Surface analysis of 2-mercapto-1-methylimidazole adsorbed on copper by X-ray photoelectron spectroscopy

A detailed analysis using X-ray photoelectron spectroscopy (XPS) is presented for the system of 2-mercapto-1-methylimidazole (MMeI) adsorbed on Cu in 3wt% NaCl solution. High-resolution and survey XPS spectra and XPS-excited Auger L₃M_4,5M_4,5 spectra were analysed in detail. Surface analysis revealed that the MMeI molecules do not lie flat on the surface via π-d interactions, but adsorb on the surface through an N-S-bridge configuration. Moreover, the characteristic Cu(I)-MMeI connection fingerprint, which is usually observed for these kinds of molecules, was not observed. Tougaard thickness analysis showed that a relatively thin MMeI surface layer (0.3-0.6nm) is formed on the Cu substrate after 1h of immersion. Herein, MMeI is considered as a Cu corrosion inhibitor for chloride solution for short-term immersion periods. Based on the XPS analysis, an explanation of why MMeI is not effective for longer-term immersion periods, compared with similar compounds, is given.