Frequency and voltage dependence of dielectric properties and electric modulus in Au/PVC + TCNQ/p-Si structure at room temperature

Au/PVC + TCNQ/p-Si structure was fabricated and real and imaginary parts of the dielectric constant (ɛ′, ɛ″), loss tangent (tanδ), and the real and imaginary parts of the electric modulus (M′, M″) and ac conductivity (σ_ac) of this structure have been investigated in wide frequency a range of 1 kHz–5 MHz at room temperature. All of these parameters were found strong function of frequency and voltage especially in the inversion and depletion regions at low frequencies due to interfacial polarization and charges at interface states (N_ss). The decrease in ɛ′ and ɛ″ with increasing frequency indicated that the interfacial dipoles have less time to orient themselves in the direction of the alternate field. While the value of M′ increase with increasing frequency and reach a maximum, M″ shows a peak and the peak position shifts to higher frequency with increasing applied voltage. The ln(σ_ac) vs ln(ω) plot of the structure for 0.5 V has three linear regions (I, II and III) with different slopes which correspond to low, intermediate and high frequency ranges, respectively. Such behavior of ln(σ_ac) vs ln(ω) plot indicated that there are three different conduction mechanisms in the Au/PVC + TCNQ/p-Si structure at room temperature.     

Comparison of physicochemical properties of bio and commercial hydroxyapatite

This article reports a physicochemical comparison of synthetic and biological Hydroxyapatite (HAp). Eight samples were separated into two groups: bio and commercial hydroxyapatite (bio-HAp and commercial-HAp). The bio-HAp group containing defat, alkaline, and calcined samples taken from bovine bone were obtained by using three different treatments, in order to establish their effect on the final product quality. The commercial-HAp group, from different sources: NIST, sigma, apafill G, coralina, and biograft, were analyzed and compared with the bio-HAp results. Thermogravimetric analysis (TG) was used in order to establish thermal degradation of the samples; structural behavior was then analyzed by X-Ray Diffraction (XRD) to found the crystalline phases, as well as the crystalline quality. Fourier Transform Infrared Spectroscopy (FTIR) was performed in order to identify the corresponding HAp functional groups within the samples. The surface morphology was analyzed by Scanning Electron Microscopy (SEM) and the elemental composition was established by using Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). It was found that the calcination process obtains HAp with comparable quality to the commercial samples. A crystallinity greater than 62% after the alkaline process was found. Additionally, the surface of the alkaline sample presents a transition behavior between dense and porous morphology.     

Kramers–Kronig transform for the surface energy loss function

A new pair of Kramers–Kronig (KK) dispersion relationships for the transformation of surface energy loss function Im[−1/(ɛ + 1)] has been proposed. The validity of the new surface KK transform is confirmed, using both a Lorentz oscillator model and the surface energy loss functions determined from the experimental complex dielectric function of SrTiO₃ and tungsten metal. The interband transition strength spectra (J_cv) have been derived either directly from the original complex dielectric function or from the derived dielectric function obtained from the KK transform of the surface energy loss function. The original J_cv trace and post-J_cv trace overlapped together for the three modes, indicating that the new surface Kramers–Kronig dispersion relationship is valid for the surface energy loss function.     

Synthesis,crystal growth and characterization of a semiorganic material: Calcium dibromide bis(glycine) tetrahydrate

Single crystals of semiorganic material calcium dibromide bis(glycine) tetrahydrate were grown from aqueous solution. The crystal belongs to monoclinic system, with a = 13.261(5) Å, b = 6.792(2) Å, c = 15.671(9) Å and β = 91.68(4)°. The presence of the elements in the title compound was confirmed by energy dispersive X-ray analysis. The solubility and metastable zone width were found. The grown crystals were tested by powder XRD, FTIR, Thermo Gravimetric and Differential Thermal Analysis, UV–vis–NIR analysis, dielectrical and mechanical studies. The transmittance of calcium dibromide bis(glycine) tetrahydrate crystal has been used to calculate the refractive index n, the extinction coefficient K and both the real ɛ_r and imaginary ɛ_i components of the dielectric constant as functions of wavelength. The optical band gap of calcium dibromide bis(glycine) tetrahydrate is 3.23 eV.     

Structure of porous vycor glass and its adsorption characteristics of water —An application of positron annihilation method

Positron lifetimes in porous Vycor glass have been measured. There are four lifetime components, and the fourth component has been assigned too-Ps annihilation in large pores of radius 34 Å. The intensityI ₄ has been correlated to a specific surface area, but the value obtained fromI ₄ by the Monte Carlo method is smaller than that obtained by the BET method. From variations in (τ₄,I ₄) against the kinetics of adsorption of water vapor, a rough picture of water adsorption is presented.     

Multi-component T1 relaxation and magnetisation transfer in peripheral nerve

We report here a study of longitudinal relaxation (T₁) and magnetisation transfer (MT) in peripheral nerve. Amphibian sciatic nerve was maintained in vitro and studied at a magnetic field strength of 3 T. A CPMG pulse sequence was modified to include either a saturation pulse to measure T₁ relaxation or an off-resonance RF irradiation pulse to measure MT. The resulting transverse relaxation (T₂) spectra yielded four components corresponding to three nerve compartments, taken to result from myelinic, axonal, and inter-axonal water, and a fourth corresponding to the buffer solution water in which the nerve sample was bathed. Each nerve component was analysed for T₁ relaxation and MT. All three nerve T₂ components exhibited unique T₁ relaxation and MT characteristics, providing further support for the assignment of the components to unique physical compartments of water. Numerical investigation of T_1sat measurements of each of the three nerve T₂ components indicates that while the two shorter-lived exhibit similar steady-state magnetisation transfer ratios (MTRs), their respective MT properties are quite different. Simulations demonstrate that mobile water exchange between these two components is not necessary to explain their similar steady-state MTR. In the context of the assignment of these two components to signal from myelinic and axonal water, this is to say that these two microanatomical regions of nerve may exhibit similar steady-state MTR characteristics despite possessing widely different MT exchange rates. Therefore, interpreting changes in MTR solely to reflect a change in degree of myelination could lead to erroneous conclusions.     

Triple point of the first monolayer of nitric oxide adsorbed on the cleavage face of magnesium bromide

This paper is the first of three articles devoted to the CO/Mo(110) chemisorption. The experimental study of adsorption and desorption kinetics was performed by several methods: thermal desorption, low energy electron diffraction and Auger electron spectroscopy. The adsorption of CO on Mo(110) presents two different states. For these two states the desorption kinetics are first order ones, the desorption energies and frequency factors have been determined (E₁ = 99 kcal mole^?1, E₂ = 50 kcal mole^?1, v₁ = 10¹⁹ s^?1, v₂, = 5 × 10¹⁰ s^?1). The dependence of sticking coefficient on surface coverage θ was investigated and was found different for the two states of adsorption. LEED shows that the adsorption is not ordered. AES investigation suggests that in the two states C and O have different positions with respect to MO atoms.     

Composition depth profiles of Bi3.15Nd0.85Ti3O12 thin films studied by X-ray photoelectron spectroscopy

In the present work, X-ray photoelectron spectroscopy (XPS) was used to investigate the composition depth profiles of Bi_3.15Nd_0.85Ti₃O₁₂ (BNT) ferroelectric thin film, which was prepared on Pt(1 1 1)/Ti/SiO₂/Si(1 0 0) substrates by chemical solution deposition (CSD). It is shown that there are three distinct regions formed in BNT film, which are surface layer, bulk film and interface layer. The surface of film is found to consist of one outermost Bi-rich region. High resolution spectra of the O 1s peak in the surface can be decomposed into two components of metallic oxide oxygen and surface adsorbed oxygen. The distribution of component elements is nearly uniform within the bulk film. In the bulk film, high resolution XPS spectra of O 1s, Bi 4f, Nd 3d, Ti 2p are in agreement with the element chemical states of the BNT system. The interfacial layer is formed through the interdiffusion between the BNT film and Pt electrode. In addition, the Ar⁺-ion sputtering changes lots of Bi³⁺ ions into Bi⁰ due to weak Bi-O bond and high etching energy.     

A theoretical study of photoelectron spectra of NbO2, MoO2 and RuO2 by cluster models

DV-Xα calculations have been applied to various small clusters of rutile-family dioxides (NbO₂, MoO₂ RuO₂). It appears that by taking into consideration the potential due to the atomic charges, the density, the ionization cross sections of the energy levels, and by summing the density of states (DOS) of the two different clusters representing surface structures, computations on even small clusters provide information which compares well with the experimental XPS spectra.     

Excitation of ultrasonic Lamb waves using a phased array system with two array probes: Phantom and in vitro bone studies

Long bones are good waveguides to support the propagation of ultrasonic guided waves. The low-order guided waves have been consistently observed in quantitative ultrasound bone studies. Selective excitation of these low-order guided modes requires oblique incidence of the ultrasound beam using a transducer-wedge system. It is generally assumed that an angle of incidence, θ_i, generates a specific phase velocity of interest, c_o, via Snell’s law, θ_i = sin⁻¹(v_w/c_o) where v_w is the velocity of the coupling medium. In this study, we investigated the excitation of guided waves within a 6.3-mm thick brass plate and a 6.5-mm thick bovine bone plate using an ultrasound phased array system with two 0.75-mm-pitch array probes. Arranging five elements as a group, the first group of a 16-element probe was used as a transmitter and a 64-element probe was a receiver array. The beam was steered for six angles (0°, 20°, 30°, 40°, 50°, and 60°) with a 1.6-MHz source signal. An adjoint Radon transform algorithm mapped the time-offset matrix into the frequency-phase velocity dispersion panels. The imaged Lamb plate modes were identified by the theoretical dispersion curves. The results show that the 0° excitation generated many modes with no modal discrimination and the oblique beam excited a spectrum of phase velocities spread asymmetrically about c_o. The width of the excitation region decreased as the steering angle increased, rendering modal selectivity at large angles. The phenomena were well predicted by the excitation function of the source influence theory. The low-order modes were better imaged at steering angle ?30° for both plates. The study has also demonstrated the feasibility of using the two-probe phased array system for future in vivo study.     

Effect of surface lay in the surface roughness evaluation using machine vision

This work explores the influence of orientation of surface lay pattern of the machined components, while quantifying the surface roughness using machine vision approach. The surface images are captured from milled low carbon steel specimens with different roughness values using a vision system with coaxial lighting arrangement at different angular orientations of the work pieces (0°, 30°, 45°, 60°, 90°, 120°, 135°, 150°, and 180°). The captured images are subjected to preprocessing in order to retain the frequency components that attribute to roughness using a Gaussian filter by adapting the filtering procedures specified in ISO 4288. Numerous image based parameters such as gray level average (G_a), gray level co-occurrence matrix based image quantification parameters namely contrast, correlation, energy or uniformity, maximum probability and differential box courting based fractal dimension are computed from the surface images captured at different angular positions of the work piece. The computed vision based parameters are compared and correlated with the roughness average (R_a) obtained using a stylus instrument and the results are analyzed. The results clearly indicated that it is important to consider the orientation of the work piece when the machine vision approach is used to quantify the surface texture parameters.     

Main channels of the decay of the giant dipole resonance in the 20,22Ne nuclei and isospin splitting of the giant dipole resonance in the 22Ne nucleus

Data published in the literature on various photonuclear reactions for the ^20,22Ne isotopes and for their natural mixture are analyzed with the aim of exploring special features of the decay of giant-dipole-resonance states in these two isotopes. With the aid of data on the abundances of the isotopes and on the energy reaction thresholds, the cross sections for the reactions ^20,22Ne[(γ, n)+(γ, np)] and ^20,22Ne[(γ, p)+(γ, np)] are broken down into the contributions from the one-nucleon reactions (γ, n) and (γ, p) and the contributions from the reactions (γ, np). The cross sections for the reactions ^20,22Ne(γ, n)^19,21Ne and ^20,22Ne(γ, p)^19,21F in the energy range E _γ=16.0–28.0 MeV and the cross sections for the reactions ^20,22Ne(γ, np)^18,20F in the energy range E _γ=23.3–28.0 MeV are estimated. The behavior of the cross-section ratio r=σ(γ, p)/σ(γ, n) for the ²²Ne nucleus as a function of energy is analyzed, and the isospin components of the giant dipole resonance in the ²²Ne nucleus are identified. The contributions of the isospin components of the giant dipole resonance in the ²²Ne nucleus to the cross sections for various photonuclear reactions are determined on the basis of an analysis of the diagram of the excitation and decay of pure isospin states in the ²²Ne nucleus and in nuclei neighboring it, which are members of the corresponding isospin multiplets. The isospin splitting of the giant dipole resonance and the ratio of the intensities of the isospin components are determined to be ΔE=4.57±0.69 MeV and R=0.24±0.04, respectively.     

Deviation from Matthiessen's rule of dilute al-alloys, 3 group model

The deviation from Matthiessen's rule has been investigated. The calculations were based upon three group model, in which the Fermi surface is split up into three regions. The mean free paths over the three major regions are denoted byL ₁,L ₂ andL ₃. Besides the Fermi surface anisotropy, the anisotropy of electron scattering with phonons and impurities have also been employed in the calculations. Simple formulae for the residual resistivity, the resistivity associated with phonon scattering and the deviation from Matthiessen's rule Δ(C, T), in terms of the anisotropic parameters, were derived. The formulae were used to throw light on the deviation from Matthiessen's rule.     

Model nuclear matter calculations in several Brueckner and Green's function theories

Model nuclear matter calculations are performed using two versions of the Brueckner theory (standard lowest order theory and a version with self-consistent “physical” onshell insertions in particle lines) and three Green's function theories (Λ ₀₀,Λ ₁₀ and Galitskii's ladder approximation). Ground state properties are derived using a strongs-wave nonlocal separable nucleon-nucleon potential. We investigate the differences between the results obtained using different theories, stemming from different treatment of the exclusion principle and of dispersive effects of the medium. The effect of the off-shell self-consistency in theΛ ₁₀ theory is found to be important.     

Life-time resolved emission spectra in CdI2 crystals

The emission spectrum of CdI₂ is composed of ultraviolet (UV), green (G) and yellow (Y and Y′) bands peaking at 3.38, 2.50, 2.16 and 2.25 eV, respectively. In order to determine the initial states of the Y- and G-luminescence, decay curves have been measured at 6 and 80 K by varying emission energy. The observed decay curves are composed of two or three exponential components. These decay components were named τ₁, τ₂, τ₃, τ_3′ and τ₄. The emission spectrum for each decay component, i.e., the life-time resolved emission spectrum, was constructed from the observed decay curves. At 6 K, three bands at 2.12, 2.49 and 2.64 eV are obtained for τ₁, τ₂ and τ₃ components, respectively. At 80 K, a dominant band for the τ₄ component and a weak band for the τ_3′ component appear on the same energy position at 2.25 eV. The origin of each emission band in the life-time resolved emission spectra will be briefly discussed.     

The impact of ultra thin silicon nitride buffer layer on GaN growth on Si (1 1 1) by RF-MBE

Ultra thin films of pure silicon nitride were grown on a Si (1 1 1) surface by exposing the surface to radio-frequency (RF) nitrogen plasma with a high content of nitrogen atoms. The effect of annealing of silicon nitride surface was investigated with core-level photoelectron spectroscopy. The Si 2p photoelectron spectra reveals a characteristic series of components for the Si species, not only in stoichiometric Si₃N₄ (Si⁴⁺) but also in the intermediate nitridation states with one (Si¹⁺) or three (Si³⁺) nitrogen nearest neighbors. The Si 2p core-level shifts for the Si¹⁺, Si³⁺, and Si⁴⁺ components are determined to be 0.64, 2.20, and 3.05 eV, respectively. In annealed sample it has been observed that the Si⁴⁺ component in the Si 2p spectra is significantly improved, which clearly indicates the crystalline nature of silicon nitride. The high resolution X-ray diffraction (HRXRD), scanning electron microscopy (SEM) and photoluminescence (PL) studies showed a significant improvement of the crystalline qualities and enhancement of the optical properties of GaN grown on the stoichiometric Si₃N₄ by molecular beam epitaxy (MBE).     

Iterative two-step temporal phase-unwrapping applied to high sensitivity three-dimensional profilometry

Although temporal phase unwrapping method can be applied to solve some problems to measure an object with steep shapes, isolated parts or fringe undersampling in three-dimensional (3D) shape measurement, it needs to acquire and process a sequence of fringe pattern images which would take much time. Servin et al. proposed a 2-step temporal phase unwrapping algorithm, which only needs the 2 extreme phase-maps to achieve exactly the same results as standard temporal unwrapping method. But this method is only validated by computer simulation, shortage of experimental demonstration, its sensitivity coefficient G is limited, and it cannot be used when the G value is larger. We proposed an iterative two-step temporal phase-unwrapping algorithm which is an extension of Servin׳s method. First, add a fringe pattern with an intermediate sensitivity, project the fringe patterns of different sensitivity onto the tested object’s surface, and collect deformed fringe patterns with a CCD camera. Then we obtain the unwrapped phase with larger sensitivity coefficient G by cascading the sensitivity coefficients. And we derive the initial phase conditions of the 2-step temporal phase unwrapping algorithm. Finally, the experimental evaluation is conducted to prove the validity of the proposed method. The results are analyzed and compared with Servin׳s method. The experimental results show that the proposed method can achieve higher sensitivity and more accurate measurement, and it can overcome the main disadvantages encountered by Servin׳s method.     

Strain-induced changes in electronic structures and work function for (0 0 1), (1 1 0) and (1 1 1) of AlCu3

Studies of strain-induced changes in surface properties of metal/alloy surface have long been concerned by lot of scientists. However, the strain effects on the work function (WF), and in particular, its physical mechanism have not been well understood. In this paper, we employed a first-principles method to study the effects of biaxial strain in WF on the (0 0 1), (1 1 0) and (1 1 1) surfaces of AlCu₃. The relationship among the WF change, atomic relaxation and charge transfer induced by strain was discussed. The calculated results showed that tensile strain decreased the WF, while the compressive strain increased the WF; a larger atomic relaxation often followed with a larger WF change. The sensitivity of the WF with respect to the strain was strongly dependent on the direction of the surface or the density of atom packed plane of the surface.