Combination of FTIR reflection absorption spectroscopy and work function measurement for in-situ studies of plasma modification of polymer and metal surfaces

An in-situ plasma cell for low and atmospheric pressure plasma treatment of polymer and metal substrates was developed. It enables the investigation of the sample surface with FTIR spectroscopy at grazing incidence as well as the simultaneous measurement of the volta potential difference between the outmost surface layer and a reference electrode in vacuum or a defined atmosphere. To demonstrate the benefits of the device, the plasma modification of a model polymer and an oxide covered metal surface has been investigated. It could be shown that even sub-monolayer surface changes, e.g., the etching of the CH3 and CH2 groups and the generation of carbonyl functions on an octadecylmercaptane (ODM) self-assembly monolayer on gold in a low-pressure oxygen plasma can be detected. Moreover, plasma induced changes of the oxidation states of iron and the thickness and composition of its oxide or oxyhydroxide layer could be monitored. The presented applications of this new in-situ analytical device prove that the measurement of work function in combination with monolayer sensitive vibrational spectroscopy provide new insight in plasma induced surface modifications.