Valence Band Photoelectron Spectroscopy Research Articles

Modification of the electronic structure of graphite by intercalation, chlorination and ion etching

Intercalation of graphite with metal chlorides, treatment of graphite with chlorine gas and argon ion etching modify the electronic structure of HOPG graphite. Using both core level and valence band photoelectron spectroscopy significant changes near the Fermi energy were detected. Charge transfer effects in intercalated graphites can be distinguished from irreversible effects arising in all three modifications from the creation of sp 3 -hybridised carbon atoms. The formation of insulating surface structures is discussed.

Anomalous bonding in SiO2 at the SiO2–Si interface

Abstract Ultraviolet photoelectron spectroscopy valence-band spectra measured at 51 eV for a series of thin oxide layers thermally grown on Si(111) and Si(100) surfaces show that anomalous bonding configurations exist in SiO2 near the interface. A comparison with theoretical density-of-states calculations indicate that these configurations cannot be related to the existence of a strained SiO2 layer with a distribution of Si–O–Si bond angles different to what is found in bulk SiO2. The results support the existence of threefold-coordinated oxygen centres as described in the valence-alternation-pair model.

A photoemission study of T1 xV 6S 8: Evidence for a low temperature phase transition

Both core level and valence band photoelectron spectroscopy were used to study the changes in the electronic structure which occur owing to the ordering transition of thallium atoms in the channel structure of Tl x V 6S 8. Analysis of the photoemission data at all temperatures reveals a significant covalent character of all bonds in the structure. The thallium atoms are not ionic at any temperature. It is concluded that the thallium atoms transfer, at low temperature, some additional charge to the vanadium sulphide. The investigations show pronounced hysteresis effects associated with the phase transition.

Metal-nonmetal transition in tungsten bronzes: A photoemission study.

${\mathrm{Na}}_{\mathrm{x}}$${\mathrm{WO}}_{3}$ and ${\mathrm{Na}}_{\mathrm{x}}$${\mathrm{Ta}}_{\mathrm{y}}$${\mathrm{W}}_{1\mathrm{\ensuremath{-}}\mathrm{y}}$${\mathrm{O}}_{3}$ bronzes are studied near the metal-nonmetal transition (MN) using core-level and valence-band photoelectron spectroscopy with synchrotron radiation. It is shown that in the semiconducting composition an impurity band with a width constant with x-y develops in the matrix p-d gap and that the density of states at the Fermi level is finite for compositions on both sides of the MN transition. These results show that the MN transition is due to localization in an impurity band in a pseudogap. This impurity band merges with the matrix conduction band when x-y increases.

Photoelectron Spectroscopy of Solids

This paper is concerned with information about electronic structure and bonding in solids which can be derived from valence band and core level photoelectron spectroscopy. The role, in research of this kind, of the excitation processes discussed elsewhere in this symposium is of concern. A number of factors contribute to the apparent chemical shifts of core levels and valence bands in solids. These factors are considered and then results for gold alloys are taken as an example of the bonding information which can be derived. Angle resolved photoelectron spectroscopy provides information about wave function symmetry as well as energy. This is reviewed and one-electron energy vs. k results for Ni metal are inspected. Such results provide the best experimental test yet devised of energy band theory and of the potentials employed.