The effect of transition probability on the shape of X-ray photoelectron spectra of diamond and silicon

X-ray photoelectron spectra of valence bands in diamond and silicon have been calculated. It is shown that the probability of electron excitation from s-states is higher than that from p-states. The density of the electron states in the valence band of these crystals differs markedly from the energy distribution of photoelectrons.     

Investigation of the band structure of germanium chalcogenides by means of photoelectron spectroscopy

The valence band photoelectron spectra of amorphous GeS, GeSe and GeTe have been measured. The ultraviolet and X-ray excited spectra show three bands associated with bonding p-states, anti-bonding and bonding s-states, respectively. In the ultraviolet photoemission spectra the p-band shows a pronounced fine structure. Features of the valence band density of states estimated on the basis of a tightbinding model are in reasonable agreement with experiment. Some problems connected with the extension of the ionicity concept of Phillips and van Vechten to the IV–VI compounds are discussed.     

A study by XPS and XRS of the participation in chemical bonding of the 3d electrons of copper,zinc and gallium

The participation of 3d electrons in chemical bonds and their part in the formation of valence bands was studied by X-ray photoelectron- and X-ray-spectroscopy for Cu, Zn and Ga phosphides, sulphides and oxides. Incomplete screening of (n + 1)s,p electrons through the nd shell leads to non-systematic changes of orbital energies and radii of the valence electrons in the first, second and third Group elements. It is reflected in the electronic structure of the respective compounds. A qualitative interpretation of XPS and XRS data for Cu, Zn, Ga phosphides is given. Possible reasons for phosphorus s band splitting for zinc and copper phosphides are considered. The interaction of 3d metal states and 3s, p third Period element states considerably affects the valence band of compounds, and this interaction should be taken into account when considering electronic structures of Cu, Zn and Ga compounds.     

Investigation of the formation of the electron structure of metallocarbonic nanoforms

Model samples of nanostructures are synthesized with the use of transition metals, with a different number of d electrons and sp elements of groups II and III with a different number of valence p electrons, as modifiers. The activity of nanostructure synthesis is investigated depending on the addition of sp elements. A procedure is developed for determining the atomic magnetic moment of the d metals and the change in the distances between atoms of the metal and the sp element via the parameters of the X-ray photoelectron spectrum of transition metals, which allows the degree of hybridization of valence electrons in the chemical bond of adjacent atoms (Me-X) to be determined. As a result of the investigation the laws of nanoform growth are found which facilitate the development of new directions in the synthesis of nanostructures with unique properties.     

Theoretical study of X-ray photoelectron spectra of BN and SiC crystals

The tight-binding method has been used to calculate the density of states and X-ray photoelectron spectra of valence electrons in BN and SiC cubic crystals. It is shown that s- and p-states of atoms of various components contribute differently to the spectrum.     

Electronic structure and X-ray spectra of transition metal sulfides NiS,CuS, and ZnS

A numerical electronic band structure calculations for sulfides NiS, CuS, and ZnS are carried out. Using the results a detailed analysis of a valence states is performed; obtained partial densities of states are compared with X-ray SL _2,3 and $ SK_{\beta _{1,3} } $ SK_{\beta _{1,3} } -emission spectra. We showed that spectrum lineshape depends on hybridization strength between various Me(3d)-orbitals and 3p-states of sulfur. The hybridization strength and the symmetry of hybrid Me(3d)-orbitals are defined by crystal lattice structure. Finally a well splitted in energy bonding and antibonding states Me(3d)-S(3p) appear while weakly hybridized Me(3d)-states mainly contribute to spectra intensity in the energy between them. A good agreement between the theoretical and the experimental spectra of valence band for considered sulfides is obtained.     

Correlation effects in the photoelectron spectra of nickel

An approximate method is presented to calculate the orbital relaxation in photoelectron spectra for systems with a continuous distribution of electron states. The results for Ni 3d-states explain the discrepancy between experimental data and band structure calculations. The degree of d-state localization is discussed.     

Valence and core state modifications in Pt3Ti

XPS data for the valence band, the Pt 4? states, and the Ti 2p states are presented for the intermetallic Pt₃Ti. Relative to the Pt valence band, the Pt₃Ti band shows a decrease in the density of states just below the Fermi level and a shift of the centroid to higher (binding) energy. Ti 2p and Pt 4? binding energies showed relatively large shifts with respect to the pure metals. These changes in the valence band density of states and core level binding energies are interpreted as arising from hybridization of the d-orbitals in both metals to form strong intermetallic bonds.     

Electronic structure of compounds at platinum - silicon (111) interface

The electronic structure of Platinum silicides produced by thin film reaction is studied using ultraviolet photoemission and Auger spectroscopy. Spectra have been taken during the various stages of Si-Pt intermixing, in order to monitor the changes in the valence band, which take place during the reaction. The experimental data are compared with semi-empirical LCAO calculations. The importance of the coupling between Silicon p and Platinum d-states in determining the basic features of the chemical bond is discussed.     

Investigation of density-of-states in TiSi2 compounds

The electronic structure of TiSi and TiSi₂ was investigated by means of the energy distribution of photoelectrons emitted from the valence band and core levels. The Ti d-states are dominant at the Fermi level, the Si s-states of both TiSi and TiSi₂ were shifted to lower binding energy. The Si p-states are modified having peaks at binding energies 2.7 and 4.2 eV for TiSi₂ and 2.8 eV for TiSi but their intensities differ widely. The Si sp-states were not detectable for TiSi and TiSi₂ nor was the core level shift for TiSi₂.     

Electronic structure of PbI2 from photoelectron spectra and the exciton problem

The valence band density of states for PbI₂ is determined from X-ray and u.v. induced photoelectron spectra. It is shown that the band derived from Pb 6s states is at 8 eV binding energy and not at the top of the valence bands as suggested by band structure and charge density calculations. A rigid shift in the predominantly iodine 5p derived bands to lower binding energy brings the band structure calculations into essential agreement with experiment. Pb 5d core level binding energies determined here are used to derive core level exciton energies of 0.7 eV from published reflectivity spectra.     

Valence bands of layer structure transition metal chalcogenides

The valence band structure of representative MX₂ layer structure compounds has been obtained by X-ray photoemission with monochromatized radiation. Chalcogen s and p and metal d band are identified and their width and position obtained. The results are compared with u.v. and He II photoemission and with recent band structure calculations.     

X-ray and UV photoelectron spectra of the oxides NbO2, MoO2 and RuO2

HeI and Mg Kα_1,2 valence band photoelectron spectra of polycrystalline samples of NbO₂, MoO₂ and RuO₂ are reported. A marked increase is observed in the intensity of the metal 4d structure, relative to that due to oxygen 2p electrons, on changing from X-ray to UV excitation. The superior resolution of the 4d signals in the HeI spectra reveals the presence of the Fermi edge in the metallic oxides MoO₂ and RuO₂. In addition, the HeI spectrum of MoO₂ shows a splitting of the metal 4d signal, confirming established ideas concerning the electronic structure of such materials.     

UV-photoemission measurements on erbium and samarium

Photoemission measurements have been made on samarium and erbium in the photon energy range 4 to 21 eV. The photoelectron energy distributions are dominated by electron emission from valence band states whereas emission from 4f-states is unimportant. The width and energy of the occupied and unoccupied 5d-bands has been determined as well as the energy relative to the Fermi level of the bottom of the valence band. A model for the unscattered yield is presented allowing a determination of the hot electron scattering length for some rare-earths using available optical and photoemission data.     

Photoemission studies of single crystals of titanium carbide

The electron distribution in the valence band from single crystals of titanium carbide has been studied by photoelectron spectroscopy with photon energies h?ω = 16.8, 21.2, 40.8 and 1486.6 eV. The most conspicious feature of the electron distribution curves for TiC is a hybridization between the titanium 3d and carbon 2p states at ca. 3–4-eV binding energy, and a single carbon 2s band at ca. 10 eV. By taking into account the strong symmetry and energy dependence of the photoionization crosssections, as well as the surface sensitivity, we have identified strong emission from a carbon 2p band at ? 2.9-eV energy. Our results are compared with several recent energy band structure calculations and other experimental data. Results from pure titanium, which have been used for reference purposes, are also presented.The valence band from single crystals of titanium carbide have been studied by means of photoelectron spectroscopy, with photon energies ranging from 16.8 to 1486.6 eV.By taking into account effects such as the symmetry and energy dependence of the photoionization cross-sections and surface sensitivity, we have found the valence band of titanium carbide to consist of two peaks. The upper part of the valence band at 3–4 eV below the Fermi level consists of a hybridization between Ti 3d and C 2p states. The C 2p states observed in our spectra were mainly excited from a band about 2.9 eV below the Fermi level. The APW^5–9, MAPW¹⁰ and EPM¹¹ band structure calculations predict a flat band of p-character between the symmetry points X′₄ and K₃, most likely responsible for the majority of C 2p excitations observed. The C 2s states, on the other hand, form a single band centered around ?10.4 eV.The results obtained are consistent with several recent energy band structure calculations^{5–11, 13} that predict a combined bonding of covalent, ionic and metallic nature.     

Densities of States and Photoelectron Spectra of Iron Disilicide

The results of band calculations of the -phase of iron disilicide by the linearized method of associated plane waves are presented. The electronic state densities and the photoelectron spectra are calculated for film and bulk samples as functions of the excitation energy. A comparison of the results obtained with the available experimental data allows the main features in the formation of the valence band of the film and bulk materials to be analyzed. It is demonstrated that the main features of the photoelectron spectra of iron disilicide are largely caused by energetically localized d-states of iron.     

Resonance photoelectron spectroscopy of TiX2 (X = S, Se, Te) titanium dichalcogenides

The photoelectron valence band spectra of TiS₂, TiSe₂, and TiTe₂ dichalcogenides are investigated in the Ti 2p-3d resonance regime. Resonance bands in the vicinity of the Fermi energy are found for TiS₂ and TiTe₂. The nature of these bands is analyzed based on model calculations of the density of electronic states in TiS₂, TiSe₂, and TiTe₂ compounds intercalated by titanium atoms. Analysis of experimental data and their comparison with model calculations showed that these bands have different origins. It is found that the resonance enhancement of an additional band observed in TiS₂ is explained by self-intercalation by titanium during the synthesis of this compound. The resonance enhancement in TiTe₂ is caused by occupation of the 3d band in Ti.     

Observation of occupied 5d states in f.c.c. Yb metal

We propose experimental evidences for the sd character of the occupied band states of f.c.c. Yb metal. Photoionization cross-section σ¹ in the range 24–65 eV, covering the 5p core electron energies have been measured for both Yb (4ƒ¹⁴6s²5d⁰) and Lu (4ƒ¹⁴6s²5d¹). Both the hv dependence of σ¹ for the Yb valence band and the presence of photoemission resonances above the 5p edges of Lu and Yb indicate the presence of occupied 5d states at the top of the valence band of solid Yb. The Yb 4ƒ σ¹ is presented in order to distinguish the 5d band resonances from the 5p-5d giant dipole autoionization decays. L_{2, 3} X-ray absorption white lines for Yb provide a measure of the 5d bandwidth.     

X-ray photoelectron spectra of halogens in coordination compounds

X-ray photoelectron data on C12p energies for more than 200 coordination compounds of transition metals have been analysed. The effects of the central atom, other ligands, and the geometrical location of the chlorine atom on the C12p energy have been considered and certain regularities have been observed. The data on Br3d and F1s lines in coordination compounds have also been considered.     

The electron structure and x-ray emission spectra of noble metal aluminides

A calculation of the electron structure of [Al₈Cu₄] and [Al₈Au₆]- clusters was performed by the XαSW SCF-method. The X-ray emission and photoelectron spectra for noble metal aluminides Al₂Cu and Al₂Au are interpreted on the base of these calculations. The question of the possible influence of d-states on the distribution of Al3s-states and the shape of the AlL_2,3-emission spectrum is discussed for Al₂Cu.