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Chemical state of Na and K ions in Na10K5 silicate glass under electron irradiation investigated by XPS with the aid of the line shape analysis
Author(s) -
Lesiak B.,
Zemek J.,
Jiricek P.,
Gedeon O.,
Jóźwik A.
Publication year - 2008
Publication title -
surface and interface analysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.52
H-Index - 90
eISSN - 1096-9918
pISSN - 0142-2421
DOI - 10.1002/sia.2922
Subject(s) - x ray photoelectron spectroscopy , chemical state , irradiation , analytical chemistry (journal) , spectral line , electron , ion , silicate , chemistry , oxide , atom (system on chip) , atomic physics , physics , nuclear magnetic resonance , organic chemistry , chromatography , astronomy , quantum mechanics , nuclear physics , computer science , embedded system
The NaK (Na10K5) silicate glass, unirradiated and electron irradiated (electron dose from 25 to 8239 Cm −2 ) is investigated using XPS. The measurements are performed in the angular‐resolved ADES‐400 spectrometer using AlKα X‐ray radiation and an electron beam of energy 2 keV. Owing to surface charging and ambiguity of identification of the atomic oxidized chemical states, the line shapes of selected XPS transitions are analyzed with the aid of the pattern recognition (PR) method. This method is based on a distance measure and deals with spectra representation as vectors in the n ‐dimensional space. The algorithm presented, called the fuzzy k‐nearest neighbor (fkNN) rule, allows for identification of ambiguous vectors with the membership vectors described by classes membership probabilities. Under electron irradiation, the Na and K content in a surface region undergoesincrease and then slow systematic decrease. The line shape analysis indicates difficult classification of XPS spectra recorded for unirradiated and irradiated glass, especially for Na 1s transition. The chemical state of Na is a mixture of elemental and oxidized form and remains unchanged for all electron doses. Larger changes in the chemical form are observed for the K atom. In an unirradiated silicate glass, a mixture of elemental and oxide form is observed with increasing content of oxide under irradiation. The alkali atoms, Na and K, exhibit a migration effect. Comparison of PR and fitting results indicates better reliability and accuracy of the PR method. Copyright © 2008 John Wiley & Sons, Ltd.