Structure and chemical analysis in thin films by in situ IR ellipsometry

Abstract

In 2007, infrared spectroscopic ellipsometry (IRSE) was introduced as a highly sensitive technique for in situ investigations of chemical and structural changes in thin polymer films. In this initial publication, the response of a mixed polyelectrolyte brush film in liquid environments was studied upon external pH stimuli. In the following decade, a variety of solid–liquid interfaces such as various types of thin polymer and oligomer thin films including possible electrochemical preparations were investigated. Typically, these studies were motivated by respective applications of the films in optoelectronic devices, sensors or biofunctional interfaces. In 2017, in situ IRSE was brought to a new level by showing the capability for sensitive and quantitative intra- and intermolecular interaction studies of thin thermoresponsive polymer films. Recently, new applications became available by the involvement of laser sources as well as by specifically designed microfluidic cells. These two issues are described in other chapters of this Encyclopedia. In the chapter “Hyperspectral and time-resolved IR laser polarimetry”, new possibilities of laser-based IR polarimetry regarding highly time-resolved studies of non-cyclic/irreversible processes and hyperspectral imaging are discussed. Examples are the sub-second spectral monitoring of a solid-to-liquid phase transition of a myristic acid film and hyperspectral ellipsometric imaging of a microfluidic chip. In the chapter “Optofluidic analysis of monolayers with infrared microscopy”, several opportunities for kinetic, chemical and structural in situ analyses of sub-monolayers with IR spectroscopy in a microfluidic μlcell are reviewed. In the present chapter we focus on IRSE as a powerful method for the analysis of thin films (from 5 to 12nm) at the silicon–liquid interface. The methodical possibilities are of high interest in various fields of research and applications, such as bioanalytics, catalysis and material science.