2006 Volume 55 Issue 4 Pages 146-151
We used time-of-flight secondary ion mass spectrometry to get a better understanding of the carbon-containing layer formed in summer and winter on copper exposed to an urban atmosphere. The positive ion mass spectra of as-exposed surfaces revealed that the chemical composition of the carbon-containing layer formed in summer was essentially the same as that formed in winter. However, the intensities of ion fragments originating from volatile organic compounds adsorbed in winter were stronger than those in summer. This is attributed to the temperature dependence of the physisorption of the compounds, assuming that the amounts of hydrocarbon contamination in the analytical instrument were the same for both samples. The positive ion mass spectra of sputtered surfaces (5 nm from the uppermost surface) showed that the chemical composition of the sputtered surface was different than that of the as-exposed surfaces. The only compound found on the sputtered surfaces was dicapryl phthalate (DCP), based on a comparison of the standard mass spectra of DCP with the observed ones. The peaks arising from DCP observed on the copper exposed in winter were higher than those in summer. This is attributed to the higher particulate organic carbon concentration observed in winter. The thicker carbon-containing layer formed on the copper exposed in winter possibly retarded the atmospheric corrosion by acting as a barrier to water adsorption on the copper patina.