Combined Investigations of the Valence Band Structure of Graphite by K X‐Ray Emission Spectroscopy and X‐Ray Photoemission Spectroscopy

Abstract

The structure of the valence band of graphite is investigated by combined application of X-ray photoelectron spectroscopy and a special X-ray emission spectroscopy which measures polarized radiation. The highly resolved K X-ray emission spectrum (XS) separated into 0-and x-bands by using their different polarisation and the X-ray photoemission spectrum (XPS) of this valence band are reported and discussed in connection with the calculated density of states. Width and overlapping range of the subbands are determined experimentally and compared with calculated values. The strong energy dependent differences between the intensities of the spectra and the density of states are interpreted by means of specific selection rules. The interpretations of the XPS are carried out with a cross section ratio a(2s)/a(2p) from 15 to 35. It is shown that the cross section of XPS for pcs-like electrons is higher than that for px-like electrons.Die Struktur des Valenzbandes von Graphit wird mit Hilfe kombinierter Anwendung derRontgenphotoelektronenspektroskopie und einer speziellenRontgenemissionsspektroskopie, welche polarisierte Strahlung mi& untersucht. Das hochaufgeloste Rontgen-KEmissionsspektrum (XS), welches in cs-und x-Banden getrennt ist, und das RontgenPhotoemissionsspektrum (XPS) dieses Valenzbandes werden mitgeteilt und im Zusammenhang mit der berechneten Zustandsdichte diskutiert. Breite und uberlappungsbereich der Subbanden werden experimentell bestimmt und mit berechneten Werten verglichen. Die stark energieabhangigen Unterschiede zwischen den Intensitaten der Spektren und der Zustandsdichte werden mit Hilfe von spezifischen Auswahlregeln interpretiert. Die Interpretationen der XPS werden mit einem Wirkungsquerschnittsverhaltnis ~(2s)/o(2p) zwischen 15 und 35 durchgefiihrt. Es wird gezeigt, daD der Wirkungsquerschnitt der Photoemissionsspektren fur pc-artige Elektronen groDer ist als jener fur px-artige Elektronen.

Triazine‐Based Graphitic Carbon Nitride: a Two‐Dimensional Semiconductor

“…This feature corresponds to 2p orbitals nearly orthogonal to the aromatic plane ( Figure S14). Due to very low overlap between the initial pp state and free photoelectron wavefunctions, such orbitals are known to have anomalously low photoionization cross sections in c-axisorientated layered materials, such as graphite [20] and h-BN. [21] Thus the absence of this peak in layered TGCN can be rationalized.…”

Triazine‐Based Graphitic Carbon Nitride: a Two‐Dimensional Semiconductor

“…This feature corresponds to 2p orbitals nearly orthogonal to the aromatic plane (Figure S14). Due to very low overlap between the initial pπ state and free photoelectron wavefunctions, such orbitals are known to have anomalously low photoionization cross sections in c ‐axis‐orientated layered materials, such as graphite20 and h‐BN 21. Thus the absence of this peak in layered TGCN can be rationalized.…”

Polarized X‐Ray Emission Spectra of Single Crystals

“…The increasing difference towards the bottom of the o band shows an increasing portion of s-like electrons. They do not contribute to the K emission because of the dipole selection rules but can be mapped preferentially by XPS [26].…”