Initial State Contributions Research Articles

An experimental study of charge distribution in crystalline and amorphous Si nanoclusters in thin silica films

Crystalline and amorphous nanoparticles of silicon in thin silica layers were examined by transmission electron microscopy, electron energy loss spectroscopy, and x-ray photoelectron spectroscopy (XPS). We used XPS data in the form of the Auger parameter to separate initial and final state contributions to the Si2p energy shift. The electrostatic charging and electron screening issues as well as initial state effects were also addressed. We show that the chemical shift in the nanocrystals is determined by initial state rather than final state effects, and that the electron screening of silicon core holes in nanocrystals dispersed in SiO2 is inferior to that in pure bulk Si.

Disorder broadening of alloy Auger spectra

Auger spectroscopy promises the means to separate initial and final state contributions to the disorder broadening of core XPS spectra in disordered alloys. Auger disorder broadening, deduced from recent ab initio results, is predicted to be greater than XPS disorder broadening for Cu 50Pd 50 and Ag 50Pd 50 alloys. Simulations are used to assess whether this effect is observable experimentally despite the greater lifetime broadening of Auger spectra. A number of cases where narrow core–core–core Auger transitions should allow clear experimental identification of this effect are identified. The prospects for determining environment-resolved Auger spectra using APECS have been investigated.

Solvent and structural effects on the kinetics of the reactions of 2‐substituted cyclohex‐1‐enylcarboxylic and 2‐substituted benzoic acids with diazodiphenylmethane

AbstractThe rate constants for the reaction of 2‐methyl‐cyclohex‐1‐enylcarboxylic, 2‐phenylcyclohex‐1‐enylcarboxylic, and 2‐methylbenzoic and 2‐phenylbenzoic acids with diazodiphenyl‐methane were determined in 14 various solvents at 30°C. To explain the kinetic results through solvent effects, the second‐order rate constants of the examined acids were correlated using the Kamlet–Taft solvatochromic equation. The correlations of the kinetic data were carried out by means of multiple linear regression analysis, and the solvent effects on the reaction rates were analyzed in terms of initial and transition state contributions. The quantitative relationship between the molecular structure and the chemical reactivity has been discussed, as well as the effect of geometry on the reactivity of the examined molecules. The geometric data of all the examined compounds corresponding to the energy minima in solvent, simulated as dielectric continuum, obtained using semiempirical MNDO‐PM3 energy calculations. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 664–671, 2007

Electronic and structural properties of implanted xenon in amorphous silicon

The electronic and structural characteristics of xenon implanted in amorphous silicon are investigated. A different implantation approach, in which xenon atoms are implanted during the film deposition, was developed. Up to about 5at.% of xenon were implanted at energy as low as 100eV. X-ray absorption spectroscopy reveals that xenon atoms are dispersed in the amorphous Si network. The xenon 3d5∕2 binding energy, from x-ray photoelectron spectroscopy, as well as the initial state contribution and relaxation energy, from x-ray excited Auger electron spectroscopy, depend on the implantation energy and indicate that the xenon atoms are trapped in voids of different sizes.

Electronic structure of xenon implanted with low energy in amorphous silicon

Electronic struture of Xe implanted in amorphous silicon (a-Si) films are investigated. Xe atoms were implanted with low energy by ion beam assisted deposition (IBAD) technique during growth of the a-Si films. The Xe implantation energy varied in the 0–300 eV energy range. X-ray photoelectron spectroscopy (XPS), X-ray Auger excited spectroscopy (XAES) and X-ray absorption spectroscopy (XAS) were used for investigating the Xe electronic structure. The Xe M 4N 45N 45 transitions were measured to extract the Auger parameter and to analyze the initial state and relaxation contributions. It was found that the binding energy variation is mainly due to initial state contribution. The relaxation energy variation also shows that the Xe trapped environment depends on the implantation energy. XAS measurements reveals that Xe atoms are dispersed in the a-Si matrix.

Initial and final state contributions to binding-energy shifts due to lattice strain: Validation of Auger parameter analyses

The validity of Auger parameter analyses to separate initial and final state contributions to core-level binding energy shifts in the growth of nanoparticles is tested; the specific concern is shifts due to lattice strain. Theoretical energies for the hole-states involved are used to avoid the approximations and assumptions normally required to justify the analyses. When the Auger transitions involve states with high lying d-holes, the Auger parameter analysis of the origin of the shifts is incorrect. When only core–hole Auger states are used, a suitable formulation will accurately reproduce the initial state origin of shifts due to lattice strain.

Solvent and structural effects on the kinetics of the reactions of cycloalkenylcarboxylic and cycloalkenylacetic acids with diazodiphenylmethane

AbstractThe rate constants for the reaction of different cycloalkenylcarboxylic, cycloalkenylacetic acids, and phenylacetic acid with diazodiphenylmethane were determined in 12 aprotic solvents at 30°C. In order to explain the kinetic results through solvent effects, the second‐order rate constant of the examined acids was correlated using the Kamlet–Taft solvatochromic equation. The correlations of the kinetic data were carried out by means of multiple linear regression analysis, and the solvent effects on the reaction rates were analyzed in terms of initial and transition state contributions. The opposite signs of the electrophilic and the nucleophilic parameters are in agreement with the well‐known mechanism of the reaction of carboxylic acids with diazodiphenylmethane. The quantitative relationship between the molecular structure and the chemical reactivity is also discussed. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 361–367, 2005

XPS study of Cu/substrate systems obtained by pulsed laser deposition

AbstractIn this paper XPS was used to study the evolution of Cu 2p3/2 peaks with the increase of the metal coverage on different types of substrate: Ni, HOPG (highly orientated pyrolytic graphite) and KBr. The results showed that: (i) the binding energy of the Cu 2p3/2 peak in the system Cu/HOPG decreases with surface coverage, while in the system Cu/Ni it increases; (ii) with the increase of the Cu coverage in all the systems studied a general trend of the Cu 2p3/2 peak is the reduction of FWHM (full width at half maximum), but the degree of the FWHM change depends greatly on the type of the substrate. The results obtained for binding energy change are discussed in relation to the initial and final state contributions. The results indicate that the final state contributes more to the change of the binding energy in the more 3‐dimensional structure Cu/HOPG system, while in the more 2‐dimensional Cu/Ni system the initial state contribution dominates. The FWHM change is analysed in terms of the size distribution of clusters and change of the lifetime of the holes left by the photoelectrons, which is affected by the size of the clusters and the degree of the hybridization between the s and d electrons. Copyright © 2004 John Wiley & Sons, Ltd.

Cluster core-level binding-energy shifts: the role of lattice strain.

Our combined experimental and theoretical analysis of the shifts, with particle size, of core-level binding energies (BE's) of metal nanoparticles on insulating supports, shows that these shifts have an important initial state contribution arising, in large part, because of lattice strain. This contribution of BE shifts has not been recognized previously. Lattice strain changes the chemical bonding between the metal atoms and this change induces BE shifts.

Final state contribution to the Si 2p binding energy shift in SiO 2/Si(1 0 0)

The Si 1s and 2p photoemission and the Si KL 2,3L 2,3 Auger emission from SiO 2/Si(1 0 0) surfaces were measured for oxide thicknesses from 0.4 to 3.8 nm using high-energy photoemission ( hν=3000 eV). The energy of the SiO 2 emission depends on the layer thickness. The Si 4+–Si 0 energy differences Δ E 1s, Δ E 2p and Δ E KLL were combined to separate the initial and final state contribution to the energy shift of the Si 4+ 2p line. Within the experimental error, the 2p initial state is constant up to about 2 nm oxide thickness, where differential charging gradually sets in. The observed variation of Δ E 2p is entirely due to final state relaxation. It is found that Δ E 1s−Δ E 2p=0.62 eV, independent of the oxide thickness.

The influence of the solvent on organic reactivity. Part II. Hydroxylic solvent effects on the reaction rates of diazodiphenylmethane with 2-(2-substituted cyclohex-1-enyl)acetic and 2-(2-substituted

The rate constants for the reaction of diazodiphenylmethane with 2-(2-substituted cyclohex-1-enyl)acetic acids and 2-(2-substituted phenyl)acetic acids, previously determined in seven hydroxylic solvents, were correlated using the total solvatochromic equation, of the form logk = logk0 + s?*+ a? + b?, the two-parameter model, logk=logk0 + s?*+ a? and a single parameter model logk = logk0 + b?, where ?*is a measure of the solvent polarity, ? represents the scale of solvent hydrogen bond acceptor basicities and ? represents the scale of solvent hydrogen bond donor acidities. The correlations of the kinetic data were carried out by means of multiple linear regression analysis and the solvent effects on the reaction rates were analyzed in terms of initial state and transition state contributions.

Interactions of ultrathin Pb films with Ru(0001) and Pd(111)

The interaction of ultrathin Pb films with Ru(0001) and Pd(111) has been studied with x-ray photoelectron spectroscopy (XPS) and thermal desorption spectroscopy (TDS). XPS and TDS show that at room temperature Pb grows onRu(0001) via a Stranski-Krastanov mechanism, i.e., after completion of the first adlayer of Pb on Ru(0001), further Pb deposition leads to the formation of three-dimensional islands. Upon annealing to 500 K, the overlayer Pb undergoes significant clustering with the extent dictated by the initial coverages. XPS results show that the Pb 4f 7 / 2 core level binding energy (BE) increases slightly (+0.3 eV) as the Pb coverage increases from 0.07 ML to multilayers. When the first monolayer of Pb/Ru(0001) has been completed, the Pb 4f 7 / 2 BE has nearly reached the BE value for bulk Pb; it is only 0.1 eV lower. At ∼ 2 ML, the Pb 4f 7 / 2 BE is equivalent to that of bulk Pb. In contrast, at room temperature, Pb alloys with the Pd(111) surface, the Pd 3d 5 / 2 BE increasing ∼ 0.8 eV with coverage from 0.07- to 4.3-ML Pb. The Pb 4f 7 / 2 BEs also increase with increasing coverage reaching the bulk value of Pb at a coverage of ∼ 2 ML. The Pb 4f 7 / 2 BE at 0.07 ML is 0.55 eV smaller than that of bulk Pb. The lineshape and position of the x-ray induced Pd Auger features (M 4 , 5 VV) also display significant changes upon alloying. For Pb/Pd alloys, annealing to 500 K does not induce further changes in the Pd (M 4 , 5 VV) Auger features. The core level BE shifts are discussed in terms of possible initial and final state contributions. In particular, the initial state BE shift mechanisms of hybridization and environmental conduction band charge density are explained in the context of prior theoretical studies. It is shown that 6s→6p hybridization in Pb can be expected to be sufficiently large to contribute to the observed BE shifts.

Revivals and entanglement from initially entangled mixed states of a damped Jaynes-Cummings model

An exact density matrix of a phase-damped Jaynes - Cummings model (JCM) with entangled Bell-like initial states formed from a model two-state atom and sets of adjacent photon number states of a single mode radiation field is presented. The entanglement of the initial states and the subsequent time evolution is assured by finding a positive lower bound on the concurrence of local 2x2 projections of the full 2xinfinity JCM density matrix. It is found that the time evolution of the lower bound of the concurrence systematically captures the corresponding collapse and revival features in atomic inversion, relative entropies of atomic and radiation, mutual entropy, and quantum deficit. The atom and radiation subsystems exhibit alternating sets of collapses and revivals in a complementary fashion due to the initially mixed states of the atom and radiation employed here. This is in contrast with the result obtained when the initial state of the dissipationless system is a factored pure state of atom and radiation, where the atomic and radiation entropies are necessarily the same. The magnitudes of the entanglement lower bound and the atomic and radiation revivals become larger as both magnitude and phase of the Bell-like initial state contribution increases. The time evolution of the entropy difference of the total system and that of the radiation subsystem exhibits negative regions called "supercorrelated" states which do not appear in the atomic subsystem. Entangled initial states are found to enhance this supercorrelated feature. Finally, the effect of phase damping is to randomize both the subsystems for asymptotically long times .

Second-order Møller–Plesset perturbation theory for computing molecular-field splitting: application to the S2p 3/2 level in C 2H 2 n+1 SF 5, n=0, 1, and 2

High-resolution molecular X-ray photoelectron spectra of second-row atoms may reveal broadening or even splitting of the 2p 3/2 peak as compared to the 2p 1/2 component of the spectrum. This splitting reflects the lifted degeneracy of atomic 2p orbitals at sites of less than cubic symmetry and is referred to as molecular-field splitting (MFS). The prospect of using second-order Møller–Plesset theory (MP2) for ab initio calculation of the MFS for sulfur 2p 3/2 levels is examined. This method is subsequently applied to compute the MFS in ethynyl, ethenyl, and ethyl sulfur pentafluoride, resulting in values of 80, 116 and 121 meV, respectively. The initial-state contribution to the splitting is analyzed in terms of asymmetry in the electron density at sulfur, on the one hand, and in terms of the sulfur-ligand overlap density and electron density at the groups bonded to sulfur, on the other. At the Koopmans' theorem level of theory, the main source of splitting in the title compounds is found to be s–d hybridization of sulfur. At post-SCF levels of theory, core-valence electron correlation contributes substantially to the MFS, in proportion to the occupational asymmetry of the S3p shell. The realization that mixing of sulfur atomic orbitals of the same parity may add important contributions to the electric-field gradient at the core, resolves the observed diversity in the relative importance of core-valence electron correlation between different classes of sulfur compounds.

Why are carboxylic acids stronger acids than alcohols? The electrostatic theory of Siggel–Thomas revisited

The electrostatic explanation of Siggel and Thomas for the acidity differences between series of acids was investigated critically. Acidities and electrostatic potentials at the protons of XOH, XNH 2, and XCH 3 derivatives (X=H, CH 3, HCO, NO 2, and F) were calculated at the Becke3LYP/6-311+G ∗∗ level. Final state (anion) relaxation energies were obtained as proposed by Siggel and Thomas. Examination of initial and final state contributions revealed deficiencies in the Siggel–Thomas method as the final-state (relaxation) energies still retain contributions from the electronic structure of the initial state. Hence, this relaxation energy is not reliable as a measure of resonance stabilisation in anion. The application of Siggel–Thomas approach in two opposite directions—dissociation of neutral acid and protonation of an anion—leads to contradictory conclusions about whether the acidity difference between methanol and formic acid is determined by the neutral acid or anion. Hence, this scheme cannot be used to determine the initial state (neutral acid) and final state (anion) contributions to acidity as proposed by Siggel and Thomas.

The calculation of initial-state effects on inner-shell ionization energies

In order to obtain chemical insight from shifts in core-ionization energies, Δ I , it is often desirable to separate the initial-state contribution, Δ V , from that caused by relaxation in the final state, Δ R . These quantities are related through Δ I =Δ V −Δ R . Whereas the chemical shift itself, Δ I , may be measured very accurately, the scope of the present contribution is to provide a tool for accurate quantification of the initial-state contribution Δ V to the measured shift. Common procedures of estimating Δ V either from Hartree–Fock orbital energies or from electrostatic potentials at nuclear positions are examined. Whereas orbital energies suffer from the neglect of valence-electron correlation, the use of electrostatic potentials does not take proper account of the finite extension of core orbitals. In order to circumvent both of these problems, a reformulation valid for any valence-correlated wave function is presented for V , the energy needed to remove a core electron without relaxation of spectator electrons. The resulting expression may be seen as an extension of Koopmans’ theorem, and reduces to the former in the case of a Hartree–Fock wave function. This extended Koopmans’ theorem is used to compare initial-state effects in X-ray photoelectron spectra for a set of simple hydrocarbons.

A study of gold ultrathin film growth on yttria-stabilized ZrO 2(100)

The initial stages, up to five equivalent monolayers, of Au growth on yttria-stabilized ZrO 2 (100) at 680 K were studied by X-ray photoelectron and X-ray induced Auger electron spectroscopy (XPS/XAES). The XPS results indicate that Au grows as three-dimensional clusters on the substrate. The coverage-dependent average coordination number for Au atoms is estimated from the observed Au 5d 5/2–5d 3/2 splitting. Analysis of the XPS and XAES results indicate that Au does not interact substantially with the substrate. The initial state contribution to the binding energy shift, as obtained by an Auger parameter analysis, and its relation with Au cluster size is discussed.

XPS and bonding: when and why can relaxation effects be ignored

Abstract The arguments behind the use of the term `chemical Shift' in X-ray photoelectron (ESCA) spectroscopy are explored. The factors that relate to initial state (chemical) vs final state (relaxation) contributions are described along with relationships to applied cases, with a particular emphasis on oxides. It is demonstrated that some major classes of oxides, such as silicates, are excellent examples of systems for which the measured binding energy shifts are directly related to differences in initial state chemistry.

Solvent Effect on the Kinetics of Oxidation of [Co(en) 2 SCH 2 CH 2 NH 2 ] 2+ by S 2 O 8 2−

The effect of the solvent on rate of the oxidation of [Co(en)2SCH2CH2NH2]2+ by S2O8 2− in aqueous mixtures of methanol (MeOH), tert-butyl alcohol (Bu t OH), acetonitrile (AN), ethylene glycol (EG) and ethylene carbonate (EC) has been analysed as regards initial and transition state contributions. From kinetic measurements and solubilities of the reactants, the Gibbs transfer functions, ΔG t°, corresponding to transfer of reactants and activated complex from water to water-organic mixtures were evaluated. The trends of the transfer functions are discussed in terms of ion-solvent interactions and the structural effects in the solvent mixtures.

Extended Fenske-Hall LCAO MO calculations of core-level shifts in solid P compounds

Extended Fenske-Hall LCAO-MO ΔSCF calculations on solids modelled as H-pseudoatom saturated clusters are reported. The computational results verify the experimentally obtained initial-state (effective atomic charges, Madelung potential) and relaxation-energy contributions to the XPS phosphorus core-level binding energy shifts measured in Na 3PO 3S, Na 3PO 4, Na 2PO 3F and NH 4PF 6 in reference to red phosphorus. It is shown that the different initial-state contributions observed in the studied phosphates are determined by local and nonlocal terms while the relaxation-energy contributions are mainly dependent on the nature of the nearest neighbors of the phosphorus atom.