Angular momentum decomposition of k = 0 Bloch functions in group IV and zincblende crystals

The angular momentum contents of $\text{k}\text{= 0}$ Bloch functions for a number of group IV and zincblende crystals are examined using a pseudopotential approach. The large amplitudes for d and f character functions found even for valence electron wave functions are related to the overlap of p and s symmetry states on different atoms. In zincblende crystals the strength of the d and f components increases around cations and decreases around anions for the valence bands. The f-like component is appreciable for the Γ₁ conduction band particularly around a cation.     

Röntgenspektroskopische Untersuchung der Struktur des Valenzbandes von Silicium,Siliciumcarbid und Siliciumdioxid

With a photon-counting concave grating spectrograph the SiL _2,3 emission bands of pure Si, SiC and SiO₂ (quartz) were investigated. The observed bands are in good agreement with recent measurements using photon-counting devices but differ markedly from those obtained with photographic registration. The comparison of these SiL _2,3 bands with the corresponding SiKβ bands observed by other authors shows that the intensity distributions are more or less complementary. For Si and SiC the experimental results are compared with recent calculations of the electronic band structure. The agreement between the measuredK andL emission bands of silicon and the calculated density of states curve of silicon is satisfactory.     

Study of mechanisms of formation of X-ray emission bands in crystals by the density functional method: The Mg <Emphasis Type="Italic">L</Emphasis><Subscript>2,3</Subscript> bands in metal and in MgO

Using the density functional method in the pseudopotential approximation, we calculate the probabilities of X-ray emission transitions and shapes of the L _2,3 X-ray emission bands of Mg in crystals of metallic magnesium and monoxide MgO. We have paid special attention to the study of mechanisms by which these bands were formed; therefore, along with the total intensities, we determine the partial s- and d-contributions. In addition, the intensities of the L _2,3 bands of Mg have been separated into contributions from direct (intra-atomic) transitions and charge-transfer crossover transitions. We show that an unexpectedly large contribution of partial d-transitions in magnesium oxide is caused by crossover transitions of electrons of valence states of ligands to the core 2p-level of Mg, i.e., charge-transfer transitions. In metallic magnesium, the contribution of these transitions proved to be insignificant. An appreciable contribution of crossover transitions has also been revealed in s-contributions of X-ray emission bands. To estimate the calculation accuracy, we have compared the shapes of theoretical spectra with the shapes of experimental L _2,3 X-ray emission bands of Mg.     

X-ray L1, L2 and L3 absorption limits of 4D transition metals

The wavelengths and energies of the L₁, L₂ and L₃ absorption limits in Zr, Nb, Ru, Rh, Pd and Ag metals have been measured and some of the previous reported values have been found to be incorrect. By comparing the energies of the absorption limits with those of the Lγ₁Ly, and Lβ_2,15, lines and also with the binding energies obtained by XPS, the electronic transitions corresponding to the respective absorption limits have been clarified. It is concluded that (i) the end level of the electronic transition corresponding to the L₁ absorption limit of Zr-Ag is the 5p-like level, and (ii) the end level corresponding to either of the L₂ and L₃, absorption limits of Zr-Pd is the 4d level, while that of Ag is, rather unexpectedly, the top of the 5s level.     

Stark-Effekt-Untersuchungen der Hyperfeinstruktur der 5s25d2D3/2- und 5s25d2D3/2-Terme im In I-Spektrum

The level-crossing technique with combined electric and magnetic fields was used to investigate the hyperfine structure of the 5s ²5d ² D _3/2- and 5s ²6d ² D _3/2-stedes of the In I-spectrum. From the shifts of the level-crossing signals due to the Stark effect of the electric field the Stark constantsβ of both states were deduced: 5s ²5d ² D _3/2: ¦β¦=0.33(3) Mc/(kV/cm)² 5s ²6d ² D _3/2: ¦β¦=6(1) Mc/(kV/cm)². By theoretical calculations with wave functions of the Coulomb approximation one can show, that the Stark effect in both states is mainly due to admixtures of the 5s ²6p- resp.5s ²7p-configuration.     

Oxidation of the porous silicon surface under the action of a pulsed ionic beam: XPS and XANES studies

The changes in the electronic structure and phase composition of porous silicon under action of pulsed ionic beams have been studied by X-ray photoelectron spectroscopy (XPS) and X-ray absorption near-edge spectroscopy (XANES) using synchrotron radiation. The Si 2p and O 1s core photoemission spectra for different photoelectron collection angles, valence band photoemission spectra, and X-ray absorption near-edge fine structure spectrain the region of Si L _2,3 edges of the initial and irradiated samples have been analyzed. It has been found that, as a result of the irradiation, a thin oxide film consisting predominantly of higher oxide SiO₂ is formed on the porous silicon surface, which increases the energy gap of the silicon oxide. Such film exhibits passivation properties preventing the degradation of the composition and properties of porous silicon in contact with the environment.     

X-ray Kβ- and L2,3-emission bands of pure silicon and silicon in MoSi compounds

The intensity distribution of K_β- and L_2,3-emission bands of pure silicon and silicon in MoSi₂, Mo₅Si₃ and Mo₃Si are investigated. Some of the aspects of the electronics structure of these compounds are discussed.     

Determination of transition probabilities for singly ionized vanadium

Transition probabilities of 211 spectral lines of VII, in the wavelength range 2340–4200 Å, have been determined by emission spectroscopy using a wall-stabilized arc as source. The lines studied belong to the transition arrays 3d⁴, 3d³4s-3d³4p (199 lines) and 3d³4p-3d³4d, 3d³5s (12 lines). Vanadium was introduced into the helium-arc discharge as the liquid VOCl₃. An important feature of this work is the determination of transition probabilities for many lines from a wide spectral range with a uniform absolute scale. The absolute A_ki values were obtained by normalizing relative A_ki values to an absolute scale set by ionic lifetime for the level y³H⁰₄. These results are compared with other experimental as well as theoretical results.     

X-ray Kβ-and L2,3-emission bands of pure silicon and silicon in ZrSi compounds

The intensity distribution of the K_β-and L_2,3-emission bands of pure silicon and silicon in ZrSi₂, Zr₃Si₂, Zr₅Si₃ and Zr₃Si are investigated. Some of the aspects of the electronic structure of these compounds are discussed.     

X-ray spectroscopic investigation of the electronic structure of α-quartz and stishovite (SiO2)

The silicon K and L_2,3 X-ray emission bands of stishovite (tetragonal SiO₂, 6:4 co-ordination) are reported and discussed along with the corresponding emission bands of α-quartz (hexagonal SiO₂, 4:2 co-ordination). While the shapes of the Si K-emission bands of stishovite and α-quartz differ considerably, those of the Si L_2,3-emission bands are similar. The measured spectra are compared with theoretical band structure calculations, and good overall agreement is found.     

Observation of hydrogen and helium satellites in a turbulent plasma

Time-resolved measurements of satellites about the (1s2s?1s3d) forbidden transition in helium, satellites both of the H_δ line of hydrogen and of its splittings and, finally, satellites of He II 4868 Å have been observed. The behavior of these satellites is correlated relative to each other and to previously reported satellites both on H_β and near the 6632 Å (1s2p?1s3p) forbidden transition in helium. The appearance of the satellites is attributed to a strong field interaction between orthogonal components of the dynamic and quasistatic electric fields generated in a plasma by an instability.     

Fundamental absorption spectra of transition metal chlorides

The optical absorption spectra of MnCl₂, FeCl₂, CoCl₂, and NiCl₂ have been measured over the energy range from 2 to 30 eV. The gross features of the spectra, especially broad bands above 10eV, are alike in all of the four materials. The charge transfer bands due to the electronic transitions from the 3p level of chlorine to the 3d and 4s levels of metal ions and the band due to the 3d → 4s transition are assigned in the spectra.     

Electronic structure of the valence bands of H2-, Mg- and Pt-phthalocyanine derived from soft X-ray emission and photoelectron emission spectra

The soft X-ray emission and photoelectron emission spectra of H₂-, Mg- and Pt- phthalocyanine (PC) obtained using synchrotron radiation are reported and compared. In this way, an overall view of the pattern of valence bands is obtained and the electronic structure determined in terms of the component partial densities of states. In particular, from the valence p → 1s carbon and nitrogen K-emission spectra we determine for all three compounds the C and N 2p-like valence-band density of states with strong maxima located at binding energies of 8, 11 and 13.5 eV (carbon 2p) and 8 eV (nitrogen 2p) below the vacuum level. For PtPC the partial density of d-like valence states is determined from photoelectron emission difference-spectra and compared to previous XPS results. The sharp (1.2 eV FWHM) maximum of the Pt-derived partial density of states, observed at 6.9 eV binding energy, is assigned to the ⁴F term of a 5d⁸6s final-state configuration. A second, broader maximum at around 9.5 eV binding energy contains contributions from other terms of this 5d⁸ configuration, as well as from a 5d⁷ satellite (shake-up multiplet).     

The calculation of logft values and spectroscopic factors for nuclei in the mass range 10–15

Wave functions obtained in previous shell-model calculations [1, 2] for states of nuclei with massesA=10–15 are used to calculate logft values and spectroscopic factors. These wave functions, which were based on a modified surface delta two-body interaction, comprise the following active shell-model spaces: the 1p _3/2 and 1p _1/2 orbitals for mass 10–14 nuclei and restricted combinations of the 1p _1/2, 2s _1/2, 1d _5/2 and 1d _3/2 orbitals for mass 15 nuclei, leading to four different calculations in the latter case. The calculated results support evidence that the modified surface delta interaction is a valid approximation to the effective interaction in light nuclei.     

Double discontinuities of wide separation in the X-ray absorption spectra of transition elements in highly oxidized compounds

The paper consists of two parts. (1) The author studied the mechanism of the appearance of the double discontinuities of wide separation in the X-ray L₁ absorption spectrum of Mo in MoO₃, which were found in the recent research about the effects of chemical combination on various X-ray absorption limits, and that of Nb in Nb₂O₅. Then he arrived at the conclusion that the discontinuity of the higher energy corresponds to the electronic transition from L₁ to 5p, and that of the lower energy is attributed to that from L₁ to the 4d, 5s state. (2) The author applied the explanation to the double discontinuities which have been observed by many researchers in the K absorption spectra of 3d transition elements in highly oxidized compounds, and showed that these double absorption discontinuities are ascribed to the electronic transitions K?4p and K ? 3d, 4s.     

Transition probabilities of OI spectral lines

Dipole transition probabilities connecting the 1s²2s²2p³(⁴S⁰)nl^3,5L_J levels are presented for (nl) up to (15,5). The calculations are based on the single-configuration Hartree-Fock wave functions with the 1s and 2s orbitals treated as a frozen core. The results generally agree well with earlier works (theoretical and experimental) on transitions involving low quantum numbers.     

Tensor polarizabilities of levels of the configurations 4f 13 6s6p and 4f 12 5d6s 2 in thulium I

The level-crossing technique with parallel electric and magnetic fields was used to measure the tensor polarizabilities of six levels of the configuration 4f ¹³ 6s6p + 4f ¹² 5d6s ² in the Tm I-spectrum. Using intermediate coupling wave functions given by Camus and the experimental values of the tensor polarizabilities, the radial integrals for electric dipole transitions from levels of the configuration 4f ¹³6s6p + 4f ¹²5d6s ² to levels of the configuration 4f ¹³ 5d6s + 4f ¹² 6s ²6p have been determined. The results areI(4f ¹³6s6p,4f ¹³5d6s)=1.98(45)ea ₀ andI(4f ¹²5d6s ²,4f ¹²6s ²6p) = 0.88(25)ea ₀. A comparison between the experimental and the calculated values of the tensor polarizabilities shows an excellent agreement, provided that these radial integrals and the radial integrals for the electric dipole transitions to the ground state configuration 4f ¹³6s ² as determined by Wallenstein from lifetime measurements are used in the calculation, instead of radial integrals computed by Camus with Hartree-Fock wave functions.     

Interpretation of auger energy shifts of silicon in solid silicon compounds

Chemical shifts of Auger transitions and photoelectron binding energies of silicon have been measured and interpreted using the quasi-atomic approach. The Si KL_2,3L_2,3 and L_2,3V₁V₁ Auger transitions and the binding energies of Si 2p and of the valence electrons at the maximum of the density of states V₁ have been investigated in solid silicon and in the compounds SiC, Si₃N₄, SiO₂, Na₂SiF₆ and T₃Si (T = V, Cr, Mn, Fe, Co, Ni). The relaxation-energy shift ΔR^ea_S(2p, 2p) describing the polarization effect (final-state effect) has been evaluated by AES and XPS measurements. Furthermore, the extra-atomic relaxation energy R^ea_D(2p) of the 2p electrons has been determined experimentally for silicon atoms in differing environments. This allows estimation of the potential parameter V(2p) describing the potential effect (initial-state effect). In general R^ea_D(2p) was found to be more sensitive to changes in chemical bonding than V2p). The behaviour of the quasi-atomic Si V₁ electrons seems to be the converse.     

Species formed at cuprite fracture surfaces; observation of O 1s surface core level shift

Surfaces of mineral cuprite prepared by fracture under UHV have been characterised by synchrotron XPS and near-edge X-ray absorption spectroscopy before and after exposure to ambient air. Before exposure of the cuprite, the Cu 2p photoelectron and Cu L_2,3-edge absorption spectra were consistent with Cu^I with very little d⁹ character. Surface-enhanced O 1s spectra from the unexposed mineral revealed a surface species, with binding energy 0.95 ± 0.05 eV below the principal cuprous oxide peak, assigned to under-coordinated oxygen. A second surface species, with binding energy about 1 eV higher than the principal peak, was assigned to either hydroxyl derived from chemisorbed water vapour or surface oxygen dimers produced by restructuring of the cuprite fracture surface. The width of the principal O 1s peak was 0.66 ± 0.02 eV. The observed Cu L₃- and O K-edge absorption spectra were in good agreement with those simulated for the cuprite structure. After exposure of the fracture surface to ambient air, the low binding energy O 1s surface species was barely discernible, the original high binding energy O 1s surface species remained of comparable intensity, new intensity appeared at an even higher (∼1.9 eV) binding energy, and the Cu L_2,3-edge spectrum indicated the presence of Cu^II, consistent with the formation of a thin surface layer of Cu(OH)₂.