PDF《Applied Surface Science》

Applied Surface Science

257 (2011) 2717C2730 Contents lists available at ScienceDirect Applied Surface Science journal homepage: www.

elsevier.com/locate/apsusc Resolving surface chemical states in XPS analysis of ?rst row transition metals, oxides and hydroxides: Cr, Mn, Fe, Co and Ni Mark C. Biesingera,b,? , Brad P. Paynec , Andrew P. Grosvenord , Leo W.M. Laua,c , Andrea R. Gersonb , Roger St.C. Smartb a Surface Science Western, The University of Western Ontario, The University of Western Ontario Research Park, Room LL31,

999 Collip Circle, London, Ontario, Canada N6G 0J3 b ACeSSS (Applied Centre for Structural and Synchrotron Studies), University of South Australia, Mawson Lakes, SA 5095, Australia c Department of Chemistry, The University of Western Ontario, London, Ontario, Canada N6A 5B7 d Department of Chemistry, University of Saskatchewan, Saskatoon, Saskatchewan, Canada S7N 5C9 a r t i c l e i n f o Article history: Received

26 August

2010 Accepted

12 October

2010 Available online

20 October

2010 Keywords: X-ray photoelectron spectroscopy Transition metals Chemical states Peak ?tting a b s t r a c t Chemical state X-ray photoelectron spectroscopic analysis of ?rst row transition metals and their oxides and hydroxides is challenging due to the complexity of their 2p spectra resulting from peak asymmetries, complex multiplet splitting, shake-up and plasmon loss structure, and uncertain, overlapping binding energies. Our previous paper [M.C. Biesinger et al., Appl. Surf. Sci.

257 (2010) 887C898.] in which we examined Sc, Ti, V, Cu and Zn species, has shown that all the values of the spectral ?tting parameters for each speci?c species, i.e. binding energy (eV), full wide at half maximum (FWHM) value (eV) for each pass energy, spinCorbit splitting values and asymmetric peak shape ?tting parameters, are not all normally provided in the literature and data bases, and are necessary for reproducible, quantitative chemical state analysis. A more consistent, practical and effective approach to curve ?tting was developed based on a combination of (1) standard spectra from quality reference samples, (2) a survey of appropriate litera- ture databases and/or a compilation of literature references and (3) speci?c literature references where ?tting procedures are available. This paper extends this approach to the chemical states of Cr, Mn, Fe, Co and Ni metals, and various oxides and hydroxides where intense, complex multiplet splitting in many of the chemical states of these elements poses unique dif?culties for chemical state analysis. The curve ?tting procedures proposed use the same criteria as proposed previously but with the additional com- plexity of ?tting of multiplet split spectra which has been done based on spectra of numerous reference materials and theoretical XPS modeling of these transition metal species. Binding energies, FWHM val- ues, asymmetric peak shape ?tting parameters, multiplet peak separation and peak area percentages are presented. The procedures developed can be utilized to remove uncertainties in the analysis of surface states in nano-particles, corrosion, catalysis and surface-engineered materials. ?

2010 Elsevier B.V. All rights reserved. 1. Introduction Chemical state identi?cation using X-ray photoelectron spec- troscopy (XPS) has become routine for most elements in the periodic table. Binding energy databases, such as the NIST Database [1] or the Phi Handbook [2], generally provide suf?cient data for the chemical state determination for uncomplicated (i.e. single peak) spectra. However, the transition metal 2p spectra pose a number of complications that these databases do not adequately address, speci?cally, shake-up and plasmon loss structures, and multiplet ? Corresponding author at: Surface Science Western, The University of Western Ontario, The University of Western Ontario Research Park, Room LL31,