Relationships between complex core level spectra and materials properties

Abstract

The XPS of many oxides are quite complex and there may be several peaks of significant intensity for each subshell. These peaks arise from many-electron effects, which normally are treated with configuration interaction (CI) wavefunctions where static correlation effects are taken into account. It is common to use semiempirical methods to determine the matrix elements of the CI Hamiltonian and there are few rigorous CI calculations where parameters are not adjusted to fit experiment. In contrast, we present, in the present work, theoretical XPS spectra obtained with rigorous CI wavefunctions for CeO 2 where the XPS are especially complex; several different core levels are studied. This study uses an embedded CeO 8 cluster model to represent bulk CeO 2 and the relativistic CI wavefunctions are determined using four-component spinors from Dirac-Fock calculations. In particular, we examine the importance of interatomic many-body effects where there is a transfer of electrons from occupied oxygen 2p orbitals into empty cation orbitals as it is common to ascribe the complex XPS to this effect. We also contrast the importance of many-body charge-transfer effects for the isoelectronic cations of Ce 4þ and La 3þ . The long-range goal of this work is to relate the XPS features to the nature of the chemical bonding in CeO 2 and we describe our progress toward this goal.

XPS primary excitation spectra of Zn 2p, Fe 2p, and Ce 3d from ZnO, α‐Fe2O3, and CeO2

“…This is supported by our analysis where we separate the peaks v and u into two peaks (peaks # 1, 2, 1 ′ , and 2 ′ ). This interpretation is supported by theoretical calculations using Dirac‐Fock and configuration‐interaction wavefunctions performed in Nelin et al showing that various peaks of significant intensity compose each subshell. Finally, peaks v , v , u and u correspond to peaks labelled 3, 4, 3 ′ , and 4 ′ in Table .…”

“…Nelin et al 44 showing that various peaks of significant intensity compose each subshell. Finally, peaks v ′′ , v ′′′ , u ′′ , and u ′′′ correspond to peaks labelled 3, 4, 3 ′ , and 4 ′ in Table 1.…”

Epitaxial growth of CeO2(111) film on Ru(0001): Scanning tunneling microscopy (STM) and x-ray photoemission spectroscopy (XPS) study

“…The multiplicity of the Ce 3d peaks increases with the appearance of new oxidation states. 30 [24][25][26][27][28][29][30][31] and the corresponding peaks deconvoluted from Fig. 3(b) are shown in Fig.…”

Computational and experimental evidence for a new TM–N3/C moiety family in non-PGM electrocatalysts

“…2,5 These alternative catalysts consist of nitrogen (N x ) coordinated transition metals (TM = Fe, Co, Ni) embedded in a mesoporous graphene matrix, i.e. 10,[16][17][18][19][20][21] It has long been recognized that differences in binding energies (BE) arise due to a change in chemical environments of the species. [6][7][8][9][10] While remarkable progress towards the implementation of highly active nitrogen doped transition metal electrocatalysts has been achieved in the past decade, [11][12][13][14] catalyst optimization is significantly hindered by the general lack of appropriate X-ray Photoelectron Spectroscopy reference spectra that allow to correlate defect abundance and ORR activity.…”

“…[6][7][8][9][10] While remarkable progress towards the implementation of highly active nitrogen doped transition metal electrocatalysts has been achieved in the past decade, [11][12][13][14] catalyst optimization is significantly hindered by the general lack of appropriate X-ray Photoelectron Spectroscopy reference spectra that allow to correlate defect abundance and ORR activity. 16,17,22 Chemical shifts can arise from a myriad of complex interactions, which often partially cancel, 23 such as electronegativity differences (charge transfer) and chemical valence. 10,[16][17][18][19][20][21] It has long been recognized that differences in binding energies (BE) arise due to a change in chemical environments of the species.…”