ for PPy|SO₄ in 0.1 M K₂SO₄ and PPy|ClO₄ in 0.1 M NaClO₄ aqueous solution. In the case of PPy|SO₄ film in ZnSO₄ solution the D values are essentially lower.     

The effect of a novel organic compound chiral macrocyclic tetraamide-I interfacial layer on the calculation of electrical characteristics of an Al/tetraamide-I/p-Si contact

The Al/tetraamide-I/p-Si Schottky barrier diode (SBD) has been prepared by adding a solution of a novel nonpolymeric organic compound chiral macrocylic tetraamide-I in chloroform on top of a p-Si substrate and then evaporating the solvent. It has been seen that the forward-bias current–voltage (I–V) characteristics of Al/tetraamide-I/p-Si SBD with a barrier height value of 0.75 eV and an ideality factor value of 1.77 showed rectifying behaviour. The energy distribution of the interface state density determined from I–V characteristics increases exponentially with bias from 5.81 × 10¹² cm⁻² eV⁻¹ at (0.59-E_v) eV to 1.02 × 10¹³ cm⁻² eV⁻¹ at (0.40-E_v) eV. It has showed that space charge limited current (SCLC) and trap charge limited current (TCLC) are the dominant transport mechanisms at large forward-bias voltages.     

The calculation of electronic properties of an Ag/chitosan/n-Si Schottky barrier diode

In this study, the film of chitosan by adding the solution of chitosan being a polymeric compound on the top of an n-Si substrate and then by evaporating solvent was formed. It was seen that the chitosan/n-Si contact demonstrated clearly rectifying behavior and the reverse curves exhibit a weak bias voltage dependence by the current–voltage (I–V) curves studied at room temperature. Average barrier height and ideality factor values for this structure were determined as 0.94 eV and 1.81, respectively. Furthermore, the energy distribution of the interface state density located in the semiconductor band gap at the chitosan/n-Si substrate in the energy range (E_c−0.785) to (E_c−0.522) eV have been determined from the I–V characteristics. The interface state density N_ss ranges from 5.39 × 10¹² cm⁻² eV⁻¹ in (E_c−0.785) eV to 1.52 × 10¹³ cm⁻² eV⁻¹ in (E_c−0.522) eV. The interface state density has an exponential rise with bias from the midgap towards the bottom of the conduction band.     

Photovoltaic devices based on polythiophenes and substituted polythiophenes

In recent years there has been considerable interest in the fabrication of photovoltaic devices using polymeric and organic materials. This paper presents work carried out using a range of polythiophenes, including some substituted with porphyrin moieties as light harvesters. Homopolymers and copolymers were investigated for their performance in photovoltaic devices, and the use of both solid polymer electrolyte and liquid electrolyte was examined. Both photoelectrochemical cells and Schottky devices were investigated. The best photoelectrochemical cell was fabricated using polyterthiophene which had V_oc=139 mV, I_sc=123.4 μA cm⁻², fill factor=0.38, and energy conversion efficiency=0.02% at a halogen lamp intensity of 317 W m⁻². The Schottky device gave a V_oc=0.5 V and I_sc of 0.98 μA cm⁻² at a halogen lamp intensity of 500 W m⁻².     

Synthesis,characterization and evaluation of cation-ordered LnBaCo2O5+δ as materials of oxygen permeation membranes and cathodes of SOFCs

LnBaCo₂O_5+δ (Ln = La, Pr, Nd, Sm, Gd, and Y) was synthesized via an EDTA–citrate complexing process. The particular Ln³⁺ dopant had a significant effect on the oxide’s phase structure/stability, oxygen content, electrical conductivity, oxygen permeability, and cathode performance. Stable, cation-ordered oxides with layered lattice structures were obtained with medium-sized Ln³⁺ ions over a wide range of oxygen partial pressures, a property essential for applications as oxygen separation membranes and solid oxide fuel cell (SOFC) cathodes. PrBaCo₂O_5+δ demonstrated the highest oxygen flux (∼5.09 × 10⁻⁷ mol cm⁻² s⁻¹ at 900 °C), but this value was still significantly lower than that of Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ perovskite (∼3.1 × 10⁻⁶ mol cm⁻² s⁻¹ at 900 °C). The observed difference was attributed to the much longer diffusion distance through a polycrystalline membrane with a layered lattice structure than through cubic perovskite because bulk diffusion was the rate-limiting step of permeation. An area-specific resistance of ∼0.213 Ω cm² was achieved at 600 °C with a PrBaCo₂O_5+δ cathode, suggesting that the layer-structured oxides were promising alternatives to ceramic membranes for SOFC cathodes.     

Studies on electrochemical copolymerization of aniline with o-phenylenediamine and degradation of the resultant copolymers via electrochemical quartz crystal microbalance and scanning electrochemical microscope

Electropolymerization of aniline in sulfuric acid solution in the presence of o-phenylenediamine (oPD) of various concentrations was investigated via the electrochemical quartz crystal microbalance (EQCM) technique. It was found that the polymerization occurred more favorably at high aniline-to-oPD molar ratios (F₁, 20 or above). The stabilities of the resultant copolymers against degradation were efficiently improved compared with that of polyaniline (PANI). The first-order kinetic constants for polymer degradation were estimated to be 2.07 × 10⁻³ s⁻¹ for polyaniline, and 3.91 × 10⁻⁴ and 1.28 × 10⁻⁴ s⁻¹ for copolymers with F₁ values of 50 and 20, respectively. The degradation product, benzoquinone, was also detected at the tip electrode of a scanning electrochemical microscope (SECM).     

Effect of growth rate on microstructure and mechanical properties of directionally solidified multiphase intermetallic Ni–Al–Cr–Ta–Mo–Zr alloy

The effect of growth rate on microstructure and mechanical properties of directionally solidified (DS) multiphase intermetallic alloy with the chemical composition Ni–21.9Al–8.1Cr–4.2Ta–0.9Mo–0.3Zr (at.%) was studied. The DS ingots were prepared at constant growth rates V ranging from 5.56 × 10⁻⁶ to 1.18 × 10⁻⁴ ms⁻¹ and at a constant temperature gradient at the solid–liquid interface of G_L = 12 × 10³ K m⁻¹. Increasing growth rate increases volume fraction of dendrites and decreases primary dendritic arm spacing, mean diameter of α-Cr (Cr-based solid solution) and γ′(Ni₃Al) precipitates within the dendrites. Room-temperature compressive yield strength, ultimate compressive strength, hardness and microhardness of dendrites increase with increasing growth rate. All room-temperature tensile specimens show brittle fracture without yielding. The brittle-to-ductile transition temperature for tensile specimens is determined to be about 1148 K. Minimum creep rate is found to depend strongly on the applied stress and temperature according to the power law with a stress exponent of n = 7 and apparent activation energy for creep of Q_a = 401 kJ/mol.     

Advances in the development of detonation technologies and equipment for coating deposition

New devices and methods for the plasma detonation deposition of coatings, which give a permanent delivery of gases and powders into the combustion chamber, have been developed. They allow one to increase the delivery accuracy and to promote an operation frequency of 2–20 Hz for these detonation devices. Non-stationary regimes of the detonation combustion of a combustible gaseous mixture are found allowing the introduction of an additional electrical energy and the control of the pulsed jet characteristics, as well as the ability to change the jet power density from 10³ to 10⁷ W cm⁻², the jet temperature from 2×10³ to 3×10⁴ K and its velocity from 600 to 8000 m s⁻¹. A new type of device has been developed. Using this device coatings from α-Al₂O₃ and hard alloy WC(88%)–Co(12%) powders have been produced. Analysis has demonstrated that these coatings are of better quality than those deposited using traditional gas-detonation technology.     

Photoluminescence studies on RF plasma-polymerized thin films

Conjugated polymers in the form of thin films play an important role in the field of materials science due to their interesting properties. Polymer thin films find extensive applications in the fabrication of devices, such as light emitting devices, rechargeable batteries, super capacitors, and are used as intermetallic dielectrics and EMI shieldings. Polymer thin films prepared by plasma-polymerization are highly cross-linked, pinhole free, and their permittivity lie in the ultra low k-regime. Electronic and photonic applications of plasma-polymerized thin films attracted the attention of various researchers. Modification of polymer thin films by swift heavy ions is well established and ion irradiation of polymers can induce irreversible changes in their structural, electrical, and optical properties. Polyaniline and polyfurfural thin films prepared by RF plasma-polymerization were irradiated with 92 MeV silicon ions for various fluences of 1 × 10¹¹ ions cm⁻², 1 × 10¹² ions cm⁻², and 1 × 10¹³ ions cm⁻². FTIR have been recorded on the pristine and silicon ion irradiated polymer thin films for structural evaluation. Photoluminescence (PL) spectra were recorded for RF plasma-polymerized thin film samples before and after irradiation. In this paper the effect of swift heavy ions on the structural and photoluminescence spectra of plasma-polymerized thin films are investigated.     

Hydrogen diffusion coefficients through Inconel 718 in different metallurgical conditions

We report hydrogen permeation studies through cold rolled, solutionized, and precipitation hardened Inconel 718 foils. The effective hydrogen diffusion coefficient is considerably higher (5.3–6.8 × 10⁻¹¹ cm²/s) for the solutionized Inconel 718 than for either the cold rolled (3.3–4.2 × 10⁻¹¹ cm²/s) or precipitation hardened (2.1–2.9 × 10⁻¹¹ cm²/s) specimens. Microstructural studies indicate that the reduced hydrogen diffusion coefficients in the latter specimens arise from hydrogen trapping at dislocations and precipitates that are present at much lower concentrations in the solutionized specimens. Also, repeated permeation transients provide evidence for irreversible hydrogen trapping in the cold rolled and precipitation hardened specimens, but such effects are insignificant in the solutionized specimens.     

Electrical properties,sintering and thermal expansion behavior of composite ceramic interconnecting materials,La0.7Ca0.3CrO3−δ/Y0.2Ce0.8O1.9 for SOFCs

This paper presents a high-performance interconnect ceramic for solid oxide fuel cells (SOFCs), based on a modification of La_0.7Ca_0.3CrO_3−δ (LCC). It was found that addition of a small amount of YDC (Y_0.2Ce_0.8O_1.9) into LCC dramatically increased the electrical conductivity. For the best system, LCC + 3 wt.% YDC, the electrical conductivity reached 104.8 S cm⁻¹ at 800 °C in air. The electrical conductivity of the specimen with 2 wt.% YDC in H₂ at 800 °C was 5.9 S cm⁻¹. With the increase of YDC content, the relative density increased, reaching 97.6% when the YDC content was 10 wt.%. The average coefficient of thermal expansion (CTE) at 30–1000 °C in air increased with YDC content, ranging from 11.12 × 10⁻⁶ K⁻¹ to 15.34 × 10⁻⁶ K⁻¹. The oxygen permeation measurement illustrated a negligible oxygen ionic conduction, indicating that it is still an electronically conducting ceramic. Therefore, it is a very promising interconnecting ceramic for SOFCs.     

Kinetic study of the electrochemical degradation of polyaniline

The kinetics of the electrochemical degradation of polyaniline (PANI) layers, deposited by electropolymerization and chemical polymerization onto platinum electrode, was investigated in an acid aqueous solution. The degradation rate was shown to depend greatly on the electrode potential applied. First-order rate constants of degradation, obtained from the kinetic data, were shown to vary between 2.87×10⁻⁵ and 3.11×10⁻³ s⁻¹ for thick PANI films, having the electrochemical charge density of 14 mC/cm², and between 2.0×10⁻⁵ and 3.60×10⁻³ s⁻¹ for thin PANI films, having the charge density of 1.5 mC/cm², within the electrode potential range of 0.3–0.9 V versus Ag/AgCl. Two linear regions were found to present on the dependencies of logarithm of the first-order degradation rate constant on electrode potential, one of them having a slope of 0.44 and 1.34 V⁻¹ within electrode potential limits of 0.3–0.6 V, and another one having a slope of 6.37 and 6.39 V⁻¹ within potential limits of 0.6–0.9 V, for thick and thin polymer films, respectively. The results obtained show that the electrochemical degradation of PANI films proceed at a remarkable rate even at low electrode potential values.     

The calculation of electronic parameters of an Ag/chitin/n-Si Schottky barrier diode

We have formed polymeric organic compound chitin film on n-Si substrate by adding a solution of polymeric compound chitin in N,N-dimethylacetamide and lithium chloride on top of an n-Si substrate and then evaporating solvent. It has been seen that the chitin/n-Si contact has demonstrated clearly rectifying behavior and the reverse curves exhibit a weak bias voltage dependence by the current–voltage (I–V) curves studied at room temperature. The barrier height and ideality factor values of 0.959 eV and 1.553, respectively, for this structure have been obtained from the forward bias I–V characteristics. Furthermore, the energy distribution of the interface state density located in the semiconductor band gap at the chitin/n-Si substrate in the energy range from (E_c − 0.897) to (E_c − 0.574) eV have been determined from the I–V characteristics. The interface state density, N_ss, ranges from 5.965 × 10¹² cm⁻² eV⁻¹ in (E_c − 0.897) eV to 1.706 × 10¹³ cm⁻² eV⁻¹ in (E_c − 0.574) eV and has an exponential rise with bias this energy range.     

Synthesis and properties of a new two-photon absorbing chromophore

This paper presents of a new, conjugated and symmetric multi-branched two-photon absorption chromophore 1,2,4,5-tetrakis(4-N-methyl-N-hydroxyethylamino)vinylphenyl benzene (TKAVPB) with D-π-D structure. The new dye built on 1,2,4,5-benzene core with four amino-branching units, which allows efficient π-electron delocalization, exhibits moderate two-photon absorption (TPA) value in the femtoseconds regime (TPA cross-section as 97 × 10⁻⁵⁰ cm⁴ s photon⁻¹ molecule⁻¹ with 200 fs laser pulses). Linear absorption, single and two-photon fluorescence spectra were experimentally studied. When pumped with 760 nm laser irradiation, TKAVPB shows strong two-photon up-conversion fluorescence with peak at 527 nm.