In these studies two ultrasensitive techniques towards surface reactions, vibrational sum frequency spectroscopy (VSFS) and quartz crystal microbalance (QCM) have been integrated for in-situ studies of the corrosion of metal surfaces. This novel combination allows spectroscopic (VSFS) and mass (QCM) information to be acquired simultaneously with a high precision. These studies have focused on reactions occurring on copper surfaces.  This metal has numerous industrial applications, but suffers from corrosion in several environments. Thus, in order to avoid degradation of the metal, effective protective films are necessary. The use of self-assembled monolayers (SAMs) of alkyl thiols to protect copper surfaces has advantages such as that objects of any shape can be coated (e.g. microelectronics where traditional coatings are too thick), and that the thickness of the film can be controlled on the �ngstr�m level by changing the chain length.The VSFS/QCM setup was used to study the oxidation of copper surfaces covered by a monolayer of octadecylthiol exposed to dry air. By monitoring changes in the non-resonant background in the sum frequency spectra due to the formation of Cu2O, VSFS (as well as QCM) allowed the detection of less than 5% of a monolayer of the oxidation product. An almost perfect correlation was found between the changes in the non-resonant background in the VSF spectra and the mass changes observed by QCM. Further, infrared reflection/absorption spectroscopy (IRAS) was used in-situ in combination with VSFS to examine the protective ability of SAMs of alkyl thiols of different chain lengths, as well as alkyl selenols adsorbed on copper surfaces. Upon exposure to humid air containing sub-ppm levels of formic acid, IRAS provided information about the nature and the kinetics of formation of the reaction products. As a complement, VSFS provided detailed information about changes in the molecular structure of the SAMs.

In-situ studies of the reactivity of copper surfaces protected by self-assembled monolayers

248th National Meeting (2014)

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