A simultaneous Kelvin Probe and Raman spectroscopy approach for in situ surface and interface analysis

A two-channel excitation and detection probe head for Raman spectroscopy was installed in the sample chamber of a height-regulated Kelvin Probe (KP). The beam of a 532nm laser could be thereby focused on the sample area directly beneath the KP needle. Scattered light from the sample surface was collected by the Raman probe head and sent to a detector system via fiber optics. This allowed a simultaneous detection of surface potentials and Raman spectra for a localized investigation of the properties of oxide covered metal substrates in atmospheres of different relative humidity and oxygen partial pressure. Initial testing of the assembled setup revealed that both analytical methods can be operated independently of each other as long as the laser is not hitting the Kelvin Probe needle. The KP detected reversible and irreversible laser-induced drying, photoelectric and structural rearrangement effects that were correlated to equivalent Raman spectra recorded on bare steel sheets, steel covered with a powdery oxide layer and after that layer was wiped off. This showed that the combined Kelvin Probe–Raman spectroscopy approach can give additional information that is not available by each technique separately. As it has the potential to provide contributions to sophisticated analytical surface and interface studies, possible applications of this experimental tool are also discussed.