Infrared reflectance-absorbance spectroscopy of thin films formed by forced dewetting of solid-fluid interfaces

An infrared reflectance-absorbance spectroscopy method for characterizing the ultrathin fluid film retained on a surface upon forced dewetting from a fluid has been developed for investigation of interfacial molecular structure at reflective substrates. This report details the optical considerations and constraints necessary to acquire IR spectral data from nanometer-thick films retained upon forced dewetting of a solid substrate from a fluid into a vapor-saturated environment. The feasibility of this method is demonstrated through successful spectral acquisition from Ag surfaces modified with 11-mercaptoundecanol forcibly dewet from water. The IR spectral results clearly illustrate that information is acquired only from the interfacial region with no contribution from the bulk liquid. Residual layer thicknesses calculated from IR absorbance values are substantiated by ellipsometry. The spectra make clear that the molecular structure of the residual layer is distinctly different from that of the bulk liquid, confirming that this method is viable for interfacial structure elucidation of thin fluid films at a variety of solid substrates.