Shake-up satellites in X-ray photoelectron spectroscopy

Shake-up satellite peaks have been reported in the core electron spectra of various types of molecules. The specific valence excitation(s) giving rise to this extra structure has been assigned largely as a result of the application of the sudden approximation coupled with other considerations, e.g. transition energies. Satellite peaks appearing in the core electron spectra of first row transition metal complexes appear to be particularly interesting since existing data indicate that their positions and intensities convey information regarding some important properties of the complex.In this work reported shake-up satellite peaks are described and analyzed. In addition, some areas requiring more experimental work are pointed out, and a few potential applications of satellite peak data are mentioned.     

内壳层电子激发(电离)诱发的电子波函数的弛豫及其对辐射跃迁概率的影响

利用多组态Dirac_Fock(MCDF)理论方法，通过对Ar原子在基组态3p⁶和激发组态1s^-14s，2s^-14s，2p^-14s，3s^-14s，3p^-14s情况下电子波函数的计算，系统地研究了不同内壳层电子激发(或电离)引起的电子波函数的弛豫现象以及由此导致的k_α和k_β线的跃迁波长和概率的变化情况，并与以往的理论结果进行了比较. 关键词： MCDF方法 弛豫效应 电子波函数 跃迁概率     

Splitting of core-level lines in photoemission spectra of transition metal compounds

The multiplet structure of core-electron binding energies in Cr 3s, Cr 3p and Cr 2p levels of CrCl₃ and CrBr₃ compounds has been investigated by X-ray photoelectron spectroscopy. The Cr 3s levels show a doublet splitting (about 4.3?eV) for the main emission in both halides. Satellites features are observed in Cr 3s, 3p and 2p levels at higher binding energies. In the Cr 3s spectrum, the main emission is assigned to unscreened intra-atomic multiplet splittings with correlation-induced satellites. The Cr 3p and 2p spectra can be better explained by the multiplet splitting arising from the interaction between valence band 3d electrons and core p holes in the crystal field. Final state screening (charge-transfer) effects do not play a major role in Cr 3s main emission nor do they affect the satellite structures in a relevant way. This explains why the Cr 3s exchange splitting in chromium halides is proportional to the local magnetic moment.     

Induction of an atomically thin ferromagnetic semiconductor in 1T′ phase ReS2 by doping with transition metals

Two-dimensional 1T′ phase ReS₂, a transition metal dichalcogenide, has a unique structure and electronic properties that are independent of thickness. The pure phase is a nonmagnetic semiconductor. Using density functional theory calculations, we show that ReS₂ can be tuned to a magnetic semiconductor by doping with transition metal atoms. The magnetism mainly comes from the dopant transition metal and neighboring Re and S atoms as a result of competition between exchange splitting and crystal field splitting. ReS₂ doped with Co can be considered as a promising diluted magnetic semiconductor owing to its strong ferromagnetism with long-range ferromagnetic interaction, high Curie temperature (above room temperature) and good stability. These findings may stimulate experimental validation and facilitate the development of new atomically thin diluted magnetic semiconductors based on transition metal dichalcogenides.     

Relation between 2p X-ray photoelectron and Kα X-ray emission spectra of manganese and iron oxides

The high resolution Mn and Fe Kα X-ray emission spectra (XES), and Mn and Fe 2p X-ray photoelectron spectra (XPS) for manganese and iron oxides were measured. The spectra were compared with those of [MnO₄]⁻, [Fe(CN)₆]⁴⁻ and [Fe(CN)₆]³⁻ ions. As the electronic structure of the latter compounds do not change with electron hole creation in the core levels, satellite peaks due to charge transfer are not observed in the 2p XPS spectra, and the peak profiles of metal 2p XPS and Kα XES are governed by the exchange splitting between 2p and valence electrons. The metal 2p XPS spectra of the oxides had satellite peaks, but the XES spectra had no satellites. FWHMs of the metal 2p_3/2 main peaks of the compounds being low spin states are smaller than those of metal Kα₁ XES spectra. However, FWHMs of Mn 2p_3/2 of the manganese oxide were nearly equal to those of Mn Kα₁ XES spectra, and those of Fe 2p_3/2 XPS spectra of the iron oxides are greater than those of Fe Kα₁ XES spectra.     

Selected studies of magnetism at high pressure

Summary Most previous studies of magnetism in various compounds under extreme conditions have been conducted over a wide pressure range at room temperature or over a wide range of cryogenic temperatures at pressures below 20 GPa (200 kbar). We present some of the most recent studies of magnetism over an extended range of temperatures and pressures far beyond 20 GPa,i.e. in regions of pressure-temperature (P-T) space where magnetism has been largely unexplored. Recent techniques have permitted investigations of magnetism in selected 3d transition metal compounds in regions ofP-T where physical properties may be drastically modified; related effects have often been seen in selected doping studies at ambient pressures. We present⁵⁷Fe and¹²⁹I M?ssbauer isotope studies covering the range 300–4 K to sub-megabar pressures in compounds such as Sr₂FeO₄, LaFeO₃ and FeI₂, representative of a broad class of 3d transition metal compounds. At ambient pressure the electronic structure of the transition metal atom in these antiferromagnetic insulators extends from 3d ⁴ to 3d ⁶ and has a distinct influence on the pressure evolution of their magnetic properties. M?ssbauer studies of these compounds are considered in conjunction with available structural and electrical transport data at pressure. Paper presented at ICAME-95, Rimini, 10–16 September 1995.     

Measurement of L subshell fluorescence yield ratios of some high Z elements by selective excitation method

The L₁, L₂ and L₃ subshells of Hf, Ta and Re atoms have been excited selectively by using microprobe XRF beam line, Indus‐2, RRCAT, India. The consequent characteristic L X‐ray photons, emitted from the targets due to creations of vacancies in L subshells, are measured using silicon drift detector (X‐123) spectrometer. As the energy of synchrotron radiation increases, the contribution of characteristic L X‐ray intensity increases. The advantage of the increase in the intensity of the characteristic L X‐ray photons with an increase in the energy of synchrotron radiation has been used to determine the L subshell fluorescence yield ratios of Hf, Ta and Re atoms by adopting the selective excitation method. The measured ratios of L subshell fluorescence yield have been compared with theoretical and other experimental values.     

Splitting of the electronic states near EF in A4C60 compounds (A = alkali metal)

The electronic structure of A₄C6₀ compounds (A=Na, K, Cs) has been studied using electron energy-loss spectroscopy. Both the low energy loss functions and Cls core excitation measurements reveal a strong splitting of the electronic states near the Fermi level in comparison with K₃C₆₀ or K₆C₆₀. This splitting indicates a lowering of the high degeneracy of the C₆₀ molecular orbitals due to a broken symmetry ground state and/or the opening of a correlation gap in these systems.     

The magnetic moment of iron in GdFe intermetallic compounds

Using the multiplet splitting in Fe containing compounds as observed in photoemission the magnetic moment of Fe in GdFe₂, GdFe₃, and Gd₂Fe₁₇ was determined to be (1.76±0.02)μ_B independent of composition. Charge transfer as a cause of this reduction in the Fe moment compared to Fe metal has been excluded. Valence band spectra support a model in which a reduced exchange splitting of the Fe 3d states is responsible for the smaller moment.     

5d-level energies of Ce and the crystalline environment. IV. Aluminates and “simple” oxides

Information on the energy of 5d-levels of Ce³⁺ ions in aluminates and “simple” oxides has been collected. The crystal field splitting of the 5d-levels is interpreted in terms of the type and size of anion polyhedron coordinating the Ce³⁺ ion. The centroid (barycenter) shift of the 5d-configuration is analyzed by a ligand polarization model providing values for the spectroscopic polarizability α_sp of the anion ligands. The data provide evidence that the centroid shift behaves independently from the crystal field splitting. By combining centroid shift and crystal field splitting, the “spectroscopic” redshift of the first electric dipole-allowed fd transition of Ce³⁺-doped in the compounds will be interpreted. The large crystal field splitting in garnet compounds and the small splitting in perovskite compounds will be discussed.     

Inner shell excitation,valence excitation and core ionization in NF3 studied by electron energy-loss and X-ray photoelectron spectroscopies

Electron energy-loss Spectroscopy (EELS) at impact energies of 2.5–3 keV has been used to obtain the electron excitation spectra for the N 1s (K-shell), F 1s (K-shell) and valence shell regions of NF₃. The inner shell spectra were recorded using small angle scattering (?1° ) while the valence shell spectrum was obtained at zero degree scattering angle. The inner shell excitation spectra show a strongly enhanced 1s→ δ^* type transition and continuum features which are typical for molecules with highly electronegative ligands. One of the peaks in an earlier published photoabsorption study of the N 1s region has been shown to be due to a N₂ impurity. The valence shell electron energy-loss spectrum shows a number of transitions which are considered to be mainly due to valence-valence type transitions, with also some evidence of Rydberg structure.The X-ray photoelectron spectra (XPS) of the N 1s and F 1s electrons along with their associated satellite structures have also been recorded using Al Kα (1486.58 eV) radiation. The vertical ionization potentials for the N 1s and F 1s electrons were found to be 414.36 (10) eV and 693.24 (10) eV, respectively. Both spectra exhibit a rich and different satellite structure. These “shake-up” features in the satellite XPS spectra are compared with continuum features of the inner shell electron energy-loss spectra and also with the valence shell spectrum.     

Variation of enhancement effect of Coster-Kronig transition of L3 X-Rays of Ba, La and Ce compounds

The Coster-Kronig (CK) enhancement effect was measured for L₃ subshell X-rays using the experimental Lα X-ray production cross-section, the fraction of Lα X-rays, L₃ subshell fluorescence yields and L₃ subshell photoionisation cross-section. The samples were excited by gamma-rays with 59.5 keV energy from a 75 mCi radioisotope source and L X-rays emitted from samples were counted by a Si(Li) detector with resolution 155 eV at 5.96 keV. Variation of enhancement effect of CK transition of L₃ X-rays of La and Ce compounds was measured to be more than that of Ba. Ba has a partially filled 6s orbital whereas La and Ce have partially filled 5d and 4f orbitals, respectively.     

An Auger and X-ray photoelectron spectroscopic study of sodium metal and sodium oxide

Photoelectron and Auger electron measurements have been made on polycrystalline films of sodium metal evaporated in ultra high vacuum, and on Na₂O produced by in-situ oxidation by dry oxygen. Most of the spectra were recorded using Mg Kα (1254 eV) radiation but excitation by 5 keV electrons or monochromatized Al Kα (1487 eV) X-rays was used for specific purposes. Core and valence electron binding energies, photoionization cross-sections relative to Na 1s, KLL and KLV Auger energies and transition probabilities are reported. Energy losses in the metal and oxide are discussed and the relative intensities of surface and bulk plasmon losses have been used to calculate mean electron escape depths in the metal. When corrections were made for experimental geometry, escape depths of 10 Å at 180 eV and 31 Å at 1200 eV were obtained. An escape depth of 23 Å at 980 eV was obtained by Na 1s-Na K-Auger intensity correlation and this is consistent with the plasmon data. Data on Auger satellite lines are presented and, in particular, evidence has been obtained which indicates that a high energy satellite should not be attributed to a plasmon gain mechanism. Valence band influences on the KLV Auger spectra are discussed with reference to the XPS spectrum and other sources of valence band information. Unexpected structure was found in the KLV spectra of the metal which, pending thorough interpretation, offsets the sensitivity and resolution advantages which these spectra otherwise offer for valence band studies.     

Band structure and high pressure study of Rh3Sc, Rh3Y and Rh3La

The electronic structure of the Rhodium based intermetallic compounds (A₃B) such as Rh₃Sc, Rh₃Y and Rh₃La are studied by the Self Consistent Tight Binding Linear Muffin Tin Orbital (TB-LMTO) method. In the present work, an attempt has been made to understand why the compounds namely Rh₃Y and Rh₃La crystallize in hexagonal structure, rather than the cubic structure, where as some of the similar rhodium based A₃B compounds namely Rh₃Ti, Rh₃Zr, Rh₃Hf, Rh₃V, Rh₃Nb, Rh₃Ta and Rh₃Sc are found to stabilize in cubic structure. In this work a prediction has been made about the structural phase transition in Rh₃Y and Rh₃La, from Hexagonal phase to Cubic phase. A report of the lattice constant, bulk moduli, cohesive energy and electronic specific heat coefficient is made and is compared with the available experimental data. Band structure and density of states histograms are also plotted. An electronic topological transition is predicted in Rh₃La, which may lead to the changes in the Fermi surface topology and hence changes the physical properties of Rh₃La.     

ESR study of Gd and Nd in RNi2 and RCo2 laves phase compounds

We report ESR study of Gd and Nd in RCo₂ and RNi₂ (R = Sc, Y, Zr, Lu, Ce) compounds. The variation of the Gd g shift from RCo₂ to RNi₂ compounds is consistent with a recent calculation of the density of states and also with the systematic behaviour demonstrated previously by us for transition metal intermetallic compounds. The Nd resonance in CeNi₂ and LuNi₂ indicate Γ₆ ground state crystalline field splitting; the Nd g value in YNi₂:Nd and LuNi₂: Nd is anomallous. Several possibilities for this anomally are discussed.     

High pressure behavior and structural properties of transition metal carbides

A pressure induced structural phase transition from NaCl-type (B₁) to CsCl-type (B₂) structure has been predicted in transition metal carbides, namely TiC, ZrC, NbC, HfC, and TaC by using an interionic potential theory with modified ionic charge (Z_m ), which includes Coulomb screening effect due to d-electron. The phase transition pressure (P_T ) relies on large volume discontinuity in pressure–volume relationship, and identifies the structural phase transition from B₁ phase to B₂ phase. The variation of second-order elastic constants with pressure follows a systematic trend identical to that observed in other compounds of NaCl-type structure. The Born criterion for stability is found to be valid in transition metal carbides.     

Role of point defects on conductivity, magnetism and optical properties in In2O3

In order to assess the effects of point defects including transition metal doping on its electronic structure, the self-consistent band structure of the transparent oxide In₂O₃ (in the Ia₃ structure) has been calculated with oxygen vacancies, oxygen and indium interstitial atoms and several transition metal dopants using density functional theory based first principles calculations. An oxygen vacancy alone does not act as a strong native donor but when combined with interstitial indium and (substitutional) transition metal doping, shallow donor levels close to the conduction band are formed. Spin polarized calculations show measurable magnetism in some of the transition metal doped systems while the dielectric functions indicate whether such systems remain transparent among other things.     

EPR of Fe3+ in acetylacetonates

EPR spectra of Fe³⁺ in Al(acac)₃ and Ga(acac)₃ single crystals were measured in the temperature range between 20 K and room temperature. In the Al compound one center was found above 140 K and three below this temperature due to a phase transition. In Ga(acac)₃ two centers with similar zero-field splitting parameters and orientations of their principal axes were observed in agreement with results for Cr³⁺. In all cases unusually large fourth-order zero-field splitting parameters for low symmetries were required for fitting and simulation of the angular dependences of the spectra. The results for the two compounds differed significantly. The orientations of the principal axes deviate considerably from those calculated from the crystal structure data by application of the superposition model. Thus like in the cases of Cr³⁺ in the same compounds and on Mn²⁺ in Zn(acac)₂·H₂O this model is not applicable, most likely due to delocalization of the conjugated π-electron systems of the ligands.     

Measurement of the fine structure splitting of the 32D multiplet of Li by stepwise excitation with cw dye lasers

The fine structure splitting of the 3²D multiplet of Li has been investigated using stepwise dye laser excitation of a strongly collimated atomic beam via the 2²P_{$\text{3}\text{2}$} level. The splitting is determined by a beat frequency measurement of two single mode dye lasers exciting the two 3²D levels. The result is Δν(3²D)=(1074±3) MHz.     

High-resolution rotational spectroscopy of iminosilylene,HNSi

By means of Fourier transform microwave spectroscopy of a supersonic beam, the fundamental rotational transition of isotopic and vibrationally excited iminosilylene, HNSi, has been detected. In addition to seven isotopic species, vibrational satellite transitions from more than 30 vibrationally excited states, including the three fundamental modes, have been detected. Those from ν₂ are particularly intense, enabling detection of transitions from as high as (0,22⁰,0) (i.e. ～10,000 cm^?1 above ground). At high spectral resolution, well-resolved nitrogen quadrupole structure has been observed in nearly every transition. Excitation of ν₁ or ν₃ changes eQq(N) little, but eQq(N) systematically decreases with increasing excitation of the ν₂ bend, from a value of 0.376(5) MHz for (0,0⁰,0) to ?2.257(5) MHz for (0,20⁰,0). With the large amount of new data in hand, it has also been possible to determine the leading vibration–rotation constants (α_i and γ_i) for ν₂ or ν₃ to high precision, and derive a revised semi-empirical equilibrium structure for this fundamental triatomic molecule. Various electronic and molecular properties of iminosilylene have been calculated at the coupled cluster level of theory, and these generally agree well with experiment and previous calculations. An unsuccessful search for HSiN, a highly polar isomer calculated to lie nearly 3 eV above HNSi, is also reported.