Modelling and analysis of modal behaviour in SOI slot waveguides

Mode behaviour for SOI slot waveguides is modelled and analysed using a numerical full vectorial method based on the film mode matching method (MMM). Only the quasi-TE mode is investigated. Waveguide heights and slot widths, as well as silicon widths are properly chosen with respect to the single mode behaviour in the slot region. Comparison between the effective index method and our side loss method shows that our single mode condition is creditable. The optical power confinement in slot region for the quasi-TE mode is also studied and presented. We demonstrate that the maximum achievable optical power confinement P-slot and the maximum normalized average optical intensity I-slot are 42% and 26 mu m(-2), respectively.

Fourier transformation study of the Franz-Keldysh Oscillation in SIN+ GaAs structures

Fourier transformation (FT) method has been used in the theoretical lineshape analysis of the Franz-Keldysh Oscillation (FKO) in detail by numerical simulation. The FKO of a set of GaAs SIN+ samples was obtained in photoreflectance measurements. The FT spectra of a part of the samples,including of the real part,imaginary part, and mode of the FT,are well consistent with the theoretical lineshapes. The ratio of the square root of the reduced mass of the light hole (LH) to the heavy hole (HH), root mu(1)/root mu(h), obtained in the analysis was in the range of 0.805 to 0.816 for different samples. In addition,the built-in electric field F-1, and the modulation field delta F = F-1 - F-2 induced by photo-modulation were also obtained in the analysis. However,for a few samples great difference was found in the lineshape of the real part and imaginary part of their FT spectra from the theoretical lineshape. In this case the mode of the FT spectra still can be used to obtain useful information.

Improved digital processing method used for image motion measurement based on hybrid opto-digital joint transform correlator

Hybrid opto-digital joint transform correlator (HODJTC) is effective for image motion measurement, but it is different from the traditional joint transform correlator because it only has one optical transform and the joint power spectrum is directly input into a digital processing unit to compute the image shift. The local cross-correlation image can be directly obtained by adopting a local Fourier transform operator. After the pixel-level location of cross-correlation peak is initially obtained, the up-sampling technique is introduced to relocate the peak in even higher accuracy. With signal-to-noise ratio >= 20 dB, up-sampling factor k >= 10 and the maximum image shift <= 60 pixels, the root-mean-square error of motion measurement accuracy can be controlled below 0.05 pixels.

Carbon monoxide adsorption on molybdenum phosphides: Fourier transform infrared spectroscopic and density functional theory studies

Molybdenum phosphide (MoP) and supported molybdenum phosphide (MoP/gamma-Al2O3) have been prepared by the temperature-programmed reduction method. The surface sites of the MoP/gamma-Al2O3 catalyst were characterized by carbon monoxide (CO) adsorption with in situ Fourier transform infrared (FT-IR) spectroscopy. A characteristic IR band at 2037 cm(-1) was observed on the MoP/gamma-Al2O3 that was reduced at 973 K. This band is attributed to linearly adsorbed CO on Mo atoms of the MoP surface and is similar to IR bands at 2040-2060 cm(-1), which correspond to CO that has been adsorbed on some noble metals, such as platinum, palladium, and rhodium. Density functional calculations of the structure of molybdenum phosphides, as well as CO chemisorption on the MoP(001) surface, have also been studied on periodic surface models, using the generalized gradient approximation (GGA) for the exchange-correlation functional. The results show that the chemisorption of CO on MoP occurred mainly on top of molybdenum, because the bonding of CO requires a localized mininum potential energy. The adsorption energy obtained is DeltaH(ads) approximate to -2.18 eV, and the vibrational frequency of CO is 2047 cm-1, which is in good agreement with the IR result of CO chernisorption on MoP/gamma-Al2O3.

Controllable synthesis of metal hydroxide and oxide nanostructures by ionic liquids assisted electrochemical corrosion method

Cu(OH)(2) nanowires have been synthesized by anodic oxidation of copper through a simple electrolysis process employing ionic liquid as an electrolyte. Controlling the electrochemical conditions can qualitatively modulate the lengths, amounts, and shapes of Cu(OH)(2) nanostructures. A rational mechanism based on coordination self-assembly and oriented attachment is proposed for the selective formation of the polycrystalline Cu(OH)(2) nanowires. In addition, the FeOOH nanoribbons, Ni(OH)(2) nanosheets, and ZnO nanospheres were also synthesized by this route, indicative of the universality of the electrochemical route presented herein. The morphologies and structures of the synthesized nanostructures have been characterized by transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), powder X-ray diffraction (XRD). Fourier transform infrared spectra (FT-IR), and thermogravimetric (TG). (C) 2007 Elsevier Masson SAS. All rights reserved

Studies on the magnetism of cobalt ferrite nanocrystals synthesized by hydrothermal method

Fe-Co/CoFe2O4 nanocomposite and CoFe2O4 nanopowders were prepared by the hydrothermal method. The structure of magnetic powders were characterized by X-ray diffraction diffractometer (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), thermal gravity analysis (TGA) and differential thermal analysis (DTA) analysis, X-ray photoelectron spectrometry (XPS), and Fourier transform infrared spectra (FTIR) techniques, while magnetic properties were determined by using a vibrating sample magnetometer (VSM) at room temperature.

Synthesis and characterization of magnetite dodecahedron nanostructure by hydrothermal method

Magnetite dodecahedral nanocrystals were fabricated using ethlenediamine tetraacetic acid (EDTA)-mediated hydrothermal route. Scanning electron microscopy images displayed that the products were almost dodecahedrons. The length of two different ribs were about 300 and 200 nm, respectively. X-ray diffraction patterns showed that the products were the cubic inverse spinel structure. Fourier transform infrared spectrum directly provided evidence of the EDTA bound to a specific surface of the precipitated magnetic nanocrystal.

Structural analysis of monoterpene glycosides extracted from Paeonia lactiflora Pall. using electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry and high-performance liquid chromatography/electrospray ionization tandem mass spectrometry

Paeoniflorin standard was first investigated by electrospray ionization Fourier transform ion cyclotron resonance tandem mass spectrometry (ESI-FTICR-MS/MS) using a sustained off-resonance irradiation (SORI) collision-induced dissociation (CID) method at high mass resolution. The experimental results demonstrated that the unambiguous elemental composition of product ions can be obtained at high mass resolution. Comparing MS/MS spectra and the experimental methods of hydrogen and deuterium exchange, the logical fragmentation pathways of paeoniflorin have been proposed. Then, the extracts of the traditional Chinese medicine Paeonia lactiflora Pall. were analyzed by high-performance liquid chromatography/electrospray ionization tandem mass spectrometry (HPLC/ESI-MS/MS). By comparison with the ESI-FTICR-MS/MS data of paeoniflorin, the isomers paeoniflorin and albiflorin in Paeonia lactiflora Pall. have been identified using HPLC/MS with CID in an ion trap and in-source CID. Furthermore, using the characteristic fragmentation pathways, the retention times (t(R)) in HPLC and MS/MS spectra, the structures of three other kinds of monoterpene glycoside compounds have been identified on-line without time-consuming isolation.

Deposition of GdVO4 : Eu3+ nanoparticles on silica nanospheres by a simple sol-gel method

The deposition and coating of GdVO4: Eu3+ nanoparticles on spherical silica was carried out using a simple sol - gel method at low temperature. The GdVO4: Eu3+-coated silica composites obtained were characterized by differential thermal analysis (DTA), thermogravimetric (TG) analysis, x-ray diffraction (XRD), Fourier-transform IR spectroscopy (FT-IR), transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS), photoluminescence spectra, and kinetic decay. It is found that the similar to 5 nm GdVO4: Eu3+ nanoparticles coating the silica spheres are crystal in the as-prepared samples and the crystallinity increases with increasing annealing temperature. The composites obtained are spherical in shape with an average size of 100 nm. The GdVO4: Eu3+ nanoparticles are linked with silica cores by a chemical bond. The photoluminescence spectra of the obtained GdVO4: Eu3+-coated silica composites are similar to those of the bulk GdVO4: Eu3+ phosphors. The strongest peak is near 617 nm, which indicates that Eu3+ is located in the low symmetry site with non-inversion centre.

A simple and effective route for the preparation of poly(vinylalcohol) (PVA) nanofibers containing gold nanoparticles by electrospinning method

Poly(vinyl alcohol) (PVA) nanofibers containing gold nanoparticles have been simply obtained by electrospinning a solution containing gold nanoparticles without the additional step of introducing other stabilizing agents. The optical property of gold nanoparticles in PVA aqueous solution was observed by UV-visible absorption spectra. Morphology of the Au/PVA nanofibers and distribution of the gold nanoparticles were characterized by transmission electron. microscopy (TEM). The structure transformation was characterized from PVA to PVA/Au composite by Fourier transform infrared spectroscopy (FTIR).

An effective layer-by-layer adsorption and polymerization method to the fabrication of polyoxometalate-polypyrrole nanoparticle ultrathin films

A layer-by-layer (LbL) adsorption and polymerization method was developed for the controllable preparation of polypyrrole (PPy) nanoparticles within ultrathin films. By repetitive adsorption of pyrrole and subsequent polymerization with 12-molybdophosphoric acid, the polyelectrolyte multilayer films containing PPy nanoparticles were fabricated. UV-visible absorption spectrocopy, Fourier transform infrared (FTIR) spectroscopy, atomic force microscopy (AFM), transmission electron microscopy (TEM) and cyclic voltammograras (CVs) were used to characterize the PPy nanoparticles and their multilayer thin films. UV-visible spectra indicate that the growth of PPy nanoparticles was regular and occurred within the polyelectrolyte films. The size of prepared PPy nanoparticles was found by TEM to increase with the increasing of polymerization cycles. The electrochemistry behavior of the multilayer thin films was studied in detail on ITO. The results suggest that the LbL adsorption and polymerization method developed herein provides an effective way to prepare PPy nanoparticles in the polymer matrix.

A novel preparation method of maleic anhydride grafted syndiotactic polystyrene and its blend performance with nylon6

This work is intended to provide a method for the preparation of maleic anhydride grafted syndiotactic polystyrene (sPS-g-MA). In particular, a novel solid reaction method by a radical grafting approach is investigated. The grafting reaction is performed at a solid state, where the syndiotactic polystyrene (sPS) is swollen in solvent at relatively low temperature compared to the conventional melt modification method. The formation of sPS-g-MA is directly confirmed by Fourier transform infrared spectroscopy and by the morphology observation of sPS/polyamide-6 (Nylon6) blends, when sPS-g-MA is used as a reactive compatibilizer.

A novel method for preparing ordered SnO2/TiO2 alternate nanoparticulate films

A novel method using LB films as precursors to prepare pure inorganic ordered film with periodic structure was developed. Surfactant-stabilized SnO2 nanoparticulate organosols and TiO2 nanoparticulate organosols were prepared and used as spreading solutions. Using LB technique, the good film-forming ability of the surfactant-stabilized SnO2 nanoparticles and TiO2 nanoparticles was confirmed by the determination of the pi -A isotherms. The surfactant-stabilized SnO2 and TiO2 nanoparticulate monolayers were fabricated on the water surface and then were transferred to solid substrates (CaF2, quartz, silicon, and so on) alternately, layer-by-layer. Then the as-deposited alternate LB film was treated at different temperatures. The as-deposited alternate LB film and the treated film were characterized by Fourier transform infrared spectroscopy, UV visible spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The results indicate that our method was successful. The as-deposited alternate LB film formed a periodic structure with a long spacing of 6.5 nm that was composed of SnO2 nanoparticles, TiO2 nanoparticles, and arachidic acid. The treated film composed of SnO2 nanoparticles and TiO2 nanoparticles formed a pure inorganic periodic structure with an ordered distance of 5.4 nm. (C) 2001 Academic Press.

In-situ Fourier transform infrared spectroelectrochemistry as a probe of the glassy carbon electrode chemically modified by nickel (II)-cyanometallates

A new nickel (II)-cyanometallates modified on glassy carbon electrode was prepared by a new method and studied by cyclic voltammetry and in situ Fourier transform infrared (FTIR) spectroelectrochemistry. It was found that the NiHCF film existed in two forms: Ni2Fe(II)-(CN)(6) and M2NiFe(II)(CN)(6), Fe(CN)(3)(6-) codeposited in the NiHCF film existing in free cation or bridged-bond state depended on the property of the cations in electrolyte: in NaCl and LiCl solution, it is in bridges-bonded, but in HCl and KCl, it is free.

Fourier有限差分法深度偏移与正演模拟

With the development of seismic exploration, the target becomes more and more complex, which leads to a higher demand for the accuracy and efficiency in 3D exploration. Fourier finite-difference (FFD) method is one of the most valuable methods in complex structure exploration, which keeps the ability of finite-differenc method in dealing with laterally varing media and inherits the predominance of the phase-screen method in stablility and efficiency. In this thesis, the accuracy of the FFD operator is highly improved by using simulated annealing algorithm. This method takes the extrapolation step and band width into account, which is more suitable to various band width and discrete scale than the commonely-used optimized method based on velocity contrast alone. In this thesis, the FFD method is extended to viscoacoustic modeling. Based on one-way wave equation, the presented method is implemented in frequency domain; thus, it is more efficient than two-way methods, and is more convenient than time domain methods in handling attenuation and dispersion effects. The proposed method can handle large velocity contrast and has a high efficiency, which is helpful to further research on earth absorption and seismic resolution. Starting from the frequency dispersion of the acoustic VTI wave equation, this thesis extends the FFD migration method to the acoustic VTI media. Compared with the convetional FFD method, the presented method has a similar computational efficiency, and keeps the abilities of dealing with large velocity contrasts and steep dips. The numerical experiments based on the SEG salt model show that the presented method is a practical migration method for complex acoustical VTI media, because it can handle both large velocity contrasts and large anisotropy variations, and its accuracy is relatively high even in strong anisotropic media. In 3D case, the two-way splitting technique of FFD operator causes artificial azimuthal anisotropy. These artifacts become apparent with increasing dip angles and velocity contrasts, which prevent the application of the FFD method in 3D complex media. The current methods proposed to reduce the azimuthal anisotropy significantly increase the computational cost. In this thesis, the alternating-direction-implicit plus interpolation scheme is incorporated into the 3D FFD method to reduce the azimuthal anisotropy. By subtly utilizing the Fourier based scheme of the FFD method, the improved fast algorithm takes approximately no extra computation time. The resulting operator keeps both the accuracy and the efficiency of the FFD method, which is helpful to the inhancements of both the accuracy and the efficiency for prestack depth migration. The general comparison is presented between the FFD operator and the generalized-screen operator, which is valuable to choose the suitable method in practice. The percentage relative error curves and migration impulse responses show that the generalized-screen operator is much sensiutive to the velocity contrasts than the FFD operator. The FFD operator can handle various velocity contrasts, while the generalized-screen operator can only handle some range of the velocity contrasts. Both in large and weak velocity contrasts, the higher order term of the generalized-screen operator has little effect on improving accuracy. The FFD operator is more suitable to large velocity contrasts, while the generalized-screen operator is more suitable to middle velocity contrasts. Both the one-way implicit finite-difference migration and the two-way explicit finite-differenc modeling have been implemented, and then they are compared with the corresponding FFD methods respectively. This work gives a reference to the choosen of proper method. The FFD migration is illustrated to be more attractive in accuracy, efficiency and frequency dispertion than the widely-used implicit finite-difference migration. The FFD modeling can handle relatively coarse grids than the commonly-used explicit finite-differenc modeling, thus it is much faster in 3D modeling, especially for large-scale complex media.