Investigation on infrared laser absorption spectroscopy measurement of acetylene trace quantities

A laser-based infrared spectrometer was developed for use in high-resolution spectroscopic analysis of trace gases in the atmosphere. Continuous wave, broadly tunable coherent infrared radiation was generated from 8 to 19 μm in a gallium selenide crystal by laser difference-frequency mixing. Measurements of acetylene trace concentrations using laser absorption spectroscopy are reported. The measurements have been performed by using the P(21), Q(11), and R(9) lines of the ν₅ band, respectively, in order to investigate optimal detection conditions: a trade-off choice between higher line absorption strength for sensitive detection and better spectral discrimination from lines overlapping for open path trace-gas monitoring applications. Minimum detectable concentrations are compared under different experimental conditions. The ν₅ R(9) line seems to be close to optimum in terms of absorption strength and freedom from spectral interference for spectroscopic detection of acetylene trace concentration at atmospheric pressure.     

Near-edge X-ray absorption fine structure spectroscopy and structural properties of Ni-doped CeO2 nanoparticles

Ni-doped CeO₂ nanoparticles were prepared by using the co-precipitation method. The prepared nanoparticles were characterized using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, field emission scanning electron microscopy (FE-SEM) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. The XRD results infer that Ni-doped CeO₂ nanoparticles have single phase nature similar to that of pure CeO₂ nanoparticles. We have calculated lattice parameters using Powder-X software, particle size using Scherer’s formula and strain using the Williamson-Hall method for all the synthesized samples. We have observed a systematic decrease in the lattice parameters, particle size and strain with an increase in Ni doping in CeO₂. The FE-SEM micrographs also confirm that Ni-doped CeO₂ have nanocrystalline behavior and particles are spherical shaped. From the Raman spectra, it is observed that the intensity of classical CeO₂ vibration modes first increases then decreases with Ni doping. The NEXAFS spectra measured at Ce M_4,5 and Ni L_3,2 edges clearly indicate that Ce ions are in the +4 valence state and Ni ions are in the +2 valence state.     

The molecular orientation of DNA bases on H-passivated Si(1 1 1) surfaces investigated by means of near edge X-ray absorption fine structure spectroscopy

Layers of the DNA bases adenine, cytosine, and guanine were deposited onto hydrogen passivated Si(1 1 1) surfaces. The average tilt angles of these molecules with respect to the substrate surface were determined by the angular dependence of the Near Edge X-ray Absorption Fine Structure (NEXAFS) of the carbon K-edge. The interpretation of the NEXAFS spectra was assisted by a semi-empirical approach to the calculation of the π^∗-transition region which employs density functional theory calculations and core level photoemission data.     

C 1s near edge X-ray absorption fine structure (NEXAFS) of substituted benzoic acids—A theoretical and experimental study

Ab initio calculations are performed to explain the discrete transitions in experimental C 1s-NEXAFS (near edge X-ray absorption fine structure) spectra of various benzoic acid derivates. Transition energies and oscillator strengths of the contributing C 1s–π^* excitations are computed using the ADC(2) (second-order algebraic-diagrammatic construction) method. This method is demonstrated to be well suited for the finite electronic systems represented by these simple organic acids. There is good agreement between experiment and theory reproducing all the relevant spectral features. Some transitions can only be assigned based on a theoretical foundation. Remaining discrepancies between experimental and computed spectra are discussed.     

Quantitative depth profiling of photoacid generators in photoresist materials by near-edge X-ray absorption fine structure spectroscopy

Near-edge X-ray absorption fine structure (NEXAFS) spectroscopy was used to quantify the surface composition and depth profiling of photoacid generators in thin film photoresist materials by varying the entrance-grid bias of a partial electron yield detector. By considering model compositional profiles, NEXAFS distinguishes the surface molar excess within the top 6 nm from the bulk. A surface enriched system, triphenylsulfonium perfluorooctanesulfonate, is contrasted with a perfluorobutanesulfonate photoacid generator, which displays an appreciable surface profile within a 6 nm segregation length scale. These results, while applied to 193-nm photoresist materials, highlight a general approach to quantify NEXAFS partial electron yield data.     

Chemical states of nitrogen in ZnO studied by near-edge X-ray absorption fine structure and core-level photoemission spectroscopies

Interaction of low-energy nitrogen ions with ZnO surface has been studied by photoemission spectroscopy (PES) around N 1s core-level and near-edge X-ray absorption fine structure (NEXAFS) around N K-edge. Nitrogen can break Zn-O bonds at the surface and form N-O, Zn-N or Zn-N-O bonds, characterised by specific chemical shifts in PES or absorption peaks in NEXAFS. A distinctive signal from molecular nitrogen has also been observed in ion-bombarded samples in both NEXAFS and PES.     

Global fitting of line intensities of acetylene molecule in the infrared using the effective operator approach

The method of effective operators has been applied to the global fitting of line intensities of the acetylene molecule in the middle infrared. Simultaneous fittings of recently observed line intensities in the cold and hot bands lying in the 13.6, 7.8, and 5 μm regions have been performed. The eigenfunctions of the effective Hamiltonian developed for the global treatment of the vibration-rotation line positions of acetylene [O.M. Lyulin, V.I. Perevalov, S.A. Tashkun, J.-L. Teffo, in: Leonid N. Sinitsa (Ed.), 13th Symposium and School on High Resolution Molecular Spectroscopy, Proceedings of SPIE, vol. 4063, 2000, pp. 126-133] have been used in the calculations. The sets of effective dipole moment parameters obtained reproduce the observed line intensities within the experimental accuracy. The importance of l-type resonance, responsible for some large differences between intensities of the same lines in subbands having opposite parities, is exhibited and discussed.     

Theoretical studies on the near edge X-ray absorption fine structure spectra of a hexanethiolate monolayer on Ag(1 0 0)

A theoretical study on the S K-edge near edge X-ray absorption fine structure (NEXAFS) of a hexanethiolate monolayer on Ag(1 0 0) has been performed by employing the multiple-scattering cluster (MSC) method. The unoccupied molecular orbitals of the system, which are closely correlated with resonances of the NEXAFS spectra, have been calculated by using the discrete variational (DV)-Xα method. The physical origins of the resonances are elucidated by these theoretical studies. It has been shown that the leading peak at 2470.3 eV is not a π*(S–C), but a resonance corresponding to the transition of 1s electrons into a hybrid orbital of the S(3p) atomic orbital of a hexanethiolate molecule and Ag atomic orbitals. The interaction between the adsorbate and the substrate induces other two weak resonances at 2475.2 and 2478.2 eV in the NEXAFS. The adsorption structure of a hexanethiolate monolayer on Ag(1 0 0) deduced from the theoretical analysis on the NEXAFS is in agreement with that from the SEXAFS of the system.     

X-ray absorption near the edge structure and x-ray photoelectron spectroscopy studies on pyrite prepared by thermally sulfurizing iron films

This paper reports how pyrite films were prepared by thermal sulfurization of magnetron sputtered iron films and characterized by x-ray absorption near edge structure spectra and x-ray photoelectron spectroscopy on a 4B9B beam line at the Beijing Synchrotron Radiation Facility. The band gap of the pyrite agrees well with the optical band gap obtained by a spectrophotometer. The octahedral symmetry of pyrite leads to the splitting of the d orbit into t_{\rm 2g} and e_{\rm g} levels. The high spin and low spin states were analysed through the difference of electron exchange interaction and the orbital crystal field. Only when the crystal field splitting is higher than 1.5 eV, the two weak peaks above the white lines can appear, and this was approved by experiments in the present work.     

Study of metglas 2605 CO by extended and near edge X-ray absorption fine structure

Extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) studies of the transition metal sites in Metglas 2605 CO (Fe₆₇Co₁₈B₁₄Si₁) illustrate differences in the two sites. The average transition metal distance, obtained by standard EXAFS analysis, is larger for iron than for cobalt sites in this material. The XANES for Co and Fe are nearly identical except for a shift of the Co fine structure to high energy relative to that of Fe; the sign and magnitude of this shift is commensurate with the EXAFS results. Finally, there was no detected polarization dependence of the EXAFS, indicating that the structural manifestations of the magnetic anisotropy in this material are smaller than the detection limits of these experiments.     

Local coordination geometry around Cu and Cu ions in silicate glasses: an X-ray absorption near edge structure investigation

We present an X-ray absorption near edge structure (XANES) study on Cu⁺ and Cu²⁺ ions in silicate glasses at the Cu K-edge, aimed to determine the geometry of the local structure around the metal. This study is based on the comparison between experimental data and theoretical calculations made in the framework of multiple scattering theory. The XANES signals relative to several clusters are simulated on the basis of known crystalline structures involving Cu⁺ and Cu²⁺ ions in silicate matrices. Concerning the Cu²⁺ in glass, the simulations suggest the presence of a square coordination of oxygen atoms around the absorber, with a possible presence of metal ions in the second shell. As for the Cu⁺ ions, the metal clustering is excluded and a linear O-Cu-O coordination is evidenced. Received 30 April 1999     

Synchrotron radiation photoelectron spectroscopy and near-edge X-ray absorption fine structure study on oxidative etching of diamond-like carbon films by hyperthermal atomic oxygen

Surface structural changes of a hydrogenated diamond-like carbon (DLC) film exposed to a hyperthermal atomic oxygen beam were investigated by Rutherford backscattering spectroscopy (RBS), synchrotron radiation photoelectron spectroscopy (SR-PES), and near-edge X-ray absorption fine structure (NEXAFS). It was confirmed that the DLC surface was oxidized and etched by high-energy collisions of atomic oxygen. RBS and real-time mass-loss data showed a linear relationship between etching and atomic oxygen fluence. SR-PES data suggested that the oxide layer was restricted to the topmost surface of the DLC film. NEXAFS data were interpreted to mean that the sp² structure at the DLC surface was selectively etched by collisions with hyperthermal atomic oxygen, and an sp³-rich region remained at the topmost DLC surface. The formation of an sp³-rich layer at the DLC surface led to surface roughening and a reduced erosion yield relative to the pristine DLC surface.     

Intracavity laser absorption spectroscopy of platinum sulfide in the near infrared

A new electronic transition of PtS with a red degraded band head at 12 460 cm⁻¹ was recorded and analyzed. Gas phase PtS was produced in a platinum-lined hollow cathode with a trace of SF₆ gas, and the spectrum was recorded at near Doppler resolution using intracavity laser absorption spectroscopy. Molecular constants for the newly identified excited state are presented.     

Density functional theory study on the structural properties and energetics of microclusters

Density functional theory calculations with B3LYP exchange-correlation functional using CEP-121G basis set have been carried out in order to elucidate the structural properties and energetics of neutral zinc telluride clusters, Zn_mTe_n (m+n6), in their ground states. The geometric structures, binding energies, vibrational frequencies and infrared intensities, Mulliken charges on atoms, HOMO and LUMO energies, the most possible dissociation channels and their corresponding energies for the clusters have been considered.     

Organic functionalization of group IV semiconductor surfaces: principles, examples, applications, and prospects

Organic functionalization is emerging as an important area in the development of new semiconductor-based materials and devices. Direct, covalent attachment of organic layers to a semiconductor interface provides for the incorporation of many new properties, including lubrication, optical response, chemical sensing, or biocompatibility. Methods by which to incorporate organic functionality to the surfaces of semiconductors have seen immense progress in recent years, and in this article several of these approaches are reviewed. Examples are included from both dry and wet processing environments. The focus of the article is on attachment strategies that demonstrate the molecular nature of the semiconductor surface. In many cases, the surfaces mimic the reactivity of their molecular carbon or organosilane counterparts, and examples of functionalization reactions are described in which direct analogies to textbook organic and inorganic chemistry can be applied. This article addresses the expected impact of these functionalization strategies on emerging technologies in nanotechnology, sensing, and bioengineering.     

Electronic structure of Alq3 and Liq using soft X-ray spectroscopy and density functional theory calculation

The electronic structure of aluminum tris-8-hydroxyquinoline (Alq₃) and 8-hydroquinolatolithium (Liq) was investigated using a combination of X-ray emission spectroscopy (XES), X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), and spectral simulation with density functional theory. The chemical bonding states of Alq₃ and Liq were analyzed using XPS core-level spectra. The band gaps of Alq₃ and Liq were measured by combining the XAS and XES results. Additionally, resonant and non-resonant XES were used to measure the density of states for O sites in the molecules.     

X-ray absorption spectroscopy study and photocatalyst application of CuO and Cu0.9Ti0.1O nanoparticles

We report detailed investigations on the electronic structure and photocatalyst application of CuO and Cu_0.9Ti_0.1O nanoparticles (NPs). The NPs were prepared by co-precipitation method and subsequent annealing. Crystal structure and morphology of the NPs were investigated by synchrotron X-ray diffraction and high resolution transmission electron microscope, respectively. The local atomic structure around the Cu atoms was investigated by the extended X-ray absorption fine structure (EXAFS) at the Cu K-edge. Electronic structure determination was done using near edge X-ray absorption fine structure (NEXAFS) at the O K-edge, Cu L-edge, Cu K-edge and Ti L-edge. From the structural and electronic structure investigations, it is inferred that the Ti substitutes the Cu in CuO lattice without forming any secondary phases and the valence state of Cu is not affected by the Ti substitution; however the Cu – O bond length is found to be shorten in the Ti doped sample. As prepared NPs exhibit excellent photocatalyst application toward the degradation of methyl orange (MO) and potassium dichromate (PD) pollutant dyes under the visible light irradiation. The mechanism of the photodegradation of MO and PD pollutants, by the smaller sized CuO and larger sized Cu_0.9Ti_0.1O NPs, is briefly discussed.     

Influence of the geometric structure on the V L3 near edge X-ray absorption fine structure from vanadium phosphorus oxide catalysts

We present the V L₃ near edge X-ray absorption fine structure (NEXAFS) of a vanadium phosphorus oxide (VPO) catalyst. The spectrum is related to the V3d–O2p hybridised unoccupied states. The overall peak position at the V L₃-absorption edge is determined by the formal oxidation state of the absorbing vanadium atom. Details of the absorption fine structure are influenced by the geometric structure of the compound. Empirically we found a linear relationship between the energy position of several absorption resonances and the V–O bond length of the participating atoms. This allows identification of the contribution of specific V–O bonds to the near edge X-ray absorption fine structure. The bond length/resonance position relationship will be discussed under consideration of relations between geometric structure and NEXAFS features observed in X-ray absorption experiments and theory.     

Analysis of the X-ray absorption fine structure near the TiL 2, 3 edge in free titanium nanoclusters

A theoretical analysis is made of the experimental TiL _{2, 3} X-ray absorption near edge structure (XANES) spectra of free titanium nanoclusters containing 15–55 or 100–120 atoms. Good agreement between experimental and simulated data is obtained using the time-dependent local density approximation.     

Theoretical study of electronic structure, chemical bonding, and X-ray absorption near edge spectroscopy in niobium and niobium monoxide

In this work, we calculate band structures, the density of state and chemical bonding of the metallic niobium (Nb) and its mono-oxide (NbO) crystals in their solid states using the Density Functional Theory and X-ray Absorption Near Edge Spectroscopy. The electronic properties of Nb and NbO are investigated using the Finite Difference Method. These theoretical results are found in good agreement with the most recent experimental data. Our calculations reveal that the NbO crystal behaves like a superconductor.