Chapter 17 - MDC-SHG spectroscopy of organic monolayer film

Abstract

The chapter discusses a variety of experimental methods including scattering, spectroscopic, electrical, and optical techniques and how they have been employed to study the molecular structure and orientational phase transition of monolayers at the air–water interface. The dielectric polarization of a monolayer with C∞-symmetry is then analyzed and it is expressed using orientational order parameters defined by Legendre polynomials. The specific properties of organic monolayers such as spontaneous polarization and nonlinear polarization are interpreted using these parameters. The importance of the development of an experimental method used for the determination of the orientational order parameters is presented. The chapter discusses Maxwell displacement current (MDC)–optical second harmonic generation (SHG) measurement used for the determination of orientational order parameters and the detection of phase transitions of a floating monolayer. Finally, the chapter shows some experimental results on 4′-n-octyl-4-cyanobiphenyl (8CB) and fatty acid. In this chapter, discussion is confined to Langmuir-monolayers, but the knowledge obtained from this study will be useful for a better understanding of mono- and multilayer films on solid surface.