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1.
ZnSe thin films have been prepared by inert gas condensation method at different gas pressures. The influence of deposition pressure, on structural, optical and electrical properties of polycrystalline ZnSe films have been investigated using X-ray diffraction (XRD), optical transmission and conductivity measurements. The X-ray diffraction study reveals the sphalerite cubic structure of the ZnSe films oriented along the (1 1 1) direction. The structural parameters such as particle size [6.65-22.24 nm], strain [4.01-46.6×10−3 lin−2 m−4] and dislocation density [4.762-18.57×1015 lin m−2] have been evaluated. Optical transmittance measurements indicate the existence of direct allowed optical transition with a corresponding energy gap in the range 2.60-3.00 eV. The dark conductivity (σd) and photoconductivity (σph) measurements, in the temperature range 253-358 K, indicate that the conduction in these materials is through an activated process having two activation energies. σd and σph values decrease with the decrease in the crystallite size. The values of carrier life time have been calculated and are found to decrease with the reduction in the particle size. The conduction mechanism in present samples has been explained, and the density of surface states [9.84-21.4×1013 cm−2] and impurity concentration [4.66-31.80×1019 cm−3] have also been calculated.  相似文献   

2.
Matthias Koch 《Surface science》2006,600(18):3586-3589
Nuclear magnetic resonance (NMR) is performed on monolayer (ML) amounts of adsorbed 129Xe on a single crystal substrate. The inherently low sensitivity of NMR is overcome by using highly nuclear spin polarized 129Xe that has been produced by optical pumping. A polarization of 0.8 is regularly achieved which is 105 times the thermal (Boltzmann) polarization. The experiments are performed with a constant flux of xenon atoms impinging on the surface, typically 4 ML/s. The chemical shift (σ) of 129Xe is highly sensitive to the Xe local environment. We measured profoundly different shifts for the Xe bulk, for the surface of the Xe bulk, and for Xe on CO/Ir(1 1 1). The growth of the bulk is seen in a phase transition like change of σ as a function of temperature at constant Xe flux. At temperatures where no bulk forms at a flux of 4 ML/s, the xenon exchange rate was measured by a spin inversion/recovery method. The exchange time of Xe is found to be 0.24 s at 63.4 K and 64.4 K and somewhat longer at 61.2 K. An analysis is given involving the desorption out of the second layer and fast mixing of first and second layer atoms at these temperatures.  相似文献   

3.
In order to develop mixed protonic and electronic conductors, we proposed a novel concept for material design that enables to control partial conductivities by fabricating solid solutions of protonic and electronic conductors. In this work, Sr-doped LaBO3 and Sr-doped CeBO3 were chosen as model compounds conducting protons and electron holes, respectively. Solid solutions of the above borates, Sr-doped La1 − xCexBO3, were prepared, and their electrical conductivities were investigated in 8.5 × 102-4.2 × 103 Pa of p(H2O) and 1.0 × 10-1.0 × 105 Pa of p(H2) at 1073 K. From the experimental results of the gas partial pressure dependences of the conductivities, major charge carrier species were identified as a function of x. It was found that proton was the major charge carrier when x < 0.2 while the contribution of the electron hole conduction became remarkable as x increased above 0.2. The contribution of the electron hole conduction can be interpreted by the percolation model.  相似文献   

4.
The two substates v4 = 20 (A1, 983.702 cm−1) and v4 = 2±2 (E, 986.622 cm−1) of the oblate symmetric top molecule, 14NF3, have been studied by high-resolution (2.5 × 10−3 cm−1) infrared spectroscopy of the overtones and 2ν4 − ν4 hot bands. Transitions of the overtone, the hot band, and the previously measured fundamental band were combined to yield 585 ground state combination differences differing in K by ±3, with Kmax = 36. Using the “loop-method,” a fit (standard deviation σ = 0.320 × 10−3 cm−1) provided a complete set of the hitherto not experimentally known axial ground state constants. In units of cm−1 these have the following values: . Upper state parameters were determined using a vibrationally isolated model. Considering l (2, 2) and l (2, −1) interactions between the v4 = 20 and v4 = 2±2 substates and effects accounting for the l (4, −2) interactions within the kl = −2 levels, 25 upper state parameters were obtained by fitting 2747 IR data (1842 transitions, 905 deduced energies, Jmax = 42, Kmax = 39) with σIR = 0.353 × 10−3 cm−1. Moreover, millimeter-wave spectroscopy furnished 86 transitions (Jmax = 16, Kmax = 13) measured on the v4 = 2 excited state. A merged fit, refining 24 parameters using the described model gave σIR = 0.365 × 10−3 cm−1 andσMMW = 0.855 × 10−6 cm−1 (26 kHz). The anharmonicity constants (in cm−1) are x44 = −0.84174 (2) and g44 =  + 0.73014 (1). In addition to this model, the D, Q, and L reductions of the rovibrational Hamiltonian were tested. Standard deviations σIR = 0.375 × 10−3 cm−1 and σMMW = 0.865 × 10−6 cm−1 were obtained for both D and L reductions, and σIR = 0.392 × 10−3 cm−1 and σMMW = 0.935 × 10−6 cm−1 for Q reduction. The unitary equivalence of the majority of the 18 tested relations between the derived parameters was satisfactorily fulfilled. This confirms that the v4 = 2 excited vibrational state can be considered in reasonable approximation to be isolated.  相似文献   

5.
In a three-components fluorophosphate glass system, the introduction of H3BO3 brings some valuable influence to the spectroscopic and thermal properties of the glasses. With H3BO3 increases from 2 to 20 mol%, Ω6, Sed4I13/2, FWHM, Tg and fluorescence lifetime change from 3.21×10−20 cm2, 1.77×10−20 cm2, 45 nm, 480 °C and 8.8 ms to 4.66×10−20 cm2, 2.11×10−20 cm2, 50 nm, 541 °C and 7.4 ms, respectively. σabs, σemi, FWHM×τf×σemi has a maximum when H3BO3 is 11 mol%. Tg and TxTg increases with H3BO3 introduction. Results showed that in fluorophosphate glasses, proper amount of B2O3 can be used as a modifier to suppress upconversion and improve spectroscopic properties, broadband property and crystallization stability of the glasses while keeps the fluorescence lifetime relatively high.  相似文献   

6.
A novel method of luminescence enhancement effect for the determination of balofloxacin (BLFX) was proposed. A new system of the BLFX-Eu3+-SDBS (sodium dodecylbenzene sulfonate) was investigated. It was found that SDBS significantly enhanced the luminescence intensity of the BLFX-Eu3+ complex (about 20-fold). Under the optimized experimental conditions, the system exhibits an excellent linear relationship between the enhanced luminescence intensity and the concentration of BLFX over the range of 1.0×10−8-8.0×10−7 mol L−1 with a correlation coefficient (R) of 0.9994, and the detection limit (3σ) of the method was determined as 2.0×10−9 mol L−1. This method has been successfully applied for the determination of BLFX in pharmaceuticals and human urine/serum samples. Compared with most of the other methods reported, the rapid and simple procedure proposed in the text offers higher sensitivity, wider linear range, and better stability.  相似文献   

7.
The [TMA]2Zn0.5Cu0.5Cl4 hybrid material was prepared and its dielectric spectra were measured in the 10−1 Hz-106 Hz frequency range and 200-305 K temperature interval. The dielectric permittivity showed a ferroelectric-paraelectric phase transition at 293 K. Double relaxation peaks are observed in the imaginary part of the electrical modulus, suggesting the presence of grain and grain boundary in the sample. The frequency dependent conductivity was interpreted in term of Jonscher's law: σ(ω)=σdc+n. The temperature dependent of the dc conductivity (σdc) was well described by the Arrhenius equation: σdcT=σo×exp(−Ea/kT).  相似文献   

8.
Thermoelectric properties of single crystalline CexSr1−xTiO3 films (0 ≤ x ≤ 0.5) have been studied by using combinatorial pulsed-laser deposition. Temperature gradient method was used for identifying an optimum growth temperature for SrTiO3 homoepitaxial growth, at which both oxygen stoichiometry and persisting layer-by-layer growth mode could be accomplished. Electrical conductivity (σ) and Seebeck coefficient (S) were measured at room temperature for the composition-spread films grown at the optimized temperature and found to be considerably higher than those reported for bulk poly-crystalline compounds. Hall measurement revealed that carrier density linearly increased with increasing x, suggesting that a trivalent Ce ions substituted divalent Sr ions to supply electrons. A maximum power factor (S2σ) was obtained for the x = 0.2 film, being 7 and 14 μW/K2 cm at 300 and 900 K, respectively.  相似文献   

9.
Optical flow (OF) method has been used in ultrasound elastography to estimate the strain distribution in tissues. However the bias of strain estimation by OF has previously been shown to be close to 20%. The objective in this paper is to improve the performance of OF-based strain estimation, a two-step OF method with a local warping technique is proposed in this paper. The local warping technique effectively decreases the decorrelation of the signals, and hence improves the performance of strain estimation. Simulations on both homogeneous and heterogeneous models with different strains are performed. Experiments on a heterogeneous tissue-mimicking phantom are also carried out. Simulation results of the homogeneous model show that the two-step OF method reduces the bias of strain estimation from 23.77% to 1.65%, and reduces the standard deviation of strain estimation from 2.9 × 103 to 0.47 × 103. Simulation results of the heterogeneous model shows that the signals-to-noise ratio (SNRe) of strain estimation is improved by 2.1 and 5.3 dB in the inclusion and background, respectively, and the contrast-to-noise ratio (CNRe) is improved by 6.8 dB. Finally, results of phantom experiments show that, by using the proposed method, the SNRe is increased by 4.0 dB and 8.9 dB in the inclusion and background, respectively, while the CNRe is increased by 13.1 dB. The proposed two-step OF method is thus demonstrated capable of improving the performance of strain estimation in OF-based elastography.  相似文献   

10.
Materials and ion transport property characterization in Solid Polymer Electrolyte (SPE) membranes: (1 − x) PEO: x KIO3, where x = 0, 10, 20, 30, 40, 50 wt.%, have been studied. SPE films have been prepared following two casting techniques: a novel hot-press (extrusion) and the traditional solution cast. Hot-press technique is a completely dry/solvent free/rapid/inexpensive procedure as compared to solution cast method and has recently been receiving wider acceptability to cast membranes of ion conducting polymeric electrolytes.‘Log σ − x’ study revealed σ-maxima at salt concentration x = 30 wt.% for SPE film prepared by both the methods. However, hot-pressed SPE film: 70 PEO: 30 KIO3 exhibited relatively higher room temperature conductivity (σ ∼ 4.40 × 10− 7 S cm− 1) than that of the solution casted film. This has been referred to as Optimum Conducting Composition (OCC) SPE film. Materials characterization in OCC SPE film has been done by XRD, FTIR and DSC techniques. These studies confirmed the complexation of salt in the polymeric host. Some basic ionic parameters viz. conductivity (σ), ionic mobility (μ), mobile ion concentration (n), ionic transference number (tion) have been determined using different experimental procedures to understand the ion transport behaviour in OCC SPE material. The temperature dependent conductivity measurement has also been carried out and the activation energy (Ea) has been computed from the linear least square fitting of ‘log σ − 1 / T’ Arrhenius plot.  相似文献   

11.
The ionic conductivity, σ, of mixtures of poly(ethylene oxide) (PEO) and lithium bis(trifluoromethanesulfone)imide (LiTFSI) was measured as a function of molecular weight of the PEO chains, M, over the range 0.2-5000 kg/mol. Our data are consistent with an expression σ = σ0 + K/M proposed by Shi and Vincent [Solid State Ionics 60 (1993)] where σ0 and K are exponential and linear functions of inverse temperature respectively. Explicit expressions for σ0 and K are provided.  相似文献   

12.
This study evaluates the robustness of a magnetic resonance (MR) fat quantification method to changes in R2* caused by an intravenous infusion of superparamagnetic iron oxide (SPIO) contrast agent. The R2* and proton density fat fraction (PDFF) were measured in liver and spine in 14 subjects using an investigational sequence (IDEAL IQ) provided by the MR scanner vendor. Measurements were made before and after SPIO infusion. Results showed SPIO significantly increased R2* in both liver (p = 8.8 × 10− 8) and spine (p =1.3 × 10− 2) but PDFFs were not significantly different in either the liver (p = 5.5 × 10− 1) or the spine (p = 5.6 × 10− 1). These results confirm that the IDEAL IQ method of fat quantification is robust to changes in R2*.  相似文献   

13.
The 96GeO-(3-χ)Al2O3-χNa2O-1NaBiO3 (χ = 0, 0.5, 1.5 molar percent designated as A1, A2 and A3) and 96GeO-(3.5-ψ)Al2O3-ψNa2O-0.5Bi2O3 (ψ = 0.5, 1, 2 molar percent designated as B1, B2 and B3) glasses were prepared by conventional melting method with the measurement of their DTA curve, fluorescence decay curve, transmission, absorption and emission spectra. The near infrared superbroadband emission characteristics of the A1, A2, B1 and B2 glasses peak at ∼1220 nm were observed when pumped by an 800 nm laser diode. The stimulated emission cross section (σp) was obtained from the emission spectra. The result indicated that the introduction of Bi5+ in NaBiO3 into raw materials could increase the emission intensity of the obtained glasses by 5.6 times than that of Bi3+ in Bi2O3, and the FWHM (Δλ) and emission lifetime (τ) at 1220 nm increased from 195 nm to 275 nm, and 280 μs to 434 μs. Meanwhile, it was found that the absorption edges were blue-shifted from 486 to 447 nm by comparing those of A1 and B1. The absorption edges were considered to be ascribed to the charge transfer from Bi3+ 6s2 to Bi5+ 6s0. Therefore we could conclude that the content of Bi5+ ions in A1 was more than that in B1 glasses. It could be deduced from the emission and absorption spectra that the stronger emission intensity and wider FWHM were due to the higher concentration of Bi5+ ion in glass. In particular, the increase of Na2O content was in proportion to the thermal stability and the value of σp × τ and σp × Δλ of glasses.  相似文献   

14.
Photoluminescence of Eu(TTA)3DPBT (TTA=thenoyltrifluoro-acetonate DPBT=2-(N,N-diethylanilin-4-yl)-4,6-bis(3,5-dimethylpyrazol-1-yl)-1,3,5-triazine) in toluene and PMMA thin film are measured with excitation at 350 and 404 nm, respectively, and analyzed using Judd-Ofelt theory. Under excitation at 350 nm, it is found that Eu(TTA)3DPBT in toluene has a larger Ω2 value (14.33×10−20 cm2) than that (12.70×10−20 cm2) of Eu(TTA)3Phen (Phen=1,10-phenanthroline) in the same solvent, and has a smaller Ω2 value (12.70×10−20 cm2) in PMMA than that (Ω2=14.09×10−20 cm2) of Eu(TTA)3Phen in PMMA. At the same time, it can be seen that under excitation at 350 nm Ω2 value of Eu(TTA)3DPBT in toluene is larger than that in PMMA. Excited by 404 nm, Ω2 of Eu(TTA)3DPBT obtained in toluene and in PMMA are the same as that excited at 350 nm. The transition probability (A), emission cross-section (σ) and the fluorescence branching ratio (β) are also evaluated. The lifetime of 5D0 metastable state is measured on 350 and 404 nm excitation, respectively. For the former situation, it is 455 μs in toluene and 640 μs in PMMA, for the latter it is 460 μs in toluene and 664 μs in PMMA. By comparing absorptions with excitations, it can be found that DPBT is more efficient than TTA as an energy donor. Phosphorescence spectra are also measured to estimate the lowest triplet level and analyze the energy transfer for DPBT and TTA, from which it is found that the energy transfer from TTA to DPBT occurs in the luminescent process.  相似文献   

15.
DC reactive sputtering was used to successfully make thin films of titanium oxynitride using titanium metallic target, argon as plasma gas and nitrogen and oxygen as reactive gases. The nitrogen partial pressure was kept constant during every deposition whereas oxygen flow rate was pulsed using a square pattern. The study consisted in analysing the influence of the shape of the pulsed rate on physical properties of these films. In order to adjust the metalloid concentration to get films with a wide range of oxygen-to-nitrogen ratios, the reactive gas pulsing process (RGPP) was used. In this process, the oxygen flow switches “on” and “off” periodically according to a duty cycle α = tON/T. Electrical conductivity of films measured against temperature was gradually modified from metallic (σ300K = 4.42 × 104 S m−1) to semi-conducting behaviour (σ300K = 7.14 S m−1) with an increasing duty cycle. Mechanical properties like nanohardness (Hn) and reduced Young's modulus (Er) of the films were investigated. Experimental values of Hn and Er obtained by nanoindentation at 10% depth ranged from 15.8 to 5.2 GPa and from 273 to 142 GPa, respectively. Evolutions of Hn and E against duty cycle were similar. A regular decrease was observed for duty cycle α ≤ 25% corresponding to the occurrence of TiOxNy phase. Higher duty cycles led to the smallest values of Hn and E and correlated with TiO2 compound composition. At last, the colour variation of these titanium oxynitrides was investigated as a function of α in the L*a*b* colour space. It was related to the chemical composition of the films.  相似文献   

16.
This paper reports the growth and spectroscopic characterization of Er3+:Sr3Y(BO3)3 crystal. Er3+:Sr3Y(BO3)3 crystal with dimensions up to ∅20×35 mm3 has been grown by Czochralski method. The polarized spectroscopic properties of Er3+:Sr3Y(BO3)3 crystal were investigated. Based on the Judd-Ofelt theory, the effective intensity parameters Ωt were obtained: Ω2=1.71×10−20 cm2, Ω4=1.39×10−20 cm2, Ω6=0.74×10−20 cm2 for π-polarization, and Ω2=1.77×10−20 cm2, Ω4=1.44×10−20 cm2, Ω6=0.65×10−20 cm2 for σ-polarization. The emission cross-section σem was calculated to be 4.75×10−21 cm2 for π-polarization at 1536 nm and 6.30×10−21 cm2 for σ-polarization at 1537 nm. The investigated results showed that Er3+:Sr3Y(BO3)3 crystal may be regarded as a potential laser host material for 1.55 μm IR solid-state lasers.  相似文献   

17.
Oxygen nonstoichiometry (δ), total conductivity (σ) and thermoelectric power (S) of the LaFe0.7Ni0.3O3 − δ sample have been studied as functions of temperature and oxygen partial pressure. Based on the results of the direct reduction of the sample in hydrogen flow at 1100 °C the absolute oxygen content (3 − δ) has been found to vary from 2.999 to 2.974 in the range of 1273-1373 K and 10− 3-0.21 atm. The point defect equilibrium models have been proposed and fitted to the set of experimental data in the form of log p(O2) = f(δ)T dependences. The values of standard thermodynamic quantities of defect formation reactions have been assessed. The joint analysis of oxygen nonstoichiometry, total conductivity and thermoelectric power has been performed using a small-polaron approach. The values of partial conductivity, partial thermopower and mobilities of electronic charge carriers have been calculated. The p-type semiconducting behavior of LaFe0.7Ni0.3O3 − δ has been explained by the higher mobility values of electron holes than those of electrons in the whole range of thermodynamic parameters studied.  相似文献   

18.
We perform two-photon coincidence subwavelength interference experiments from double slit using independent photons obtained from a pseudo-thermal light source produced by (i) slowly rotating ground glass (RGG) with turbid solution of a different density and (ii) RGG. The turbid solution is water solution containing 3 μm diameter polystyrene microspheres. It is found that the visibility of the obtained interference pattern decreases in first experiment with increasing the density of the turbid solution from N = 1010 spheres m−3 to N = 1014 spheres m−3. However, the results are reported here for the density of N = 1014 spheres m−3. The visibility obtained with RGG with turbid solution having N = 1014 spheres m−3is 23% which increases to 27% with RGG but the resolution decreases. The effect of coherence width of source in two-photon interference pattern is also studied with pseudo-thermal light obtained by RGG. It was observed that on increasing the coherence width the visibility of interference fringes increased and quality of the fringe reduced and when the coherence width was more then slit separation, in coincidence measurements, no interference pattern appeared. The results are used to explore the classical subwavelength interference nature with thermal light.  相似文献   

19.
High resolution infrared spectra of 121SbHD2 and 123SbHD2 have been studied in the region of ν1, the Sb-H stretching fundamental, from 1780 to 1990 cm−1. The 2ν1 stretching overtone band of 123SbHD2, located in the 3640-3790 cm−1 range, has also been investigated. The SbHD2 molecule is an asymmetric rotor of Cs symmetry with the asymmetry parameter κ = 0.61. The ν1 band is of hybrid type, formed by strong C-type and weak B-type transitions, and almost unperturbed. For 123SbHD2, 2092 transitions have been assigned: 70% of these belong to the C component, the other 30% are of B-type. The assigned transitions have been fitted using a Watson type S-reduced Hamiltonian in the IIIl representation, with a standard deviation of the fit σ = 0.45 × 10−3 cm−1. In order to determine the ground state parameters all possible ground state combination differences (GSCD) have been generated from the ν1 transitions. In total, 3942 GSCD up to J = 27,  = 25, and  = 20 have been fitted with σ = 0.52 × 10−3 cm−1. Only C-type transitions have been observed in the weak 2ν1 overtone band. The 556 assigned transitions have been fitted with σ = 2.6 × 10−3 cm−1 using the same Hamiltonian as for ν1. In the ν1 band of 121SbHD2 771 C-type transitions have been assigned, and the v1=1 spectroscopic constants obtained from a fit with σ = 0.70 × 10−3 cm−1. Using 618 GSCD the ground state spectroscopic constants of 121SbHD2 have been derived with σ = 1.0 × 10−3 cm−1. The molecular parameters for the ground and the v1=1 states of the two isotopologues agree well. The quartic theoretical ab initio force field of SbH3 has been used to predict all relevant spectroscopic parameters for 123SbHD2, 121SbHD2, 123SbH2D, and 121SbH2D. Relations between the harmonic frequencies and between the anharmonicity constants obtained in the expanded local mode theory, for the XH3 → XH2D/XHD2 isotopic substitution, have been compared with those obtained in the present study.  相似文献   

20.
The triangular-shaped Au/ZnO nanoparticle arrays were fabricated on fused quartz substrate using nanosphere lithography. The structural characterization of the Au/ZnO nanoparticle arrays was investigated by atomic force microscopy. The absorption peak due to the surface plasmon resonance of Au particles at the wavelength of about 570 nm was observed. The nonlinear optical properties of the nanoparticle arrays were measured using the z-scan method at a wavelength of 532 nm with pulse duration of 10 ns. The real and imaginary part of third-order nonlinear optical susceptibility, Re χ(3) and Im χ(3), were determined to be 1.15 × 10−6 and −5.36 × 10−7 esu, respectively. The results show that the Au/ZnO nanoparticle arrays have great potential for future optical devices.  相似文献   

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