XPS investigation of ultra-high-vacuum storage effects on carbon fibre surfaces

Prolonged storage in ultra-high vacuum (UHV) can give rise to chemical modifications of carbon fibre surfaces. In the case of fibres contaminated before insertion into the UHV chamber, surface contaminants can be desorbed during storage. When uncontaminated carbon fibres are inserted into the chamber, layers of hydrocarbons can be progressively built up, probably coming from the UHV system. The effects can be conveniently monitored in situ, in the analysis chamber of an XPS spectrometer. A careful analysis of the Cls regions provided evidence that the higher the level of contaminants and/or the content of oxidized species on the fibres' surface, the more evident the influence of the UHV storage time on XPS spectra. These findings suggest that preliminary tests on time-dependent modifications of the surface status of carbon fibres under UHV conditions can provide a more reliable XPS analysis.