A spectrometric study of a 40 MHz inductively coupled plasma—VI: Argon continuum in the visible region of the spectrum

The nature of a pure Ar continuum observed in ICP-AES has been studied in the 400–700 nm range. The radiative recombination is predominant below 500 nm, but bremsstrahlung must be considered above 500 nm. The electron temperature T_e deduced from the ratio of an Ar line to the adjacent continuum is about 10,000 K, which is significantly different from the excitation temperatures previously measured in this source. The electron number density (n_e) determined from the continuum is in good agreement with the value determined from the Stark effect on Ar 1549.5 nm line and about 5 × 10²⁰ m^?3. The continuum varies with the input power and the carrier gas flow rate. This is mainly due to the variation of n_e.     

Electrophysical properties of poly(<Emphasis Type="Italic">N</Emphasis>-vinylcarbazole)-carbon nanotubes composite films

The specific features of charge carrier transport in poly(N-vinylcarbazole) films doped with single-wall carbon nanotubes have been investigated. The mobilities of electrons and holes in ITO-polymer composite-Al samples have been determined by the time-of-flight method and by measuring the voltage-current characteristics of steady-state currents. According to the time-of-flight experiments, in the films of a poly(N-vinylcarbazole)-0.26 wt % single-wall carbon nanotubes composite, the drift mobility of electrons lies within (1.2–4.5) × 10^?6 cm²/(V s) and exceeds the mobility of holes by a factor of 5. The shape of the transient current suggests the dispersion character of transport of electrons and holes. With an increase in the concentration of single-wall nanotubes from 0.26 to 0.43 wt %, the conductivity of the composite films increases by two orders of magnitude; that is, the threshold of conductivity percolation has been achieved. A simple model is proposed to describe the transport of charge carriers in the polymer system under study.     

Analysis of lattice thermal conductivity and phonon-phonon scattering relaxation rate: Application to Ge

The three-phonon scattering relaxation rates and their temperature exponents have been analysed in the frame of Guthrie's classification of the phonon-phonon scattering events as class I and class II events and as a result of this, a new expressionτ _3ph ^-1 =(B _N,I+B _U,Ie^-θ/αT) g(w)T ^m I ^(T)+(B _N,II+B _U,IIe^-θ/αT)g(w)T ^mII^(T) for the three phonon scattering relaxation rates has been proposed for the first time to calculate the lattice thermal conductivity of a sample. Using the expression proposed above, the lattice thermal conductivity of Ge has been analysed in the temperature range 2–1000K and result obtained shows a very good agreement with the experimental data. The percentage contributions due to three-phonon normal and umklapp processes are also reported. The role of four phonon processes is also included at high temperatures. To estimate an approximate value of the scattering strength and the phonon conductivity, the analytical expression is also obtained in the frame of the expression proposed above forτ _3ph ^-1 .     

Microstructural,magnetic and crystal field investigations of nanocrystalline Dy3+ doped zinc oxide

Dy³⁺ doped zinc oxide was prepared by co-precipitation method. The as-prepared samples were annealed at different temperatures to obtain the samples with different particle sizes. The crystallographic phases of all the samples were confirmed by X-ray diffraction (XRD) patterns. Rietveld analysis of the XRD pattern of the sample annealed at 80 °C showed that most of the Dy³⁺ ions were substituted in the Zn²⁺ site of the hexagonal ZnO lattice. But in case of samples annealed at higher temperatures, a fraction of Dy³⁺ ions comes out from the ZnO lattice and this fraction increases with the increase of annealing temperature. The sizes of nanoparticles and the lattice strains of all the samples were obtained from the Hall–Williamson plot. High resolution transmission electron microscopy showed that ZnO nanoparticles are more or less spherical. Magnetic susceptibilities (χ) of some selected samples measured in the temperature range of 300–14 K indicate that the samples are paramagnetic. Values of χ were successfully fitted by Curie–Weiss law. A good theoretical simulation of χ of the sample annealed at 80 °C has been achieved using the one-electron crystal field interaction of the Dy³⁺ ions with its diamagnetic neighbors in the hexagonal single crystal.     

Few‐Layer Nanosheets of n‐Type SnSe2

Layered p‐block metal chalcogenides are renowned for thermoelectric energy conversion due to their low thermal conductivity caused by bonding asymmetry and anharmonicity. Recently, single crystalline layered SnSe has created sensation in thermoelectrics due to its ultralow thermal conductivity and high thermoelectric figure of merit. Tin diselenide (SnSe₂), an additional layered compound belonging to the Sn‐Se phase diagram, possesses a CdI₂‐type structure. However, synthesis of pure‐phase bulk SnSe₂ by a conventional solid‐state route is still remains challenging. A simple solution‐based low‐temperature synthesis is presented of ultrathin (3–5 nm) few layers (4–6 layers) nanosheets of Cl‐doped SnSe₂, which possess n‐type carrier concentration of 2×10¹⁸ cm^?3 with carrier mobility of about 30 cm² V^?1 s^?1 at room temperature. SnSe₂ has a band gap of about 1.6 eV and semiconducting electronic transport in the 300–630 K range. An ultralow thermal conductivity of about 0.67 Wm^?1 K^?1 was achieved at room temperature in a hot‐pressed dense pellet of Cl‐doped SnSe₂ nanosheets due to the anisotropic layered structure, which gives rise to effective phonon scattering.     

Temperature dependence of the thermophysical properties of Bi1.5Sb0.5Te3

The thermophysical properties (thermal diffusivitya, specific heatC _p and thermal conductivity λ), of Bi_1.5Sb_0.5Te₃ were measured in the temperature range 300–700 K. The results showed that the contribution of the charge carriers to the thermal conduction is negligibly small in comparison with the contribution of phonons at high temperatures. On the other hand, the heat conduction due to the simultaneous thermal diffusion of electrons and holes is important as well as the lattice thermal conduction. The explanation of the results was supported by using electrical conductivity measurements and X-ray diffraction.     

A new approach to lattice thermal conductivity: Application to Ge

The new expression τ _3ph ^?1 =g(ω) (B_N + B_UE^?Θ/αT)T^m is proposed for the three-phonon scattering relaxation rate, considering contributions due to three-phonon normal and umklapp processes, which give a new approach to the lattice thermal conductivity. With use of the above expression, the lattice thermal conductivity of Ge has been calculated in the entire temperature range 2–1000 K: good agreement is found between the experimental and calculated values of the phonon conductivity in the entire temperature range of investigation. Analytical expressions are also obtained to calculate an approximate value of the lattice thermal conductivity. The role of four-phonon processes is also included in the present study.     

Evaluation of the structural,optical and electrical properties of AZO thin films prepared by chemical bath deposition for optoelectronics

Aluminum doped zinc oxide (AZO) thin films for electrode applications were deposited on glass substrates using chemical bath deposition (CBD) method. The influence of deposition time on the structural, morphological, and opto-electrical properties of AZO films were investigated. Structural studies confirmed that all the deposited films were hexagonal wurtzite structure with polycrystalline nature and exhibited (002) preferential orientation. There is no other impurity phases were detected for different deposition time. Surface morphological images shows the spherically shaped grains are uniformly arranged on to the entire film surface. The EDS spectrum confirms the presence of Zn, O and Al elements in deposited AZO film. The observed optical transmittance is high (87%) in the visible region, and the calculated band gap value is 3.27 eV. In this study, the transmittance value is decreased with increasing deposition time. The room temperature PL spectrum exposed that AZO thin film deposited at (60 min) has good optical quality with less defect density. The minimum electrical resistivity and maximum carrier concentration values were observed as 8.53 × 10⁻³(Ω cm) and 3.53 × 10¹⁸ cm⁻³ for 60 min deposited film, respectively. The obtained figure of merit (ϕ) value 3.05 × 10⁻³(Ω/sq)^{- 1} is suggested for an optoelectronic device.     

Electrical,Optical, and Structural Properties of SnO2: F Films as a Function of Fluoride Precursor Concentration and Temperature

Atmospheric pressure chemical vapor deposition (APCVD) employing the precursor system of tin tetrachloride, ethyl formate, and 2,2,2‐trifluoroethyl trifluoroacetate vapors that were transported to hot glass substrates to deposit fluorine doped tin dioxide thin films. The system is optimized with respect to the substrate deposition temperature and to the amount of fluoride added to the precursor stream and the resultant structural, electrical and optical properties compared. Increasing the substrate temperature from 360 °C to 610 °C resulted in an approximately linear increase in thickness of the tin dioxide films. However, the resistivity decreased from 1.8 × 10^–2 Ω · cm at 360 °C to a minimum of 5.9 × 10^–4 Ω · cm at 560 °C and increased to 9.4 × 10^–4 Ω · cm at 610 °C. While maintaining a substrate temperature of 560 °C different amounts of fluorine precursor was introduced into the carrier stream, from 0 mL · h^–1 to 5 mL · h^–1, resulting in a decrease in resistivity (ρ) from 5.3 × 10^–2 Ω · cm at 0 mL · h^–1 to a minimum of 5.9 × 10^–4 Ω · cm at 2 mL · h^–1 and then increased to 1.0 × 10^–3 Ω · cm at 5 mL · h^–1. As the amount of fluoride is increased a concommittent increase in carrier concentration results until the point of overdoping the film produces an increase in scattering sites that increases resistivity. Best films were deposited at 560 °C and when the fluoride precursor flow rate was 2 mL · h^–1.     

Preparation and characterization of Al and Mn doped ZnO (ZnO: (Al,Mn)) transparent conducting oxide films

This paper presents the electro-optical, chemical and structural properties of doped-ZnO films deposited by DC-reactive magnetron sputtering at room temperature using the bi-dopant Al and Mn. A minimum resistivity of 3.46×10⁻⁴ Ω cm, exceeding 75.0% average transmittance (380–800 nm), and fundamental band gap of 3.48±0.01 eV have been obtained. XPS analyses show that Zn uniformly remains in the valence state of Zn²⁺; all of the Al and a little amount of Mn with valence state of Mn⁴⁺ are supposed to have donor effect, while dominant Mn²⁺ will induce to form more oxygen vacancies and this proposal has been verified by O 1s XPS results. It has been concluded that the presence of more oxygen vacancies will attenuate the effect of hybridization of p–d orbitals in the matrix of ZnO. It has been found that all the as-deposited films have c-axis preferred orientation with flat and smooth surface (RMS surface roughness is of the order of ∼3 nm over 5×5 μm² area).     

Synthesis and properties of magnetic fluids produced on the basis of magnetite particles

Magnetic fluids based on magnetite synthesized by the chemical condensation method at temperatures of 25, 40, 60, and 80°C were obtained and studied. Magnetite particles were examined by X-ray phase and X-ray fluorescence analyses and electron microscopy. The average size of the coherent scattering region of magnetite particles was 13–17 nm, depending on the synthesis temperature. Magnetic fluids were synthesized from magnetite particles obtained at 25 and 80°C, with water and octane serving as carrier fluids. The NMR method was used to determine the saturation magnetization and average magnetic moment of the particles: for water-based magnetic fluids, 2100 A m^–1 and 5.7 × 10^–19 A m² at magnetite particle synthesis temperature of 25°C and 3670 A m^–1 and 4.6 × 10^–19 A m² at magnetite particle synthesis temperature of 80°C; for octane-based magnetic fluids, 2250 A m^–1 and 4.1 × 10^–19 A m² at magnetite particle synthesis temperature of 25°C.     

Point defects in reduced strontium titanate

Strontium titanate single crystals have been carefully reduced at temperatures ranging from 1200 to 1400°C in oxygen partial pressures of 10^?7?10^?12 atm and quenched to room temperature where optical absorption coefficients, Hall coefficients, mass densities and lattice parameters were measured. (Optical absorption coefficients and Hall coefficients were also measured at 77 K). The predominant defects at room temperature were found to be doubly ionized oxygen vacancies and conduction band electrons. No evidence was found for singly ionized oxygen vacancies as has been suggested by some workers.Optical absorption in the visible and ultraviolet frequency region was found to be dependent upon the concentration of free carriers. For photon energies of 0.5 eV to about 1 eV, a free carrier absorption effect occurs which may be due to intraband transitions. Three peaks occur at photon energies of 1.66, 2.44, and 2.95 eV and may be due to phonon assisted interband transitions among the titanium d-like conduction bands.     

Thermal decomposition kinetics of bisthiourea cadmuim(II) tetrathiocyanato diammine chromate(III)

Cadmium thiourea reinickate undergoes two-stage thermal decomposition on heating. The DTG peak temperatures are 291 and 469°C and the corresponding DTA temperatures are 255 and 490°C. The kinetic parameters for the first stage decomposition are E* ≈ 120kJ mole^?1; Z ≈ 1.2 × 10⁸ cm³ mole^?1 sec^?1 and ΔS* ≈ ?95 J mole^?1 K^?1. For the second stage, E* ≈ 133 kJ mole^?1; Z ≈ 6.1 × 10⁵ cm^?1 mole^?1 sec^?1 and ΔS* ≈ ?142 J mole^?1 K^?1.     

Electrical transport properties of Zn doped ZnO

Electrical resistivity and Hall effect measurements at 77–373°K are presented for Zn doped ZnO crystals. The crystals have been doped systematically at 600–1100°C in controlled pressures of Zn. The concentration of electrons at room temperature is in the range n_RT = 2.5 × 10¹⁶, to 3.6 × 10¹⁸, cm^?3. The donor level E_D and the concentrations of donors N^D and acceptors N_A have been calculated from a best fit to the experimental relationships log n versus $\text{1}\text{T}$ and log μ_H versus log T. At dilute concentrations of donors, two donor levels have been observed, E_D^I = 0.043–0.045 eV and a deeper level E^II_D greater than 0.165 eV. The ZnO was found to behave as a metal at N_D ～ 6 × 10¹⁸, cm^?3.At least two different donors have to be assumed in order to explain the experimental results. It is suggested that interstitial Zn is the electrical active donor at higher doping levels. The nature of the other donor is not clear. Neither 1s¹ H-type nor 1s² He-type donors seem to explain all the observations consistently.     

Application of Thermal Lens Spectrometry to the Study of Chemical Adsorption in a Layer of a Nafion Solid Electrolyte

Thermal lens spectrometry was used to study Langmuir–Blodgett films of a weakly absorbing Nafion polyelectrolyte membrane on the surface of inert polyethylene terephthalate (PET) and glass substrates and to estimate the amount of Nafion (number of layers) using a change in the thermal characteristics of the sample. The sensitivity of thermal lens measurements at the wavelength of the exciting radiation 532.0 nm is comparable to that of solid-state spectrophotometry in the region of the maximum absorbance of Nafion (275 nm). However, the high locality of thermal lens spectrometry (the area of the signal generation zone is 100 μm²) ensures the estimation of the uniformity of the deposition of the polyelectrolyte layer. To increase the absorbance of the layer of the applied polyelectrolyte, the latter is saturated with a colored compound (ferroin). The adsorption of ferroin into the Nafion layer on the PET surface was confirmed; the absorbance of ferroin in the Nafion layer is in the range of 1 × 10–5^–5 × 10^–4 units of absorbance, which corresponds to the surface concentration of ferroin 1 × 10^–11–4 × 10^–10 mol/cm².     

Thermal crystallization kinetic and electrical properties of partly crystallized amorphous indium oxide thin films sputtering deposited in the presence or the absence of water vapor

Partly crystallized amorphous indium oxide thin films were deposited under water vapor atmosphere by magnetron sputtering. XRD analysis revealed that appropriate water vapor could suppress the film’s crystallinity. In situ thermal crystallization process was monitored by high-temperature XRD. The crystallization data were analyzed using the Kolmogorov–Johnson–Mehl–Avrami equation. The kinetic exponent n is determined to be approx. 1/2 and 3/2 for film deposited in the absence and the presence of water vapor, respectively. The activation energy of crystallization for film deposited under 1 × 10^?5 Torr water vapor pressure was determined to be 30.7 kJ mol^?1, which is higher than 18.9 kJ mol^?1 for film deposited in the absence of water vapor. The increased activation energy caused by the chemically bonded hydrogen and embedded O–H bonds from the water vapor resulted in the suppression of crystallization. Introduction of appropriate water vapor during the deposition decreased the resistivity because of the increase of Hall mobility. The resistivity of the films after annealing increased due to the evaporation of water vapor resulted in crystal defects.     

Pulsed photoconductivity and current oscillations in poly(vinyl chloride)

Transient photocurrents in poly(vinyl chloride) films are shown to be due to photo-injection of electrons from metallic cathodes. Most of the injected electrons are promptly trapped, but some drift across the sample to the anode under the influence of an external electric field. The mobility of these electrons, determined by transient photoconductivity techniques, is 4.7 ± 0.5 × 10^?4 cm²/V-sec at 27°C, and rises to 3.4 ± 0.5 × 10^?3 cm²/V-sec at 43°C, the measuring cell having been evacuated to a pressure of 10^?6 torr at both temperatures. Diffusion of helium into the samples appears to decrease the electron, mobility. It is suggested that electron transport is correctly described by using an energy-band model for intramolecular motion and an activated hopping model for intermolecular transfer. Oscillations observed in the transient photocurrents in the frequency range 10³–10⁵ Hz are attributed to electron avalanche formation at the anode, with photosuccessors.     

Sol–gel synthesized vanadium doped TiO2 photocatalyst: physicochemical properties and visible light photocatalytic studies

Vanadium doped titanium dioxide (V–TiO₂) photocatalyst was synthesized by the sol–gel method using ammonium vanadate as vanadium source. The prepared samples were characterized by XRD, N₂ adsorption–desorption method, UV–Vis DRS, Fourier transform infrared (FTIR), scanning electron microscope–energy dispersive X-ray and photoluminescence (PL) analysis. The results show that V⁵⁺ ions were successfully incorporated into the crystal lattice of TiO₂ as a consequence, not only an obvious decrease in the band gap and a red shift of the absorption threshold into the visible light region was recorded for the V modified TiO₂, but, also a decrease in photogenerated electrons and holes recombination rate was observed as demonstrated by PL analysis. FTIR study indicated that in undoped TiO₂ sample the acetate group favored a bidentate bridging mode of binding with titanium atoms, whereas a bidentate chelating mode of linkage was observed in V–TiO₂ powders. The crystallite size of the samples calcined at 300 and 500 °C were decreased beyond the molar ratio of 200:1 (V:Ti), this may be due to dopant presence in the grain boundaries hindering the crystal growth. The photocatalytic activities for both pure and vanadium doped TiO₂ powders were tested in the discoloration of a reactive dyestuff, methylene blue, under visible light. The 100:1 (V:Ti) doped photocatalyst, calcined at 300 °C showed enhanced photocatalytic activity under visible light with a rate constant (k_obs) of 5.024 × 10^?3 min^?1 which is nearly five times higher than that of pure TiO₂, as result of low band gap value, high specific surface area and a decrease in recombination rate.     

Thermal decomposition of metal complexes. X. uranyl nitrate—phenylurea complexes

The kinetics and mechanism of the thermal association process (solid—solid interaction) and the reverse dissociative process

(where n-2–5;=m1–4; n+ m= 3–6) is discussed. The “ activation energy” and the reaction order have been evaluated. It was found that the associative reaction is chemically controlled whereas the dissociative process is physical in nature; therefore no mutual agreement was found between theE^*_a values relative to the two associative and dissociative processes.     

Anomalies in the enthalpy of freezing in alpha-phase indium—lead,due to brillouin-zone effects

The enthalpy of freezing has been measured with DTA using electrical calibration for 33 compositions of indium—lead in the range 6.9–7.9 at.% lead, at which range the electron—lattice interaction causes anomalies in several physical and structural properties. Enthalpies of mixing, ΔH_m^s, have been calculated. The results reveal three maximum and minimum pairs corresponding to partial shift of the Fermi surface to higher Brillouin zones in three steps at 7.1, 7.2 and 7.3–7.4 at.% lead. These details in the overlapping have not been found earlier. The observed change in ΔH_m^s in the steps is about 1 meV atoms^?1.