How the solid state matrix affects the chemical shift of core-level binding energies: A novel method to take the induction effect into account

The interpretation of chemical shifts in high resolution photoemission core level spectra of mixed oxides as they occur in high-k dielectrics requires that charge transfer beyond the first coordination shell be taken into account. We present a scheme which allows us to include these so-called induction effects. The method is a judicious extension of Sanderson’s original approach towards network structures. At each point of departure from Sanderson, our method is tested successfully against the rigorous Sanderson formalism. For three examples of relevance in semiconductor technology, our new method yields results in excellent agreement with experiment.     

Electronic properties of tin dichalcogenides (SnS2 and SnSe2)

Using Phillips and Van Vechten's theory the homopolar gap (E_h), ionic gap (E_c) and Penn gap (E_p) have been derived for the layered compound semiconductors SnS₂ and SnSe₂. The values of E_p so derived have been found to be in agreement with the values obtained from the Grimes-Cowley modification of the Penn model, and also with the reflectance spectra of the respective materials. Using the above data the Phillips ionicity has been calculated and the octahedral coordination of SnS₂ and SnSe₂ has been discussed on the basis of the calculated value of ionicity. The bond electronic polarizability has been evaluated using Chemla's approach and the values so obtained have been found in agreement with the values obtained from the Clausius-Mossottirelation. The Varshni formula has been shown to explain fairly well the temperature dependence of energy gap and the constants involved have been derived. The calculated isobaric temperature gradient of E_g[($\text{?E}{}_{\mathrm{g}}\text{?T)}{}_{\mathrm{p}}$] has been found to be in accordance with the reported values, and the electron lattice interaction has been evaluated.     

An analytical model of the heat of chemisorption: A perturbation LCAO MO approach

An analytical LCAO MO perturbation model has been developed for treating the heat of chemisorption Q of an adsorbate A monolayer on a transition metal M film. The model combines parameters of the metal band (the Fermi level E_F, band width W = W^occ + W^vac, the d occupancy N_d, density of states n(?), etc.) with those of the local A-M interactions (the adorbital energy ?_A, off-diagonal matrix elements β_AM, etc.). The major cases of A's having lone pair, singly occupied, and vacant adorbitals have been considered, and the analytical expressions for Q as well as some numerical estimations are presented. The relative values of Q seem to be crucially dependent on the ratio β/(?_A ? E_F). The Q vs. N_d plots for the donor and radical A's are rather flat, typically Q decreasing monotonically as N_d increases, but for the acceptor A's the plots are very parameter dependent and show a variety of trends. The results obtained agree with straightforward computations and (scarce) experimental data.     

Energy expression of the chemical bond between atoms in metal oxides

The chemical bond between atoms in metal oxides is expressed in an energy scale. Total energy is partitioned into the atomic energy densities of constituent elements in the metal oxide, using energy density analysis. The atomization energies, ΔE_M for metal atom and ΔE_O for O atom, are then evaluated by subtracting the atomic energy densities from the energy of the isolated neutral atom, M and O, respectively. In this study, a ΔE_O vs. ΔE_M diagram called atomization energy diagram is first proposed and used for the understanding of the nature of chemical bond in various metal oxides. Both ΔE_M and ΔE_O values reflect the average structure as well as the local structure. For example their values vary depending on the vertex, edge or face sharing of MO₆ octahedron, and also change with the overall density of binary metal oxides. For perovskite-type oxides it is shown that the ΔE_O value tends to increase by the phase transition from cubic to tetragonal phase, regardless of the tilting-type or the 〈1 0 0〉 displacement-type transition. The bond formation in spinel-type oxides is also understood with the aid of the atomization energies. The present approach based on the atomization energy concept will provide us a new clue to the design of metal oxides.     

Intensity ratios of the KL1L1, KL23L23 oxygen Auger lines in different compounds

A simple model is proposed to interpret the relative intensities of the KLL oxygen Auger lines of several compounds. The basic assumption is that the intensity ratios depend on the atomic charges of the L₁ and L₂₃ orbitals localized at the oxygen site. The appropriate atomic charges can be calculated after Pauling's scale of electronegativity. The theoretical intensity ratios are compared with experimental results of different authors.     

Electron impact ionization of positive ions

A binary encounter model with Vriens' expression for σ_ΔE and quantum mechanical velocity distribution for the bound electron has been used to calculate electron impact ionization cross sections for ions. The calculated cross sections agree well with experimental observations.     

Determination de la Configuration Electronique Locale dans le Selenium Trigonal et le Tellure Trigonal a Partir de l'Anisotropie du Deplacement Chimique de la R.M.N.

The chemical shift tensor is calculated in a molecular model involving a modified sp³ hybridization. The introduction of two parameters, the first one allowing the direction of the hybrid orbitals involved in the bonds to deviate from the bond axes, and the second one giving the relative molecular orbital energies, enables us to account for N.M.R. experimental data on selenium and tellurium. It follows from the values of these parameters that the local electronic configuration is made up for selenium of two bonding orbitals within the chain and two equivalent lone pairs oriented such as the overlap between second neighbours is minimum; and for tellurium of two bonding orbitals within the chain and two non equivalent lone pairs, one of which having a p symmetry, oriented in such a way that the overlap between second neighbours is maximum. The local differences due to these configurations are discussed with respect to differences in the properties of the two elements.     

Phase transition in iodine: a chemical picture

The phase transition under pressure in iodine is analyzed using the electron localization function (ELF), explaining that the increase of the c/a ratio under compression is due to the presence of the lone pairs.A probabilistic interpretation is given for ELF.     

Effect of chemical ordering on the crystallization behavior of Se90Te10−xSnx (x=2, 4, 6, and 8) chalcogenide glasses

Ternary Se₉₀Te_10−xSn_x (x=2, 4, 6, and 8) chalcogenide glassy alloys have been prepared by melt quenching technique. Various crystallization parameters, such as onset (T_c) and peak (T_p) crystallization temperatures, activation energy of crystallization (E_c) and Avrami exponent (n) have been determined for these alloys. T_c and T_p have been determined directly from the non-isothermal differential scanning calorimeter (DSC) thermograms. The value of E_c has been calculated from the variation of both T_c and T_p with the heating rate (β) according to Kissinger, Takhor, Augis–Bennett and Ozawa models while Augis–Bennett method has been used to deduce the value of n for the studied samples. The obtained values of the crystallization parameters have been correlated with the character and the energy of the chemical bonds through the calculation of the heteronuclear bond energies of the constituent atoms using Pauling principle. In addition to that, Tichy–Ticha model was used to estimate the mean bond energy of the average cross-linking per atom 〈E_cl〉, the average bond energy per atom of the remaining matrix 〈E_rm〉, and the overall mean bond energy 〈E〉 of the studied glasses. Results reveal that both of T_c and T_p decreases with increases Sn content. This is may be attributed to the decreasing in the overall mean bond energy 〈E〉. Besides, the plot of E_c (and also T_g) against 〈E〉 was found to be non linear, which contradicts the well known linear correlation between E_c and T_g with 〈E〉 as suggested by Tichy–Ticha model. This discrepancy may be due to the fact that the Tichy–Ticha linear correlation model was based on the assumption of covalent glassy network, while in the present glassy alloys, Se–Te binary doped with heavy elements such as Sn exhibit iono-covalent bonding. The calculated values of the ionicity are in support of this argument.     

Elastic backscattering of electrons from surfaces

A Monte Carlo algorithm is proposed for calculating the elastic reflection coefficient, η_E, for elements. The algorithm accounts for the multiple elastic scattering of electrons in solids. The calculated values of η_E compare well with the literature data for elements with atomic number up to 47 and at primary energies above 2 keV. The proposed Monte Carlo method makes it possible to determine the functional relation between η_E and the inelastic mean free path, λ. This relation turned out to be non-linear, arid it deviates from a similar relation based on published earlier single elastic scattering model. The deviation is especially pronounced for elements with medium atomic numbers. The calculated function $\text{η}{}_{\mathrm{<mtext>E</mtext>}}\text{=}\text{f}\text{(λ)}$ offers a convenient method for determining the inelastic mean free path. The values of λ derived in the present work from published experimental values of η_E compare very well with the literature data.     

Useful applications of the electron localization function in high-pressure crystal chemistry

The main features of a new computational code aimed at the topological analysis of the electron localization function (ELF) in crystals are hereby presented. Besides the complete localization of all critical points, the code is able to determine the limiting surfaces that define the chemical regions associated with the so-found maxima (or attractors) of the ELF. Hence, integrations of density operators within these basins provide charges and volumes to cores, bonds and lone pairs. Two illustrative applications have been selected. Firstly, we examine the Z dependence of basin compressibilities in the elements of the first two rows of the periodic table, and secondly, we focus our attention on the chemical changes across the pathway of the zinc blende-rocksalt phase transition in BeO.     

Collision-strength dependence of solar emission lines of Si(X) and S(XII)

We have calculated the normalized populations of 15 levels in Si(X) and S(XII) ions in an optically thin medium, under steady-state condition, by using (i) constant collision strengths computed at the incident electron energy kT_e and (ii) incident electron-energy-dependent collision strengths. To calculate intensity ratios for solar emission lines, one may use constant collision strengths at the electron energy E'.     

Energy bands and electronic density of states in liquid palladium

Calculations are presented of the energy bands E(k) and electronic density of states N(E) using a liquid generalization of Andersen's version of the KKR equations of band theory. The method is applied to liquid Pd using a muffin-tin potential in the renormalized free atom approximation (RFA) with Slater exchange, and a comparison is made with earlier resistivity calculations by the authors using the same potential model. Some observations are made regarding the value and future applications of this approach.     

Electron Energy Loss Spectroscopy study of the near surface region of the ternary Co-Cr-Mo alloy

Nature of the characteristic electron energy losses in the second electron emission spectra from the ternary Co-Cr-Mo alloy surface are studied in the low energy range of the primary electron energy E₀. The main types of losses were found: surface and bulk plasmons and their hybrid modes, interband transitions and ionization losses. For Co, Cr, Mo and Co-Cr-Mo alloy the experimental values of the plasmon energy were established to be less than it was predicted by free-electron gas model. Excess of conductive electrons in the surface layers for Co, Cr and Mo was observed by dependence of the surface plasmon dispersion from E₀, while for Co-Cr-Mo alloy the situation is quit opposite. Such behavior is explained by the complex phase structure of the ternary alloy. The analysis of intensity lines of plasmons from E₀ showed deeply changed alloy profile. Ionization Spectroscopy was used for studying the alloy elements distributing on the depth. Mo atoms preferred segregation in the outermost layers of Co-Cr-Mo alloy and enrichment with Cr competitive atoms in underlayers is displayed.     

Calculations of vacancy formation energies and divacancy binding energies for noble metals using pseudopotential formalism

Vacancy formation energies (E^f_1v) and divacancy binding energies (E^B_2v) for noble metals have been calculated using the Moriarty's pseudopotential. While the calculated E^f_1v are coincident with the experimental values except Cu, E^B_2v agree with them for all the metals tolerably.     

Study on Stereochemical Activity of Lone Pair Electrons in Sulfur and Halogen Coordinated Antimony(III) Complexes by 121Sb Mössbauer Spectroscopy

We have measured ¹²¹Sb Mössbauer spectra at 20 K for 52 compounds of antimony(III). An Sb(III) atom with the electron configuration [Kr] 4d ¹⁰5s ² has a lone pair electrons. The stereochemical property of the lone pair has been found to depend very much on the kinds of atoms surrounding the antimony atom and the configurations of the coordinating atoms.     

Ferroelectric (Na1/2Bi1/2)TiO3 thin films showing photoluminescence properties

Polycrystalline lead-free (Na_1/2Bi_1/2)TiO₃ (NBT) ferroelectric thin films doped with 1 mol% of rare earth (RE) elements are processed on Pt-terminated silicon substrates using a solution deposition method. The thin films that exhibit single-phase perovskite structure show photoluminescence properties with highest intensities in the wavelength range between 700 and 850 nm, depending on RE element. The ferroelectric properties of the pure NBT film (P _r: 20.5 µC cm^?2, E _c: 150 kV cm^?1) are somewhat decreased for the doped films, which is ascribed to decreasing of the number of Bi lone pairs through the substitution of Bi with RE elements in the perovskite lattice.     

Determination of ionicity in zinc chalcogenides by X-ray absorption study

K-absorption edges and associated extended fine structure is recorded for zinc and zinc chalcogenides using a 40 cm, automatic scanning, Cauchois type X-ray spectrometer. It is observed that there is a correlation between the positive X-ray K-absorption edge chemical shift and Phillips' electronegativity difference C for zinc chalcogenides. The bond lengths for these compounds are determined using Lytle, Chivate et al. and Levy's methods. These bond lengths are observed to tally well with X-ray crystallographic data. The covalent energy gaps in Phillips' theory are determined using bond lengths determined by Chivate et al.'s method. Values of ionicities are obtained from X-ray spectroscopically determined values of C and E_h and are compared with Phillips' spectroscopically determined ionicities for zinc chalcogenides. It is shown that X-ray spectroscopically determined values of ionicities for these compounds show a more correct chemical trend.     

Calculation of the surface energy of bcc transition metals by using the second nearest-neighbor modified embedded atom method

The surface energies for 24 surfaces of all bcc transition metals Fe, Cr, Mo, W, V, Nb and Ta have been calculated by using the second nearest-neighbor modified embedded atom method. The results show that, for all bcc transition metals, the order among three low-index surface energies E_(1 1 0) < E_(1 0 0) < E_(1 1 1) is in agreement with experimental results and E_(1 1 0) is also the lowest surface energy for various surfaces. So that from surface energy minimization, the (1 1 0) texture should be favorable in the bcc films. This is also consistent with experimental results. The surface energy for the other surfaces increases linearly with increasing angle between the surfaces (h k l) and (1 1 0). Therefore, a deviation of a surface orientation from (1 1 0) can be used to estimate the relative values of the surface energy.     

Some regularities within the Stark widths and shifts of resonance ion lines from Li to Ca

A periodic dependence of the Stark widths and shifts of resonance lines, for singly- and doubly-ionized elements, has been found on nuclear charge number Z. These periodicities were found for Griem's theoretical values of the Stark parameters of resonance lines of some singly charged ions from Li to Ca; for other singly- and doubly- charged ions, this parameter was calculated from Griem's semiempirical formula. The dependence of the Stark parameters of the resonance lines on atomic polarizability X has been determined and used to estimate Stark widths and shifts for other singly-charged ions. These values are compared with estimates derived form Griem's semiempirical formula for the Gaunt factor g = 0.2.