scispace - formally typeset
Search or ask a question

Showing papers on "Absorption spectroscopy published in 2003"


Journal ArticleDOI
TL;DR: In this article, it was shown that the lowest energy feature in the region of the absorption spectrum is associated with an interchain absorption, the intensity of which is correlated with the degree of order in the polymer.
Abstract: The absorption spectrum of polythiophene and its derivative poly(3-hexylthiophene) (P3HT) is usually described in terms of an intrachain exciton coupled to a single phonon mode. We show that this model is too simplistic for highly ordered, regioregular P3HT and that, analogous to the case of charged polarons in this material, interchain interactions must be taken into account to correctly describe the absorption spectrum. We show that the lowest energy feature in the $\ensuremath{\pi}\ensuremath{-}{\ensuremath{\pi}}^{*}$ region of the absorption spectrum is associated with an interchain absorption, the intensity of which is correlated with the degree of order in the polymer. Correspondingly, we show that the emission from P3HT also exhibits contributions from both interchain and intrachain states, in a manner similar to that recently shown for poly(phenylenevinylene). Having reinterpreted the physical origin of the features in the absorption and emission spectra of P3HT, we then model these spectra and show how they evolve as the degree of order in the polymer is changed by varying several physical parameters including temperature and regioregularity of the polymer.

908 citations


Journal ArticleDOI
TL;DR: In this paper, the authors present a re-analysis of the FD-excitation, absorption, reflection, and emission spectra of Eu2+ in inorganic compounds.

882 citations


Journal ArticleDOI
TL;DR: In this paper, the authors present an overview of the different relationships existing between IR spectra and microstructure of sol-gel silica films as they actually appear from current literature.
Abstract: Infrared (IR) spectroscopy is one of the most popular analytical techniques used to characterize sol-gel silica materials in their different stages. The method represents, in particular, a simple and versatile tool to investigate the microstructural evolution in gels and films, as a function of temperature and synthesis parameters. Several studies have shown that sol-gel IR absorption spectra exhibit, with respect to silica melt glass spectra, some specific features closely related to the peculiarities of sol-gel processing. Furthermore, because of the differences between silica bulk gels and films the spectra- microstructure correlation must be especially evaluated for thin films. IR spectroscopy has been used to evaluate residual porosity, Si-O-Si bonding rearrangements during drying and firing stages and to model the microstructure evolution during film processing. Some questions are still, however, arising around the interpretations of the IR spectra, in particular about the presence of cyclic species in the microstructure and disorder-induced vibrational modes. An attempt is made here to present an overview of the different relationships existing between IR spectra and microstructure of sol-gel silica films as they actually appear from current literature.

860 citations


Journal ArticleDOI
TL;DR: In this article, X-ray diffraction and transmission electron microscopy were used to characterize the structural properties of anatase nano-drone nano-dioxide and showed a blue shift in the absorption edge of the diffuse reflectance ultraviolet spectrum.

788 citations


Journal ArticleDOI
TL;DR: In this paper, the authors used the scanning imaging absorption spectrometer for atmospheric chartography (SCIAMACHY) pre-flight model satellite spectrometers to measure the gas-phase absorption spectra of the most important atmospheric trace gases (O3, NO2, SO2, O2, H2O, CO, CO2, CH4, and N2O) in the 230-2380 nm range at medium spectral resolution and at several temperatures between 203 and 293
Abstract: Using the scanning imaging absorption spectrometer for atmospheric chartography (SCIAMACHY) pre-flight model satellite spectrometer, gas-phase absorption spectra of the most important atmospheric trace gases (O3, NO2, SO2, O2, OClO, H2CO, H2O, CO, CO2, CH4, and N2O) have been measured in the 230–2380 nm range at medium spectral resolution and at several temperatures between 203 and 293 K. The spectra show high signal-to-noise ratio (between 200 up to a few thousands), high baseline stability (better than 10−2) and an accurate wavelength calibration (better than 0.01 nm) and were scaled to absolute absorption cross-sections using previously published data. The results are important as reference data for atmospheric remote-sensing and physical chemistry. Amongst other results, the first measurements of the Wulf bands of O3 up to their origin above 1000 nm were made at five different temperatures between 203 and 293 K, the first UV-Vis absorption cross-sections of NO2 in gas-phase equilibrium at 203 K were recorded, and the ultraviolet absorption cross-sections of SO2 were measured at five different temperatures between 203 and 296 K. In addition, the molecular absorption spectra were used to improve the wavelength calibration of the SCIAMACHY spectrometer and to characterize the instrumental line shape (ILS) and straylight properties of the instrument. It is demonstrated that laboratory measurements of molecular trace gas absorption spectra prior to launch are important for satellite instrument characterization and to validate and improve the spectroscopic database.

630 citations


Journal ArticleDOI
TL;DR: In this article, the photoreduction of silver ions by citrate, catalyzed on silver seeds, is used to synthesize disk-shaped silver nanoparticles in solution, characterized by transmission electron microscopy (TEM), atomic force microscopy, optical absorption spectroscopy, and by measuring the silver ion concentration during the reaction.
Abstract: The photoreduction of silver ions by citrate, catalyzed on silver seeds, is used to synthesize disk-shaped silver nanoparticles in solution. The reaction is characterized by transmission electron microscopy (TEM), atomic force microscopy (AFM), optical absorption spectroscopy, and by measuring the silver ion concentration during the reaction. The irradiation wavelength determines the final shape of these particles due to the shape dependence of the Ag plasmon spectrum. The quantum yield of this reaction has been calculated, and a growth mechanism is outlined.

473 citations


01 Jan 2003
TL;DR: In this paper, the size and shape effects in surface plasmon resonance have been studied and a growth mechanism was proposed for Ag particle growth from adsorbed Ag silver ions in the presence of citrate.
Abstract: The photoreduction of silver ions by citrate, catalyzed on silver seeds, is used to synthesize disk-shaped silver nanoparticles in solution. The reaction is characterized by transmission electron microscopy (TEM), atomic force microscopy (AFM), optical absorption spectroscopy, and by measuring the silver ion concentration during the reaction. The irradiation wavelength determines the final shape of these particles due to the shape dependence of the Ag plasmon spectrum. The quantum yield of this reaction has been calculated, and a growth mechanism is outlined. Introduction. Silver particles provide an ideal system for study of size and shape effects in the surface plasmon resonance; indeed, this sensitivity is a tool to monitor the shape of the particles during their synthesis via the optical extinction spectrum. Plasmon resonances concentrate an incident electromagnetic field via near-field enhancement; this antenna effect is the source of surface enhanced Raman scattering (SERS). The intense Ag resonance allows single molecule observation in SERS, 1-5 enables coupled Ag particles to form a subwavelength waveguide, 6 and enables sensitive colorimetric DNA screening. 7,8 Henglein 9,10 has shown that the physical and chemical properties of finely divided, nm-sized Ag particles are strongly modified by the adsorption of nucleophilic species and that Ag particles catalyze thermal and optical electro- chemical reactions. For example, core/shell metallic particles can be grown. 11 Indeed, adsorption of chemical species modifies the Fermi level of both the metal and the reactant, like a polarized nanoelectrode. Combining these effects, we now report controlled pho- tochemical Ag particle growth from adsorbed Ag silver ions in the presence of citrate. If different shapes and sizes are present in a seed colloid, the particle with the largest plasmon absorption cross-section at the laser wavelength initially grows fastest. The reaction accelerates for those shapes whose plasmons move into resonance with the photochemical wavelength as growth occurs. This effect allows control of shape in the dominant photoproduct by choice of photo- chemical wavelength. There have been previous observations of reduced silver formation by irradiation of citrate and Ag ion, however, without control of shape or size. 12,13

429 citations


Journal ArticleDOI
TL;DR: Initial observations in the application of femtosecond time-resolved absorption techniques to the study of the photophysics of transition metal complexes are described and examples detailing these dynamics as they occur in the charge-transfer excited states of transition-metal polypyridyl chromophores are included.
Abstract: Our research is concerned with the application of femtosecond time-resolved absorption techniques to the study of the photophysics of transition metal complexes. The focus is to understand the events that characterize the process of excited-state evolution from the time a photon is absorbed by a molecule to the formation of the lowest-energy excited state of the system. This Account describes our initial observations in this area and includes examples detailing these dynamics as they occur in the charge-transfer excited states of transition-metal polypyridyl chromophores.

379 citations


Journal ArticleDOI
TL;DR: The presented type of biosensing can be a cost-effective and easy to use alternative to conventional biosensing techniques, and also the interband absorption of the particles changes, will be demonstrated.
Abstract: The absorption spectrum of noble metal spherical nanoparticles is known to be strongly influenced by the dielectric constant of the surrounding material, and as such, these particles are well suited for biosensing applications. To perform biosensing using nanoparticles on a substrate, the metal particles are covalently attached onto quartz using an organic adhesion layer of mercaptosilanes. The particles in solution are characterized by UV-vis spectroscopy and transmission electron microscopy, while those attached to the quartz are characterized with UV-vis spectroscopy and atomic force microscopy. Antibodies are attached to the metal nanoparticles, and the antigen recognition is monitored via the change of light absorption when this binding event occurs. Not only is the absorbance originating from plasmon resonances of the particles influenced by the dielectric properties of molecules attached to the nanospheres but also the interband absorption of the particles changes, which will be demonstrated in this report. A light absorption change is detected when a molecular recognition occurs between the bioreceptor molecules attached to the nanoparticle and a biomolecular counterpart. This change in absorption can be very large when adhered molecules are at resonance (interband transitions). In addition, the presented type of biosensing can be a cost-effective and easy to use alternative to conventional biosensing techniques.

364 citations


Journal ArticleDOI
TL;DR: In this paper, the authors used terahertz time-domain spectroscopy to measure the full dielectric function of the monosaccharides glucose and fructose and the disaccharide sucrose in the frequency range 0.5-4.0 THz.

351 citations


Journal ArticleDOI
TL;DR: In this paper, the authors present x-ray absorption and emission experiments and ab initio calculations showing that the size of carbon diamond must be reduced to at least 2 nm in order to observe an increase of its optical gap, at variance with Si and Ge where quantum confinement effects persist up to 6-7 nm.
Abstract: We present x-ray absorption and emission experiments and ab initio calculations showing that the size of carbon diamond must be reduced to at least 2 nm, in order to observe an increase of its optical gap, at variance with Si and Ge where quantum confinement effects persist up to 6-7 nm. In addition, our calculations show that the surface of nanodiamond particles larger than approximately 1 nm reconstructs in a fullerenelike manner, giving rise to a new family of carbon clusters: bucky diamonds. Signatures of these surface reconstructions are compatible with pre-edge features observed in measured absorption spectra.

Journal ArticleDOI
TL;DR: In this article, a new highly sensitive method for incoherent broad-band cavity-enhanced absorption measurements of gaseous samples, using a white-light source is demonstrated.

Journal ArticleDOI
TL;DR: A combined Density Functional/Time Dependent Density functional study of the molecular structure, electronic states, and optical absorption spectrum of [Ru(4,4'-COOH-2,2'-bpy)(2)(NCS)(2)], a widely used charge-transfer sensitizer in nanocrystalline TiO(2) solar cells.
Abstract: We present a combined Density Functional/Time Dependent Density Functional study of the molecular structure, electronic states, and optical absorption spectrum of [Ru(4,4‘-COOH-2,2‘-bpy)2(NCS)2], a widely used charge-transfer sensitizer in nanocrystalline TiO2 solar cells. Calculations have been performed both for the complex in vacuo and in ethanol and water solvents, using a continuum model to account for solute−solvent interactions. Inclusion of the solvent leads to important changes of the energies and composition of the molecular orbitals of the complex; as a consequence, whereas the computed spectrum for the Ru-complex in vacuo deviates from the experimental one in both energy and shape, the spectra calculated in the presence of the solvent are in good agreement with the experiment. The first two absorption bands are found to originate from mixed ruthenium-NCS to bipyridine-π* transitions rather than to pure metal-to-ligand-charge-transfer (MLCT) transitions, whereas the third band arises from intra...

Journal ArticleDOI
TL;DR: The electrogenerated chemiluminescence (ECL) spectrum of CdSe/ZnSe nanocrystals (NCs) dispersed in a CH2Cl2 solution containing 0.1 M TBAP was obtained by stepping the potential between +2.3 and −2.
Abstract: The electrogenerated chemiluminescence (ECL) spectrum of CdSe/ZnSe nanocrystals (NCs) dispersed in a CH2Cl2 solution containing 0.1 M TBAP was obtained by stepping the potential between +2.3 and −2...

Journal ArticleDOI
TL;DR: The results confirm the previously proposed "exciplex" structure of the MLCT state in Lewis basic solvents and indicate that the amount of charge transferred from copper to the dmp ligand upon photoexcitation is similar to the charge difference at the copper center between the ground-state copper(I) and copper(II) complexes.
Abstract: The molecular structure and dynamics of the photoexcited metal-to-ligand-charge-transfer (MLCT) state of [CuI(dmp)2]+, where dmp is 2,9-dimethyl-1,10-phenanthroline, in acetonitrile have been investigated by time-domain pump-probe X-ray absorption spectroscopy, femtosecond optical transient spectroscopy, and density functional theory (DFT). The time resolution for the excited state structural determination was 100 ps, provided by single X-ray pulses from a third generation synchrotron source. The copper ion in the thermally equilibrated MLCT state has the same oxidation state as the corresponding copper(II) complex in the ground state and was found to be penta-coordinate with an average nearest neighbor Cu−N distance 0.04 A shorter than that of the ground state [CuI(dmp)2]+. The results confirm the previously proposed “exciplex” structure of the MLCT state in Lewis basic solvents. The evolution from the photoexcited Franck-Condon MLCT state to the thermally equilibrated MLCT state was followed by femtosec...

Journal ArticleDOI
TL;DR: The potential of modern XANES theory is demonstrated by presenting first simulations of the dichroism in the XANes spectra of the PSII manganese complex.
Abstract: X-ray absorption spectroscopy (XAS) has become a prominent tool for the element-specific analysis of transition metals at the catalytic center of metalloenzymes. In the present study the information content of X-ray spectra with respect to the nuclear geometry and, in particular, to the electronic structure of the protein-bound metal ions is explored using the manganese complex of photosystem II (PSIII) as a model system. The EXAFS range carries direct information on the number and distances of ligands as well as on the chemical type of the ligand donor function. For first-sphere ligands and second-sphere metals (in multinuclear complexes), the determination of precise distances is mostly straightforward, whereas the determination of coordination numbers clearly requires more effort. The EXAFS section starts with an exemplifying discussion of a PSII spectrum data set with focus on the coordination number problem. Subsequently, the method of linear dichroism EXAFS spectroscopy is introduced and it is shown how the EXAFS data leads to an atomic resolution model for the tetra-manganese complex of PSII. In the XANES section the following aspects are considered: (1) Alternative approaches are evaluated for determination of the metal-oxidation state by comparison with a series of model compounds. (2) The interpretation of XANES spectra in terms of molecular orbitals (MOs) is approached by comparative multiple-scattering calculations and MO calculations. (3) The underlying reasons for the oxidation-state dependence of the XANES spectra are explored. Furthermore, the potential of modern XANES theory is demonstrated by presenting first simulations of the dichroism in the XANES spectra of the PSII manganese complex.

Journal ArticleDOI
TL;DR: In this article, the reduction of diazonium salts in an aprotic medium permits the attachment of substituted aryl groups to a variety of metals: Co, Ni, Cu, Zn, Pt, and Au.
Abstract: The reduction of diazonium salts in an aprotic medium permits the attachment of substituted aryl groups to a variety of metals: Co, Ni, Cu, Zn, Pt, and Au. These aryl groups are strongly bonded to the metal as they resist sustained rinsing under sonication in organic solvents. The organic layers have been characterized by cyclic voltammetry, infrared reflection absorption spectroscopy, X-ray photoelectron spectroscopy, Rutherford backscattering, electrochemical impedance spectroscopy, and atomic force microscopy. From these data it is possible to propose a structure for these grafted layers.

Journal ArticleDOI
TL;DR: In this paper, concentrated citrate-reduced silver nanocolloids for use as pigments in ink-jet inks were prepared and X-ray diffraction pattern, optical properties (UV−visible spectroscopy), size and zeta potentials of the nanoparticles were studied.
Abstract: Stabilized concentrated citrate-reduced silver nanocolloids for use as pigments in ink-jet inks were prepared. Carboxymethyl cellulose was used as a polymeric stabilizer providing both electrostatic and steric stabilization. X-ray diffraction pattern, optical properties (UV−visible spectroscopy), size (TEM and dynamic light scattering), and zeta potentials of the nanoparticles were studied. It was shown that the product is silver with cubic symmetry. Absorption spectra are characterized, as a rule, by asymmetric absorption bands with maxima at 417−440 nm and shoulders at 350−352 and 380−382 nm. TEM images of unstabilized and stabilized colloids indicate the formation of nanoparticles of different shapes (spheres, hexagons, cubes, and rods) with rather wide size distribution in the range from several nanometers (spheres) up to several hundreds of nanometers (rods). CMC was found to be an effective stabilizer of silver nanoparticles, and the average particle size at CMC concentrations from 0.025 to 0.2 wt %...

Journal ArticleDOI
TL;DR: Transmission electron microscopy, atomic force microscopy and UV-vis-NIR absorption spectroscopy have revealed that deoxyribonucleic acid (DNA) molecules dissolve single-walled carbon nanotubes in an aqueous solution as mentioned in this paper.
Abstract: Transmission electron microscopy, atomic force microscopy, and UV-vis-NIR absorption spectroscopy have revealed that deoxyribonucleic acid (DNA) molecules dissolve single-walled carbon nanotubes in an aqueous solution.

Journal ArticleDOI
TL;DR: In this paper, the effects of the erbium concentration, crystal size, crystal phase, and different processing temperatures on the upconverted emission of Er3+ in BaTiO3 and TiO2 nanocrystals are reported.
Abstract: The effects of the erbium concentration, crystal size, crystal phase, and different processing temperatures on the upconverted emission of Er3+ in BaTiO3 and TiO2 nanocrystals are reported. A cw diode laser at 975 nm was used as a pump source for resonant sequential excitation of the 4I11/2 and 4F7/2 levels. Green and red upconversion emission at 550 and 670 nm were observed from these oxide nanocrystals with 975 nm excitation. With the same Er3+ concentration, the upconversion emission intensity from BaTiO3 was higher than that observed in the TiO2 host. In the TiO2 matrix, the maximum upconversion emission intensity of Er3+ was found for samples calcined at 800 °C where both the anatase and the rutile phases were present. The observed emission characteristics and the pump intensity dependence of the luminescence intensity confirm that the upconverted emission in these materials is produced by two-photon excited-state absorption (ESA) processes.

Journal ArticleDOI
TL;DR: In this paper, an observation of the broad absorption line (BAL) quasar PG 1115+080 performed with the XMM-Newton observatory reveals the second case of relativistic X-ray-absorbing outflow in a BAL quasar.
Abstract: We report on an observation of the broad absorption line (BAL) quasar PG 1115+080 performed with the XMM-Newton observatory. Spectral analysis reveals the second case of a relativistic X-ray-absorbing outflow in a BAL quasar. The first case was revealed in a recent observation of APM 08279+5255 with the Chandra X-Ray Observatory. As in the case of APM 08279+5255, the observed flux of PG 1115+080 is greatly magnified by gravitational lensing. The relatively high redshift (z = 1.72) of the quasar places the redshifted energies of resonant absorption features in a sensitive portion of the XMM-Newton spectral response. The spectrum indicates the presence of complex low-energy absorption in the 0.2-0.6 keV observed energy band and high-energy absorption in the 2-5 keV observed energy band. The high-energy absorption is best modeled by two Gaussian absorption lines with rest-frame energies of 7.4 and 9.5 keV. Assuming that these two lines are produced by resonant absorption due to Fe XXV Kα, we infer that the X-ray absorbers are outflowing with velocities of ~ 0.10c and ~ 0.34c, respectively. We have detected significant variability of the energies and widths of the X-ray BALs in PG 1115+080 and APM 08279+5255 over timescales of 19 and 1.8 weeks (proper time), respectively. The BAL variability observed from APM 08279+5255 supports our earlier conclusion that these absorbers are most likely launched at relatively small radii of 1016(Mbh/M8)1/2 cm. A comparison of the ionization properties and column densities of the low-energy and high-energy absorbers indicates that these absorbers are likely distinct; however, higher spectral resolution is needed to confirm this result. Finally, we comment on prospects for constraining the kinematic and ionization properties of these X-ray BALs with the next generation of X-ray observatories.

Journal ArticleDOI
TL;DR: In this article, a density functional approach was applied to three-dimensional crystallites of about 140 atoms, and the model clusters were chosen as octahedral fragments of the face centered cubic (fcc) bulk, exhibiting (111) and (001) facets.
Abstract: Adsorption of CO on nanosize Pd particles was studied theoretically by density functional method and spectroscopically by means of infrared reflection absorption spectroscopy (IRAS) and sum frequency generation (SFG). A density functional approach was applied to three-dimensional crystallites of about 140 atoms. The model clusters were chosen as octahedral fragments of the face centered cubic (fcc) bulk, exhibiting (111) and (001) facets. Bare and adsorbate-decorated cluster models were calculated with Oh symmetry constraints. Various types of adsorption sites were inspected: 3-fold hollow, bridge, and on-top positions at (111) facets; 4-fold hollow and on-top sites at (001) facets; bridge positions at cluster edges; on-top positions at cluster corners; and on single Pd atoms deposited at regular (111) facets. Adsorption properties of the relatively small regular cluster facets (111) and (001) are calculated similar to those of corresponding ideal (infinite) Pd surfaces. However, the strongest CO bonding...

Journal ArticleDOI
TL;DR: In this paper, the authors present near edge X-ray absorption spectra of manganese oxides at the Mn L2,3, Mn K, and O K edges to investigate the relative sensitivity of the edges to bonding and structure.
Abstract: We present near edge X-ray absorption spectra of manganese oxides at the Mn L2,3, Mn K, and O K edges to investigate the relative sensitivity of the edges to bonding and structure. Collectively, the spectra probe local electronic structure and intermediate range crystal structure. Spin independent full multiple scattering calculations of the Mn K edge give good agreement with data above threshold and qualitatively reproduce the prepeak that is observed for each compound. We show that the apparent prepeak for MnO is not due to p-d hybridization at the Mn atom (in accordance with symmetry principles) or quadrupolar transitions but originates from multiple scattering within the fifth shell. We present spin dependent multiple scattering calculations of the O K edge and show that this edge allows for a more direct description of the 3d states than either the Mn L edge or K edge prepeak, which are complicated by multiplet effects.

Journal ArticleDOI
TL;DR: In this paper, a (0001) wurtzite single-crystal structure with a rocking curve width of 0.98° was obtained from X-ray diffraction measurements.
Abstract: Epitaxial ZnO thin films doped with 7% Mn have been made by reactive rf magnetron sputtering onto (112_0) sapphire substrates at 400 °C. X-ray diffraction measurements reveal that the Zn0.93Mn0.07O film has a (0001) wurtzite single-crystal structure with a rocking curve width of 0.98°. UV–VIS absorption spectra show a band gap of 3.25 eV for pure ZnO films and 3.31 eV for the Zn0.93Mn0.07O film with states extending into the gap. The Auger electron spectroscopy shows homogeneous distribution of Mn in the film. The magnetic properties of the Zn0.93Mn0.07O film have been measured by a superconducting quantum interference device magnetometer at various temperatures with fields up to 5 T. No ferromagnetic ordering has been observed at temperature at 5 K. Instead, paramagnetic characteristics with a Curie–Weiss behavior have been observed.

Journal ArticleDOI
TL;DR: In this article, the effects of vibrational anharmonicity on the infrared spectra of polycyclic aromatic hydrocarbon molecules (PAHs) in the neutral and, particularly, cationic states were compared to density functional theory calculations.
Abstract: Infrared spectroscopy of a variety of interstellar sources shows strong mid-IR emission bands, which are generally attributed to emission from highly vibrationally excited polycyclic aromatic hydrocarbon molecules (PAHs) in the neutral and, particularly, cationic states. Over the past decade, various experimental methods have been developed to record the infrared spectra of cationic PAHs in the laboratory. In this paper, we discuss available experimental spectra obtained with matrix isolation spectroscopy (MIS), infrared multiple-photon dissociation of trapped ions (MPD), dissociation spectroscopy of ionic PAH van der Waals clusters (VDW), and infrared emission (IRE). Moreover, we compare these experimental spectra to density functional theory (DFT) calculations. The main body of experimental data relies on MIS and MPD spectra, and we present a detailed comparison of results from these methods, providing linear and multiple-photon absorption data, respectively. The effects of multiple-photon absorption, as encountered in MPD, and multiple-photon emission, occurring in interstellar spectra, are carefully assessed with the use of mathematical models, which include the effects of vibrational anharmonicity. We show that an analysis of the multiple-photon and linear data can provide important information on the anharmonicity parameters, which is otherwise difficult to attain. This is illustrated with a detailed comparison of the linear and multiple-photon absorption spectra of the naphthalene cation, yielding experimental anharmonicity parameters for the IR-active modes in the 500-1700 cm-1 range.

Journal ArticleDOI
TL;DR: In this paper, the local atomic environment of Cd bound to the cell wall of the gram-positive bacterium Bacillus subtilis was determined by X-ray absorption fine structure (XAFS) spectroscopy.

Journal ArticleDOI
TL;DR: In this paper, a new method for the synthesis of luminescent nano-sized particles is introduced, which is based on applying direct precipitation from high-boiling polyalcohol solutions.

Journal ArticleDOI
TL;DR: In this paper, structural and electronic investigations were conducted on lithium nickel oxide-based particles used in positive electrodes of 18650-type high-power Li-ion cells, and they identified a <5 nm thick modified layer on the surface of the oxide particles, which results from the loss of Ni and Li ordering in the layered R{bar 3}m structure.
Abstract: Structural and electronic investigations were conducted on lithium nickel oxide-based particles used in positive electrodes of 18650-type high-power Li-ion cells. K-edge X-ray absorption spectroscopy (XAS) revealed trivalent Ni and Co ions in the bulk LiNi{sub 0.8}Co{sub 0.2}O{sub 2} powder used to prepare the high power electrode laminates. Using oxygen K-edge XAS, high resolution electron microscopy, nanoprobe diffraction, and electron energy-loss spectroscopy, we identified a <5 nm thick modified layer on the surface of the oxide particles, which results from the loss of Ni and Li ordering in the layered R{bar 3}m structure. This structural change was accompanied by oxygen loss and a lowering of the Ni- and Co-oxidation states in the surface layer. Growth of this surface layer may contribute to the impedance rise observed during accelerated aging of these Li-ion cells.

Journal ArticleDOI
Abstract: We have investigated the local electronic and atomic structure of the LiMn0.5Ni0.5O2 electrode during the first charge and discharge process using in situ X-ray absorption spectroscopy (XAS) of the Mn and Ni K-edges. The Ni K-edge structure in the XANES spectrum shifts to higher energy during charge and shifts back reversibly during discharge in the higher voltage region of ∼4 V, whereas the Mn K-edge structure does not appear to exhibit a rigid edge shift. Further Li-ion intercalation during extended discharge in the 1-V plateau leads to the reduction of Mn4+ ions suggesting that the charge compensation in this region is achieved via the reduction of Mn4+ ions to Mn2+. Mn K-edge EXAFS results indicate that a small amount of Li is found in the Ni2+/Mn4+ layers. These Li ions in the transition metal layers are primarily present in the second coordination shell of Mn and not around Ni. Ni K-edge EXAFS fitting results suggest that the oxidation process upon Li deintercalation takes place in two steps: Ni2+ ...