Transmission optique,en lumiere polarisse,de couches tres minces de potassium,sous incidence oblique

The transmission factors of potassium thin films have been determined for incidence angles of 0°, 45°, 70°, the electric field E being either parallel or perpendicular to the incidence plane. These factors present important differences according to the polarization. Evidence has been found for the existence of two anomalous absorption bands. These bands can be connected with the existence of two plasma frequencies, which are associated with an electric field component parallel or perpendicular to the thin film.     

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.     

Syntheses, crystal structures, visible and near-IR luminescent properties of ternary lanthanide (Dy, Tm) complexes containing 4,4,4-trifluoro-1-phenyl-1,3-butanedione and 1,10-phenanthroline

The ligands 4,4,4-trifluoro-1-phenyl-1,3-butanedione (Hbfa) and 1,10-phenanthroline (phen) were used to prepare ternary lanthanide (Ln) complexes [Dy(bfa)₃phen and Tm(bfa)₃phen]. Crystal data: Dy(bfa)₃phen C₄₂H₂₆F₉N₂O₆Dy, triclinic, P1¯, a=9.9450(6) Å, b=14.0944(9) Å, c=14.6043(9) Å, α=82.104(1)°, β=87.006(1)°, γ=76.490(1)°, V=1971.1(2) Å³, Z=2; Tm(bfa)₃phen C₄₂H₂₆F₉N₂O₆Tm, triclinic, P1¯, a=9.898(5) Å, b=13.918(5) Å, c=14.753(5) Å, α=83.517(5)°, β=86.899(5)°, γ=76.818(5)°, V=1965.3(14) Å³, Z=2. The coordination number of the central Ln³⁺ (Ln=Dy, Tm) ion is eight, with six oxygen atoms from three Hbfa ligands and two nitrogen atoms from the phen ligand. The photophysical properties of the two complexes were studied by absorption spectra, diffuse reflectance spectra, and emission spectra. They show the characteristic luminescence of the corresponding Ln³⁺ ion in both visible and near-IR (NIR) region. Additionally, the energy transfer mechanisms between the ligands and central Ln³⁺ ions were discussed.     

Synthesis, growth, and characterization of a non-linear optical crystal-glycine lithium chloride

A new non-linear optical material, glycine lithium chloride, was synthesized and single crystals were grown by slow evaporation solution growth technique at constant temperature from its aqueous solution. Transparent and well-crystallized hexagonal prisms were obtained by controlled evaporation at a constant temperature of 45 °C. The grown crystals were characterized by X-ray diffraction methods, Fourier transforms infrared spectroscopy, and optical absorption spectrum. Single crystal X-ray diffraction analysis revealed that the crystal lattice of glycine lithium chloride is hexagonal with unit cell a = b = 7.023 Å, c = 5.478 Å, α = β = 90°, γ = 120°, V = 234 Å³. The dielectric response of the crystal with varying frequencies was studied. The second harmonic generation efficiency of the crystal was studied and is found to be larger than KDP.     

Vectorial structures of non-paraxial linearly polarized Gaussian beam and their beam propagation factors

Based on the vectorial structure of non-paraxial electromagnetic beam and non-paraxial vectorial moment theory, the relationship of the beam waists, the divergence angles and the beam propagation factors among non-paraxial linearly polarized Gaussian beam, its TE and TM terms have been presented, respectively. The analytical beam propagation factors are given and further discussed at the highly non-paraxial case. The maximum divergence angles in the x-direction of non-paraxial linearly polarized Gaussian beam, its TE and TM terms are all 54.7°, and those in the y-direction are limited to be 63.4°, 67.7° and 39.2°, respectively. As TE and TM terms are orthogonal and can be detached at the far field, the potential applications of the isolated TE and TM terms are deserved further investigation.     

Linear birefringence parameters determination of a multi-order wave plate via phase detection at large oblique incidence angles

In order to characterize the linear birefringence parameters (LBPs) of a multi-order wave plate (MWP) including ordinary refractive index n_o, extraordinary refractive index n_e and the order number precisely, phase retardation measurement by means of large oblique incidence angle on the MWP has been proposed and demonstrated. However, the effects of spatial shifting and multiple reflections by the MWP depress the accuracy of the measurements significantly. Thus, we propose a retro-reflected geometry in a polarized heterodyne interferometer that can determine the LBPs of a MWP precisely. This method is not only able to reduce the spatial shifting effect but also avoids multiple reflections of the emerging beams. Experimentally, the oblique incidence angle in a range from 30° to 44° was scanned and the highest sensitivity ever for measurements of n_o and n_e for an uncoated MWP was obtained. The detection sensitivity for the refractive indices (n_o,n_e, n_o−n_e) of an uncoated MWP can be up to 10⁻⁶.     

Microwave structural studies of organoselenium compounds 1. Microwave spectra, molecular structure, and methyl barrier to internal rotation of dimethyl diselenide

The rotational spectra of nine isotopomers of dimethyl diselenide, CH₃SeSeCH₃, have been measured with a molecular-beam Fourier transform microwave spectrometer. The spectra were complex due to the presence of many isotopomers in natural abundance and the splitting caused by the interactions with two methyl internal rotors. The spectra were assigned and fit to experimental precision to an effective rotational Hamiltonian for molecules with two periodic internal motions. The spectra of the symmetric isotopomers are consistent with a C₂ equilibrium structure. The rotational constants were used to determine the r_s structure of the C-Se-Se-C frame with the results r(SeSe)=2.306(3) Å, r(SeC)=1.954(6) Å, ?(CSeSe)=99.8(2)°, ?(CSeSeC)=85.2(1)°. A barrier to internal rotation of the methyl groups of 395 ± 2 cm⁻¹ was derived from the internal rotation splittings.     

Effect of surface steps on sputtering and surface defect formation: molecular-dynamics study of 5 keV Xe bombardment of Pt(1 1 1) at glancing incidence angles

Using molecular-dynamics simulation, we study sputtering and defect formation induced by 5 keV Xe⁺ ion impact on a Pt(1 1 1) surface at oblique and glancing incidence angles. Impact on a terrace produces yield maxima at ?=60-65° incidence angle towards the surface normal. Beyond 75-80°, no damage is produced due to projectile ion reflection. Impact on a dense-packed step, however, produces defects in sizeable numbers up to glancing incidence, ?=85°. The dependence of the yields on the incidence angle and distance of the impact point of the projectile to the step are discussed.     

Effects of evolving surface morphology on yield during focused ion beam milling of carbon

We investigate evolving surface morphology during focused ion beam bombardment of C and determine its effects on sputter yield over a large range of ion dose (10¹⁷-10¹⁹ ions/cm²) and incidence angles (Θ = 0-80°). Carbon bombarded by 20 keV Ga⁺ either retains a smooth sputtered surface or develops one of two rough surface morphologies (sinusoidal ripples or steps/terraces) depending on the angle of ion incidence. For conditions that lead to smooth sputter-eroded surfaces there is no change in yield with ion dose after erosion of the solid commences. However, for all conditions that lead to surface roughening we observe coarsening of morphology with increased ion dose and a concomitant decrease in yield. A decrease in yield occurs as surface ripples increase wavelength and, for large Θ, as step/terrace morphologies evolve. The yield also decreases with dose as rippled surfaces transition to have steps and terraces at Θ = 75°. Similar trends of decreasing yield are found for H₂O-assisted focused ion beam milling. The effects of changing surface morphology on yield are explained by the varying incidence angles exposed to the high-energy beam.     

Molecular dynamics simulation of low-energy bombardment of Pt (1 1 1) surface by Cu atoms with various incident angles

The low-energy bombardment of Pt (1 1 1) surface by Cu atoms with various incident angles (θ) is studied with MD simulations. In the case of near-normal incidence (θ≤20°), the result of energy deposition is similar to that of θ=0°. In contrast, in the case wherein the incident angles are higher than 60°, the incident atom cannot penetrate through the first layer and is scattered directly on the surface. The low-energy deposition has no obvious effect on the substrate. For 20°≤θ≤60°, the oblique incidence contributes to uniformity of nucleation and layer-by-layer growth of film as well as the layer-by-layer removal of atoms in the surface layers. Based on our MD simulations, the mechanism behind the deposition and thin film formation is related to the horizontal component and the vertical component of the impact momentum.     

Growth characteristics of inclined columns produced by Glancing Angle Deposition (GLAD) and colloidal lithography

Nanocolumns were produced by performing Glancing Angle Deposition (GLAD) onto self-assembled template arrays consisting of platinum coated polystyrene spheres. By varying the angle of incidence (θ = 35°, 10° and 5°) and the deposited surface mass density it was possible to control the shape of the individual columns. The changes in column shape as function of the amount of mass deposited on the respective surfaces were characterized by monitoring the increase in the length and width of the structures. Interestingly the column shape development followed a power law behaviour. The power law exponents retrieved from the length and width increment as function of the deposited surface mass density decreased from 1.06 to 0.46 and 0.71 to 0.09, respectively, as θ changed from 35° to 5°. The changes in the power law exponents indicate that the growth of the nano-columns is influenced by both surface diffusion and shadowing effects. A detailed understanding of the underlying processes governing the nanocolumn growth might be utilized in the design of new functional nanomaterials.     

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.     

Nanostructuring of Fe films by oblique incidence deposition on a FeSi2 template onto Si(1 1 1): Growth, morphology, structure and faceting

The growth of thin Fe films deposited at oblique incidence on an iron silicide template onto Si(1 1 1) single crystal has been investigated as a function of Fe thickness (0 < t_Fe ? 180 monolayers (MLs)) and incidence angle (0 ? θ ? 80°). The growth mode is determined in situ by means of scanning tunnelling microscopy (STM) and low energy electron diffraction (LEED). Stripes oriented perpendicularly to the incident atomic flux are formed for θ ? 30°. Self-correlation functions are used to extract characteristic lengths from STM images. The correlation lengths in the direction of the incident flux (ξ_x) and perpendicular to the atomic flux (ξ_y) grow with different powers versus time (ξ_x∝t^σ and ξ_y∝t^ρ, with σ = 0.34 ± 0.03 and ρ = 0.67 ± 0.03) following the exact solution of the (1 + 1) dimensional Kardar-Parisi-Zhang (KPZ) equation. The root mean square roughness follows also a scaling law for t_Fe < 120 ML leading to a growth exponent β = 0.73 ± 0.02. Shadowing and steering effects are discussed on the basis of our STM data.     

Synthesis, microstructure, dielectric and magnetic properties of Cu substituted Ni-Li ferrites

Cu substituted Ni-Li spinel ferrites were prepared by a conventional sol-gel auto-combustion method. The structure, surface morphology, dielectric and magnetic properties were investigated by X-ray diffraction, infrared spectroscopy, scanning electron microscopy, impedance spectroscopy and vibrating sample magnetometer, respectively. X-ray diffraction studies reveal the single phase spinel structure of the ferrites and the crystallite size varies from 23 to 35 nm. Incorporation of Cu in the Ni-Li ferrites increases the grain size. The dielectric parameters such as ε´, ε′′, loss tan δ and ac conductivity (σ_ac) have been measured for the annealed samples in the temperature range from 35 to 200 °C and over the frequency range from 10¹ to 10⁷ Hz. The saturation magnetization and coercivity show a dependence on the composition and microstructure. The values of saturation magnetization vary from 25.6 to 33.6 emu/g with increase in x for samples annealed at 600 °C. The values of the coercivity increase from 170 to 203 Oe with increase in x.     

Ground-state constants, ab initio anharmonic force field, and equilibrium structure of F2BOH

The millimeterwave spectra of F₂¹⁰BOH and F₂¹¹BOH (difluorohydroxyborane) have been measured in their ground vibrational state. Accurate rotational and centrifugal distortion constants have been determined. The equilibrium geometry and anharmonic force fields have been calculated at the CCSD(T) level of theory. The ab initio centrifugal distortion constants and rotation-vibration interaction constants are compared to the experimental values. Some discrepancies are found and discussed. Particularly, it is explained why the semi-experimental structure is not reliable. The best equilibrium structure is: r_e(BF_cis) = 132.29 pm, r_e(BF_trans) = 131.29 pm, r_e(BO) = 134.48 pm, r_e(OH) = 95.74 pm, ∠_e(FBF) = 118.36°, ∠_e(F_cisBO) = 122.25°, and ∠_e(BOH) = 113.14°.     

Ablation yield and angular distribution of ablated particles from laser-irradiated metals: The most fundamental determining factor

Five metals (Zn, Cu, Ni, Ti, and Mo) were irradiated with 150 shots of a Q-switched Nd:YAG pulsed laser in a vacuum of 10⁻³ torr. The ions projected out of the laser-produced plasma (LPP) plume were detected by CR-39 detectors positioned at −15°, 0°, 30°, 60°, and 90° with respect to the target-surface normal at a distance of 5 cm from the target in each case. The angular distribution of LPP ions, which is characterized by the exponent n of cosⁿ θ distribution, is given by n = 2.5-11 for the five target metals. The value of the exponent n has no systematic correlation with the square-root of atomic mass of the target metals but exhibits systematic dependence on the room temperature Debye-Waller's thermal parameter B or the mean-square amplitude of atomic vibrations 〈u²〉. Likewise, the ablation yield (atoms/shot) of the twelve target metals investigated by Thestrup et al. (2002) [8] under identical irradiation conditions is a function of the room temperature B-factor or 〈u²〉.     

Transition wavelengths for helium atom in weakly coupled hot plasmas

We have investigated the effect of surrounding plasmas on several singly excited and doubly excited meta-stable bound states of helium atom using highly correlated basis functions for singly excited S, P, D states and CI-type basis functions for doubly excited meta-stable D states. Plasma effect is taken care of by using a screened Coulomb (Yukawa) potential obtained from the Debye model that admits a variety of plasma conditions, and such a model plays an important role in plasma spectroscopy. The wavelengths for transitions from the 1snp ¹P° (n=2,3)→1s²¹S^e, 1snp ³P° (n=2,3)→1s2s ³S^e, 2pnp ¹P^e (n=3,4)→1s2p ¹P°, 2pnp ³P^e (n=2,3)→1s2p ³P°, 2pnd ¹D° (n=3,4)→1s3d ¹D^e, 2pnd ³D° (n=3,4)→1s3d ³D^e, 2p3p ¹P^e→2pnd ¹D° (n=3,4), 2pnd ¹D°(n=3, 4)→2p4p ¹P^e, 2pnp ³P^e (n=2,3)→2p3d ³D°, and 2pnp ³P^e (n=2,3)→2p4d ³D° of helium atom in plasmas for various Debye lengths are reported.     

Preparation, characterization and dye adsorption properties of γ-Fe2O3/SiO2/chitosan composite

A γ-Fe₂O₃/SiO₂/chitosan composite was prepared by water-in-oil emulsification, and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM). Effects of various factors, including adsorbent dosage, initial dye concentration, solution pH, and competing anions, on the adsorption of methyl orange from aqueous solutions by the resulting composite were studied by batch adsorption experiments. The adsorption kinetics was found to follow the pseudo-second-order kinetic model, and intraparticle diffusion was related to the adsorption, but not as a sole rate-controlling step. The equilibrium adsorption data were well described by the Freundlich isotherm model. Evaluation of the thermodynamic parameters ΔG°, ΔH°, and ΔS° revealed that the adsorption process was naturally feasible, spontaneous, and exothermic. The composite was proven to be efficient, suitable and promising for the removal of methyl orange from aqueous solutions since it has a relatively higher adsorption capacity than other low-cost adsorbents.