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X-ray Absorption (x-ray + absorption)
Terms modified by X-ray Absorption Selected AbstractsHigh Covalence in CuSO4 and the Radicalization of Sulfate: An X-Ray Absorption and Density Functional Study.CHEMINFORM, Issue 9 2005Robert K. Szilagyi Abstract For Abstract see ChemInform Abstract in Full Text. [source] In situ X-Ray Absorption of Co/Mn/TiO2 Catalysts for Fischer,Tropsch Synthesis.CHEMINFORM, Issue 50 2004Fernando Morales No abstract is available for this article. [source] Time-dependent density functional theory calculations of X-ray absorptionINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 4-5 2003J. J. Rehr Abstract There has been dramatic progress in recent years both in calculations and in the interpretation of X-ray absorption spectra (XAS). Often an independent-electron approximation with final state potentials is adequate. However, for soft X-rays (i.e., energies less than about 1 keV) local field effects can be important. Such local fields arise from the dynamic screening of both the external X-ray field and the coupling to the core hole created in the absorption process. These effects require a theory that goes beyond the independent-electron approximation. We developed an efficient approach for treating such effects in molecules and solids based on a generalization of time-dependent density functional theory (TDDFT), with a local approximation for the screening response. The approach has been implemented in our self-consistent, real-space Green's function code FEFF8 in terms of screened dipole transition matrix elements. Typical results are discussed for the XAS of the N4,5 edges of solid Xe and for the L2,3 edges of 3d transition metals. Our approach accounts for the deviations of the L3/L2 intensity branching ratio from the 2:1 value of the independent electron approximation. For the N4,5 edges of Xe, the approach also accounts for the observed fine structure. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003 [source] X-ray absorption by macromolecular crystals: the effects of wavelength and crystal composition on absorbed doseJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 4 2004James W. Murray Radiation damage restricts the useful lifetime for macromolecular crystals in the X-ray beam, even at cryotemperatures. With the development of structural genomics pipelines, it will be essential to incorporate projected crystal lifetime information into the automated data collection software routines. As a first step towards this goal, a computer program, RADDOSE, is presented which is designed for use by crystallographers in optimizing the amount of data that can be obtained from a particular cryo-cooled crystal at synchrotron beamlines. The program uses the composition of the crystal and buffer constituents, as well as the beam energy, flux and dimensions, to compute the absorption coefficients and hence the theoretical time taken to reach an absorbed dose of 2,×,,Gy, the so-called `Henderson limit'. At this dose, the intensity of the diffraction pattern is predicted to be halved. A `diffraction,dose efficiency' quantity is introduced, for the convenient comparison of absorbed dose per diffracted photon for different crystals. Four example cases are considered, and the implications for anomalous data collection are discussed in the light of the results from RADDOSE. [source] Search for occult secondary osteoporosis: impact of identified possible risk factors on bone mineral densityJOURNAL OF INTERNAL MEDICINE, Issue 5 2002H. A. Deutschmann Abstract. Deutschmann HA, Weger M, Weger W, Kotanko P, Deutschmann MJ, Skrabal F (Krankenhaus der Barmherzigen Brüder, Marschallgasse, Teaching Hospital of the Karl-Franzens University Graz, Austria). Search for occult secondary osteoporosis: impact of identified possible risk factors on bone mineral density. J Intern Med 2002; 252: 389,397. Objectives. To determine whether the use of more elaborate diagnostic tests can identify possible risk factors for secondary osteoporosis and to evaluate the impact of these possible risk factors on the severity of bone disease in the study population. Design. Cross-sectional study. Setting and participants. ,We have investigated 377 subjects (285 females, 92 males) with osteoporosis (T-score less than ,2.5 in dual energy X-ray absorption) or nontraumatic lumbar vertebral fractures; these patients were referred to our hospital, a secondary care centre, for evaluation and treatment of osteoporosis. Results. Osteoporosis without attributable risk factor was diagnosed in 106 women (37%) and 30 men (33%). In 241 patients (179 women, 62 men) one or more possible risk factors for osteoporosis (in this paper also called subclinical disease) were revealed. The most common were lactose malabsorption, disturbed exocrine pancreatic function and renal tubular disturbances, including renal hypercalciuria, incomplete renal tubular acidosis and mild phosphate diabetes. The number of possible risk factors in the individual patient was significantly related to the severity of osteoporosis as assessed by Z-scores (Spearman correlation r = ,0.43, P < 0.001, n = 172 for females; r = ,0.28, P < 0.05, n = 65 for males). Conclusions. All the identified subclinical diseases would have remained undetected if the currently accepted guidelines for the investigation of patients with osteoporosis were applied. The statistically significant correlation between the number of identified possible risk factors and the severity of bone disease in the individual patient strongly suggests the pathogenetic significance of the identified subclinical diseases. It is yet to be shown, whether specific treatment of these subclinical diseases yields additional improvement of bone mass as compared with standard treatment of osteoporosis. [source] Combining two structural techniques on the micrometer scale: micro-XAS and micro-Raman spectroscopyJOURNAL OF SYNCHROTRON RADIATION, Issue 5 2007V. Briois X-ray absorption and Raman spectroscopies are complementary in the sense that both give very precise information about the local structure of a sample, both are not restricted to crystalline materials, and in both cases the volumes of the material probed are similar. The X-ray technique has the advantage of being element- and orbital-selective, and sensitive to orientational effects owing to polarization selection rules. In many cases, however, its analysis can present some ambiguity. Combining the two techniques on a micrometer scale could therefore be a very powerful method structurally. In this paper the experimental set-up developed at the LUCIA beamline and its application to a natural mineral are described. [source] X-ray birefringence and dichroism obtained from magnetic materialsJOURNAL OF SYNCHROTRON RADIATION, Issue 4 2001S. W. Lovesey In the past decade, synchrotron radiation has triggered a surge in studies of the polarization dependence of X-ray beams passing through non-isotropic materials. A vast range of experimental results concerning polarization-dependent absorption (dichroism) and dispersion (birefringence, for example) are available from materials which are either magnetic or exhibit preferred directions due to the local atomic environment. This article aims to bring together the diversity of modern experiments in this field with established methods of optical calculus, in a way that highlights the simplicity of the underlying physics. A useful framework is formed when observable quantities, in the X-ray case, are related to atomic variables of the sample material. Atomic descriptions of absorption spectra with various levels of complexity are considered, and some well documented sum-rules are encountered. The framework is the most general allowed within the electric dipole approximation. By way of illustration, dichroic X-ray absorption by two materials with highly anisotropic properties and magnetic ions with different valence shells are considered; namely, a 3d -transition ion in ferrous niobate, and a lanthanide ion in dysprosium borocarbide. Both materials display interesting magnetic properties that are challenging to interpret at an atomic level of detail, and it is shown how absorption experiments can contribute to resolving some issues. [source] Time-resolved measurements of supersonic fuel sprays using synchrotron X-raysJOURNAL OF SYNCHROTRON RADIATION, Issue 6 2000Christopher F. Powell A time-resolved radiographic technique has been developed for probing the fuel distribution close to the nozzle of a high-pressure single-hole diesel injector. The measurement was made using X-ray absorption of monochromatic synchrotron-generated radiation, allowing quantitative determination of the fuel distribution in this optically impenetrable region with a time resolution of better than 1,µs. These quantitative measurements constitute the most detailed near-nozzle study of a fuel spray to date. [source] Organic matter from comet 81P/Wild 2, IDPs, and carbonaceous meteorites; similarities and differencesMETEORITICS & PLANETARY SCIENCE, Issue 10 2009S. Wirick Sections were analyzed using a scanning transmission X-ray microscope (SXTM) and carbon X-ray absorption near edge structure (XANES) spectra were collected. We compared the carbon XANES spectra of these Wild 2 samples with a database of spectra on thirty-four interplanetary dust particles (IDPs) and with several meteorites. Two of the particles analyzed are iron sulfides and there is evidence that an aliphatic compound associated with these particles can survive high temperatures. An iron sulfide from an IDP demonstrates the same phenomenon. Another, mostly carbon free containing particle radiation damaged, something we have not observed in any IDPs we have analyzed or any indigenous organic matter from the carbonaceous meteorites, Tagish Lake, Orgueil, Bells and Murchison. The carbonaceous material associated with this particle showed no mass loss during the initial analysis but chemically changed over a period of two months. The carbon XANES spectra of the other four particles varied more than spectra from IDPs and indigenous organic matter from meteorites. Comparison of the carbon XANES spectra from these particles with 1. the carbon XANES spectra from thirty-four IDPs (<15 micron in size) and 2. the carbon XANES spectra from carbonaceous material from the Tagish Lake, Orgueil, Bells, and Murchison meteorites show that 81P/Wild 2 carbon XANES spectra are more similar to IDP carbon XANES spectra then to the carbon XANES spectra of meteorites. [source] Iron oxidation state in impact glass from the K/T boundary at Beloc, Haiti, by high-resolution XANES spectroscopyMETEORITICS & PLANETARY SCIENCE, Issue 11 2005Gabriele Giuli The samples have been analyzed by Fe K-edge high-resolution X-ray absorption near edge structure (XANES) spectroscopy to obtain data on both the Fe oxidation state and the coordination number. The pre-edge peak of our high-resolution XANES spectra display noticeable variations indicative of significant changes in the Fe oxidation state spanning a wide range from about 20 to 75 mol% trivalent Fe. All data plot along the same trend, falling between two mixing lines joining a point calculated as the mean of a group of tektites studied so far (consisting of four- and five-coordinated Fe2+) to [4]Fe3+ and [5]Fe3+, respectively. Thus, the XANES spectra can be interpreted as a mixture of [4]Fe2+, [5]Fe2+, [4]Fe3+, and [5]Fe3+. There is no evidence for six-fold coordinated Fe; however, its presence in small amounts cannot be excluded from XANES data alone. Our observations can be explained by two possible scenarios: either these impact glasses formed under very reducing conditions and, because of their small size, were easily oxidized in air while still molten, or they formed under a variety of different oxygen fugacities resulting in different Fe oxidation states. In the first case, the oxidation state and coordination number would imply similar formation conditions as splash-form tektites, followed by progressive oxidation. [source] Differences in X-ray absorption due to cadmium treatment in Saponaria officinalis leavesMICROSCOPY RESEARCH AND TECHNIQUE, Issue 1 2004Lucia Reale Abstract A method for detecting cadmium uptake in leaves of Saponaria officinalis doped with a solution of cadmium acetate is described. The technique based on the exposure of dried leaves to X-rays of a wavelength close to that of the metal K-edge could be useful for phytoremediation studies as it could reveal the bioaccumulation in plants due to the treatment either in vivo or in vitro with heavy metals. X-ray microradiography measurements are in agreement with those from peroxidase enzyme assay utilized to follow the oxidative damage induced by heavy metals. At present, as we will see in this report, microradiography has still poorer sensitivity in comparison with enzyme assay, but it has the advantage of being faster, not destructive, and usable even at very high doping levels, where the enzyme assay technique results are fully saturated. Further analysis of the optical density values could lead to a quantitative measurement of the heavy metal in the sample. Thus, the technology developed in this article could be useful for tracing the intake in phytoremediation studies. Microsc. Res. Tech. 64:21,29, 2004. © 2004 Wiley-Liss, Inc. [source] The XMM-SSC survey of hard-spectrum XMM,Newton sources , I. Optically bright sourcesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2007M. J. Page ABSTRACT We present optical and X-ray data for a sample of serendipitous XMM,Newton sources that are selected to have 0.5,2 versus 2,4.5 keV X-ray hardness ratios which are harder than the X-ray background. The sources have 2,4.5 keV X-ray flux ,10,14 erg cm,2 s,1, and in this paper we examine a subsample of 42 optically bright (r < 21) sources; this subsample is 100 per cent spectroscopically identified. All but one of the optical counterparts are extragalactic, and we argue that the single exception, a Galactic M star, is probably a coincidental association rather than the correct identification of the X-ray source. The X-ray spectra of all the sources are consistent with heavily absorbed power laws (21.8 < log NH < 23.4), and all of them, including the two sources with 2,10 keV intrinsic luminosities of <1042 erg s,1, appear to be absorbed active galactic nuclei (AGN). The majority of the sources show only narrow emission lines in their optical spectra, implying that they are type 2 AGN. Three sources have 2,10 keV luminosities of >1044 erg s,1, and two of these sources have optical spectra which are dominated by narrow emission lines, that is, are type 2 QSOs. Only a small fraction of the sources (7/42) show broad optical emission lines, and all of these have NH < 1023 cm,2. This implies that ratios of X-ray absorption to optical/ultraviolet extinction equivalent to >100 times the Galactic gas-to-dust ratio are rare in AGN absorbers (at most a few per cent of the population), and may be restricted to broad absorption line QSOs. Seven objects appear to have an additional soft X-ray component in addition to the heavily absorbed power law; all seven are narrow emission-line objects with z < 0.3 and 2,10 keV intrinsic luminosities <1043 erg s,1. We consider the implications of our results in the light of the AGN unified scheme. We find that the soft components in narrow-line objects are consistent with the unified scheme provided that >4 per cent of broad-line AGN (BLAGN) have ionized absorbers that attenuate their soft X-ray flux by >50 per cent. In at least one of the X-ray-absorbed BLAGN in our sample the X-ray spectrum requires an ionized absorber, consistent with this picture. [source] XMM,Newton observations of GB B1428+4217: confirmation of intrinsic soft X-ray absorptionMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2004M. A. Worsley ABSTRACT We report the results of XMM,Newton observations of the X-ray bright, radio-loud blazar GB B1428+4217 at a redshift of z= 4.72. We confirm the presence of soft X-ray spectral flattening at energies ,0.7 keV as reported in previous ROSAT and BeppoSAX observations. At hard X-ray energies, the spectrum is consistent with a power law, although we find that the spectral slope varied between both XMM,Newton observations and it is also significantly different from that reported previously. Whilst we cannot rule out intrinsic cold absorption to explain the spectral depression, we favour a dust-free warm absorber. Cold absorption requires a column density ,1.4,1.6 × 1022 cm,2, whilst a warm absorber could have up to ,1023 cm,2 and an ionization parameter ,102. The spectrum of GB B1428+4217 shows remarkable parallels with that of the z= 4.4 blazar PMN J0525,3343, in which the available evidence is also most consistent with a warm absorber model. [source] Electronic state of carbon in carbonaceous chondrite meteoritesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 11 2007A. V. Okotrub Abstract Electronic state of carbon occurred in the carbonaceous chondrite meteorites has been probed using X-ray emission (XES), X-ray absorption (XAS), and X-ray photoelectron (XPS) spectroscopy. The XES and XAS spectra of seven meteorites Orgueil, Mighei, Murchison, Murray, Staroe Boriskino, Isna, and Kainsaz were compared to the graphite and detonation nanodiamonds spectra. The carbon in the meteorites was found to be presented by the graphite-like component mainly, which ratio to the diamond-like component decreases with the meteorite age. The strong charging effect was found in the XPS C 1s-spectra of the youngest meteorites Kainsaz and Isna that can be due to encapsulation of nanocarbon granules within the dielectric silicate matrix. The presence of the letter species in the chondrites was supported by Raman spectroscopy. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Spin-polarized XANES: theoretical analysis of the Ni K-edge of NiF2PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 15 2005G. Smolentsev Abstract Theoretical interpretations of spin-dependent X-ray absorption near edge structure (XANES) spectra measured by selectively monitoring of the Ni K-beta emission while scanning the excitation energy through the Ni K absorption edge have been performed. Analysis is based on a combination of self-consistent spin-polarized calculation of muffin-tin potential and a full multiple scattering theory of X-ray absorption. This approach allows us to separate the influence of dipole transition matrix elements and the density of empty electronic states on spin-dependent XANES. It is found that the matrix elements affect splitting between spin-up and spin-down spectra only near the absorption threshold, while differences in densities of states slightly shift the spectra in the region 25,35 eV above the main edge. The effects of the multielectron-term-dependent broadening of spin-dependent XANES and mixing of purely spin-polarized spectra were taken into account. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] VUV-ellipsometry on GaN: Probing conduction band properties by core level excitationsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 13 2005N. Esser Abstract Spectral ellipsometry is a widely used method for analysing optical properties of materials. In particular electronic interband transitions of many semiconductor materials have been intensively studied employing ellipsometry from the near-infrared to the ultra-violet (UV) spectral range. Electronic excitations involving core-levels, on the other hand, have been a domain of synchrotron based X-ray absorption spectroscopy or electron loss spectroscopy. We apply spectral ellipsometry in the vacuum-UV spectral range to study core level excitations in GaN. The results proof that VUV-ellipsometry is a very versatile tool to obtain information on the p-like component of the density of states (DOS) related to the conduction bands of GaN. Excitations of the 3d core level of Ga are shown to be linked to the partial DOS at the Ga site within the lattice (complementary to the information obtained on nitrogen sites by X-ray absorption at the N1s edge). (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Study of metal-oxide-semiconductor capacitors with r.f. magnetron sputtering TiOxNy films dielectric layerPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3-4 2010Katia Franklin Albertin Abstract A set of MOS capacitors with TiOxNy films as gate dielectric layer was fabricated and characterized. The TiOxNy films were deposited by reactive r.f. magnetron sputtering varying the nitrogen and oxygen partial pressure in a Ar/N2/O2 gaseous mixture. The TiOxNy films were characterized by, Rutherford Backscattering (RBS), X-ray absorption near edge spectroscopy (XANES) in oxygen K-edge (O-K), optical absorption and High Resolution Transmission Electron Microscopy (HRTEM). Capacitance-voltage (1MHz) and current-voltage measurements were performed to obtain the effective dielectric constant, the effective oxide thickness (EOT), the leakage current density, and the interface quality. MOS capacitors results show that the TiOxNyfilms dielectric constant varies from 28 to 80, present a good interface quality with silicon, and the leakage current density values are in the order of 0.25 mA/cm2 for VG = ,2V, which is acceptable for high performance logic circuits and low power circuits fabrication. The leakage current density is reduced in 2 orders of magnitude for increasing nitrogen concentration (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Impact of Annealing on the Conductivity of Amorphous Carbon Films Incorporating Copper and Gold Nanoparticles Deposited by Pulsed Dual Cathodic ArcPLASMA PROCESSES AND POLYMERS, Issue S1 2009Jose Luis Endrino Abstract The influence of annealing in argon at 300,°C on the conductivity, phase stability and electronic structure of hydrogen-free amorphous carbon (a-C) films containing copper (a-C:Cu) and gold (a-C:Au) nanoclusters was investigated. The motivation of this work is twofold: (1) to study the thermal stability of a-C:Cu and a-C:Au films and (2) to point out the relevance of X-ray absorption near edge structure (XANES) technique to study the structural evolution of metal-doped a-C nanocomposites. The films were produced at room temperature using a selective-bias pulsed dual-cathode arc deposition technique. Compositional analysis was performed with secondary neutral mass spectroscopy whereas grazing incidence X-ray diffraction (GIXRD) was used to monitor phase transformation and identify the dispersion or agglomeration of the crystallites within the carbon matrix. XANES spectra at the C-K was used to investigate the effect of annealing in argon on the electronic structure of the a-C matrix, while Cu K and Au L-edges were investigated on a-C:Cu and a-C:Au samples, respectively, to study the nanocluster evolution. XANES showed that the a-C host matrix increased its graphitic character and that stress was relieved upon annealing. No relevant changes were observed in the Au arrangements in a-C:Au films. In the case of the a-C:Cu samples, the Cu-K XANES spectra indicated the formation of Cu2O crystals which correlated well with GIXRD spectra and the decrease in conductivity. [source] Analysis of multiple crystal forms of Bacillus subtilis BacB suggests a role for a metal ion as a nucleant for crystallizationACTA CRYSTALLOGRAPHICA SECTION D, Issue 5 2010M. Rajavel Bacillus subtilis BacB is an oxidase that is involved in the production of the antibiotic bacilysin. This protein contains two double-stranded ,-helix (cupin) domains fused in a compact arrangement. BacB crystallizes in three crystal forms under similar crystallization conditions. An interesting observation was that a slight perturbation of the crystallization droplet resulted in the nucleation of a different crystal form. An X-ray absorption scan of BacB suggested the presence of cobalt and iron in the crystal. Here, a comparative analysis of the different crystal forms of BacB is presented in an effort to identify the basis for the different lattices. It is noted that metal ions mediating interactions across the asymmetric unit dominate the different packing arrangements. Furthermore, a normalized B -factor analysis of all the crystal structures suggests that the solvent-exposed metal ions decrease the flexibility of a loop segment, perhaps influencing the choice of crystal form. The residues coordinating the surface metal ion are similar in the triclinic and monoclinic crystal forms. The coordinating ligands for the corresponding metal ion in the tetragonal crystal form are different, leading to a tighter packing arrangement. Although BacB is a monomer in solution, a dimer of BacB serves as a template on which higher order symmetrical arrangements are formed. The different crystal forms of BacB thus provide experimental evidence for metal-ion-mediated lattice formation and crystal packing. [source] Natural and Prosthetic Heart Valve Calcification: Morphology and Chemical Composition CharacterizationARTIFICIAL ORGANS, Issue 4 2010Raquel F. Weska Abstract Calcification is the most common cause of damage and subsequent failure of heart valves. Although it is a common phenomenon, little is known about it, and less about the inorganic phase obtained from this type of calcification. This article describes the scanning electron microscopy (SEM)/energy dispersive X-ray spectroscopy and Ca K -edge X-ray absorption near edge structure (XANES) characterization performed in natural and bioprosthetic heart valves calcified in vivo (in comparison to in vitro-calcified valves). SEM micrographs indicated the presence of deposits of similar morphology, and XANES results indicate, at a molecular level, that the calcification mechanism of both types of valves are probably similar, resulting in formation of poorly crystalline hydroxyapatite deposits, with Ca/P ratios that increase with time, depending on the maturation state. These findings may contribute to the search for long-term efficient anticalcification treatments. [source] Structure determination of a novel protein by sulfur SAD using chromium radiation in combination with a new crystal-mounting methodACTA CRYSTALLOGRAPHICA SECTION D, Issue 8 2005Yu Kitago A novel and easy crystal-mounting technique was developed for the sulfur SAD method using Cr,K, radiation (2.29,Å). Using this technique, the cryo-buffer and cryoloop around the protein crystal can be removed before data collection in order to eliminate their X-ray absorption. The superiority and reproducibility of the data sets with this mounting technique were demonstrated using tetragonal hen egg-white lysozyme crystals. The structure of a novel protein, PH1109, from Pyrococcus horikoshii OT3 was solved using this technique. At the wavelength of Cr,K, radiation, the anomalous signal ,|,F|,/,|F|, of PH1109 is expected to be 1.72% as this protein of 144 residues includes four methionines and two cysteines. Sulfur SAD phasing was performed using SHELXD and SHELXE. In the case of the data set obtained using this novel crystal-mounting technique, 54.9% of all residues were built with side chains automatically by RESOLVE. On the other hand, only 16.0% were built with side chains for the data set collected using the standard cryoloop. These results indicated that this crystal-mounting technique was superior to the standard loop-mounting method for the measurement of small anomalous differences at longer wavelength and yielded better results in sulfur-substructure solution and initial phasing. The present study demonstrates that the sulfur SAD method with a chromium source becomes enhanced and more practical for macromolecular structure determination using the new crystal-mounting technique. [source] Spectroscopic Characteristics of Differently Produced Single-Walled Carbon NanotubesCHEMPHYSCHEM, Issue 13 2009Zhongrui Li Prof. Dr. Abstract Single-walled carbon nanotubes (SWNTs) synthesized with different methods are investigated by using multiple characterization techniques, including Raman scattering, optical absorption, and X-ray absorption near edge structure, along with X-ray photoemission by following the total valence bands and C 1s core-level spectra. Four different SWNT materials (produced by arc discharge, HiPco, laser ablation, and CoMoCat methods) contain nanotubes with diameters ranging from 0.7 to 2.8 nm. The diameter distribution and the composition of metallic and semiconducting tubes of the SWNT materials are strongly affected by the synthesis method. Similar sp2 hybridization of carbon in the oxygenated SWNT structure can be found, but different surface functionalities are introduced while the tubes are processed. All the SWNTs demonstrate stronger plasmon resonance excitations and lower electron binding energy than graphite and multiwalled carbon nanotubes. These SWNT materials also exhibit different valence-band X-ray photoemission features, which are considerably affected by the nanotube diameter distribution and metallic/semiconducting composition. [source] | ||||||||||||||||