Optimizing the PMIRRAS signal from a multilayer system and application to self-assembled monolayers in contact with liquids

Polarization modulation infrared reflection absorption spectroscopy (PMIRRAS) has become a powerful technique for the study of thin films on metal surfaces. We present a simple tool which allows the calculation and optimization of the PMIRRAS signal in multilayer systems. In order to illustrate the technique, an in situ experimental study of self-assembled monolayers on gold in contact with a μm thick water film is presented and the results compared with the calculation. A systematic series of measurements was performed on such a system and the signal intensity was recorded as a function of incident angle of the infrared beam. A strong, but broad peak in the signal-to-noise is observed at about 70° for an absorption peak at 1115 cm−1, but its position strongly depends on the thickness of the water layer. This and other examples illustrate the importance of the calculations and simulations for the optimization of experimental parameters.