Valence X-ray Photoelectron Spectra Research Articles

Analysis of AES of 2nd Period Element-containing Substances and Valence XPS of the Four Solid Ones by DFT Calculations Using the Model Molecules

Experimental Auger electron spectra (AES) of 2nd period elements and valence X-ray photoelectron spectra (VXPS) of four solid substances [LiF, graphite, GaN, SiO2] are analyzed by density-functional theory (DFT) calculations using the model molecules of the unit cell. For the calculations, we use Gaussian09 program at B3LYP/6-31G (d, p) level to estimate VXPS, core-electron binding energies, and (Li ~ F)-KVV AES of the solid substances. In the AES simulations, we evaluate theoretical kinetic energies of the AES with our modified calculation method. The modified kinetic energies correspond to the final-state holes at the ground state in DFT calculations. Simulated KVV AES of the (Li ~ O) atoms with the maximum kinetic energies of the atoms agree considerably well to the experimental AES results. Calculated VXPS of the four substances are also in good accordance with the experimental ones. The kinetic energy formula of AES at the ground state appears to work better, despite its great simplicity.

Analysis of valence XPS and AES of (PP, P4VP, PVME, PPS, PTFE) polymers by DFT calculations using the model molecules

We simulated valence X-ray photoelectron spectra (VXPS) of five [(CH2CH(CH3))n {poly(propyrene) PP}, ((CH2CH(C5NH4))n {poly(4-vinyl-pyridine) P4VP}, (CH2CHO(CH3))n {poly(vinyl methyl ether) PVME}, (C6H4S)n {poly(phenylene) sulphide PPS}, (CF2CF2)n {poly(tetrafluoroethylene) PTFE}] polymers by density-functional theory (DFT) calculations using the model oligomers. The spectra reflect the differences in the chemical structures between each polymer, since the peak intensities of valence band spectra are seen to be due to photo-ionization cross-section of (C, N, O, S, F) atoms by considering the orbital energies and cross-section values of the polymer models, individually. In the Auger electron spectra (AES) simulations, theoretical kinetic energies of the AES are obtained with our modified calculation method. The modified kinetic energies correspond to two final-state holes at the ground state and at the transition-state in DFT calculations, respectively. Experimental peaks of (C, N, O)- KVV, and S L2,3VV AES for each polymer are discussed in detail by our modified calculation method.

Analysis of valence XPS and AES of C, N, O, and F-containing substances by DFT calculations using the model molecules

Experimental valence X-ray photoelectron spectra (VXPS) and Auger electron spectra (AES) of (Li, C, N, O, F) elements of four solid substances [graphite, GaN, SiO2, LiF] are analyzed by density-functional theory calculations using the model molecules of the unit cell. For the calculations, we use deMon density functional theory (DFT) program to estimate VXPS, core-electron binding energies, and (Li, C, N, O, F)-KVV AES of the solid substances. In the AES simulations, we evaluate theoretical kinetic energies of the AES with our modified calculation method. The modified kinetic energies correspond to two final-state holes at the ground state and at the transition-state in DFT calculations, respectively. Experimental KVV AES of the (Li, C, N, O) atoms in the substances agree considerably well to simulation of AES obtained with the maximum kinetic energies of the atoms, while, the experimental F KVV AES of LiF is almost in accordance with the spectra from the transition-state kinetic energy calculations.

X‐ray photoelectron and carbon Kα emission measurements and calculations of O‐, CO‐, N‐, and S‐containing substances

AbstractX‐ray fluorescence measurements for O‐containing [polyethylene oxide, polyvinyl alcohol, polyvinyl methyl ether], CO‐containing [polyvinyl methyl ketone, polyethylene terephthalate], N‐containing [poly‐4‐vinylpyridine (P4VP), polyaniline oligomer (PAO)], and S‐containing [polyphenylene sulfide] substances are presented. Carbon Kα X‐ray emission spectra (XES) and X‐ray photoelectron spectra (XPS) are compared with our DFT calculations performed with the Amsterdam density functional (ADF) program. The combined analysis of valence XPS and carbon Kα XES allows us to determine the individual contributions from pσ‐ and pπ‐bonding molecular orbitals of the polymers. The ΔSCF calculations yield the accurate C1s core‐electron binding energies (CEBEs) for all carbon sites of the organic compound. We calculate all CEBEs of the model molecules using the ΔEKS approach. Our simulated C1s photoelectron and C Kα emission spectra are in good agreement with our measurements. We also obtain WD (work function and the other energies) values for the polymers and PAO from the difference between calculated (gas‐phase) and measured (solid) CEBE values. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 162–172, 2007

Analysis of X-ray photoelectron spectra of electrochemically prepared polyaniline by DFT calculations using model molecules

In order to clarify the electronic state of polyaniline synthesized electrochemically, we analyzed valence X-ray photoelectron spectra (XPS) and core-electron binding energies of N, N′-Diphenyl-1,4-phenylenediamine and polyaniline by deMon density-functional theory calculations (DFT) using the molecule and model molecule, respectively. Polyaniline has been synthesized electrochemically from two different thin films on platinum plates in oxidation and reduction states, respectively. Valence XPS of the conductive polymers were analyzed by deMon DFT calculations using model tetramers of the four chemical structural formulae (1S, 2S, 1A, and 2A) which MacDiarmid and co-workers proposed. We can conclude that the oxidized polyanililine corresponds to the 2A type, while the reduction form approximated the 1S type.

Analysis of Valence XPS of Hydrocarbon Polymers Modified by He-Ion Bombardment

Surface analysis of hydrocarbon polymers (polyethylene (PE), polypropylene (PP), polystyrene (PS)) by He-ion bombardment was performed from the theoretical and experimental valence X-Ray photoelectron spectra (XPS). The polymers were He-ion bombarded at an energy of 150 keV with fluences between 1 × 1012 and 1 × 1015 ions cm-2. The bombardment destroys the chemical bonds of the polymer surface and activates carbon atoms near the surfaces. They may produce radicals and recombine with oxygen in the residual gas and/or atmospheric oxygen. We consider that experimental results for valence XPS of the polymers due to the bombardment are simulated by deMon density-functional theory (DFT) calculations using the model trimers, or dimer of neutral, radical, cationized, and oxidized compounds.

Soft X-ray fluorescence measurements of polyimide films

Fluorescent X-ray emission spectroscopy has been used for the first time to study the electronic structure of polyimide films (PMDA-ODA) prepared on Si-substrates by spin-coating and ionized cluster beam deposition (ICBD) methods. The observed C Kα and O Kα X-ray emission spectra that probe the C 2p and O 2p partial density of states in the valence band, respectively, were compared with X-ray photoelectron valence band spectra. Theoretical simulations of X-ray energies and intensities for polyimide were performed with molecular orbital (MO) calculations of the model monomer, containing 41 atoms, utilizing a semi-empirical Hydrogenic Atoms in Molecules, V. 3 (HAM/3) method. Calculated Al Kα photoelectron spectra were obtained using Gaussian lineshape functions of an approximate linewidth (0.10 Ik for the model molecule): Ik=I′k−WD, as indicated for analysis of valence X-ray photoelectron spectra for 63 polymers from some of our previous work. Theoretical C Kα and O Kα X-ray emission and valence X-ray photoelectron spectra show good agreement with the experimental results, and were used to identify certain spectral features.

Theoretical Valence XPS and UV-Visible Absorption Spectra of Four Leuco Dyes Using MO Calculations

Abstract Semiempirical HAM/3 MO program was used to obtain the theoretical valence X-ray photoelectron spectra (XPS) of the two leuco dyes (2′-anilino-6′-diethylamino-3′-methylspiro[isobenzofuran-1(3H),9′-[9H]xanthene]-3-one (DEAMAF) and 3,3-bis(4-dimethylaminophenyl)-6-dimethylamino-1(3H)-isobenzofuranone (CVL)) and UV-visible adsorption spectra of the four leuco dyes (DEAMAF, CVL, 2′-chloro-6′-diethylamino-3′-methylspiro[isobenzofuran-1(3H),9′-[9H]xanthene]-3-one (DEAMCF), and 3′,6′-bis(diethylamino)-spiro[isobenzofuran-1(3H),9′-[9H]xanthene]-3-one (Rhodamine B base). The calculated Al Kα photoelectron spectra were obtained using Gaussian lineshape functions of an approximate linewidth 0.10Ek (Ek = Ek′ − WD), where E′k is the vertical ionization potential (VIP) of each MO and WD is a shift to account for sample work function, polarization energy and other energy effects. On the other hand, the absorption curves were simulated with Gaussian lineshape functions of a constant linewidth of 0.02 eV. The theoretical valence energy levels corresponded well to the spectra of two leuco dyes observed 0—40 eV, while the simulated adsorption spectra were shifted for a good fit with the experimental solution spectra in the range of 250—700 nm.

Analysis of valence XPS of (CH 2CHR) n (R = H, CH 3, OH and F), (CH 2CH 2NH) n and (CH 2CH 2O) n polymers by the semiempirical HAM/3 MO method using the n-mer ( n = 2, 3, 4, 5) model

The valence X-ray photoelectron spectra (XPS) of six representative polymers [CH 2CHR) n (RH, CH 3, OH, F), (CH 2CH 2NH) n and (CH 2CH 2O) n ] were analysed by a semi empirical HAM/3 MO method using model molecules [H(CH 2CHR) n H, (RH, CH 3, OH, F), H 2N(CH 2CH 2NH) n H, and HO(CH 2CH 2O) n H] with n = 2 to 5. The calculated AlK α photo electron spectra were obtained using Gaussian functions of an approximate linewidth (0.10 I k ); I k = I′ k − WD, where I′ k is the vertical ionization potential (VIP) of each MO and WD is a shift to account for sample work function, polarization energy and other effects. To explain the broader linewidth for the inner valence spectra, we propose that the lifetime of the 2s hole states are shorter because the holes can be filled by 2p electrons in ultra-violet emission or radiationless transition. The theoretical spectra showed good agreement with the observed spectra of the polymers between 0–40 eV. The present results suggest that the spectra can be analysed by the calculations for model trimers.

Simulation of the Valence X-Ray Photoelectron Spectra of 16 Polymers by the Semiempirical HAM/3 MO Method Using the Model Molecules

The HAM/3 method was used to provide a better assignment of the valence X-ray photoelectron spectra of 16 polymers involving nitrogen, oxygen, fluorine, a glucose unit, and a benzene nucleus using the monomer, dimer or trimer model molecules without consideration of the contraction factor of the energy scale. The calculated Al Kα photoelectron spectra were obtained using Gaussian functions of a fixed approximate linewidth, 0.10 Ik and Ik = I′k − WD, where I′k is the vertical ionization potential of each MO and WD is an approximate shift to account for the work function of the sample and other energy (polarization energy and so on) effects. We assumed that WD corresponds to the shift that we must apply before we can compare the calculated spectrum for the single model molecule with the observed spectrum for the solid. The approximate linewidth corresponds to the experimental result that the inner valence spectra are broader. The theoretical spectra showed good agreement with the spectra of the polymers obs...

Diagonal 2ph-TDA Green's function simulation of the valence X-ray photoelectron spectra of n-alkane compounds: a theoretical search for conformational signatures

With the aim of improving and validating theoretical quantum mechanical tools for tracking conformational signatures in the XPS spectra of n-alkane compounds, the XPS spectra of model structures are simulated by means of direct Green's function schemes and compared to available experimental records obtained in the gas and solid phases. Calculations are performed using the minimal STO-3G and 3-21G basis sets, and self-energy expansions derived at several levels of decoupling approximation: second-order, shifted Born collision (SBC) and diagonal two-particle—hole Tamm—Dankoff approximation (2ph-TDA). The latter scheme is shown to be accurate enough to generate reliable relative line positions and convoluted photoionization intensities in the inner valence region, which is of fundamental importance for the identification of secondary molecular structures from XPS spectra. Preventing overcounting of self-energy diagrams containing a diagonal ladder part is crucial in that respect. As a byproduct, this method of simulation is applied to some particular conformations of C 9H 20 modeling the topmost layer of polyethylene in crystalline form, enabling the identification of fold structures at the extreme surface of lamellar crystals of polyethylene.

Preliminary theoretical search for possible conformational signatures in the valence X-ray photoelectron spectra of ordered polyethylene surfaces

With the aim of searching for conformational signatures in polymer valence XPS spectra, exploratory ab initio STO-3G calculations have been performed on three conformations of n-C13H28. These structures are intended to model ideal polymer surfaces rich either in folds emerging perpendicularly to the basal plane or in zig-zag planar chains oriented parallel to the surface. The simulated spectra based on these calculations indicate that there is limited hope of relating valence XPS spectral features to conformational changes in saturated hydrocarbons.

Interstitial atoms in metal-metal bonded arrays: The synthesis and characterization of heptascandium decachlorodicarbide, Sc 7Cl 10C 2, and comparison with the interstitial-free Sc 7Cl 10

Reaction of Sc strips, ScCl/sub 3/, and graphite at 860-1000/sup 0/C gives Sc/sub 7/Cl/sub 10/C/sub 2/ in quantitative yields, with transport occurring at the higher temperatures; adventitious carbon will also produce the phase. The compound has been shown to be isostructural with Er/sub 7/I/sub 10/ by single-crystal X-ray diffraction (a = 18.620 (4) A, b = 3.4975 (6) A, c = 11.810 (2) A, ..beta.. = 99.81 (2)/sup 0/; space group C2/m, Z = 2, R = 0.029, R/sub w/ = 0.046 for 676 reflections, MoK..cap alpha.., 2 theta < 50/sup 0/). The phase contains double chains of condensed scandium octahedra sharing edges with a carbon approximately centered in each (anti d(Sc-C) = 2.31 A) together with isolated scandium atoms in a parallel chain of chloride octahedra. The arrangement is very similar to that in the previously known Sc/sub 7/Cl/sub 10/, from which the heavy atom arrangement can be derived by displacement of all metal atoms by b/2 so as to convert chlorine functions on the metal chain from face-capping to edge-bridging. The driving force for this is thought to be the reduction of carbon-chlorine repulsive interactions. Core and valence x-ray photoelectron spectra (XPS) for Sc/sub 7/Cl/sub 10/, Sc/sub 7/Cl/submore » 10/Cl/sub 2/, Sc/sub 2/Cl/sub 2/C, ScCl/sub 3/, and Sc are presented to demonstrate the appearance of a carbide-like state for the interstitial, the presence of two different types of scandium in the first two compounds, the oxidation of the chain that accompanies the carbon insertion, and a substantial Sc-C covalency. The latter arises through mixing of the interstitial's 2s and 2p valence orbitals with metal-metal bonding cluster orbitals of the same symmetry. 37 references, 6 figures, 7 tables.« less

Condensed five-membered heterocycles with potentialities as conducting polymers: ab initio electronic structures and theoretical valence X-ray photoelectron spectra

The electronic structures of pyrrolo-[2,3-b]- and -[3,2-b]-pyrroles, and the equivalent thienopyrroles and thienothiophenes have been investigated by MNDO and STO-3G ab initio calculations on model molecules. In agreement with previously reported u.v. photoelectron spectral data and semiempirical calculations, the [3,2-b] derivatives display lower ionization potentials than their [2,3-b] homologues. For two compounds, a discrepancy regarding the nature of the HOMO is found between these theoretical results and ours. As experimental X-ray photoelectron spectral data have to be obtained, simulated valence X-ray spectra based on the molecular intensity model proposed by Gelius have been calculated.

Electronic structure of uranium halides and oxyhalides in the solid state. An x-ray photoelectron spectral study of bonding ionicity

Core and valence X-ray photoelectron spectra of 18 uranium halides (U/sup 3 +/ to U/sup 5 +/) and oxyhalides (U/sup 3 +/ to U/sup 6 +/) (fluorides, chlorides, and bromides) are described. The results are discussed, as a function of halogen nature and compounds stoichiometry, in terms of ionicity of the bonds, of U 5f participation in bonding, and effect of oxygen. Evidence is produced that UF/sub 3/ has an unexpectedly strong covalent character. The experimental study of uranium halides (F, Cl, Br) and oxyhalides has brought to light some important information about the nature of chemical bonding in these compounds: (a) The combined examination of valence photoelectron peaks (particularly U 5f), core levels, and U 4f shake-up satellites is a powerful tool in the determination of the ionicity of the solid. Only core level chemical shifts are not sufficient by themselves. (b) There is evidence for U 5f participation in chemical bonding; this contribution increases when the compound becomes more covalent. (c) Ionicity is largest for the higher halides (higher uranium oxidation state) and with the more electronegative halogens; and exception to this rule is UF/sub 3/, which is more covalent than UCl/sub 3/. (d) The oxygen in oxyhalidesmore » shows a growing tendency to form uranyl groups, as the uranium oxidation state goes up. These uranyl groups have covalent bonding and behave as a single species vs. the halogen.« less

The Electronic Structures of Linear Dicyano Complexes

Abstract Molecular orbital (MO) calculations in the discrete variational Xα (DV-Xα) scheme have been made on linear dicyano complexes, [Ag(CN)2]−, [Au(CN)2]−, and [Hg(CN)2], to clarify their electronic structures. The valence X-ray photoelectron spectra (XPS) for these compounds are also reported. The calculated energy levels are consistent with the XPS results. The relative magnitudes of the bond overlap populations show a good correlation with those of the force constants obtained from infrared data. The calculated MO features show that the mixing of the metal (n+1)s orbital is important in stabilizing the linear L–M–L bonds, especially in the partial cancellation of the antibonding character of the σg-type highest occupied molecular orbital.

X-ray photoelectron spectroscopic study of π electron delocalization in polyphenyls — a comparison with acenes and polystyrene

High resolution core and valence X-ray photoelectron spectra of biphenyl, p-terphenyl, p-quaterphenyl and p-polyphenyl clarify the electronic structure of these aromatic compounds. Comparison with similar data for the lowest acenes (benzene, naphthalene, anthracene and tetracene) and polystyrene permits an evaluation of electron delocalization in relation to the electrical properties. Energy gaps of 5.8 eV for polystyrene and 4.0 eV for p-polyphenyl are obtained.