A system for it in situ studies of atmospheric corrosion of metal films using soft x-ray spectroscopy

Forsberg, Johan1; Duda, Laurent1; Olsson, Anders1; Schmitt, Thorsten1; Andersson, Joakim1; Nordgren, Joseph1; Hedberg, Jonas1; Leygraf, Christofer1; Aastrup, Teodor1; Wallinder, Daniel1; Guo, Yinghua2 1Sweden; 2United States

We have constructed a versatile chamber ("atmospheric corrosion cell") for in situ soft x-ray absorption spectroscopy, soft x-ray emission spectroscopy and resonant inelastic x-ray scattering (RIXS) of metal surfaces and films in a corrosive atmosphere allowing novel electronic structure studies. A metal film is deposited (by resistive evaporation) onto a thin (100 nm) silicon nitride or carbon membrane prior to mounting in the atmospheric corrosion cell. The membrane is used to separate the corrosion cell interior from a beamline vacuum chamber and is easily exposed to synchrotron radiation for x-ray absorption and x-ray emission measurements. Relevant parameters of the internal atmosphere can be controlled and atmospheric corrosion takes place in the metal film. Moreover, we have developed a version that includes a QCM (quartz crystal microbalance) in order to monitor the corrosion process through mass change.
We find that the Fe L-edge emission spectra show characteristic dd-excitations of metal oxides and that the O K-edge spectra vary considerably in width. By comparison to well-characterized reference compounds one may identify the composition of the corrosion product. Measurements on several reference compounds and corrosion of an iron film have been performed using pure humidified synthetic air. Since the relative air humidity has a strong influence on the number of surface adlayers present it is crucial to study the effect of atmospheric humidity on both the reference samples and the corrosion products. We also discuss the effect of additional airborne pollutants, such as sulphur dioxide and ozone, on the corrosion process and the spectral effects.

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