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A Chemical View on X‐ray Photoelectron Spectroscopy: the ESCA Molecule and Surface‐to‐Bulk XPS Shifts
Author(s) -
Delesma Francisco A.,
Van den Bossche Maxime,
Grönbeck Henrik,
Calaminici Patrizia,
Köster Andreas M.,
Pettersson Lars G. M.
Publication year - 2018
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.201701135
Subject(s) - x ray photoelectron spectroscopy , chemical shift , binding energy , molecule , chemistry , chemical bond , atom (system on chip) , chemical state , transition metal , ionization , ionization energy , atomic physics , crystallography , analytical chemistry (journal) , nuclear magnetic resonance , physics , organic chemistry , ion , computer science , embedded system , catalysis
In this paper we remind the reader of a simple, intuitive picture of chemical shifts in X‐ray photoelectron spectroscopy (XPS) as the difference in chemical bonding between the probed atom and its neighbor to the right in the periodic table, the so called Z+1 approximation. We use the classical ESCA molecule, ethyl trifluoroacetate, and 4 d ‐transition metals to explicitly demonstrate agreement between core‐level shifts computed as differences between final core‐hole states and the approach where each core‐ionized atom is replaced by a Z+1 atom. In this final state, or total energy picture, the XPS shift arises due to the more or less unfavorable chemical bonding of the effective nitrogen in the carbon geometry for the ESCA molecule. Surface core level shifts in metals are determined by whether the Z+1 atom as an alloy segregates to the surface or is more soluble in the bulk. As further illustration of this more chemical picture, we compare the geometry of C 1 s and O 1 s core‐ionized CO with that of, respectively, NO + and CF + . The scope is not to propose a new method to compute XPS shifts but rather to stress the validity of this simple interpretation.