Depth Profiling of Polymers by Vibrational Spectroscopy

Abstract

Depth profiling has become an important application of the vibrational microspectroscopy of heterogeneous solid samples. This chapter discusses the experimental and theoretical aspects of depth profiling by both infrared and Raman spectroscopy. Various means, such as microtoming, exist to prepare the sample for analysis. Such methods are destructive but require only a small amount of sample. Infrared spectroscopy is restricted to destructive approaches, except for the ATR technique where limited depth profiling is possible using different internal reflection elements. Raman microspectroscopy can be used in the same way as IR and has the benefit of much better spatial resolution. However, if the Raman microspectrometer is operated in confocal mode it is also possible, without any sample preparation, for spectra to be collected from within the sample, a process known as “optical slicing”. While there have been some reports demonstrating the efficacy of this approach, there have also been warnings relating to the accuracy of the method. The latest experimental and theoretical studies are discussed in order to define the current state‐of‐the‐art in confocal Raman depth profiling.

Analysis of Thin-Film Polymers Using Attenuated Total Internal Reflection–Raman Microspectroscopy

“…Two methods commonly employed for molecular surface analysis and thin-film analysis of microscopic areas are attenuated total reflection infrared (ATR-IR) microspectroscopy, and confocal Raman microspectroscopy. [9][10][11] Both methods have gained popularity over the last 17 years; however, both have drawbacks when films whose thickness is less than 1 lm are studied. In a standard IR accessory using a germanium hemisphere, the limiting penetration depth at 700 wavenumbers is approximately 1 lm.…”