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Optical Absorption Spectra (optical + absorption_spectrum)
Selected AbstractsFabrication of Hollow Metal "Nanocaps" and Their Red-Shifted Optical Absorption Spectra,ADVANCED MATERIALS, Issue 10 2005J. Liu Cap-shaped metal nanoparticles (see Figure) have optical spectra with significant absorption in the infrared. Such shapes, produced by physical vapor deposition onto a polymer-particle template, can be readily separated from one another provided that deposition is carried out at an inclination to the plane of the template. The effect of composition, angle of deposition, and thickness on the properties of the cap-shaped particles is discussed. [source] The study of structural changes of amorphous Ge2Sb2Te5 films after annealing by optical absorption spectroscopyPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 3 2010Tamihiro Gotoh Abstract Optical absorption spectra of post-annealed Ge2Sb2Te5 films were measured in the photon energy range from 0.5 to 3.5,eV. Optical absorption edge and Urbach slope parameter changed slightly with increase in annealing temperature and then abrupt changes occurred at around crystallization temperature. The band gaps of amorphous and cubic Ge2Sb2Te5 are 0.74 and 0.54,eV, respectively. The spectroscopic method is demonstrated to be suitable for evaluation of structural disorder and crystalline composition in phase-change materials. [source] Conducting and transparent SWNT/polymer compositesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 13 2006Urszula Dettlaff-Weglikowska Abstract Flexible, transparent and conducting poly(methyl methacrylate) (PMMA) composites films were prepared using SOCl2 functionalized SWNTs. Optical absorption spectra measured on composite films confirm that the composite preparation procedure preserves the electronic properties (position of the Fermi level) of the p-doped nanotubes in the polymer matrix. Due to the doping effect of SOCl2 the electrical conductivity of the composites is improved by a factor of 5. The light transmission of the composite films depends on the film thickness and on the nanotube concentration. The optical transmittance of visible light at 500 nm was found to be 92% for 0.1 wt% SWNT loading and 46% for 0.5 wt% SWNT loading. The thickness of the specimens was approximately 20 µm. Conductivity measurement of the thin films performed with the four lead method revealed values 3.5 × 10,3 S/cm and 4.7 × 10,1 S/cm, respectively. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Optical absorption and EPR spectral studies of vauqueliniteCRYSTAL RESEARCH AND TECHNOLOGY, Issue 8 2006K. Nagamuni Reddy Abstract Vauquelinite - a mineral - was investigated by EPR, NIR and optical spectroscopic techniques. EPR studies on powder sample confirm the presence of Cu(II) and Fe(III) impurity in the mineral. Optical absorption spectrum also indicates that Cu(II) impurity is present in rhombically distorted octahedral structure and Fe(III) in octahedral structure. NIR results are due to water fundamentals and phosphate combination tone. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Solvothermal Synthesis, Crystal Structures, and Properties of New Selenidoantimonates [Ln(en)4(SbSe4)] (Ln = La, Nd) and [Sm(en)4]SbSe4·0.5en: The First Example of an SbSe43, Anion Acting as a Ligand to a Lanthanide ComplexEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 14 2006Ding-Xian Jia Abstract Three new lanthanide selenidoantimonates [Ln(en)4(SbSe4)] [Ln = La (1), Nd (2)] and [Sm(en)4]SbSe4·0.5en (3) (en = ethylenediamine) were first synthesized by treating LnCl3, Sb, and Se in a stoichiometric ratio with en under mild solvothermal conditions. Compounds 1 and 2 are isostructural. The Ln3+ ion has a nine-coordinate environment involving eight N atoms from four en ligands and one Se atom from the SbSe43, anion forming a distorted bicapped pentagonal bipyramid. [La(en)4(SbSe4)] and [Nd(en)4(SbSe4)] are the first examples of solvothermally synthesized selenidoantimonates with an SbSe43, anion acting as a ligand in a lanthanide complex. The crystal structure of 3 contains an isolated bicapped trigonal-prismatic coordinated [Sm(en)4]3+ cation, a tetrahedral SbSe43, anion, and half a free en molecule in its asymmetric unit. The bandgaps of 2.22 eV for 1, 2.33 eV for 2, and 2.54 eV for 3 have been derived from optical absorption spectra. Compound 1 loses the en ligands in one step, whereas compound 2 loses them in two steps. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Spectroscopic and DNA-binding characterization of the isolated heme-bound basic helix,loop,helix-PAS-A domain of neuronal PAS protein 2 (NPAS2), a transcription activator protein associated with circadian rhythmsFEBS JOURNAL, Issue 11 2006Yuji Mukaiyama Neuronal PAS domain protein 2 (NPAS2) is a circadian rhythm-associated transcription factor with two heme-binding sites on two PAS domains. In the present study, we compared the optical absorption spectra, resonance Raman spectra, heme-binding kinetics and DNA-binding characteristics of the isolated fragment containing the N-terminal basic helix,loop,helix (bHLH) of the first PAS (PAS-A) domain of NPAS2 with those of the PAS-A domain alone. We found that the heme-bound bHLH-PAS-A domain mainly exists as a dimer in solution. The Soret absorption peak of the Fe(III) complex for bHLH-PAS-A (421 nm) was located at a wavelength 9 nm higher than for isolated PAS-A (412 nm). The axial ligand trans to CO in bHLH-PAS-A appears to be His, based on the resonance Raman spectra. In addition, the rate constant for heme association with apo-bHLH-PAS (3.3 × 107 mol,1·s,1) was more than two orders of magnitude higher than for association with apo-PAS-A (< 105 mol,1·s,1). These results suggest that the bHLH domain assists in stable heme binding to NPAS2. Both optical and resonance Raman spectra indicated that the Fe(II),NO heme complex is five-coordinated. Using the quartz-crystal microbalance method, we found that the bHLH-PAS-A domain binds specifically to the E-box DNA sequence in the presence, but not in the absence, of heme. On the basis of these results, we discuss the mode of heme binding by bHLH-PAS-A and its potential role in regulating DNA binding. [source] Spectral, kinetic, and redox properties of basic fuchsin in homogeneous aqueous and sodium dodecyl sulfate micellar mediaINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 12 2003N. Ramanathan Effect of anionic surfactant on the optical absorption spectra and redox reaction of basic fuchsin, a cationic dye, has been studied. Increase in the absorbance of the dye band at 546 nm with sodium dodecyl sulfate (SDS) is assigned to the incorporation of the dye in the surfactant micelles with critical micellar concentration (CMC) of 7.3 × 10,3 mol dm,3. At low surfactant concentration (<5 × 10,3 mol dm,3) decrease in the absorbance of the dye band at 546 nm is attributed to the formation of a dye,surfactant complex (1:1). The environment, in terms of dielectric constant, experienced by basic fuchsin inside the surfactant micelles has been estimated. The association constant (KA) for the formation of dye,SDS complex and the binding constant (KB) for the micellization of dye are determined. Stopped-flow studies, in the premicellar region, indicated simultaneous depletion of dye absorption and formation of new band at 490 nm with a distinct isosbestic point at 520 nm and the rate constant for this region increased with increasing SDS concentration. The reaction of hydrated electron with the dye and the decay of the semireduced dye are observed to be slowed down in the presence of SDS. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 629,636, 2003 [source] Template-Assisted Fabrication of Dense, Aligned Arrays of Titania Nanotubes with Well-Controlled Dimensions on Substrates,ADVANCED MATERIALS, Issue 22 2004S. Sander Dense arrays of vertically aligned titania nanotubes (see Figure) are created directly on silicon substrates by combining atomic layer deposition with an alumina template-based fabrication approach. This method enables excellent control over the nanotube dimensions, including their wall thickness, diameter, and height. Nanotubes were fabricated with tube walls thin enough (<,3,nm) to exhibit a wall-thickness- dependent blue-shift in the optical absorption spectra of the arrays. [source] A novel epitaxially grown LSO-based thin-film scintillator for micro-imaging using hard synchrotron radiationJOURNAL OF SYNCHROTRON RADIATION, Issue 5 2010Paul-Antoine Douissard The efficiency of high-resolution pixel detectors for hard X-rays is nowadays one of the major criteria which drives the feasibility of imaging experiments and in general the performance of an experimental station for synchrotron-based microtomography and radiography. Here the luminescent screen used for the indirect detection is focused on in order to increase the detective quantum efficiency: a novel scintillator based on doped Lu2SiO5 (LSO), epitaxially grown as thin film via the liquid phase epitaxy technique. It is shown that, by using adapted growth and doping parameters as well as a dedicated substrate, the scintillation behaviour of a LSO-based thin crystal together with the high stopping power of the material allows for high-performance indirect X-ray detection. In detail, the conversion efficiency, the radioluminescence spectra, the optical absorption spectra under UV/visible-light and the afterglow are investigated. A set-up to study the effect of the thin-film scintillator's temperature on its conversion efficiency is described as well. It delivers knowledge which is important when working with higher photon flux densities and the corresponding high heat load on the material. Additionally, X-ray imaging systems based on different diffraction-limited visible-light optics and CCD cameras using among others LSO-based thin film are compared. Finally, the performance of the LSO thin film is illustrated by imaging a honey bee leg, demonstrating the value of efficient high-resolution computed tomography for life sciences. [source] Effects of oxygen ion implantation in spray-pyrolyzed ZnO thin filmsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 5 2006K. P. Vijayakumar Abstract ZnO thin films, prepared using the chemical spray pyrolysis technique, were implanted using 100 keV O+ ions. Both pristine and ion-implanted samples were characterized using X-ray diffraction, optical absorption, electrical resistivity measurements, thermally stimulated current measurements and photoluminescence. Samples retained their crystallinity even after irradiation at a fluence of ,1015 ions/cm2. However, at a still higher fluence of 2 × 1016 ions/cm2, the films became totally amorphous. The optical absorption edge remained unaffected by implantation and optical absorption spectra indicated two levels at 460 and 510 nm. These were attributed to defect levels corresponding to zinc vacancies (VZn) and oxygen antisites (OZn), respectively. Pristine samples had a broad photoluminescence emission centred at 517 nm, which was depleted on implantation. In the case of implanted samples, two additional emissions appeared at 425 and 590 nm. These levels were identified as due to zinc vacancies (VZn) and oxygen vacancies (VO), respectively. The electrical resistivity of implanted samples was much higher than that of pristine, while photosensitivity decreased to a very low value on implantation. This can be utilized in semiconductor device technology for interdevice isolation. Hall measurements showed a marked decrease in mobility due to ion implantation, while carrier concentration slightly increased. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Nano-floating gate capacitor with SnO2 quantum dots distributed in polyimide dielectricsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 4 2009Dong Uk Lee Abstract Self-assembled SnO2 quantum dots were fabricated by a chemical process between a BPDA-PDA polyamic acid and a Sn film. A nano-floating gate capacitor having metal,insulator,semiconductor structure has been formed on p-type Si substrate with SnO2 quantum dots and dielectric polymer layer. The size and density of fabricated SnO2 quantum dot were about 15 nm and 2.4 × 1011 cm,2, respectively. The electrical properties of the nano-floating gate capacitor have been investigated by measuring capacitance,voltage characteristics. Then, the flat-band voltage shift due to charging of the electron in SnO2 quantum dot was ranged from 1.2 V to 4 V. And the transmission electron microscopy and the optical absorption spectra have been measured to investigate the morphology and absorbance of the SnO2 quantum dots embedded in polyimide. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Raman scattering spectra of CdS nanocrystals fabricated by a reverse micelle methodPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2009Aishi Yamamoto Abstract Raman scattering (RS) spectra of CdS nanocrystals (NCs) fabricated by a reverse micelle method were studied and were analysed using a phonon confinement model. One broad and red-shifted RS peak due to the LO phonon confined in CdS NCs was observed. The RS spectra were calculated using a phonon confinement model with the NC sizes estimated from the optical absorption spectra. The calculated RS spectra as suming that the NCs have the wurtzite structure reproduce the experimental spectra better than those assuming zincblende structure, which is consistent with the result of transmission electron microscope (TEM) observations. Our finding indicates that the crystal structure of the nanocrystal can be determined by the analyses of Raman scattering spectral shape. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] BGO glasses: structural and optical characterizationPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2005S. Polosan Abstract Mixtures of 30% Bi2O3 and 70% GeO2 (in molar percents) were prepared followed by the solid state reaction at 700 °C for 30 min. or 24 h using an Al2O3 crucible. After melting at 1050 °C for 10 min. the melt was poured into a preheated graphite plate and then naturally cooled to room temperature (RT). X-ray diffraction measurements (XRD) on the resulting BGO glasses have been performed, and optical absorption spectra recorded at room temperature on the samples obtained using various preparation conditions. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Effects of hydrostatic stress on the density of impurity states and donor-related optical absorption spectra in GaAs,(Ga,Al)As quantum wellsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2003S. Y. López Abstract The effects of hydrostatic stress on the density of donor impurity states and donor-related optical absorption spectra in a GaAs,(Ga,Al)As quantum well are investigated. The shallow-donor binding energy for different well widths and different values of the hydrostatic stress has been calculated. It has been found that for wider well widths the binding energy increases slowly with hydrostatic stress contrary to the behavior of the binding energy for wells with smaller widths. In particular, it has been found that the binding energy does not change appreciably with the impurity position when the width of the well is small and for large values of hydrostatic stress. Two structures in both the density of states and the optical absorption spectra, associated with impurities located close to the center and to the edges of the structure, are obtained. Also, it has been observed that the density of states and the optical absorption spectra depend strongly on the applied hydrostatic stress. [source] Structure, electrical and optical properties of (PVA/LiAsF6) polymer composite electrolyte filmsPOLYMER ENGINEERING & SCIENCE, Issue 5 2010Madhu Mohan Varishetty In this work, Li+ ion conducting polymer composite electrolyte films (PECs) were prepared based on poly (vinyl alcohol) (PVA), lithium hexafluoro arsenate (LiAsF6), and ceramic filler TiO2 using solution cast technique. The XRD and FTIR spectra were used to determine the complexation of the PVA polymer with LiAsF6 salt. The ionic conductivities of the (PVA + LiAsF6) and (PVA + LiAsF6 + TiO2) films have been determined by the A.C. impedance measurements in the temperature range 320,440 K. The maximum conductivity was found to be 5.10 × 10,4 S cm,1 for PVA:LiAsF6 (75:25) + 5 wt% TiO2 polymer composite film at 320 K. The calculation of Li+ ion transference number was carried out by the combination of A.C. impedance and D.C. polarization methods and is found to be 0.52 for PVA:LiAsF6 (75:25) + 5 wt% TiO2 film. Optical properties such as direct energy gap, indirect energy gap, and optical absorption edge values were investigated in pure PVA and salt complexed PVA films from their optical absorption spectra in the wavelength range of 200,600 nm. The absorption edge was found at 5.76 eV for undoped film, while it is observed at 4.87 and 4.70 eV for 20 and 25 wt% LiAsF6 doped films, respectively. The direct band gaps for these undoped and salt doped PVA films were found to be 5.40, 5.12, and 4.87 eV, respectively, whereas the indirect band gaps were determined as 4.75, 4.45, and 4.30 eV. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers [source] Density Functional Study of Two Seven-Membered Unconventional Fullerenes C58F17CF3 and C58F18CHINESE JOURNAL OF CHEMISTRY, Issue 8 2010Chunmei Tang Abstract The density functional method is used to study the structure, electronic properties, static linear polarizabilities, and optical absorption spectra of two seven-membered unconventional fullerene derivatives C58F17CF3 and C58F18. It is calculated that three sites chosen to locate the CF3 are isoenergetic. The energy gaps of C58F18 and C58F17CF3 are much larger than that of C58, indicating the fluorination and trifluoromethylation of C58 can remarkably enhance the kinetic stability. The density of states explore that the influence of CF3 to the energy levels is mainly distributed in the energy range from ,10 to ,2 eV. However, when the CF3 substitutes for F in C58F18, the bond lengths, energy gaps, static linear polarizabilities, and optical absorption spectra all show small variety. [source] Effect of composition on the optical properties of the quaternary CuxAg1,xInTe2 thin filmsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2003E. A. El-Sayad Abstract Thin films of CuxAg1,xInTe2 solid solutions (x = 0.25, 0.50 and 0.75) were deposited by thermal evaporation of prereacted materials on glass substrates. X-ray diffraction (XRD) studies has revealed that the as-deposited and thermally annealed films are polycrystalline with single-phase of a tetragonal chalcopyrite structure as that of bulk material with (112) predominant reflecting plane. The films compositions were confirmed by using energy dispersive analysis of X-rays (EDAX). The refractive index, n, and the extinction coefficient, k, of the annealed films with different compositions were determined in the spectral range, 400,2500 nm. Three characteristic energy gaps have been determined from the analysis of optical absorption spectrum for each composition. The three energy gaps are attributed to the optical transitions from the valence sub-bands to the conduction band minimum. Besides, a fourth energy gap has also been obtained for each composition, which may be attributed to the transition from the copper 3d-level to the conduction band minimum. However, the band gaps showed linear variation with the value of x. [source] Molten-salt Synthesis and Properties of ZnS with Hexagonal Prism MorphologyCHINESE JOURNAL OF CHEMISTRY, Issue 10 2007Jin-Song LIU Abstract ZnS with hexagonal prism morphology has been synthesized successfully by molten-salt method with ZnS nanoparticles as precursors, and the ZnS nanoparticles were prepared by one-step solid-state reaction of Zn(CH3COO)2·2H2O with Na2S·9H2O at ambient temperature. Crystal structure and morphology of the product were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and HRTEM. Ultraviolet-visible optical absorption spectrum of the ZnS hexagonal prism shows a distinct red shift from that of bulk ZnS crystals and photoluminescence spectrum exhibits strong emissions at 380 and 500 nm, respectively. Further experiments were designed and the formation mechanism of the ZnS hexagonal prism has been also discussed in brief. [source] | ||||||||||||||||