An influence of deposition temperature on structural,optical and electrical properties of sprayed ZnO thin films of identical thickness

Nanocrystalline ZnO thin films were deposited at different temperatures (T_s = 325 °C–500 °C) by intermittent spray pyrolysis technique. The thickness (300 ± 10 nm) independent effect of T_s on physical properties was explored. X-Ray diffraction analysis revealed the growth of wurtzite type polycrystalline ZnO films with dominant c-axis orientation along [002] direction. The crystallite size increased (31 nm–60 nm) and optical band-gap energy decreased (3.272 eV–3.242 eV) due to rise in T_s. Scanning electron microscopic analysis of films deposited at 450 °C confirmed uniform growth of vertically aligned ZnO nanorods. The films deposited at higher T_s demonstrated increased hydrophobic behavior. These films exhibited high transmittance (>91%), low dark resistivity (～10^?2 Ω-cm), superior figure of merit (～10^?3 Ω^?1) and low sheet resistance (～10² Ω/□). The charge carrier concentration (η -/cm³) and mobility (μ – cm²V^?1s^?1) are primarily governed by crystallinity, grain boundary passivation and oxygen desorption effects.     

Optically stimulated luminescence (OSL) and thermally assisted OSL in Eu2+ – Doped BaSO4 phosphor

BaSO₄:Eu²⁺ phosphor has been investigated for its photoluminescence (PL), thermoluminescence (TL), TL kinetics, optically stimulated luminescence (OSL) and thermally assisted OSL (TA-OSL) response. PL spectra showed the characteristic emission of Eu²⁺ ion at 375 nm when excited by 320 nm. The luminescence lifetime has been measured as 40 and 628 μs of fast and slow components respectively. The TL parameters such as trap depth (E), frequency factor (s) and the order of kinetics (b) are determined. The phosphor is found to be 6 and 4 times more sensitive than CaSO₄:Dy and α-Al₂O₃:C, respectively, in TL mode. However, its OSL sensitivity is 75% of α-Al₂O₃:C. It is found to possess three OSL components having photoionization cross-sections of 1.4 × 10⁻¹⁷, 1.2 × 10⁻¹⁸ and 5.2 × 10⁻¹⁹ cm² respectively. The temperature dependence of OSL studies showed that integrated TA-OSL signal increases with stimulation temperature between 50 and 250 °C, while between 260 and 450 °C the signal intensity decreases. This behavior is interpreted to arise from competing effects of thermal assistance (activation energy E_A = 0.063 ± 0.0012 eV) and depletion of trapped charges. This increase of OSL at elevated temperature can be employed for enhancing the sensitivity of phosphor for radiation dosimetry.     

Preparation and TSL studies in Tb activated LiMgPO4 phosphor

LiMgPO₄:Tb³⁺ phosphor was synthesized by solid state reaction. The thermally stimulated luminescence (TSL) glow curve of Tb doped LiMgPO₄ exhibits a main TSL peak at 170 °C with shoulders at 100 and 260 °C on either side of this peak. The TSL sensitivity of the phosphor was found to be about 2.5 times that of CaSO₄:Dy phosphor. TSL emission and photoluminescence (PL) studies show that Tb³⁺ ion acts as luminescence centre in this phosphor. The kinetic parameters, namely activation energy (E) and frequency factor (s) associated with the main glow peak have been determined using peak shape method. The activation energy and frequency factor obtained are 1.35 ± 0.03 eV and (6.53 ± 0.43) × 10¹⁴ s^?1 respectively. The paper discusses the dosimetric characteristics like dose response, fading, energy response and minimum detectable dose and results thereof.     

Temperature and orientation dependences of the grain-boundary diffusion coefficient of antimony in copper bicrystals

An investigation is made of the diffusion of antimony through the bulk and along grain boundaries in copper bicrystals containing a symmetric 〈100〉 misorientation boundary with misorientation angles from 20 to 37.2°. The bicrystals are grown by the method of horizontal zone recrystallization. The temperature range for these studies is 480–580 °C, where the solubility of Sb in Cu is about 6 atomic % and practically temperature-independent. The concentration profiles are obtained by x-ray spectral microanalysis, and the grain-boundary diffusion parameters are computed by the method of Whipple and Suzuoka. The orientation dependence of the triple product P=sδD _b (where s is the segregation coefficient, δ the width of the grain boundary, and D _b the grain-boundary diffusion coefficient) is nonmonotonic, with a maximum for the special ∑5 misorientation boundary (36.9°). The effective activation energy for grain-boundary diffusion ranges from ∼70 kJ/mol for ∑5 to140 kJ/mol for general boundaries. Fiz. Tverd. Tela (St. Petersburg) 39, 1153–1157 (July 1997)     

Spray pyrolised Al/ZnO: Al heterojunction: Effect of Al on junction properties

Al/ZnO: Al heterojunction was fabricated by depositing ZnO: Al film on Al substrate by spray pyrolysis technique at 220 °C substrate temperature. XRD, SEM and EDAX techniques were used to study the properties of thin films. Heterojunction properties were studied by I–V and C–V measurements. The fabricated Al/ZnO: Al junctions were rectifying in character. The room temperature ideality factors of Al/ZnO: Al junctions are found to vary from 2.56 to 5.45. The reverse saturation currents are 5.21 × 10⁻⁹, 1.35 × 10⁻⁶, 1.99 × 10⁻⁶, 9.99 × 10⁻⁷ and 1.02 × 10⁻⁷ A for Al/ZnO: Al junctions. Junction forward current depends on doping concentrations and temperature, whereas reverse saturation current remains independent for Al concentration. The built-in-potential calculated from capacitance for Al/ZnO: Al junctions are 2.74, 2.60, 2.0, 2.50 and 2.43 V corresponding to 1, 2, 3, 4 and 5 mol% of Al. X-ray diffraction study confirmed that the films are polycrystalline, orientated in (0 0 2) plane. Scanning electron microscopy study confirmed circular ring patterns with inside ribbon type structure for Al doped ZnO films.     

χ polarization induced in molecular glass of conjugated compound by all-optical poling

The paper presents the first report on χ⁽²⁾ polarization induced in molecular glass of conjugated compound by all-optical poling. Transparent thin film of molecular glass of 1,4-bis[2-[4-[N,N-di(p-tolyl)amino]phenyl]vinyl]benzene (BTAPVB) was prepared using a spin-cast technique. Dipolar as well as octupolar components in BTAPVB contributed to the formation of photoinduced χ⁽²⁾ polarization. Growth rate of χ⁽²⁾ polarization has good linear relation with E_ω⁴E_2ω, which suggested that the simultaneous processes of two-photon (ω + 2ω) and three-photon (ω + ω + ω) excitation on the same electronic level contributed to the formation of photoinduced χ⁽²⁾ polarization.     

Preparation of highly efficient Al-doped ZnO photocatalyst by combustion synthesis

Novel Al-doped ZnO (AZO) photocatalysts with different Al concentrations (0.5–6.0 mol%) were prepared through a facile combustion method and followed by calcination at 500 °C for 3 h. The obtained nanopowders were characterized by powder X-ray diffraction (XRD), scanning electron microscope (SEM) combined with EDX, transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FTIR), UV–vis spectroscopy and photoluminescence spectroscopy. The XRD patterns of AZO nanopowders were assigned to wurtzite structure of ZnO with the smallest crystallite size about 11 nm consistent with the results from TEM. The doping of Al in ZnO crystal structure successfully suppressed the growth of ZnO nanoparticles confirmed by XRD patterns. The absorption spectra analysis showed that the optical band gap energy (E_g) for the AZO nanopowders were in the range of 3.12–3.21 eV and decreased with increasing of Al dopant. The photocatalytic activities of the samples were evaluated by photocatalytic degradation of methyl orange under visible light (λ ≥ 420 nm) and sunlight irradiation. The results showed that the AZO photocatalyst doped with 4.0 mol% Al exhibited five times enhanced photocatalytic activity compared to pure ZnO. The enhanced photocatalytic activity could be attributed to extended visible light absorption, inhibition of the electron–hole pair's recombination and enhanced adsorptivity of MO dye molecule on the surface of AZO nanopowders.     

Bulk and surface properties of ionic salt CsH5(PO4)2

We report a comparative study of transport and thermodynamic properties of single-crystal and polycrystalline samples of the ionic salt CsH₅(PO₄)₂ possessing a peculiar three-dimensional hydrogen-bond network. The observed potential of electrolyte decomposition ≈ 1.3 V indicates that the main charge carriers in this salt are protons. However, in spite of the high proton concentration, the conductivity appears to be rather low with a high apparent activation energy E_a ≈ 2 eV, implying that protons are strongly bound. The transport anisotropy though is not large, correlates with the crystal structure: the highest conductivity is found in the [001] direction (σ_130 °C ∼ 5.6 × 10^− 6 S cm^− 1) while the minimal conductivity is in the [100] direction (σ_130 °C ∼ 10 ⁻⁶ S cm^− 1). The conductivity of polycrystalline samples appears to exceed the bulk one by 1–3 orders of magnitude with a concomitant decrease of the activation energy (E_a ≈ 1.05 eV), which indicates that a pseudo-liquid layer with a high proton mobility is formed at the surface of grains. Infrared and Raman spectroscopy used to study the dynamics of the hydrogen-bond system in single-crystal and polycrystalline samples have confirmed the formation of such a modified surface layer in the latter. However, no bulk phase transition into the superionic disordered phase is observed in CsH₅(PO₄)₂ up to the melting point T_melt ∼ 151.6 °C, in contrast to its closest relative compound CsH₂PO₄.     

Vibrational analysis of the a3Σ+-X1Σ+ and b3Π-X1Σ+ band systems of GeS

Spectra of GeS have been obtained in a chemiluminescent flame produced by the reaction Ge + OCS → GeS + CO. Neither of the known band systems, D¹Π-X¹Σ⁺ and E¹Σ⁺-X¹Σ⁺, was observed, but two new band systems in the regions 350–400 and 420–650 nm were obtained. By comparison with similar systems in isovalent molecules, these were assigned as b³Π₁-X¹Σ⁺ and a³Σ⁺-X¹Σ⁺, respectively. Vibrational assignments were made with the help of the germanium isotope effect and vibrational constants were obtained for the states involved. Approximate Morse potential Franck-Condon factors were computed and were shown to fit the general trend of the intensity distribution for both systems. Addition of active nitrogen to the flame was shown to increase the intensity of the b-X system by an order of magnitude while hardly affecting the a-X system. Constants (in cm^?1) obtained for the two new states are: a³Σ⁺: T_e = 21986.3 ± 2.3, ω_e = 388.9 ± 1.0, ω_ex_e = 1.35 ± 0.11; b³Π₁: T_e = 27192.0 ± 1.8, ω_e = 435.4 ± 1.1, ω_ex_e = 1.68 ± 0.20.     

Effects of deposition temperature and hydrogen flow rate on the properties of the Al-doped ZnO thin films and amorphous silicon thin-film solar cells

A compound of 98 mol% ZnO and 1 mol% Al₂O₃ (AZO, Al:Zn = 98:2) was sintered at 1350 °C as a target and the AZO thin films were deposited on glass using a radio frequency magnetron sputtering system. The effects of deposition temperature (from room temperature to ～300 °C) on the optical transmission spectrum of the AZO thin films were studied. The Burstein–Moss shift was observed and used to prove that defects in the AZO thin films decreased with increasing deposition temperature. The variations in the optical band gap (E _g) values of the AZO thin films were evaluated from plots of (αhv)²=c(hν?E _g), revealing that the measured E _g values increased with increasing deposition temperature. The effects of the H₂ flow rate during deposition (0 %～11.76 %, deposition temperature of 200 °C) on the crystallization, morphology, resistivity, carrier concentration, carrier mobility, and optical transmission spectrum of the AZO thin films were measured. The chemical structures of the Ar-deposited and 2 % H₂-flow rate-deposited AZO thin films (both were deposited at 200 °C) were investigated by XPS to clarify the mechanism of improvement in resistivity. The prepared AZO thin films were also used as transparent electrodes to fabricate amorphous silicon thin-film solar cells, and their properties were also measured.     

Dynamics of [n.3]paracyclophanes (n = 2 – 4) as studied by NMR. Obtaining separate Arrhenius parameters for two dynamic processes in [4.3]paracyclophane

Extending our earlier findings for [3.3]paracyclophane, NMR line shape studies of the conformational dynamics in [3.2] and [4.3]paracyclophanes are reported, of which the former is conformationally homogeneous and the latter occurs in two enantiomeric forms. For [3.2]paracyclophane, the Arrhenius activation energy E_a = 11.6 ± 0.1 kcal/mol and preexponential factor log (A/s^?1) = 12.92 ± 0.07 were found. In [4.3]paracyclophane, the conformational dynamics are quite complicated because, apart from interconversions of each enantiomer into itself proceeding via inversion of the propano bridge with rate constant k₁, the enantiomers mutually rearrange with rate constant k₂ due to inversion of the butano bridge. The determination of Arrhenius parameters from dynamic ¹H spectra of the aromatic protons for these two conformational processes (E_a = 11.2 ± 0.5 kcal/mol and log (A/s^?1) = 13.6 ± 0.5 for the former, and E_a = 9.7 ± 0.4 kcal/mol and log (A/s^?1) = 13.2 ± 0.4 for the latter) is the highlight of this work. In the investigated temperature range, in [4.3]paracyclophane, the occurrence of other conformational processes beyond those mentioned above can be excluded, because they would produce different line shape patterns than those actually observed. Copyright © 2013 John Wiley & Sons, Ltd.     

Conductivities of electrolytes based on PEI-b-PEO-b-PEI triblock copolymers with lithium and copper TFSI salts

Tri block-copolymer poly(iminoethylene)-b-poly(oxyethylene)-b-poly(iminoethylene) with a poly(oxyethylene) central block (PEI-b-PEO-b-PEI) were used as a “dual” matrix for polymer electrolytes having selectivity for hard cations (Li⁺/PEO) in one phase and for soft cations (Cu²⁺/PEI) in the other. Conductivity measurements were recorded for 20:1, 12:1 and 8:1 coordinating atom (O or/and N) to cation (Li⁺, Cu²⁺) ratios, for each of the three complexes studied: PEI-b-PEO-LiTFSI-b-PEI, PEI-Cu(TFSI)₂-b-PEO-b-PEI-Cu(TFSI)₂ and PEI-Cu(TFSI)₂-b-PEO-LiTFSI-b-PEI-Cu(TFSI)₂. For either low (20 °C) or high temperature (80 °C) the highest conductivity was given by the polymer electrolyte based on Cu(TFSI)₂ with N/Cu²⁺ = 20:1 (10^− 6, respectively 2 × 10^− 4 S cm^− 1). In the present paper, the conductivity evolution is discussed in relation with the polymer structure, the type and the concentration of the salt and the thermal behavior of our systems.     

Parelektrische Resonanz von Li+ in KCl

Parelectric resonance (PER) absorption spectra of Li⁺-centers in KCl crystals are measured at 35 and 9 GHz. Measurements for the microwave fieldE ₁ parallel and perpendicular to the static fieldE ₀ for three different orientations relative to the crystal axes can be explained by using the following offcenter tunneling model for the Li⁺-center: The dipole momentp=6.3±0.3 Debye is in [111] direction. Tunneling transitions are possible parallel to the [100] and [110] axis. The corresponding matrix elements are 11.3±0.5 and 3.2±0.5 GHz. The zero field splittings are 9.8±1.5; 22.6±1 and 35.4±3 GHz. Measurements under application of an uniaxial pressureP ₀ support this analysis.     

Microwave spectroscopic study of the conformations,relative energies,and dipole moments of ethyl cyanoformate

The microwave spectrum of ethyl cyanoformate displays a-type band spectra from three nearly prolate conformers. High-resolution spectra of the two more stable species have been assigned. One form, designated extended, has rotational constants A″ = 6453.3(4) MHz, B″ = 1500.47(6) MHz, C″ = 1236.36(6) MHz, which are consistent with a syn-anti [τ₁ (OCOC) = 0°, τ₂ (COCC) = 180°] structure. The second form, labeled compact, has rotational constants A″ = 6787.8(7) MHz, B″ = 1549.38(8) MHz, C″ = 1406.80(8) MHz, which are consistent with a syn-gauche [τ₁ (OCOC) = 0°, τ₂ (COCC) ～ 90°] structure. The extended form is marginally more stable, ΔE = 55 ± 27 cm^?1. The extended conformer has dipole moment components μ_a = 4.44(7), μ_b ～ 0 D and the compact conformer has dipole moment components μ_a = 4.25(7), μ_b = 0, μ_c = 1.08(23) D. The third conformer (relative energy 600 ± 140 cm^?1) has the most intense band series even at ?63°C. the bands of this conformer are unresolvable into individual rotational transitions.     

Structural,vibrational study and superprotonic behavior of a new mixed dipotassium hydrogenselenate dihydrogenphosphate K2(HSeO4)1.5(H2PO4)0.5

Ongoing studies of the KHSeO₄–KH₂PO₄ system aiming at developing novel proton conducting solids resulted in the new compound K₂(HSeO₄)_1.5(H₂PO₄)_0.5 (dipotassium hydrogenselenate dihydrogenphosphate). The crystals were prepared by a slow evaporation of an aqueous solution at room temperature. The structural properties of the crystals were characterized by single-crystal X-ray analysis: K₂(HSeO₄)_1.5(H₂PO₄)_0.5 (denoted KHSeP) crystallizes in the space group P 1¯ with the lattice parameters: a = 7.417(3) Å, b = 7.668(2) Å, c = 7.744(5) Å, α = 71.59(3)°, β = 87.71(4)° and γ = 86.04(6)°. This structure is characterized by HSeO₄⁻ and disordered (H_xSe/P)O₄⁻ tetrahedra connected to dimers via hydrogen bridges. These dimers are linked and stabilized by additional hydrogen bonds (O–H–O) and hydrogen bridges (O–H…O) to build chains of dimers which are parallel to the [0, 1, 0] direction at the position x = 0.5.The differential scanning calorimetry diagram showed two anomalies at 493 and 563 K. These transitions were also characterized by optical birefringence, impedance and modulus spectroscopy techniques. The conductivity relaxation parameters of the proton conductors in this compound were determined in a wide temperature range. The transport properties in this material are assumed to be due to H⁺ protons hopping mechanism.     

The influence of annealing temperature and tellurium (Te) on electrical and dielectrical properties of Al/p-CIGSeTe/Mo Schottky diodes

p-CuIn_0.7Ga_0.3(Se_(1?x)Te_x)₂ type thin films were synthesized by thermal evaporation method on Mo coated glass substrates. To obtain Al/CuIn_0.7Ga_0.3(Se_(1?x)Te_x)₂/Mo Schottky diode structure for two compositions of x = 0.0 and 0.6, Al metal was evaporated on upper surface of CuIn_0.7Ga_0.3(Se_(1?x)Te_x)₂ as a front contact. Al/p-CuIn_0.7Ga_0.3(Se_(1?x)Te_x)₂/Mo structures were annealed temperature range from 150 °C to 300 °C for 10 min under vacuum. The electrical and dielectrical properties of Al/p-CuIn_0.7Ga_0.3(Se_(1?x)Te_x)₂ (CIGSeTe) Schottky barrier diodes (SBD) have been investigated. Capacitance–Voltage (C–V) characteristics, Conductance–Voltage (G/w–V) characteristics and interface state density were studied in order to obtain electrical and dielectrical parameters. The effects of interface state density (N_ss), series resistance (R_s), the dielectric constant (?′), dielectric loss (?″), dielectric loss tangent (tan δ), ac electrical conductivity (σ_ac) and carrier doping densities were calculated from the C–V and G/w–V measurements and plotted as a function of annealing temperature. It was observed that the values of carrier doping density N_A for annealing temperature at 150 °C decreased from 2.83 × 10⁺¹⁵ cm^?3 to 2.87 × 10⁺¹⁴ cm^?3 with increasing Te content from x = 0.0 to 0.6. The series resistance for x = 0.0 found to be between 10 and 75 Ω and between 50 and 230 Ω for x = 0.6 in the range of annealing temperature at 150–300 °C.     

Ionic conductivity of polymer electrolyte membranes based on polyphosphazene with oligo(propylene oxide) side chains

A polyphosphazene [NP(NHR)₂]_n with oligo[propylene oxide] side chains − R = –[CH(CH₃)–CH₂O]_m–CH₃ (m = 6 – 10) was synthesized by living cationic polymerisation and polymer-analogue substitution of chlorine from the intermediate precursor [NPCl₂]_n using the corresponding primary amine RNH₂. The polymer had an average molecular weight of 3.3 × 10⁵ D. Polymer electrolytes with different concentrations of dissolved lithium triflate (LiCF₃SO₃) were prepared. Mechanically stable polymer electrolyte membranes were formed using UV radiation induced crosslinking of the polymer salt mixture in the presence of benzophenone as photoinitiator. The glass transition temperature of the parent polymer was found to be − 75 °C before cross linking. It increases after crosslinking and with increasing amounts of salt to a maximum of − 55 °C for 20 wt.% LiCF₃SO₃. The ionic conductivity was determined by impedance spectroscopy in the temperature range 0–80 °C. The highest conductivity was found for a salt concentration of 20 wt.% LiCF₃SO₃: 6.5 × 10^− 6 S·cm^− 1 at 20 °C and 2.8 × 10^− 4 S cm^− 1 at 80 °C. The temperature dependence of the conductivities was well described by the MIGRATION concept.     

Structural and electrical properties of VO2/ZnO nanostructures

We examined the structural and electrical properties of uniformly-oriented VO₂/ZnO nanostructures. VO₂ was deposited on ZnO templates by using a direct current-sputtering deposition. Scanning electron microscope and transmission electron microscope measurements indicated that b-oriented VO₂ were uniformly crystallized on ZnO templates with different lengths. VO₂/ZnO formed nanorods on ZnO nanorods with length longer than 250 nm. X-ray absorption fine structure at the V K edge of VO₂/ZnO showed M₁ and R phases of VO₂ at 30 and 100 °C, respectively, suggesting structural-phase transition occurring between the two temperatures. Temperature-dependent resistance measurements of VO₂/ZnO nanostructures revealed metal-to-insulator transition at 65 °C and 55 °C during a heating and a cooling, respectively, regardless of ZnO length. Asymmetry behavior of resistance curves from VO₂/ZnO nanostructure during a heating and a cooling was attributed from a strong bond of VO₂ and ZnO.     

A plasma resonance study of valley transfer in (001) Si inversion layers

We observed the two-dimensional plasmons of the two-component electron plasma in the (001) Si-inversion layer resulting from simultaneous population of the [001] valley, E₀, and the [010] valley, E₀′, subbands under a compressional uniaxial stress along [010]. Our data show an onset of electron transfer from E₀ to E₀′ at X = (1.4 ± 0.1) kbar for n = 1.67 × 10¹² cm^?2 and X = (1.2 ± 0.2) kbar for n = 2.60 × 10¹² cm^?2, consistent with the theory of Takada and Ando that includes the electron-electron correlation effects.     

The motions of hydrogen impurities in α-Palladium-hydride

The intensity distribution of inelastically scattered thermal and hot neutrons on hydrogen impurities in α-palladium hydride has been studied as a function of concentration, temperature, momentum transfer and different annealing procedures. In up-scattering experiments the first and second harmonics appear at E₁^H = (66 ± 4) me V and E₂^H = (135 ± 15) meV respectively, and the hydrogen band modes have a frequency distribution as expected from measured dispersion curves for pure palladium. For deuterium the first harmonic appears at E₁^D = (48 ± 4) meV. The width of the hydrogen local mode E₁^H changes from 30 to 20 me V and its position from 63 to 66 meV, when the hydrogen concentration is altered from 2.7 to 0.2 at.%. After an extended annealing procedure and at the lowest concentration of 0.2 at.%, the local mode appears in down-scattering experiments at E₁^H = (68.5 ± 2) meV with a full width at half height ΔE₁^H = 4 meV, which is purely instrumental. For higher concentrations and insufficient annealing of the sample, cluster of hydrogen atoms are formed even in the α-phase, as indicated by the increasing width of the local mode. The peak intensity of the E₁^H mode decreases upon changing the temperature from 423 to 673°K. Upon changing the direction of the k-vector from the [1,0,0]- to the [1,1,0]-direction, the peak intensity of the local mode decreases by a factor of ten. These observations indicate the existence of anhannonic effects along the [l,l,0]-direction.