Nanosized surface films on brass alloys by XPS and XAES

Abstract

Chemical state identification and quantification based on photoelectron spectra is challenging in the case of copper and zinc and their alloys. In this work an analytical strategy for simultaneous chemical state identification and quantification of copper and zinc chemical states in complex layered systems is presented. This approach is based on the curve fitting of the multicomponent X-ray excited Auger spectra, CuL₃M_4.5M_4.5 and ZnL₃M_4.5M_4.5, that clearly distinguish metallic and oxide components and result in separated I_LMM,met and I_LMM,ox peak areas. On reference copper and zinc compounds, showing only a single chemical state, the intensity ratio R between photoelectron I_2p and Auger intensity I_LMM was determined. R_met was obtained using pure metals and a sputtered brass alloy Cu37Zn. R_ox was calculated using the pure oxides. Based on these experimental intensity ratios, R, a quantification factor, k = R_ox/R_met, is calculated for both copper and zinc. This quantification factor k is independent of the instrument employed for the analysis, as proved here by using different spectrometers. The factor k is then used to transfer the experimental Auger intensity ratio (I_LMM,met/I_LMM,ox) into the I_2p,met/I_2p,ox intensity ratio, which is required for the quantitative analysis by XPS. The potential of this approach based on XPS and XAES for the patina studies on copper alloys, relevant in various fields including corrosion and cultural heritage, is presented for Cu37Zn model brass alloy after different surface pre-treatments. This approach has proven to be successful.