“Infrared reflection absorption spectroscopy“ (IRRAS) is an established analytical technique for the characterization of adsorbed matter and thin layers on metal surfaces. In IRRAS experiments, the sample is investigated in reflection geometry under grazing incidence (typically 80°). The sensitivity of this method can be significantly enhanced by employing the polarization modulation technique (PM). In particular the disturbing atmospheric absorptions, caused by water vapour and CO2, are thereby eliminated. The PM-IRRAS technique takes advantage of the different absorption of p- and s-polarized light at large angles of incidence. The ultrathin layers on metal surfaces interact with the p-polarized fraction of light, but not with the s-polarized one.
PM-IRRAS studies the high-frequency modulation between s- and p-polarization, allowing the simultaneous measurement of two signals: 1. the difference spectrum between s- and p-polarized light and 2. the corresponding sum spectrum. The PMA 50 module is capable of simultaneous data acquisition by utilizing 24Bit dual-channel ADC. Compared to the classical IRRAS method, PMA 50’s dual channel measurement provides an essential advantage: a reference measurement is no longer required! Thus it is possible to study very thin films, adsorbed molecules from the gas phase and organic (sub-)monolayers on reflecting surfaces in detail.